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diff --git a/doc/rfc/rfc4656.txt b/doc/rfc/rfc4656.txt new file mode 100644 index 0000000..59b3bbd --- /dev/null +++ b/doc/rfc/rfc4656.txt @@ -0,0 +1,3139 @@ + + + + + + +Network Working Group S. Shalunov +Request for Comments: 4656 B. Teitelbaum +Category: Standards Track A. Karp + J. Boote + M. Zekauskas + Internet2 + September 2006 + + + A One-way Active Measurement Protocol (OWAMP) + +Status of This Memo + + This document specifies an Internet standards track protocol for the + Internet community, and requests discussion and suggestions for + improvements. Please refer to the current edition of the "Internet + Official Protocol Standards" (STD 1) for the standardization state + and status of this protocol. Distribution of this memo is unlimited. + +Copyright Notice + + Copyright (C) The Internet Society (2006). + +Abstract + + The One-Way Active Measurement Protocol (OWAMP) measures + unidirectional characteristics such as one-way delay and one-way + loss. High-precision measurement of these one-way IP performance + metrics became possible with wider availability of good time sources + (such as GPS and CDMA). OWAMP enables the interoperability of these + measurements. + +Table of Contents + + 1. Introduction ....................................................2 + 1.1. Relationship of Test and Control Protocols .................3 + 1.2. Logical Model ..............................................4 + 2. Protocol Overview ...............................................5 + 3. OWAMP-Control ...................................................6 + 3.1. Connection Setup ...........................................6 + 3.2. Integrity Protection (HMAC) ...............................11 + 3.3. Values of the Accept Field ................................11 + 3.4. OWAMP-Control Commands ....................................12 + 3.5. Creating Test Sessions ....................................13 + 3.6. Send Schedules ............................................18 + 3.7. Starting Test Sessions ....................................19 + 3.8. Stop-Sessions .............................................20 + 3.9. Fetch-Session .............................................24 + + + +Shalunov, et al. Standards Track [Page 1] + +RFC 4656 One-way Active Measurement Protocol September 2006 + + + 4. OWAMP-Test .....................................................27 + 4.1. Sender Behavior ...........................................28 + 4.1.1. Packet Timings .....................................28 + 4.1.2. OWAMP-Test Packet Format and Content ...............29 + 4.2. Receiver Behavior .........................................33 + 5. Computing Exponentially Distributed Pseudo-Random Numbers ......35 + 5.1. High-Level Description of the Algorithm ...................35 + 5.2. Data Types, Representation, and Arithmetic ................36 + 5.3. Uniform Random Quantities .................................37 + 6. Security Considerations ........................................38 + 6.1. Introduction ..............................................38 + 6.2. Preventing Third-Party Denial of Service ..................38 + 6.3. Covert Information Channels ...............................39 + 6.4. Requirement to Include AES in Implementations .............39 + 6.5. Resource Use Limitations ..................................39 + 6.6. Use of Cryptographic Primitives in OWAMP ..................40 + 6.7. Cryptographic Primitive Replacement .......................42 + 6.8. Long-term Manually Managed Keys ...........................43 + 6.9. (Not) Using Time as Salt ..................................44 + 6.10. The Use of AES-CBC and HMAC ..............................44 + 7. Acknowledgements ...............................................45 + 8. IANA Considerations ............................................45 + 9. Internationalization Considerations ............................46 + 10. References ....................................................46 + 10.1. Normative References .....................................46 + 10.2. Informative References ...................................47 + Appendix A: Sample C Code for Exponential Deviates ................49 + Appendix B: Test Vectors for Exponential Deviates .................54 + +1. Introduction + + The IETF IP Performance Metrics (IPPM) working group has defined + metrics for one-way packet delay [RFC2679] and loss [RFC2680] across + Internet paths. Although there are now several measurement platforms + that implement collection of these metrics [SURVEYOR] [SURVEYOR-INET] + [RIPE] [BRIX], there is not currently a standard that would permit + initiation of test streams or exchange of packets to collect + singleton metrics in an interoperable manner. + + With the increasingly wide availability of affordable global + positioning systems (GPS) and CDMA-based time sources, hosts + increasingly have available to them very accurate time sources, + either directly or through their proximity to Network Time Protocol + (NTP) primary (stratum 1) time servers. By standardizing a technique + for collecting IPPM one-way active measurements, we hope to create an + environment where IPPM metrics may be collected across a far broader + mesh of Internet paths than is currently possible. One particularly + compelling vision is of widespread deployment of open OWAMP servers + + + +Shalunov, et al. Standards Track [Page 2] + +RFC 4656 One-way Active Measurement Protocol September 2006 + + + that would make measurement of one-way delay as commonplace as + measurement of round-trip time using an ICMP-based tool like ping. + + Additional design goals of OWAMP include: being hard to detect and + manipulate, security, logical separation of control and test + functionality, and support for small test packets. (Being hard to + detect makes interference with measurements more difficult for + intermediaries in the middle of the network.) + + OWAMP test traffic is hard to detect because it is simply a stream of + UDP packets from and to negotiated port numbers, with potentially + nothing static in the packets (size is negotiated, as well). OWAMP + also supports an encrypted mode that further obscures the traffic and + makes it impossible to alter timestamps undetectably. + + Security features include optional authentication and/or encryption + of control and test messages. These features may be useful to + prevent unauthorized access to results or man-in-the-middle attacks + that attempt to provide special treatment to OWAMP test streams or + that attempt to modify sender-generated timestamps to falsify test + results. + + In this document, the key words "MUST", "REQUIRED", "SHOULD", + "RECOMMENDED", and "MAY" are to be interpreted as described in + [RFC2119]. + +1.1. Relationship of Test and Control Protocols + + OWAMP actually consists of two inter-related protocols: OWAMP-Control + and OWAMP-Test. OWAMP-Control is used to initiate, start, and stop + test sessions and to fetch their results, whereas OWAMP-Test is used + to exchange test packets between two measurement nodes. + + Although OWAMP-Test may be used in conjunction with a control + protocol other than OWAMP-Control, the authors have deliberately + chosen to include both protocols in the same RFC to encourage the + implementation and deployment of OWAMP-Control as a common + denominator control protocol for one-way active measurements. Having + a complete and open one-way active measurement solution that is + simple to implement and deploy is crucial to ensuring a future in + which inter-domain one-way active measurement could become as + commonplace as ping. We neither anticipate nor recommend that + OWAMP-Control form the foundation of a general-purpose extensible + measurement and monitoring control protocol. + + OWAMP-Control is designed to support the negotiation of one-way + active measurement sessions and results retrieval in a + straightforward manner. At session initiation, there is a + + + +Shalunov, et al. Standards Track [Page 3] + +RFC 4656 One-way Active Measurement Protocol September 2006 + + + negotiation of sender and receiver addresses and port numbers, + session start time, session length, test packet size, the mean + Poisson sampling interval for the test stream, and some attributes of + the very general [RFC 2330] notion of packet type, including packet + size and per-hop behavior (PHB) [RFC2474], which could be used to + support the measurement of one-way network characteristics across + differentiated services networks. Additionally, OWAMP-Control + supports per-session encryption and authentication for both test and + control traffic, measurement servers that can act as proxies for test + stream endpoints, and the exchange of a seed value for the pseudo- + random Poisson process that describes the test stream generated by + the sender. + + We believe that OWAMP-Control can effectively support one-way active + measurement in a variety of environments, from publicly accessible + measurement beacons running on arbitrary hosts to network monitoring + deployments within private corporate networks. If integration with + Simple Network Management Protocol (SNMP) or proprietary network + management protocols is required, gateways may be created. + +1.2. Logical Model + + Several roles are logically separated to allow for broad flexibility + in use. Specifically, we define the following: + + Session-Sender The sending endpoint of an OWAMP-Test session; + + Session-Receiver The receiving endpoint of an OWAMP-Test session; + + Server An end system that manages one or more OWAMP-Test + sessions, is capable of configuring per-session + state in session endpoints, and is capable of + returning the results of a test session; + + Control-Client An end system that initiates requests for + OWAMP-Test sessions, triggers the start of a set + of sessions, and may trigger their termination; + and + + Fetch-Client An end system that initiates requests to fetch + the results of completed OWAMP-Test sessions. + + + + + + + + + + +Shalunov, et al. Standards Track [Page 4] + +RFC 4656 One-way Active Measurement Protocol September 2006 + + + One possible scenario of relationships between these roles is shown + below. + + +----------------+ +------------------+ + | Session-Sender |--OWAMP-Test-->| Session-Receiver | + +----------------+ +------------------+ + ^ ^ + | | + | | + | | + | +----------------+<----------------+ + | | Server |<-------+ + | +----------------+ | + | ^ | + | | | + | OWAMP-Control OWAMP-Control + | | | + v v v + +----------------+ +-----------------+ + | Control-Client | | Fetch-Client | + +----------------+ +-----------------+ + + (Unlabeled links in the figure are unspecified by this document and + may be proprietary protocols.) + + Different logical roles can be played by the same host. For example, + in the figure above, there could actually be only two hosts: one + playing the roles of Control-Client, Fetch-Client, and Session- + Sender, and the other playing the roles of Server and Session- + Receiver. This is shown below. + + +-----------------+ +------------------+ + | Control-Client |<--OWAMP-Control-->| Server | + | Fetch-Client | | | + | Session-Sender |---OWAMP-Test----->| Session-Receiver | + +-----------------+ +------------------+ + + Finally, because many Internet paths include segments that transport + IP over ATM, delay and loss measurements can include the effects of + ATM segmentation and reassembly (SAR). Consequently, OWAMP has been + designed to allow for small test packets that would fit inside the + payload of a single ATM cell (this is only achieved in + unauthenticated mode). + + + + + + + + +Shalunov, et al. Standards Track [Page 5] + +RFC 4656 One-way Active Measurement Protocol September 2006 + + +2. Protocol Overview + + As described above, OWAMP consists of two inter-related protocols: + OWAMP-Control and OWAMP-Test. The former is layered over TCP and is + used to initiate and control measurement sessions and to fetch their + results. The latter protocol is layered over UDP and is used to send + singleton measurement packets along the Internet path under test. + + The initiator of the measurement session establishes a TCP connection + to a well-known port, 861, on the target point and this connection + remains open for the duration of the OWAMP-Test sessions. An OWAMP + server SHOULD listen to this well-known port. + + OWAMP-Control messages are transmitted only before OWAMP-Test + sessions are actually started and after they are completed (with the + possible exception of an early Stop-Sessions message). + + The OWAMP-Control and OWAMP-Test protocols support three modes of + operation: unauthenticated, authenticated, and encrypted. The + authenticated or encrypted modes require that endpoints possess a + shared secret. + + All multi-octet quantities defined in this document are represented + as unsigned integers in network byte order unless specified + otherwise. + +3. OWAMP-Control + + The type of each OWAMP-Control message can be found after reading the + first 16 octets. The length of each OWAMP-Control message can be + computed upon reading its fixed-size part. No message is shorter + than 16 octets. + + An implementation SHOULD expunge unused state to prevent denial-of- + service attacks, or unbounded memory usage, on the server. For + example, if the full control message is not received within some + number of minutes after it is expected, the TCP connection associated + with the OWAMP-Control session SHOULD be dropped. In absence of + other considerations, 30 minutes seems like a reasonable upper bound. + +3.1. Connection Setup + + Before either a Control-Client or a Fetch-Client can issue commands + to a Server, it has to establish a connection to the server. + + First, a client opens a TCP connection to the server on a well-known + port 861. The server responds with a server greeting: + + + + +Shalunov, et al. Standards Track [Page 6] + +RFC 4656 One-way Active Measurement Protocol September 2006 + + + 0 1 2 3 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | | + | Unused (12 octets) | + | | + |+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Modes | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | | + | Challenge (16 octets) | + | | + | | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | | + | Salt (16 octets) | + | | + | | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Count (4 octets) | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | | + | MBZ (12 octets) | + | | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + The following Mode values are meaningful: 1 for unauthenticated, 2 + for authenticated, and 4 for encrypted. The value of the Modes field + sent by the server is the bit-wise OR of the mode values that it is + willing to support during this session. Thus, the last three bits of + the Modes 32-bit value are used. The first 29 bits MUST be zero. A + client MUST ignore the values in the first 29 bits of the Modes + value. (This way, the bits are available for future protocol + extensions. This is the only intended extension mechanism.) + + Challenge is a random sequence of octets generated by the server; it + is used subsequently by the client to prove possession of a shared + secret in a manner prescribed below. + + Salt and Count are parameters used in deriving a key from a shared + secret as described below. + + Salt MUST be generated pseudo-randomly (independently of anything + else in this document). + + Count MUST be a power of 2. Count MUST be at least 1024. Count + SHOULD be increased as more computing power becomes common. + + + + +Shalunov, et al. Standards Track [Page 7] + +RFC 4656 One-way Active Measurement Protocol September 2006 + + + If the Modes value is zero, the server does not wish to communicate + with the client and MAY close the connection immediately. The client + SHOULD close the connection if it receives a greeting with Modes + equal to zero. The client MAY close the connection if the client's + desired mode is unavailable. + + Otherwise, the client MUST respond with the following Set-Up-Response + message: + + 0 1 2 3 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Mode | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | | + . . + . KeyID (80 octets) . + . . + | | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | | + . . + . Token (64 octets) . + . . + | | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | | + . . + . Client-IV (16 octets) . + . . + | | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + Here Mode is the mode that the client chooses to use during this + OWAMP-Control session. It will also be used for all OWAMP-Test + sessions started under control of this OWAMP-Control session. In + Mode, one or zero bits MUST be set within last three bits. If it is + one bit that is set within the last three bits, this bit MUST + indicate a mode that the server agreed to use (i.e., the same bit + MUST have been set by the server in the server greeting). The first + 29 bits of Mode MUST be zero. A server MUST ignore the values of the + first 29 bits. If zero Mode bits are set by the client, the client + indicates that it will not continue with the session; in this case, + the client and the server SHOULD close the TCP connection associated + with the OWAMP-Control session. + + + + + + +Shalunov, et al. Standards Track [Page 8] + +RFC 4656 One-way Active Measurement Protocol September 2006 + + + In unauthenticated mode, KeyID, Token, and Client-IV are unused. + Otherwise, KeyID is a UTF-8 string, up to 80 octets in length (if the + string is shorter, it is padded with zero octets), that tells the + server which shared secret the client wishes to use to authenticate + or encrypt, while Token is the concatenation of a 16-octet challenge, + a 16-octet AES Session-key used for encryption, and a 32-octet HMAC- + SHA1 Session-key used for authentication. The token itself is + encrypted using the AES (Advanced Encryption Standard) [AES] in + Cipher Block Chaining (CBC). Encryption MUST be performed using an + Initialization Vector (IV) of zero and a key derived from the shared + secret associated with KeyID. (Both the server and the client use + the same mappings from KeyIDs to shared secrets. The server, being + prepared to conduct sessions with more than one client, uses KeyIDs + to choose the appropriate secret key; a client would typically have + different secret keys for different servers. The situation is + analogous to that with passwords.) + + The shared secret is a passphrase; it MUST not contain newlines. The + secret key is derived from the passphrase using a password-based key + derivation function PBKDF2 (PKCS #5) [RFC2898]. The PBKDF2 function + requires several parameters: the PRF is HMAC-SHA1 [RFC2104]; the salt + and count are as transmitted by the server. + + AES Session-key, HMAC Session-key and Client-IV are generated + randomly by the client. AES Session-key and HMAC Session-key MUST be + generated with sufficient entropy not to reduce the security of the + underlying cipher [RFC4086]. Client-IV merely needs to be unique + (i.e., it MUST never be repeated for different sessions using the + same secret key; a simple way to achieve that without the use of + cumbersome state is to generate the Client-IV values using a + cryptographically secure pseudo-random number source: if this is + done, the first repetition is unlikely to occur before 2^64 sessions + with the same secret key are conducted). + + + + + + + + + + + + + + + + + + +Shalunov, et al. Standards Track [Page 9] + +RFC 4656 One-way Active Measurement Protocol September 2006 + + + The server MUST respond with the following Server-Start message: + + 0 1 2 3 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | | + | MBZ (15 octets) | + | | + | +-+-+-+-+-+-+-+-+ + | | Accept | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | | + | Server-IV (16 octets) | + | | + | | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Start-Time (Timestamp) | + | | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | MBZ (8 octets) | + | | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + The MBZ parts MUST be zero. The client MUST ignore their value. MBZ + (MUST be zero) fields here and after have the same semantics: the + party that sends the message MUST set the field so that all bits are + equal to zero; the party that interprets the message MUST ignore the + value. (This way, the field could be used for future extensions.) + + Server-IV is generated randomly by the server. In unauthenticated + mode, Server-IV is unused. + + The Accept field indicates the server's willingness to continue + communication. A zero value in the Accept field means that the + server accepts the authentication and is willing to conduct further + transactions. Non-zero values indicate that the server does not + accept the authentication or, for some other reason, is not willing + to conduct further transactions in this OWAMP-Control session. The + full list of available Accept values is described in Section 3.3, + "Values of the Accept Field". + + If a negative (non-zero) response is sent, the server MAY (and the + client SHOULD) close the connection after this message. + + Start-Time is a timestamp representing the time when the current + instantiation of the server started operating. (For example, in a + multi-user general purpose operating system, it could be the time + when the server process was started.) If Accept is non-zero, Start- + + + +Shalunov, et al. Standards Track [Page 10] + +RFC 4656 One-way Active Measurement Protocol September 2006 + + + Time SHOULD be set so that all of its bits are zeros. In + authenticated and encrypted modes, Start-Time is encrypted as + described in Section 3.4, "OWAMP-Control Commands", unless Accept is + non-zero. (Authenticated and encrypted mode cannot be entered unless + the control connection can be initialized.) + + Timestamp format is described in Section 4.1.2. The same + instantiation of the server SHOULD report the same exact Start-Time + value to each client in each session. + + The previous transactions constitute connection setup. + +3.2. Integrity Protection (HMAC) + + Authentication of each message (also referred to as a command in this + document) in OWAMP-Control is accomplished by adding an HMAC to it. + The HMAC that OWAMP uses is HMAC-SHA1 truncated to 128 bits. Thus, + all HMAC fields are 16 octets. An HMAC needs a key. The HMAC + Session-key is communicated along with the AES Session-key during + OWAMP-Control connection setup. The HMAC Session-key SHOULD be + derived independently of the AES Session-key (an implementation, of + course, MAY use the same mechanism to generate the random bits for + both keys). Each HMAC sent covers everything sent in a given + direction between the previous HMAC (but not including it) and up to + the beginning of the new HMAC. This way, once encryption is set up, + each bit of the OWAMP-Control connection is authenticated by an HMAC + exactly once. + + When encrypting, authentication happens before encryption, so HMAC + blocks are encrypted along with the rest of the stream. When + decrypting, the order, of course, is reversed: first one decrypts, + then one checks the HMAC, then one proceeds to use the data. + + The HMAC MUST be checked as early as possible to avoid using and + propagating corrupt data. + + In open mode, the HMAC fields are unused and have the same semantics + as MBZ fields. + +3.3. Values of the Accept Field + + Accept values are used throughout the OWAMP-Control protocol to + communicate the server response to client requests. The full set of + valid Accept field values are as follows: + + 0 OK. + + 1 Failure, reason unspecified (catch-all). + + + +Shalunov, et al. Standards Track [Page 11] + +RFC 4656 One-way Active Measurement Protocol September 2006 + + + 2 Internal error. + + 3 Some aspect of request is not supported. + + 4 Cannot perform request due to permanent resource limitations. + + 5 Cannot perform request due to temporary resource limitations. + + All other values are reserved. The sender of the message MAY use the + value of 1 for all non-zero Accept values. A message sender SHOULD + use the correct Accept value if it is going to use other values. The + message receiver MUST interpret all values of Accept other than these + reserved values as 1. This way, other values are available for + future extensions. + +3.4. OWAMP-Control Commands + + In authenticated or encrypted mode (which are identical as far as + OWAMP-Control is concerned, and only differ in OWAMP-Test), all + further communications are encrypted with the AES Session-key (using + CBC mode) and authenticated with HMAC Session-key. The client + encrypts everything it sends through the just-established OWAMP- + Control connection using stream encryption with Client-IV as the IV. + Correspondingly, the server encrypts its side of the connection using + Server-IV as the IV. + + The IVs themselves are transmitted in cleartext. Encryption starts + with the block immediately following the block containing the IV. + The two streams (one going from the client to the server and one + going back) are encrypted independently, each with its own IV, but + using the same key (the AES Session-key). + + The following commands are available for the client: Request-Session, + Start-Sessions, Stop-Sessions, and Fetch-Session. The command Stop- + Sessions is available to both the client and the server. (The server + can also send other messages in response to commands it receives.) + + After the client sends the Start-Sessions command and until it both + sends and receives (in an unspecified order) the Stop-Sessions + command, it is said to be conducting active measurements. Similarly, + the server is said to be conducting active measurements after it + receives the Start-Sessions command and until it both sends and + receives (in an unspecified order) the Stop-Sessions command. + + While conducting active measurements, the only command available is + Stop-Sessions. + + These commands are described in detail below. + + + +Shalunov, et al. Standards Track [Page 12] + +RFC 4656 One-way Active Measurement Protocol September 2006 + + +3.5. Creating Test Sessions + + Individual one-way active measurement sessions are established using + a simple request/response protocol. An OWAMP client MAY issue zero + or more Request-Session messages to an OWAMP server, which MUST + respond to each with an Accept-Session message. An Accept-Session + message MAY refuse a request. + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +Shalunov, et al. Standards Track [Page 13] + +RFC 4656 One-way Active Measurement Protocol September 2006 + + + The format of Request-Session message is as follows: + + 0 1 2 3 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | 1 | MBZ | IPVN | Conf-Sender | Conf-Receiver | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Number of Schedule Slots | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Number of Packets | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Sender Port | Receiver Port | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Sender Address | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | | + | Sender Address (cont.) or MBZ (12 octets) | + | | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Receiver Address | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | | + | Receiver Address (cont.) or MBZ (12 octets) | + | | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | | + | SID (16 octets) | + | | + | | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Padding Length | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Start Time | + | | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Timeout, (8 octets) | + | | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Type-P Descriptor | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | MBZ (8 octets) | + | | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | | + | HMAC (16 octets) | + | | + | | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + + +Shalunov, et al. Standards Track [Page 14] + +RFC 4656 One-way Active Measurement Protocol September 2006 + + + This is immediately followed by one or more schedule slot + descriptions (the number of schedule slots is specified in the + "Number of Schedule Slots" field above): + + 0 1 2 3 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Slot Type | | + +-+-+-+-+-+-+-+-+ MBZ (7 octets) | + | | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Slot Parameter (Timestamp) | + | | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + These are immediately followed by HMAC: + + 0 1 2 3 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | | + | HMAC (16 octets) | + | | + | | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + All these messages constitute one logical message: the Request- + Session command. + + Above, the first octet (1) indicates that this is the Request-Session + command. + + IPVN is the IP version numbers for Sender and Receiver. When the IP + version number is 4, 12 octets follow the 4-octet IPv4 address stored + in Sender Address and Receiver Address. These octets MUST be set to + zero by the client and MUST be ignored by the server. Currently + meaningful IPVN values are 4 and 6. + + Conf-Sender and Conf-Receiver MUST be set to 0 or 1 by the client. + The server MUST interpret any non-zero value as 1. If the value is + 1, the server is being asked to configure the corresponding agent + (sender or receiver). In this case, the corresponding Port value + SHOULD be disregarded by the server. At least one of Conf-Sender and + Conf-Receiver MUST be 1. (Both can be set, in which case the server + is being asked to perform a session between two hosts it can + configure.) + + + + + +Shalunov, et al. Standards Track [Page 15] + +RFC 4656 One-way Active Measurement Protocol September 2006 + + + Number of Schedule Slots, as mentioned before, specifies the number + of slot records that go between the two blocks of HMAC. It is used + by the sender to determine when to send test packets (see next + section). + + Number of Packets is the number of active measurement packets to be + sent during this OWAMP-Test session (note that either the server or + the client can abort the session early). + + If Conf-Sender is not set, Sender Port is the UDP port from which + OWAMP-Test packets will be sent. If Conf-Receiver is not set, + Receiver Port is the UDP port OWAMP-Test to which packets are + requested to be sent. + + The Sender Address and Receiver Address fields contain, respectively, + the sender and receiver addresses of the end points of the Internet + path over which an OWAMP test session is requested. + + SID is the session identifier. It can be used in later sessions as + an argument for the Fetch-Session command. It is meaningful only if + Conf-Receiver is 0. This way, the SID is always generated by the + receiving side. See the end of the section for information on how + the SID is generated. + + Padding length is the number of octets to be appended to the normal + OWAMP-Test packet (see more on padding in discussion of OWAMP-Test). + + Start Time is the time when the session is to be started (but not + before Start-Sessions command is issued). This timestamp is in the + same format as OWAMP-Test timestamps. + + Timeout (or a loss threshold) is an interval of time (expressed as a + timestamp). A packet belonging to the test session that is being set + up by the current Request-Session command will be considered lost if + it is not received during Timeout seconds after it is sent. + + Type-P Descriptor covers only a subset of (very large) Type-P space. + If the first two bits of the Type-P Descriptor are 00, then the + subsequent six bits specify the requested Differentiated Services + Codepoint (DSCP) value of sent OWAMP-Test packets, as defined in + [RFC2474]. If the first two bits of Type-P descriptor are 01, then + the subsequent 16 bits specify the requested PHB Identification Code + (PHB ID), as defined in [RFC2836]. + + Therefore, the value of all zeros specifies the default best-effort + service. + + + + + +Shalunov, et al. Standards Track [Page 16] + +RFC 4656 One-way Active Measurement Protocol September 2006 + + + If Conf-Sender is set, the Type-P Descriptor is to be used to + configure the sender to send packets according to its value. If + Conf-Sender is not set, the Type-P Descriptor is a declaration of how + the sender will be configured. + + If Conf-Sender is set and the server does not recognize the Type-P + Descriptor, or it cannot or does not wish to set the corresponding + attributes on OWAMP-Test packets, it SHOULD reject the session + request. If Conf-Sender is not set, the server SHOULD accept or + reject the session, paying no attention to the value of the Type-P + Descriptor. + + To each Request-Session message, an OWAMP server MUST respond with an + Accept-Session message: + + 0 1 2 3 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Accept | MBZ | Port | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-| + | | + | SID (16 octets) | + | | + | | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | | + | MBZ (12 octets) | + | | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | | + | HMAC (16 octets) | + | | + | | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + In this message, zero in the Accept field means that the server is + willing to conduct the session. A non-zero value indicates rejection + of the request. The full list of available Accept values is + described in Section 3.3, "Values of the Accept Field". + + If the server rejects a Request-Session message, it SHOULD not close + the TCP connection. The client MAY close it if it receives a + negative response to the Request-Session message. + + The meaning of Port in the response depends on the values of Conf- + Sender and Conf-Receiver in the query that solicited the response. + If both were set, the Port field is unused. If only Conf-Sender was + set, Port is the port from which to expect OWAMP-Test packets. If + + + +Shalunov, et al. Standards Track [Page 17] + +RFC 4656 One-way Active Measurement Protocol September 2006 + + + only Conf-Receiver was set, Port is the port to which OWAMP-Test + packets are sent. + + If only Conf-Sender was set, the SID field in the response is unused. + Otherwise, SID is a unique server-generated session identifier. It + can be used later as handle to fetch the results of a session. + + SIDs SHOULD be constructed by concatenation of the 4-octet IPv4 IP + number belonging to the generating machine, an 8-octet timestamp, and + a 4-octet random value. To reduce the probability of collisions, if + the generating machine has any IPv4 addresses (with the exception of + loopback), one of them SHOULD be used for SID generation, even if all + communication is IPv6-based. If it has no IPv4 addresses at all, the + last four octets of an IPv6 address MAY be used instead. Note that + SID is always chosen by the receiver. If truly random values are not + available, it is important that the SID be made unpredictable, as + knowledge of the SID might be used for access control. + +3.6. Send Schedules + + The sender and the receiver both need to know the same send schedule. + This way, when packets are lost, the receiver knows when they were + supposed to be sent. It is desirable to compress common schedules + and still to be able to use an arbitrary one for the test sessions. + In many cases, the schedule will consist of repeated sequences of + packets: this way, the sequence performs some test, and the test is + repeated a number of times to gather statistics. + + To implement this, we have a schedule with a given number of slots. + Each slot has a type and a parameter. Two types are supported: + exponentially distributed pseudo-random quantity (denoted by a code + of 0) and a fixed quantity (denoted by a code of 1). The parameter + is expressed as a timestamp and specifies a time interval. For a + type 0 slot (exponentially distributed pseudo-random quantity), this + interval is the mean value (or 1/lambda if the distribution density + function is expressed as lambda*exp(-lambda*x) for positive values of + x). For a type 1 (fixed quantity) slot, the parameter is the delay + itself. The sender starts with the beginning of the schedule and + executes the instructions in the slots: for a slot of type 0, wait an + exponentially distributed time with a mean of the specified parameter + and then send a test packet (and proceed to the next slot); for a + slot of type 1, wait the specified time and send a test packet (and + proceed to the next slot). The schedule is circular: when there are + no more slots, the sender returns to the first slot. + + The sender and the receiver need to be able to reproducibly execute + the entire schedule (so, if a packet is lost, the receiver can still + attach a send timestamp to it). Slots of type 1 are trivial to + + + +Shalunov, et al. Standards Track [Page 18] + +RFC 4656 One-way Active Measurement Protocol September 2006 + + + reproducibly execute. To reproducibly execute slots of type 0, we + need to be able to generate pseudo-random exponentially distributed + quantities in a reproducible manner. The way this is accomplished is + discussed later in Section 5, "Computing Exponentially Distributed + Pseudo-Random Numbers". + + Using this mechanism, one can easily specify common testing + scenarios. The following are some examples: + + + Poisson stream: a single slot of type 0. + + + Periodic stream: a single slot of type 1. + + + Poisson stream of back-to-back packet pairs: two slots, type 0 + with a non-zero parameter and type 1 with a zero parameter. + + Further, a completely arbitrary schedule can be specified (albeit + inefficiently) by making the number of test packets equal to the + number of schedule slots. In this case, the complete schedule is + transmitted in advance of an OWAMP-Test session. + +3.7. Starting Test Sessions + + Having requested one or more test sessions and received affirmative + Accept-Session responses, an OWAMP client MAY start the execution of + the requested test sessions by sending a Start-Sessions message to + the server. + + The format of this message is as follows: + + 0 1 2 3 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | 2 | | + +-+-+-+-+-+-+-+-+ | + | MBZ (15 octets) | + | | + | | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | | + | HMAC (16 octets) | + | | + | | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + The server MUST respond with an Start-Ack message (which SHOULD be + sent as quickly as possible). Start-Ack messages have the following + format: + + + +Shalunov, et al. Standards Track [Page 19] + +RFC 4656 One-way Active Measurement Protocol September 2006 + + + 0 1 2 3 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Accept | | + +-+-+-+-+-+-+-+-+ | + | MBZ (15 octets) | + | | + | | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | | + | HMAC (16 octets) | + | | + | | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + If Accept is non-zero, the Start-Sessions request was rejected; zero + means that the command was accepted. The full list of available + Accept values is described in Section 3.3, "Values of the Accept + Field". The server MAY, and the client SHOULD, close the connection + in the case of a rejection. + + The server SHOULD start all OWAMP-Test streams immediately after it + sends the response or immediately after their specified start times, + whichever is later. If the client represents a Sender, the client + SHOULD start its OWAMP-Test streams immediately after it sees the + Start-Ack response from the Server (if the Start-Sessions command was + accepted) or immediately after their specified start times, whichever + is later. See more on OWAMP-Test sender behavior in a separate + section below. + +3.8. Stop-Sessions + + The Stop-Sessions message may be issued by either the Control-Client + or the Server. The format of this command is as follows: + + 0 1 2 3 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | 3 | Accept | MBZ | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Number of Sessions | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | MBZ (8 octets) | + | | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + This is immediately followed by zero or more session description + records (the number of session description records is specified in + + + +Shalunov, et al. Standards Track [Page 20] + +RFC 4656 One-way Active Measurement Protocol September 2006 + + + the "Number of Sessions" field above). The session description + record is used to indicate which packets were actually sent by the + sender process (rather than skipped). The header of the session + description record is as follows: + + 0 1 2 3 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-| + | | + | SID (16 octets) | + | | + | | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Next Seqno | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Number of Skip Ranges | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + This is immediately followed by zero or more Skip Range descriptions + as specified by the "Number of Skip Ranges" field above. Skip Ranges + are simply two sequence numbers that, together, indicate a range of + packets that were not sent: + + 0 1 2 3 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-| + | First Seqno Skipped | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Last Seqno Skipped | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + Skip Ranges MUST be in order. The last (possibly full, possibly + incomplete) block (16 octets) of data MUST be padded with zeros, if + necessary. This ensures that the next session description record + starts on a block boundary. + + Finally, a single block (16 octets) of HMAC is concatenated on the + end to complete the Stop-Sessions message. + + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | | + | HMAC (16 octets) | + | | + | | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + All these records comprise one logical message: the Stop-Sessions + command. + + + +Shalunov, et al. Standards Track [Page 21] + +RFC 4656 One-way Active Measurement Protocol September 2006 + + + Above, the first octet (3) indicates that this is the Stop-Sessions + command. + + Non-zero Accept values indicate a failure of some sort. Zero values + indicate normal (but possibly premature) completion. The full list + of available Accept values is described in Section 3.3, "Values of + the Accept Field". + + If Accept had a non-zero value (from either party), results of all + OWAMP-Test sessions spawned by this OWAMP-Control session SHOULD be + considered invalid, even if a Fetch-Session with SID from this + session works for a different OWAMP-Control session. If Accept was + not transmitted at all (for whatever reason, including the TCP + connection used for OWAMP-Control breaking), the results of all + OWAMP-Test sessions spawned by this OWAMP-control session MAY be + considered invalid. + + Number of Sessions indicates the number of session description + records that immediately follow the Stop-Sessions header. + + Number of Sessions MUST contain the number of send sessions started + by the local side of the control connection that have not been + previously terminated by a Stop-Sessions command (i.e., the Control- + Client MUST account for each accepted Request-Session where Conf- + Receiver was set; the Control-Server MUST account for each accepted + Request-Session where Conf-Sender was set). If the Stop-Sessions + message does not account for exactly the send sessions controlled by + that side, then it is to be considered invalid and the connection + SHOULD be closed and any results obtained considered invalid. + + Each session description record represents one OWAMP-Test session. + + SID is the session identifier (SID) used to indicate which send + session is being described. + + Next Seqno indicates the next sequence number that would have been + sent from this send session. For completed sessions, this will equal + NumPackets from the Request-Session. + + Number of Skip Ranges indicates the number of holes that actually + occurred in the sending process. This is a range of packets that + were never actually sent by the sending process. For example, if a + send session is started too late for the first 10 packets to be sent + and this is the only hole in the schedule, then "Number of Skip + Ranges" would be 1. The single Skip Range description will have + First Seqno Skipped equal to 0 and Last Seqno Skipped equal to 9. + This is described further in the "Sender Behavior" section. + + + + +Shalunov, et al. Standards Track [Page 22] + +RFC 4656 One-way Active Measurement Protocol September 2006 + + + If the OWAMP-Control connection breaks when the Stop-Sessions command + is sent, the receiver MAY not completely invalidate the session + results. It MUST discard all record of packets that follow (in other + words, that have greater sequence number than) the last packet that + was actually received before any lost packet records. This will help + differentiate between packet losses that occurred in the network and + packets the sending process may have never sent. + + If a receiver of an OWAMP-Test session learns, through an OWAMP- + Control Stop-Sessions message, that the OWAMP-Test sender's last + sequence number is lower than any sequence number actually received, + the results of the complete OWAMP-Test session MUST be invalidated. + + A receiver of an OWAMP-Test session, upon receipt of an OWAMP-Control + Stop-Sessions command, MUST discard any packet records -- including + lost packet records -- with a (computed) send time that falls between + the current time minus Timeout and the current time. This ensures + statistical consistency for the measurement of loss and duplicates in + the event that the Timeout is greater than the time it takes for the + Stop-Sessions command to take place. + + To effect complete sessions, each side of the control connection + SHOULD wait until all sessions are complete before sending the Stop- + Sessions message. The completed time of each session is determined + as Timeout after the scheduled time for the last sequence number. + Endpoints MAY add a small increment to the computed completed time + for send endpoints to ensure that the Stop-Sessions message reaches + the receiver endpoint after Timeout. + + To effect a premature stop of sessions, the party that initiates this + command MUST stop its OWAMP-Test send streams to send the Session + Packets Sent values before sending this command. That party SHOULD + wait until receiving the response Stop-Sessions message before + stopping the receiver streams so that it can use the values from the + received Stop-Sessions message to validate the data. + + + + + + + + + + + + + + + + +Shalunov, et al. Standards Track [Page 23] + +RFC 4656 One-way Active Measurement Protocol September 2006 + + +3.9. Fetch-Session + + The format of this client command is as follows: + + 0 1 2 3 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | 4 | | + +-+-+-+-+-+-+-+-+ | + | MBZ (7 octets) | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Begin Seq | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | End Seq | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | | + | SID (16 octets) | + | | + | | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | | + | HMAC (16 octets) | + | | + | | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + Begin Seq is the sequence number of the first requested packet. End + Seq is the sequence number of the last requested packet. If Begin + Seq is all zeros and End Seq is all ones, complete session is said to + be requested. + + If a complete session is requested and the session is still in + progress or has terminated in any way other than normally, the + request to fetch session results MUST be denied. If an incomplete + session is requested, all packets received so far that fall into the + requested range SHOULD be returned. Note that, since no commands can + be issued between Start-Sessions and Stop-Sessions, incomplete + requests can only happen on a different OWAMP-Control connection + (from the same or different host as Control-Client). + + + + + + + + + + + + +Shalunov, et al. Standards Track [Page 24] + +RFC 4656 One-way Active Measurement Protocol September 2006 + + + The server MUST respond with a Fetch-Ack message. The format of this + server response is as follows: + + 0 1 2 3 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Accept | Finished | MBZ (2 octets) | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Next Seqno | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Number of Skip Ranges | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Number of Records | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | | + | HMAC (16 octets) | + | | + | | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + Again, non-zero in the Accept field means a rejection of command. + The server MUST specify zero for all remaining fields if Accept is + non-zero. The client MUST ignore all remaining fields (except for + the HMAC) if Accept is non-zero. The full list of available Accept + values is described in Section 3.3, "Values of the Accept Field". + + Finished is non-zero if the OWAMP-Test session has terminated. + + Next Seqno indicates the next sequence number that would have been + sent from this send session. For completed sessions, this will equal + NumPackets from the Request-Session. This information is only + available if the session has terminated. If Finished is zero, then + Next Seqno MUST be set to zero by the server. + + Number of Skip Ranges indicates the number of holes that actually + occurred in the sending process. This information is only available + if the session has terminated. If Finished is zero, then Skip Ranges + MUST be set to zero by the server. + + Number of Records is the number of packet records that fall within + the requested range. This number might be less than the Number of + Packets in the reproduction of the Request-Session command because of + a session that ended prematurely, or it might be greater because of + duplicates. + + If Accept was non-zero, this concludes the response to the Fetch- + Session message. If Accept was 0, the server then MUST immediately + send the OWAMP-Test session data in question. + + + +Shalunov, et al. Standards Track [Page 25] + +RFC 4656 One-way Active Measurement Protocol September 2006 + + + The OWAMP-Test session data consists of the following (concatenated): + + + A reproduction of the Request-Session command that was used to + start the session; it is modified so that actual sender and + receiver port numbers that were used by the OWAMP-Test session + always appear in the reproduction. + + + Zero or more (as specified) Skip Range descriptions. The last + (possibly full, possibly incomplete) block (16 octets) of Skip + Range descriptions is padded with zeros, if necessary. + + + 16 octets of HMAC. + + + Zero or more (as specified) packet records. The last (possibly + full, possibly incomplete) block (16 octets) of data is padded + with zeros, if necessary. + + + 16 octets of HMAC. + + Skip Range descriptions are simply two sequence numbers that, + together, indicate a range of packets that were not sent: + + 0 1 2 3 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-| + | First Seqno Skipped | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Last Seqno Skipped | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + Skip Range descriptions should be sent out in order, as sorted by + First Seqno. If any Skip Ranges overlap or are out of order, the + session data is to be considered invalid and the connection SHOULD be + closed and any results obtained considered invalid. + + Each packet record is 25 octets and includes 4 octets of sequence + number, 8 octets of send timestamp, 2 octets of send timestamp error + estimate, 8 octets of receive timestamp, 2 octets of receive + timestamp error estimate, and 1 octet of Time To Live (TTL), or Hop + Limit in IPv6: + + + + + + + + + + + +Shalunov, et al. Standards Track [Page 26] + +RFC 4656 One-way Active Measurement Protocol September 2006 + + + 0 1 2 3 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + 00| Seq Number | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + 04| Send Error Estimate | Receive Error Estimate | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + 08| Send Timestamp | + 12| | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + 16| Receive Timestamp | + 20| | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + 24| TTL | + +-+-+-+-+-+-+-+-+ + + Packet records are sent out in the same order the actual packets were + received. Therefore, the data is in arrival order. + + Note that lost packets (if any losses were detected during the + OWAMP-Test session) MUST appear in the sequence of packets. They can + appear either at the point when the loss was detected or at any later + point. Lost packet records are distinguished as follows: + + + A send timestamp filled with the presumed send time (as computed + by the send schedule). + + + A send error estimate filled with Multiplier=1, Scale=64, and S=0 + (see the OWAMP-Test description for definition of these quantities + and explanation of timestamp format and error estimate format). + + + A normal receive error estimate as determined by the error of the + clock being used to declare the packet lost. (It is declared lost + if it is not received by the Timeout after the presumed send time, + as determined by the receiver's clock.) + + + A receive timestamp consisting of all zero bits. + + + A TTL value of 255. + +4. OWAMP-Test + + This section describes OWAMP-Test protocol. It runs over UDP, using + sender and receiver IP and port numbers negotiated during the + Request-Session exchange. + + + + + + +Shalunov, et al. Standards Track [Page 27] + +RFC 4656 One-way Active Measurement Protocol September 2006 + + + As with OWAMP-Control, OWAMP-Test has three modes: unauthenticated, + authenticated, and encrypted. All OWAMP-Test sessions that are + spawned by an OWAMP-Control session inherit its mode. + + OWAMP-Control client, OWAMP-Control server, OWAMP-Test sender, and + OWAMP-Test receiver can potentially all be different machines. (In a + typical case, we expect that there will be only two machines.) + +4.1. Sender Behavior + +4.1.1. Packet Timings + + Send schedules based on slots, described previously, in conjunction + with scheduled session start time, enable the sender and the receiver + to compute the same exact packet sending schedule independently of + each other. These sending schedules are independent for different + OWAMP-Test sessions, even if they are governed by the same OWAMP- + Control session. + + Consider any OWAMP-Test session. Once Start-Sessions exchange is + complete, the sender is ready to start sending packets. Under normal + OWAMP use circumstances, the time to send the first packet is in the + near future (perhaps a fraction of a second away). The sender SHOULD + send packets as close as possible to their scheduled time, with the + following exception: if the scheduled time to send is in the past, + and is separated from the present by more than Timeout time, the + sender MUST NOT send the packet. (Indeed, such a packet would be + considered lost by the receiver anyway.) The sender MUST keep track + of which packets it does not send. It will use this to tell the + receiver what packets were not sent by setting Skip Ranges in the + Stop-Sessions message from the sender to the receiver upon completion + of the test. The Skip Ranges are also sent to a Fetch-Client as part + of the session data results. These holes in the sending schedule can + happen if a time in the past was specified in the Request-Session + command, or if the Start-Sessions exchange took unexpectedly long, or + if the sender could not start serving the OWAMP-Test session on time + due to internal scheduling problems of the OS. Packets that are in + the past but are separated from the present by less than Timeout + value SHOULD be sent as quickly as possible. With normal test rates + and timeout values, the number of packets in such a burst is limited. + Nevertheless, hosts SHOULD NOT intentionally schedule sessions so + that such bursts of packets occur. + + Regardless of any scheduling delays, each packet that is actually + sent MUST have the best possible approximation of its real time of + departure as its timestamp (in the packet). + + + + + +Shalunov, et al. Standards Track [Page 28] + +RFC 4656 One-way Active Measurement Protocol September 2006 + + +4.1.2. OWAMP-Test Packet Format and Content + + The sender sends the receiver a stream of packets with the schedule + specified in the Request-Session command. The sender SHOULD set the + TTL in IPv4 (or Hop Limit in IPv6) in the UDP packet to 255. The + format of the body of a UDP packet in the stream depends on the mode + being used. + + For unauthenticated mode: + + 0 1 2 3 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Sequence Number | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Timestamp | + | | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Error Estimate | | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | + | | + . . + . Packet Padding . + . . + | | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + + + + + + + + + + + + + + + + + + + + + + + + +Shalunov, et al. Standards Track [Page 29] + +RFC 4656 One-way Active Measurement Protocol September 2006 + + + For authenticated and encrypted modes: + + 0 1 2 3 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Sequence Number | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | | + | MBZ (12 octets) | + | | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Timestamp | + | | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Error Estimate | | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | + | MBZ (6 octets) | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | | + | HMAC (16 octets) | + | | + | | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | | + . . + . Packet Padding . + . . + | | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + The format of the timestamp is the same as in [RFC1305] and is as + follows: the first 32 bits represent the unsigned integer number of + seconds elapsed since 0h on 1 January 1900; the next 32 bits + represent the fractional part of a second that has elapsed since + then. + + So, Timestamp is represented as follows: + + 0 1 2 3 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Integer part of seconds | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Fractional part of seconds | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + + + + + +Shalunov, et al. Standards Track [Page 30] + +RFC 4656 One-way Active Measurement Protocol September 2006 + + + The Error Estimate specifies the estimate of the error and + synchronization. It has the following format: + + 0 1 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + |S|Z| Scale | Multiplier | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + The first bit, S, SHOULD be set if the party generating the timestamp + has a clock that is synchronized to UTC using an external source + (e.g., the bit should be set if GPS hardware is used and it indicates + that it has acquired current position and time or if NTP is used and + it indicates that it has synchronized to an external source, which + includes stratum 0 source, etc.). If there is no notion of external + synchronization for the time source, the bit SHOULD NOT be set. The + next bit has the same semantics as MBZ fields elsewhere: it MUST be + set to zero by the sender and ignored by everyone else. The next six + bits, Scale, form an unsigned integer; Multiplier is an unsigned + integer as well. They are interpreted as follows: the error estimate + is equal to Multiplier*2^(-32)*2^Scale (in seconds). (Notation + clarification: 2^Scale is two to the power of Scale.) Multiplier + MUST NOT be set to zero. If Multiplier is zero, the packet SHOULD be + considered corrupt and discarded. + + Sequence numbers start with zero and are incremented by one for each + subsequent packet. + + The minimum data segment length is, therefore, 14 octets in + unauthenticated mode, and 48 octets in both authenticated mode and + encrypted modes. + + The OWAMP-Test packet layout is the same in authenticated and + encrypted modes. The encryption and authentication operations are, + however, different. The difference is that in encrypted mode both + the sequence number and the timestamp are protected to provide + maximum data confidentiality and integrity protection, whereas in + authenticated mode the sequence number is protected while the + timestamp is sent in clear text. Sending the timestamp in clear text + in authenticated mode allows one to reduce the time between when a + timestamp is obtained by a sender and when the packet is shipped out. + In encrypted mode, the sender has to fetch the timestamp, encrypt it, + and send it; in authenticated mode, the middle step is removed, + potentially improving accuracy (the sequence number can be encrypted + and authenticated before the timestamp is fetched). + + In authenticated mode, the first block (16 octets) of each packet is + encrypted using AES Electronic Cookbook (ECB) mode. + + + +Shalunov, et al. Standards Track [Page 31] + +RFC 4656 One-way Active Measurement Protocol September 2006 + + + Similarly to each OWAMP-Control session, each OWAMP-Test session has + two keys: an AES Session-key and an HMAC Session-key. However, there + is a difference in how the keys are obtained: in the case of OWAMP- + Control, the keys are generated by the client and communicated (as + part of the Token) during connection setup as part of Set-Up-Response + message; in the case of OWAMP-Test, described here, the keys are + derived from the OWAMP-Control keys and the SID. + + The OWAMP-Test AES Session-key is obtained as follows: the OWAMP- + Control AES Session-key (the same AES Session-key as is used for the + corresponding OWAMP-Control session, where it is used in a different + chaining mode) is encrypted, using AES, with the 16-octet session + identifier (SID) as the key; this is a single-block ECB encryption; + its result is the OWAMP-Test AES Session-key to use in encrypting + (and decrypting) the packets of the particular OWAMP-Test session. + Note that all of OWAMP-Test AES Session-key, OWAMP-Control AES + Session-key, and the SID are comprised of 16 octets. + + The OWAMP-Test HMAC Session-key is obtained as follows: the OWAMP- + Control HMAC Session-key (the same HMAC Session-key as is used for + the corresponding OWAMP-Control session) is encrypted, using AES, + with the 16-octet session identifier (SID) as the key; this is a + two-block CBC encryption, always performed with IV=0; its result is + the OWAMP-Test HMAC Session-key to use in authenticating the packets + of the particular OWAMP-Test session. Note that all of OWAMP-Test + HMAC Session-key and OWAMP-Control HMAC Session-key are comprised of + 32 octets, while the SID is 16 octets. + + ECB mode used for encrypting the first block of OWAMP-Test packets in + authenticated mode does not involve any actual chaining; this way, + lost, duplicated, or reordered packets do not cause problems with + deciphering any packet in an OWAMP-Test session. + + In encrypted mode, the first two blocks (32 octets) are encrypted + using AES CBC mode. The AES Session-key to use is obtained in the + same way as the key for authenticated mode. Each OWAMP-Test packet + is encrypted as a separate stream, with just one chaining operation; + chaining does not span multiple packets so that lost, duplicated, or + reordered packets do not cause problems. The initialization vector + for the CBC encryption is a value with all bits equal to zero. + + Implementation note: Naturally, the key schedule for each OWAMP-Test + session MAY be set up only once per session, not once per packet. + + + + + + + + +Shalunov, et al. Standards Track [Page 32] + +RFC 4656 One-way Active Measurement Protocol September 2006 + + + HMAC in OWAMP-Test only covers the part of the packet that is also + encrypted. So, in authenticated mode, HMAC covers the first block + (16 octets); in encrypted mode, HMAC covers two first blocks (32 + octets). In OWAMP-Test HMAC is not encrypted (note that this is + different from OWAMP-Control, where encryption in stream mode is + used, so everything including the HMAC blocks ends up being + encrypted). + + In unauthenticated mode, no encryption or authentication is applied. + + Packet Padding in OWAMP-Test SHOULD be pseudo-random (it MUST be + generated independently of any other pseudo-random numbers mentioned + in this document). However, implementations MUST provide a + configuration parameter, an option, or a different means of making + Packet Padding consist of all zeros. + + The time elapsed between packets is computed according to the slot + schedule as mentioned in Request-Session command description. At + that point, we skipped over the issue of computing exponentially + distributed pseudo-random numbers in a reproducible fashion. It is + discussed later in a separate section. + +4.2. Receiver Behavior + + The receiver knows when the sender will send packets. The following + parameter is defined: Timeout (from Request-Session). Packets that + are delayed by more than Timeout are considered lost (or "as good as + lost"). Note that there is never an actual assurance of loss by the + network: a "lost" packet might still be delivered at any time. The + original specification for IPv4 required that packets be delivered + within TTL seconds or never (with TTL having a maximum value of 255). + To the best of the authors' knowledge, this requirement was never + actually implemented (and, of course, only a complete and universal + implementation would ensure that packets do not travel for longer + than TTL seconds). In fact, in IPv6, the name of this field has + actually been changed to Hop Limit. Further, IPv4 specification + makes no claims about the time it takes the packet to traverse the + last link of the path. + + The choice of a reasonable value of Timeout is a problem faced by a + user of OWAMP protocol, not by an implementor. A value such as two + minutes is very safe. Note that certain applications (such as + interactive "one-way ping" might wish to obtain the data faster than + that. + + As packets are received, + + + timestamp the received packet; + + + +Shalunov, et al. Standards Track [Page 33] + +RFC 4656 One-way Active Measurement Protocol September 2006 + + + + in authenticated or encrypted mode, decrypt and authenticate as + necessary (packets for which authentication fails MUST be + discarded); and + + + store the packet sequence number, send time, receive time, and the + TTL for IPv4 (or Hop Limit for IPv6) from the packet IP header for + the results to be transferred. + + Packets not received within the Timeout are considered lost. They + are recorded with their true sequence number, presumed send time, + receive time value with all bits being zero, and a TTL (or Hop Limit) + of 255. + + Implementations SHOULD fetch the TTL/Hop Limit value from the IP + header of the packet. If an implementation does not fetch the actual + TTL value (the only good reason not to do so is an inability to + access the TTL field of arriving packets), it MUST record the TTL + value as 255. + + Packets that are actually received are recorded in the order of + arrival. Lost packet records serve as indications of the send times + of lost packets. They SHOULD be placed either at the point where the + receiver learns about the loss or at any later point; in particular, + one MAY place all the records that correspond to lost packets at the + very end. + + Packets that have send time in the future MUST be recorded normally, + without changing their send timestamp, unless they have to be + discarded. (Send timestamps in the future would normally indicate + clocks that differ by more than the delay. Some data -- such as + jitter -- can be extracted even without knowledge of time difference. + For other kinds of data, the adjustment is best handled by the data + consumer on the basis of the complete information in a measurement + session, as well as, possibly, external data.) + + Packets with a sequence number that was already observed (duplicate + packets) MUST be recorded normally. (Duplicate packets are sometimes + introduced by IP networks. The protocol has to be able to measure + duplication.) + + If any of the following is true, the packet MUST be discarded: + + + Send timestamp is more than Timeout in the past or in the future. + + + Send timestamp differs by more than Timeout from the time when the + packet should have been sent according to its sequence number. + + + In authenticated or encrypted mode, HMAC verification fails. + + + +Shalunov, et al. Standards Track [Page 34] + +RFC 4656 One-way Active Measurement Protocol September 2006 + + +5. Computing Exponentially Distributed Pseudo-Random Numbers + + Here we describe the way exponential random quantities used in the + protocol are generated. While there is a fair number of algorithms + for generating exponential random variables, most of them rely on + having logarithmic function as a primitive, resulting in potentially + different values, depending on the particular implementation of the + math library. We use algorithm 3.4.1.S from [KNUTH], which is free + of the above-mentioned problem, and which guarantees the same output + on any implementation. The algorithm belongs to the ziggurat family + developed in the 1970s by G. Marsaglia, M. Sibuya, and J. H. Ahrens + [ZIGG]. It replaces the use of logarithmic function by clever bit + manipulation, still producing the exponential variates on output. + +5.1. High-Level Description of the Algorithm + + For ease of exposition, the algorithm is first described with all + arithmetic operations being interpreted in their natural sense. + Later, exact details on data types, arithmetic, and generation of the + uniform random variates used by the algorithm are given. It is an + almost verbatim quotation from [KNUTH], p.133. + + Algorithm S: Given a real positive number "mu", produce an + exponential random variate with mean "mu". + + First, the constants + + Q[k] = (ln2)/(1!) + (ln2)^2/(2!) + ... + (ln2)^k/(k!), 1 <= k <= 11 + + are computed in advance. The exact values which MUST be used by all + implementations are given in the next section. This is necessary to + ensure that exactly the same pseudo-random sequences are produced by + all implementations. + + S1. [Get U and shift.] Generate a 32-bit uniform random binary + fraction + + U = (.b0 b1 b2 ... b31) [note the binary point] + + Locate the first zero bit b_j and shift off the leading (j+1) bits, + setting U <- (.b_{j+1} ... b31) + + Note: In the rare case that the zero has not been found, it is + prescribed that the algorithm return (mu*32*ln2). + + S2. [Immediate acceptance?] If U < ln2, set X <- mu*(j*ln2 + U) and + terminate the algorithm. (Note that Q[1] = ln2.) + + + + +Shalunov, et al. Standards Track [Page 35] + +RFC 4656 One-way Active Measurement Protocol September 2006 + + + S3. [Minimize.] Find the least k >= 2 such that U < Q[k]. Generate k + new uniform random binary fractions U1,...,Uk and set V <- + min(U1,...,Uk). + + S4. [Deliver the answer.] Set X <- mu*(j + V)*ln2. + +5.2. Data Types, Representation, and Arithmetic + + The high-level algorithm operates on real numbers, typically + represented as floating point numbers. This specification prescribes + that unsigned 64-bit integers be used instead. + + u_int64_t integers are interpreted as real numbers by placing the + decimal point after the first 32 bits. In other words, conceptually, + the interpretation is given by the following map: + + u_int64_t u; + + u |--> (double)u / (2**32) + + The algorithm produces a sequence of such u_int64_t integers that, + for any given value of SID, is guaranteed to be the same on any + implementation. + + We specify that the u_int64_t representations of the first 11 values + of the Q array in the high-level algorithm MUST be as follows: + + #1 0xB17217F8, + #2 0xEEF193F7, + #3 0xFD271862, + #4 0xFF9D6DD0, + #5 0xFFF4CFD0, + #6 0xFFFEE819, + #7 0xFFFFE7FF, + #8 0xFFFFFE2B, + #9 0xFFFFFFE0, + #10 0xFFFFFFFE, + #11 0xFFFFFFFF + + For example, Q[1] = ln2 is indeed approximated by 0xB17217F8/(2**32) + = 0.693147180601954; for j > 11, Q[j] is 0xFFFFFFFF. + + Small integer j in the high-level algorithm is represented as + u_int64_t value j * (2**32). + + Operation of addition is done as usual on u_int64_t numbers; however, + the operation of multiplication in the high-level algorithm should be + replaced by + + + +Shalunov, et al. Standards Track [Page 36] + +RFC 4656 One-way Active Measurement Protocol September 2006 + + + (u, v) |---> (u * v) >> 32. + + Implementations MUST compute the product (u * v) exactly. For + example, a fragment of unsigned 128-bit arithmetic can be implemented + for this purpose (see the sample implementation in Appendix A). + +5.3. Uniform Random Quantities + + The procedure for obtaining a sequence of 32-bit random numbers (such + as U in algorithm S) relies on using AES encryption in counter mode. + To describe the exact working of the algorithm, we introduce two + primitives from Rijndael. Their prototypes and specification are + given below, and they are assumed to be provided by the supporting + Rijndael implementation, such as [RIJN]. + + + A function that initializes a Rijndael key with bytes from seed + (the SID will be used as the seed): + + void KeyInit(unsigned char seed[16]); + + + A function that encrypts the 16-octet block inblock with the + specified key, returning a 16-octet encrypted block. Here, + keyInstance is an opaque type used to represent Rijndael keys: + + void BlockEncrypt(keyInstance key, unsigned char inblock[16]); + + Algorithm Unif: given a 16-octet quantity seed, produce a sequence of + unsigned 32-bit pseudo-random uniformly distributed integers. In + OWAMP, the SID (session ID) from Control protocol plays the role of + seed. + + U1. [Initialize Rijndael key] key <- KeyInit(seed) [Initialize an + unsigned 16-octet (network byte order) counter] c <- 0 + + U2. [Need more random bytes?] Set i <- c mod 4. If (i == 0) set s + <- BlockEncrypt(key, c) + + U3. [Increment the counter as unsigned 16-octet quantity] c <- c + 1 + + U4. [Do output] Output the i_th quartet of octets from s starting + from high-order octets, converted to native byte order and + represented as OWPNum64 value (as in 3.b). + + U5. [Loop] Go to step U2. + + + + + + + +Shalunov, et al. Standards Track [Page 37] + +RFC 4656 One-way Active Measurement Protocol September 2006 + + +6. Security Considerations + +6.1. Introduction + + The goal of authenticated mode is to let one passphrase-protect the + service provided by a particular OWAMP-Control server. One can + imagine a variety of circumstances where this could be useful. + Authenticated mode is designed to prohibit theft of service. + + An additional design objective of the authenticated mode was to make + it impossible for an attacker who cannot read traffic between OWAMP- + Test sender and receiver to tamper with test results in a fashion + that affects the measurements, but not other traffic. + + The goal of encrypted mode is quite different: to make it hard for a + party in the middle of the network to make results look "better" than + they should be. This is especially true if one of client and server + does not coincide with either sender or receiver. + + Encryption of OWAMP-Control using AES CBC mode with blocks of HMAC + after each message aims to achieve two goals: (i) to provide secrecy + of exchange, and (ii) to provide authentication of each message. + +6.2. Preventing Third-Party Denial of Service + + OWAMP-Test sessions directed at an unsuspecting party could be used + for denial of service (DoS) attacks. In unauthenticated mode, + servers SHOULD limit receivers to hosts they control or to the OWAMP- + Control client. + + Unless otherwise configured, the default behavior of servers MUST be + to decline requests where the Receiver Address field is not equal to + the address that the control connection was initiated from or an + address of the server (or an address of a host it controls). Given + the TCP handshake procedure and sequence numbers in the control + connection, this ensures that the hosts that make such requests are + actually those hosts themselves, or at least on the path towards + them. If either this test or the handshake procedure were omitted, + it would become possible for attackers anywhere in the Internet to + request that large amounts of test packets be directed against victim + nodes somewhere else. + + In any case, OWAMP-Test packets with a given source address MUST only + be sent from the node that has been assigned that address (i.e., + address spoofing is not permitted). + + + + + + +Shalunov, et al. Standards Track [Page 38] + +RFC 4656 One-way Active Measurement Protocol September 2006 + + +6.3. Covert Information Channels + + OWAMP-Test sessions could be used as covert channels of information. + Environments that are worried about covert channels should take this + into consideration. + +6.4. Requirement to Include AES in Implementations + + Notice that AES, in counter mode, is used for pseudo-random number + generation, so implementation of AES MUST be included even in a + server that only supports unauthenticated mode. + +6.5. Resource Use Limitations + + An OWAMP server can consume resources of various kinds. The two most + important kinds of resources are network capacity and memory (primary + or secondary) for storing test results. + + Any implementation of OWAMP server MUST include technical mechanisms + to limit the use of network capacity and memory. Mechanisms for + managing the resources consumed by unauthenticated users and users + authenticated with a KeyID and passphrase SHOULD be separate. The + default configuration of an implementation MUST enable these + mechanisms and set the resource use limits to conservatively low + values. + + One way to design the resource limitation mechanisms is as follows: + assign each session to a user class. User classes are partially + ordered with "includes" relation, with one class ("all users") that + is always present and that includes any other class. The assignment + of a session to a user class can be based on the presence of + authentication of the session, the KeyID, IP address range, time of + day, and, perhaps, other factors. Each user class would have a limit + for usage of network capacity (specified in units of bit/second) and + memory for storing test results (specified in units of octets). + Along with the limits for resource use, current use would be tracked + by the server. When a session is requested by a user in a specific + user class, the resources needed for this session are computed: the + average network capacity use (based on the sending schedule) and the + maximum memory use (based on the number of packets and number of + octets each packet would need to be stored internally -- note that + outgoing sessions would not require any memory use). These resource + use numbers are added to the current resource use numbers for the + given user class; if such addition would take the resource use + outside of the limits for the given user class, the session is + rejected. When resources are reclaimed, corresponding measures are + subtracted from the current use. Network capacity is reclaimed as + soon as the session ends. Memory is reclaimed when the data is + + + +Shalunov, et al. Standards Track [Page 39] + +RFC 4656 One-way Active Measurement Protocol September 2006 + + + deleted. For unauthenticated sessions, memory consumed by an OWAMP- + Test session SHOULD be reclaimed after the OWAMP-Control connection + that initiated the session is closed (gracefully or otherwise). For + authenticated sessions, the administrator who configures the service + should be able to decide the exact policy, but useful policy + mechanisms that MAY be implemented are the ability to automatically + reclaim memory when the data is retrieved and the ability to reclaim + memory after a certain configurable (based on user class) period of + time passes after the OWAMP-Test session terminates. + +6.6. Use of Cryptographic Primitives in OWAMP + + At an early stage in designing the protocol, we considered using + Transport Layer Security (TLS) [RFC2246, RFC3546] and IPsec [RFC2401] + as cryptographic security mechanisms for OWAMP; later, we also + considered DTLS. The disadvantages of those are as follows (not an + exhaustive list): + + Regarding TLS: + + + TLS could be used to secure TCP-based OWAMP-Control, but it would + be difficult to use it to secure UDP-based OWAMP-Test: OWAMP-Test + packets, if lost, are not resent, so packets have to be + (optionally) encrypted and authenticated while retaining + individual usability. Stream-based TLS cannot be easily used for + this. + + + Dealing with streams, TLS does not authenticate individual + messages (even in OWAMP-Control). The easiest way out would be to + add some known-format padding to each message and to verify that + the format of the padding is intact before using the message. The + solution would thus lose some of its appeal ("just use TLS"). It + would also be much more difficult to evaluate the security of this + scheme with the various modes and options of TLS; it would almost + certainly not be secure with all. The capacity of an attacker to + replace parts of messages (namely, the end) with random garbage + could have serious security implications and would need to be + analyzed carefully. Suppose, for example, that a parameter that + is used in some form to control the rate were replaced by random + garbage; chances are that the result (an unsigned integer) would + be quite large. + + + Dependent on the mode of use, one can end up with a requirement + for certificates for all users and a PKI. Even if one is to + accept that PKI is desirable, there just isn't a usable one today. + + + + + + +Shalunov, et al. Standards Track [Page 40] + +RFC 4656 One-way Active Measurement Protocol September 2006 + + + + TLS requires a fairly large implementation. OpenSSL, for example, + is larger than our implementation of OWAMP as a whole. This can + matter for embedded implementations. + + Regarding DTLS: + + + Duplication and, similarly, reordering are network phenomena that + OWAMP needs to be able to measure; yet anti-replay measures and + reordering protection of DTLS would prevent the duplicated and + reordered packets from reaching the relevant part of the OWAMP + code. One could, of course, modify DTLS so that these protections + are weakened or even specify examining the messages in a carefully + crafted sequence somewhere in between DTLS checks; but then, of + course, the advantage of using an existing protocol would not be + realized. + + + In authenticated mode, the timestamp is in the clear and is not + protected cryptographically in any way, while the rest of the + message has the same protection as in encrypted mode. This mode + allows one to trade off cryptographic protection against accuracy + of timestamps. For example, the APAN hardware implementation of + OWAMP [APAN] is capable of supporting authenticated mode. The + accuracy of these measurements is in the sub-microsecond range. + The errors in OWAMP measurements of Abilene [Abilene] (done using + a software implementation, in its encrypted mode) exceed 10us. + Users in different environments have different concerns, and some + might very well care about every last microsecond of accuracy. At + the same time, users in these same environments might care about + access control to the service. Authenticated mode permits them to + control access to the server yet to use unprotected timestamps, + perhaps generated by a hardware device. + + Regarding IPsec: + + + What we now call authenticated mode would not be possible (in + IPsec you can't authenticate part of a packet). + + + The deployment paths of IPsec and OWAMP could be separate if OWAMP + does not depend on IPsec. After nine years of IPsec, only 0.05% + of traffic on an advanced backbone network, such as Abilene, uses + IPsec (for comparison purposes with encryption above layer 4, SSH + use is at 2-4% and HTTPS use is at 0.2-0.6%). It is desirable to + be able to deploy OWAMP on as large a number of different + platforms as possible. + + + + + + + +Shalunov, et al. Standards Track [Page 41] + +RFC 4656 One-way Active Measurement Protocol September 2006 + + + + The deployment problems of a protocol dependent on IPsec would be + especially acute in the case of lightweight embedded devices. + Ethernet switches, DSL "modems", and other such devices mostly do + not support IPsec. + + + The API for manipulating IPsec from an application is currently + poorly understood. Writing a program that needs to encrypt some + packets, to authenticate some packets, and to leave some open -- + for the same destination -- would become more of an exercise in + IPsec than in IP measurement. + + For the enumerated reasons, we decided to use a simple cryptographic + protocol (based on a block cipher in CBC mode) that is different from + TLS and IPsec. + +6.7. Cryptographic Primitive Replacement + + It might become necessary in the future to replace AES, or the way it + is used in OWAMP, with a new cryptographic primitive, or to make + other security-related changes to the protocol. OWAMP provides a + well-defined point of extensibility: the Modes word in the server + greeting and the Mode response in the Set-Up-Response message. For + example, if a simple replacement of AES with a different block cipher + with a 128-bit block is needed, this could be accomplished as + follows: take two bits from the reserved (MBZ) part of the Modes word + of the server greeting; use one of these bits to indicate encrypted + mode with the new cipher and another one to indicate authenticated + mode with the new cipher. (Bit consumption could, in fact, be + reduced from two to one, if the client is allowed to return a mode + selection with more than a single bit set: one could designate a + single bit to mean that the new cipher is supported (in the case of + the server) or selected (in the case of the client) and continue to + use already allocated bits for authenticated and encrypted modes; + this optimization is unimportant conceptually, but it could be useful + in practice to make the best use of bits.) Then, if the new cipher + is negotiated, all subsequent operations simply use it instead of + AES. Note that the normal transition sequence would be used in such + a case: implementations would probably first start supporting and + preferring the new cipher, and then drop support for the old cipher + (presumably no longer considered secure). + + + + + + + + + + + +Shalunov, et al. Standards Track [Page 42] + +RFC 4656 One-way Active Measurement Protocol September 2006 + + + If the need arises to make more extensive changes (perhaps to replace + AES with a 256-bit-block cipher), this would be more difficult and + would require changing the layout of the messages. However, the + change can still be conducted within the framework of OWAMP + extensibility using the Modes/Mode words. The semantics of the new + bits (or single bit, if the optimization described above is used) + would include the change to message layout as well as the change in + the cryptographic primitive. + + Each of the bits in the Modes word can be used for an independent + extension. The extensions signaled by various bits are orthogonal; + for example, one bit might be allocated to change from AES-128 to + some other cipher, another bit might be allocated to add a protocol + feature (such as, e.g., support for measuring over multicast), yet + another might be allocated to change a key derivation function, etc. + The progression of versions is not a linear order, but rather a + partial order. An implementation can implement any subset of these + features (of course, features can be made mandatory to implement, + e.g., new more secure ciphers if they are needed). + + Should a cipher with a different key size (say, a 256-bit key) become + needed, a new key derivation function for OWAMP-Test keys would also + be needed. The semantics of change in the cipher SHOULD then in the + future be tied to the semantics of change in the key derivation + function (KDF). One KDF that might be considered for the purpose + might be a pseudo-random function (PRF) with appropriately sized + output, such as 256 bits (perhaps HMAC-SHA256, if it is then still + considered a secure PRF), which could then be used to derive the + OWAMP-Test session keys from the OWAMP-Control session key by using + the OWAMP-Control session key as the HMAC key and the SID as HMAC + message. + + Note that the replacement scheme outlined above is trivially + susceptible to downgrade attacks: a malicious party in the middle can + flip modes bits as the mode is negotiated so that the oldest and + weakest mode supported by the two parties is used. If this is deemed + problematic at the time of cryptographic primitive replacement, the + scheme might be augmented with a measure to prevent such an attack + (by perhaps exchanging the modes again once a secure communications + channel is established, comparing the two sets of mode words, and + dropping the connection should they not match). + +6.8. Long-term Manually Managed Keys + + OWAMP-Control uses long-term keys with manual management. These keys + are used to automatically negotiate session keys for each OWAMP- + Control session running in authenticated or encrypted mode. The + number of these keys managed by a server scales linearly with (and, + + + +Shalunov, et al. Standards Track [Page 43] + +RFC 4656 One-way Active Measurement Protocol September 2006 + + + in fact, is equal to) the number of administratively different users + (perhaps particular humans, roles, or robots representing sites) that + need to connect to this server. Similarly, the number of different + manual keys managed by each client is the number of different servers + that the client needs to connect to. This use of manual long-term + keys is compliant with [BCP107]. + +6.9. (Not) Using Time as Salt + + A natural idea is to use the current time as salt when deriving + session keys. Unfortunately, this appears to be too limiting. + + Although OWAMP is often run on hosts with well-synchronized clocks, + it is also possible to run it on hosts with clocks completely + untrained. The delays obtained thus are, of course, not directly + usable; however, some metrics, such as unidirectional loss, + reordering, measures of congestion such as the median delay minus + minimum, and many others are usable directly and immediately (and + improve upon the information that would have been provided by a + round-trip measurement). Further, even delay information can be + useful with appropriate post-processing. Indeed, one can even argue + that running the clocks free and post-processing the results of a + mesh of measurements will result in better accuracy, as more + information is available a posteriori and correlation of data from + different hosts is possible in post-processing, but not with online + clock training. + + Given this, time is not used as salt in key derivation. + +6.10. The Use of AES-CBC and HMAC + + OWAMP relies on AES-CBC for confidentiality and on HMAC-SHA1 + truncated to 128 bits for message authentication. Random IV choice + is important for prevention of a codebook attack on the first block + (it should also be noted that, with its 128-bit block size, AES is + more resistant to codebook attacks than are ciphers with shorter + blocks; we use random IV anyway). + + HMAC MUST verify. It is crucial to check for this before using the + message; otherwise, existential forgery becomes possible. The + complete message for which HMAC verification fails MUST be discarded + (both for short messages consisting of a few blocks and potentially + for long messages, such as a response to the Fetch-Session command). + If such a message is part of OWAMP-Control, the connection MUST be + dropped. + + Since OWAMP messages can have different numbers of blocks, the + existential forgery attack described in example 9.62 of [MENEZES] + + + +Shalunov, et al. Standards Track [Page 44] + +RFC 4656 One-way Active Measurement Protocol September 2006 + + + becomes a concern. To prevent it (and to simplify implementation), + the length of any message becomes known after decrypting its first + block. + + A special case is the first (fixed-length) message sent by the + client. There, the token is a concatenation of the 128-bit challenge + (transmitted by the server in the clear), a 128-bit AES Session-key + (generated randomly by the client, encrypted with AES-CBC with IV=0), + and a 256-bit HMAC-SHA1 Session-key used for authentication. Since + IV=0, the challenge (a single cipher block) is simply encrypted with + the secret key. Therefore, we rely on resistance of AES to chosen + plaintext attacks (as the challenge could be substituted by an + attacker). It should be noted that the number of blocks of chosen + plaintext an attacker can have encrypted with the secret key is + limited by the number of sessions the client wants to initiate. An + attacker who knows the encryption of a server's challenge can produce + an existential forgery of the session key and thus disrupt the + session; however, any attacker can disrupt a session by corrupting + the protocol messages in an arbitrary fashion. Therefore, no new + threat is created here; nevertheless, we require that the server + never issues the same challenge twice. (If challenges are generated + randomly, a repetition would occur, on average, after 2^64 sessions; + we deem this satisfactory as this is enough even for an implausibly + busy server that participates in 1,000,000 sessions per second to go + without repetitions for more than 500 centuries.) With respect to + the second part of the token, an attacker can produce an existential + forgery of the session key by modifying the second half of the + client's token while leaving the first part intact. This forgery, + however, would be immediately discovered by the client when the HMAC + on the server's next message (acceptance or rejection of the + connection) does not verify. + +7. Acknowledgements + + We would like to thank Guy Almes, Mark Allman, Jari Arkko, Hamid + Asgari, Steven Van den Berghe, Eric Boyd, Robert Cole, Joan + Cucchiara, Stephen Donnelly, Susan Evett, Sam Hartman, Kaynam + Hedayat, Petri Helenius, Scott Hollenbeck, Russ Housley, Kitamura + Yasuichi, Daniel H. T. R. Lawson, Will E. Leland, Bruce A. Mah, + Allison Mankin, Al Morton, Attila Pasztor, Randy Presuhn, Matthew + Roughan, Andy Scherrer, Henk Uijterwaal, and Sam Weiler for their + comments, suggestions, reviews, helpful discussion and proof-reading. + +8. IANA Considerations + + IANA has allocated a well-known TCP port number (861) for the OWAMP- + Control part of the OWAMP protocol. + + + + +Shalunov, et al. Standards Track [Page 45] + +RFC 4656 One-way Active Measurement Protocol September 2006 + + +9. Internationalization Considerations + + The protocol does not carry any information in a natural language, + with the possible exception of the KeyID in OWAMP-Control, which is + encoded in UTF-8. + +10. References + +10.1. Normative References + + [AES] Advanced Encryption Standard (AES), + http://csrc.nist.gov/encryption/aes/ + + [BCP107] Bellovin, S. and R. Housley, "Guidelines for + Cryptographic Key Management", BCP 107, RFC 4107, + June 2005. + + [RFC2104] Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: + Keyed-Hashing for Message Authentication", RFC 2104, + February 1997. + + [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate + Requirement Levels", BCP 14, RFC 2119, March 1997. + + [RFC2330] Paxson, V., Almes, G., Mahdavi, J., and M. Mathis, + "Framework for IP Performance Metrics", RFC 2330, May + 1998. + + [RFC2474] Nichols, K., Blake, S., Baker, F., and D. Black, + "Definition of the Differentiated Services Field (DS + Field) in the IPv4 and IPv6 Headers", RFC 2474, + December 1998. + + [RFC2679] Almes, G., Kalidindi, S., and M. Zekauskas, "A One- + way Delay Metric for IPPM", RFC 2679, September 1999. + + [RFC2680] Almes, G., Kalidindi, S., and M. Zekauskas, "A One- + way Packet Loss Metric for IPPM", RFC 2680, September + 1999. + + [RFC2836] Brim, S., Carpenter, B., and F. Le Faucheur, "Per Hop + Behavior Identification Codes", RFC 2836, May 2000. + + [RFC2898] Kaliski, B., "PKCS #5: Password-Based Cryptography + Specification Version 2.0", RFC 2898, September 2000. + + + + + + +Shalunov, et al. Standards Track [Page 46] + +RFC 4656 One-way Active Measurement Protocol September 2006 + + +10.2. Informative References + + [APAN] Z. Shu and K. Kobayashi, "HOTS: An OWAMP-Compliant + Hardware Packet Timestamper", In Proceedings of PAM + 2005, http://www.springerlink.com/index/ + W4GBD39YWC11GQTN.pdf + + [BRIX] Brix Networks, http://www.brixnet.com/ + + [ZIGG] J. H. Ahrens, U. Dieter, "Computer methods for + sampling from the exponential and normal + distributions", Communications of ACM, volume 15, + issue 10, 873-882, 1972. + http://doi.acm.org/10.1145/355604.361593 + + [MENEZES] A. J. Menezes, P. C. van Oorschot, and S. A. + Vanstone, Handbook of Applied Cryptography, CRC + Press, revised reprint with updates, 1997. + + [KNUTH] D. Knuth, The Art of Computer Programming, vol.2, 3rd + edition, 1998. + + [Abilene] One-way Latency Measurement (OWAMP), + http://e2epi.internet2.edu/owamp/ + + [RIJN] Reference ANSI C Implementation of Rijndael, + http://www.esat.kuleuven.ac.be/~rijmen/ + rijndael/rijndaelref.zip + + [RIPE] RIPE NCC Test-Traffic Measurements home, + http://www.ripe.net/test-traffic/. + + [SURVEYOR] Surveyor Home Page, + http://www.advanced.org/surveyor/. + + [SURVEYOR-INET] S. Kalidindi and M. Zekauskas, "Surveyor: An + Infrastructure for Network Performance Measurements", + Proceedings of INET'99, June 1999. + http://www.isoc.org/inet99/proceedings/4h/4h_2.htm + + [RFC1305] Mills, D., "Network Time Protocol (Version 3) + Specification, Implementation and Analysis", RFC + 1305, March 1992. + + [RFC2246] Dierks, T. and C. Allen, "The TLS Protocol Version + 1.0", RFC 2246, January 1999. + + + + + +Shalunov, et al. Standards Track [Page 47] + +RFC 4656 One-way Active Measurement Protocol September 2006 + + + [RFC2401] Kent, S. and R. Atkinson, "Security Architecture for + the Internet Protocol", RFC 2401, November 1998. + + [RFC3546] Blake-Wilson, S., Nystrom, M., Hopwood, D., + Mikkelsen, J., and T. Wright, "Transport Layer + Security (TLS) Extensions", RFC 3546, June 2003. + + [RFC4086] Eastlake, D., 3rd, Schiller, J., and S. Crocker, + "Randomness Requirements for Security", BCP 106, RFC + 4086, June 2005. + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +Shalunov, et al. Standards Track [Page 48] + +RFC 4656 One-way Active Measurement Protocol September 2006 + + +Appendix A: Sample C Code for Exponential Deviates + + The values in array Q[] are the exact values that MUST be used by all + implementations (see Sections 5.1 and 5.2). This appendix only + serves for illustrative purposes. + + /* + ** Example usage: generate a stream of exponential (mean 1) + ** random quantities (ignoring error checking during initialization). + ** If a variate with some mean mu other than 1 is desired, the output + ** of this algorithm can be multiplied by mu according to the rules + ** of arithmetic we described. + + ** Assume that a 16-octet 'seed' has been initialized + ** (as the shared secret in OWAMP, for example) + ** unsigned char seed[16]; + + ** OWPrand_context next; + + ** (initialize state) + ** OWPrand_context_init(&next, seed); + + ** (generate a sequence of exponential variates) + ** while (1) { + ** u_int64_t num = OWPexp_rand64(&next); + <do something with num here> + ... + ** } + */ + + #include <stdlib.h> + + typedef u_int64_t u_int64_t; + + /* (K - 1) is the first k such that Q[k] > 1 - 1/(2^32). */ + #define K 12 + + #define BIT31 0x80000000UL /* See if first bit in the lower + 32 bits is zero. */ + #define MASK32(n) ((n) & 0xFFFFFFFFUL) + + #define EXP2POW32 0x100000000ULL + + typedef struct OWPrand_context { + unsigned char counter[16];/* Counter (network byte order).*/ + keyInstance key; /* Key to encrypt the counter.*/ + unsigned char out[16]; /* The encrypted block.*/ + + + + +Shalunov, et al. Standards Track [Page 49] + +RFC 4656 One-way Active Measurement Protocol September 2006 + + + } OWPrand_context; + + /* + ** The array has been computed according to the formula: + ** + ** Q[k] = (ln2)/(1!) + (ln2)^2/(2!) + ... + (ln2)^k/(k!) + ** + ** as described in algorithm S. (The values below have been + ** multiplied by 2^32 and rounded to the nearest integer.) + ** These exact values MUST be used so that different implementation + ** produce the same sequences. + */ + static u_int64_t Q[K] = { + 0, /* Placeholder - so array indices start from 1. */ + 0xB17217F8, + 0xEEF193F7, + 0xFD271862, + 0xFF9D6DD0, + 0xFFF4CFD0, + 0xFFFEE819, + 0xFFFFE7FF, + 0xFFFFFE2B, + 0xFFFFFFE0, + 0xFFFFFFFE, + 0xFFFFFFFF + }; + + /* this element represents ln2 */ + #define LN2 Q[1] + + /* + ** Convert an unsigned 32-bit integer into a u_int64_t number. + */ + u_int64_t + OWPulong2num64(u_int32_t a) + { + return ((u_int64_t)1 << 32) * a; + } + + /* + ** Arithmetic functions on u_int64_t numbers. + */ + + /* + ** Addition. + */ + u_int64_t + OWPnum64_add(u_int64_t x, u_int64_t y) + + + +Shalunov, et al. Standards Track [Page 50] + +RFC 4656 One-way Active Measurement Protocol September 2006 + + + { + return x + y; + } + + /* + ** Multiplication. Allows overflow. Straightforward implementation + ** of Algorithm 4.3.1.M (p.268) from [KNUTH]. + */ + u_int64_t + OWPnum64_mul(u_int64_t x, u_int64_t y) + { + unsigned long w[4]; + u_int64_t xdec[2]; + u_int64_t ydec[2]; + + int i, j; + u_int64_t k, t, ret; + + xdec[0] = MASK32(x); + xdec[1] = MASK32(x>>32); + ydec[0] = MASK32(y); + ydec[1] = MASK32(y>>32); + + for (j = 0; j < 4; j++) + w[j] = 0; + + for (j = 0; j < 2; j++) { + k = 0; + for (i = 0; ; ) { + t = k + (xdec[i]*ydec[j]) + w[i + j]; + w[i + j] = t%EXP2POW32; + k = t/EXP2POW32; + if (++i < 2) + continue; + else { + w[j + 2] = k; + break; + } + } + } + + ret = w[2]; + ret <<= 32; + return w[1] + ret; + } + + + /* + + + +Shalunov, et al. Standards Track [Page 51] + +RFC 4656 One-way Active Measurement Protocol September 2006 + + + ** Seed the random number generator using a 16-byte quantity 'seed' + ** (== the session ID in OWAMP). This function implements step U1 + ** of algorithm Unif. + */ + + void + OWPrand_context_init(OWPrand_context *next, unsigned char *seed) + { + int i; + + /* Initialize the key */ + rijndaelKeyInit(next->key, seed); + + /* Initialize the counter with zeros */ + memset(next->out, 0, 16); + for (i = 0; i < 16; i++) + next->counter[i] = 0UL; + } + + + /* + ** Random number generating functions. + */ + + /* + ** Generate and return a 32-bit uniform random value (saved in the + **less significant half of the u_int64_t). This function implements + **steps U2-U4 of the algorithm Unif. + */ + u_int64_t + OWPunif_rand64(OWPrand_context *next) + { + int j; + u_int8_t *buf; + u_int64_t ret = 0; + + /* step U2 */ + u_int8_t i = next->counter[15] & (u_int8_t)3; + if (!i) + rijndaelEncrypt(next->key, next->counter, next->out); + + /* Step U3. Increment next.counter as a 16-octet single + quantity in network byte order for AES counter mode. */ + for (j = 15; j >= 0; j--) + if (++next->counter[j]) + break; + + /* Step U4. Do output. The last 4 bytes of ret now contain + + + +Shalunov, et al. Standards Track [Page 52] + +RFC 4656 One-way Active Measurement Protocol September 2006 + + + the random integer in network byte order */ + buf = &next->out[4*i]; + for (j=0; j<4; j++) { + ret <<= 8; + ret += *buf++; + } + return ret; + } + + /* + ** Generate an exponential deviate with mean 1. + */ + u_int64_t + OWPexp_rand64(OWPrand_context *next) + { + unsigned long i, k; + u_int32_t j = 0; + u_int64_t U, V, J, tmp; + + /* Step S1. Get U and shift */ + U = OWPunif_rand64(next); + + while ((U & BIT31) && (j < 32)) { /* Shift until first 0. */ + U <<= 1; + j++; + } + /* Remove the 0 itself. */ + U <<= 1; + + U = MASK32(U); /* Keep only the fractional part. */ + J = OWPulong2num64(j); + + /* Step S2. Immediate acceptance? */ + if (U < LN2) /* return (j*ln2 + U) */ + return OWPnum64_add(OWPnum64_mul(J, LN2), U); + + /* Step S3. Minimize. */ + for (k = 2; k < K; k++) + if (U < Q[k]) + break; + V = OWPunif_rand64(next); + for (i = 2; i <= k; i++) { + tmp = OWPunif_rand64(next); + if (tmp < V) + V = tmp; + } + + /* Step S4. Return (j+V)*ln2 */ + + + +Shalunov, et al. Standards Track [Page 53] + +RFC 4656 One-way Active Measurement Protocol September 2006 + + + return OWPnum64_mul(OWPnum64_add(J, V), LN2); + } + +Appendix B: Test Vectors for Exponential Deviates + + It is important that the test schedules generated by different + implementations from identical inputs be identical. The non-trivial + part is the generation of pseudo-random exponentially distributed + deviates. To aid implementors in verifying interoperability, several + test vectors are provided. For each of the four given 128-bit values + of SID represented as hexadecimal numbers, 1,000,000 exponentially + distributed 64-bit deviates are generated as described above. As + they are generated, they are all added to each other. The sum of all + 1,000,000 deviates is given as a hexadecimal number for each SID. An + implementation MUST produce exactly these hexadecimal numbers. To + aid in the verification of the conversion of these numbers to values + of delay in seconds, approximate values are given (assuming + lambda=1). An implementation SHOULD produce delay values in seconds + that are close to the ones given below. + + SID = 0x2872979303ab47eeac028dab3829dab2 + SUM[1000000] = 0x000f4479bd317381 (1000569.739036 seconds) + + SID = 0x0102030405060708090a0b0c0d0e0f00 + SUM[1000000] = 0x000f433686466a62 (1000246.524512 seconds) + + SID = 0xdeadbeefdeadbeefdeadbeefdeadbeef + SUM[1000000] = 0x000f416c8884d2d3 (999788.533277 seconds) + + SID = 0xfeed0feed1feed2feed3feed4feed5ab + SUM[1000000] = 0x000f3f0b4b416ec8 (999179.293967 seconds) + + + + + + + + + + + + + + + + + + + + +Shalunov, et al. Standards Track [Page 54] + +RFC 4656 One-way Active Measurement Protocol September 2006 + + +Authors' Addresses + + Stanislav Shalunov + Internet2 + 1000 Oakbrook Drive, Suite 300 + Ann Arbor, MI 48104 + + EMail: shalunov@internet2.edu + WWW: http://www.internet2.edu/~shalunov/ + + + Benjamin Teitelbaum + Internet2 + 1000 Oakbrook Drive, Suite 300 + Ann Arbor, MI 48104 + + EMail: ben@internet2.edu + WWW: http://people.internet2.edu/~ben/ + + + Anatoly Karp + Computer Sciences Department + University of Wisconsin-Madison + Madison, WI 53706 + + EMail: akarp@cs.wisc.edu + + + Jeff W. Boote + Internet2 + 1000 Oakbrook Drive, Suite 300 + Ann Arbor, MI 48104 + + EMail: boote@internet2.edu + + + Matthew J. Zekauskas + Internet2 + 1000 Oakbrook Drive, Suite 300 + Ann Arbor, MI 48104 + + EMail: matt@internet2.edu + + + + + + + + + +Shalunov, et al. Standards Track [Page 55] + +RFC 4656 One-way Active Measurement Protocol September 2006 + + +Full Copyright Statement + + Copyright (C) The Internet Society (2006). + + This document is subject to the rights, licenses and restrictions + contained in BCP 78, and except as set forth therein, the authors + retain all their rights. + + This document and the information contained herein are provided on an + "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS + OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET + ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, + INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE + INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED + WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. + +Intellectual Property + + The IETF takes no position regarding the validity or scope of any + Intellectual Property Rights or other rights that might be claimed to + pertain to the implementation or use of the technology described in + this document or the extent to which any license under such rights + might or might not be available; nor does it represent that it has + made any independent effort to identify any such rights. Information + on the procedures with respect to rights in RFC documents can be + found in BCP 78 and BCP 79. + + Copies of IPR disclosures made to the IETF Secretariat and any + assurances of licenses to be made available, or the result of an + attempt made to obtain a general license or permission for the use of + such proprietary rights by implementers or users of this + specification can be obtained from the IETF on-line IPR repository at + http://www.ietf.org/ipr. + + The IETF invites any interested party to bring to its attention any + copyrights, patents or patent applications, or other proprietary + rights that may cover technology that may be required to implement + this standard. Please address the information to the IETF at + ietf-ipr@ietf.org. + +Acknowledgement + + Funding for the RFC Editor function is provided by the IETF + Administrative Support Activity (IASA). + + + + + + + +Shalunov, et al. Standards Track [Page 56] + |