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+
+Network Working Group M. Maher
+Request for Comments: 2331 USC/ISI
+Category: Standards Track April 1998
+
+
+ ATM Signalling Support for IP over ATM - UNI Signalling 4.0 Update
+
+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 (1998). All Rights Reserved.
+
+Abstract
+
+ This memo describes how to efficiently use the ATM call control
+ signalling procedures defined in UNI Signalling 4.0 [SIG40] to
+ support IP over ATM environments as described in RFC 2225 [LAUB98]
+ and in RFC 2332 [LUC98]. Among the new features found in UNI
+ Signalling 4.0 are Available Bit Rate signalling and traffic
+ parameter negotiation. This memo highlights the features of UNI
+ Signalling 4.0 that provide IP entities capabilities for requesting
+ ATM service in sites with SVC support, whether it is private ATM or
+ publicly provisioned ATM, in which case the SVC support is probably
+ configured inside PVPs.
+
+ This document is only relevant to IP when used as the well known
+ "best effort" connectionless service. In particular, this means that
+ this document does not pertain to IP in the presence of implemented
+ IP Integrated Services. The topic of IP with Integrated Services
+ over ATM will be handled by a different specification or set of
+ specifications being worked on in the ISSLL WG.
+
+ This specification is a follow-on to RFC 1755, "ATM Signaling Support
+ for IP over ATM", which is based on UNI 3.1 signalling [UNI95].
+ Readers are assumed to be familiar with RFC 1755.
+
+
+
+
+
+
+
+
+
+Maher Standards Track [Page 1]
+
+RFC 2331 IP over ATM Signalling - SIG 4.0 Update April 1998
+
+
+Table of Contents
+
+ 1. Conventions ............................................... 2
+ 2. Overview .................................................. 2
+ 3. Use of Protocol Procedures ................................ 3
+ 3.1 VC Teardown........................................... 3
+ 4. Overview of Call Establishment Message Content ............ 3
+ 5. Description of Information Elements ....................... 4
+ 5.1 ATM Adaptation Layer Parameters ...................... 4
+ 5.2 Broadband Low Layer Information ..................... 5
+ 5.3 Traffic Management Issues and Related IEs............. 5
+ 5.3.1 ATM Traffic Descriptor ........................ 6
+ 5.3.1.1 Tagging vs. Dropping ................. 7
+ 5.3.2 Traffic Parameter Negotiation .................. 7
+ 5.3.3 Broadband Bearer Capability .................... 8
+ 5.3.4 QoS Parameter .................................. 8
+ 5.3.4.1 Signalling of Individual QoS Parameters 8
+ 5.4 ATM Addressing Information ........................... 9
+ 6. ABR Signalling In More Detail ............................ 9
+ 7. Frame Discard Capability .................................. 10
+ 8. Security Considerations ................................... 10
+ 9. Acknowledgements........................................... 10
+ 10. References ................................................ 10
+ 11. Author's Address .......................................... 12
+ Appendix A Sample Signalling Messages ........................ 13
+ Appendix B ABR and nrt-VBR Signalling Guidelines for IP Routers 15
+ Appendix C Combinations of Traffic Related Parameters ........ 18
+ Full Copyright Statement ...................................... 26
+
+1. Conventions
+
+ The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
+ "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
+ document are to be interpreted as described in RFC 2119 [BRA97].
+
+2. Overview
+
+ UNI Signalling version 4.0 (SIG 4.0) is the ATM Forum follow-on
+ specification to UNI 3.1 signalling (UNI 3.1). Among the new features
+ in SIG 4.0, those of particular interest to IP over ATM environments
+ are:
+
+ o Available Bit Rate (ABR) Signalling for Point-to-Point Calls
+ o Traffic Parameter Negotiation
+ o Frame Discard Support
+ o Leaf Initiated Join (LIJ) Capability
+ o ATM Anycast Capability
+ o Switched Virtual Path (VP) Service
+
+
+
+Maher Standards Track [Page 2]
+
+RFC 2331 IP over ATM Signalling - SIG 4.0 Update April 1998
+
+
+ This memo highlights the first three capabilities listed above. The
+ last three capabilities are not discussed because models for their
+ use in IP over ATM environments have not yet been defined. The ION
+ WG is considering the applicability of LIJ and Group Addressing to
+ the RFC2022 problem space. Furthermore, Anycast addressing is being
+ explored as a technique for supporting server discovery in ATM
+ networks.
+
+3. Use of Protocol Procedures
+
+ Section 3 in RFC 1755 introduces requirements of virtual circuit (VC)
+ management intended to prevent VC thrashing, excessive VC
+ consumption, and other related problems. This section updates RFC
+ 1755's requirements related to VC teardown.
+
+3.1. VC Teardown
+
+ In environments running layer 3 (L3) signalling protocols, such as
+ RSVP [RSVP], over ATM, data VCs might correspond to L3 reserved flows
+ (even if the VC is a 'best effort' VC). In such environments it is
+ beneficial for VCs to be torn down only when the L3 reservation has
+ expired. In other words, it is more efficient for the sender of a L3
+ reserved flow to initiate VC tear-down when the receiver(s) has
+ ceased refreshing the reservation. To support such L3 behavior,
+ systems implementing a Public ATM UNI interface and serving as the
+ _called_ party of a VCC MUST NOT use an inactivity timer on such a
+ VCC by default. A system MAY use an inactivity timer on such a VCC
+ if configured to do so.
+
+4. Overview of Call Establishment Message Content
+
+ Signalling messages are structured to contain mandatory and optional
+ variable length information elements (IEs). A SETUP message which
+ establishes an ATM connection to be used for IP and multiprotocol
+ interconnection calls MUST contain the following IEs:
+
+ AAL Parameters
+ ATM Traffic Descriptor
+ Broadband Bearer Capability
+ Broadband Low Layer Information
+ QoS Parameter
+ Called Party Number
+ Calling Party Number
+
+ and MAY, under certain circumstance contain the following IEs:
+
+
+
+
+
+
+Maher Standards Track [Page 3]
+
+RFC 2331 IP over ATM Signalling - SIG 4.0 Update April 1998
+
+
+ Calling Party Subaddress
+ Called Party Subaddress
+ Transit Network Selection
+
+ (New in SIG 4.0:)
+ Minimum Acceptable ATM Traffic Descriptor
+ Alternative ATM Traffic Descriptor
+ ABR Setup Parameters
+ ABR Additional Parameters
+ Connection Scope Selection
+ Extended QoS Parameters
+ End-to-End Transit Delay
+
+ In SIG 4.0, like UNI 3.1, the AAL Parameters and the Broadband Low
+ Layer Information IEs are optional in a SETUP message. However, in
+ support of IP over ATM these two IEs MUST be included. Appendix A
+ shows a sample setup message.
+
+5. Description of Information Elements
+
+ This section describes the coding of, and procedures surrounding,
+ information elements in SETUP and CONNECT messages. The first two IEs
+ described, ATM Adaptation Layer Parameters and Broadband Low Layer
+ Information, are categorized as having significance only to the end-
+ points of an ATM call supporting IP. That is, the network does not
+ process these IEs.
+
+5.1. ATM Adaptation Layer (AAL) Parameters
+
+ The AAL Parameters IE carries information about the ATM adaptation
+ layer to be used on the connection. The parameters specified in this
+ IE are the same as specified in [PER95].
+
+
+ Format and field values of AAL Parameters IE
+
+ ----------------------------------------------------------
+ | aal_parameters |
+ ----------------------------------------------------------
+ | aal_type 5 (AAL 5) |
+ | fwd_max_sdu_size_identifier 140 |
+ | fwd_max_sdu_size 65,535 (desired IP MTU) |
+ | bkw_max_sdu_size_identifier 129 |
+ | bkw_max_sdu_size 65,535 (desired IP MTU) |
+ | sscs_type identifier 132 |
+ | sscs_type 0 (null SSCS) |
+ ----------------------------------------------------------
+
+
+
+
+Maher Standards Track [Page 4]
+
+RFC 2331 IP over ATM Signalling - SIG 4.0 Update April 1998
+
+
+ This shows maximum size MTUs. In practice, most sites have used 9180
+ IP MTUs for ATM [RFC1626].
+
+5.2. Broadband Low Layer Information
+
+ Selection of an encapsulation to support IP over an ATM VCC is done
+ using the Broadband Low Layer Information (B-LLI) IE, along with the
+ AAL Parameters IE, and the B-LLI negotiation procedure. B-LLI
+ negotiation is described in [PER95] in Appendix D. The procedures
+ remain the same for this SIG 4.0 based specification.
+
+ Format of B-LLI IE indicating LLC/SNAP encapsulation
+
+ ----------------------------------------------------------
+ | bb_low_layer_information |
+ ----------------------------------------------------------
+ | layer_2_id 2 |
+ | user_information_layer 12 (lan_llc - ISO 8802/2) |
+ ----------------------------------------------------------
+
+5.3. Traffic Management Issues and Related IEs
+
+ The ATM Forum Traffic Management Sub-working group has completed
+ version 4.0 of their specification [TMGT40]. This latest version
+ focuses primarily on the definition of the ABR service category. As
+ opposed to the Unspecified Bit Rate (UBR) traffic class, ABR uses a
+ rate-based flow control mechanism to assure certain traffic
+ guarantees (bandwidth and delay). There has been much debate on
+ whether IP benefits from ABR, and if so, how IP should use ABR. The
+ IP Integrated Services (IIS) and RSVP models in IP add complexity to
+ this issue because mapping IIS traffic classes to ATM traffic classes
+ is not straightforward.
+
+ This document attempts only to present the required IP to ATM
+ signaling interface for IP over ATM systems that do not support IIS
+ as yet. It is an attempt to cause IP over ATM vendors to support
+ enough options for signalling the traffic characteristics of VCs
+ serving non-IIS IP datagrams. This specification also aims to give
+ guidance to ATM system administrators so that they can configure
+ their IP over ATM entities to conform to the varied services that
+ their ATM provider may have sold to them. By definition, IP without
+ IIS cannot be expected to provide a signalling interface that is
+ flexible and allows application specific traffic descriptors. The
+ topic of IP over ATM signalling for IP _with_ IIS is to be presented
+ in other specifications being produced by the ISSLL WG of the IETF.
+
+ An IP over ATM interface may be configured to support all the defined
+ ATM Service Categories (ASC). They are:
+
+
+
+Maher Standards Track [Page 5]
+
+RFC 2331 IP over ATM Signalling - SIG 4.0 Update April 1998
+
+
+ - CBR
+ - CBR with CLR specified (loss-permitting CBR)
+ - ABR
+ - UBR
+ - real time VBR
+ - non-real time VBR
+
+ The ATM Traffic Descriptor IE, Broadband Bearer Capability IE, and
+ the QoS Parameter IE together define the signalling view of ATM
+ traffic management. Additionally, the Extended QoS parameters IE and
+ the End-to-end Transit Delay IE may be used to provide more specifics
+ about traffic requirements, however this note does not provide
+ explicit recommendations on their use. Annex 9 of [SIG40] describes
+ a set of allowable combinations of traffic and QoS related
+ paramenters defined for SIG 4.0. This set includes all forms of
+ non-IIS IP signaling configurations that MUST be implemented in ATM
+ endsystems to accommodate varied sites' needs. The principle is that
+ IP over ATM service may be available in different sites by different
+ types of procured ATM service; for one site, a CBR PVP might be
+ cost-effective and then the SVCs that IP over ATM without IIS must
+ establish must be CBR. Similarly, VBR or ABR PVPs could be
+ provisioned. The intent of this document is to specify the use of
+ the most sensible parameters within this non-IIS configuration. For
+ instance, for non-IIS VBR, the SCR value may need to be hand-
+ configured for IP users, or for ABR, the PCR value may be link-rate
+ with a 0 MCR.
+
+ For the reader's convenience, we have replicated the tables found in
+ Annex 9 of [SIG40] in Appendix C of this document. Ideally this
+ document could recommend specific values for the various table
+ parameters that would offer the most sensible IP over ATM service.
+ Nevertheless, it is not possible to mandate specific values given the
+ varied scenarios of procured ATM service.
+
+5.3.1. ATM Traffic Descriptor
+
+ Even with the newly defined ABR ASC, the most convenient model for
+ supporting IP still corresponds to the best effort capability, the
+ UBR ASC. The rationale for this assertion stems from the fact that a
+ non-IIS IP service has no notion of the performance requirements of
+ the higher layers it supports. Therefore, if a site's configuration
+ allows use of UBR, users SHOULD signal for it using the IE's and
+ parameters pertaining to the UBR ATC. See Appendix C for the list of
+ those IE's and parameters.
+
+ Although we consider the UBR ASC the most natural ASC for best-effort
+ IP, ATM vendors that implement VBR and ABR services could possibly
+ create hooks for convenient use of these services. If this is the
+
+
+
+Maher Standards Track [Page 6]
+
+RFC 2331 IP over ATM Signalling - SIG 4.0 Update April 1998
+
+
+ case, IP routers may perhaps have the most to gain from use of VBR or
+ ABR services because of the large aggregated traffic volume they are
+ required to forward. See Appendix B for detailed suggestions on VBR
+ and ABR signalling for IP routers. We simply note here that, in
+ support of ABR service, two new subfields have been added in SIG 4.0
+ to the Traffic Descriptor IE. These fields are the forward and
+ backward 'Minimum Cell Rate' fields.
+
+5.3.1.1. Tagging vs. Dropping
+
+ The Traffic Descriptor IE contains a 'tagging' subfield used for
+ indicating whether the network is allowed to tag the source's data
+ cells. Tagging in the network may occur during periods of congestion
+ or when the source's traffic has violated the traffic contract for
+ the connection. See Section 4 of [TMGT40] for an explanation of ATM
+ connection conformance and the Usage Parameter Control (UPC)
+ function.
+
+ SIG 4.0 and TMGT 4.0 define two modes of UBR, UBR.1 which disables
+ tagging and UBR.2 which enables tagging (see Appendix C). In some
+ network environments there is no potential for UBR traffic sources to
+ violate the connection traffic contract because, either the user's
+ terminal equipment supports traffic shaping, or the network does not
+ enforce PCR. In such environments, the user SHOULD specify 'no
+ tagging' in the SETUP message (UBR.1). Specifying 'no tagging'
+ indicates to the network that cells should be dropped during periods
+ of congestion instead of being randomly marked/tagged as low
+ priority. Cells of packets that the source itself has marked as low
+ priority are dropped first, thereby preserving the source's
+ characterization of the traffic.
+
+ On the other hand, when the network applies PCR to the UPC function,
+ meaning it enforces PCR, and traffic shaping is not enabled at the
+ source, the source has the potential to violate the traffic contract
+ and SHOULD therefore signal for tagging (UBR.2). Tagging allows the
+ source's non-conforming cells to be tagged and forwarded instead of
+ dropped.
+
+5.3.2. Traffic Parameter Negotiation
+
+ SIG 4.0 allows certain traffic parameters to be negotiated during the
+ call establishment phase Traffic parameters cannot be 'renegotiated'
+ after the call is active. Two new IEs make negotiation possible:
+
+ - the Minimum Acceptable ATM Traffic Descriptor IE allows
+ negotiation of PCR parameters
+
+
+
+
+
+Maher Standards Track [Page 7]
+
+RFC 2331 IP over ATM Signalling - SIG 4.0 Update April 1998
+
+
+ - the Alternative ATM Traffic Descriptor IE allows negotiation of
+ other traffic parameters
+
+ A SETUP or CONNECT message may include ONLY one of the above IEs.
+ That is, the calling party may only offer an 'alternative' or
+ 'minimum' to the requested traffic parameters. (See Section 8 of
+ [SIG40].) IP over ATM entities SHOULD take advantage of this
+ capability whenever possible. In order to do so, IP over ATM entities
+ SHOULD specify PCR _equal_ to the link rate in the ATM Traffic
+ Descriptor IE of the SETUP message and a minimum of zero PCR in the
+ Minimum Acceptable ATM Traffic Descriptor IE.
+
+5.3.3. Broadband Bearer Capability
+
+ A new field in UNI signalling 4.0 called, 'ATM Transfer Capability'
+ (ATC), has been defined in the Broadband Bearer Capability IE for the
+ purpose of explicitly specifying the desired ATM traffic category.
+ The figure below shows the allowable ATC values.
+
+ Format and field values of Broadband Bearer Capability IE
+
+ -------------------------------------------------------------
+ | bb_bearer_capability |
+ ------------------------------------------------------------|
+ | spare 0 |
+ | bearer_class bcob-x,c,a or VP |
+ | transfer_capability cbr, rt-vbr, nrt-vbr, abr |
+ | susceptibility_to_clipping 0 (not suscept) |
+ | spare 0 |
+ | user_plane_configuration pt-to-pt, pt-to-mpt |
+ -------------------------------------------------------------
+
+5.3.4. QoS Parameter
+
+ Inclusion of the QoS Parameter IE is not mandatory in SIG 4.0. It
+ may be omitted from a SETUP message _if and only if_ the Extended QoS
+ Parameters IE is included (see next section). This specification
+ makes no explicit recommendation on the use of the QoS related IEs.
+
+5.3.4.1. Two IEs for Signalling of Individual QoS Parameters
+
+ SIG 4.0 allows for signalling of individual QoS parameters for the
+ purpose of giving the the network and called party a more exact
+ description of the desired delay and cell loss characteristics. The
+ two individual QoS related IEs, Extended QoS Parameters IE and End-
+ to-End Transit Delay IE, can be used in the SETUP and CONNECT
+ signaling messages in place of the 'generic' QoS Parameter IE. Note
+ that inclusion of these two IEs depends on the type of ATM service
+
+
+
+Maher Standards Track [Page 8]
+
+RFC 2331 IP over ATM Signalling - SIG 4.0 Update April 1998
+
+
+ category requested (see Annex 9 in [SIG40]).
+
+5.4. ATM Addressing Information
+
+ ATM addressing information is carried in the Called Party Number,
+ Calling Party Number, and, under certain circumstance, Called Party
+ Subaddress, and Calling Party Subaddress IE. The ATM Forum ILMI
+ Specification 4.0 [ILMI40] provides the procedure for an ATM
+ endsystem to learn its own ATM address from the ATM network, for use
+ in populating the Calling Party Number IE.
+
+ Format and field values of Called Party Number IE
+
+ ----------------------------------------------------------
+ | called_party_number |
+ ----------------------------------------------------------
+ | type_of_number (international number / unknown) |
+ | addr_plan_ident (ISDN / ATM Endsystem Address) |
+ | addr_number (E.164 / ATM Endsystem Address) |
+ ----------------------------------------------------------
+
+6. ABR Signaling In More Detail
+
+ The IEs and procedures pertaining to ABR signalling are briefly
+ described in this section. Nevertheless, this document makes no
+ specific recommendation on when to use the ABR service category for
+ IP VCCs or give suggestions on appropriate values for the various
+ parameters in the ABR related IEs.
+
+ Two new IEs have been defined for ABR signaling:
+
+ o ABR Setup Parameters
+ o ABR Additional Parameters
+
+ These IEs may be optionally included in a SETUP or CONNECT message.
+ The ABR Setup Parameters IE contains the following subfields:
+
+ - Forward/Backward ABR Initial Cell Rate
+ - Forward/Backward ABR Transient Buffer Exposure
+ - Cumulative RM Fixed Round Trip Time
+ - Forward/Backward Rate Increment Factor
+ - Forward/Backward Rate Decrease Factor
+
+ The ABR Additional Parameters IE contains one subfield:
+
+ - Forward/Backward Additional Parameters Record
+
+
+
+
+
+Maher Standards Track [Page 9]
+
+RFC 2331 IP over ATM Signalling - SIG 4.0 Update April 1998
+
+
+ The Additional Parameters Record value is a compressed encoding of a
+ set of ABR parameters (see [SIG40] and [ABRS]).
+
+7. Frame Discard Capability
+
+ The frame discard capability in SIG 4.0 is primarily based on the
+ 'Partial and Early Packet Discard' strategy [ROM94]. Its use is
+ defined for any of the ATM services, except for loss-less CBR. Frame
+ discard signaling MUST be supported by all IP over ATM entities and
+ it is RECOMMENDED that frame discard be signaled for all IP SVCs
+ because it has been proven to increase throughput under network
+ congestion. Signaling for frame discard is done by setting the frame
+ discard bit in the 'Traffic Management Options' subfield in the
+ Traffic Descriptor IE. It is possible that not all network entities
+ in the SVC path support frame discard, but it is required that they
+ all forward the signaling.
+
+8. Security Considerations
+
+ The ATM Forum Security sub-working group is currently defining
+ security mechanisms in ATM. The group has yet to produce a
+ specification, therefore it is premature to begin defining IP over
+ ATM signalling's use of ATM security. The ATM Forum is working on
+ authentication mechanisms for signalling and on mechanisms for
+ providing data integrity and confidentiality (e.g encryption). Lack
+ of these ATM security mechanisms prevents the authentication of the
+ originator of signalling messages, such as, connection setup request
+ or connection teardown request. IP Security (RFC1825) can be applied
+ to IP datagrams over ATM VCs to overcome the lack of security at the
+ ATM layer.
+
+9. Acknowledgements
+
+ The authors would like to thank the members of the ION working group
+ for their input. Special thanks to K.K. Ramakrishnan and Kerry
+ Fendick who contributed Appendix B of this document.
+
+REFERENCES
+
+ [ABRS] ATM Forum, "Addendum to UNI Signalling v4.0 for ABR Parameter
+ Negotiation", af-sig-0076.000; available at
+ ftp://ftp.atmforum.com/pub.
+
+ [ABRT] ATM Forum, "Addendum to Traffic Management v4.0 for ABR
+ Parameter Negotiation", af-tm-0077.000; available at
+ ftp://ftp.atmforum.com/pub.
+
+
+
+
+
+Maher Standards Track [Page 10]
+
+RFC 2331 IP over ATM Signalling - SIG 4.0 Update April 1998
+
+
+ [RFC1122] Braden, R., Editor, "Requirements for Internet Hosts --
+ Communication Layers", STD 3, RFC 1122, October 1989.
+
+ [RFC1633] Braden, R., Clark, D., and S. Shenker, "Integrated Service
+ in the Internet Architecture: An Overview", RFC 1633, June 1994.
+
+ [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
+ Requirement Levels", BCP 14, RFC 2119, March 1997.
+
+ [RFC1483] Heinanen, J., "Multiprotocol Encapsulation over ATM
+ Adaptation Layer 5", RFC 1483, July 1993.
+
+ [ILMI40] ATM Forum, "Integrated Local Management Interface (ILMI)
+ Specification Version 4.0", af-ilmi-0065.000, finalized September
+ 1996; available at ftp://ftp.atmforum.com/pub.
+
+ [ISO8473] ISO/IEC 8473, Information processing systems - Data
+ communications - Protocol for providing the connectionless-mode
+ network service, 1988.
+
+ [ISO9577] Information Technology - Telecommunication and information
+ exchange between systems - Protocol identification in the network
+ layer ISO/IEC TR9577 (International Standards Organization: Geneva,
+ 1990)
+
+ [LAUB98] Laubach, M., and J. Halpern, "Classical IP and ARP over
+ ATM", RFC 2225, April 1998.
+
+ [LUC98] Luciani, J., Katz, D., Piscitello, D., Cole, B., and N.
+ Doraswamy, "NBMA Next Hop Resolution Protocol (NHRP)", RFC 2332,
+ April 1998.
+
+ [RFC1755] Perez*, M., et. al., "ATM Signaling Support for IP over
+ ATM", RFC 1755, February 1995. (* see author's information below)
+
+ [ROM94] Romanow, A., and Floyd, S., Dynamics of TCP Traffic over ATM
+ Networks. IEEE JSAC, V. 13 N. 4, May 1995, p. 633-641. Abstract. An
+ earlier version appeared in SIGCOMM '94, August 1994, pp. 79-88.
+
+ [RFC2205] Braden, R., Zhang, L., Berson, S., Herzog, S., and S.
+ Jamin, "Resource ReSerVation Protocol (RSVP) - Version 1 Functional
+ Specification", RFC 2205, September 1997.
+
+ [SIG40] ATM Forum, "ATM User-Network Interface (UNI) Signalling
+ Specification Version 4.0", af-sig-0061.000, finalized July 1996;
+ available at ftp://ftp.atmforum.com/pub.
+
+
+
+
+
+Maher Standards Track [Page 11]
+
+RFC 2331 IP over ATM Signalling - SIG 4.0 Update April 1998
+
+
+ [TMGT40] ATM Forum, "Traffic Management Specification Version 4.0",
+ af-tm-0056.000, finalized April 1996; available at
+ ftp://ftp.atmforum.com/pub.
+
+ [UNI95] ATM Forum, "ATM User-Network Interface Specification Version
+ 3.1", Prentice Hall, Upper Saddle River, NJ, 1995.
+
+Author's Address
+
+ Maryann P. Maher (formerly Maryann Perez)
+ USC/ISI
+ 4350 N. Fairfax Drive, Suite 620
+ Arlington VA 22203
+
+ EMail: maher@isi.edu
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+Maher Standards Track [Page 12]
+
+RFC 2331 IP over ATM Signalling - SIG 4.0 Update April 1998
+
+
+Appendix A. A Sample SIG 4.0 SETUP Message
+
++--------------------------------------------------------------------+
+ SETUP
+
+ Information Elements/
+ Fields Value/(Meaning)
+ -------------------- ---------------
+
+aal_parameters
+ aal_type 5 (AAL 5)
+ fwd_max_sdu_size_ident 140
+ fwd_max_sdu_size (xmit IP MTU value)
+ bkw_max_sdu_size_ident 129
+ bkw_max_sdu_size (recv IP MTU, 0 for disallowing return traffic)
+ sscs_type identifier 132
+ sscs_type 0 (null SSCS)
+
+traffic_descriptor
+ fwd_peak_cell_rate_0_1_ident 132
+ fwd_peak_cell_rate_0_1 (link rate)
+ bkw_peak_cell_rate_0_1_ident 133
+ bkw_peak_cell_rate_0_1 (link rate)
+ traff_mngt_options_ident 191
+ fwd_frame_discard 1 (on)
+ bkw_frame_discard 1 (on if return traffic indicated)
+ spare 0
+ tagging_bkw 1 (on)
+ tagging_fwd 1 (on if return traffic indicated)
+ best_effort_indication 190 (on)
+
+minimum_acceptable_traffic_descriptor
+ fwd_peak_cell_rate_0_1_ident 132
+ fwd_peak_cell_rate_0_1 0
+ bkw_peak_cell_rate_0_1_ident 133
+ bkw_peak_cell_rate_0_1 0
+
+bb_bearer_capability /* a coding for specifying UBR like service */
+ spare 0
+ bearer_class 16 (BCOC-X)
+ spare 0
+ atm_transfer_capability 10 (nrt-vbr)
+ susceptibility_to_clipping 0 (not susceptible to clipping)
+ spare 0
+ user_plane_configuration 0 (point_to_point)
+
+
+
+
+
+
+Maher Standards Track [Page 13]
+
+RFC 2331 IP over ATM Signalling - SIG 4.0 Update April 1998
+
+
+bb_low_layer_information
+ layer_2_id 2
+ user_information_layer 12 (lan_llc - ISO 8802/2)
+
+qos_parameter
+ qos_class_fwd 0 (class 0)
+ qos_class_bkw 0 (class 0)
+
+called_party_number
+ type_of_number (international number / unknown)
+ addr_plan_ident (ISDN / ATM Endsystem Address)
+ number (E.164 / ATM Endsystem Address)
+
+calling_party_number
+ type_of_number (international number / unknown)
+ addr_plan_ident (ISDN / ATM Endsystem Address)
+ presentation_indic (presentation allowed)
+ spare 0
+ screening_indic (user_provided verified and passed)
+ number (E.164 / ATM Endsystem Address)
+
++--------------------------------------------------------------------+
+
+ Figure 1.
+ Sample contents of SETUP message
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+Maher Standards Track [Page 14]
+
+RFC 2331 IP over ATM Signalling - SIG 4.0 Update April 1998
+
+
+Appendix B. ABR and VBR Signaling Guidelines for IP Routers
+
+ When ATM is used to interconnect routers that are supporting a best
+ effort service, the ATM connection typically carries an aggregation
+ of IP flows, e.g., all best effort IP traffic between a pair of
+ routers. With the efforts undertaken by ATM to be more "packet
+ friendly" (e.g., frame discard), it is useful to examine ways that a
+ VC can provide service comparable to or better than that of a
+ dedicated or leased "link" in terms of performance and packet loss.
+
+ For ATM connections used to interconnect routers, a non-zero
+ bandwidth reservation may be required to achieve consistently
+ adequate performance for the aggregate set of flows. The support of
+ bandwidth commitments for an ATM connection carrying IP traffic helps
+ to assure that a certain fraction of each link's capacity is reserved
+ for the total IP traffic between the routers. Reserving bandwidth
+ for the aggregation of best-effort traffic between a pair of routers
+ is analogous to provisioning a particular link bandwidth between the
+ routers. There are at least 3 service classes defined in the ATM
+ Traffic Management specification that provide varying degrees of
+ capability that are suitable for interconnecting IP routers: UBR, ABR
+ and VBR non-real-time. Although the use of best-effort service (UBR)
+ at the ATM layer is the most straightforward and uncomplicated, it
+ lacks the capability to enforce bandwidth commitments.
+
+ Note that we are talking of providing a "virtual link" between
+ routers, for the aggregate traffic. The provisioning is for the
+ aggregate. It is therefore distinct from the per-flow bandwidth
+ reservations that might be appropriate for Integrated Services.
+
+ Even best-effort IP flows, when supported on an aggregate basis, have
+ some broad service goals. The primary one is that of keeping packet
+ loss rate reasonably small. A service class that strives to achieve
+ this, keeping in mind the tradeoff between complexity and adequate
+ service, is desirable. It has been recommended in this memo that UBR
+ be the default service for this. UBR with (some form of) packet
+ discard has the desirable goal of being simple in function, and it
+ appears that vendors will be supporting it. However, when available,
+ it may be quite worthwhile to consider ABR and VBR non-real-time
+ service classes.
+
+ Because AAL5 frames with missing cells are discarded by the receiver,
+ ATM bandwidth commitments are most useful if supported in the form of
+ a committed rate of cell delivery in complete, non-errored AAL5
+ frames delivered to the receiver. In addition, it is desirable for
+ the ATM connection to deliver additional complete frames, beyond this
+ commitment, on a best-effort basis.
+
+
+
+
+Maher Standards Track [Page 15]
+
+RFC 2331 IP over ATM Signalling - SIG 4.0 Update April 1998
+
+
+ These characteristics can be achieved through the ABR service
+ category through the use of a Minimum Cell Rate, if the ABR service
+ is supported by the ATM endpoints and if efficient frame discard is
+ supported at the ABR source. The mechanisms put in place for the ABR
+ service strive to keep loss quite low within the ATM network.
+
+ The parameters that should be specified by the end system are (i) the
+ Peak Cell Rate (likely the link rate), (ii) the Minimum Cell Rate
+ (the committed rate), and (iii) the Cumulative RM Fixed Round-Trip
+ Time. The remaining parameter values, if left unspecified by the
+ calling party, are selected by the network or are chosen from the
+ default values specified in the ATM Forum Traffic Management
+ specification.
+
+ Parameters (i) and (ii) are contained in the mandatory Traffic
+ Descriptor IE, whereas parameter (iii) is contained in the mandatory
+ ABR Setup Parameters IE. Other paramenters in the ABR Setup
+ Parameters IE may be omitted. (Note that the third IE which pertains
+ to ABR signalling, the ABR Additional Parameters IE, is an optional
+ IE and therefore need not be included.) Parameter (iii) is dependent
+ on the hardware of the end system, so that the default value
+ specified for that hardware should be used. In the absense of such a
+ default, a value of zero MAY be specified by the end system. Entities
+ using ABR connections for IP over ATM SHOULD take advantage of
+ parameter negotiation by specifying Peak Cell Rate equal to the link
+ rate in the ATM Traffic Descriptor IE of the SETUP message. The value
+ selected for the Minimum Cell Rate is implementation specific. Note
+ that the MCR also MAY be negotiated if an MCR parameter is included
+ by the end system in the Minimum Acceptable ATM Traffic Descriptor
+ IE. The use of MCR negotiation by the end system is implementation
+ specific. Also, note that Frame Discard MAY be requested for ABR
+ connections as well as for UBR connections. Although the ABR service
+ attempts to minimize cell loss, the use of Frame Discard may improve
+ throughput when cell loss is not eliminated.
+
+ ATM recognizes in addition to the service class (UBR, ABR, etc.), a
+ notion of a QoS class. The QoS class specifies the type of guarantee
+ requested of the network when the call is setup. This is distinct
+ from the service class requested for the connection, and the
+ specification of the traffic parameters (which specify what the
+ source's traffic will look like). QoS class 0 is the "simplest", and
+ is called the Unspecified QoS class. In the context of ABR (and VBR
+ non-realtime below), we are only concerned with the QoS class
+ providing an assurance of acceptable loss behavior for the
+ connection.
+
+
+
+
+
+
+Maher Standards Track [Page 16]
+
+RFC 2331 IP over ATM Signalling - SIG 4.0 Update April 1998
+
+
+ The Unspecified QoS Class (QoS Class 0) MUST be requested for ABR
+ connections. In this context, QoS Class 0 corresponds to a network-
+ specific objective for the cell loss ratio. Networks in general are
+ expected to support a low Cell Loss Ratio for ABR sources that adjust
+ cell flow in response to control information.
+
+ The VBR-nrt service category provides an alternate means of achieving
+ these characteristics. These characteristics may be obtained with
+ VBR-nrt connections for which (i) the VBR.3 conformance definition is
+ used, (ii) a Sustainable Cell Rate (SCR) and Maximum Burst Size
+ (MBS), and Peak Cell Rate (PCR) are specified, and (iii) both tagging
+ and frame discard are requested. A request for tagging indicates
+ that best-effort delivery is desired for traffic offered in excess of
+ the SCR and MBS. A request for frame discard indicates to the
+ network that the user desires allocations of committed and excess
+ bandwidth to translate into corresponding throughputs at the frame
+ level.
+
+ As with UBR connections, entities using VBR-nrt connections for IP
+ over ATM should take advantage of parameter negotiation by specifying
+ PCR equal to the link rate in the ATM Traffic Descriptor IE of the
+ SETUP message and PCR equal to SCR in the Minimum Acceptable Traffic
+ descriptor. The selection of SCR, MBS, and CLR (cell loss ratio)
+ should be implementation specific. However, for IP over ATM, an MBS
+ value of N*(Maximum MTU) is RECOMMENDED, where N>=1 with a default of
+ 2 and where Maximum MTU is equal to 192 cells (consistent with an IP
+ MTU size of 9180 bytes [RFC1626]).
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+Maher Standards Track [Page 17]
+
+RFC 2331 IP over ATM Signalling - SIG 4.0 Update April 1998
+
+
+Appendix C. Combinations of Traffic Related Parameters
+
+ This appendix contains a copy of the five tables found in Annex 9 of
+ [SIG40] which show the allowable combinations of traffic and QoS
+ related parameters in a SIG 4.0 SETUP message.
+
++--------------------------------------------------------------------+
+|ATM Service Category| CBR |
+|--------------------|---------------|---------------|---------------|
+| Conformance |CBR.1 (note 10)| (note 4) | (note 4) |
+|--------------------|---------------|---------------|---------------|
+| Bearer Capability | | | |
+|--------------------|---------------|---------------|---------------|
+| BB Bearer Class | A | X | VP | A | X | VP^| A | X | VP^|
+|--------------------|---------------|----|-----|----|----|-----|----|
+| ATM Transfer | | | 4,5,| | | 4,5,| |
+| Capability (note 1)| 7 | abs| or 6| 5 | abs| or 6| 5 |
+|--------------------|---------------|---------------|---------------|
+| Traffic Descriptor | | | |
+| for a given dir. | | | |
+|--------------------|---------------|---------------|---------------|
+| PCR (CLP=0) | | | S |
+|--------------------|---------------|---------------|---------------|
+| PCR (CLP=0+1) | S | S | S |
+|--------------------|---------------|---------------|---------------|
+| SCR, MBS (CLP=0) | | | |
+|--------------------|---------------|---------------|---------------|
+| SCR, MBS (CLP=0+1) | | | |
+|--------------------|---------------|---------------|---------------|
+| Best Effort | | | |
+|--------------------|---------------|---------------|---------------|
+| Tagging | N | N | Y/N |
+|--------------------|---------------|---------------|---------------|
+| Frame Discard | Y/N | Y/N | Y/N |
+|--------------------|---------------|---------------|---------------|
+| QoS Classes | * | * | * |
+|--------------------|---------------|---------------|---------------|
+| Transit Delay | O | O | O |
+|--------------------|---------------|---------------|---------------|
+| Peak-to-Peak CDV | O | O | O |
+|--------------------|---------------|---------------|---------------|
+| CLR (CLP=0)~ | | O | O |
+|--------------------|---------------|---------------|---------------|
+| CLR (CLP=0+1)~ | O | | |
++--------------------------------------------------------------------+
+
+
+
+
+
+
+Maher Standards Track [Page 18]
+
+RFC 2331 IP over ATM Signalling - SIG 4.0 Update April 1998
+
+
++--------------------------------------------------------------------+
+|ATM Service Category| Real Time VBR |
+|--------------------|---------------|---------------|---------------|
+| Conformance |VBR.1 (note 10)| VBR.2 | VBR.3 |
+|--------------------|---------------|---------------|---------------|
+| Bearer Capability | | | |
+|--------------------|---------------|---------------|---------------|
+| BB Bearer Class | C | X | VP | C | X | VP | C | X | VP |
+|--------------------|---------------|----|-----|----|----|-----|----|
+| ATM Transfer | | | 1 | | | 1 | |
+| Capability | 19 | 9 | or 9| 9 | 9 | or 9| 9 |
+|--------------------|---------------|---------------|---------------|
+| Traffic Descriptor | | | |
+| for a given dir. | | | |
+|--------------------|---------------|---------------|---------------|
+| PCR (CLP=0) | | | |
+|--------------------|---------------|---------------|---------------|
+| PCR (CLP=0+1) | S | S | S |
+|--------------------|---------------|---------------|---------------|
+| SCR, MBS (CLP=0) | | S | S |
+|--------------------|---------------|---------------|---------------|
+| SCR, MBS (CLP=0+1) | S | | |
+|--------------------|---------------|---------------|---------------|
+| Best Effort | | | |
+|--------------------|---------------|---------------|---------------|
+| Tagging | N | N | Y/N |
+|--------------------|---------------|---------------|---------------|
+| Frame Discard | Y/N | Y/N | Y/N |
+|--------------------|---------------|---------------|---------------|
+| QoS Classes | * | * | * |
+|--------------------|---------------|---------------|---------------|
+| Transit Delay(nt.2)| O | O | O |
+|--------------------|---------------|---------------|---------------|
+| Peak-to-Peak CDV | O | O | O |
+|--------------------|---------------|---------------|---------------|
+| CLR (CLP=0)~ | | O | O |
+|--------------------|---------------|---------------|---------------|
+| CLR (CLP=0+1)~ | O | | |
++--------------------------------------------------------------------+
+
+
+
+
+
+
+
+
+
+
+
+
+Maher Standards Track [Page 19]
+
+RFC 2331 IP over ATM Signalling - SIG 4.0 Update April 1998
+
+
++--------------------------------------------------------------------+
+|ATM Service Category| Real Time VBR |
+|--------------------|---------------|---------------|---------------|
+| Conformance | (note 4,7) | (note 4,8) | (note 4) |
+|--------------------|---------------|---------------|---------------|
+| Bearer Capability | | | |
+|--------------------|---------------|---------------|---------------|
+| BB Bearer Class | X | X | X | C or VP^|
+|--------------------|---------------|---------------|-----|---------|
+| ATM Transfer | | | | |
+| Capability | 1 or 9 | 1 or 9 | 1or9| 9 |
+|--------------------|---------------|---------------|---------------|
+| Traffic Descriptor | | | |
+| for a given dir. | | | |
+|--------------------|---------------|---------------|---------------|
+| PCR (CLP=0) | S | | |
+|--------------------|---------------|---------------|---------------|
+| PCR (CLP=0+1) | S | S | S |
+|--------------------|---------------|---------------|---------------|
+| SCR, MBS (CLP=0) | | | |
+|--------------------|---------------|---------------|---------------|
+| SCR, MBS (CLP=0+1) | | | S |
+|--------------------|---------------|---------------|---------------|
+| Best Effort | | | |
+|--------------------|---------------|---------------|---------------|
+| Tagging | Y/N | N | N |
+|--------------------|---------------|---------------|---------------|
+| Frame Discard | Y/N | Y/N | Y/N |
+|--------------------|---------------|---------------|---------------|
+| QoS Classes | * | * | * |
+|--------------------|---------------|---------------|---------------|
+| Transit Delay(nt.2)| O | O | O |
+|--------------------|---------------|---------------|---------------|
+| Peak-to-Peak CDV | O | O | O |
+|--------------------|---------------|---------------|---------------|
+| CLR (CLP=0)~ | O | O | O |
+|--------------------|---------------|---------------|---------------|
+| CLR (CLP=0+1)~ | | | |
++--------------------------------------------------------------------+
+
+
+
+
+
+
+
+
+
+
+
+
+Maher Standards Track [Page 20]
+
+RFC 2331 IP over ATM Signalling - SIG 4.0 Update April 1998
+
+
++--------------------------------------------------------------------+
+|ATM Service Category| Non-Real Time VBR |
+|--------------------|---------------|---------------|---------------|
+| Conformance |VBR.1 (note 10)| VBR.2 | VBR.3 |
+|--------------------|---------------|---------------|---------------|
+| Bearer Capability | | | |
+|--------------------|---------------|---------------|---------------|
+| BB Bearer Class | C | X | VP |C | X | VP|C | X | VP|
+|--------------------|---------------|--|--------|---|--|--------|---|
+| ATM Transfer | | |abs,0,2,|abs| |abs,0,2,|abs|
+| Capability | 11 |ab| 8,10 |10 |ab| 8,10 |10 |
+|--------------------|---------------|---------------|---------------|
+| Traffic Descriptor | | | |
+| for a given dir. | | | |
+|--------------------|---------------|---------------|---------------|
+| PCR (CLP=0) | | | |
+|--------------------|---------------|---------------|---------------|
+| PCR (CLP=0+1) | S | S | S |
+|--------------------|---------------|---------------|---------------|
+| SCR, MBS (CLP=0) | | S | S |
+|--------------------|---------------|---------------|---------------|
+| SCR, MBS (CLP=0+1) | S | | |
+|--------------------|---------------|---------------|---------------|
+| Best Effort | | | |
+|--------------------|---------------|---------------|---------------|
+| Tagging | N | N | Y |
+|--------------------|---------------|---------------|---------------|
+| Frame Discard | Y/N | Y/N | Y/N |
+|--------------------|---------------|---------------|---------------|
+| QoS Classes | * | * | * |
+|--------------------|---------------|---------------|---------------|
+| Transit Delay(nt.2)| (note 3) | (note 3) | (note 3) |
+|--------------------|---------------|---------------|---------------|
+| Peak-to-Peak CDV | | | |
+|--------------------|---------------|---------------|---------------|
+| CLR (CLP=0)~ | | O | O |
+|--------------------|---------------|---------------|---------------|
+| CLR (CLP=0+1)~ | O | | |
++--------------------------------------------------------------------+
+
+
+
+
+
+
+
+
+
+
+
+
+Maher Standards Track [Page 21]
+
+RFC 2331 IP over ATM Signalling - SIG 4.0 Update April 1998
+
+
++--------------------------------------------------------------------+
+|ATM Service Category| Non-Real Time VBR |
+|--------------------|---------------|---------------|---------------|
+| Conformance | (note 4,7) | (note 4,8) | (note 4) |
+|--------------------|---------------|---------------|---------------|
+| Bearer Capability | | | |
+|--------------------|---------------|---------------|---------------|
+| BB Bearer Class | C | X | C | X |C | X |VP^|
+|--------------------|-------|-------|-------|-------|--|--------|---|
+| ATM Transfer | |abs,0,2| |abs,0,2| |abs,0,2,|abs|
+| Capability | abs |8 or 10| |8 or 10|ab| 8 or10 |10 |
+|--------------------|---------------|---------------|---------------|
+| Traffic Descriptor | | | |
+| for a given dir. | | | |
+|--------------------|---------------|---------------|---------------|
+| PCR (CLP=0) | S | | |
+|--------------------|---------------|---------------|---------------|
+| PCR (CLP=0+1) | S | S | S |
+|--------------------|---------------|---------------|---------------|
+| SCR, MBS (CLP=0) | | | |
+|--------------------|---------------|---------------|---------------|
+| SCR, MBS (CLP=0+1) | | | S |
+|--------------------|---------------|---------------|---------------|
+| Best Effort | | | |
+|--------------------|---------------|---------------|---------------|
+| Tagging | Y/N | N | N |
+|--------------------|---------------|---------------|---------------|
+| Frame Discard | Y/N | Y/N | Y/N |
+|--------------------|---------------|---------------|---------------|
+| QoS Classes | * | * | * |
+|--------------------|---------------|---------------|---------------|
+| Transit Delay(nt.2)| (note 3) | (note 3) | (note 3) |
+|--------------------|---------------|---------------|---------------|
+| Peak-to-Peak CDV | | | |
+|--------------------|---------------|---------------|---------------|
+| CLR (CLP=0)~ | O | O | O |
+|--------------------|---------------|---------------|---------------|
+| CLR (CLP=0+1)~ | | | |
++--------------------------------------------------------------------+
+
+
+
+
+
+
+
+
+
+
+
+
+Maher Standards Track [Page 22]
+
+RFC 2331 IP over ATM Signalling - SIG 4.0 Update April 1998
+
+
++--------------------------------------------------------------------+
+|ATM Service Category| ABR | UBR |
+|--------------------|---------------|---------------|---------------|
+| Conformance | ABR | UBR.1 | UBR.2 |
+|--------------------|---------------|---------------|---------------|
+| Bearer Capability | | | |
+|--------------------|---------------|---------------|---------------|
+| BB Bearer Class | C | X | VP |C | X | VP|C | X | VP|
+|--------------------|---------------|--|--------|---|--|--------|---|
+| ATM Transfer | | |abs,0,2,|abs| |abs,0,2,|abs|
+| Capability | 12 |ab| 8,10 |10 |ab| 8,10 |10 |
+|--------------------|---------------|---------------|---------------|
+| Traffic Descriptor | | | |
+| for a given dir. | | | |
+|--------------------|---------------|---------------|---------------|
+| PCR (CLP=0) | | | |
+|--------------------|---------------|---------------|---------------|
+| PCR (CLP=0+1) | S | S | S |
+|--------------------|---------------|---------------|---------------|
+| SCR, MBS (CLP=0) | | S | S |
+|--------------------|---------------|---------------|---------------|
+| SCR, MBS (CLP=0+1) | S | | |
+|--------------------|---------------|---------------|---------------|
+| ABR MCR | (note 6) | | |
+|--------------------|---------------|---------------|---------------|
+| Best Effort | | S (note 9) | S (note 9) |
+|--------------------|---------------|---------------|---------------|
+| Tagging | N | N | N |
+|--------------------|---------------|---------------|---------------|
+| Frame Discard | Y/N | Y/N | Y/N |
+|--------------------|---------------|---------------|---------------|
+| QoS Classes | 0 | 0 | 0 |
+|--------------------|---------------|---------------|---------------|
+| Transit Delay(nt.2)| | | |
+|--------------------|---------------|---------------|---------------|
+| Peak-to-Peak CDV | | | |
+|--------------------|---------------|---------------|---------------|
+| CLR (CLP=0)~ | | | |
+|--------------------|---------------|---------------|---------------|
+| CLR (CLP=0+1)~ | | | |
++--------------------------------------------------------------------+
+
+ ab, abs = absent.
+
+ Y/N = either "Yes" or "No" is allowed.
+
+
+
+
+
+
+Maher Standards Track [Page 23]
+
+RFC 2331 IP over ATM Signalling - SIG 4.0 Update April 1998
+
+
+ O = Optional. May be specified using:
+
+ - an additional QoS parameter encoded i the Extended QoS
+ parameters information element or the end-to-end transit
+ information element; or,
+
+ - objectives implied from the QoS class If an Extended
+ QoS Parameters IE is not present in the message, then any
+ value of this parameter is acceptable. If neither the
+ parameter nor the Extended QoS Parameters IE is present,
+ then the objective for this parameter is determined from
+ the QoS class in the QoS Parameter IE.
+
+ S = Specified.
+
+ (blank) = Unspecified.
+
+ * = allowed QoS class values are a network option. Class 0 is
+ always for alignment with ITU-T.
+
+ ^ = (note 5).
+
+ ~ = (note 11).
+
+ Note 1 - Values 0,1,2,4,6, and 8 are not used on transmission
+ but shall be understood on reception.
+
+ Note 2 - Maximum end-2-end transit delay objectives may only be
+ specified for the forward direction.
+
+ Note 3 - Maximum end-2-end transit delay objectives may be
+ specified for the ATM Service Category of Non-real
+ Time VBR for reasons of backward compatibility with
+ ITU-T Recommendations.
+
+ Note 4 - Included for reasons of backward compatibility with
+ UNI 3.1and ITU-T Recommendations. With these
+ conformance definitions, the CLR commitment is only
+ for the CLP=0 traffic stream.
+
+ Note 5 - Included to allow switched virtual paths to use the
+ UNI 3.1 conformance definitions.
+
+ Note 6 - Optional in the user-to-network direction. Specified
+ in the network-to-user direction.
+
+
+
+
+
+
+Maher Standards Track [Page 24]
+
+RFC 2331 IP over ATM Signalling - SIG 4.0 Update April 1998
+
+
+ Note 7 - This combination should be treated as if the received
+ PCR (CLP=0) parameter were a SCR (CLP=0) parameter and
+ a MBS (CLP=0) parameter with a value of 1.
+
+ Note 8 - This combination should be treated as if an additional
+ SCR (CLP=0) parameter were received with the same
+ value as a PCR (CLP=0+1) parameter and a MBS (CLP=0)
+ parameter with a value of 1.
+
+ Note 9 - The best effort parameter applies to both the forward
+ and backward directions.
+
+ Note 10 - This combination should only be used when the CLR
+ commitment on CLP=0+1 is required versus CLR
+ commitment on CLP=0 traffic, since these combinations
+ are not supported by UNI 3.0/3.1 nor ITU-T Q.2931.
+
+ Note 11 - In this table the CLR commitment is shown as two
+ entries to indicated explicitly whether the CLR
+ commitment is for the CLP=0 or the CLP=0+1 cells.
+
+
+
+
+
+
+
+
+
+
+
+
+
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+
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+
+
+
+
+
+
+Maher Standards Track [Page 25]
+
+RFC 2331 IP over ATM Signalling - SIG 4.0 Update April 1998
+
+
+Full Copyright Statement
+
+ Copyright (C) The Internet Society (1998). All Rights Reserved.
+
+ This document and translations of it may be copied and furnished to
+ others, and derivative works that comment on or otherwise explain it
+ or assist in its implementation may be prepared, copied, published
+ and distributed, in whole or in part, without restriction of any
+ kind, provided that the above copyright notice and this paragraph are
+ included on all such copies and derivative works. However, this
+ document itself may not be modified in any way, such as by removing
+ the copyright notice or references to the Internet Society or other
+ Internet organizations, except as needed for the purpose of
+ developing Internet standards in which case the procedures for
+ copyrights defined in the Internet Standards process must be
+ followed, or as required to translate it into languages other than
+ English.
+
+ The limited permissions granted above are perpetual and will not be
+ revoked by the Internet Society or its successors or assigns.
+
+ This document and the information contained herein is provided on an
+ "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
+ TASK FORCE DISCLAIMS 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.
+
+
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+Maher Standards Track [Page 26]
+