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+Network Working Group K. Murakami
+Request for Comments: 2173 M. Maruyama
+Category: Informational NTT Laboratories
+ June 1997
+
+
+ A MAPOS version 1 Extension - Node Switch Protocol
+
+Status of this Memo
+
+ This memo provides information for the Internet community. This memo
+ does not specify an Internet standard of any kind. Distribution of
+ this memo is unlimited.
+
+Abstract
+
+ This document describes a MAPOS extension, Node Switch Protocol, for
+ automatic node address assignment. MAPOS is a multiple access
+ protocol for transmission of network-protocol datagrams, encapsulated
+ in High-Level Data Link Control (HDLC) frames, over SONET/SDH. NSP
+ automates the HDLC address configuration of each node. Using NSP, a
+ node retrieves its HDLC address from the switch to which it is
+ connected.
+
+1. Introduction
+
+ MAPOS[1], Multiple Access Protocol over SONET(Synchronous Optical
+ Network)/SDH(Synchronous Digital Hierarchy)[2][3][4][5], is a
+ protocol for transmission of HDLC frames over SONET/SDH. A SONET
+ switch provides multiple access capability to each node. In MAPOS,
+ each node has a unique HDLC address within a switch. The address is
+ equivalent to the port number of the switch to which the node is
+ connected. This document describes an extension to MAPOS, Node
+ Switch Protocol, which enable automatic HDLC address assignment.
+ First, it explains the addressing of MAPOS. Then, it describes the
+ NSP protocol for automatic HDLC node address assignment.
+
+2. Node Address Format
+
+ This section describes MAPOS Version 1 address format in single and
+ multiple switch environment.
+
+
+
+
+
+
+
+
+
+
+Murakami & Maruyama Informational [Page 1]
+
+RFC 2173 MAPOS June 1997
+
+
+2.1 Address Format
+
+ In MAPOS network, each end node has a unique HDLC address. As shown
+ in Figure 1, the address length is 8 bits. The LSB is always 1 which
+ indicates the end of the field. When a SONET switch receives an HDLC
+ frame, it forwards the frame based on the address in the frame
+ header.
+
+ In unicast, MSB is 0 and the rest of the bits are the port number to
+ which a node is connected. Since the LSB is always 1, the minimum and
+ maximum addresses are 0x01 and 0x7F, respectively. Address 0x01 is
+ reserved and is assigned to the control processor in a SONET switch.
+
+ In broadcast, MSB is 1 and the rest of the bits are all 1s. In
+ multicast, MSB is 1 and the rest of the bits, except for the LSB,
+ indicate the group address.
+
+ +-------------+-+
+ | | | | | | | | |
+ | |port number|1|
+ +-+-----------+-+
+ ^ ^
+ | |
+ | +------- EA bit (always 1)
+ |
+ 1 : broadcast, multicast
+ 0 : unicast
+
+ Figure 1 Address format
+
+2.2 Address in multi-switch environment
+
+ In a multi-switch environment, variable-length subnet addressing is
+ used. Each switch has a switch number that is unique within the
+ system. Subnetted node addresses consist of the switch number and the
+ port number to which a node is connected. The address format is "0
+ <switch number> <node number> 1" for a unicast address, "all 1" for
+ the broadcast address, and "1 <group address> 1" for a multicast
+ address.
+
+ The address 0x01 is reserved and is assigned to the control processor
+ in the "local" switch. That is, it indicates the switch itself to
+ which the node is connected. The addresses of the form "0 <switch
+ number> <all 0> 1" are reserved, and indicates the control processor
+ of the switch designated by the switch number.
+
+ In Figure 2, the switch numbers are two bits long. Node N1 is
+ connected to port 0x3 of switch S1 numbered 0x1 (01 in binary). Thus,
+
+
+
+Murakami & Maruyama Informational [Page 2]
+
+RFC 2173 MAPOS June 1997
+
+
+ the node address is 0 + 01 + 00011, that is, 00100011(0x23). Node N3
+ has an address 01001001(0x49), since the switch number of S2 is 0x2
+ (10 in binary) and the port number is 0x09. Note that all the port
+ numbers are odd because the LSBs are always 1.
+
+ +------+
+ | node |
+ | N1 |
+ +------+
+ | 00100011(0x23)
+ |
+ |0x3 |0x3
+ +------+ +---+----+ +---+----+ +------+
+ | node +----+ SONET +-------+ SONET +-----+ node |
+ | N2 | 0x5| Switch |0x9 0x5| Switch |0x9 | N3 |
+ +------+ | S1 | | S2 | +------+
+ 00100101(0x25) | 0x1 | | 0x2 | 01001001(0x49)
+ +---+----+ +---+----+
+ |0x7 |0x7
+
+
+ Figure 2 Addressing in Multiple Switch Environment
+
+4 NSP(Node-Switch Protocol)
+
+ This section describes the NSP protocol used for automatic node
+ address assignment.
+
+4.1 NSP protocol
+
+ NSP is introduced to provide an automatic node address assignment
+ function in MAPOS version 1. It reduces the administrative overhead
+ of node address configuration for each node and prevents troubles
+ such as address inconsistency and collision. When a node is connected
+ to a switch and receives SONET signal correctly, the node sends an
+ address request packet to the control processor in the local switch.
+ The destination address of this packet is 00000001(0x01). When the
+ control processor receives the packet, it replies with an address
+ assignment packet. The destination is the assigned node address. If
+ the node does not receive the address assignment packet within 5
+ seconds, it retransmits the address request packet. The
+ retransmission continues until the node successfully receives the
+ address assignment packet.
+
+ Whenever a node detects a transmission error such as carrier loss or
+ out-of-synchronization, it SHOULD send an address request packet to
+ the control processor and verify its current address. In addition, a
+ node MUST verify its address by sending address request packets every
+
+
+
+Murakami & Maruyama Informational [Page 3]
+
+RFC 2173 MAPOS June 1997
+
+
+ 30 seconds. The switch regards them as keep-alive packets and
+ utilizes them to detect the node's status. If it has not received a
+ request packet for more than 90 seconds, it assumes that the node
+ went down. In addition, it also assumes the node went down when a
+ switch detects a SONET signal failure.
+
+4.2 Packet Format
+
+ The HDLC protocol field of a NSP frame contains 0xFE03 (hexadecimal)
+ as defined by the "MAPOS Version 1 Assigned Numbers" [6]. The
+ information field contains the NSP packet as shown in Figure 3.
+
+
+ +-----------+------------+
+ I command I address I
+ +-----------+------------+
+ I<- 32bit ->I<- 32 bit ->I
+
+ Figure 3 NSP packet format
+
+ The command field is 32 bits long and has the following values (in
+ decimal);
+
+ 1 address request
+ 2 address assignment
+ 3 reject(error)
+
+ The length of the address field is 32bits. In address request
+ packets, the NSP address field SHOULD be filled with zeroes, although
+ the switch ignores it. In address assignment packets, the assigned
+ address is placed in the least significant byte of the field. The
+ rest of the field is padded with zeroes. When the switch can not
+ assign the address for some reason, the switch replies with a reject
+ command (the values is 3). The value of the address field is
+ undefined.
+
+4.3 Consideration for special cases
+
+ There are two special cases to consider. One is a point-to-point
+ connection without a switch. The other is loop-back, that is, direct
+ connection between the input and the output of the same port.
+
+4.3.1 point-to-point
+
+ In the case of a point-to-point connection shown in Figure 4, a node
+ sends an address request packet to the other node. The destination
+ address is 00000001(0x01), that is usually a control processor in a
+ switch. When a node receives the address request, it detects the
+
+
+
+Murakami & Maruyama Informational [Page 4]
+
+RFC 2173 MAPOS June 1997
+
+
+ point-to-point connection by examining both the destination address
+ and the command contained. Then, it MUST reply with an address
+ assignment packet. The assigned address MUST be 00000011(0x03). Since
+ both nodes send an address request to each other, both of them get
+ address 00000011(0x03). Since any address can be used in point-to-
+ point environment, there is no problem even if both of the nodes have
+ the same address.
+
+ ---- address request ----> 0x01
+ 0x03 <---- address assignment ----
+ +------+ +------+
+ | node +--------------------------------+ node |
+ +------+ +------+
+ 0x01 <---- address request ----
+ ---- address assignment ----> 0x03
+
+ Figure 4 Point-to-point connection
+
+4.3.2 loop-back
+
+ Another special case is loop-back where the output port of a node is
+ simply connected to its input port as shown in Figure 5. In this
+ case, the same mechanism as that for point-to-point can be applied
+ without modification. A node sends an address request packet
+ destined to 00000001(0x01). The node then receives the same packet.
+ Since the destination is 00000001(0x01), it replies with an address
+ assignment packet, containing the assigned address 00000011(0x03), to
+ the address 0000 0011(0x03). Thus, the node obtains the address
+ 00000011(0x03).
+
+ ---- address request ----> 0x01
+ +------+ --- address assignment --> 0x03
+ | +-------------->-----------------+
+ | node + |
+ | +--------------<-----------------+
+ +------+
+
+ Figure 5 Loop-back Configuration
+
+
+
+
+
+
+
+
+
+
+
+
+
+Murakami & Maruyama Informational [Page 5]
+
+RFC 2173 MAPOS June 1997
+
+
+5. Security Considerations
+
+ Security issues are not discussed in this memo.
+
+References
+
+ [1] Murakami, K. and M. Maruyama, "MAPOS - Multiple Access Protocol
+ over SONET/SDH, Version 1," RFC-2171, June 1997.
+
+ [2] CCITT Recommendation G.707: Synchronous Digital Hierarchy Bit
+ Rates (1990).
+
+ [3] CCITT Recommendation G.708: Network Node Interface for
+ Synchronous Digital Hierarchy (1990).
+
+ [4] CCITT Recommendation G.709: Synchronous Multiplexing Structure
+ (1990).
+
+ [5] American National Standard for Telecommunications - Digital
+ Hierarchy - Optical Interface Rates and Formats Specification,
+ ANSI T1.105-1991.
+
+ [6] Maruyama, M. and K. Murakami, "MAPOS Version 1 Assigned
+ Numbers," RFC-2172, June, 1997.
+
+Acknowledgements
+
+ The authors would like to acknowledge the contributions and
+ thoughtful suggestions of John P. Mullaney, Clark Bremer, Masayuki
+ Kobayashi, Paul Francis, Toshiaki Yoshida, and Takahiro Sajima.
+
+Authors' Address
+
+ Ken Murakami
+ NTT Software Laboratories
+ 3-9-11, Midori-cho
+ Musashino-shi
+ Tokyo 180, Japan
+ E-mail: murakami@ntt-20.ecl.net
+
+ Mitsuru Maruyama
+ NTT Software Laboratories
+ 3-9-11, Midori-cho
+ Musashino-shi
+ Tokyo 180, Japan
+ E-mail: mitsuru@ntt-20.ecl.net
+
+
+
+
+
+Murakami & Maruyama Informational [Page 6]
+