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Network Working Group                                        K. MurakamiRequest for Comments: 2173                                   M. MaruyamaCategory: Informational                                 NTT Laboratories                                                               June 1997A MAPOS version 1 Extension - Node Switch ProtocolStatus 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 19972.1 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 format2.2 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 Environment4 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 everyMurakami & 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 theMurakami & 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 connection4.3.2 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 ConfigurationMurakami & Maruyama          Informational                      [Page 5]

RFC 2173                         MAPOS                         June 19975. 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.netMurakami & Maruyama          Informational                      [Page 6]