RFC 2173
A MAPOS version 1 Extension - Node Switch Protocol
RFC 2173: A MAPOS version 1 Extension - Node Switch Protocol 🦋
okay bestie, this one is by Ken Murakami and Mitsuru Maruyama from NTT Laboratories 💖. It's dated June 1997 and filed as Category: Informational 🎀, so it's giving info, not a standard. Its header has no Obsoletes or Updates line, so it isn't replacing or changing any other RFC ✨.
Status of this Memo 🌸
okay so this memo just provides information for the Internet community 🫶. It does not specify an Internet standard of any kind, and distribution is unlimited, so share away 💅.
Abstract ✨
this doc describes a MAPOS extension called Node Switch Protocol (NSP) 🦋, which handles automatic node address assignment. MAPOS is a multiple access protocol for sending network-protocol datagrams inside High-Level Data Link Control (HDLC) frames over SONET/SDH 🌈. NSP automates the HDLC address configuration for each node, so a node gets its HDLC address from the switch it's plugged into 💜. no more manual address config, bestie 🙈.
1. Introduction 🌈
so MAPOS[1] is short for Multiple Access Protocol over SONET(Synchronous Optical Network)/SDH(Synchronous Digital Hierarchy)[2][3][4][5] 🍓. It's a protocol for sending HDLC frames over SONET/SDH. a SONET switch gives each node multiple access capability 💅. in MAPOS, every node has a unique HDLC address inside its switch, and that address is the same as the port number of the switch the node is connected to 🎀.
this document describes NSP, an extension to MAPOS that enables automatic HDLC address assignment ✨. first it explains MAPOS addressing, then it walks through how NSP does the automatic node address assignment 🧚.
2. Node Address Format 🎀
this section covers the MAPOS Version 1 address format in both single-switch and multi-switch environments 💖.
2.1 Address Format
in a MAPOS network, each end node has a unique HDLC address 👑. as Figure 1 shows, the address is 8 bits long. the LSB is always 1, which marks the end of the field 🫶. when a SONET switch gets an HDLC frame, it forwards the frame based on the address in the frame header 🔥.
for unicast, the MSB is 0 and the rest of the bits are the port number the node is connected to 🦋. since the LSB is always 1, the minimum and maximum addresses are 0x01 and 0x7F 💅. address 0x01 is reserved and is assigned to the control processor in a SONET switch 👑.
for broadcast, the MSB is 1 and the rest of the bits are all 1s 🌈. for multicast, the MSB is 1 and the rest of the bits, except 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 🧚. every switch has a switch number that is unique within the system 💜. subnetted node addresses are made of the switch number plus the port number the node is connected to 🎀. the unicast format is 0 <switch number> <node number> 1, the broadcast address is all 1, and the multicast format is 1 <group address> 1 💅.
the address 0x01 is reserved and is assigned to the control processor in the "local" switch 👑. that means it points at the switch the node is connected to, the switch itself 🫶. addresses of the form 0 <switch number> <all 0> 1 are reserved, and they point at the control processor of the switch with that switch number 🦋.
in Figure 2, the switch numbers are two bits long 🌸. node N1 is connected to port 0x3 of switch S1, which is numbered 0x1 (01 in binary), so its address is 0 + 01 + 00011, which is 00100011(0x23) 🔥. node N3 has the address 01001001(0x49), because switch S2 is numbered 0x2 (10 in binary) and the port number is 0x09 ✨. notice that every port number is odd, since 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 covers the NSP protocol used for automatic node address assignment 🌈.
4.1 NSP protocol
NSP exists to give MAPOS version 1 an automatic node address assignment function 🧚. it cuts down the admin work of configuring each node's address and stops problems like address inconsistency and collisions 💅. when a node is connected to a switch and receives the SONET signal correctly, it sends an address request packet to the control processor in the local switch 🦋. the destination address of that packet is 00000001(0x01) 🎀. when the control processor gets the packet, it replies with an address assignment packet, and the destination of that reply is the assigned node address ✨. if the node doesn't get the address assignment packet within 5 seconds, it retransmits the address request packet 🙈. retransmission keeps going until the node successfully receives the address assignment packet 💖.
whenever a node detects a transmission error, like carrier loss or out-of-synchronization, it SHOULD send an address request packet to the control processor and verify its current address 😭. on top of that, a node MUST verify its address by sending address request packets every 30 seconds 🫶. the switch treats these as keep-alive packets and uses them to track the node's status 👑. if it hasn't received a request packet for more than 90 seconds, it assumes the node went down 💀. it also assumes the node went down when the switch detects a SONET signal failure 🔥.
4.2 Packet Format
the HDLC protocol field of an NSP frame contains 0xFE03 (hexadecimal), as defined by the "MAPOS Version 1 Assigned Numbers" [6] 🍓. the information field carries the NSP packet, shown in Figure 3 ✨.
+-----------+------------+
I command I address I
+-----------+------------+
I<- 32bit ->I<- 32 bit ->I
Figure 3 NSP packet formatthe command field is 32 bits long and takes these values (in decimal) 🎀:
1 address request
2 address assignment
3 reject(error)the address field is also 32 bits long 💅. in address request packets, the NSP address field SHOULD be filled with zeroes, even though the switch ignores it 🌸. in address assignment packets, the assigned address goes in the least significant byte of the field, and the rest of the field is padded with zeroes 🧚. if the switch can not assign the address for some reason, it replies with a reject command (value 3) 😭. the value of the address field in that case is undefined 🙈.
4.3 Consideration for special cases
there are two special cases to think about 🦋. one is a point-to-point connection without a switch. the other is loop-back, which is a direct connection between the input and the output of the same port 🌈.
4.3.1 point-to-point
in the 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), which is usually a control processor in a switch 👑. when a node receives the address request, it detects the point-to-point connection by checking both the destination address and the command in the packet 🫶. 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 end up with address 00000011(0x03) 💅. any address can be used in a point-to-point environment, so there's no problem even when both 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 own input port, as Figure 5 shows 🌸. here the same mechanism used for point-to-point works without any changes 🧚. the node sends an address request packet destined to 00000001(0x01), then it receives that same packet 🦋. since the destination is 00000001(0x01), it replies with an address assignment packet containing the assigned address 00000011(0x03), sent to the address 0000 0011(0x03) 💜. so the node ends up with the address 00000011(0x03) 🙈.
---- address request ----> 0x01
+------+ --- address assignment --> 0x03
| +-------------->-----------------+
| node + |
| +--------------<-----------------+
+------+
Figure 5 Loop-back Configuration5. Security Considerations 💀
ok this is the dramatic part 😭, but the memo says security issues are not discussed in this memo. so no security guidance is given here, and that's something to keep in mind 🫶.
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 thank John P. Mullaney, Clark Bremer, Masayuki Kobayashi, Paul Francis, Toshiaki Yoshida, and Takahiro Sajima for their contributions and thoughtful suggestions 💖✨.
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📦 where this page comes from
- ietf: rfc2173 1997-06
- 💖 girlified by claude-haiku-5-5 on : a language model's rewrite of the original, under its terms