MAPOS 16 - Multiple Access Protocol over SONET/SDH with 16 Bit Addressing
RFC 2175

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Network Working Group                                        K. Murakami
Request for Comments: 2175                                   M. Maruyama
Category: Informational                                 NTT Laboratories
                                                               June 1997

               MAPOS 16 - Multiple Access Protocol over
                    SONET/SDH with 16 Bit Addressing

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.

Authors' note

   This memo documents MAPOS 16, a multiple access protocol for
   transmission of network-protocol datagrams, encapsulated in HDLC
   frames with 16 bit addressing, over SONET/SDH.  The primary
   difference with MAPOS version 1 is that it has 16 bit address field
   that offers significant wide address space. This document is NOT the
   product of an IETF working group nor is it a standards track
   document.  It has not necessarily benefited from the widespread and
   in depth community review that standards track documents receive.

Abstract

   This document describes the protocol MAPOS 16, Multiple Access
   Protocol over SONET/SDH with 16 Bit Addressing, for transmitting
   network-protocol datagrams over SONET/SDH.  The primary difference
   with MAPOS version 1 is that it has 16 bit address field that offers
   significant wide address space. It first describes the major
   differences between MAPOS and MAPOS 16 briefly. Then, it explains the
   header format and its 16 bit address format.

1. Introduction

   MAPOS is a multiple access protocol for transmission of High-level
   Datalink Control (HDLC) frames over the Synchronous Optical Network /
   Synchronous Digital Hierarchy(SONET/SDH)[1][2][3][4]. It provides
   multiple access capability to SONET/SDH, an inherently point-to-point
   link.

   MAPOS version 1[5] focuses on the frame format compatibility with the
   conventional PPP[6], resulting with its narrow 8 bit address field.
   In contrast to MAPOS version 1, MAPOS 16 has a 16 bit address space.

Murakami & Maruyama          Informational                      [Page 1]
RFC 2175                        MAPOS 16                       June 1997

   In this document, header format and its 16 bit format are described.
   It also explains that 16 bit addressing has minimal influence on the
   conventional MAPOS protocol family such as Node-Switch Protocol[7]
   and Switch-Switch Protocol[8].

2. MAPOS 16 Frame Format

   Like MAPOS version 1, MAPOS 16 framing is based on the HDLC-like
   framing used in PPP-over-SONET/SDH, described in RFC-1662[6].
   However, the address field is extended to 16 bits, and the control
   field in the MAPOS version 1 is omitted for maintain the 32bit
   alignment of the header.

   Figure 2 shows the MAPOS 16 frame format.  Logical Link Control
   (LLC), and Sublayer/Sub-Network Access Protocol (SNAP) are not used.
   It does not include the bytes for transparency.  The fields are
   transmitted from left to right.

           +----------+---------------------+----------+
           |          |                     |          |
           |   Flag   |       Address       | Protocol |
           | 01111110 |        16bits       |  16 bits |
           +----------+---------------------+----------+
              +-------------+------------+----------+-----------
              |             |            |          | Inter-frame
              | Information |    FCS     |   Flag   | fill or next
              |             | 16/32 bits | 01111110 | address
              +-------------+------------+----------+------------

                        Figure 2.  Frame format

     Flag Sequence

     Flag sequence is used for frame synchronization.  Each frame begins
     and ends with a flag sequence 01111110 (0x7E).  If a frame
     immediately follows another, one flag sequence may be treated as
     the end of the preceding frame and the beginning of the immediately
     following frame.  When the line is idle, the flag sequence is to be
     transmitted continuously on the line.

     Address

     The address field contains the destination HDLC address.  A frame
     is forwarded by a switch based on this field.  It is 16 bits wide.
     The LSB of the first byte indicates the continuation of this field,
     and must always be 0. The LSB of the second byte indicates the end
     of this field, and must always be 1.  The MSB of the first byte is

Murakami & Maruyama          Informational                      [Page 2]
RFC 2175                        MAPOS 16                       June 1997

     used to indicate if the frame is a unicast or multicast frame.  The
     MSB of 0 means unicast, with the remaining thirteen bits indicating
     the destination node address including two E/A bits. MSB of 1 means
     multicast, with the remaining thirteen bits indicating the group