IPv4 over MAPOS Version 1
RFC 2176

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Network Working Group                                        K. Murakami
Request for Comments: 2176                                   M. Maruyama
Category: Informational                                 NTT Laboratories
                                                               June 1997

                       IPv4 over MAPOS Version 1

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 a mechanism for supporting Version 4 of the
   Internet Protocol (IPv4) on Version 1 of the Multiple Access Protocol
   over SONET/SDH.  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 a protocol for transmission of the Internet
   Protocol Version 4 (IPv4) over Multiple Access Over SONET/SDH (MAPOS)
   version 1. MAPOS is a link layer protocol and provides multiple
   access capability over SONET/SDH links. IP runs on top of MAPOS. This
   document explains IP datagram encapsulation in HDLC frame of MAPOS,
   and the Address Resolution Protocol (ARP).

1. Introduction

   Multiple Access Protocol over SONET/SDH (MAPOS) [1] is a high-speed
   link-layer protocol that provides multiple access capability over
   SONET/SDH. Its frame format is based on the HDLC-like framing [2] for
   PPP.  A component called "Frame Switch" [1] allows multiple nodes to
   be connected together in a star topology to form a LAN. Using long
   haul SONET/SDH links, the nodes on such a "SONET-LAN" can span over a
   wide geographical area. The Internet Protocol (IP) [3] datagrams are
   transmitted in MAPOS HDLC frames [1].

   This document describes a protocol for transmission of IP datagrams
   over MAPOS version 1 [1]. It explains IP datagram encapsulation in
   HDLC frame of MAPOS, and ARP (Address Resolution Protocol) for
   mapping between IP address and HDLC address.

Murakami & Maruyama          Informational                      [Page 1]
RFC 2176                         MAPOS                         June 1997

2. Frame Format for Encapsulating IP Datagrams

   An IP datagram is transmitted in a MAPOS HDLC frame.  The protocol
   field of the frame must contain the value 0x0021 (hexadecimal) as
   defined by the "MAPOS Version 1 Assigned Numbers" [4].  The
   information field contains the IP datagram.

   The information field may be one to 65,280 octets in length; the
   MTU(Maximum Transmission Unit) of MAPOS is 65,280 octets.  Although
   the large MTU size can suppress the overhead of IP header processing,
   it may cause fragmentation anywhere along the path from the source to
   the destination and result in performance degradation. To cope with
   the issue, Path MTU discovery [5] may be used.

3. Address Mapping

   This section explains MAPOS ARP and the mapping of special addresses.

3.1 ARP cache

   Each node on a MAPOS network maintains an "ARP cache" that maps
   destination IP addresses to their corresponding 8-bit HDLC addresses.
   Entries are added to this cache either manually or by the Address
   Resolution Protocol described below.  Entries are removed from this
   cache manually, by the UNARP mechanism, or by ARP cache validation
   mechanism.  An implementation must provide a mechanism for manually
   adding or removing arbitrary ARP cache entries.

3.2 Address Resolution Protocol (ARP)

   This subsection describes MAPOS ARP protocol and its packet format.

3.2.1 Overview

   The MAPOS ARP is similar to that for ethernet.  Prior to sending an
   IP datagram, the node must know the destination HDLC address
   corresponding to the destination IP address. When its ARP cache does
   not contain the corresponding entry, it uses ARP to translate the IP
   address to the HDLC address. That is, it broadcasts an ARP request
   containing the destination IP address.  In response to the request,
   the node which has the IP address sends an ARP reply containing the
   HDLC address. The returned HDLC address is stored in the ARP cache.

3.2.2 ARP Frame Format

   The protocol field for an ARP frame must contain 0xFE01 (hexadecimal)
   as defined by the "MAPOS Version 1 Assigned Numbers" [4]. The
   information field contains the ARP packet as shown below.

Murakami & Maruyama          Informational                      [Page 2]
RFC 2176                         MAPOS                         June 1997

           +-------------------------+------------------------+
           |  Hardware Address Space | Protocol Address Space |
           |       (25:MAPOS)        |     (2048 in Dec)      |
           |    16 bits              |   16 bits              |
           +------------+------------+------------------------+