RFC 2176 (rfc2176) - Page 2 of 6

IPv4 over MAPOS Version 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