RFC 2176 (rfc2176) - Page 2 of 6
IPv4 over MAPOS Version 1
Alternative Format: Original Text Document
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