RFC 1051 (rfc1051) - Page 2 of 4
Standard for the transmission of IP datagrams and ARP packets over ARCNET networks
Alternative Format: Original Text Document
RFC 1051 IP and ARP on ARCNET March 1988
On networks where some hosts do not support extended packet format,
the IP Maximum Transmission Unit (MTU) should be set to 253, though
implementors are encouraged to support the extended packet format
mode of operation.
Because the ARCNET maximum packet length is less than the Internet
default MTU, implementations are strongly encouraged to support IP
level fragmentation and reassembly. Hosts not supporting this should
take steps to discourage others from sending fragmented packets, such
as using the TCP Maximum Segment Size option [4].
The frame format is:
Normal Packet Extended Packet
+----------------+ +----------------+
| ALERT* | | ALERT* |
+----------------+ +----------------+
| SOH (1) | | SOH (1) |
+----------------+ +----------------+
| SID | | SID |
+----------------+ +----------------+
| | | |
+ DID + + DID +
| | | |
+----------------+ +----------------+
| COUNT | | NUL (0) |
+----------------+ + +
| SYSTEM CODE | | COUNT |
+----------------+ +----------------+
| | | SYSTEM CODE |
: DATA : +----------------+
| | | |
+----------------+ : DATA :
| | | |
+ CRC + +----------------+
| | | |
+----------------+ + CRC +
| |
+----------------+
ALERT*: Six mark bits signifying the beginning of a frame.
SID: Sender's node ID.
DID: Receipient's node ID (repeated for reliability).
COUNT: Length of data and system code (one's complement).
SYSTEM CODE: 240 for IP, 241 for ARP (decimal).
DATA: Is either an IP or an ARP packet, padded with NULs so
as to not be between 254 and 256 octets long.
CRC: Cyclic redundancy check (CRC-16).
Prindeville
