Ethertalk Packet Formats

EtherTalk Packet Formats - Draft Proposal May 18, 1987 Apple Network Systems Development Scope: this document specifies details of AppleTalk packets sent on Ethernet. Details: AppleTalk packets on Ethernet are sent using Ethernet protocol type $8098. They contain the standard 1~-byte Ethernet header (destination, source, type) followed by the full AppleTalk packet as defined in Inside AppleTalk. Specifically, an AppleTalk packet consists of the three-byte ALAP header (ALAP destination, source, type), followed by the ALAP data field, the first two bytes of which must be the ALAP data field length (the high six bits of the length field are ALAP protocol-dependent). If the packet is being broadcast, the ALAP destination must be $FF. Ethernet packets have a minimum size of 60 bytes. Including the Ethernet header, an EtherTalk packet could be as small as 19 bytes. Thus small EtherTalk packets must be padded to 60 bytes in length. The pad bytes should all be zeroes. Note that the receiving node can determine the actual packet length from the ALAP data field length bytes. The maximum size of an EtherTalk packet is 603 + 14, or 617 bytes. Ethernet Oestinatio '' Ethernet Source Ethernet rotocol T e $8098 ALAP dest ALAP source ALAP type LAP data length ALAP data Pad flf needed) May 18, 1987 EtherTalk Draft -- Apple CONFIDENTIAL 1