3Com corebuilder 3500 Implementation Manual page 423

Key Concepts 423
Destination node — A 6-byte field that contains the physical address
of the destination node.
Destination socket — A 2-byte field that contains the socket address
of the packet's destination process.
Source network — A 4-byte field that contains the source node
network number. If a sending node sets this field to 0, the source's
local network number is unknown.
Source node — A 6-byte field that contains the source node physical
address. Broadcast addresses are not allowed.
Source socket — A 2-byte field that contains the socket address of
the process that transmitted the packet.
Packet data — A field that contains information for upper-layer
network processes.