Understanding the network.pdf - Back to Home

• DDP checksum (long header only)—This 16-bit field is used for
error detection resulting from router-to-router transmissions.
The checksum, together with the datagram at the source, is
used by the router at arrival to verify data integrity.
• Destination network address (long header only)—This is a
16-bit network address.
• Source network address (long header only)—This is a 16-bit
network address.
• Destination node ID (long header only)—This is an 8-bit node
address.
• Source node ID (long header only)—This is an 8-bit node
address.
• Destination socket number (short and long header)—This is an
8-bit socket address.
• Source socket number (short and long header)—This is an 8-bit
socket address.
• DDP type (short and long header)—This is an 8-bit field used to
indicate the transport layer protocol.
DDP Broadcasts
Three types of DDP broadcasts exist:
• Network-specific broadcast
• Network-wide broadcast
• Zone-specific broadcast
The way the broadcast is interpreted by the node is determined by the
node address field in the packet's destination network address. If the
network number is any value other than zero, a datagram with a
destination node ID of $FF (255) is examined by all nodes. However,
the datagram is only accepted by nodes with the corresponding
network number.
If the network number is zero ($00000000), the broadcast is intended
for the local network segment. If the packet is a network-wide packet,
the network address is zero and the node address is $FF, and all
nodes on the segment accept the packet. If the packet is intended to
be a zone-specific broadcast, it has the same addressing as a
network-wide packet. However, it is up to the ULP to determine if the
packet is relevant to the node. Because the packet is addressed as a