Understanding the network.pdf - Back to Home

network-wide broadcast, the node accepts the packet. After it's
accepted, the zone information is checked, and anything not intended
for the node isdiscarded. Zone-specific broadcasts with DDP are
dependent on ZIP, zone multicasting function and addressing, for
correct handling.
DDP Datagram Assembly and Delivery
DDP datagram delivery uses a local and remote delivery model. ULP
sends data to DDP for delivery. DDP determines which delivery model
to use based on the network number of the destination address. If the
destination address is within the range of the local network, a DDP
short header is encapsulated along with the data and sent to Layer 2
for local delivery. If the destination is out of range, the datagram is
encapsulated with a long header, handed to Layer 2, and sent to the
router for delivery. AppleTalk networks are limited to 15 hops.
Extended DDP headers have a hop count field, which is incremented
by 1 each time the datagram passes through a router. When the
counter reaches 15, the packet is discarded.
AppleTalk Layer 4 (Transport) Protocols
AppleTalk's Layer 4 protocols all contribute to providing the following
end-to-end transport services for ULP data between end-nodes:
• Routing table creation and maintenance
• AppleTalk internetwork transport services over TCP/IP
• End-node ratability
• Binary network addressing (physical addressing) to
network-named entity (contextual addressing) translation
services
• Connection-oriented socket data transport
Routing Table Maintenance Protocol
AppleTalk routing is a dynamic process. Although network addresses
are statically set, node addresses are usually assigned dynamically,
so static addressing has a very limited value. End-nodes can
determine if a datagram is to be delivered locally or remotely. If the
destination is remote, the router takes over. The router's main job is
to maintain information about different network segments that are