System information

Troubleshooting AppleTalk 9-179

Datagram Delivery Protocol

Figure 9-3 AppleTalk Entities

Datagram Delivery Protocol

AppleTalk’s primary network-layer protocol is the Datagram Delivery Protocol (DDP). DDP

provides connectionless service between network sockets. Sockets can be assigned either statically

or dynamically.

AppleTalk addresses, which are administered by the DDP, consist of two components: a 16-bit

network number and an 8-bit node number. The two components are usually written as decimal

numbers, separated by a period (for example, 10.1 means network 10, node 1). When an 8-bit socket

identifying a particular process is added to the network number and node number, a unique process

on a network is speciﬁed.

AppleTalk Phase 2 distinguishes between nonextended and extended networks. In a nonextended

network such as LocalTalk, each AppleTalk node number is unique. Nonextended networks were the

sole network type deﬁned in AppleTalk Phase 1. In an extended network such as EtherTalk and

TokenTalk, each network number/node number combination is unique.

Zones are deﬁned by the AppleTalk network manager during the router conﬁguration process. Each

node in an AppleTalk network belongs to a single speciﬁc zone. Extended networks can have

multiple zones associated with them. Nodes on extended networks can belong to any single zone

associated with the extended network.

The Transport Layer

AppleTalk’s transport layer is implemented by several protocols: Routing Table Maintenance

Protocol (RTMP), AppleTalk Update Routing Protocol (AURP), AppleTalk Echo Protocol (AEP),

AppleTalk Transaction Protocol (ATP), and Name Binding Protocol (NBP).

Node

Network 1

Network 3

Network 2

Network 4

Network 5

Zone A

Zone B

Zone C

Router