7-6 CHAPTER 7: ROUTING IN AN APPLETALK® ENVIRONMENT

because it is closely related to the Ethernet and token ring LAPs. This protocol is usually included in the definition of each LAP, so it does not appear in the reference model. See the section “About AARP” later in this chapter for more information about this protocol.

The Datagram The network layer accepts data from the layers above it and divides the data Delivery Protocol into packets that can be sent over the network through the layers below it.

(DDP) The Datagram Delivery Protocol (DDP) transfers data in packets called datagrams.

Datagram delivery is the basis for building other AppleTalk services, such as electronic mail. The DDP allows AppleTalk to run as a process-to-process, best-effort delivery system in which the processes running in the nodes of interconnected networks can exchange packets with each other.

End-to-End Services The transport layer and the session layer provide end-to-end services in the AppleTalk network. These services ensure that routers transmit data accurately between one another. Each layer includes four protocols that work together to support these services. This section describes these protocols and provides more detail for those that you can view using the LANplex Administration Console.

Transport Layer Protocols

An AppleTalk internet has four transport layer protocols:

Routing Table Maintenance Protocol (RTMP)

AppleTalk Echo Protocol (AEP)

AppleTalk Transaction Protocol (ATP)

Name Binding Protocol (NBP)

Routing Table Maintenance Protocol (RTMP). The protocol maintains information about AppleTalk addresses and connections between different networks. It specifies that each router 1) learns about new routes from the other routers and 2) deletes routes after a certain period if the local router no longer broadcasts the route to the network.

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3Com 2500 manual Routing in AN Appletalk Environment