540 CHAPTER 21: A PPLE T ALK R OUTINGTransport Layer ProtocolsThe transport layer and the session layer provide end-to-end services inthe AppleTalk network. These services ensure that routers transmit dataaccurately between one another. Each layer includes four protocols thatwork together to support these services. This section describes theseprotocols and provides more detail for the protocols that you can viewusing the Administration Console.An AppleTalk intranet has four transport layer protocols:n Routing Table Maintenance Protocol (RTMP)n Appletalk Echo Protocol (AEP)n AppleTalk Transaction Protocol (ATP)n Name Binding Protocol (NBP)Routing Table Maintenance Protocol (RTMP) This protocolmaintains information about AppleTalk addresses and connectionsbetween different networks. It specifies that each router:n Learns new routes from other routersn Deletes a route if the local router has not broadcast the route to thenetwork for a certain period of timeEach router builds a routing table for dynamic routing operations in anAppleTalk intranet. Every 10 seconds, each router sends an RTMP datapacket to the network. Routers use the information that they receive inthe RTMP broadcasts to build their routing tables. Each entry in therouting table contains these items:n Network rangen Distance in hops to the destination networkn Interface number of the destination networkn State of each port (good, suspect, bad, or really bad)
