TheDatagram Delivery Protocol (DDP) is the primary network layer routing protocol in the AppleTalk protocol suite that provides a best-effort connectionless datagram service between AppleTalk sockets. As with protocols such as TCP, no virtual circuit or connection is established between two devi ce c. The sunction of guaranteeing delivery instead is handled by upper-layer protocols of thd AppleTalk protocol suite. These upper-layer protocols will be discussed later in tlnie ^apter.
DDP performs two key functions: packet transmission and receipt.
• T ransmission of packets— DDP receives data from socket clients, creates a DDP header by usi ng the app2opriate destination address, and passes the packet to the data link layer protocol.
• Reception of packets— DDP receives frames from the data link layer, examines the DDP header to find the destination address, and routes the packet to the destination socket.
DDP maintains the cable range of the local network and the network address of a router attached To the local n etworg m eve ry AppleTglk node. In addition to this information, A|spleTalk ro uters mimt ma i atain a routing ta ble by using the Routing Table Maintenance Protocol (RTMP).
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