计算机网络英文版课件5.pptVIP

江西师大软件学院 Computer networkChapter 5The Network Layer 郭 斌 E_mail: jxnuit@163.com The Network Layer The network layer is mainly concerned with getting packets from the source all the way to the destination, providing end-to-end transmission. Provides services to the transport layer Carry through congestion control Internetworking Topics Network Layer Design Issues Routing Algorithms Congestion Control Algorithms Internetworking The Network Layer in the Internet Network Layer Design Issues Store-and-Forward Packet Switching Services Provided to the Transport Layer Implementation of Connectionless Service Implementation of Connection-Oriented Service Comparison of Virtual-Circuit and Datagram Subnets Store-and-Forward Packet Switching At the network layer, the packet is delivered by intermediate routers hop by hop using store-and-forward packet switching. Services Provided to the Transport Layer The network layer services have been designed with the following goals in mind. The services should be independent of the routers technology. The transport layer should be shielded from the number, type, and topology of the routers present. The network addresses made available to the transport layer should use a uniform numbering plan, even across LANs and WANs. Two type: Connectionless services Connection-oriented services Implementation of Connectionless Service No advance setup is needed. Packets are injected into the subnet individually and routed independently of each other. The packets are called datagrams and the subnet is called a datagram subnet. Implementation of Connection-Oriented Service A route from the source machine to the destination machine must be set up in advance, and stored in tables inside the routers.That route is used for all traffic flowing over the connection. This connection is called a VC (virtual circuit) and the subnet is called a virtual-circuit subnet. Comparison of Virtual-Circuit and Datagram Subnets Routing Algorithms Shortest Pat