文档介绍：Computer network Chapter 5 The Network Layer
郭 斌
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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 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