Knowledge points: two services provided by WAN: Data report and virtual phone. Grouping forwarding mechanism three wide area networks: X.25 network and frame relays and wide area network using ATM technology first clarify the difference between node switches and routers: Switches It is used for a single network; the router is used in multiple networks. Data reports and virtual circuits: Data report services are unconnected network services; (so-called unconnected service is also the best effort to send packets to destination) It does not have any promise to the host) The virtual circuit service is a connection-oriented network service; (a bit of telephone communication, must be built first, but you will be a traditional call. It no longer It is necessary to take a line from beginning to end to the end, but only a piece of link is interrupted. The advantage is that the quality of service is guaranteed. (Ref refer to the dispute between OSI and ARPNET)) Group forwarding mechanism: first clarify two Concept: Forwarding and routing. Forwarding, when the switching node receives the packet, find out the forwarding table according to its destination address, and find out which interface should be sent from the node. Routing is the process of constructing the routing table. Routing table It is based on a certain routing algorithm, and the forwarding is constructed according to the routing table. Order: Receive the Group -> Routing Algorithm Constructing Routing Table -> By constructed a transfer table by routing table -> Forward In the node switch finds the relevant knowledge point: hierarchical address forwarding table without the source station address Next Tip congestion control: Concept: In a certain period of time, if the demand for a resource in the network exceeds the resource The available parts that can be provided, the performance of the network is deteriorated. This is called congestion. Congestion control is closely related to traffic control, but there is also differences: It can be understood that congestion control is a global variable that the network can withstand existing network loads; and flow control is often only the control of traffic between points between points. The congestion state reaches a certain extent to cause a deadlock problem: one is a direct deadlock, which is a large number of groups to be sent to each other. At this time, both sides have a cache, so that the other party cannot receive the group. The other is to reload deadlocks due to the congestion of the caching of the router. (Reading) X.25 network and frame relay network and the difference between the ATM network: X.25: Background: Based on the connection-oriented virtual circuit service, the computer price is high, the communication quality is high, and the error rate is high. At this time, the quality of service is guaranteed, and the smart is done in the X.25 network in the network.
