第一章数据通信基本原理.ppt

* . Emphasize: Routers perform the network layer functions depicted in the figure. * Purpose: Routers provide access into the corporate network via WAN connections. Emphasize: A main office must be able to support multiple types of connections. Note: The lightning bolt represents a WAN connection. The dotted lines represent DDR connections. The solid bolts can be packet switched or leased lines. * Purpose: This figure describes the transport layer. Emphasize: Two transport layer protocols in the IP stack are TCP and UDP. TCP will offer more reliability because it is connection oriented. UDP guarantees no reliability. Sequence Packet Exchange (SPX) is the transport layer protocol used by IPX. It is also connection oriented. Newer versions of IPX support TCP and UDP as well. * Purpose: This figure illustrates a TCP connection being established. Emphasize: The exchange is sometimes referred to as the “three-way-handshake.” The initiating host requests a synchronization. The receiver acknowledges the synchronization and specify synchronization parameters in the opposite direction. The receiver acknowledges the synchronization and a connection is established. * Emphasize: This figure summarizes the different collision domains and broadcast domains on various network devices. It is important that students understand the difference between the two domains. * Purpose: This figure reintroduces the heirarchical model presented earlier in this chapter. Its intention is to use help explain where in the network different network devices may be placed. * Purpose: This page defines local services. Emphasize: A local service is when the entities that provide these common functions reside on the same subnet or virtual network as the user. Local services remain in specific area of the network. Traffic to and from local services is confined between a server, a switch, and an end user. Local traffic does not enter the network backbone or move through a router. Local services