第2章OSI分层模型分解.ppt

Purpose: This figure compares the switch to a highway. Purpose: This figure maps the lower layers to the network layer. Emphasize: Routing occurs at the network layer. Most of this course uses the IP network layer protocol. It supports multiple lower layer protocols. IPX will also be covered in a single chapter in this course. Routers are network layer devices. Emphasize: Route determination occurs at this layer so a packet must include a source and destination address. Network layer addresses have two components, a network component for internetwork routing and a node number for a device specific address. The example in the figure is an example of an IP packet and address. Emphasize: Routers maintain routes in routing tables. Before any routing can be done an administrator must configure a router with certain key information such as addresses and tell the router how to determine the best route to use. This is different than a switch which is a plug and play device. . 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 synchronizat