数据教程课件Chapter 10 connecting networks 2.ppt

Chapter Ten Connecting Networks Example Routing Tables A→F Routing – The Problem Choose the best path from A to X, knowing (at A) only the logical address of X. “Best” could mean – Smallest number of hops – Shortest time delay – Least congested – Cheapest – Administratively allowed – Easiest to discover – Any combination of the above Solution must be reasonably quick and guaranteed to avoid loops Routing Algorithm The way to define the routing tables Four types: Centralized routing: 集中式路由 Distributed routing: 分布式路由 Static routing: 静态路由 Adaptive routing: 自适应路由 Centralized Routing All interconnection is generated and maintained at a single central location. That location broadcasts this information to all network nodes. Routing matrix A→F： A-B-E-F Distributed Routing There is no central control. Each node must determine and maintain its own routing tables. – Know the neighbors and cost of getting to them – Determine cost for neighbors to send to a destination Static Routing Assumes conditions do not change Defined once, but have to update manually Reality Nodes are added or removed Networks are added or removed Changing traffic patterns Adaptive Routing A→E: A-D-C-E Summary of 4 types of routing Summary Summary Summary Review Questions: 1，2，3，8，9 Exercises: 2，3， Required Reading： Ch10.1-10.4 * Layer 3 Connections: Routers Thus, routers are often called “layer 3 devices”. They operate at the third layer, or OSI network layer, of the packet. The device that connects a LAN to a WAN or a WAN to a WAN. A router accepts an outgoing packet, removes any LAN headers and trailers, and encapsulates the necessary WAN headers and trailers. Because a router has to make wide area network routing decisions, the router has to dig down into the network layer of the packet to retrieve the network destination address. Chapter Ten – Connecting Networks Layer 3 Connections: Routers Chapter Ten – Connecting Networks Which way is the best? The blue one which is