Day 12 Chapter 13 WAN Technologies and Routing

Classification of Networks LAN – spans a single building or campus MAN – Spans a city WAN – Spans multiple cities, countries, or continents

WANs The WAN network must allow a lot of simultaneous communication between computers Key difference between LANs and WANs is scalability – WANS can grow as needed The long-distance leased lines (Ch. 12) are connected to packet switches (i.e. routers) Individual computers are then connected to the routers Each router is a computer that can receive and send packets See Figure 13.1, p. 202, to see logical diagram of a router

Forming a WAN See Figure 13.2, p. 203 to see how 4 routers are connected Connections between routers represent high-speed, long-distance connections Notice there are multiple paths that a packet may take in the network

Operation of WAN Wide area packet switching uses “store and forward” approach The router reads the packet and stores it in memory The packet is examined and the router determines over which interface the packet should be sent out Packets are held in memory until the output device is available

Physical addressing in WAN WANs use a hierarchical addressing scheme Simple scheme uses an address with two parts (IP): –First part identifies packet switch –Second part identifies computer attached to that packet switch See Figure 13.3 for example of addresses

Next-Hop Forwarding Router selects an outgoing path over which to forward a packet The path is selected based upon the destination address stored in the packet The router stores information to determine the next router (next hop) the packet should be sent to See Figure 13.4, p. 202 for example of routing table Note- the next hop does not depend upon packet’s source or on the path it has taken so far

Routing Table The router needs to only examine the first part of the hierarchical address The entire routing table can be shortened to contain one entry per destination packet switch See Figure 13.5, p. 204

Routing in a WAN Fundamental concept – switching capacity can be increased without adding individual computers Router can be added to interior of a network to handle load These routers do not have computers attached These are called interior routers Routers to which computers are attached directly are called exterior packet switches

Homework Read Chapter 13 of your text: WAN Technologies and Routing. Study Dijkstra’s Algorithm that finds the shortest path in a WAN