Chapter 4 Notes - IS450

Chapter 4 Notes - IS450 - 1 IS 450/650 The Network Layer...

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Unformatted text preview: 1 IS 450/650 The Network Layer Announcements & Reminders: Homework 4 will be online tonight and due Monday 12/6. Suggestion: do it this week. Homework 5 will be online this week and also due Monday 12/6. Homework 6 will be due Monday 12/13. Well skip routing, sections 4.54.8. This is covered well in IS 452, so its more important that we cover link layer well. 12/13 Grad paper due. Monday 12/20 6pm final exam Starting Monday 10/25 no laptops, no exceptions. Too many people are doing less than well in the course. Cell phones & laptops off . Reminder: if printing the notes, consider printing 4-up (4 pages per side) or 2-up or 6-up or some such. Generated November 22, 2010. 2 Internetworking We can connect limited numbers of hosts together in a LAN, but LANS fail to scale. The transport layer has facilities for process-to-process communications, but no facilities to distinguish among individual machines. We need something in between. This layer is the network layer, layer 3. In the simplest case, we can connect a pair of networks with a layer-3 switch, i.e., a router : Ultimately we need to be able to interconnect multiple networks with multiple routers: 3 The Internet as a Cloud Conceptually, users view the Internet as some big thing they can plug any computer into: 4 Peeking Into the Cloud The Internet however is an interconnected set of (many) physical networks: 5 Where Are We? So a recent phrase was physical networks, as in The Internet is an interconnected set of many physical net- works. Each individual network is a LAN, layers 1 & 2 We interconnect them at the network layer. So now we concentrate on layer 3: just below the transport layer (TCP, UDP, DCCP, etc.); a couple layers below applications; relying on links (layer 2) to deliver data locally. 6 Switches, Layers 2 & 3 Typically LANs connect to other LANs through routers: The router works at the network layer, so: Ethernet broadcasts usually arent forwarded. Forwarding decisions are made by IP address, not MAC address. 7 Store and Forward When a router receives a packet, it can forward the packet, queue the packet to forward later, or drop the packet. The router has multiple ports, and ideally can receive and forward on multiple ports concurrently. Each port is on a different LAN. If the router is sending and receiving on multiple LANs concurrently, collective throughput can be high. 8 Network Layer Addressing Conceptually, a network layer address is hierarchical: (site, host at site) . The site above is often referred to as the network num- ber . A similarly hierarchical address scheme youre familiar with is the phone number....
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Chapter 4 Notes - IS450 - 1 IS 450/650 The Network Layer...

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