Course Hero Logo

Some link layers like a cellular connection for a

Course Hero uses AI to attempt to automatically extract content from documents to surface to you and others so you can study better, e.g., in search results, to enrich docs, and more. This preview shows page 23 - 26 out of 119 pages.

Some link layers, like a cellular connection for a smartphone, aWiFi connection, or a satellite or cable modem, are shared con-
16CHAPTER2. NETWORKARCHITECTUREFigure 2.2: Carrier Sense/Collision Detectionnections and need techniques like CSMA/CD to insure fair accessto the many different computers connected to the network. Otherlink layers like fiber optic cables and leased lines are generallynot shared and are used for connections between routers. Thesenon-shared connections are still part of the Link layer.The engineers working on Link layer technologies focus solvingthe issues so computers can transmit data across a single linkthat ranges in distance from a few meters to as long as hundredsof kilometers.But to move data greater distances, we need tosend our packets through multiple routers connected by multiplelink layers.Each time our packet passes through another linklayer from one router to another we call it a “hop”. To send datahalfway around the world, it will pass through about 20 routers,or make 20 “hops”.2.2The Internetwork Layer (IP)Once your packet destined for the Internet makes it across thefirst link, it will be in a router. Your packet has a source address
2.2. THEINTERNETWORKLAYER(IP)17and destination address and the router needs to look at the des-tination address to figure out how to best move your packet to-wards its destination. With each router handling packets destinedfor any of many billions of destination computers, it’s not possiblefor every router to know the exact location and best route to ev-ery possible destination computer. So the router makes its bestguess as to how to get your packet closer to its destination.Each of the other routers along the way also does its best to getyour packet closer to the destination computer.As your packetgets closer to its final destination, the routers have a better ideaof exactly where your packet needs to go.When the packetreaches the last link in its journey, the link layer knows exactlywhere to send your packet.We use a similar approach to route ourselves when going on hol-iday. A holiday trip also has many hops. Perhaps the first hop isdriving your car or taking a cab or bus to a train station.Thenyou take a local train from your small town to a larger city. In thelarger city you take a long-distance train to a large city in anothercountry.Then you take another local train to the small villagewhere you will stay for your holiday. When you get off the train,you take a bus, and when you get off the bus, you walk to yourhotel.If you were on the train between the two large cities and youasked the conductor the exact location of your hotel in the smallvillage, the conductor would not know. The conductor only knowshow to get you closer to your destination, and while you are onthe long-distance train that is all that matters. When you get onthe bus at your destination village, you can ask the bus driverwhich stop is closest to your hotel. And when you get off the bus

Upload your study docs or become a

Course Hero member to access this document

Upload your study docs or become a

Course Hero member to access this document

End of preview. Want to read all 119 pages?

Upload your study docs or become a

Course Hero member to access this document

Term
Spring
Professor
José Pérez
Tags
The Land, Internet Protocol Suite

Newly uploaded documents

Show More

  • Left Quote Icon

    Student Picture

  • Left Quote Icon

    Student Picture

  • Left Quote Icon

    Student Picture