Introduction to Local Area Networks1-*

What is a Local Area Network?A local area network is a network whose size is not large. For example, the size may be a room, a department, a company, a campus, etc.A network that covers a place that is city-wide is called a metropolitan network.A network that spans states or countries is called a wide area network.1-*

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Why We Study Local Area Networks?You are using local area networks (e.g., Ethernets, wireless LANs, NFS, MWs neighborhood, etc.) everyday and everywhere.You better know them well.This course is aimed to be self-contained. If you have taken course, that is good. If not, that is still OK. We will spend the first four weeks on the basics that are covered in .After taking this course, you will have hand-on experiences of using and configuring a switch.

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How Is a Local Area Network Implemented?1-*

End host (PC)A computer network physically is composed of end hosts, intermediate routers/switches, andtransmission links. (like nodes and edges in a graph)Router/SwitchLink1-*

A computer network is used to transfer a piece ofdata from one node (traffic source) to any other node (traffic destination). sourcedestinationdata1-*

sourcedestinationA computer network also needs protocols so thatdifferent nodes can talk to and work with each other to finish a job. dataHey, you send too fast!Hey, your 3rd data is lost.Error control protocolsCongestion control protocols1-*

Computer Networks Protocols Are Very ComplexFraming (PPP, SLIP)Medium access control (Ethernet 802.3, WLAN 802.11)Addressing (IP, Appletalk)Routing (RIP, OSPF)Error control (ARQ) and congestion control (TCP)Quality of service (RSVP, Diffserv, IntServ)Security (IPsec)WWW (HTTP), FTP, Telnet, Bit-torrents (P2P)For examples:1-*

Protocol Layering Is Used To Manage Complex ProtocolsThe ISO OSI seven-layer reference model1-*

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The Internet TCP/IP Protocol Stacktransportapplicationnetworkphysical1-*

Why You Study Computer Networks As A Student?Learn how computer networks work todayAs numerous protocols are emerging and fading out rapidly, understanding protocol principles is far more important than knowing protocol details.E.g., instead of memorizing how frequently routers exchange their hello messages and when to declare a router is dead in RIP, it is more important to understand why doing this protocol allows a router to detect that its neighboring router is dead.1-*

Why You Study Computer Networks As A Student (contd)?Learn the real reasons behind the designs of todays computer networksOnce you know the reasons, you can apply them to other places.E.g., Knowing why Ethernet uses Manchester encoding is more important than knowing that Ethernet uses Manchester encoding to encode signals.1-*

Why We Study Computer Networks As An Engineer?Try to achieve the following ideal goals:A users data can be transferred from one node to any other node reliably, in-sequence, and spontaneously.A networks resources (e.g., bandwidth) can be efficiently and fully utilized to reduce the operation costs.However, sometimes these goals are conflicting,which makes achieving these goals at the same time very hard!1-*

Welcome to the Internet! Internets topology1-*

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