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At the end of this class, you will be able to:
• List the basic components of a network
• Diagram how ADSL and cable modems work
• Analyze the advantages that networks can provide
• Understand in a general way how networks work
“Any sufficiently advanced technology is indistinguishable from magic.”
Arthur C. Clarke
Learning Objectives
A computer network is anycomputer system that linkstwo or more computers
There are three essentialcomponents in a network: Hardware Software People
Basic Network Anatomy
Costallows people to share hardware
Efficiency & Productivityallows people to share data and software
Opportunityallows people to work together in ways that are otherwise difficult or impossible
Why is networking important?
Linking Up: Network Basics
Visualization of a Network A computer network can be pictured or modeled
as a graph where each “node” in the graph represents a device on the network Means we can use concepts from graph theory when
designing networks
A LAN is a network in which the computers are physically close to each other (ex: same building)
– They typically share peripherals (printers)
– Each computer and shared peripheral is a node on the LAN
LAN (Local Area Network)
Physical Media for NetworksNetworks are built on physical media.
Plain Old Telephone Service (POTS) Twisted pair (Category 5) Coaxial Cable (TV) Fiber optic Wireless/infrared
Line of sight Wireless/radio
All have various characteristics, but all can send a signal from one point to another point
“Never in history has
distance meant less.”
Alvin Toffler
Fiber Optic Cables
Fiber optic cables are replacing aging copper lines They use light waves to carry information They provide data rates over one billion bits per
second (high bandwidth) They offer extremely low error rates Signals travel extremely fast across them (low
delay)
a
Terminal
Modem
Modem
Analogsignals
Phone line
Digitalsignals
Digitalsignals
Computer
The word modem comes from theterms modulation and demodulation
ModulationDemodulation
How a Modem Works
Modems Computers understand digital signals Telephone lines use analog signals Modem converts the digital signal from computer to
analog and vice-versa
The Network Interface A Network Interface Card
(NIC): Is needed to connect directly
to a network Can add an additional port to
the computer Controls the flow of data
between the RAM and the network cable
Converts the computer’s digital signals into the type required for the particular network
Most common today is ETHERNET
ADSL: How it Works
Copper wirePOTSDigital data
To work properly the ADSL modem must be located within a certain distance from the phone company’s answering ADSL modem.
Network Performance How “fast” a network performs is classified in
two ways: Bandwidth – how much information can be sent
(usually measured in bits per second, or bps) Bandwidth is affected by the amount of network traffic,
software protocols, and type of network connection
Propagation delay – how long it takes for data to physically travel across a connection
Delay is affected by the amount of network traffic, software protocols, and type of network connection
Client
ServerClient software sends requests from the user to the server
Server software responds to client requests by providing data
Client/Server Model
The peer-to-peer model allows every computer on the network to be both client and server
Many networks use a hybrid of client/server and peer-to-peer
Examples of P2P: BitTorrent, Gnutella, Kazaa, etc
Advantages? Disadvantages?
Peer-to-Peer Model
Packets and Routing Messages sent across a computer network are
often broken into small pieces called packets Each packet is then routed from point to point
by devices called routers The receiver then reassembles the original
message from the individual packets. Animation from CD (Chapter 9, TCP/IP)
We need to be able to… agree on how messages will be sent and
received divide the message into manageable pieces
(packets) find the “address” of a computer reassemble the message at the receiver resend pieces if they are lost
All of these details are handled by a protocol
Protocols A network protocol is a set of rules which govern
how computers “talk” to each other Covers details such as:
How big should each packet be? How do we determine if a packet is lost? How do we reassemble messages? How do we route a packet across the network? How do we identify a particular computer on the
network? A collection of protocols is called a protocol
suite
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