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Communication and Networking. Networking. A computer network is a collection of computing devices that are connected in various ways in order to communicate and share resources Usually, the connections between computers in a network are made using physical wires or cables

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Networking

  • A computer network is a collection of computing devices that are connected in various ways in order to communicate and share resources

  • Usually, the connections between computers in a network are made using physical wires or cables

    • However, some connections are wireless, using radio waves or infrared signals

  • The generic term node or host to refer to any device on a network

  • A key issue related to computer networks is the data transfer rate, the speed with which data is moved from one place on a network to another


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Networking

  • Computer networks have opened up an entire frontier in the world of computing called the client/server model

    • A file server is a computer that stores and manages files for multiple users on a network

    • A Web server is a computer dedicated to responding to requests (from the browser client) for Web pages

    • A mail server is a computer that stores email messages for multiple users and routes the messages to the email clients when a request is made.

    • Network printers …

Client/Server interaction


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Communication Basics

  • Properties of Transmission:

    • Each link has common attributes

    • 1. Type of signal communicated (analog or digital)

    • 2. The speed at which the signal is transmitted.

    • 3. The type of data movement allowed on the channel.

    • 4. The method used to transport the data.

    • 5. Single channel and multichannel transmission.


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Communication Basics

  • 1. Type of signal communicated.

    • Analog - A continuously changing signal similar to that found in voice transmission (e.g., phone lines).

    • Digital - Signals consist of pulses of electrical energy that represent 0’s or 1’s.


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Communication Basics

  • MODEM - MOdulator DEModulator

    • Outgoing: Converts binary data from computer (digital) into telephone compatible signals (analog).

    • Incoming: Converts telephone signal (analog) into binary data for the computer (digital).


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Communication Basics

  • 3. Type of data movement.

    • Three types of data movement can occur on a channel:

      • Simplex transmission - One way transmission.

      • Half-duplex transmission - Can flow only one way at a time.

      • Full-duplex transmission - Two-way transmission at the same time.


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Communication Basics

  • 4. Method of transmission.

    • Two types of data transmission, each requiring a different modem.

  • Asynchronous transmission

    • data is sent one byte at a time, with each string of bits making up the byte bracketed with special control bits

  • Synchronous transmission

    • data is sent in blocks, with start and stop bit patterns (synch bytes) at the beginning and end of the blocks


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Communication Basics

  • 5. Single channel versus multi-channel transmission

    • Channel - A path of a signal.

    • Single channel - Capable of only sending/receiving one signal at a time.

      • Phone line - Single line = single phone call at a time.

    • Multi-channel - Capable of more than one channel at a time.

      • Fiber-optic cable, microwaves, Satellite transmissions.


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Communication Basics

  • How is it possible to measure the capacity of communications links?

  • Bandwidth

    • In Digital:

      • Number of bits per second (bps) that can be sent over a link.

      • Wider bandwidth, the more diverse kinds of information can be sent.

      • Simplest is voice, most sophisticated is moving videos.

    • In Analog:

      • The difference between the highest and lowest frequencies that can be sent over an analog link (like phone lines).

      • Measurement is given in hertz (Hz).

    • For both: The wider the bandwidth, the more information can flow over the channel.


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Communication Basics

Typical cable bandwidths used in local area networks.

Cable: Typical Bandwidth:

Twisted Pair 10 to 100 Mbps

Coaxial Cable 10 to 100 Mbps

Fiber-optic cable 100 to 200 Mbps

The bandwidths of different services offered by a telephone company:

Service: Bandwidth

ISDN 64 Kbps

T1 1.544 Mbps

T3 44.736 Mbps

STS-1 51.840 Mbps

STS-3 155.250 Mbps

STS-12 622.080 Mbps

STS-24 1.244160 Gbps

STS-48 2.488320 Gbps

Mbps = megabytes per second (millions Gbps=Gigabytes per second (billions)


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Types of Networks

  • A local-area network (LAN) connects a relatively small number of machines in a relatively close geographical area

  • A wide-area network (WAN) connects two or more local-area networks over a potentially large geographic distance

    • Often one particular node on a LAN is set up to serve as a gateway to handle all communication going between that LAN and other networks

  • Communication between networks is called internetworking

    • The Internet, as we know it today, is essentially the ultimate wide-area network, spanning the entire globe


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Types of Networks

Local-area networks connected across a distance to create a wide-area network


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Intranets and Extranets

  • Intranet - an organization’s internal private network that uses the infrastructure and standards of the Internet and the WWW

  • Extranets - private intranets that connect not only internal personnel but also selected suppliers and other strategic parties


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Firewalls

  • A firewall is a machine and its software that serve as a special gateway to a network, protecting it from inappropriate access

    • Filters network traffic that comes in, checking the validity of the messages as much as possible and perhaps denying some messages altogether

    • Enforces an organization’s access control policy


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Types of LAN Topologies (Configurations)

  • Star topology

    • Centers around one node to which all others are connected and through which all messages are sent.

    • Everything depends on the central host; if it goes down the whole network goes down.


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Types of LAN Topologies (Configurations)

  • Ring topology

    • Connects all nodes in a closed loop on which messages travel in one direction.

    • A message sent out from one node is passed along to each node in between until the target node received the message.

    • More reliable than star network since one machine going down does not affect all of the connections.


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Types of LAN Topologies (Configurations)

  • Bus topology

    • All nodes are connected to a single communication line (bus) that carries messages in both directions

    • Most reliable type of network

    • The primary protocol used for bus networks is called Ethernet which has become the industry standard for local-area networks

      • Messages are broadcast across the bus and picked up by the recipient

      • If two nodes send messages at the same time, this results in “collision” in which case, the protocol forces the nodes to wait for a random period of time and then retransmit.


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Types of LANs

  • Client/server LAN:

    • Clients - microcomputers that request data; and

    • Server - a powerful microcomputer that manages shared devices


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Types of LANs

  • Peer-to-peer LAN

    • all microcomputers on the network communicate directly with one another without relying on a server



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Components of LANs

Hub A device that repeats or broadcasts the network stream of information to individual nodes ( usually personal computers)

Switch A device that receives packets from its input link, and then sorts them and transmits them over the proper link that connects to the node addressed.

Bridge A link between two networks that have identical rules of communication.

Gateway A link between two different networks that have different rules of communication.

Router A node that sends network packets in one of many possible directions to get them to their destination.


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Communication Channels

  • Communications channel

    • the path (physical medium) over which information travels in a telecommunications system from its source to its destination

  • The physical media used to connect the networks are:

    • Twisted pair

    • coaxial cable

    • fiber optic cable

    • and Wireless channels


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Communication Channels

  • Twisted pair:

    • Two wires twisted together.

    • Less susceptible to acting like an antenna and picking up radio frequency information or appliance noise.

    • Used by the telephone company.


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Communication Channels

  • Coaxial cable:

    • One wire is formed into a tube which is electrically grounded.

    • The other wire is placed down the center of this tube and the space between is filled with a special nonconducting material.


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Communication Channels

  • Fiber-optic cable:

    • Optical cable allowing light to pass along the cable.

    • Light is electromagnetic, and because of its higher frequencies, transmits a lot more information through a single strand.


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Communication Channels

  • Three types of wireless communication commonly used

    • Infrared:

      • Commonly used in TV and VCR remote controls.

      • Use infrared frequencies of electromagnetic radiation that behave much like visible light.

      • Must be in the line of sight.

      • Often used to connect keyboards, mice, and printers.

    • Radio frequency:

      • Uses radio frequencies.

      • Not commonly used because of the possible interference from other sources of electromagnetic radiation.

    • Microwave:

      • Often used to communicate with distant locations.

      • Must be line of sight.

      • Satellite communications use microwaves.


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