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Basics ofCommunication & Networking

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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

• 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

• 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

• 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

• 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 MbpsCoaxial Cable 10 to 100 MbpsFiber-optic cable 100 to 200 Mbps

The bandwidths of different services offered by a telephone company:Service: BandwidthISDN 64 KbpsT1 1.544 MbpsT3 44.736 MbpsSTS-1 51.840 MbpsSTS-3 155.250 MbpsSTS-12 622.080 MbpsSTS-24 1.244160 GbpsSTS-48 2.488320 Gbps

Mbps = megabits per second (millions) Gbps=Gigabits 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 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

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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.

GatewayA 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.

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.

GatewayA 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.