Telecommunications & Networks

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Lecture Topics

1. Telecommunication Networks2. Network Components3. Network Topologies4. Network Protocols5. Network Types6. Network Architectures

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Communication NetworksCommunication Networks

A system that is set up for the communication of information from one location to another. Example: The mail system in the old west.

Telecommunication Networks or just Networks A system that is set up for the communication

of information by electronic means.Example: The transmission of information

between personal computers

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Network Components1.Sender and receiver2.Channel3.Message4.Noise

Sender ReceiverChannel

Noise

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1. Sender and Receiver These are input and output devices like Pcs, handheld

computers, terminals etc that send or receive information.

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2. Channels – Channel MediumsChannel Medium

A telecommunications channel is the medium used to send information from the sender to the receiver. In older communication channels this medium was the mailperson used to carry the messages from New York to Los Angeles.

1. Twisted pair (cat 5 shown here)–looks similar to telephone cable–has square plastic RJ-45 connector

2. Coaxial cable–resembles cable-TV cable–round, silver BNC connector

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Channels3. Fiber-optic cable is a

bundle of extremely thin tubes of glass

Each optical fiber (tube) is thinner than a human hair

Consists of strong inner support wire, multiple strands of optical fiber and a tough outer cable

Transmit pulses of lightUSB, serial, parallel,

SCSI, and Firewire connections

4. Infrared light can also carry data signals, but for short distances with a clear line of sight. Best for transmitting between notebook computers and a printer, or between a PDA and a desktop computer

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ChannelsChannel Characteristics

1.Transmission RateThe rate at which a channel transfers data from one computer to another. Measured in bits per second.

2.BandwidthThe maximum volume of data the network can carry.

3.Transmission Mode (Two modes)1.Asynchronous Transmission

Data is transmitted one byte at a time. Like a mailperson carrying one letter at a time. Every byte has a starting bit and an ending bit so that the receiver knows when a byte begins and when it ends.

2.Synchronous TransmissionData is transmitted as blocks of bytes at a time which is faster than asynchronous transmission.

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Channels

4. Transmission Direction (Three directions)Simplex: A device can send or receive data but

not do both like in TV sets.Half-Duplex: The sender and receiver devices

can alternate in sending and receiving data like in walkie-talkies.

Full Duplex: Both sender and receiver devices can send and receive data at the same time like in the phone.

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Channels4. Transmission Signal (Two types)

Information transfers through the channel in the form of electromagnetic signals.

Analog Signals: These are continuous signals represented as waves. Eg. temperature or telephones. Messages are transmitted by changing the amplitude and frequency of waves.

Digital Signals: These are represented in the form of zeros and ones and are the way computers transmit information. Less susceptible to channel noise.

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Analog Signal SpecificsFrequencyWavelengthAmplitude

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Messages and Packets

When you transmit data, it is broken up into small pieces called packets

A packet is a parcel of data that is sent across a networkHas the address of its senderHas the address of the receiverHas some data

When they reach the destination, they are put back together into their original form.

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Network Topologies

Star Topology Bus Topology

Ring Topology

The geometric configuration of devices in the network.

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Network Topologies - Bus Bus Topology

Connects all devices in the network to a central channel.Signals from devices are intercepted from all other devices but

only the addressed device will respond.There is no central host or server.The channel in the network can handle one message at a time. Advantages:

Makes it easy to add or remove devices from the network without affecting network performance.

If one of the devices in the network fails, the network will not fail.

DisadvantagesThe network performance decreases as the number of devices

in the network increases because each device checks to see if the signal transmitted from another device is for it or not

If two devices send a message at the same time, a “message collision” will occur and the messages will need to be resent.

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Network Topologies-RingRing Topology

Devices are arranged in a ring. A device can communicate directly with any

other device in the network.There is no central host or server for the

network.Advantages:

If one of the devices in the network fails, the network will not fail.

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Network Topologies-StarStar Topology

There is a central server or host in the network. Applied when some processing should be centralized and

some of it left on the devices. Signals between devices (messages) absolutely go through

the central host which functions as the traffic controller. The channel in the network can handle one message at a

time.Advantages:

Makes it easy to add or remove devices from the network. If one of the devices in the network fails, the network will not

fail.Disadvantages

If the central host fails, the network will fail. Also as the distance between the host and any device

increases, the cost increases significantly.

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Network Protocols

Three major components of a protocol:A set of characters that mean the same for

the sender and receiver.A set of rules for timing and sequencing

messages.A set of methods for detecting and

correcting errors.

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Network Protocol ExamplesProtocol Summary

Protocol Cable Speed Topology

Ethernet Twisted Pair, Coaxial, Fiber

10 Mbps Linear Bus, Star, Tree

Fast Ethernet

Twisted Pair, Fiber 100 Mbps Star

LocalTalk Twisted Pair .23 Mbps Linear Bus or Star

Token Ring Twisted Pair 4 Mbps - 16 Mbps

Star-Wired Ring

FDDI Fiber 100 Mbps Dual ring

ATM Twisted Pair, Fiber 155-2488 Mbps

Linear Bus, Star, Tree

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Ethernet Ethernet (10 Mbs).

Node listens to cable and transmits when everything is clear. If collision occurs, nodes will attempt again after a random period of

time. Fast Ethernet (100 Mbs). Gigabit Ethernet (1GB). 10 Gigabit Ethernet

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Protocol Type – Token RingToken Ring.

A single electronic token moves around the ring.

If a node wishes to transmit waits for an empty token and attaches data to it.

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How do I set up a simple LAN?

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Network TypesLAN (Local Area Networks)

A network that links devices in a local area and within a radius of 2000 feet.

They use bus or ring topologiesUsed to share resources in an office such as printers,

scanners, file servers etc.They require extensive wiring. A solution to that

nowadays is to create a wireless LAN.LANs communicate with other LANs through

gateways that can translate protocol standards from one network to the other.

For one LAN to access the resources of another bridges or routers are used if the distance increases.

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Network TypesWAN (Wide Area Networks)

Span from several miles to entire continentsLines might be leased or purchased

Integrated Services Digital Network (ISDN) Transmitting data over a phone line

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Network TypesVirtual Private Networks (VPNs):

How do they workThrough Public MediumsTunneling

Cost ReductionCost savings on the calls (1K to 2K per call per person)Operating Costs of supporting remote users

Modem pools Other support

Elimination of dedicated linesNo need for multiple access linesSavings increase if company is decentralized

geographicallyFlexibility

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Network Architecture

Client ServerPeer-To-Peer

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Network ArchitectureClient Server

Fat ClientFat ServerThree-Tier (Distributed)Multi-tier (Distributed)

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Three-Tier (Distributed)

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Fat Server

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Fat Client

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Internet Implementation