Telecommunications Media

Introduction

The intervening link, such as telephone wire, cable or microwaves, that connects two physically distant hardware devices.

When a message is transmitted, one of the hardware units is designated as the sender and the other as the receiver.

Two classes of communications media: Wire & Wireless

Wire Media

Twisted Pair Wires - A communications medium consisting of wire strands twisted in sets of two and bound into a cable.

Coaxial Cable - A transmission medium, consisting of a center wire inside a grounded, cylindrical shield, capable of sending data at high speeds.

Fiber Optic Cable - A transmission medium composed of hundreds of hair - thin, transparent fibers along which lasers carry data as light waves.

Wire Media

Twisted Pair Cable

Twisted pairs are two color coded,

insulated copper wires that are twisted

around each other.

A twisted pair cable consist of one or

more twisted pairs in a common jacket.

Wires are twisted to reduce crosstalk and

outside interference.

Twisted Pair Cable

Two types of twisted pair cabling– Unshielded Twisted Pair (UTP)

– Shielded Twisted Pair (STP)

STP is same as UTP except that STP has a braided foil shield around the twisted pair (to decrease electrical interference).

UTP is simply twisted pair cabling that is unshielded.

Coaxial Cable

It has two conductors sharing same axis.

A solid copper wire runs down from the

center surrounded by plastic foam.

The foam is surrounded by a second

conductor, a wire mesh tube.

Coaxial Cable

This wire mesh protects the wire from electrical interference. It is often called shield.

A plastic jacked forms the cover of the cable, providing protection & insulation.

Two types: – Thinnet (185 meters)

– Thicknet (500 meters)

Fiber Optic Cable

The advantages of fiber optics over other media include speed, size, weight, security, and longevity.

For example, the standard optical cable, operates at a transmission rate of up to 2.4 gigabits per second per fibre.

This rate is sufficient to transmit the text in all the volumes of Encyclopedia Britannica in less than one second.

Summary of Cable Types

CharacteristicsTwisted-

PairCoaxial

Fiber-Optic

Wireless

Cost Least More ExpensiveMost

Expensive

Maximum Length

100 meters

185 meters - 500

meters

>10 miles 2 miles

Transmission Rates

10 Mbps - 100 Mbps

10 Mbps

100 Mbps or more

10 Mbps

Summary of Cable Types

CharacteristicsTwisted-

PairCoaxial

Fiber-Optic

Wireless

FlexibilityMost

flexibleFair Fair Limited

Ease of Installation

Very Easy

Easy Difficult Somewhat difficult

Interference Susceptible

Better than UTP, more susceptible

than STP

Not Susceptible

Susceptible

Summary of Cable Types

Characteristics

Twisted-Pair

CoaxialFiber-Optic

Wireless

Special Features

Often pre-installed; similar to

wiring used in telephone

systems

Easiest Installation

Supports voice, data, and video at

highest transmission

speeds

Very flexible

Physical Topology

Star Bus StarBus or Star

Summary of Cable Types

Characteristics

Twisted-Pair

CoaxialFiber-Optic

Wireless

Preferred uses Networks

Medium size

networks with high security needs

Networks of any size requiring

high speed and data security

WANs and

radio/TV communic

ations

Wireless Media

They support communications in situations in which physical wiring is impractical.

Widely used media for wireless communication– Radio Waves– Microwave technology– Cellular technology– Infrared technology

Microwave technology

Microwaves are high frequency radio

signals, which produce better throughput

and performance.

Two types of microwave data

communication systems

– terrestrial microwave stations

– communications satellite

Terrestrial Microwave

A ground station that receives microwave signals, amplifies them, and passes them on to another station, are known as terrestrial microwave stations.

Distance between stations are between 25 to 30 miles.

Stations are placed on tall buildings to avoid obstacles.

Terrestrial Microwave

Stations needs not to be within actual sight of each other

However, they should have a clear path along which to communicate.

When one station, receives a message from another, it amplifies it and passes it on to the next station.

Communications Satellites

An earth orbiting device developed to reduce the cost of long distance transmission.

The distance between the earth and satellite is 50,000 kilometers (22,300 miles)

Satellites maintain geosynchronous orbits.

Communications Satellites

Geosynchronous means that, because the satellites travels at the same speed as the earth’s rotation, they appear to remain stationary over a given spot on the globe.

Both terrestrial microwave stations and communications satellite are ideal for applications such as television and radio broadcasting.

Cellular Technology

Cellular phones are mobile telephones. Cellular phones use radio waves, operate

by keeping in contact with cellular antennae.

Calling areas are divided into zones measuring 10 miles wide, called cells, each with its own antenna.

Cellular Technology

Antennae perform two essential functions:– They enable a moving cellular phone to

transmit and receive.– They provide an interface with the regular

public phone network. Busy executive, salesperson, truck driver,

or real-estate agent, benefit from this technology.

Infrared Technology

As opposed to microwave and cellular technologies, which use radio waves, infrared technology sends data as light rays.

The remote controls used for television, VCR, and CD players use this technology.

They have good throughput, but the signals cannot penetrate walls or other objects, and they are diluted by strong light sources.

Adapting Computers to Telecommunications Media

Sending Data over Media

Data Transmission is the process of sending data electronically over a distance. It may involve sending data from one computer to another, or between a remote peripheral and a computer.

Analog - Transmission of data as continuous wave patterns.

Digital - Transmission of data as 0 & 1 bits.

Simplex Transmission

Simplex communication is a mode in which data only flows in one direction. Because most modern communications require a two-way interchange of data and information, this mode of transmission is not as popular as it once was.

However, one current usage of simplex communications in business involves certain point-of-sale terminals in which sales data is entered without a corresponding reply.

Half-Duplex Transmission

Half-duplex communication adds ability for a two-way flow of data between computer terminals.

In this directional mode, data travels in two directions, but not simultaneously. Data can only move in one direction when data is not being received from the other direction.

This mode is commonly used for linking computers together over telephone lines.

Full-Duplex Transmission

The fastest directional mode of communication is full-duplex communication

Here, data is transmitted in both directions simultaneously on the same channel.

This type of communication can be thought of as similar to automobile traffic on a two-lane road. Full-duplex communication is made possible by devices called multiplexers.

Sending Data over Media

Bandwidth - The difference between the highest

and lowest frequencies that a transmission

medium can accommodate. Bit rate (bps)- A measure of a transmission

medium’s speed (number of bits per second) Parallel Transmission - Data transmission in

which each bit in a byte follows its own path simultaneously with all other bits. (LPT1)

Sending Data over Media

Serial transmission - Data transmission in which every bit in a byte must travel down the same path in succession.

Serial Transmission (RS 232, EIA 232) – A standard which defines that data is transmitted serially through a serial port. Most PCs are equipped with RS-232 serial ports, which can be used for modems, printers, scanners etc.

Asynchronous Transmission

Conversely, asynchronous transmission involves the sending and receiving of one byte of data at a time.

In this case, the line sits idle a lot of the time. Furthermore, each character sent must be packaged with a “start bit” and “stop bit” resulting in substantial transmission overhead.

This type of transmission is most often used by microcomputers and other systems characterized by slow speeds.

Synchronous Transmission

Large volumes of information can be transmitted at a single time with synchronous transmission. This type of transmission involves the simultaneous flow of several bytes of data.

Synchronous transmission is made possible by a buffer at the workstation, a storage area large enough to hold a block of characters.

Synchronous Transmission

As soon as the buffer is filled, all the characters in it are sent up to the line to the destination computer.

Because no idle time occurs between transmission of individual characters in the block – and because less transmission overhead is required – this method allows more efficient utilization of the line.

Types of Telephone Connections

Dial-up lines – the type of telephone connections found in most homes and businesses-let you call anywhere in the world.

Dedicated (Leased) Lines – provides a permanent connection between two points.

Dial-up lines are cheaper, but they are slower, and busy signals often prevent connections.

Network Interface Cards

A NIC is an add-in-board that plugs into an expansion slot within the system unit.

These often connect to coaxial cables or UTP between the workstations in local networks, which span small areas like an office building or college campus.

Dedicated (Leased) Lines are often used with Routers or Bridges.

Modems

A communications device that enables digital computers and their support devices to communicate over analog media.

The modem is an acronym for "MOdulator- DEModulator."

A modem converts the digital signals into continuous analog signals (Modulation), and converts from analog to digital (Demodulation).

Modems

Modem enables digital microcomputers

to communicate both voice and data

across analog telephone lines.

Modems today support both data & fax.

Communications speeds are expressed in

bits per second (bps).

Modems

A baud is commonly used to specify signals

per second for modem speed.

The modems usually operate at 2400, 9600,

14400, 28800 and 57600 bits per second (bit

rate)

The higher the speed, the faster users can

transmit a document and therefore the cheaper

your line costs.

Types of Modems

For example, transmitting a 100-page single-spaced report takes 25 minutes at 2400 bps. It takes 6 1/4 minutes at 9600 bps, about 4 1/6 minutes at 14400 bps, and 2 1/12 minutes at 28800 bps.

1. External vs. Internal Modems

2. Standard vs. Intelligent Modems

3. Short-Haul and Wireless Modems

External vs. Internal Modems

External Modem: This is a modem separated from the system unit in the computer case. It is connected to the serial port of the computer by means of a cable. It is connected to the telephone wall jack by another cable.

Internal Modem: An internal modem is a circuit board (a modem card) that can be added to the system unit of the computer. It takes one of the expansion slots.

Standard vs. Intelligent Modems

Standard Modems: Most modems used today are called standard modems. These modems are usually operated by commands entered from a microcomputer keyboard. Users control the functions (dialing, etc.) of a modem through the keyboard.

The command ATDSX4, for example, indicates that pay attention (AT), dial stored telephone number (DS), and then display the progress of the call (X4).

Standard vs. Intelligent Modems

Intelligent Modems: Intelligent modems are

also called advanced modems. These modems

can accept new instructions and then respond

to the commands while transmitting data and

information. These can be done by

microprocessor chips and internal read only

memory (ROM) contained in the modem.

These modems are more expensive.

Short-Haul and Wireless Modems

Short-Haul Modems are devices that transmit signals down the cable through any COM1 port.

They sometimes are called modem eliminators, because they do not require an external power source.

They are also called line drivers that can send data for a distance of more than one mile.

This type of modem can be used within or across several buildings in a company or a university campus.

Short-Haul and Wireless Modems

Wireless Modems: Wireless modems transmit the data signals through the air instead of by using a cable. They sometimes are called a radio frequency modem.

This type of modem is designed to work with cellular technology, and wireless local area networks. Wireless modems are not yet perfected, but the technology is rapidly improving.

ISDN

Integrated Services Digital Network is a digital phone service that operates over ordinary dial-up phone lines or over dedicated lines leased for private use.

ISDN gives access to two or more (single channel of 64 kbps)

To use ISDN, a special ISDN adapter is used instead of modem.

Cable Modems

Its uses hybrid system based on coaxial cables and fiber optic cables.

Interfacing device is known as cable modem.

Speed range is between 2 – 30 mbps. Put it another way, it would take 46

minutes to transmit a 10 MB file by 28.8 kbps modem and only 8 seconds by 10 mbps cable modem.

DSL

Digital Subscriber Line is the successor to ISDN.

It uses digital filtering method to turn twisted pair copper wires into digital lines with megabit per second speeds.

DSL provides different speeds for transmission downstream (from service provider to the user) and upstream (from the user to the provider)

Network Topologies

Introduction

The way in which the connections are made is called the topology of the network.

Topology refers to the physical layout of the network, especially the locations of the computers and how the cable is run between them.

The three most common topologies are the bus, the star and, the ring.

Bus Network

Bus, or linear, architecture connects all

computers to a single central cable.

There is no host computer or file server.

The bus topology is often used when a

network installation is small, simple or

temporary.

How a Bus Network Works

Only one computer at a time can send a message and accept the information.

Another important issue in bus networks is termination. Without termination, when the signal reaches the end of the wire, it bounces back and travels back up the wire. This is called ringing.

To prevent ringing, terminators are attached at either end of the segment.

Advantages of the Bus

The bus is simple, reliable & easy to use. The bus requires the least amount of

cable to connect the computers It is less expensive than other cabling

arrangements. It is easy to extend a bus. A repeater can also be used to extend a

bus.

Disadvantage of the Bus

Heavy network traffic slows down a bus considerably. As more computers are added interruption among each other increases instead of communicating.

Each connection weakens the electrical signal.

It is difficult to troubleshoot a bus. A crack in the central cable will stop the whole network.

Star Topology

In star topology all devices are connected to a central unit through point to point links.

The central unit may be a host computer or a file server.

The host computer is usually a minicomputer or a mainframe.

In contrast, the file server is a large-capacity hard-disk storage device. Also, called a network server.

How a Star Network Works

Each computer/server on a star network communicates with a central hub.

A network hub is called in many different names such as concentrator, multistation access unit, transceiver, or repeater.

How a Star Network Works

It serves two purposes. First, they provide an easy way to connect network cables. Second, hubs act as repeaters or amplifiers.

You can expand a star network by placing another hub allowing several more computers or hubs to be connected to that hub.

Advantages of the Star

It is easy to modify and add new computers without disturbing the rest of the network.

Single computer failure do not bring down the whole network.

The hub can detect and isolate the offending computer or network cable and allow the rest of the network to continue operating.

Disadvantages of the Star

If the central hub fails, the whole network fails to operate.

It costs more to a cable a star network because all network cable must be pulled to one central point, requiring more cable than other networking topologies.

Ring Networks

In a ring topology, each computer is connected to the next computer, with the last one connected to the first.

Like the bus network, no single central computer exists in the ring configuration. Messages are simply transferred from one computer to the next until they arrive at their intended destinations.

How a Ring Network Works

Each computer on the ring topology has a particular address. As the messages pass around the ring, the computers validate the address.

If the message is not addressed to it, the node transmits the message to the next computer on the ring.

This type of network is commonly used in systems that connect widely dispersed mainframe computers.

How a Ring Network Works

A ring network allows organizations to engage in distributed data processing system in which computers can share certain resources with other units while maintaining control over their own processing functions. However, a failure in any of the linked computers can greatly affect the entire network.

The ring arrangement is the least frequently used with microcomputers.

How a Ring Network Works

However, as stated, it often is used to link mainframes over wide geographical areas to build distributed data processing system.

The loss of a mainframe usually does not restrain the operation of the network, but a cable problem will stop the network altogether.

Advantages of the Ring

Every computer is given equal access to the token, no computer can monopolize the network.

The fair sharing of the network allows the network to function in a useful, if slower, manner rather that fail once capacity is exceeded as more users are added.

Disadvantages of the Ring

Failure of one computer on the ring can

affect the whole network.

It is difficult to troubleshoot a ring

network.

Adding or removing computers disrupts

the network.

Local Area Networks

Local Area Networks

A Local Area Network, or LAN, is a group of computers that are connected by some hardware source, be it wire, fiber, or radio waves.

A typical LAN consists of a server, and a printer/other peripheral sharer, the physical connections to the computers, and the clients or workstations.

Two types of LANs: Peer-to-Peer, and Client Server- Base.

Peer-to-Peer LANs

A LAN in which all of the user workstations and shared peripheral devices operate on the same level.

A peer-to-peer network can be set up for a very modest investment. All you need are network cards, cables, and Microsoft® Windows® 95, which has a built-in peer-to-peer network operating system.

Peer-to-Peer LANs

You can use peer-to-peer networking to keep your staff fully informed of your daily schedule by allowing them to access and view your business calendar as a shared file on your system.

Employees can easily share files and file folders (directories) in a peer-to-peer network.

Peer-to-Peer LANs

They can easily let one or more colleagues access files on their computer's hard disk, so there's no more trading back and forth of disks, and files are always available-even if the employee is out to lunch.

To give your customers royal treatment, you can make your customer database available on the network.

Peer-to-Peer LANs

In this way, customers spend less time on hold, and don't get that bounced-around feeling when they have to be transferred.

The employee who answers the call can ask them how their last purchase is doing, giving the customer personalized attention. Customers are more satisfied, and your employees get more work done in less time.

Client Server LANs

In a client/server network, clients are connected by cable to a centralized server.

The server provides centralized security, backup, and recovery capability and controls access to sensitive files and expensive peripherals (such as color printers and modems).

Client Server LANs

A dedicated server improves data

integrity, because the most current

version of a document will be saved in

one location.

This type of network requires a network

operating system, such as Microsoft

Windows NT Server.

Client Server LANs

With client/server networking one can:

set passwords with different security levels for different files,

set access times,

and define access permissions and limitations to confidential data such as payroll and contracts.

Client Server LANs

Client/server networking gives you the resources to host and administer your own Web site on your server.

New software now makes it easy to create Web pages and manage a Web site.

Then, all is required to establish a domain name (Web address) and connect to an Internet service provider (ISP).

Client Server LANs

A server should support a wide variety of

clients-such as Macintosh, Windows 95,

and Windows NT-and communicate with

other systems-such as NetWare and

UNIX-using multiple network protocols.

LAN Devices

Repeaters -Required Bridge Hub and Switch

Advantages of LANs

Share documents Quickly schedule meetings Manage group projects. Send and receive electronic mail. Reduce the time spent in meetings and

traveling between your offices, suppliers, and customers.

Reduces the cost by making the most of expensive printers and peripherals by sharing them.

Is your company ready for a LAN?

Do you have five or more computers? Do more than three of your employees share

one printer? Does your company have, or plan to have e-mail

or Internet access? Do your employees frequently need access to

customer records, inventory or financial information?

Do your employees work regularly with large or graphic-intensive files?

Even one yes means your company is ready for a LAN.

Wide Area Networks

Overview

WANs are usually required for high

volume, long distance data traffic.

Two types of WANs

– Enterprise networks

– Global networks

Enterprise Networks

When a network connects a company’s branch offices and divisions, it becomes an enterprise - wide network.

For example, a corporation may have sites on every continent, all of which are interconnected to form one wide area network.

Global Networks

When a network span several countries and continents and includes many types of organizations and individuals, it can be labeled global.

These networks serve multinational corporations and scientific, and military establishments. The Internet, often called “network of networks” fits that definition.

WAN Devices

Routers

ATM

Frame Relay

Gateways

Multiplexers

Concentrators

Communications Protocols

What is a Protocol?

A communication protocol is a collection of procedures to establish, maintain, and terminate transmission between devices.

Protocols specify how devices will physically connect to a network, how data will be packaged for transmission, how receiver devices will acknowledge signals from sender devices and how errors will be handled.

LAN Protocols

The two most common LAN architectures are Ethernet and Token Ring.

Ethernet – A collection of protocols that specify a standard way of setting up a bus based LAN.

Token Ring – A ring based LAN that uses token to control transmission of messages.

Fiber Distributed Data Interface (FDDI)

Ethernet

Traditional Topology Bus

Other Topologies Star

Access method CSMA/CD

Specifications IEEE 802.3

Transfer Speed 10 Mbps or 100 Mbps

Cable Types Twisted Pair and Coaxial

Token Ring

Traditional Topology Ring

Other Topologies Star

Access method CSMA/CA

Specifications IEEE 802.5

Transfer Speed 4 Mbps or 16 Mbps

Cable Types Twisted Pair

WAN Protocols

Transmission Control Protocol/Internet

Protocol (TCP/IP)

TCP/IP relies on a procedure known as

packet switching.

Circuit Switching

It creates a physical connection between two devices such as phones or computers.

Packet Switching

Messages are broken up into packets,

each of which includes a header with

source, destination, and intermediate

node address information.

Individual packets don’t always follow the

same route. This is called independent

routing.

Packet Switching

Independent routing offers two Advantages– Bandwidth can be managed by splitting data

onto different routes in a busy circuit.

– It a certain link in the network goes down during the transmission, the remaining packets can be sent through another route.

Packet Switching

Packet Switching restricts packets to a maximum length.

The short length of message allow the switching devices to store packet data in memory without writing any of it to disk.

By cutting the disk out of the process, packet switching works far more quickly and efficiently.