Chp07_Networking and Telecommunications

Telecommunications and Networks

Chapter 07

Networking and Telecommunications

By. Shafiq A. Chachar2

What is Telecommunications

Science and practice of transmitting information by electromagnetic means.

A wide variety of information transferred through a telecommunications system, includes voice and music, still-frame and full-motion pictures, computer files and applications, and telegraphic data.



Trends in Telecommunications

Industry Trends – Toward more competitive vendors, carriers, alliances and network services, accelerated by deregulation and the growth of the Internet and WWW.

Technology Trends – Toward extensive use of Internet, digital fiber optic, and wireless technologies to create high speed local and global internetworks for voice, data, images, audio, and video communications.



Trends in Telecommunications

Application Trends – Toward the pervasive use of the internet, enterprise intranets and interorganizational extranets to support electronic business and commerce, enterprise collaboration, and strategic advantage in local and global markets.



Business Value of Networks

Overcome geographic barriers Overcome time barriers Overcome cost barriers Overcome structural barriers



Internet Applications

Surf Email Discuss Chat Buy and Sell Download Compute Long Distance Calls Video Conference



Business value of Internet

Generate new revenue from online sales Reduce costs through online sales and customer

support. Attract new customers via Web marketing and

advertising and online sales. Increase the loyalty of existing customers. Develop new Web based markets and

distribution channels for existing products. Develop new information base products

accessible on Web.



Business Value of Extranet

Companies an extranet to achieve certain strategic benefits, including– increasing the speed of business-to-business

transactions– reducing errors on intercompany transactions– reducing costs of telecommunications– increasing the volume of business with partners– exchanging business-to-business documents (similar

to EDI)– checking on inventory and order status from suppliers– collaborating with business partners on joint projects



Business Value of Intranet

Communication and Collaboration– Fax, email, voicemail, paging, groupware,

discussion groups, chat, audio and video conferencing.

Web Publishing– newsletters, technical drawings, product

catalogs, search engines. Business Operation and Management

– Order processing, inventory, sales management, portals.



Telecom Applications

Facsimile Voice Mail Electronic Mail Newsgroups Internet Relay

Chat Network Games

Video Conferencing Exchanging Files Paging Workgroup Computing Transaction Processing



Telecommunications Components

Networks Media Processors Software Channels Topology/architecture



Network Model

Five basic categories:– Terminals– Processors– Channels– Computers– Control Software



Types of Networks

Wide Area Network Local Area Network Virtual Private Network Client Server Network Network Computing Peer to Peer Networks

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.




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)




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

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.



ISDN Lines

ISDN (Integrated Services Digital Network) is a set of standards for digital transmission of data over standard copper telephone lines.

With ISDN, the same telephone line that could carry only one computer signal, now can carry three or more signals at once, through the same line, using a technique called multiplexing.



ISDN Lines

ISDN requires that both ends of the connection have an ISDN modem. This type of modem is different from the type used in dial-up connections.

ISDN lines also require a special ISDN telephone for voice communications. Home and business users who choose ISDN lines benefit from faster Web page downloads and clearer videoconferencing. ISDN connections also produce voice conversations that are very clear.



DSL Lines DSL is another digital line alternative for the small

business or home user. DSL (digital subscriber line) transmits at fast speeds

on existing standard copper telephone wiring. Some of the DSL installations can provide a dial tone, so you can use the line for both voice and data.

To connect to DSL, a customer must have a special network card or DSL modem. Similar to ISDN modems, a DSL modem is different from the modem used for dial-up connections.

Some experts predict that DSL eventually will replace ISDN because it is much easier to install and can provide much faster data transfer rates.



DSL

ADSL is one of the more popular types of DSLs. ADSL (asymmetric digital subscriber line) is a type of DSL that supports faster transfer rates when receiving data (the downstream rate) than when sending data (the upstream rate).

ADSL is ideal for Internet access because most users download more information from the Internet than they upload.



CATV A cable modem, sometimes called a

broadband modem, is a modem that sends and receives data over the cable television (CATV) network. With more than 100 million homes wired for cable television, cable modems provide a faster Internet access alternative to dial-up for the home user. Cable modems currently can transmit data at speeds much faster than either a dial-up modem or ISDN. Today, many home and business users are taking advantage of the resources available on the Internet and other networks with high-speed cable service.



CATV CATV service enters your home through a single

line. To access the Internet using the cable service,

the cable company installs a splitter inside your house.

From the splitter, one part of the cable runs to your televisions and the other part connects to the cable modem.

A cable modem usually is a stand-alone (separate) device that you connect with a cable to a USE port or a port on a network interface card in your computer.



T-Carrier Lines

A T-carrier line is any of several types of digital lines that carry multiple signals over a single communications line. Whereas a standard dial-up telephone line carries only one signal, digital T-carrier lines use a technique called multiplexing so that multiple signals can share the telephone line.

T-carrier lines provide extremely fast data transfer rates. Only medium to large companies usually can afford the investment in T-carrier lines because these lines also are so expensive.



T-Carrier Lines

The most popular T-carrier line is the T1 line. Businesses often use T1 lines to connect to the Internet. Many service providers also use T1 lines to connect to the Internet backbone.

A T3 line is equal in speed to 28 T1 lines. T3 lines are quite expensive. Main users of T3 lines include large companies, telephone companies, and service providers connecting to the Internet backbone.

The Internet backbone itself also uses T3 lines.



ATM Asynchronous transfer mode (ATM) is a service that

carries voice, data, video, and multimedia at extremely high speeds.

Telephone networks, the Internet, and other networks with large amounts of traffic use ATM.

ATM (asynchronous transfer mode) is a dedicated-connection switching technology that organizes digital data into 53-byte cell units and transmits them over a physical medium using digital signal technology. Individually, a cell is processed asynchronously relative to other related cells and is queued before being multiplexed over the transmission path.

Some experts predict that ATM eventually will become the Internet standard for data transmission, replacing T3 lines.



Comparison of Transfer Rates

Type of Line Transfer Rates

Dial-up Up to 56 Kbps

ISDN (BRI) Up to 128 Kbps

ADSL 128 Kbps-8.45 Mbps

Cable TV (CATV) 128 Kbps-2.45 Mbps

T1 1.544 Mbps

T3 44 Mbps

ATM 155 to 622 Mbps



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.

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

Characteristics Twisted-Pair Coaxial Fiber-

Optic Wireless

Cost Least More Expensive Most 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




Characteristics Twisted-Pair Coaxial Fiber-

Optic Wireless

Flexibility Most flexible Fair Fair Limited

Ease of Installation

Very Easy Easy Difficult Somewhat

difficult

Interference Susceptible

Better than UTP, more susceptible

than STP

Not Susceptible Susceptible




Characteristics

Twisted-Pair Coaxial Fiber-

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 Star Bus or

Star




Characteristics

Twisted-Pair Coaxial Fiber-

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 Microwave

– Terrestrial Microwave– Communications Satellite

Radio Wave– Cellular Technology

Light Rays– 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 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.



Applications of Wireless Media

Wireless LANS– Wi Fi– BlueTooth

Wireless Web– WAP– WML



Wi-Fi

Wi-Fi (short for "wireless fidelity") is the popular term for a high-frequency wireless local area network (WLAN).

It can also be installed for a home network. Wi-Fi is specified in the 802.11b specification from the

Institute of Electrical and Electronics Engineers (IEEE) The 802.11b (Wi-Fi) technology operates in the 2.4

GHz range offering data speeds up to 11 megabits per second.

Unless adequately protected, a Wi-Fi wireless LAN can be susceptible to access from the outside by unauthorized users



BlueTooth Bluetooth is a industry specification that describes how

mobile phones, computers, and personal digital assistants (PDAs) can easily interconnect with each other and with home and business phones and computers using a short-range wireless connection.

Bluetooth requires that a low-cost transceiver chip be included in each device. The transceiver transmits and receives in a previously unused frequency band of 2.45 GHz that is available globally (with some variation of bandwidth in different countries). In addition to data, up to three voice channels are available.

The technology got its unusual name in honor of Harald Bluetooth, king of Denmark in the mid-tenth century.



WAP

WAP (Wireless Application Protocol) is a specification for a set of communication protocols to standardize the way that wireless devices, such as cellular telephones and radio transceivers, can be used for Internet access, including e-mail, the World Wide Web, newsgroups, and Internet Relay Chat (IRC).

The WAP was conceived by four companies: Ericsson, Motorola, Nokia, and Unwired Planet (now Phone.com). The Wireless Markup Language (WML) is used to create pages that can be delivered using WAP.



WML

WML (Wireless Markup Language), is a language that allows the text portions of Web pages to be presented on cellular telephones and personal digital assistants (PDAs) via wireless access.

WML is part of the Wireless Application Protocol (WAP) that is being proposed by several vendors to standards bodies.

WML is an open language offered royalty-free. Specifications are available at Phone.com's Web site.

Telecommunications Processors



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.



Multiplexor

It allows a single communication channel to carry simultaneous data transmissions for many terminals.

A single line can be shared by several terminals.

Accomplished in two ways– FDM– TDM



Internetwork Processors

Switch Hub Routers Gateway Bridges



Telecommunication Software

Network Management functions include:– Traffic Management – Manage network resources and

traffic to avoid congestion and optimize telecommunications service levels to users.

– Security – Provide authentication, encryption, and auditing functions, and enforce security policies

– Network Monitoring – Troubleshoot and watch over the network, informing administrators of potential problems before they occur.

– Capacity Planning – Survey network resources and traffic pattern and users’ needs to determine how best to accommodate and needs of the network as it grows and changes.



Telecommunication Software

iPlanet Portal Server developed by Sun Microsystems and Netscape’s iPlanet software servers for the Internet, Intranet and Extranet.

These software are also known as middleware.

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.




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.




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 9x,

and Windows NT-and communicate with

other systems-such as NetWare and

UNIX-using multiple network protocols.



Advantages of Client/Server Computing Shared programs and data. Program and

data files held on a file server can be shared by all the PCs in the network. With system of stand-alone each computer has its own data files, and there is unnecessary duplication of data.

The value of some information increases with its availability. A system where everyone uses the same data will help to improve data processing, communication, and decision-making.



Advantages of Client/Server Computing Shared work-loads. Each PC in a network can do the

same work. With stand-alone PCs, A does job 1, B does job 2, C does job 3 and so on. In a network, any PC (A, B or C) could do any job (1, 2 or 3). This means that in a peak period for job 1, say, two or more people can share the work without having to leave their own desk.

Scalability. A client server system is highly scalable. In other words instead of having to buy computing power in large quantities you can buy just the amount of power you need to do the job. When you need more clients you simply add more clients or another server.



Advantages of Client/Server Computing Shared equipment. For example, five PCs

might share a single printer, whereas with stand-alone PCs, each PC would have to be given its own separate printer, or else not have access to one at all.

Communication and time management. LANs can be linked up to the office communications network, thus adding to the processing capabilities in an office. Electronic mail can be used to send messages, memos and electronic letters node to node. Electronic calendar and diary facilities can also be used.



Advantages of Client/Server Computing

Management information. They enable information to be moved to a separate server, allowing managers to make ad hoc enquiries without disrupting the main system.



Disadvantages of Client/Server Computing There will be costs involved in installing

cabling and buying a server and the necessary software.

There will be administrative costs in maintaining the system.

Expertise in network administration will have to be acquired. Nobody in the company has enough knowledge at present, so outsiders may have to be employed to give advice, or training will have to be given to an employee.



LAN Devices

Repeaters– Repeaters are devices that amplify signals along a

network. They are necessary because signals often have to travel farther than would otherwise be possible over the wires or cables that carry them.

Bridge– Two networks based on similar technology—such as a

LAN in one city and similar LAN in another—communicate via a device called a bridge. Bridges can also be used to partition one large LAN into two smaller ones.



LAN Devices

Hub– A hub provides a common connection point for a group

of devices in a network. When a packet arrives at the hub, it is transmitted to all other network nodes connected to that hub.

Switch– A switch transmits packets on a network, but instead

of sending them to all nodes on the network like a hub, it sorts out the packets and only sends them to the proper node. This allows each node on the network to use the full capacity of the network channel; with a hub the network capacity is shared among the nodes.



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.

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– Routers are used in large WANs—like the Internet—to

pass packets along to their destinations. Most data is broken down into more than one packet and the individual packets may be routed over the same or different paths—the path taken is determined by the routers on the network. When a packet is received by a router, the router passes it along to the next router. If one part of the network is congested or out of service, a router can choose to send a packet by an alternate route.



WAN Devices

Gateways– A gateway is a collection of hardware and

software resources that enable devices on one network to communicate with those on-another, dissimilar network. Computers on a LAN, for instance, require a gateway to access the internet.



WAN Devices

Multiplexers– High-speed communications lines are expensive and

almost always have far greater capacity than a single device can use.

– Because of this, networks can run more efficiently if several low-speed devices share one line.

– A multiplexer makes this possible by combining the messages of several devices and sending them along a single high-speed path.

– When they reach their destination, the individual messages are separated from one another.



WAN Devices

Concentrators– A concentrator is a type of multiplexer that

combines multiple messages and sends them via a single transmission medium in such a way that all the individual messages are simultaneously active, instead of being sent as a single combined message.

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.



Network Architectures

TCP/IP– Short for transmission control protocol/Internet

protocol, TCP/IP is a technology that manages the transmission of data by breaking it up into packets.

– When a computer sends data over the Internet, the data is divided into small pieces, or packets.

– Each packet contains the data, as well as the recipient (destination), origin (sender), and the sequence information used to reassemble the data at the destination. These packets travel along the fastest available path to the recipient's computer via devices called routers.



Bandwidth

Bandwidth is the frequency range of a telecommunications channels, it determines the channel’s maximum transmission rate.– Narrow band– Broad band



Circuit Switching

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

It remains open until the communication session is completed.

In message switching, a message is transmitted a block at a time from one switching device to another.



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.

Chp07_Networking and Telecommunications

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