NETWORKS AND TELECOMMUNICATION

TECHNOLOGIES BASICS

IntroductionWhen PCs first appeared in businesses software

programs, were designed for a single user. There were few obvious advantages of connecting PCs, and the technology was not adequate for doing so.

As computers spread throughout business, developers begun offering complex software designed for multiple users.

Many organizations rapidly learned the importance of connecting PCs.

Data communication- the electronic transfer of data between computers- became a major focus the computer industry.

During the past decade, networking technology has become the most explosive area of growth in the entire computer industries.

A network, is a collection of computers and other hardware components interconnected by communication channels that allow sharing of resources and information.

Uses of NetworksA network is a set of technologies – including

hardware, software, and media- that can be used to connect computers together, enabling them to communicate, exchange information, and share resources in real time.

Networks allows users to access shared data and programs almost instantly.

Networks open up new ways to communicate such as email and instant messaging.

By allowing users to share expensive hardware resources such as printers, networks reduce the cost of running an organization.

Uses/ importance of networkPersonal communication/ interactive

entertainment:-Video conferencing – enables real-time

communication over a distance by allowing people at two or more sites to communicate with each other by seeing a video picture of the people at the other side.

Audio/ tele-conferencing- provides an audio link similar to that of a conventional telephone.

Data-conferencing- enables participants at two or more sites to have a shared workspace on their computer desktops.

Easier data backup

Types of NetworksLAN - Local Area Networks- A Local

Area Network (LAN) is a relatively small network that is confined to a small geographic area, such as a single office or a building. Laptops, desktops, servers, printers, and other networked devices that make up a LAN are located relatively close to each other. A key characteristic is that all of the equipment that comprises a LAN, is owned by a s-ingle entity.

Types of networks Wide Area Networks-A Wide Area

Network (WAN) covers a significantly larger geographic area than LANs or MANs. A WAN uses public networks, telephone lines, and leased lines to tie together smaller networks such as LANs and MANs over a geographically dispersed area. Connecting devices in different geographic areas together for information sharing, WANs are an important piece of enterprise networks.

Types of computer networks cont..Hybrid Networks:-Campus Area Networks -

Networking spanning with multiple LANs but smaller than a Metropolitan area network, MAN. This kind of network mostly used in relatively large universities or local business offices and buildings.

Wireless - Local Area NetworkA LAN, local area networks based on wireless network technology mostly referred as Wi-Fi. Unlike LAN, in   WLAN no wires are used, but radio signals are the medium for communication. Wireless network cards are required to be installed in the systems for accessing any wireless network around. Mostly wireless cards connect to wireless routers for communication among computers or accessing WAN, internet.

Metropolitan Area NetworkThe term Metropolitan Area Network (MAN) is typically used to describe a network that spans a citywide area or a town. MANs are larger than traditional LANs and predominantly use high-speed media, such as fiber optic cable, for their backbones. MANs are common in organizations that need to connect several smaller facilities together for information sharing. This is often the case for hospitals that need to connect treatment facilities, outpatient facilities, doctor's offices, labs, and research offices for access to centralized patient and treatment information. MANs share many of the same security threats as LANs, but on a larger scale.

Personal Area Network-A more recent term used to describe a type of network is a Personal Area Network (PAN). PAN networks are usually wireless, established in an on-demand or ad-hoc fashion when needed to communicate between two or more devices. PAN networks can be used between devices owned by two different parties, or between two devices owned by one person, such as a PDA and a laptop or mobile phone. These networks are usually characterized as short-range, often limited to 10 meters or less in range.An example of a PAN technology is Bluetooth wireless networking. Bluetooth is designed as a cable-replacement technology, allowing users to discard the serial and USB cables used by many of today's peripheral devices and rely on a Bluetooth PAN for communication. Bluetooth PANs support up to 7 devices in a single network and can be used for proprietary protocols (such as PDA synchronization) or standards-based protocols, including Internet access over IP and the Bluetooth Network Encapsulation Protocol (BNEP).

NETWORK STRUCTUREServer based Networks - As the

name suggests server-based networking is a network where resources, files and security are all handled by dedicated servers. Such systems often require specialist software such as network operating systems and hardware such as print servers.

AdvantagesCan easily cope

with thousands of users.

Backup, security and account control are all central.

Software can be shared between the computers.

Disadvantages If one of the

servers go down all the users are affected and it may even bring the whole network down.

More expensive to setup and maintain.

Client/Server networksClient/server systems allow the network to

centralize functions and applications in one or more dedicated file servers. The file servers become the heart of the system, providing access to resources and providing security.

Individual workstations (clients) have access to the resources available on the file servers. The system provides the mechanism to integrate all the components of the network and allow multiple users to simultaneously share the same resources irrespective of physical location.

Advantages Centralized - Resources and data security are

controlled through the server.Scalability - Any or all elements can be replaced

individually as needs increase.Flexibility - New technology can be easily

integrated into system.Interoperability - All components

(client/network/server) work together.Accessibility - Server can be accessed remotely

and across multiple platforms.

Disadvantages

Expense - Requires initial investment in dedicated server.

Maintenance - Large networks will require a staff to ensure efficient operation.

Dependence - When server goes down, operations will cease across the network.

Peer-to-peer NetworksPeer-to-peer network systems allow users to share

resources and files located on their computers and to access shared resources found on other computers. However, they do not have a file server or a centralized management source.

In a peer-to-peer network, all computers are considered equal; they all have the same abilities to use the resources available on the network.

Peer-to-peer networks are designed primarily for small to medium local area networks.

Advantages Less initial expense -

No need for a dedicated server.

Setup - An operating system (such as Windows XP) already in place may only need to be reconfigured for peer-to-peer operations.

DisadvantagesDecentralized - No

central repository for files and applications.

Security - Does not provide the security available on a client/server network.

NETWORK TOPOLOGIES Topology is the logical layout of cables and

devices that connects the nodes of the network.

Network topologies are categorized into the following basic types:

busstartreemesh

Bus topologyBus networks use a common backbone to

connect all devices. A single cable, the backbone functions as a

shared communication medium that devices attach or tap into with an interface connector.

A device wanting to communicate with another device on the network sends a broadcast message onto the wire that all other devices see, but only the intended recipient actually accepts and processes the message.

Bus topology

Advantages Easy to connect a

computer or peripheral to a linear bus.

Requires less cable length than a star topology.

DisadvantagesEntire network shuts down

if there is a break in the main cable.

Terminators are required at both ends of the backbone cable.

Difficult to identify the problem if the entire network shuts down.

Not meant to be used as a stand-alone solution in a large building

Star TopologyA star topology is designed with each node (file server,

workstations, and peripherals) connected directly to a central network hub, switch, or concentrator.

Data on a star network passes through the hub, switch, or concentrator before continuing to its destination. The hub, switch, or concentrator manages and controls all functions of the network. It also acts as a repeater for the data flow. This configuration is common with twisted pair cable; however, it can also be used with coaxial cable or fiber optic cable.

Star topology

Advantages Easy to install and

configure.No disruptions to

the network when connecting or removing devices.

Easy to detect faults and to remove parts.

Disadvantages Requires more cable

length than a linear topology.

If the hub, switch, or concentrator fails, nodes attached are disabled.

More expensive than linear bus topologies because of the cost of the hubs, etc.

Tree or Expanded Star TopologyA tree topology combines

characteristics of linear bus and star topologies. It consists of groups of star-configured workstations connected to a linear bus backbone cable. Tree topologies allow for the expansion of an existing network, and enable schools to configure a network to meet their needs.

Advantages Point-to-point

wiring for individual segments.

Supported by several hardware and software vendors

Disadvantages Overall length of each

segment is limited by the type of cabling used.

If the backbone line breaks, the entire segment goes down.

More difficult to configure and wire than other topologies.

Mesh Topology Mesh topologies involve the concept of

routes. Unlike each of the previous topologies, messages sent on a mesh network can take any of several possible paths from source to destination.

Some WANS, most notably the Internet, employ mesh routing.

A mesh network in which every device connects to every other is called a full mesh. 

Advantages Point-to-point line configuration

makes identification and isolation of faults easy.

Messages travel through a dedicated line, directly to the intended recipient; privacy and security are thus enhanced.

Should a fault occur in a given link, only those communications between that specific pair of devices sharing the link will be affected.

DisadvantagesThe more extensive the

network, in terms of scope or of physical area, the greater the investment necessary to build it will be, due, among other considerations, to the amount of cabling and the number of hardware ports it will require. For this reason, such networks are uncommon.

NETWORK MEDIAMedia refers to the means used to link a

network’s nodes together.There are many different types of

transmission media, the most popular being twisted pair wire, coaxial cable and fiber optic.

In wireless networks, the atmosphere itself acts as a medium because it carries the wireless signals that nodes and servers use to communicate.

Wire-Based MediaTwisted-pair - comes in two varieties: shielded and

unshielded. Unshielded twisted pair (UTP) is the most popular.

The cable has four pairs of wires inside the jacket. Each pair is twisted with a different number of twists per inch to help eliminate interference from adjacent pairs and other electrical devices.

The tighter the twisting, the higher the supported transmission rate and the greater the cost per foot.

The EIA/TIA (Electronic Industry Association/Telecommunication Industry Association) has established standards of UTP.

Twisted Pair cableAdvantages UTP is less expensive

than dedicated coaxial or fiber.

UTP is physically smaller than coax and many other cable types .

UTP is a very easy media to install and reconfigure .

TP is easy to terminate .

DisadvantagesSusceptible to

electromagnetic interference  and eavesdroppings

Can produce signaling delay, known as skew, in video application that send information across multiple parallel signal wires.

Wire-Based media cont….Coaxial Cable-comprises of a central

conductor, the part of the cable carrying the signal, that is surrounded by a dielectric, or non-conducting insulator, a solid woven metal shielding layer and a protective plastic outer coating.

Coaxial CableAdvantagesLargely immune to

electric noiseCan carry data at

higher rates over long distances than UTP.

Installation is relatively simple though the bulky and thicker cables are difficult

DisadvantagesIt is susceptible to

EMI and eavesdropping although it resists EMI better than TP

Reconfiguration is difficult.

Fiber Optic CableConsists of an extremely thin cylinder of glass called the

core, that is surrounded by a concentric layer of glass known as cladding.

Light travels along the cable core known as waveguide. The purpose of cladding is to reflect the light signals back into the waveguide as efficiently as possible so that the light signal travels along the waveguide by multiple (internal) reflections.

The center core of fiber cables is made from glass or plastic fibers. A plastic coating then cushions the fiber center, and kevlar fibers help to strengthen the cables and prevent breakage. The outer insulating jacket made of teflon or PVC.

It transmits light rather than electrical signal, eliminating the problem of electrical interference.

This makes it ideal for certain environments that contain a large amount of electrical interference.

It has also made it the standard for connecting networks between buildings, due to its immunity to the effects of moisture and lighting.

Fiber optic cable has the ability to transmit signals over much longer distances than coaxial and twisted pair. It also has the capability to carry information at vastly greater speeds.

This capacity broadens communication possibilities to include services such as video conferencing and interactive services. The cost of fiber optic cabling is comparable to copper cabling; however, it is more difficult to install and modify.

10BaseF refers to the specifications for fiber optic cable carrying Ethernet signals.

There are two common types of fiber cables -- single mode and multimode. Multimode cable has a larger diameter; however, both cables provide high bandwidth at high speeds. Single mode can provide more distance, but it is more expensive.

NETWORK PROTOCOLSProtocols are procedures or rules used

by networked computers to communicate. For two computers to communicate they must have a protocol in common.

Some of the most common protocols today include:

TCP/IP- the protocol of the Internet and is required on any computer that must communicate across the Internet.

IPX/SPX – a proprietary protocol of Novell, IPX/SPX has been used in most versions of the Netware network operating system for networking offices throughout the world. Newer versions of Netware also support TCP/IP

NetBIOS/NetBEUI – a relatively simple protocol that has no real configurable parameters, NetBIOS/NetBEUI sends message to every computer that can receive them. It is an excellent protocol for networking small offices or homes, but it does not expand well into larger environments.

DATA COMMUNICATION WITH STANDARD TELEPHONE LINES AND MODEMS

Data communication is the transmission of electronic data over some media e.g. cables, microwaves

Elements/components of data communication:-Message – the message is the information (data) to be

communicatedSender/transmitter – the device that sends the data messageReceiver – the device that receives the dataMedium – transmission medium is the physical path by which a

message travels from sender to receiver e.g. cables wireless transmission media etc.

Protocol – rules that govern data communication. It represents an agreement between the communicating devices.

Data TransmissionData may be transferred from one device

to another by means of some communication media.

The electromagnetic or light waves that transfer data from one device to another device in encoded form are called signals. Data transmissions across the network can occur in two forms i.e.:

Analog signalDigital signal

Analog SignalingThe transfer of data in the form of

electrical signals or continuous waves is called analog signal or analog data transmission.

An analog signal is measured in volts and its frequency in hertz (Hz).

Digital SignalingThe transfer of data in the form of digit is

called digital signal or digital data transmission.

Digital signals consist of binary digits 0 & 1. Electrical pulses are used to represent binary digits.

Data transmission between computers is in the form of digital signals.

Digital Data Connections To transfer digital data over analog telephone

lines, computers must use modems. When a computer sends data, its modem

translates digital data into analog signals for transmission over standard telephone lines.

At the receiving end, the computer’s modem converts the analog signals back into digital data.

Using digital connections, businesses and homes can transmit data many times faster than is possible over standard phone lines.

Connecting to the internet through wiresThere are many ways to obtain access to

the internet. The method varies according to the type of computer system being used and the types of connections offered.

Some connections are dial-up, must be initiated every time you desire internet access.

Other connection types remain open available 24/7

Dial-up ConnectionsUsed in homes, small offices and individuals to connect to

the internet by use of telephone lines and a 56kbs modem.The easiest way to create this kind of connection is by

setting up an account with an internet service provider (ISP).

The ISP maintains bank of modems at its facility to process the incoming dial-up requests from customers

the computer uses it modem to dial a telephone number given by the ISP. This

establishes a connection between the computer and the ISP server.

It is temporary – it begins when ISP’s server “answers” the call and ends when the PC or ISP’s server “hang up”

High speed broadband connectionsThe term broadband refers to the

wide bandwidth characteristics of a transmission medium and its ability to transport multiple signals and traffic types simultaneously.

To be considered broadband, the connection must be able to transmit data at a rate faster than dial up connection.

Integrated Service Digital Network (ISDN) ServiceI a digital telephone service that

simultaneously transmits voice, data and control signaling over a single telephone line.

ISDN service operates on standard phone lines but requires a special modem and phone service.

Digital Subscriber Line (DSL) ServiceSimilar to ISDN in its use of the telephone

network, but it uses more advanced digital signal processing and algorithms to compress more signals through the telephone lines.

It provides simultaneous data, voice and fax transmission on the same line

Cable modemMany cable television companies now use a portion

of their network’s bandwidth to offer internet access through existing cable Tv connections

This internet connection option is called cable modem service because of the need to use a special cable modem to connect.

Cable TV transmit data over coaxial cable which transmits data as much as 100 times more than common telephone lines.

User can access internet from his/her computer and watch cable TV at the same time over the same cable connection and without the two data streams interfering each other

Wireless connectionsWireless networks use high frequency radio

signals, infrared light beams, or lasers to communicate between the workstations, servers, or hubs. Each workstation and file server on a wireless network has some sort of transceiver/antenna to send and receive the data.

Information is relayed between transceivers as if they were physically connected. For longer distance, wireless communications can also take place through cellular telephone technology, microwave transmission, or by satellite.

Wireless standards and speedsThe Wi-Fi Alliance is a global, non-profit

organization that helps to ensure standards and interoperability for wireless networks, and wireless networks are often referred to as WiFi (Wireless Fidelity). The original Wi-Fi standard (IEEE 802.11) was adopted in 1997. Since then many variations have emerged (and will continue to emerge). Wi-Fi networks use the Ethernet protocol.

Wireless standards and speeds

Standard Max Speed Typical range802.11a 54mbps 150 feet802.11b 11 Mbps 300 feet802.11g 54 Mbps 300 feet802.11n 100 Mbps 300+ feet