Chapter -16Computer Networking

1. NetworkA network is a collection of autonomous computers and devices connected to each other in order to allows computers to communicate with each other and share resources(Printers, CD-ROMs, Modems etc.) and information(Files and programs). ARPANET designed for US DOD was the first computer network.

A network in general is composed of a wide variety of nodes that are connected by transmission media. Networks supply their users with communication channels. The exchange of messages is controlled by communication protocols.

2. Need for Networking(Goals/Advantages)i) Resource Sharing. A network makes available programs or applications, data and peripherals available to anyone on the network irrespective of the physical location of the resources and the user, subject to access permissions.ii) Communication and collaboration. A network allows users to share files, view other people's work, and exchange ideas more efficiently. We can use e-mail and instant messaging tools to communicate quickly and to store messages for future reference.iii) Reliability. A network makes it easier to back up data on another computer( offsite server), a set of tapes, CDs, or other backup systems which helps to recover data in case of any hardware or software failure.iv) Security. Sensitive files and programs on a network are password protected and access is also restricted to authorized users. These can also be designated as “copy inhibit”, in order to stop illegal copying of programs.v) Cost. Personal computers have better price/performance ratio than mini computers. Several PC’s can be interconnected, with data stored on one shared file server machine. Besides, networkable versions of softwares are cheaper than individual licensed copies of the software. vi) Remote access: A network allows greater mobility while maintaining the same level of productivity. With remote access users are able to access the same files, data, and messages even when they're not in the office. This access can even be given to mobile handheld devices. vii) Centralized software management. Shared programs, on a network allows for easier installation and upgrading of the programs on one single file server, instead of installing and upgrading individual workstations.viii) Workgroup Computing. Workgroup software like Microsoft BackOffice enables many users to contribute to a document concurrently. This allows for interactive teamwork. Also workload on individuals can be reduced by distributing work among different users on many workstations.

3. Disadvantages of Networksi) Server faults stop applications being available to workstations.ii) Network faults can cause loss of data or unavailability of resources.iii) User work dependent upon network.iv) System open to hackers.v) Network management can become difficult.

4. Applications of Networksi) Resource sharing. Networks allow users to share:-

-Peripherals. Expensive hardware can be installed on a server computer and allow access to users in a controlled and cost effective manner. This leads to efficient resource utilization.- File sharing. Softwares can be installed centrally, instead of buying licenses for every machine. Data can be shared between applications and users.- Share storage. Users can save their work on a central file server, which makes it easier to take backups also.

ii) Access to remote databases. Users can access remote databases over networks such as public libraries, make reservations for airplanes, trains etc. It also promotes e-commerce.iii) Communication medium. E-mail, video conferencing, chatting facilities makes it easier to transmit information and messages around the globe in a matter of seconds. Net meetings enable users to discuss issues without being physically present at the same location.

5. Evolution of NetworksThe precursor to the Internet, ARPANET was the first wide area packet switching network,created by the United States Defense Advanced Research Project Agency (DARPA) in 1969 . ARPANET joined computers of different types, running various operating systems by implementing communication protocols common for all computers participating in the network. The ARPANet began by linking four locations: Stanford University, UCLA, UC Santa Barbara, and the University of Utah.In mid 80’s, another federal agency, the National Science Foundation, created a new, high-capacity network called NSFnet, which was more capable than ARPANET.NSFnet allowed only academic research on its network. Another network called ‘Commercial Internet Exchange (CIX) ‘ was formed in 1991 for commercial use. The Internet was formed as a combination of the NSFnet, ARPAnet, the CIX, and about 10,000 other networks.

The Internet - The Internet is a worldwide/ global network of computer networks that evolved from the first network ARPANET. It enables users to share information along multiple channels using the standardized Internet Protocol Suite (TCP/IP). The Interspace - The Interspace is a client/server software program that allows multiple users to communicate online with real-time audio, video and text chat in dynamic 3D environments.

Intranet – Intranet is the generic term for a collection of private computer networks within an organization. Intranets utilize standard network hardware and software technologies like Ethernet, WiFi,TCP/IP, Web browsers and Web servers. An

organization's intranet typically includes Internet access but is firewalled so that its computers cannot be reached directly from the outside.

ExtranetAn extranet is a private network that uses Internet technology and the public telecommunication system to securely share part of a business's information or operations with suppliers, vendors, partners, customers, or other businesses. An extranet can be viewed as part of a company's intranet that is extended to users outside the company. An extranet requires security and privacy. These can include firewall server management, use of digital certificates or similar means of user authentication, encryption of messages etc.

Companies can use an extranet to:

• Exchange large volumes of data using Electronic Data Interchange (EDI)

• Share product catalogs exclusively with wholesalers or those "in the trade"

• Collaborate with other companies on joint development efforts

• Jointly develop and use training programs with other companies

• Provide or access services provided by one company to a group of other companies, such as an online banking application managed by one company on behalf of affiliated banks

• Share news of common interest exclusively with partner companies

6. How does Internet work?

The Internet is network of networks. A computer is not directly connected to the Internet. Rather it is connected to smaller networks which in turn are connected through gateways to the Internet backbone.

Backbone Network A backbone is a larger transmission line that carries data gathered from smaller lines that interconnect with it. e.g. a backbone is a line or set of lines that LANs connect to for a WAN connection or within a LAN to span distances efficiently.

Internet Backbone. Backbones typically consist of network routers and switches connected by fiber optic or Ethernet cables. The trunk line has multiple fiber optic cables combined together to increase the capacity. (The National Science Foundation (NSF) created the first high-speed backbone in 1987. Computers normally do not connect to a backbone directly. Instead, the networks of Network Service Providers or NSPs or connect to these backbones and computers access the backbone indirectly.

7. Network Terminology

i) Nodes(Workstations). A node is an active electronic device that is attached to a network, and is capable of sending, receiving, or forwarding information over a communications channel. Nodes can be computers, personal digital assistants (PDAs), cell phones, or various other network appliances.

ii) Server. A network server is a computer designed to process requests and facilitate the sharing of data, software and hardware resources (e.g. printers, modems etc.) on the network. Network servers typically are configured with additional processing, memory and storage capacity to handle the load of servicing clients. A network may have multiple servers each of which is identified by a unique name.Servers can be of two types:

• Dedicated ● Non-DedicatedDedicated Servers – A dedicated server is a computer in a network reserved for serving the needs of the network. It’s only job is to help workstations access sharable data, software and hardware resources. It does-not double up as a workstation. Dedicated servers may be categorized as File servers, Printer servers, Modem servers etc. A network that uses a dedicated server is known as Master Slave networks.

Non-Dedicated Server- It refers to a workstation that can double up as a server also. Since it performs the job of both a workstation and a server it is slower and requires more memory. The networks using such a server are known as Peer-to-Peer networks.

iii) Network Interface Unit(NIU). A NIC/NIU is a device that is attached to both the workstation and the server and helps to establish communication between the server and workstations. The NIU is also called the Terminal Access Point(TAP) or Network Interface Card(NIC). The NIC manufacturer assigns a unique physical address to each NIC card known as the MAC Address. A MAC address isa 6-byte address with each byte separated by a colon e.g. 10:B5:03:63:2E:FCMAC addresses map to logical IP addresses through the Address Resolution Protocol (ARP).

8. Switching TechniquesIn a network, a switch is a device that channels incoming data from any of multiple input ports to the specific output port that will take the data toward its intended destination. The trip from one switch point to another in the network is called a hop. The time a switch takes to figure out where to forward a data unit is called its latency.Different types of switching techniques are:

• Circuit Switching. Circuit switching is a method of communicating in which a dedicated communications path is established between two devices through one or more intermediate switching nodes. The telephone system uses

circuit switching where a specific physical path to the number you are calling is reserved for the duration of your call. During that time, no one else can use the physical lines involved.There are three phases in circuit switching:

o Establisho Transfero Disconnect

• Packet Switching. Packet switching is a method of transmitting messages through a communication network, in which long messages are subdivided into short packets of fixed block size.

Breaking communication down into packets allows the same data path to be shared among many users in the network.

Each packet carries the identification of the intended recipient, data used to assist in data correction and the position of the packet in the sequence.

Each packet is treated individually by the switching centre and may be sent to the destination by a totally different route to all the others.

Packet switching is a form of store-and-forward switching system in which messages are stored in the memory at the switch nodes and then transmitted to their destination and then deleted as soon as the receipt at the next node is acknowledged.

• Message Switching. In this technique no physical path is established in advance in between sender and receiver. Instead, when the sender has a block of data (no limit on the size of a block) to be sent, it is stored in the first switching office (i.e. router) then forwarded later at one hop at a time. It is a form of store-and-forward network. The data packets are stored on the disk till they are forwarded. Message switching is thus an example of a delay system or a queuing system. Message switching is still used for telegraph traffic.

9. Transmission Media

Transmission media or communication channel refers to the media used to connect two or more workstations in a network for the purpose of conveying information from a sender (or transmitter) to a receiver. Transmission media can be divided into two categories: guided (cables) and unguided (waves through air, water or vacuum). Examples cables, microwave transmission, radio waves, infrared, telephone lines, satellites etc.

GUIDED MEDIA

• Twisted pair cable.

Twisted-pair cable is a VGM(Voice grade medium) cabling that is used for telephone communications and most modern Ethernet networks. It consists of a pair of identical wires wrapped together in a double helix. The pairs are twisted to provide protection against crosstalk, the noise generated by adjacent pairs.

Crosstalk- The bleeding of a signal from one wire to another and which can corrupt signal and cause network errors. This form of signal interference is called crosstalk.

Advantages Disadvantages

Simple structure Cannot carry signals over long distances without repeaters

Flexible Low bandwidth; unsuitable for broadband applications

Easily connected Maximum data rate of 10 mbps

Easy to install and maintain

Low weight and inexpensive

Why are cables twisted? When electrical current flows through a wire, it creates a small, circular magnetic field around the wire. When two wires in an electrical circuit are placed close together, their magnetic fields are the exact opposite of each other. Thus, the two magnetic fields cancel each other out. They also cancel out any outside magnetic fields. Twisting the wires can enhance this cancellation effect. Using cancellation together with twisting the wires, cable designers can effectively provide self-shielding for wire pairs within the network media. )

Two basic types of twisted-pair cable exist: unshielded twisted pair (UTP) and shielded twisted pair (STP).

• UTP Cable

UTP cable is used for variety of electronic communications. The UTP cables can have maximum segment length of 100 meters and is available in following five categories:

• STP Cable

Type Use

Category 1 Voice Only; No data (Telephone Wire)

Category 2 Data to 4 Mbps (LocalTalk)

Category 3 Data to 10 Mbps (Ethernet)

Category 4 Data to 20 Mbps (16 Mbps Token Ring)

Category 5 Data to 1000 Mbps (Fast Ethernet)

Shielded twisted-pair (STP) This type of cable comes with shielding of the individual pairs of wires, which further protects it from external interference and crosstalk. However it is more expensive and difficult to install and requires proper grounding at both ends. Like UTP, this also has a maximum segment length of 100 meters.

• Coaxial Cable

Coaxial cable, or coax, is a cable with a white insulator which surrounds the central copper wire and that this is surrounded by metal foil. Above this there is electrical shielding consisting of layers of braided wire, and, finally, a rubberized coating. Coaxial cabling is the primary type of cabling used by the cable television industry and is also widely used for computer networks, such as Ethernet. Although more expensive than standard telephone wire, it is much less susceptible to interference and can carry much more data. The two types of coaxial cables are i) Thicknet(maximum segment length- 500m) & ii) Thinnet(maximum segment length-185m)

• Optical Fibre

An optical fiber (or fibre) is a glass or plastic fiber that carries light along its length. Fibre optic cables are increasingly replacing copper conductors in WANs and MANs because of their unique properties:

• Lower signal loss per unit distance (resulting in longer distances between repeaters)

• Higher Capacity (allowing operation at higher data rates)

• Smaller physical size (allowing more fibres in a duct or trunk)

• Immune to interference

• Provides electrical isolation between local and remote nodes

Refer also to comparison table for guided media in book

• Micro wave

When a frequency is higher than 3 GHz, it is named microwave. Microwave signals can be transmitted along a straight, unobstructed line from a transmitter to a receiver and can carry audio and video information. Microwave transmission consists of a transmitter, receiver and the atmosphere. Distances of 100Km between towers are feasible. The microwave transmission is a line-of-sight transmission.

Features:

• Use a highly directional antenna to minimize interference. • Frequencies used for transfer of information are dedicated.

• Usually supports point- to-point transmission.

• Microwave signals can cross through walls and physical barriers.

• In general, it is relatively expensive but it may be the cheapest form of transmission over rough and mountainous terrain.

• Data rates up to 500 Mbps are possible.

• Microwave propagation is susceptible to weather effects like rains, thunder storms etc.

• It is an insecure communication

• Radio Wave

The transmission making use of radio frequencies is termed as radio-wave transmission. Radio frequencies are allocated to different operators normally in the range of about 10 miles. Each different radio signal uses a different sine wave frequency. Radio waves are used for wireless transmission of sound messages, or information, for communication, as well as for maritime and aircraft navigation. A radio setup has two parts: The transmitter and The receiver. Radio wave can be classified by frequency and wavelength.

• Satellite

Satellite communication is special case of microwave relay system. It uses the synchronous satellite to relay the radio signal transmitted from the ground station. In satellite communication the earth station consists of a satellite dish that functions as an antenna and communication equipment to transmit and receive data from satellites passing overhead. A number of communication satellites, owned by both governments and private organizations, have been placed in stationary orbits about 22,300 miles above the earth’s surface. These satellites act as relay stations for communication signals. They accept data/signals, amplify them, and retransmit them to another earth station. Using such a setup, data can be transmitted to other side of the earth in only one step. Most communication satellites have multiple, independent reception and transmission devices known as transponders.

• Infrared

Infrared technology allows computing devices to communicate via short-range wireless signals. With infrared, computers can transfer files and other digital data bidirectionally. The infrared transmission technology used in computers is similar to that used in consumer product remote control units such as TV remotes, automotive doors, wireless speakers etc. The infrared light transmits data through the air and can propagate throughout a room, but will not penetrate walls. The infrared transmission has become common in PDAs. It is a secure transmission.

• Laser

Laser transmission requires direct line-of-sight. It is unidirectional like mircrowave, but has much higher speed than microwaves. The laser transmission requires the use of a laser transmitter and a photo-sensitive receiver at each end. The laser transmission is point-to-point transmission, typically between buildings.

10. Data communication terms

• Data Channel. A channel is the medium used to carry information or data from one point to another.• Frequency. Frequency is the number wave cycles repeated per second, measured in Hz (hertz). So one cycle per second

would equal 1Hz. So if you have a 100MHz cable this means that the cable can transfer 100,000,000 wave cycles of current in one second. One cycle of a wave could be from one peak in a wave to the next peak.

• Bit rate. Each 1 and 0 or on and off in a current represents one bit of data. Bit rate is the number of bits of data transfered in one second, measured in bps (bits per second). In relation, the bit rate is equal to the baud per second multiplied by the number of bits per baud (bps = baud per second * bits per baud). So, if one symbol (01010101 or 11000111) contains 8 bits and changing 1000 bauds per second, would yield a rate of 1000 baud and 8000bps or 8Mbps (8 Megabits per second).

• Baud, or baud rate. It is the number of times a current or data signal changes state or symbols per second. It is named after Emile Baudot. This is similar to bit rate except that each symbol usually consists of more than 1 bit. So in a system with 3 bit symbols operating at 1000 baud will have a 3000 bit/s bit rate.

• Bandwidth. Bandwidth is the difference between the upper and lower frequencies of a given piece of spectrum and is measured in Hz. This is essentially the amount of space available to transmit data through the air or over a wire. Bandwidth is determined by the frequency, speed, and distance of a signal. Channel capacity is the maximum data rate that can be carried over a certain medium given several factors including the amount of bandwidth available. The greater the bandwidth, the greater the channel capacity. High bandwidth channels are called broadband channels and low bandwidth channels are called narrowband channels. For digital devices, the bandwidth is usually expressed in bits per second(bps) or bytes per second. For analog devices, the bandwidth is expressed in cycles per second, or Hertz (Hz). Also Known As: throughput.

• Broadband. The term broadband refers to any type of transmission technique that carries several data channels over a common wire. DSL service, for example, combines separate voice and data channels over a single telephone line. In home networking, "broadband" usually refers to high-speed Internet access using this transmission technique. Both DSL and cable modem are common broadband Internet technologies. To qualify as a broadband Internet service, the technology should as a general guideline support network bandwidth of at least 256 Kbps in one direction.

• BaseBand. A type of data transmission in which digital or analog data is sent over a single unmultiplexed channel, such as an Ethernet LAN. Baseband transmission use TDM(Time Division Modulation) to send simultaneous bits of data along the full bandwidth of the transmission channel. (In other words it refers to analog or digital data prior to any modification i.e. before they are merged with other signals (multiplexed) or intermixed into a carrier wave (modulated).

• Bus. Device on a computer's motherboard that provides a data path between the CPU and attached devices (keyboard, mouse, disk drives, video cards, etc.). A computer bus receives a data signal from the CPU and drops it off at the appropriate device (for example, the contents of a file in RAM are sent, via the bus, to a disk drive to be stored permanently). Conversely, data signals from devices are sent back to the CPU. On a network, a bus provides the data path between the various computers and devices.

• Data Transfer Rate. DTR is the speed at which data can be transmitted between devices. This is sometimes referred to as throughput. The DTR of a device is often expressed in kilobits or megabits per second, abbreviated as kbps and mbps respectively. It might also be expressed in Kilobytes or Megabytes, or KB/sec and MB/sec.(Directly proportional to bandwidth)

Extra explanation - Bandwidth example: If you think about a cable with signal being sent across it as a highway and the data bits in the signal as the cars. If two car lengths is one wave length and both cars travel from point A to point B in one second, then the frequency would equal 1Hz because one wave cycle was completed in one second. Now, if we needed two bits of data (cars) to be

transfered in one second from point A to point B across the cable (highway) then the bandwidth would be 1Hz. If we needed to get more cars across the highway in the same amount of time then the distance of the highway (cable) or the distance between the cars (data bits) would have to decrease and the speed of the cars could stay the same.

Baud Rate vs Bitrate As you may have already guessed by both terms containing the word rate, these are used to measure speeds in connectivity. The baud rate is a measure of how many symbols are being transmitted each signal. A symbol is any waveform change or electrical pulse that is used to transmit data along the medium. On the other hand, the bitrate is a measure of the number of bits that are being transmitted. Previously, baud and bitrates are used interchangeably because older modulation techniques only allowed one bit to be contained in each symbol. Now, each symbol can contain more than bits resulting in the bitrate being much higher than the baud rate. With these cases, it is no longer accurate to interchangeably use bitrate and baud rate as they are no longer equal. The gross bitrate is equal to the baud rate multiplied by number of bits contained in each symbol. Since the baud rate does not discriminate whether the information it is transmitting is data or just signaling information used by the hardware to sync, determine the path, and many other things. The baud rate includes overhead. So if each symbol contains 4 bits, the net bitrate is slightly less than four times of the baud rate. The difference is usually very small and should not affect the data transmission too much.

Summary: 1. The baud rate is a measure of the number of symbols being transmitted each second while the bitrate is a measure of the number of bits being transmitted each second 2. Each symbol that is being measured by the baud rate can contain one or more bits 3. The baud rate always includes the overhead in the measurement while the bitrate does not 4. The maximum baud rate is equal to the passband bandwidth while the bitrate can be much higher

11. Types of NetworkOne way to categorize the different types of computer network designs is by their scope or scale.

• LAN(Local Area Network) A local area network (LAN) is a computer network covering a small physical area, like a home, office, or small group of buildings, such as a school, or an airport. The following are the main characteristics of LANs

o smaller geographic rangeo typically owned, controlled, and managed by a single person or organization.o higher data-transfer rateso They also tend to use certain connectivity technologies, primarily Ethernet and Token Ring.

LAN configuration consists of –

o A file server – stores all of the software that controls the network, as well as the software and hardware which can be shared by the computers attached to the network.

o Workstation - computers attached to the file server (Mac or PCs). These are less powerful than the server.

o Network Interface Cards

o Cables used to connect NIC in each computer.

• MAN(Metropolitan Area Network) MANs, are large computer networks than LANs ranging from several blocks of buildings to entire cities . They typically use wireless infrastructure or Optical fiber connections to link their sites. A MAN might be owned and operated by a single organization. They will often provide means for internetworking of local networks. Metropolitan area networks can span up to 50km, devices used are modem and wire/cable e.g. cable TV networks.

WAN(Wide Area Network) A WAN spans a large geographic area, such as a state, province or country. WANs often connect multiple smaller networks, such as local area networks (LANs) or metro area networks (MANs). The world's most popular WAN is the Internet. Computers connected to a WAN are often connected through public networks, such as telephone system, or through leased lines or satellites. A network device called a router connects LANs to a WAN. WANs tend to use technology like ATM, Frame Relay and X.25 for connectivity over the longer distances.

Difference between LAN and WANLAN WAN

1 LAN is restricted to limited geographical area of few kilometers.

WAN covers great distance and operate nationwide or even worldwide.

2 Operate at Data rates between 1 to 10 mbps

Data rate less than 1 mbps

3 In LAN, the computer terminals and peripheral devices are connected with wires and coaxial cables.

WANs are basically an interconnection between smaller LANs requiring a series of routers, and bridges. Communication is done through telephone lines and satellite links.

4 A single LAN network is cheaper to set up Cost of setup is higher with more workstations and more hardware connection requirements and the need for

a leased line5 LAN is generally broadcast schema WAN is point-to-point.6 Complete ownership by a single

organizationOwned by multiple organizations or government

7 Few data transmission errors occur in LAN. It is because in LAN the distance covered is negligible.

Comparatively higher error rates.

8 Ethernet and Wi-Fi are the most current technologies used in a LAN

Frame Relay, X.25, SONET are the main protocols used in a WAN

Some other types of networks are:• Wireless Local Area Network - A LAN based on wireless network technology is referred to 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.

• Campus Area Network - a network spanning multiple LANs but smaller than a MAN, such as on a university or local business campus.

• Storage Area Network - connects servers to data storage devices through a technology like Fibre Channel.

• System Area Network - links high-performance computers with high-speed connections in a cluster configuration. Also known as Cluster Area Network.

12. Network Topologies

The term topology in the context of communication network refers to the pattern of interconnection of nodes, routers and other devices in the network. According to the physical arrangements of workstations and nature of work, there are three major types of network topology. They are star topology, bus topology and ring topology. The factors affecting the choice of a given topology are:

o Cost- Installation cost should be the minimum. Includes the cost of the communication channel and interconnecting devices etc.

o Flexibility- Topology should allow for easy reconfiguration of the network. This involves adding new nodes, deleting and moving existing nodes.

o Reliability- Ease of fault detection (node or network fails to operate) and rectification. Also whether the fault causes the entire network to fail or other nodes can continue to function.

a) Point-to-Point Link- A P-P link relies upon two functions- transmit and receive. The main characteristic of P-P network is that each station receives exactly from one transmitter and sends to exactly one receiver. These functions can occur over the same wires or separate wires(for better performance).

b) Star topology – A 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.

Advantages of a Star Topology

• Easy to install and wire.

• No disruptions to the network when connecting or removing devices.

• Easy to detect faults and to remove parts.

• More suited for larger networks

• Cabling types can be mixed.

Disadvantages of a Star Topology

• 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.

c) Bus topology - A linear bus topology consists of a main run of cable with a terminator at each end All nodes (file server, workstations, and peripherals) are connected to the linear cable. A connector connects each computer or server to the bus cable. The source transmits a signal that travels in both directions and passes all machines unless it finds the system with IP address, the intended recipient. The data is ignored in case the address is unmatched.

Advantages of a Linear Bus Topology

• Easy to connect a computer or peripheral to a linear bus.(Easy to extend)

• Requires less cable length than a star topology.

Disadvantages of a Linear Bus Topology

• Entire 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.

• Fault identification is difficult as network is not centralized in any particular node.

d) Ring topology - A network topology that is set up in a circular fashion in which data travels around the ring in one direction and each device on the right acts as a repeater to strengthen the signal as it moves ahead. FDDI, SONET or Token Ring technologies are used to build ring technology. A token, or small data packet, is continuously passed around the network which is reserved when a device needs to transmit by attaching the data packet to it.

Advantages of a Ring Topology

• Short cable length

• No wiring closet space required

• Suitable for optical fibres

Disadvantages of a Ring Topology

• Node failure causes network failure.

• Difficult to diagnose faults.

• Network expansion and reconfiguration is difficult.

e) Tree topology – A 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 organizations to configure a network to meet their needs.

Advantages of a Tree Topology

• Point-to-point wiring for individual segments.

• Supported by several hardware and software venders.

Disadvantages of a Tree Topology

• 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.

5-4-3 Rule - A consideration in setting up a tree topology using Ethernet protocol is the 5-4-3 rule. One aspect of the Ethernet protocol requires that a signal sent out on the network cable reach every part of the network within a specified length of time. Each concentrator or repeater that a signal goes through adds a small amount of time. This leads to the rule that between any two nodes on the network there can only be a maximum of 5 segments, connected through 4 repeaters/concentrators. In addition, only 3 of the segments may be populated (trunk) segments if they are made of coaxial cable. A populated segment is one that has one or more nodes attached to it . In Figure 4, the 5-4-3 rule is adhered to. The furthest two nodes on the network have 4 segments and 3 repeaters/concentrators between them.

f) Mesh Topology - Mesh topologies involve the concept of routes. Each node on a mesh is connected to more than one node so that a messages sent on a mesh network can take any of several possible paths from source to destination. A mesh network in which every device connects to every other is called a full mesh. This is generally used in long distance networking.

Benefits

• extensive backup, rerouting and pass through capabilities.

• enables communication even when there is a intermediate node failure using an alternative route.

13. Network DevicesInternetworking devices are products used to connect networks. As computer networks grow in size and complexity, so do the internetworking devices used to connect them. The main purpose of having these devices is:

• To allow a greater number of nodes to be connected to the network.

• To extend the distance over which a network can extend.

• To localize traffic on the network.

• To can merge existing networks.

• To isolate network problems so that they can be diagnosed more easily.

Modem.( Short for modulator-demodulator.) It is a computer peripheral that allows you to connect and communicate with other computer via telephone line. Modem changes the digital data from your computer into analog data(modulation), a format that can be carried over telephone lines and reconverts the analog signal back into digital data)demodulation) that the recipient computer can understand. The standard interface for connecting external modems to computers is called RS-232. There are also modems that come as an expansion board that you can insert into a vacant expansion slot. These are sometimes called onboard or internal modems.

RJ-45. The Registered Jack-45 connector is commonly used for network cabling and for telephony applications. It is an eight wire connector which is commonly used to connect computers on the local area networks, especially Ethernets. It is similar to

telephone connector RJ-11 except that it has eight wires as compared to 4 in RJ-11.

EHTERNET CARD. Type of LAN card developed by Xerox Corp. along with DEC and Intel. It uses a Bus or Star topology. Supports data transfer rates of upto 10 Mbps.

Hub. It is a device that connects PCs together. In general, it is a "dumb" device, as when one PC sends data onto the wire, the hub simply forwards the packets to all the other devices connected to it. Each device is responsible for determining which packets are destined for it and ignoring the others. They typically share bandwidth between all the ports. Hubs can be of the following types:

• Active Hubs – These electrically amplify the signal as it moves from one connected device to another. Active hubs(concentrators) are used like repeaters to extend the length of a network.

• Passive Hubs – These allow the signal to pass from one computer to another without any change.

Switch. A switch is a device that is used to segment networks into different subnetworks called subnets or LAN segments. Switches control the flow of network by inspecting data packets as they are received, determining the source and destination device of that packet, and forwarding it to the appropriate port only. By delivering each message only to the connected device it was intended for, a network switch conserves network bandwidth and offers generally better performance than a hub. Switches differ from hubs in that they can have ports of different speed. Switches and hubs are often used in the same network; the hubs extend the network by providing more ports, and the switches divide the network into smaller, less congested sections.

A Repeater is a network device that amplifies and restores signals for long-distance transmission. Repeaters are of two kinds: amplifier and signal repeater. The first simply amplifies all incoming signals along with any concurrent noise. The second type collects the inbound packet and then retransmits the packet as if it were starting from the source station. Repeaters do not have any capability of directing network traffic or deciding what particular route that certain data should take.

Bridge. A bridge is a device that connects a local area network (LAN) to another local area network that uses the same protocol (for example, Ethernet ortoken ring). It helps to filter data traffic at a network boundary and reduce network traffic by dividing the LAN into segments. A bridge knows all of the addresses on each side of the bridge and inspects incoming traffic to decide whether to forward or discard it. These LANs follow the same standards but may use different hardware systems and cabling media.

Router A router is an intelligent device that forwards data packets along networks. A router is connected to at least two networks, commonly two LANs or WANs or a LAN and its ISP's network. Routers are located at gateways, the places where

two or more networks connect. Each router stores the IP address and cost of its neighbouring routers in a routing table. It is different from Bridge as this uses logical address while bridge uses physical address.

A router is the "smartest" device of them all. A router records the address information of everything connected to it like a switch. But it also records the address of the next closest router in the network. (You can program this as the "default gateway.") A router reads even more of the information in the address of a packet and makes an intelligent decision about what to do with the data based on the address. For example, if a router receives an outbound packet that has a destination address that is not in it's table, it forwards the packet to the default gateway, rather than every device attached like a switch does. This is how data

moves onto, and through, the Internet. Routers are also capable of looking at the source address of a data packet and making decisions based on that as well. This means they can tell the difference between traffic that originates on your network and traffic that comes from outside. Switches and hubs can't do that (at least in a home user's price range). This means that if a router receives an inbound packet that is addressed to something not attached to it, it simply drops it and your local network doesn't have to deal with it. A switch would forward it to all your networked devices and force them to decide whether or not is should be read. This can clog up your local network with useless traffic.

Gateway. A gateway is a network point that acts as an entrance to another network. The main job of a gateway is to connect dissimilar networks. It establishes an intelligent connection between a local network and external network with completely different structures. It is capable of performing both data translation and protocol conversion (e.g. Ethernet LAN to SNA (Systems Network Architecture)). In homes, the gateway is the ISP that connects the user to the internet. In enterprises, the gateway node often acts as a proxy server and a firewall. A gateway can be implemented in hardware, software or both, but they are usually implemented by software installed within a router.

14. Network Design

The 80-20 rule. 80/20 means No more than 20 percent of the network traffic should be able to move across a backbone and 80 percent of the traffic on a network segment should be local. This is to ensure that there is less network traffic congestion and proper use of bandwidth.

LAN Hardware- When to use Hubs/Bridges/Switches/Routers. Repeaters- distance between 2 computers/Hubs more than 100 m approx.Hub – used to connect more than 2 computers with each other. (Problems – share bandwidth, cannot filter network traffic).Bridge – used to segment two LANS. Can filter network traffic based on MAC address.Switch – Provides each segment with dedicated bandwidth.Router- Filters network traffic based on IP addresses.

15. Communication Protocols

Protocol. A network protocol defines rules and conventions for communication between network devices. Protocols for computer networking all generally use packet switching techniques to send and receive messages in the form of packets. Network protocols perform the following functions:

• Provide mechanism for devices to identify and make connections with each other(wired /wireless).• Specify formatting rules for how data is packaged into messages, sent and received.• Support message acknowledgement and data compression.• The type of error checking to be used.

Internet ProtocolsThe Internet Protocol family contains a set of related (and among the most widely used network protocols. Besides Internet Protocol (IP) itself, higher-level protocols like TCP, UDP, HTTP, and FTP all integrate with IP to provide additional capabilities. Similarly, lower-level Internet Protocols like ARP and ICMP also co-exist with IP. These higher level protocols interact more closely with applications like Web browsers while lower-level protocols interact with network adapters and other computer hardware.Routing ProtocolsRouting protocols are special-purpose protocols designed specifically for use by network routers on the Internet. Common routing protocols include EIGRP, OSPF and BGP.

Some common Protocolsa. HTTP Short for Hypertext Transfer Protocol, the underlying protocol used by the World Wide Web. It defines how messages are formatted and transmitted, and what actions Web servers and browsers should take in response to various commands. HTTP protocol is a stateless and connectionless protocol because each command is a request and is executed independently, without any knowledge of the requests that were executed before it. In this protocol the communication generally takes place over a TCP/IP protocol.

b. FTP-Short for File Transfer Protocol, the protocol for exchanging files over the Internet it uses the Internet's TCP/IP protocols to enable data transfer. FTP is most commonly used to download a file from a server using the Internet or to upload a file to a server (e.g., uploading a Web page file to a server). It's also commonly used to download programs and other files to your computer from other servers. You need to logon to an FTP server. However, publicly available files are easily accessed using anonymous FTP.

Objectives of FTP were:

1. to promote sharing of files (computer programs and/or data),2. to encourage indirect or implicit (via programs) use of remote computers,3. to shield a user from variations in file storage systems among hosts, and4. to transfer data reliably and efficiently.

FTP works in the same way as HTTP for transferring Web pages from a server to a user's browser and SMTP for transferring electronic mail across the Internet.

c. TCP/IP. TCP/IP (Transmission Control Protocol/Internet Protocol) is the basic communication language or protocol of the Internet. TCP/IP is a two-layer program.

• The higher layer, Transmission Control Protocol, is responsible for ensuring that a message or a file is divided into smaller packets, numbers the packets, and then forwards them individually to the IP program layer to be transmitted over the Internet. Because a message is divided into a number of packets, each packet can, if necessary, be sent by a different route across the Internet and therefore arrive in a different order than the order they were sent in. They are received by a TCP layer that reassembles the packets into the original message. Thus TCP guarantees delivery of data and also guarantees that packets will be delivered in the same order in which they were sent. TCP is known as a connection-oriented protocol, which means that a connection is established and maintained until such time as the message or messages to be exchanged by the application programs at each end have been exchanged.

• The lower layer, Internet Protocol, handles the address part of each packet so that data is transmitted from one computer to another. Each computer (known as a host) on the Internet has at least one IP address that uniquely identifies it from all other computers on the Internet. Each packet of data contains both the sender's Internet address and the receiver's address and is sent first to a gateway computer for routing. IP is a connectionless protocol, which means that there is no continuing connection between the end points that are communicating. Each packet that travels through the Internet is treated as an independent unit of data without any relation to any other unit of data.

A gateway computer understands a small part of the Internet. The gateway computer reads the destination address and forwards the packet to an adjacent gateway that in turn reads the destination address and so forth across the Internet until one gateway recognizes the packet as belonging to a computer within its immediate neighborhood or domain. That gateway then forwards the packet directly to the computer whose address is specified.

d. SLIP/PPP – Majority of the people use telephone lines and modem to connect to the internet. There are mainly two main modem protocols:

• SLIP: Serial Line Internet Protocol. An old protocol, low in controls. It sends a frame composed only of data to be sent followed by an end of transmission character (the END character, the ASCII code of which is 192). A SLIP frame looks like this:

Data to be transmitted

END

• PPP: PPP can be defined as an encapsulation method for transmitting multiple- protocol datagrams over point-to-point links. PPP is a layered protocol starting with the Link Control Protocol (LCP), for setting up, configuring, and monitoring the connection to ensure that the connection remains reliable. In addition, by using Network Control Protocols (NCPs), different network- layer protocols can be used dynamically. The IP Control Protocol (IPCP) permits the transport of IP packets over a PPP link.

Expansion of network protocols • MIME- Multipurpose Internet Mail Extensions• SMTP- Simple Mail Transfer Protocol• NNTP – Network News Transfer Protocol• Gopher - TCP/IP application layer protocol designed for distributing, searching, and retrieving documents

over the Internet. • WAIS – Wide Area Information Server; Client server text searching system. • UDP- User Datagram Protocol

16. Wireless/Mobile computingWireless telecommunications is the transfer of information between two or more points that are not physically connected. Wireless networks utilize radio waves and/or microwaves to maintain communication channels between computers. Advantages of wireless include mobility and elimination of unsightly cables. Disadvantages of wireless include the potential for radio interference due to weather, other wireless devices, or obstructions like walls. It encompasses various types of fixed, mobile, and portable two-way radios, cellular telephones, personal digital assistants (PDAs), and wireless networking. Other examples of wireless technology include GPS units, Garage door openers , home entertainment system control boxes- TV and VCR remotes, wireless computer peripherals(mouse, keyboards , headphones, printers), radio receivers, satellite television, broadcast television and cordless telephones. Wireless networks use Wi-Fi (wireless fidelity) technology for providing network coverage to offices, public places, and other small workplaces. A wireless access point device is used to provide wire free network coverage in the designated area.

Mobile refers to the use of small and portable computing device typically having a display screen with touch input and/or a miniature keyboard and weighting less than 2 pounds (0.91 kg).These devices include laptops, notebook PCs, tablet PCs, palmtops, personal digital assistant (PDAs) and other hand held devices. A radio-signaling device is installed inside these devices for receiving and transmitting electronic data.

• General Packet Radio Service (GPRS) -- a packet-based wireless communication service that provides continuous connection to the Internet for mobile phone and computer users

• Enhanced Data GSM Environment (EDGE) -- a faster version of the Global System for Mobile (GSM) wireless service

• Universal Mobile Telecommunications System (UMTS) -- a broadband, packet-based system offering a consistent set of services to mobile computer and phone users no matter where they are located in the world

• Wireless Application Protocol (WAP) -- 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

• i-Mode -- the world's first "smart phone" for Web browsing, first introduced in Japan; provides color and video over telephone sets

• Wireless can be divided into:

• Fixed wireless -- the operation of wireless devices or systems in homes and offices, and in particular, equipment connected to the Internet via specialized modems

• Mobile wireless -- the use of wireless devices or systems aboard motorized, moving vehicles; examples include the automotive cell phone and PCS (personal communications services)

• Portable wireless -- the operation of autonomous, battery-powered wireless devices or systems outside the office, home, or vehicle; examples include handheld cell phones and PCS units

• IR wireless -- the use of devices that convey data via IR (infrared) radiation; employed in certain limited-range communications and control systems

Wireless/Mobile Computing Technologiesa) Global System for Mobile Communication (GSM) - a digital mobile telephone system used in Europe, Australia. Africa, Asia and other parts of the world; the de facto wireless telephone standard in Europe. GSM uses narrowband TDMA(Time Division Multiple Access) which allows eight simultaneous calls on the same radio frequency. It is used in digital cellular and PCS-based systems. GSM is also the basis for Integrated Digital Enhanced Network(IDEN). The key element in GSM mobile phones is the SIM(Subscriber Identity Module) card which is a small removable chip that gives a cellular device is unique phone number.

b) CDMA(Code-Division Multiple Access)- It is a technique used for digital communication, and wireless technology in particular, that involves multiplexing(which allows numerous signals to occupy a single transmission channel, optimizing the use of available bandwidth.). It refers to any of several protocols used in so-called second-generation (2G) and third-generation (3G) wireless communications The technology is used in ultra-high-frequency (UHF) cellular telephone systems in the 800-MHz and 1.9-GHz bands. CDMA employs analog-to-digital conversion (ADC) in combination with spread spectrum techniques. Here data is sent in small pieces over a number of discrete frequencies available for use. Each user’s signal is spread over the entire bandwidth by unique spreading code. At the receiver end, the same unique code is used to recover the signal.

c) WLL(Wireless in local loop)- CDMA stands for Code Division Multiple Access. It is a technique used for digital communication, and wireless technology in particular, that involves multiplexing(which allows numerous signals to occupy a single transmission channel, optimizing the use of available bandwidth.). It refers to any of several protocols used in so-called second-generation (2G) and third-generation (3G) wireless communications The technology is used in ultra-high-frequency (UHF) cellular telephone systems in the 800-MHz and 1.9-GHz bands. CDMA employs analog-to-digital conversion (ADC) in combination with spread spectrum techniques. Here data is sent in small pieces over a number of discrete frequencies available for use. Each user’s signal is spread over the entire bandwidth by unique spreading code. At the receiver end, the same unique code is used to recover the signal.

d) 3G and EDGE - 3G(Third Generation) or UMTS(Universal Mobile Telecommunications System) mobile communications technology is a broadband, packet-based transmission of text, digitized voice, video, and multimedia at data rates up to and possibly higher than 2 megabits per second(Mbps), offering a consistent set of services to mobile computer and phone users no matter where they are located in the world. 3G can work over wireless air interfaces such as GSM, TDMA and CDMA.EDGE – Enhanced data for global evolution (EDGE) is a radio based high-speed mobile data standard, intended to enable second-generation global system for mobile communication (GSM) and time division multiple access (TDMA) networks to transmit multimedia applications such as streaming television, audio and video to mobile phones at speeds up to 384 Kbps. As it was initially developed just for GSM systems, it has also been called GSM384. Ericsson intended the technology for those network operators who failed to win spectrum auctions for third-generation networks to allow high-speed data transmission.

e) SMS – Short Message Service is also often referred to as texting, sending text messages or text messaging. The service allows for short text messages to and from a mobile phone, fax or Web. Including spaces, text messages traditionally can’t exceed 160 characters. SMS messages often use T9 predictive technology. The acronym T9 stands for Text on 9 keys. T9 predictive texting makes SMS messaging faster especially for non-QWERTY cell phones without full keyboards. MMS(Multimedia Messaging Service), which is often used to send pictures, extends upon SMS and allows for longer content lengths.

f) Email – Electronic Mail is a method of exchanging digital messages from an author to one or more recipients. Modern email operates across the Internet or other computer networks. Today's email systems are based on a store-and-forward model. Email servers accept, forward, deliver and store messages. Neither the users nor their computers are required to be online simultaneously; they need connect only briefly, typically to an email server, for as long as it takes to send or receive messages. Computers use the TCP/IP protocol suite to send email messages in the form of packets. An email message consists of three components, the message envelope, the message header, and the message body. The message header contains control information, including, minimally, an originator's email address and one or more recipient addresses. Usually descriptive information is also added, such as a subject header field and a message submission date/time stamp.

Advantages of Email

1. Cheap. Once you’re online, there is no further expense.

2. Easy to reference. Sent and received messages and attachments can be stored safely, logically and reliably.3. Easy to use. Once you’re set up, sending and receiving messages is simple. That goes for a host of other email functions.

Data storage and contacts can be accessed quickly and easily.4. Easy to prioritize. Incoming messages have subject lines that mean you can delete without opening. 5. Fast. Email is by far the fastest form of written communication.6. Global. Web based email means you can access your messages anywhere online.7. Good for the planet. Reduces use of paper for general and routine communication.8. Info at your fingertips. Storing data online means less large, space taking file cabinets, folders and shelves. You can

access information far quicker if you learn how to use email this way.

9. Leverage. Send the same message to any number of people. Adaptations are simple, too. If you have a product or service to sell, email is an effective medium to get your message out.

Disadvantages of Email

1. Emotional responses. Some emails cause upset or anger. A reply in the heat of the moment can’t be retracted.

2. Information overload. Too many people send too much information

3. Lacks the personal touch. Some things are best left untyped. Email will never beat a hand written card or letter when it comes to relationships.

4. Misunderstandings. Emails from people who don’t take the time to read what they write before clicking ‘send’. Time is wasted, either to clarify or, worse, acting on a misinterpretation of the message.

5. Spam. Many people send unwanted emails to others. These are called spam mails. It takes a lot of time to filter out the unwanted emails from those that are really important.

6. Wastage of time. Over checking messages is time wasted on low value, passive activity.

7. Viruses. Emails may carry viruses. These are small programs that harm your computer system. They can read out your email address book and send themselves to a number of people around the world.

8. Emails cannot really be used for official business documents. They may be lost and you cannot sign them.9. Your mailbox may get flooded with emails after a certain time so you have to empty it from time to time.

g) Voice Mail refers to e-mail systems that support audio. Users can leave spoken messages for one another and listen to the messages by executing the appropriate command in the e-mail system.

h) Chat refers to real-time communication between two users via computer. Once a chat has been initiated, either user can enter text by typing on the keyboard and the entered text will appear on the other user's monitor.

i) Video Conferencing – It refers to conducting a conference between two or more participants at different sites by using computer networks to transmit audio and video data. Each participant has a video camera, microphone, and speakers mounted on his or her computer. As the two participants speak to one another, their voices are carried over the network and delivered to the other's speakers, and whatever images appear in front of the video camera appear in a window on the other participant's monitor. Multipoint videoconferencing allows three or more participants to sit in a virtualconference room and communicate as if they were sitting right next to each other.

17. Internetworking terms and concepts

World Wide Web. A gateway is a network point that acts as an entrance to another network. The main job of a gateway is to connect dissimilar networks. It establishes an intelligent connection between a local network and external network with completely different structures. It is capable of performing both data translation and protocol conversion (e.g. Ethernet LAN to SNA