COMPUTER SKILLS

COMP101

Introduction to

Computer Networks

Chapter 4

Definitions and Terminologies

Computer Network

A network consists of two or more computers that are linked in order to share resources (such as printers and CD-ROMs), exchange files, or allow electronic communications. The connections between nodes are established using either cable media or wireless media. Protocol A protocol is a set of rules that governs the communications between computers on a network.

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Network Main Components

The three main components of computer network are:

o The Computer System A stand-alone systems, along with peripheral devices, capable of performing information input, output, storage and processing.

o The communication System provide a vehicle of carrying information from one point to another by conditioning it appropriately

o The Networking System Networking systems provide the capability of efficient use of transmission and switching resources and provide with rules that govern communication among computer systems and software programs.

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Network Classifications

There are several ways of classifying data networks, such as:

Geographical Classification of Networks

Classification of Networks by Type of Services

Classification of Networks by Type of Topology

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Geographical Classification of Networks

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Following is a classification based on (roughly) the geographical scope:

Figure 1

Local Area Networks (LANs)

LANs are (usually) small networks that provide a high-speed physical and logical connection among a group of stations. They typically encompass a walk-able geographic area, owned and administered by the user and are mainly used either for hardware sharing or as access networks for greater geographical scale. Most commonly used LAN is the Ethernet (Fig.2).

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LAN Example

8 Figure 2

Metropolitan Area Networks (MANs)

MANs are networks between a LAN and WAN. They are a type of interconnecting networks for big businesses in a metropolitan area. Usually, they have interconnecting (switching) devices instead of user desktop computers as their nodes, but it is possible to have user computers directly attached to a MAN(Figure 3) .

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MAN Example

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Figure 3

Wide Area Networks (WANs)

WANs cover a general geographical area that may vary from a small office area to the whole world (or even more!) (Figure. 4). Usually, network providers and big businesses own such networks. WANs are mostly heterogeneous, meaning, a large variety of LANs and equipment. or other WANs can constitute a single WAN. An example of a WAN is the Internet

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WAN Example

12 Figure 4

Classification of Networks by Type of Services

According to this classification, networks can be divided in to two main categories:

o Peer-to-peer networks

o Client/Server networks

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Peer-to-peer networks

In peer-to-peer networking there are no dedicated servers or hierarchy among the computers.

All of the computers are equal and therefore known as peers.

Each computer serves as Client/Server and there is no one assigned to be an administrator responsible for the entire network.

Peer-to-peer networks are good choices for needs of small organizations where: o the users are allocated in the same general area, o security is not an issue and the organization o the network will have limited growth within the foreseeable future.

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Peer-to-peer network Example

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Figure 5

Client/Server networks

The term Client/server refers to the concept of sharing the work involved in processing data between the client computer and the server.

Client-server describes the relationship between two computer programs in which one program, the client program, makes a service request to another, the server program.

Email exchange, web access and database access, are based on the client-server model.

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Client/Server network Example

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Figure 6

Classification of Networks By Type of Topology

The topology is the network architecture used to interconnect the networking equipment. In addition, there is a logical topology that is defined by how the nodes interact with one another through the transmission media protocol.

There are three topology types used in LANs, WANs, and MANs, as discussed in the following: o Bus topology, o Star topology o Ring topology

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Bus Topology

Bus topology was the basis for most of the original LAN networks.

Bus topology is a single length of transmission medium with nodes connected to it.

Most installations consist of multiple cable lengths connected by repeaters.

19 Figure 7

Star Topology

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Star topology consists of a central node off which all other nodes are connected by a single path.

Figure 8

Ring Topology

In ring topology , each node is attached to its neighbor. The transmission signal moves around the ring in one direction and is

repeated, instead of just passed, as it moves from node to node. When a station transmits a data message, the transmission is picked

up by the next station on the ring, examined, then retransmitted to the downstream neighbor.

This process is continued until the transmitted signal is returned to the host that started the transmission, which then removes the data from the network.

21 Figure 9

Cables in data communications

Most of these cables belong to either twisted pair copper or co-axial categories. The vendors are limited in their choice of manufacturing due to standardization of data cables.

We distinguish two types of media:

o Guided media

o Unguided media

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Guided Media: Twisted Pair Copper Cables

A twisted pair copper cable consists of two copper wires twisted together to carry communications signal efficiently.

The twisting is done to minimize the electromagnetic interference.

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Figure 10

Guided Media: Unshielded Twisted-Pair (UTP)

Consists of one or more insulated wire pairs encased in a plastic sheath

Does not contain additional shielding

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Figure 11

Guided Media: Shielded Twisted-Pair (STP)

STP cable consists of twisted wire pairs that are individually insulated and surrounded by shielding made of metallic substance.

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Figure 12

Guided Media: Coaxial Cable

Has been used for long distance telephone and cable television for a long time.

It has the capacity of a large number of voice signals. It has also been quite popular in Local Area Networks (LAN)s. Co-ax is still the cable for cable TV and runs to most of the modern homes these days.

It is much less susceptible to interference and crosstalk than twisted pair. It provides much higher data rates, suitable for transmission to longer distances.

26 Figure 13

Guided Media: Optical Fiber Cable (OFC)

The OFC is a very thin glass or plastic cable consisting of three concentric cylinders: the innermost core, the outer-most jacket and the cladding in-between.

Typical diameters vary from a few μm to about a 100 μm.

27 Figure 14

Unguided Media: wireless: Atmospheric Transmission Media

• Information is transmitted by sending electromagnetic signals through the vacuum of outer space and through a medium such as air.

• Signals are not guided in any specific direction.

• Wireless transmission can be used as the medium in LAN, MAN, and WAN environments.

28 Figure 15

Internetworking Devices

Network devices are products used to expand or connect networks. They can control the amount of traffic on a network and speed up the flow of data over a network. Next, we provide some such devices:

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Network Interface Card

To be able to talk or to be connected to an Internet service provider, a computer needs what is called a Network Interface Card, or NIC , also called Network Adapter. This card, usually found inside the computer, is the gateway into which you plug an Ethernet cable. This card is linked to the motherboard through an adapter slot

30 Figure 16

Repeater

The number of nodes on a network and the length of cable used influence the quality of communication on the network which can generate attenuation: degradation of signal clarity.

Repeaters work against attenuation by repeating signals that they receive on a network. They typically clean and regenerate the digital transmission in the process.

31 Figure 17

Hub (Concentrator)

A network hub but commonly refers to a multiport repeater broadcasts the same data out of each of its ports to all connected nodes.

It can be used to create multiple levels of hierarchy of stations. The stations connect to the hub with RJ-45 connector having maximum segment length of 100 meters. This type of interconnected set of stations is easy to maintain and diagnose.

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Example of Hub

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Figure 18

Switches

Switches connect devices together on a computer network, by using packet switching to receive, process and forward data to the destination device. Unlike less advanced network hubs, a network switch forwards data only to one or multiple devices that need to receive it, rather than broadcasting the same data out of each of its ports to all nodes (as do hubs).

34 Figure 19

Modem

Modem, short for modulator-demodulator is an electronic device that converts a computer’s digital signals into specific frequencies to travel over telephone or cable television lines. At the destination, the receiving modem demodulates the frequencies back into digital data. Computers use modems to communicate with one another over a network.

35 Figure 20

Wireless Network

A wireless network enables people to communicate and access applications and information without wires.

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Benefits of Wireless Network

Convenience. Access your network resources from any location within your wireless network's coverage area or from any Wi-Fi hotspot.

Mobility. You're no longer tied to your desk, as you were with a wired connection. You and your employees can go online in conference room meetings, for example.

Productivity. Wireless access to the Internet and to your company's key applications and resources helps your staff get the job done and encourages collaboration.

Easy setup. You don't have to string cables, so installation can be quick and cost-effective.

Expandable. You can easily expand wireless networks with existing equipment, while a wired network might require additional wiring.

Security. Advances in wireless networks provide robust security protections.

Cost. Because wireless networks eliminate or reduce wiring costs, they can cost less to operate than wired networks.

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Wireless networks disadvantages

Higher loss-rates due to interference Emissions of, e.g., engines, lightning Restrictive regulations of frequencies Frequencies have to be coordinated, useful frequencies are almost all occupied Low data transmission rates Local some Mbit/s, regional currently, e.g., 53kbit/s with GSM/GPRS Lower security, simpler active attacking Radio interface accessible for everyone, base station can be simulated, thus attracting calls from mobile phones Always shared medium As the same medium is shared by many users, it is very important to provide secure access mechanisms.

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Wireless Technologies: Bluetooth Bluetooth is a wireless technology for exchanging data over short

distances.

Using a special radio frequency to transmit data creates a short range network.

It is very secure and can connect several devices (items of electronic equipment) at the same time.

Bluetooth is particularly convenient in certain situations – for example, when transferring files from one mobile phone to another.

Sending music and photos between a PC and a mobile phone.

Many modern cars now have Bluetooth capabilities, allowing you to use your phone while you are driving.

In general, every smartphone is able to pair with Bluetooth devices. Many newer printers equipped with a Bluetooth facility.

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Bluetooth (Cont.)

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Figure 21

Wireless Technologies: IEE 802.11 (Wi-Fi)

Wi-Fi is the standard wireless local area network (WLAN) technology for connecting computers and myriad electronic devices to each other and to the Internet.

Every laptop, tablet and smartphone comes with Wi-Fi, as well as most security cameras and home theater devices.

Printers and scanners may also support Wi-Fi, and home appliances increasingly use it for control and notifications.

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Wireless Technologies: RFID

RFID (Radio Frequency Identification) An RFID system has readers and tags that communicate

with each other by radio.

RFID tags are so small and require so little power that they don’t even need a battery to store information and exchange data with readers.

RFID is a technique that uses radio waves to track and identify people, animal, objects, and shipments.

RFID can identify individual objects at rates of over 1,000 tags per second.

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Wireless Technologies: IEEE 802.16 (WiMax)

WiMax (Worldwide Interoperability for Microwave Access)

WiMAX is a broadband wireless system and has been developed for use as broadband wireless access (BWA) for fixed and mobile stations and will be able to provide a wireless alternative for last mile broadband access in the 2 GHz to 66 GHz frequency range.

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