Transmission Media and Network Devices in Computer Networks | Lecture notes Computer Science

Chapter -IV

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Introduction to Computer Skill and its application

4. DATA COMMUNICATION AND COMPUTER NETWORKS

4.1 Data Communication: A communication system can be defined as the collection of hardware &

software that facilitates intersystem exchange of information between different devices. Data

communication is the exchange of data between two devices via some form of wired or wireless

transmission medium. It includes the transfer of data, the method of transfer and the preservation of

the data during the transfer process.

4.1.1 Data Communication Components:

There are five basic components in data communication system:

i. Message: It is the information that is to be communicated

ii. Sender: The sender is the device that sends the message

iii. Receiver: The Receiver is the device that receives the message.

iv. Medium: The transmission medium is the physical path that communicates the message from

sender to receiver.

v. Protocols: Protocols refers to a set of rules that coordinates the exchange of information.

4.1.2 Data Transmission Mode: It refers to the direction of signal flow between two linked devices.

Following are the three types of transmission modes:

i. Simplex: Simplex transmission is unidirectional. The information flows in one direction across

the circuit, with no capability to support response in other direction. Only one of the

communicating devices transmits information, the other can only receive it.

ii. Half Duplex: In this mode, each communicating device can receive and transmit information,

but not at the same time. When one device is sending, the other can only receive at that point of

time.

iii. Full-Duplex: This mode allows both communicating devices to transmit and receive data

simultaneously.

4.1.3 Data Communication Measurement: The measurement of quantity of data that can be passed

down a communicating link in a given time is done in terms of bandwidth. Fundamentally, bandwidth

refers to the maximum volume of information that can be transferred over any communication

medium. A narrow range of frequencies in a communication system is analogous to a narrow road.

Wider bandwidth permits more rapid information flow. Thus, wider the bandwidth of a

communication system, the more data it can transmit in a given period of time. The communication

data transfer rate is measured in a unit called baud. In general usage, baud is identical to bits per

second.

In the popular digital context, the level of bandwidth falls into three categories:

Narrowband: In narrowband, there is a single transmission channel of 64 Kbps or less. There

can also be a number of 64Kbps transmissions (N x 64Kbps) but not more than 1.544 Mbps.

Wideband: In wideband, the bandwidth capacity lies between 1.544Mbps (also called T1

Lines) and 45 Mbps ( T3 Lines)

Broadband: The bandwidth capacity in broadband is equal to 45Mbps or a T3 line.

4.2 Transmission Medium: Transmission media refers to the physical media through which

communication signals (data & signals) are transmitted. The information or a signal transmitted from

one device to another is through electromagnetic signals. An electromagnetic signal is the combination

of electric and magnetic fields, vibrating in conjunction with each other. These signals can travel

through vacuum, air or any other transmission medium. Voice signals are generally transmitted as

current over metal cables. Radio frequencies are generally transmitted through air or space. Third type

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Introduction to Computer Skill and its application

4. DATA COMMUNICATION AND COMPUTER NETWORKS

4.1 Data Communication: A communication system can be defined as the collection of hardware & software that facilitates intersystem exchange of information between different devices. Data communication is the exchange of data between two devices via some form of wired or wireless transmission medium. It includes the transfer of data , the method of transfer and the preservation of the data during the transfer process. 4.1.1 Data Communication Components: There are five basic components in data communication system: i. Message : It is the information that is to be communicated ii. Sender : The sender is the device that sends the message iii. Receiver : The Receiver is the device that receives the message. iv. Medium : The transmission medium is the physical path that communicates the message from sender to receiver. v. Protocols: Protocols refers to a set of rules that coordinates the exchange of information. 4.1.2 Data Transmission Mode: It refers to the direction of signal flow between two linked devices. Following are the three types of transmission modes: i. Simplex : Simplex transmission is unidirectional. The information flows in one direction across the circuit, with no capability to support response in other direction. Only one of the communicating devices transmits information, the other can only receive it. ii. Half Duplex : In this mode, each communicating device can receive and transmit information, but not at the same time. When one device is sending, the other can only receive at that point of time. iii. Full - Duplex : This mode allows both communicating devices to transmit and receive data simultaneously. 4.1.3 Data Communication Measurement: The measurement of quantity of data that can be passed down a communicating link in a given time is done in terms of bandwidth. Fundamentally, bandwidth refers to the maximum volume of information that can be transferred over any communication medium. A narrow range of frequencies in a communication system is analogous to a narrow road. Wider bandwidth permits more rapid information flow. Thus, wider the bandwidth of a communication system, the more data it can transmit in a given period of time. The communication data transfer rate is measured in a unit called baud. In general usage, baud is identical to bits per second. In the popular digital context, the level of bandwidth falls into three categories:  Narrowband : In narrowband, there is a single transmission channel of 64 Kbps or less. There can also be a number of 64Kbps transmissions (N x 64Kbps) but not more than 1.544 Mbps.  Wideband : In wideband, the bandwidth capacity lies between 1.544Mbps (also called T Lines) and 45 Mbps ( T3 Lines)  Broadband : The bandwidth capacity in broadband is equal to 45Mbps or a T3 line. 4.2 Transmission Medium: Transmission media refers to the physical media through which communication signals (data & signals) are transmitted. The information or a signal transmitted from one device to another is through electromagnetic signals. An electromagnetic signal is the combination of electric and magnetic fields, vibrating in conjunction with each other. These signals can travel through vacuum , air or any other transmission medium. Voice signals are generally transmitted as current over metal cables. Radio frequencies are generally transmitted through air or space. Third type

Introduction to Computer Skill and its application

of electromagnetic energy is the visible light which is currently being used for communication through fiber optic cable. Transmission medium can be divided into two broad categories: Guided Media and Unguided media. 4.2.1 Guided Media: Guided media use a cabling system that guide the data signals along a specific path. The data signals are bound by the cabling system. It is also known as bound medium. There are four basic types of guided media: open wire, twisted pair, coaxial cable and optical fiber. i. Open Wire : Open wire is traditionally used to describe the electrical wire system or power transmission wires strung along power poles. No shielding or protection from noise interference is used. It is not recommended for long data transmission distances. ii. Twisted Pair Cable : Made of two or more pairs of insulated copper wires twisted together. May be unshielded or shielded (UTP/STP). Examples telephone wire installation. Unshielded Twisted Pair (UTP) Cable: Unshielded twisted pair (UTP) is the most popular and is generally the best option for most networking today. This is because:  It's cheaper than other types of cabling.  It's easy to work with.  It permits transmission rates considered impossible ten years ago. Fig: Unshielded twisted pair The quality of UTP may vary from telephone-grade wire to extremely high-speed cable. 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 called crosstalk 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 and rated five categories of wire. Categories of Unshielded Twisted Pair Type Use Category 1 Voice Only (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 100 Mbps (Fast Ethernet) Unshielded Twisted Pair Connector The standard connector for unshielded twisted pair cabling is an RJ-45 connector. This is a plastic connector that looks like a large telephone-style connector. A slot allows the RJ-45 to be inserted only

Introduction to Computer Skill and its application

Coaxial Cable Connectors The most common type of connector used with coaxial cables is the Bayone-Neill-Concelman (BNC) connector. Different types of adapters are available for BNC connectors, including a T-connector, barrel connector, and terminator. Connectors on the cable are the weakest points in any network. To help avoid problems with your network, always use the BNC connectors that crimp, rather than screw, onto the cable. Fig. BNC connector iv. Fiber Optic Cable : Fiber optic cabling consists of a center glass core surrounded by several layers of protective materials (See fig. 5). It transmits light rather than electronic signals 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. Fig.5. Fiber optic cable Facts about fiber optic cables:  Outer insulating jacket is made of Teflon or PVC.  Kevlar fiber helps to strengthen the cable and prevent breakage.  A plastic coating is used to cushion the fiber center.  Center (core) is made of glass or plastic fibers. Fiber Optic Connector The most common connector used with fiber optic cable is an ST connector. It is barrel shaped, similar to a BNC connector. A newer connector, the SC, is becoming more popular. It has a squared face and is easier to connect in a confined space.

Introduction to Computer Skill and its application

Cable Summary Specification Cable Type Maximum length 10BaseT Unshielded Twisted Pair 100 meters 10Base2 Thin Coaxial 185 meters 10Base5 Thick Coaxial 500 meters 10BaseF Fiber Optic 2000 meters 100BaseT Unshielded Twisted Pair 100 meters Installing Cable - Some Guidelines: When running cable, it is best to follow a few simple rules:  Always use more cable than you need. Leave plenty of slack.  Test every part of a network as you install it. Even if it is brand new, it may have problems that will be difficult to isolate later.  Stay at least 3 feet away from fluorescent light boxes and other sources of electrical interference.  If it is necessary to run cable across the floor, cover the cable with cable protectors.  Label both ends of each cable.  Use cable ties (not tape) to keep cables in the same location together. 4.2.2 Unguided Media: Unguided transmission media is data signals that flow through the air. They are not guided or bound to a fixed channel to follow. Wireless systems are used where normal cabling cannot be used. If great distances must be travelled or cables cannot be run, wireless systems provide a necessary but expensive solution. i. Infra-red : Using Infrared emitters, these types of connections can be used for small networks where -cables cannot be laid as an entire network media or as a point-to-point signalling method over medium distances. ii. Radio Frequency : Radio frequency (RF) is used where longer distances are needed or cables cannot go. Signals wary in strength (Amplitude) and tone (Frequency) in order to offer a broad range of services, from short-range to extremely long-range. iii. Microwave: Microwave transmissions are normally used in satellite communications, and are point-to-point transmissions. They are meant for extremely long-range communications, and are extremely expensive.

Introduction to Computer Skill and its application

4.4.1. Classification Based on Coverage Area i. Local Area Network (LAN): A local area network or LAN is a computer network that spans only a small geographical area, such as an office, building or campus. It cconnects computers & other devices within a limited physical area s.a. an office, classroom, building etc. It uses a variety of telecommunication media s.a. ordinary telephone wiring, coaxial cable etc. to interconnect workstation & other devices. To communicate each PC has a circuit board called a network interface card (NIC). Most LANs uses a more powerful microcomputer having a larger hard disk capacity, called a file server or network server that contains a Network Operating System Program that controls communication and the use and sharing of network resources. ii. Metropolitan Area Network (MAN): Metropolitan Area Networks or MANs are large computer networks usually spanning a campus or a city. They typically use wireless infrastructure or optical fiber connections to link their sites. For instance a university or college may have a MAN that joins together many of their local area networks (LANs) situated around site of a fraction of a square kilometer. It may cover a group of nearby corporate offices or a city and could either be private or public. It can support both data & voice, and might even be related to the local cable television network. iii. Wide Area Network (WAN): A computer network that spans a relatively large geographical area. Typically, a WAN consists of two or more LANs. Computers connected to a wide-area network are often connected through public networks, such as the telephone system. They can also be connected through leased lines or satellites. The largest WAN in existence is the internet.

Introduction to Computer Skill and its application

WANS differ from LANS in the following ways:  WANs cover greater distance.  WAN speeds are slower.  WANs can be connected on demand or be permanently connected. LANs have permanent connections between stations.  WANs can use public or private network transports. LANs typically use private transports.  WANs can use either full- or half-duplex communications. LANs typically use half-duplex communications. 4.4.2 Classification Based on Security and Access  Based on security and access, we may classify networks into peer-to-peer and client/server networks technologies: Peer-to-peer networks – all computers are equal - they are peers. Each computer can be a client that requests resources and a server that provides resources upon request. They s are characterized by the following:  Security is not centralized; each computer is responsible to check access rights for its resources.  Network is not scalable; it is good only for a few number of computers (10).  Each user is responsible for local backup.  No specialized operating system is required; the operating systems used in standalone computers like Windows NT 4.0 Workstation, Windows 95/98, Windows 2000 Pro, etc. are sufficient. Client/server networks – there exist dedicated servers which only provide resources/services when requested. They characterized by the following:  Security is centralized and tighter. All user accounts are stored in the same database on the server.  The network is highly scalable; you can have tens of thousands of workstations in the network.  Backup is centralized and is done by a person responsible for the job (backup operator).  Specialized networking operating systems are required, such as Windows NT 4.0 server, Windows 2000 server, Novell NetWare, etc.

Introduction to Computer Skill and its application

 File Server May Fail. Although a file server is no more susceptible to failure than any other computer, when the files server "goes down," the entire network may come to a halt. When this happens, the entire may lose access to necessary programs and files.  Cables May Break. The Topology chapter presents information about the various configurations of cables. Some of the configurations are designed to minimize the inconvenience of a broken cable; with other configurations, one broken cable can stop the entire network. 4.5 Network Topologies: The physical configuration of a network that determines how the network's computers are connected is called network topology. Common configurations include the bus, star and ring topologies. It refers to the layout of connected devices on a network. i. The Bus Topology  In a bus topology, all computers are connected to a single cable.  The cable is terminated at its ends to avoid signal bouncing.  When a computer wants to send data to another computer, it places the data and address of the recipient computer on the cable. Only the computer whose address is included with the data accepts the data. Advantages of a Bus Topology  Easy to connect a computer or peripheral to a linear bus.  Requires less cable length than a star topology. Disadvantages of a 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.  Network can slow down in heavy traffic. ii. The Star Topology  Each computer in a star topology is connected to a central device (hub) by a separate cable.  When a computer wants to send data to another computer, it sends the data and address of the recipient computer to the hub, which in turn, sends it to every computer connected to it. Only the computer whose address is included with the data accepts the data. Advantages of a Star Topology  Easy to install and wire.  No disruptions to the network then connecting or removing devices.  Easy to detect faults and to remove parts.  Failure of one computer does not affect the rest of the network Disadvantages of a Star Topology  Requires more cable length than a linear topology.  If the hub or concentrator fails, nodes attached are disabled.  More expensive than linear bus topologies because of the cost of the concentrators. iii. The Ring Topology  Each computer is connected directly to two other computers in the network.  Data moves down a one-way path from one computer and if the next computer is the recipient it accepts the data; otherwise it amplifies it and sends it to the next computer down in the path.  Any break disrupts the entire network and hence the physical ring topology is seldom used.

Introduction to Computer Skill and its application

Advantages of a Ring Topology  System provides equal access for all computers.  Performance is even despite many users. Disadvantages of a Ring Topology  Failure of one computer can impact the rest of the network.  Problems are hard to isolate.  Network reconfiguration disrupts operation. iv. The Mesh Topology  Each computer is directly connected to every other computer.  A mesh topology can become quite complex as wiring and connections increase rapidly with the increase of computers to connect. For n computers, n(n-1)/ cables are required.  Today, the mesh topology is rarely used, and then only in a WAN environment and only because the mesh topology is fault tolerant. Computers or network devices can switch between these multiple, redundant connections if the need arises. On the con side, the mesh topology is expensive and quickly becomes too complex. Advantages of a Mesh Topology  System provides increased redundancy and reliability as well as ease of troubleshooting. Disadvantages of a Mesh Topology  System is expensive to install because it uses a lot of cabling. 4.6 Considerations When Choosing a Topology :  Money. A linear bus network may be the least expensive way to install a network; you do not have to purchase concentrators.  Length of cable needed. The linear bus network uses shorter lengths of cable.  Future growth. With a star topology, expanding a network is easily done by adding another concentrator.  Cable type. The most common cable in schools is unshielded twisted pair, which is most often used with star topologies.

Transmission Media and Network Devices in Computer Networks, Lecture notes of Computer Science

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Partial preview of the text

Download Transmission Media and Network Devices in Computer Networks and more Lecture notes Computer Science in PDF only on Docsity!

Introduction to Computer Skill and its application

4. DATA COMMUNICATION AND COMPUTER NETWORKS

Introduction to Computer Skill and its application

Introduction to Computer Skill and its application

Introduction to Computer Skill and its application

Introduction to Computer Skill and its application

Introduction to Computer Skill and its application

Introduction to Computer Skill and its application

Introduction to Computer Skill and its application