Dr. J. VijiPriya - Information Communication and Technology Chapter 7 Data Communication and...

Information and Information and Communication Communication TechnologyTechnology

Chapter 7 Data Communication and

Computer Networks

9/12/2015

Dr. J. VijiPriya, Assistant Professor, Hawassa University, Ethiopia 1

Data CommunicationData Communication collection of hardware & software facilitates intersystem exchange of information

between different devices via wired or wireless transmission medium

transfer of data, the method of transfer and the preservation of the data during the transfer process

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Data Communication Data Communication ComponentsComponentsFive basic componentsMessage:

◦ information to be communicatedSender:

◦ device sends the messageReceiver:

◦ device receives the message.Medium:

◦ physical path communicates the message from sender to receiver.

Protocols: ◦ set of rules coordinates the exchange of information.

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Data Transmission ModeData Transmission Mode◦ refers to the direction of signal flow between two linked devices

Simplex: ◦ Unidirectional◦ Only one of the communicating devices transmits information,

the other can only receive it. Half Duplex:

◦ each communicating device can receive and transmit information, but not at the same time.

Full- Duplex: ◦ both communicating devices to transmit and receive data

simultaneously

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Data Transmission Mode Data Transmission Mode con…con…

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Data Communication Data Communication MeasurementMeasurement

measurement of quantity of data passed down a communicating link in a given time in terms of bandwidth

Bandwidth refers to the maximum volume of information

transferred over any communication medium communication data transfer rate is measured in a

unit called baud (bits per second) level of bandwidth falls into three categories:

◦ Narrowband: (bandwidth capacity lies between 64Kbps and 1.544 Mbps.)

◦ Wideband: (etween1.544Mbps (T1 Lines) and 45 Mbps ( T3 Lines))

◦ Broadband: (equal to 45Mbps or a T3 line)

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Common Network DevicesCommon Network DevicesThe Network Interface Card (NIC) expansion card installed in to connect (interface) computer to the network. provides the physical, electrical, and electronic connections to the

network media built in to the motherboard of the computer

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Common Network Devices Common Network Devices Con…Con…The Repeater amplifies (or repeats) network signals to extend the maximum

reach of a network receive network signals on one port, amplify and repeat them out

on the other port. interconnect different media types

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Common Network Devices Common Network Devices Con…Con…The Hub central device in a star topology. receive a signal on one port and repeat it to all other ports

(multiport repeaters)

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Common Network Devices Common Network Devices Con…Con…

The Bridge logically separates a single network into two segments keep traffic meant for stations on one segment on that side of the

bridge and not let that traffic pass to the other side. improve network performance because traffic is not propagated

unnecessarily on all network segments

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Common Network Devices Common Network Devices Con…Con…The Ethernet Switch high-performance multi-interface bridges subdivide larger networks prevent the unnecessary flow of network traffic from one segment

to another or in the case of cross-segment traffic direct the frames only across the segments containing the source

and destination hosts

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Common Network Devices Common Network Devices Con…Con…The Router connects multiple, dissimilar, network segments into an

internetwork. special-purpose computer than a simple electronic device reads source and destination address of a packet and forwards it

based on the information it gathers about the network. make intelligent decisions about the best way to forward packets.

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Computer NetworkComputer Network collection of two or more computers connected

together to share information and resources interconnected by telephone lines, coaxial cables,

satellite links, radio and/or some other communication technique.

small network or larger internet, a worldwide networkthree primary categories

◦ based on the size of the network, the distance it covers, and the type of link used in interconnection

1. Local Area Network (LAN).2. Metropolitan Area Network (MAN) 3. Wide Area Network (WAN)

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Local Area Network (LAN)Local Area Network (LAN) spans only a small geographical area, such as an office, building or

campus. uses a variety of telecommunication media, ordinary telephone wiring,

coaxial cable etc. To communicate, each PC has a circuit board called a network interface

card (NIC) uses file server or network server having a larger hard disk capacity contains network Operating System Program that controls

communication, sharing of network resources

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Metropolitan Area Network Metropolitan Area Network (MAN)(MAN) large computer networks usually spanning a campus or a city. use wireless infrastructure or optical fiber connections to link their

sites. support both data & voice, and related to the local cable television

network.

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Wide Area Network (WAN):Wide Area Network (WAN):

spans a relatively large geographical area, consists of two or more LANs

are often connected through public networks, such as the telephone system, Internet.

connected through leased lines or satellites

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WANS differ from LANS WANS differ from LANS

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LAN WAN

smaller distance greater distance

Faster speed slower speed

permanently connected permanently connected

private network transports public or private network transports

half-duplex communications full- or half-duplex communications

Peer-to-Peer NetworksPeer-to-Peer Networks all computers are equal (peers) . a client that requests resources and a server that provides resources

upon requestThey are characterized by the following: Security is not centralized; each computer is responsible to check

access rights for its resources Network is not scalable; good only for a few number of computers

(10) Each user is responsible for local backup No specialized operating system is required; Windows NT 4.0

Workstation, Windows 95/98, Windows 2000 Pro, etc. are sufficient

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Client/Server NetworksClient/Server Networks there exist dedicated servers provide resources/services when

requested.They are 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; tens of thousands of workstations in

the network. Backup is centralized, done by backup operator Specialized networking operating systems are required, such as

Windows NT 4.0 server, Windows 2000 server, Novell NetWare, etc.

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Network TopologiesNetwork Topologies the physical configuration of a network determines how the network's computers are

connected bus, star mesh and ring topologies

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Network Topologies con…Network Topologies con…The 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

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Network Topologies con…Network Topologies con…

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

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Network Topologies con…Network Topologies con…The Star Topology Each computer 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 The hub sends it every computer connected to it Only the computer whose address is included with the data accepts

the data.

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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

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Network Topologies con…Network Topologies con…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

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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

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Network Topologies con…Network Topologies con…The Mesh Topology Each computer is directly connected to every other computer. complex as wiring and connections increase rapidly with the

increase of computers to connect. For n computers, n(n-1)/2 cables are required Today rarely used only in a WAN environment because the mesh

topology is fault tolerant

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Network Topologies con…Network Topologies con…Advantages of a Mesh Topology System provides increased redundancy and reliability as well as

ease of troubleshooting

Disadvantages of a Mesh Topology System is complex expensive to install because it uses a lot of cabling

Considerations When Choosing a Topology: Money Length of cable needed Future growth Cable type

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Media AccessMedia AccessCarrier Sense/Multiple Access with Collision Detection

(CSMA/CD) used in Ethernet networks When a protocol that uses CSMA/CD has data to transmit,

1. it first senses if a signal is already on the wire (a carrier), indicating that someone is transmitting currently

2. If no one else is transmitting, it attempts a transmission and then listens to hear if someone else tried to transmit at the same time

3. If someone else transmits at the exact same time, a condition known as a collision occurs

4. Both senders "back off" and don't transmit until some random period of time has passed

5. They then both retry

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Media Access con…Media Access con…Carrier Sense/Multiple Access with Collision

Detection (CSMA/CD)

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Media Access con…Media Access con…Token Passing : uses a special packet called a token.1. The first computer turned on creates the token2. It then passes the token on to the next computer3. The token passes around the network until a computer that has data to

send takes the token off the network, modifies it, and puts it back on the network along with the data it has to send

4. Each station between the sender and the receiver along the network reads the destination address in the token

5. If the destination address doesn't match its own, the station simply sends the package on its way

6. When the destination station recognizes its address in the destination address of the token, the NIC copies the data into the station's memory and modifies the token, indicating it has received the data.

7. The token continues around the network until the original sender receives the token back again.

8. If the original sender has more data to send, the process repeats itself. If not, the sender modifies the token to indicate that the token is "free" for anyone else to use

With this method, there are no collisions (as in CSMA/CD networks) because everyone has to have "permission" to transmit (via the token).

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Media Access con…Media Access con…Token Passing

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Dr. J. VijiPriya - Information Communication and Technology Chapter 7 Data Communication and...

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