Data Communication and Computer Networks Data Communication Components Data Transmission Mode Common Network Devices Network Topologies Media Access

1. Information and CommunicationInformation and Communication
TechnologyTechnology
Chapter 7
Data Communication and Computer
Networks
9/12/2015
Dr. J. VijiPriya, Assistant Professor,
Hawassa University, Ethiopia 1

2. 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
9/12/2015
Dr. J. VijiPriya, Assistant Professor,
Hawassa University, Ethiopia 2

3. Data Communication ComponentsData Communication Components
Five basic components
Message:
◦ information to be communicated
Sender:
◦ device sends the message
Receiver:
◦ device receives the message.
Medium:
◦ physical path communicates the message from sender to receiver.
Protocols:
◦ set of rules coordinates the exchange of information.
9/12/2015
Dr. J. VijiPriya, Assistant Professor,
Hawassa University, Ethiopia 3

4. 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
9/12/2015
Dr. J. VijiPriya, Assistant Professor,
Hawassa University, Ethiopia 4

5. Data Transmission Mode con…Data Transmission Mode con…
9/12/2015
Dr. J. VijiPriya, Assistant Professor,
Hawassa University, Ethiopia 5

6. Data Communication MeasurementData Communication Measurement
 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)
9/12/2015
Dr. J. VijiPriya, Assistant Professor,
Hawassa University, Ethiopia 6

7. Common Network DevicesCommon Network Devices
The 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
9/12/2015
Dr. J. VijiPriya, Assistant Professor,
Hawassa University, Ethiopia 7

8. Common Network Devices Con…Common Network Devices 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
9/12/2015
Dr. J. VijiPriya, Assistant Professor,
Hawassa University, Ethiopia 8

9. Common Network Devices Con…Common Network Devices Con…
The Hub
 central device in a star topology.
 receive a signal on one port and repeat it to all other ports (multiport repeaters)
9/12/2015
Dr. J. VijiPriya, Assistant Professor,
Hawassa University, Ethiopia 9

10. Common Network Devices Con…Common Network Devices 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
9/12/2015
Dr. J. VijiPriya, Assistant Professor,
Hawassa University, Ethiopia 10

11. Common Network DevicesCommon 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
9/12/2015
Dr. J. VijiPriya, Assistant Professor,
Hawassa University, Ethiopia 11

12. Common Network Devices Con…Common Network Devices 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.
9/12/2015
Dr. J. VijiPriya, Assistant Professor,
Hawassa University, Ethiopia 12

13. 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 network
three 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)
9/12/2015
Dr. J. VijiPriya, Assistant Professor,
Hawassa University, Ethiopia 13

14. 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
9/12/2015
Dr. J. VijiPriya, Assistant Professor,
Hawassa University, Ethiopia 14

15. Metropolitan Area NetworkMetropolitan 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.
9/12/2015
Dr. J. VijiPriya, Assistant Professor,
Hawassa University, Ethiopia 15

16. 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
9/12/2015
Dr. J. VijiPriya, Assistant Professor,
Hawassa University, Ethiopia 16

17. WANS differ from LANSWANS differ from LANS
9/12/2015
Dr. J. VijiPriya, Assistant Professor,
Hawassa University, Ethiopia 17
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

18. Peer-to-Peer NetworksPeer-to-Peer Networks
 all computers are equal (peers) .
 a client that requests resources and a server that provides resources upon request
They 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
9/12/2015
Dr. J. VijiPriya, Assistant Professor,
Hawassa University, Ethiopia 18

19. 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.
9/12/2015
Dr. J. VijiPriya, Assistant Professor,
Hawassa University, Ethiopia 19

20. Network TopologiesNetwork Topologies
 the physical configuration of a network
 determines how the network's computers are connected
 bus, star mesh and ring topologies
9/12/2015
Dr. J. VijiPriya, Assistant Professor,
Hawassa University, Ethiopia 20

21. 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
9/12/2015
Dr. J. VijiPriya, Assistant Professor,
Hawassa University, Ethiopia 21

22. 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
9/12/2015
Dr. J. VijiPriya, Assistant Professor,
Hawassa University, Ethiopia 22

23. 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.
9/12/2015
Dr. J. VijiPriya, Assistant Professor,
Hawassa University, Ethiopia 23

24. Network Topologies con…Network Topologies con…
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
9/12/2015
Dr. J. VijiPriya, Assistant Professor,
Hawassa University, Ethiopia 24

25. 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
9/12/2015
Dr. J. VijiPriya, Assistant Professor,
Hawassa University, Ethiopia 25

26. Network Topologies con…Network Topologies con…
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
9/12/2015
Dr. J. VijiPriya, Assistant Professor,
Hawassa University, Ethiopia 26

27. 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
9/12/2015
Dr. J. VijiPriya, Assistant Professor,
Hawassa University, Ethiopia 27

28. 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
9/12/2015
Dr. J. VijiPriya, Assistant Professor,
Hawassa University, Ethiopia 28

29. Media AccessMedia Access
Carrier 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
9/12/2015
Dr. J. VijiPriya, Assistant Professor,
Hawassa University, Ethiopia 29

30. Media Access con…Media Access con…
Carrier Sense/Multiple Access with Collision Detection
(CSMA/CD)
9/12/2015
Dr. J. VijiPriya, Assistant Professor,
Hawassa University, Ethiopia 30

31. Media Access con…Media Access con…
Token Passing : uses a special packet called a token.
1. The first computer turned on creates the token
2. It then passes the token on to the next computer
3. 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).
9/12/2015
Dr. J. VijiPriya, Assistant Professor,
Hawassa University, Ethiopia 31

32. Media Access con…Media Access con…
Token Passing
9/12/2015
Dr. J. VijiPriya, Assistant Professor,
Hawassa University, Ethiopia 32