Data Communication and Network - Transmission Medium and Switching

Transmission Medium
and Switching
Chapter-2
Mr. C. P. Divate
Department of Computer Engineering

What is Topology?
 Topology defines the structure of the network of how all the components are
interconnected to each other. There are two types of topology: physical and logical
topology.
 Physical topology is the geometric representation of all the nodes in a network.

Bus Topology
 The bus topology is designed in such a way that all the stations are connected through
a single cable known as a backbone cable.
 Each node is either connected to the backbone cable by drop cable or directly connected
to the backbone cable.
 When a node wants to send a message over the network, it puts a message over the
network. All the stations available in the network will receive the message whether it
has been addressed or not.

Bus Topology
 The bus topology is mainly used in 802.3 (ethernet) and 802.4 standard networks.
 The configuration of a bus topology is quite simpler as compared to other topologies.
 The backbone cable is considered as a "single lane" through which the message is
broadcast to all the stations.
 The most common access method of the bus topologies is CSMA (Carrier Sense Multiple
Access).

Bus Topology
 This network requires Coaxial cable as backbone cable and BNC connectors to join
each node.
 Each node can be connected to backbone cable using T Type BNC connector.

Bus Topology
 The network can expand with another bus network simple by joining using connectors.
 At the end of cable there is a necessity to connect cable terminator to avoid the data
signal loss.

Bus Topology
 CSMA(Carrier Sense Multiple Access) : It is a media access control used to control the data
flow so that data integrity is maintained, i.e., the packets do not get lost.

Bus Topology
1) There are two alternative ways of handling the problems that
occur when two nodes send the messages simultaneously.
1) CSMA CD: CSMA CD (Collision détection)
2) CSMA CA: CSMA CA (Collision Avoidance)

Bus Topology
 CSMA/CD: CSMA/CD (Collision détection): CSMA CD (Collision detection) is an
access method used to detect the collision. Once the collision is detected, the sender
will stop transmitting the data. Therefore, it works on "recovery after the collision".

Bus Topology
 CSMA CA: CSMA CA (Collision Avoidance): is an access method used to avoid the
collision by checking whether the transmission media is busy or not. If busy, then the
sender waits until the media becomes idle. This technique effectively reduces the
possibility of the collision. It does not work on "recovery after the collision".

Bus Topology
 Advantages of Bus topology:
1) Low-cost cable: In bus topology, nodes are directly connected to the cable without
passing through a hub. Therefore, the initial cost of installation is low.
2) Moderate data speeds: Coaxial or twisted pair cables are mainly used in bus-based
networks that support upto 10 Mbps.
3) Familiar technology: Bus topology is a familiar technology as the installation and
troubleshooting techniques are well known, and hardware components are easily
available.
4) Limited failure: A failure in one node will not have any effect on other nodes.
5) It is easy to set up, handle, and implement.
6) It is best-suited for small networks.
7) It costs very less.

Bus Topology
 Disadvantages of Bus topology:
1) Extensive cabling: A bus topology is quite simpler, but still it requires a lot of cabling.
2) Difficult troubleshooting: It requires specialized test equipment to determine the cable faults. If any fault
occurs in the cable, then it would disrupt the communication for all the nodes.
3) Signal interference: If two nodes send the messages simultaneously, then the signals of both the nodes
collide with each other.
4) Reconfiguration difficult: Adding new devices to the network would slow down the network.
5) Attenuation: For long distance data flow attenuation is a loss of signal leads to communication issues.
Repeaters are used to regenerate the signal.
6) Small network: It is applicable to design small LAN with limited Computers as node.
7) Less secured: Each device on the network “sees” all the data being transmitted, thus posing a security
risk.
8) It is heavily dependent on the central bus. A fault in the bus leads to network failure.
9) It is suitable for networks with low traffic. High traffic increases load on the bus, and the network
efficiency drops.
10) This network topology can perform well only for a limited number of nodes. When the number of devices
connected to the bus increases, the efficiency decreases.
11) The cable length is limited. This limits the number of network nodes that can be connected.

Ring Topology
 Ring topology is like a bus topology, but with connected ends.
 The node that receives the message from the previous computer will retransmit to the
next node.
 It has no terminated ends, i.e., each node is connected to other node and having no
termination point.

Ring Topology
 The data flows in one direction, i.e., it is unidirectional.
 The data flows in a single loop continuously known as an endless loop.
 The data in a ring topology flow in a clockwise direction.

Ring Topology
 The most common access method of the ring topology is token passing.
 Token passing: It is a network access method in which token is passed from one node
to all other nodes network before accessing the media.
 Token: It is a test frame that circulates around the network.
 Failure of any host results in failure of the whole ring. Thus, every connection in the
ring is a point of failure. There are methods which employ one more backup ring.

Ring Topology
Working of Token passing
 A token moves around the network, and it is passed from computer to computer until it
reaches the destination.
 The sender modifies the token by putting the address along with the data.
 The data is passed from one device to another device until the destination address
matches. Once the token received by the destination device, then it sends the
acknowledgment to the sender.
 In a ring topology, a token is used as a carrier.

Ring Topology
Advantages of Ring topology:
 The data being transmitted between two nodes passes through all the intermediate nodes. A
central server is not required for the management of this topology.
 The traffic is unidirectional and the data transmission is high-speed.
 In comparison to a bus, a ring is better at handling load.
 The adding or removing of network nodes is easy, as the process requires changing only two
connections.
 The configuration makes it easy to identify faults in network nodes.
 In this topology, each node has the opportunity to transmit data. Thus, it is a very organized
network topology.
 It is less costly than a star topology.

Ring Topology
Advantages of Ring topology:
 Network Management: Faulty devices can be removed from the network without
bringing the network down.
 Product availability: Many hardware and software tools for network operation and
monitoring are available.
 Cost: Twisted pair cabling is inexpensive and easily available. Therefore, the installation
cost is very low.
 Reliable: It is a more reliable network because the communication system is not
dependent on the single host computer.

Ring Topology
Disadvantages of Ring topology:
 Difficult troubleshooting: It requires specialized test equipment to determine the cable
faults. If any fault occurs in the cable, then it would disrupt the communication for all the
nodes.
 Failure: The breakdown in one station leads to the failure of the overall network.
 Reconfiguration difficult: Adding new devices to the network would slow down the
network.
 Delay: Communication delay is directly proportional to the number of nodes. Adding new
devices increases the communication delay.
 Small network: It is applicable to design small LAN with limited Computers as node.
 Less Security: Data sent from one node to another has to pass through all the intermediate
nodes. This makes the transmission slower in comparison to that in a star topology.
 The movement or changes made to network nodes affect the entire network’s performance.
 The transmission speed drops with an increase in the number of nodes.
 There is heavy dependency on the wire connecting the network nodes in the ring.

Star Topology
 Star topology is an arrangement of the network in which every node is connected to the
central hub, switch or a central computer.
 Star topology is the most popular topology in network implementation.
 Hubs or Switches are mainly used as connection devices in a physical star topology.

Star Topology
 UTP cable and RJ-45 (Registered Jack-45) connectors are used to connect the
computers.
 UTP cable CAT5 cable is required for making connection between computer and switch
using RJ45 Connector.
 The central switch is required, to connect computers.

Star Topology
Crimping Connections
1) Straight Trough Connection.
2) Cross Over Connection

Star Topology Cable connectivity between networking devices

Star Topology
Operation of HUB and Switch
Switch

Star Topology
Operation of Router in network

Star Topology
 Simple operations: Due to its centralized nature, the topology offers simplicity of operation.
 Isolate path: It also achieves isolation of each device in the network.
 Easy Updates: Adding or removing network nodes is easy, and can be done without affecting the
entire network.
 Easy fault Detect and correction: Due to the centralized nature, it is easy to detect faults in the
network devices.
 More security: As the analysis of traffic is easy, the topology poses lesser security risk.
 Traffic control: Data packets do not have to pass through many nodes, like in the case of a ring
network. Thus, with the use of a high-capacity central hub, traffic load can be handled at fairly
decent speeds.
 Limited failure/ More Reliable: As each station is connected to the central hub with its own cable,
therefore failure in one cable will not affect the entire network.
 Familiar technology: Star topology is a familiar technology as its tools are cost-effective.
 Easily expandable: It is easily expandable as new stations can be added to the open ports on the
hub.
 Cost effective: Star topology networks are cost-effective as it uses inexpensive UTP cable.
 High data speeds: It supports a bandwidth of approx. 100Mbps. Ethernet 100BaseT is one of the
most popular Star topology networks.
Advantages of Star Topology:

Star Topology
 A Central point of failure: If the central hub or switch goes down, then all the
connected nodes will not be able to communicate with each other.
 Cable: Sometimes cable routing becomes difficult when a significant amount of
routing is required.
Disadvantages of Star Topology:

Tree topology
 Tree topology is a type of network topology
in which the nodes are arranged in the
design of a tree
 Tree topology combines the characteristics
of bus topology and star topology.
 A tree topology is a type of structure in
which all the computers are connected
with each other in hierarchical fashion.
 The top-most node in tree topology is
known as a root node, and all other nodes
are the descendants of the root node.
 There is only one path exists between two
nodes for the data transmission. Thus, it
forms a parent-child hierarchy.
 As the leaf nodes can add one or more
nodes in the hierarchical chain, this
topology provides high scalability.

Tree Topology
 Support for broadband transmission: Tree topology is mainly used to provide
broadband transmission, i.e., signals are sent over long distances without being
attenuated.
 Easily expandable: We can add the new device to the existing network. Therefore, we
can say that tree topology is easily expandable.
 Easily manageable: In tree topology, the whole network is divided into segments
known as star networks which can be easily managed and maintained.
 Error detection: Error detection and error correction are very easy in a tree topology.
 Limited failure: The breakdown in one station does not affect the entire network.
 Point-to-point wiring: It has point-to-point wiring for individual segments.
Advantages of Tree Topology:

Tree Topology
 Difficult troubleshooting: If any fault occurs in the node, then it becomes difficult to
troubleshoot the problem.
 High cost: Devices required for broadband transmission are very costly.
 Failure: A tree topology mainly relies on main bus cable and failure in main bus cable
will damage the overall network.
 Reconfiguration difficult: If new devices are added, then it becomes difficult to
reconfigure.
Disadvantages of Tree Topology:

Mesh topology
 Mesh technology is an arrangement of the
network in which computers are
interconnected with each other through
various redundant connections.
 There are multiple paths from one
computer to another computer.
 It does not contain the switch, hub or any
central computer which acts as a central
point of communication.
 Mesh topology can be formed by using the
formula:
Number of cables = (n*(n-1))/2;
 Where n is the number of nodes that
represents the network.

Mesh topology in WAN / Internet
 The Internet is an example of the mesh topology.
 Mesh topology is mainly used for WAN implementations where communication failures are
a critical concern.
 Mesh topology is mainly used for wireless networks.

Types of Mesh topology
 Mesh topology is divided into two categories:
1) Fully connected mesh topology
2) Partially connected mesh topology
 Full Mesh Topology: In a full mesh
topology, each computer is connected to all
the computers available in the network.
 Partial Mesh Topology: In a partial mesh
topology, not all but certain computers are
connected to those computers with which
they communicate frequently.

Mesh Topology
 Reliable: The mesh topology networks are very reliable as if any link breakdown will
not affect the communication between connected computers.
 Fast Communication: Communication is very fast between the nodes.
 Easier Reconfiguration: Adding new devices would not disrupt the communication
between other devices.
 Less congestion: As there are several paths for communication so data can pass
through any path in network.
 Less Cost: As wireless routers can establish mess topology, hence the cost of cable is
reduced.
 Portable: Mesh topology network can be established at any location or site.
Advantages of Mesh Topology:

Mesh Topology
 Cost: A mesh topology contains a large number of connected devices such as a router
and more transmission media than other topologies.
 Management: Mesh topology networks are very large and very difficult to maintain and
manage. If the network is not monitored carefully, then the communication link failure
goes undetected.
 Efficiency: In this topology, redundant connections are high that reduces the
efficiency of the network.
 Administration: there is a need of network administration for monitoring and
maintenance of mesh network.
 Security: network can be accessed by any person if not provide security like password.
 Complex: Owing to its complexity, the administration of a mesh network is difficult.
Disadvantages of Mesh Topology:

Hybrid topology
 The combination of two or more different
topologies in one network is known as
Hybrid topology.
 A Hybrid topology is a connection between
different links (coaxial cable, CAT, optical
fiber, Wireless etc.) and nodes to transfer
the data.
 When two or more different topologies are
combined together is termed as Hybrid
topology and if similar topologies are
connected with each other will not result
in Hybrid topology. For example, if there
exist a ring topology in one branch of
ICICI bank and bus topology in another
branch of ICICI bank, connecting these
two topologies will result in Hybrid
topology.

Hybrid Topology
 Reliable: If a fault occurs in any part of the network will not affect the functioning of
the rest of the network.
 Scalable: Size of the network can be easily expanded by adding new devices without
affecting the functionality of the existing network.
 Flexible: This topology is very flexible as it can be designed according to the
requirements of the organization.
 Effective: Hybrid topology is very effective as it can be designed in such a way that the
strength of the network is maximized and weakness of the network is minimized.
Advantages of Hybrid Topology:

Hybrid Topology
 Complex design: The major drawback of the Hybrid topology is the design of the
Hybrid network. It is very difficult to design the architecture of the Hybrid network.
 Costly Hub: The Hubs used in the Hybrid topology are very expensive as these hubs
are different from usual Hubs used in other topologies.
 Costly infrastructure: The infrastructure cost is very high as a hybrid network
requires a lot of cabling, network devices, etc.
 Management: Hybrid topology networks are very large and very difficult to maintain
and manage. If the network is not monitored carefully, then the communication link
failure goes undetected.
 Administration: there is a need of network administration for monitoring and
maintenance of mesh network.
 Security: network can be accessed by any person if not provide security like password.
Disadvantages of Topology:

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OSI Reference Model
 OSI stands for Open System Interconnection is a reference model that describes how information
from a software application in one computer moves through a physical medium to the software
application in another computer.
 OSI consists of seven layers, and each layer performs a particular network function.

 OSI model was developed by the International Organization for Standardization (ISO)
in 1984, and it is now considered as an architectural model for the inter-computer
communications.
 OSI model divides the whole task into seven smaller and manageable tasks. Each layer is
assigned a particular task.
 Each layer is self-contained, so that task assigned to each layer can be performed
independently.
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OSI Reference Model
7. Application Layer
6. Presentation Layer
5. Session Layer
4. Transport Layer
3. Network Layer
2. Data Link Layer
1. Physical Layer

 The OSI model is divided into two layers: upper layers and lower
layers.
 Upper Layer:
• The upper layer of the OSI model mainly deals with the
application related issues, and they are implemented only in the
software.
• The application layer is closest to the end user. Both the end
user and the application layer interact with the software
applications.
• An upper layer refers to the combination just above lower layer.
 Lower Layer:
• The lower layer of the OSI model deals with the data transport
issues.
• The data link layer and the physical layer are implemented in
hardware and software.
• The physical layer is the lowest layer of the OSI model and is
closest to the physical medium.
• The physical layer is mainly responsible for placing the
information on the physical medium.
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Characteristics of OSI Model:
Upper layer
Lower layer

 There are the seven OSI layers.
 Each layer has different functions.
 A list of seven layers are given below:
1) Physical Layer
2) Data-Link Layer
3) Network Layer
4) Transport Layer
5) Session Layer
6) Presentation Layer
7) Application Layer
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Functions of the OSI Layers in OSI Model:

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 The main functionality of the physical layer is to transmit the individual bits from one node to
another node.
 It is the lowest layer of the OSI model.
 It establishes, maintains and deactivates the physical connection.
Physical layer
Host-1 Host-2

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 Line Configuration: It defines the way how two or more devices can be connected physically
(Wired/Wireless).
 Data Transmission: It defines the transmission mode whether it is simplex, half-duplex or
full-duplex mode between the two devices on the network.
 Topology: It defines the way how network devices are arranged.
 Signals: It determines the type of the signal used for transmitting the information.
 Encoding: Digital to Analog / Light signal conversion at sender host for respective
transmission medium Coaxial, Ethernet and Wi-Fi / Fiber Optic cable.
 Decoding: Analog / Light to Digital signal conversion at Receiver host for respective
transmission medium Coaxial, Ethernet and Wi-Fi / Fiber Optic cable.
Functions of a Physical layer:

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 Examples of hardware in the physical layer are Cables, network adapters, ethernet, repeaters,
networking hubs, switches, brides and routers etc.
Components of a Physical layer:
1) Cables 1) Connectors
Bayonet Neill–Concelman)
registered jack
1) Connectors Name
SC- subscriber connector
LC- Line Construction
FC- Ferrule Connector or
Fiber Channel
ST- straight tip

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Electromagnetic spectrum for type of signal on Transmission Medium on network

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AS per requirement of speed of data transmission Network designer have to select type of cable for
computer network

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2) Network Interface Card (NIC ) in HOST
RJ45 Connector Port
BNC Connector Port
Fiber cable Connector Port
Wi-Fi Connector Port

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3) Repeater

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4) HUB

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5) Switch

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7) Bridge

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6) Bridge

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6) Router

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Router

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6) Router works in Unicast an Multicast Mode

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7) Gateway

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Repeater
1) Repeater
/ Hub
2) Switch
3) Router
4) Gateway

1) Physical characteristics of interfaces and medium : the purpose of the physical
layer is to transport a raw bit stream from one machine to another.
 Various physical media can be used for the actual transmission.
 Each one has its own position in terms of bandwidth, delay, cost, and ease of
installation and maintenance.
2) Representation of bits : The physical layer data consists of a stream of bits
(sequence of 0’s or 1’s) with no interpretation.
 To be transmitted, bits must be encoded into signals--electrical or optical.
 The physical layer defines the type of encoding (how 0’s and 1’s are changed to
signals).
3) Data rate : The transmission rate-the number of bits sent each second-is also defined
by the physical layer. In other words, the physical layer defines the duration of a bit,
which is how long it takes for transmission over transmission medium.
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Functions of a Physical layer in details:
Major duties of the physical layer are as follows :

4) Synchronization of bits : The sender and receiver not only must use the same bit
rate but also must be synchronized at the bit level.
 In other words, the sender and the receiver clocks must be
synchronized.
5) Line configuration : The physical layer is concerned with the connection of
devices to the media.
 In a point-to-point configuration, two devices are connected through a dedicated
link.
 In a multipoint configuration, a link is shared among several devices.
6) Physical topology : The physical topology defines how devices are connected to
make a network.
 Devices can be connected by using a mesh topology (every device is connected to
every other device)
 A star topology (devices are connected through a central device)
 A ring topology (each device is connected to the next, forming a ring)
 A bus topology (every device is on a common link)
 A hybrid topology (this is a combination of two or more topologies).
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7) Transmission mode : The physical layer also defines the direction of
transmission between two devices:
 Simplex
Half-duplex
Full-duplex.
In simplex mode, only one device can send and the other
canonly receive. The simplex mode is a one-way communication.
In the half-duplex mode, two devices can send and receive, but not
at the same time.
In a full-duplex (or simply duplex) mode, two devices can send and
receive at the same time.
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 Media is a general term used to describe the data path that forms
the physical channel between sender and receiver.
 Transmission media can be twisted pair wire such as that used for
telephone installation, wire media are referred to as Bounded Media
and wireless media are sometimes referred to as Unbounded Media.
 Bandwidth, noise, radiation and attenuation are considered while
using the different transmission media.
 Higher bandwidth transmission media supports higher data rates.
 Attenuation limits the usable distance that data can travel on the
media.
 Noise is related to electrical signal noise that can cause distortion of
the data signal and data errors.
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14
 Radiation is the leakage of signal from the media caused
by undesirable electrical characteristic of the transmission media.
 The transmission medium is the physical path between transmitter and receiver in a
data transmission system.
 In transmission medium, communication is in the form of electromagnetic waves.
 The characteristics and quality of transmission are determined both bythe
characteristics of the medium and the characteristics of signal.

 Design Factors:
◦ Bandwidth : The greater the bandwidth the higher the data rate can be
achieved.
◦ Transmission Impairments : such as attenuation, limit the distance
(repeater spacing) for guided media. Twisted pair generally suffer more
impairment than co-axial cable.
◦ Interference
◦ Number of Receivers
 Guided or Unguided Media :
◦ Depending on the type of application and geographical situation
suitable guided or unguided media is chosen.
◦ For long distance point-to-point transmission guided media are suitable.
◦ For long distance broadcasting transmission unguided media are chosen.
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 TP is least expensive and most widely used.
 TP consists of two insulated copper wire arranged in regular spiral pattern.
 A wire pair act as a signal communication link.
 TP may used to transmit both analog and digital signals.
 For analog signal amplifiers are required about every 5 to 6 km. for digital signals,
repeaters are required every 2 or 3 km.
 TP is most commonly used medium for in the telephone network.
 Compared to other commonly used transmission media, TP is limited in distance,
bandwidth and data rate when two copper wire conduct electric signal in close
proximity, a certain amount of electromagnetic inference occurs (EMI). This type of
inference is called Cross Talk. Twisting the copper wire reduces cross talk.
 Twisted pair cable comes in two varieties.
 Unshielded twisted pair (UTP) cable.
 Shielded twisted pair (STP) cable.

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 UTP is a set of twisted pairs of cable within a plastic sheet. UTP is ordinary telephone wire.
 This is the least expensive of all the transmission media commonly used for LAN, and is
easy to work with and simple to install.
 UTP is subject to external electromagnetic inference.
 Category 3 and category 5 UTP are commonly used in computer networks.
 UTP can transfer data at 1 to 100 Mbps over a distance of 100 meters.
 The difference between cat3 and cat5 cable is the number of twists in the cable per unit
distance cat5 is much more tightly twisted.
 TP cable contains eight separate wires with four pairs.
 Four of them are solid colors (Blue, Green, Orange and Brown), while the other four are
striped with white.

 Category 5 : Used in local network. It supports upto 100 Mbps data transmission speed.
 Category 4 : It support transmission speed of 16 Mbps and three twist per foot.
 Category 3 : It supports data transmission speed upto 10 Mbps. Atleast three twist per feet
and used in telephone system.
 Category 2 : It supports data transmission speed upto 4 Mbps and suitable for voice data
transmission.
 Category 1 : mostly used in telephone system. Cat1 is suitable for voice and low speed
data communication.
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CHARACTERISTICS OF UTP :
 Transmission rate of 10-100 Mbps.
 UTP is less expensive than FOC and co-axial cable.
 Maximum cable segment of UTP is 100 meters.
 UTP cable is very flexible and easy to work.
 Most susceptible to electrical interference or cross talk.
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ADVANTAGES OF UTP:
 UTP is easy to terminate.
 Cost of installation is less.
 High installed base.
DISADVANTAGES OF UTP :
 It is very noisy.
 It covers less distance.
 UTP suffers from interference.

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APPLICATION OF TP CABLES :
 Twisted Pair can used for both analog and digital signals.
 Twisted Pair cable are used in telephone network.
 In LAN, TP wires mainly use for low cost, low performance application.
 STP offers a protective sheathing around the copper wire. STP provides better performance
at lower data rates. They are not commonly used in networks.
 Installation of STP is easy. Special connectors are required for installation.
 Cost is moderately expensive.
 Distance is limited to 100 meters for 500 meters.
 STP suffers from outside interference but not as much UTP.

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 RJ45 is a type of connector commonly used for Ethernet networking.
 It looks similar to a telephone jack, but is slightly wider.
 Since Ethernet cables have an RJ45 connector on each end,
 Ethernet cables are sometimes also called RJ45 cables.
 The "RJ" in RJ45 stands for "registered jack," since it is a standardized networking
interface.
 Each RJ45 connector has eight pins, which means an RJ45 cable contains eight separate
wires.
 Four of them are solid colors (Blue, Green, Orange and Brown), while the other four are
striped with white.
Connector for Twisted Pair Cable RJ45

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Crimping of Twisted Pair Cable RJ45
Click to see the video
Click to see how to Crimp Twisted Pair Cable with RJ45 connector
RJ45 cables can be wired in two different ways. One version is called T-568A and the other is
T-568B. These wiring standards are listed below:

 It is made up of two conductors that shares the common axis.
 It consists of a hollow outer cylindrical conductor that surrounds a single inner wire
conductor.
 Coaxial cable is used to transmit both analog
and digital signals.
 Data transfer rate of coaxial cable is in between
TP and FOC.
 It is relatively inexpensive.
 The cost for thin coaxial cable is less than STP.
 Thick coaxial cable must be grounded and
terminated.
 A typical data rate for today’s coaxial network is
10 Mbps, although potential is higher.
 It suffers from attenuation.

 Coaxial cable is classified by size (RG) and by
the cable resistance to direct or alternative
electric currents.
 RG means Rating Government.
 50 ohm, RG-8 and RG-11 for thick
Ethernet.
 50 ohm, RG-58 used for thin Ethernet.
 75 ohm, RG-59 used for cable TV.
 93 ohm, RG-62 used for ARC net

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CHARACTERISTICS OF CO-AXIAL CABLE :
 10 Mbps is transmission rate.
 Maximum cable length for thinnet is 185 meters and thicknet is 500 meters.
 Flexible and easy to work with thinnet for small distance.
 Ethernet designation to 10 base 2 (thinnet) or 10 base 5 (thicknet).
 Less expensive than FOC but more expensive than TP.
 Good resistance to electrical interference.
APPLICATION OF CO-AXIAL CABLE :
 In analog and digital transmission.
 In telephone networks.
 In Ethernet LANs.
 In cable TV network.

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ADVANTAGES OF CO-AXIAL CABLE :
 Coaxial cable used for both data transmission i.e. analog and digital
data transmission.
 It has higher bandwidth.
 Easy to handle and relatively inexpensive as compared to FOC.
 It uses for longer distance at higher data rates.
 Excellent noise immunity.
DISADVANTAGES OF CO-AXIAL CABLE :
 Distance is limited.
 Number of nodes connection is limited.
 Proper connectors and termination is must.

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 Coaxial cable connectors are used to connect cables to other devices.
 High-quality connectors offer reliable, long-lasting connections.
 There are two distinct connector styles; male and female.
 Male connectors have a protruding metal pin in the center, whereas female connectors have
a receptacle to receive that pin.
 Within digital, video, audio, RF, and microwave industries, there are several varieties of
coaxial cable connector types.
Type of Connectors for Coaxial cable
 Following are the types of Coaxial Cables,
1) BNC Bayonet Neil-Concelman (BNC)-
i. Originally designed for military use.
ii. The coaxial connector used for quick connect/disconnect in RF equipment and test
instruments like radio, television, and video signal.
iii. are best suited for frequencies below 4GHz,

89
Type of Connectors for Coaxial cable
2) TNC Threaded Neil-Concelman (TNC)-
i. It is the threaded version of a BNC connector.
ii. It performs better microwave frequencies than BNC connectors.
iii. TNC Connectors are weatherproof, miniature units that operate up to 12 GHz and are
commonly used in cellular phone and RF/antenna connections to resolve leakage and stability
issues

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Striping of Coaxial Cable RJ45
Click to see the video
Click to see how to striping coaxial Cable
with BNC connector

 Fiber optic cable is a cable that uses light signals for communication.
 Fiber optic is a cable that holds the optical fibers coated in plastic that are used to send the data by
pulses of light.
 Fiber optics provide faster data transmission than copper wires. It is a light pipe which is used to
carry a light beam from one place to another place.
 Light is an electromagnetic signal and can be modulated by information. since the frequency of light
is extremely high hence it can be achieved with excellent reliability.
 The modulated light travel along the fiber and at the far end, are converted to an electrical signal by
means of a photo electric cell. Thus the original input signal is recovered at the far end.
91

Basic elements of Fiber optic cable:
 Core: The optical fiber consists of a narrow strand of glass or plastic known as a core. A core is a
light transmission area of the fiber. The more the area of the core, the more light will be transmitted
into the fiber.
 Cladding: The concentric layer of glass is known as cladding. The main functionality of the cladding
is to provide the lower refractive index at the core interface as to cause the reflection within the core
so that the light waves are transmitted through the fiber.
 Jacket(Buffer): The protective coating consisting of plastic is known as a jacket. The main purpose
of a jacket is to preserve the fiber strength, absorb shock and extra fiber protection.
92

 FOC transmits light signal rather than electrical signals. Each fiber has a inner
core of glass or plastic that conducts light. the inner core is surrounded by
cladding, a layer of glass that reflects the light back into core.
 A cable may contain a single fiber, but often fibers are bundled together in the
centre of the cable.
 FOC may be multimode or signal mode. Multimode fibers use multiple light paths
whereas signal mode fibers allow a single light path and are typically used with
laser signaling. It is more expansive and greater bandwidth.
93

1) Plastic Core and Plastic Cladding
2) GlassCore with Plastic Cladding (often called PCS fiber, plastic-clad silica)
3) Glass Core and Glass Cladding.
94
 Plastic fibers have several advantages over glass fibers.
 Plastic fibersare more flexible and, consequently,
more rugged than glass.
 They are easy to install, can better withstand stress, are
less expensive, and weight approximately 60% less than
glass.
 The disadvantages of plastic fibersis their high
attenuation characteristics; they do not propagate light
as efficiently as glass.
 Plastic fibers are limited to relatively short runs, such
as within a single building or a building complex.
1) Plastic Core and Plastic Cladding

95
 Fibers with glass cores exhibit low attenuation characteristics.
 PCS fibers are slightly better than SCS fibers.
 PCS fibers are less affected by radiation and are therefore more attractive to
military applications.
2) PCS- Class Core and Plastic Cladding

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 SCS fiber have the best
propagation characteristics and
they are easier to terminate than
PCS fibers.
 SCS cables are the least rugged,
and they are more susceptible to
increase in attenuation when
exposed to radiation.
 The selection of fiber for a given
application is a function of specific
system requirements. They are
always trade-offs based on the
economics and logistics of a
particular application.
3) Glass Core and Glass Cladding.

 Transmission rate of 100 Gbps.
 Not affected by the electrical interference.
 Most expensive cable.
 FOC support cable length of 10 km or more.
 It supports voice, video and data.
 It provides most secure media.
 Commonly used as backbones between buildings and token
ring networks.
 Not very flexible, difficult to work.
97

 Wide Bandwidth
 Low Losses
 Immune to Cross Talk
 Interference Immune
 Lightweight
 Small Size
 More Strength
 Security
 Long Distance Transmission
 Environment Immune
 Safe and Easy Installation
 Reliable
 Accuracy
98

High Initial Cost :
 The initial installation or setting up cost is very high compared to
all other systems.
Maintenance and Repairing Cost :
 The maintenance and repairing of fiber optics systems is not only
difficult but expensive also.
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Clicking for video to attach Fiber cable to connectors
Terminate The Fiber optical cable to connector

100
Types of Fiber Optical Cable
Connectors
• SC- subscriber connector
• ST- straight tip
• LC- Line Construction
• FC- Ferrule Connector or Fiber Channel
The main difference between APC and UPC connectors is the fiber endface. APC connectors feature a
fiber endface that is polished at an eight-degree angle; UPC connectors are polished with no angle.

101
 An unguided transmission transmits the electromagnetic waves without using any
physical medium. Therefore it is also known as wireless transmission.
 In unguided media, air is the media through which the electromagnetic energy can flow
easily.
 Unguided transmission is broadly classified into three categories:
1) Radio waves 2) Microwaves 3) Infrared

 Radio waves are the electromagnetic waves that are transmitted in all the directions of free space.
 Radio waves are omnidirectional, i.e., the signals are propagated in all the directions.
 The range in frequencies of radio waves is from 10 Khz to 1 Ghz.
 In the case of radio waves, the sending and receiving antenna are not aligned, i.e., the wave sent by
the sending antenna can be received by any receiving antenna.
 An example of the radio wave is FM radio.
 Radio waves includes following types :
i. Short wave.
ii. Very High Frequency (VHF) television and FM radio.
iii. Ultra High Frequency (UHF) radio and television.
 Various kind of antennas can be used to broadcast radio signals.
 The power of the radio frequency signal is determined by the antenna and transreceiver (a
device that transmit and receive a signal over a medium such a copper, radio waves, or fiber
optic cables). 103

 Radio waves are easy to generate.
 They can travel long distances.
 They can penetrate building easily so they are widely used for
communication both indoor and outdoors.
 Radio waves are omni directional.
 The properties of radio waves are frequency dependent. At low
frequencies, radio waves pass through obstacles well, but the power
falls off sharply with distance from the source.
 At high frequencies, radio waves are subject to interference from motors
and other electrical equipment.
 Low frequency and medium frequency range cannot be used for data
transfer because of their very small bandwidth.
104

 A Radio wave is useful for multicasting when there is one sender and
many receivers.
 An FM radio, television, cordless phones are examples of a radio wave.
105
Applications Of Radio waves:
 Radio transmission is mainly used for wide area networks and mobile
cellular phones.
 Radio waves cover a large area, and they can penetrate the walls.
 Radio transmission provides a higher transmission rate.
Advantages Of Radio transmission:

Microwaves are of two types:
 Terrestrial microwave
 Satellite microwave communication.
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Microwaves

 Terrestrial Microwave transmission is a technology that transmits the focused beam of a radio
signal from one ground-based microwave transmission antenna to another.
 Microwaves are the electromagnetic waves having the frequency in the range from 1GHz to 1000
GHz.
 Microwaves are unidirectional as the sending and receiving antenna is to be aligned, i.e., the waves
sent by the sending antenna are narrowly focused.
 In this case, antennas are mounted on the towers to send a beam to another antenna which is km
away.
 It works on the line of sight transmission, i.e., the antennas mounted on the towers are the direct
sight of each other.
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Terrestrial Microwave Transmission

 Frequency range: The frequency range of terrestrial microwave is from 4-6 GHz to 21-23 GHz.
 Bandwidth: It supports the bandwidth from 1 to 10 Mbps.
 Short distance: It is inexpensive for short distance.
 Long distance: It is expensive as it requires a higher tower for a longer distance.
 Attenuation: Attenuation means loss of signal. It is affected by environmental conditions and
antenna size.
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Characteristics of Microwave:

109
Design of Microwave Communication

110
Design of Microwave Communication

 Microwave transmission is cheaper than using cables.
 It is free from land acquisition as it does not require any land for the installation
of cables.
 Microwave transmission provides an easy communication in terrains as the
installation of cable in terrain is quite a difficult task.
 Communication over oceans can be achieved by using microwave transmission.
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Advantages Of Microwave:

112
Disadvantages Of Microwave:
 Eavesdropping: An eavesdropping creates insecure communication. Any
malicious user can catch the signal in the air by using its own antenna.
 Out of phase signal: A signal can be moved out of phase by using microwave
transmission.
 Susceptible to weather condition: A microwave transmission is susceptible to
weather condition. This means that any environmental change such as rain,
wind can distort the signal.
 Bandwidth limited: Allocation of bandwidth is limited in the case of microwave
transmission.

 Mobile telephone network uses microwave communication.
 Wireless LAN.
 Point-to-point communication between stations.
 Line –of sight communication.
113

114
Satellite Microwave Communication
 A satellite is a physical object that revolves around the earth at a known height.
 Satellite communication is more reliable nowadays as it offers more flexibility than cable
and fiber optic systems.
 We can communicate with any point on the globe by using satellite communication.
 How Does Satellite work?
The satellite accepts the signal that is transmitted from the earth station, and it
amplifies the signal. The amplified signal is retransmitted to another earth station.

115
Advantages Of Satellite Microwave Communication:
 The coverage area of a satellite microwave is more than the terrestrial microwave.
 The transmission cost of the satellite is independent of the distance from the centre of the
coverage area.
 Satellite communication is used in mobile and wireless communication applications.
 It is easy to install.
 It is used in a wide variety of applications such as weather forecasting, radio/TV signal
broadcasting, mobile communication, etc.

116
Disadvantages Of Satellite Microwave Communication:
 Satellite designing and development requires more time and higher cost.
 The Satellite needs to be monitored and controlled on regular periods so that it remains
in orbit.
 The life of the satellite is about 12-15 years. Due to this reason, another launch of the
satellite has to be planned before it becomes non-functional.

 An infrared transmission is a wireless technology used for communication over
short ranges.
 The frequency of the infrared in the range from 300 GHz to 400 THz.
 It is used for short-range communication such as data transfer between two cell
phones, TV remote operation, data transfer between a computer, VCR and stereos
all use infrared communication and cell phone resides in the same closed area.
 They do not pass through solid objects.
 An infrared system in one room of a building will not interfere with a similar
system in adjacent rooms.
 Infrared light is suitable for indoor wireless.
117

 It supports high bandwidth, and hence the data rate will be very high.
 Infrared waves cannot penetrate the walls. Therefore, the infrared communication
in one room cannot be interrupted by the nearby rooms.
 An infrared communication provides better security with minimum interference.
 Infrared communication is unreliable outside the building because the sun rays
will interfere with the infrared waves.
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Characteristics Of Infrared:

The data link layer is responsible for moving frames from one hop (node) to the next.
119
 This layer is responsible for the error-free transfer of data frames.
 It defines the format of the data on the network.
 It provides a reliable and efficient communication between two or more devices.
 It is mainly responsible for the unique identification of each device that resides on a
local network.

The data link layer is responsible for moving frames from one hop (node) to the next.
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 The Data Link Layer protocols are Ethernet, token ring, FDDI and PPP.
 An important characteristic of a Data Link Layer is that datagram can be handled by
different link layer protocols on different links in a path. For example, the datagram is
handled by Ethernet on the first link, PPP on the second link.

121
It contains two sub-layers:
1) Logical Link Control Layer
 It is responsible for transferring the packets to the Network layer of the receiver that is
receiving.
 It identifies the address of the network layer protocol from the header.
 It also provides flow control.
2) Media Access Control Layer
 A Media access control layer is a link between the Logical Link Control layer and the
network's physical layer.
 It is used for transferring the packets over the network.

122
It contains two sub-layers:
1) Logical Link Control Layer
2) Media Access Control Layer

▶Following services are provided by the Data Link Layer:
123
Functions of the Data-link layer

Framing.
124

Framing.
125
 The data link layer divides the stream of bits received from the network layer into
manageable data units called frames.
 The DLL breaks the stream into discrete frames and computes the checksum for each
frames.
 At the destination the checksum is recomputed.
 At breaking of bit stream by inserting spaces or time gaps is called framing.
 Since it is difficult and risky to count on timing and mark the start and end of each
frame, various simple method used for framing are,
 Character count
 Starting and ending character, with character stuffing.
 Starting and ending flags, with bit stuffing.

 Physical addressing: The Data link layer adds a header to the frame that contains a
destination address. The frame is transmitted to the destination address mentioned in
the header. If the frame is intended for a system outside the sender's network, the
receiver address is the address of the device that connects the network to the next one
126

127
Flow control
1) Rate Based Flow Control: If the rate at which the data are absorbed by the receiver is
less than the rate at which data are produced in the sender, the data link layer imposes
a flow control mechanism to avoid overwhelming the receiver.
2) Feedback based flow control: Flow control mechanism is incorporated which includes a
feedback mechanism requesting transmitter a retransmission of incorrect message block.

128
1) Stop and Wait Flow control
The primitives of stop and wait protocol are:
Sender side
Rule 1: Sender sends one data packet at a time.
Rule 2: Sender sends the next packet only when it
receives the acknowledgment of the previous packet.
Therefore, the idea of stop and wait protocol in the
sender's side is very simple, i.e., send one packet at a
time, and do not send another packet before receiving
the acknowledgment.
Receiver side
Rule 1: Receive and then consume the data packet.
Rule 2: When the data packet is consumed, receiver
sends the acknowledgment to the sender.
Therefore, the idea of stop and wait protocol in the
receiver's side is also very simple, i.e., consume the
packet, and once the packet is consumed, the
acknowledgment is sent. This is known as a flow
control mechanism.

129
1) Disadvantages of Stop and Wait protocol
1. Problems occur due to lost data 2. Problems occur due to lost acknowledgment

130
1) Disadvantages of Stop and Wait protocol
3. Problem due to the delayed data or
acknowledgment
Delay in ACK
 The most common retransmission
technique is known as Automatic Repeat
Request.
 Retransmission of data in three cases :
 Damaged frames
 Lost frames
 Lost acknowledgements.

131
Sliding Window Flow control
 The sliding window is a technique for sending multiple frames at a time. It controls the data packets
between the two devices where reliable and gradual delivery of data frames is needed.
 In this technique, each frame has sent from the sequence number. The sequence numbers are used
to find the missing data in the receiver end. The purpose of the sliding window technique is to avoid
duplicate data, so it uses the sequence number.

132
Types of Sliding Window Flow control
 Go-Back-N ARQ
 Selective Repeat ARQ
Go-Back-N ARQ

133
Types of Sliding Window Flow control
 Go-Back-N ARQ
 Selective Repeat ARQ
Selective Repeat ARQ

Error Detection:
134
 When data is transmitted from one device to another device, the system does not
guarantee whether the data received by the device is identical to the data transmitted
by another device.
 An Error is a situation when the message received at the receiver end is not identical to
the message transmitted.
 Due to error the data Integrity features lost in data communication.
 Data integrity refers to the accuracy and consistency (validity) of data over its
lifecycle.
 Errors can be introduced by signal attenuation and noise.
 It also uses a mechanism to recognize duplicate frames.
 Data Link Layer protocol provides a mechanism to detect one or more errors.
 This is achieved by adding error detection bits in the frame and then receiving node can
perform an error check.
 The data link layer adds reliability to the physical layer by adding mechanisms to
detect and retransmit damaged or lost frames.

Error Detection:
135
Types Of Errors Error Detection Techniques
Errors can be classified into two categories:
i. Single-Bit Error
ii. Burst Error

Error Detection:
136
Types Of Errors Error
1) Single-Bit Error:
 The only one bit of a given data unit is changed from 1 to 0 or from 0 to 1.
 In the following figure, the message which is sent is corrupted as single-bit, i.e., 0 bit is changed to 1.
 Single-Bit Error does not appear more likely in Serial Data Transmission. For example,
Sender sends the data at 10 Mbps, this means that the bit lasts only for 1 ?s and for a single-bit
error to occurred, a noise must be more than 1 ?s.
 Single-Bit Error mainly occurs in Parallel Data Transmission. For example, if eight wires are
used to send the eight bits of a byte, if one of the wire is noisy, then single-bit is corrupted per
byte.

Error Detection:
137
Types Of Errors Error
2) Burst Error:
 The two or more bits are changed from 0 to 1 or from 1 to 0 is known as Burst Error.
 The Burst Error is determined from the first corrupted bit to the last corrupted bit..
 The duration of noise in Burst Error is more than the duration of noise in Single-Bit.
 Burst Errors are most likely to occurr in Serial Data Transmission.
 The number of affected bits depends on the duration of the noise and data rate.

Error Detection:
138
Error Detecting Techniques:
The most popular Error Detecting Techniques are:
a) Single parity check / Vertical Redundancy Check (VRC)
b) Two-dimensional parity check /Longitudinal Redundancy Check (LRC)
c) Checksum
d) Cyclic redundancy check

Error Detection:
139
1) Single-Bit Error Detection: Parity Check / Vertical Redundancy Check (VRC)
 It is also known as Vertical Redundancy Check (VRC) or Parity Check

Error Detection:
140
 If even number of bits are changed during transmission the Vertical Redundancy
Check (VRC) or Parity Check

Error Detection:
141
Examples of Single-Bit Error Detection: Parity Check / Vertical Redundancy Check (VRC)

Error Detection:
142
Advantages :
 Parity bit/ VRC can detect all single bit error.
 The major disadvantage of using this method for error detection is that it is not able to
detect burst error if the number of bits changed is even, i.e. 2, 4, 6, 8, …….etc.
Disadvantages :
It can also detect burst errors but only in those cases where number of bits changed is odd,
i.e. 1, 3, 5, 7, …….etc.

Error Detection:
143
2) Two-Dimensional Parity Check / Longitudinal Redundancy Check (LRC) :
At Sender / Transmitter End

Error Detection:
144
At Receiver End

Error Detection:
145
 Performance can be improved by using Two-Dimensional Parity / Longitudinal Redundancy
Check which organizes the data in the form of a table.
 In Two-Dimensional Parity check / Longitudinal Redundancy Check, a block of bits is divided
into rows.
 Parity check bits are computed for each column, which is equivalent to the single-parity check
for that column.
 In order to detect an error, a redundant bits(Parity bits / LRC) are added to the whole data block
and this block is transmitted to receiver.
 The receiver uses this redundant row to detect error.
 At the receiving end, the column-wise parity bits /LRC are again computed the received data.
 The incoming parity bits are compared with the computed parity bits from at receiver.
 After checking the data for errors, receiver accepts the data and discards the redundant row of
bits.

Error Detection:
146
Advantage :
 LRC is used to detect burst errors.
Disadvantage :
 The main problem with LRC is that, it is not able to detect error if even no of bits in a data unit
same columns are changed /damaged.
Example : If data 110011 010101 is changed to 010010110100.

Error Detection:
147
Examples of Single-Bit Error Detection: Parity Check

Error Detection:
148
Drawback of Two-Dimensional Parity Check
 If two bits in one data unit are corrupted
and two bits exactly the same position
in another data unit are also corrupted,
then 2D Parity checker will not be able
to detect the error.
 This technique cannot be used to detect
the 4-bit errors or more in some cases.

Error Detection:
149
3) Checksum Error Detection
 A Checksum is an error detection technique based on the concept of redundancy.

Error Detection:
150
Checksum
 A Checksum is an error detection technique based on the concept of redundancy.
 It is divided into two parts:
i. Checksum Generator ii. Checksum Checker

Error Detection:
151
Checksum Error Detection Algorithm at Sender and Receiver
Checksum Generator
The Sender follows the given steps:
i. The block unit is divided into k
sections, and each of n bits.
ii. All the k sections are added together
by using one's complement to get the
sum.
iii. The sum is complemented and it
becomes the checksum field.
iv. The original data and checksum field
are sent across the network.
Checksum Checker
The Receiver follows the given steps:
i. The block unit is divided into k
sections and each of n bits.
ii. All the k sections are added together
by using one's complement algorithm
to get the sum.
iii. The sum is complemented.
iv. If the result of the sum is zero, then
the data is accepted otherwise the data
is discarded.

Error Detection:
152
Find Error by check sum method for following data

Error Detection:
153
4) Cyclic redundancy check Error Detection
 CRC is a
redundancy error
technique used to
determine the
burst error in
data transmission
in computer
network.

Error Detection:
154
 CRC is a redundancy error technique used to determine the error in data transmission in
computer network.
 Cyclic Redundancy Check (CRC) is an error detection method.
 It is based on binary division.
CRC Generator-
 CRC generator is an algebraic polynomial represented as a bit pattern.
 Consider the CRC generator is x7 + x6 + x4 + x3 + x + 1.
 Bit pattern is obtained from the CRC generator using the following rule-
 The power of each term gives the position of the bit and the coefficient gives the
value of the bit.
 The corresponding binary pattern is obtained as-

Error Detection:
155
Cyclic Redundancy Check Algorithm at Sender and Receiver
At Sender Side
1) Sender has a generator G(x)
polynomial.
2) Sender appends (n-1) zero bits to the
data.
Where n= no of bits in generator
3) Dividend appends the data with
generator G(x) using modulo 2
division (arithmetic).
4) Remainder of (n-1) bits will be CRC.
At Receiver Side
1) Receiver has same generator G(x).
2) Receiver divides received data (data
+ CRC) with generator.
3) If remainder is zero, data is
correctly received.
4) Else, there is error.

Error Detection:
156
 A Cyclic redundancy is an error detection technique based on the concept of
Appended data bits(i.e.000…), Divisor and cyclic redundancy check (CRC).

Error Detection:
157
 Examples to solve:
Problem-01: A bit stream 1101011011 is transmitted using the standard CRC method.
The generator polynomial is x4+x+1. What is the actual bit string transmitted?
Solution-
 The generator polynomial G(x) = x4 + x + 1 is encoded as 10011.
 Clearly, the generator polynomial consists of 5 bits.
 So, a string of 4 zeroes is appended to the bit stream to be transmitted.
 The resulting bit stream is 11010110110000.
Now, the binary division is performed as-

Error Detection:
158
From here, CRC = 1110.
Now,
The code word to be transmitted is obtained by
replacing the last 4 zeroes of
11010110110000 with the CRC.
Thus, the code word transmitted to the receiver
= 11010110111110.

Error Detection:
159
Problem-02: A bit stream 10011101 is transmitted using the standard CRC method. The
generator polynomial is x3+1.
1) What is the actual bit string transmitted?
2) Suppose the third bit from the left is inverted during transmission. How
will receiver detect this error?
Solution-
Part-01:
 The generator polynomial G(x) = x3 + 1 is encoded as 1001.
 Clearly, the generator polynomial consists of 4 bits.
 So, a string of 3 zeroes is appended to the bit stream to be transmitted.
 The resulting bit stream is 10011101000.
Now, the binary division is performed as-

Error Detection:
160
From here, CRC = 100.
Now,
 The code word to be transmitted is obtained by
replacing the last 3 zeroes of 10011101000 with
the CRC.
 Thus, the code word transmitted to the receiver =
10011101100.

Error Detection:
161
Problem-02: A bit stream 10011101 is transmitted using the standard CRC method. The
generator polynomial is x3+1.
1) What is the actual bit string transmitted?
2) Suppose the third bit from the left is inverted during transmission. How
will receiver detect this error?
Solution- The code word transmitted to the receiver = 10011101100.
Part-02: According to the question,
 Third bit from the left gets inverted during transmission.
 So, the bit stream received by the receiver = 10111101100.
Now,
 Receiver receives the bit stream = 10111101100.
 Receiver performs the binary division with the same generator polynomial as-

Error Detection:
162
From here,
 The remainder obtained on division is a non-zero
value.
 This indicates to the receiver that an error occurred
in the data during the transmission.
 Therefore, receiver rejects the data and asks the
sender for retransmission.

Error Detection:
163
Properties Of CRC Generator- The algebraic polynomial chosen as a CRC generator should
have at least the following properties-
Rule-01:
 It should not be divisible by x.
 This condition guarantees that all the burst errors of length equal to the length of
polynomial are detected.
Rule-02:
 It should be divisible by x+1.
 This condition guarantees that all the burst errors affecting an odd number of bits are
detected.

Error Correction.
164
 Error Correction codes are used to detect and correct the errors when data is
transmitted from the sender to the receiver.
 Error Correction can be handled in two ways:
1) Backward error correction / Error Control: Once the error is discovered, the
receiver requests the sender to retransmit the entire data unit.
2) Forward error correction: In this case, the receiver uses the error-correcting
code which automatically corrects the errors.

Error Correction.
165
Categories of Error Control:

Error Correction.
166
1) Backward error correction / Error Control:
i) Stop-and-wait ARQ
 Stop-and-wait ARQ is a technique used to
retransmit the data in case of damaged or lost
frames.
 This technique works on the principle that the
sender will not transmit the next frame until it
receives the acknowledgement of the last
transmitted frame.
Two possibilities of the retransmission:
i. Damaged Frame – (case of Error correction)
ii. Lost Frame - (case of flow control)

Error Correction. : Backward error correction / Error Control:
167
Four features are required for the retransmission:
1) The sending device keeps a copy of the last transmitted
frame until the acknowledgement is received. Keeping the
copy allows the sender to retransmit the data if the frame is
not received correctly.
2) Both the data frames and the ACK frames are numbered
alternately 0 and 1 so that they can be identified
individually. Suppose data 1 frame acknowledges the data 0
frame means that the data 0 frame has been arrived
correctly and expects to receive data 1 frame.
3) If an error occurs in the last transmitted frame, then the
receiver sends the NAK frame which is not numbered. On
receiving the NAK frame, sender retransmits the data.
4) It works with the timer. If the acknowledgement is not
received within the allotted time, then the sender assumes
that the frame is lost during the transmission, so it will
retransmit the frame.
Stop-and-wait ARQ

Error Correction.
168
ii) Sliding Window ARQ
 Sliding Window ARQ is a technique used for
continuous transmission error control.
Two protocols used in sliding window ARQ:
1) Go-Back-n ARQ
2) Selective-Reject ARQ

Error Correction. : Backward error correction / Error Control:
169
Three Features used for retransmission:
1. In this case, the sender keeps the copies of all the transmitted
frames until they have been acknowledged. Suppose the frames
from 0 through 4 have been transmitted, and the last
acknowledgement was for frame 2, the sender has to keep the copies
of frames 3 and 4 until they receive correctly.
2. The receiver can send either NAK or ACK depending on the
conditions. The NAK frame tells the sender that the data have been
received damaged. Since the sliding window is a continuous
transmission mechanism, both ACK and NAK must be numbered for
the identification of a frame. The ACK frame consists of a number
that represents the next frame which the receiver expects to receive.
The NAK frame consists of a number that represents the damaged
frame.
3. The sliding window ARQ is equipped with the timer to handle the
lost acknowledgements. Suppose then n-1 frames have been sent
before receiving any acknowledgement. The sender waits for the
acknowledgement, so it starts the timer and waits before sending
any more. If the allotted time runs out, the sender retransmits one
or all the frames depending upon the protocol used.
Sliding Window ARQ

Error Correction.
170
Categories of Error Control- Sliding Window ARQ- :
i) Go-Back-n ARQ: In Go-Back-N ARQ protocol, if one frame is lost or damaged, then it
retransmits all the frames after which it does not receive the positive ACK.
Three possibilities can occur for
retransmission:
1) Damaged Frame (Case of Error
Correction)
2) Lost Data Frame (case of flow
control)
3) Lost Acknowledgement(case of
flow control)

Error Correction.
171
Categories of Error Control: Sliding Window ARQ-
ii) Selective-Reject ARQ: Selective-Reject ARQ
technique is more efficient than Go-Back-n
ARQ.
 In this technique, only those frames are
retransmitted for which negative
acknowledgement (NAK) has been received.
 The receiver storage buffer keeps all the
damaged frames on hold until the frame in
error is correctly received.
 The receiver must have an appropriate logic
for reinserting the frames in a correct order.
 The sender must consist of a searching
mechanism that selects only the requested
frame for retransmission.

Error Correction.
172
2) Forward error correction: In this case, the receiver uses the error-correcting code
which automatically corrects the errors.
Hamming Code Error correction
 Hamming code is a error-correction codes that can be used to detect and correct the
errors that can occur when the data is moved or stored from the sender to the receiver.
 It is technique developed by R.W. Hamming for error correction.
 Redundant bits –
 Redundant bits are extra binary bits that are generated and added to the information-
carrying bits of data transfer to ensure that no bits were lost during the data transfer.
 The number of redundant bits can be calculated using the following formula:
2r ≥ m + r + 1 where, r = redundant bit, m = data bit
 e.g. Suppose the number of data bits is 7, then the number of redundant bits can be
calculated using:
2
4
≥ 7 + 4 + 1 i.e. 16 ≥ 12
Thus, the number of redundant bits= 4

Error Correction.
173
Hamming Code Error Correction
a) Determining the position of redundant bits –
These redundancy bits are placed at the positions which correspond to the power of 2.
As in the above example:
 The number of data bits = 7
 The number of redundant bits = 4
 The total number of bits = 11
 The redundant bits are placed at positions corresponding to power of 2=> 1, 2, 4, and 8

Error Correction.
174
b) Determining and place the Data bits positions–
Suppose the data to be transmitted is 1011001, the bits will be placed as follows:

Error Correction.
175
d) Determining the Redundant bits positions(R1) Using Even Parity–
R1 bit is calculated using parity check at all the bits positions
whose binary representation includes a 1 in the least significant
position. R1: bits 1, 3, 5, 7, 9, 11
R1, 1, 0, 1, 1,1 R1=0

Error Correction.
176
R2, 1, 0, 1, 0,1
whose binary representation includes a 1 in the second position
from the least significant bit. R2: bits 2,3,6,7,10,11
R1=0
R2=1

Error Correction.
177
R4, 0, 0, 1
R1=0
R2=1
R4=1
whose binary representation includes a 1 in the third position
from the least significant bit. R4: bits 4, 5, 6, 7

Error Correction.
178
R8, 1, 0, 1
R1=0
R2=1
R4=1
R8=0
whose binary representation includes a 1 in the fourth position
from the least significant bit. R8: bit 8,9,10,11

Error Correction.
179
Thus, the data transferred is:
R1=0
R2=1
R4=0
R8=0

Error Correction: Forward error correction
180
6) Error Detection by Hamming Code– Suppose in the above example the 6th bit is changed from 0 to 1
during data transmission,
then it gives new parity values in the binary number:

Error Correction: Forward error correction
181
Hamming Code Error Correction 7) Error Corrections By Hamming Code–
Here, The bits give the binary number as 0110
whose decimal representation is 6.
Thus, the bit 6 contains an error. To correct the
error the 6th bit is changed from 1 to 0.
Let the Received Bit Frame is 
Find the Redundant Bits using Even Parity at
Receiving End
Recovered Data at Receiving End is

Half-Duplex & Full-Duplex Communication:
182

Half-Duplex & Full-Duplex Communication:
183

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