Learn Network Services, Topology and Social Relationships

Objective
At the end of this Unit
You will learn
 Network services
 Layered architecture
 Network topology
ARCHANAAJITH

Social relation
In social science, a social relation or social interaction
refers to a relationship between two , three or more
individuals (e.g. a social group).
Normally social network is filled with peoples.
Social networking allow users to share ideas, activities,
events, and interests within their individual networks.
In addition, To protect user privacy, social networks
usually have controls that allow users to choose who can
view their profile, contact them, add them to their list of
contacts, and so on.

Social Network
Popular methods now combine many of these, with Face
book and Twitter widely used worldwide.

Pictorial Representation of Social
Networks
5 ARCHANAAJITH
Simple
Complex
ARCHANAAJITH

Aim for Networking
The main aim for networking is Communication
Communication means sharing something

FUNDAMENTAL CONCEPTS
Communication
Means Sharing of information.
Sharing may be
Local
Transmits information locally
Remote
Sending information to remote places.
Data
Concepts or information is called data.
Data communication
Sharing of information between two devices

Characteristics/Effectiveness of Data Communication
Delivery
Accuracy
Timeless
Components in data communication
Protocol Protocol
Medium
Sender Receiver

Data Communication Model
Step1
Step2
Step3
---------
----------
Step N Medium
Sender Receiver
Step1
Step2
Step3
---------
----------
Step N
Protocol Stack Protocol Stack

Data Communication Model
 PROTOCOLS
 Specifies common set of rules and signals which
computers on the network use to communicate.
 Protocol suite or protocol stack
 The total package of protocols.

Real Life Data Communication
Medium
Sender MODEM
MUX
Receiver MODEM De MUX

Transmission Modes
12 ARCHANAAJITH

Mode of Transmission
Transmission can be classified into two according to the
direction of data flow.
Unidirectional Simplex
Bidirectional Half Duplex
 Full Duplex

13 ARCHANAAJITH
Full – Full Duplex
ARCHANAAJITH

Mode of Transmission.
Unidirectional (Simplex)
Information is communicated in only one direction.
It can be implemented by single wire.
Examples
One way street
Communication from CPU to monitor.
Communication from Keyboard to CPU.
Communication from Computer to printer.
Communication from Microphone to speaker.
TV or radio broadcasting

Mode of Transmission
Simplex
Half Duplex
Cannot perform two direction at a time
Sender Receiver
Direction of Data Flow
Sender Receiver

Half duplex
Information is communicated in both direction, but not
simultaneously.
It requires definite turn around time to change from transmitting
mode to receiving mode.
Due to this delay communication is slower .
It can be implemented by two wire. One for Data and other is
ground
Examples
One line traffic in narrow bridges.
Walkie-talkies.
CB (Citizen’s Band) Radio

Mode of Transmission
Full Duplex
It can perform two direction at a time
Full –Full Duplex
It can perform two direction but not between same two stations
Sender Receiver
Receiver Sender
Receiver/Sender

Full duplex
Information is communicated in both direction simultaneously.
It can be implemented by as two wire or four wire circuit.
In two wire circuit, total channel capacity is divided in to two.
 In four wire circuit , channel capacity can be increased.
Examples
Two way traffic.
Telephone Conversation.

Computer Networks
19 ARCHANAAJITH

Network
In its simplest form, networking is defined as two computers
being linked together, either physically through a cable or
through a wireless device.
Computer network consists of two or more computers linked
together to exchange data and share resources
A computer network, often simply referred to as a network, is a
collection of hardware components and computers
interconnected by communication channels that allow
sharing of resources and information.

What is a Computer network
5/15/2023
21 ARCHANAAJITH
• A popular example of a computer network is the
Internet, which allows millions of users to share
information

An example of a network
Node
Router
Internet
Segment
Hub
Hub
Bridge

Networks Fundamentals
Network Goals or aims
1.Resource sharing.---- May be Software of Hardware
2.High reliability.---Alternative Sources of data
Important in banks, military, Air traffic control
3.Saving of money
Money can be saved if we go through Client server model
4.Data Sharing.
5.System performance can be improved.
6.Powerful communication medium.

1. Resource sharing.

Network Issues/Criteria
To consider a network is effective and efficient, it must meet
some criteria
Performance
Reliability.
Security
Performance
Transit time :Time taken to Transmit
Response Time :Time taken to get a response

Network Issues/Criteria
Response Time
It depends on the following factors.
1. No of users. (Traffic Load).
2. Types of medium
3. Type of hardware included in the network.
4. Software were not updated.
5. Lack of education
6. Improper instruction

 Reliability
 It depends on the following factors.
1. Frequency of failure.
2. Recovery time after failure.
3. Catastrophe----- prevent network from Fire hazards, Earth
quakes, Theft
Security
Protecting Data from
1. Un authorized access
2. Virus

Un authorized access
It has two levels
Lower level------Improper/Week password
Higher level------Encryption techniques

Network Functions
Addressing--- Identify sender and receiver
Routing--- Find the path between sender and receiver
Flow Control----Traffic flow can be controlled
Congestion control
Security
Backup
Failure monitoring
Traffic Monitoring
Accountability
Internetworking
Network Management
Error detection and correction

Network Applications
Marketing and Sales
Financial services
Manufacturing
Email
Directory services
Information services
Teleconferencing
Cellular telephone
Cable Television

TYPES OF CONNECTIONS
1. POINT-TO-POINT
Provides a direct link between two devices.
Eg. Each computer is connected directly to a
printer .
2. MULTI-POINT/MULTI DROP
Provides a link between three or more devices on a
network.
It will share the link/Channel capacity

TYPES OF CONNECTIONS
Multi point
It is two types
 Time sharing
 Sharing the link turn by turn
 Spatially shared
 Sharing of link simultaneously
Two relationship is possible in multi point connection
Peer- to –peer
 All the nodes has equal right to access the link
Primary-Secondary
One will be master and other will be slave

What is a TYPES OF CONNECTIONS
 Computers on the network are equals
 No file server
 Users decides which files and peripherals to share
 It is not suited for networks with many computers
Easy to set up; Home networks
Peer-to-Peer

Network Components
Physical Media
Interconnecting Devices
Computers
Networking Software

Network Components
 Physical media
Cables- Telephone lines, coaxial cable,
microwave, satellites, wireless, and fiber optic
cables
Interconnecting Devices
Routers- Devices that examine the data transmitted and
send it to its destination
 Switches- High speed electronic switches
maintain connections between computers
 Protocols- Standards that specify how network
components communicate with each other
ARCHANAAJITH

Physical Media
Networking media can be
defined simply as the
means by which signals
(data) are sent from one
computer to another
(either by cable or
wireless means).
Introduction to Computer Networks
43 ARCHANAAJITH
ARCHANAAJITH

Networking Devices
HUB, Switches, Routers,
Wireless Access Points,
Modems etc.
44 ARCHANAAJITH
ARCHANAAJITH

Topology
 A network's topology is comparable to the blueprints
of a new home in which components such as the
electrical system, heating and air conditioning
system, and plumbing are integrated into the
overall design.
 Taken from the Greek work "Topos" meaning "Place,"
 Specifies the geometric arrangement of the network or a
description of the layout of a specific region.
46 ARCHANAAJITH
ARCHANAAJITH

Topology
 A network topology is the basic design of a computer
network.
 It details how the network components such as
nodes and links are interconnected.
 Topology, in relation to networking, describes the
configuration of the network; including the location
of the workstations and wiring connections.

NETWORK TOPOLOGY
 It is two types
 Logical
 Physical
 The complete physical structure of the cable (or data-
transmission media) is called the physical topology .
 The way in which data flows through the network (or
data-transmission media) is called the logical topology.

NETWORK TOPOLOGY
 Network topology can be classified in to
1. BUS
2. STAR
3. MESH
4. TREE
5. RING
6. HYBRID

Bus Topology
51 ARCHANAAJITH
ARCHANAAJITH

Bus Topology
 The simplest and one of the most common of all
topologies
 Bus consists of a single cable, called a Backbone, that
connects all workstations on the network using a
single line.
 Each workstation has its own individual signal that
identifies it and allows for the requested data to be
returned to the correct originator.
 In the Bus Network, messages are sent in both
directions from a single point and are read by the node
(computer or peripheral on the network) identified by
the code with the message.
52 ARCHANAAJITH

Bus Topology
 Most Local Area Networks (LANs) are Bus
Networks because the network will continue
to function even if one computer is down.
 This topology works equally well for either
peer to peer or client server.

53 ARCHANAAJITH

Star Topology
 All devices connected with a Star setup
communicate through a central Hub by cable
segments.

 Signals are transmitted and received through the
Hub.
 It is the simplest and the oldest and all the
telephone switches are based on this.
 In a star topology, each device has separate
connection to the network.


Star Topology
5/15/2023
56 ARCHANAAJITH

Ring Topology
ARCHANAAJITH
57 ARCHANAAJITH

Ring Topology
 All the nodes in a Ring Network are connected in a
closed circle of cable.
 Messages that are transmitted travel around the ring
until they reach the computer that they are
addressed to, the signal being refreshed by each
node.
 In a ring topology, the network signal is passed
through each network card of each device and
passed on to the next device.

Ring Topology
 Each device processes and retransmits the
signal, so it is capable of supporting many
devices in a somewhat slow but very orderly
fashion.
 Important feature is that everybody gets a
chance to send a packet and it is
guaranteed that every node gets to send a
packet in a finite amount of time.

Ring Topology
5/15/2023
60 ARCHANAAJITH

Mesh Topology
 The mesh topology connects all devices
(nodes) to each other for redundancy and fault
tolerance
It is used in WANs to interconnect LANs and
for mission critical networks like those used
by banks and financial institutions.
Implementing the mesh topology is expensive
and difficult
5/15/2023
62

Mesh Topology
5/15/2023
63 ARCHANAAJITH
Full Mesh
ARCHANAAJITH

Tree Topology
5/15/2023
65 ARCHANAAJITH

Tree Topology
5/15/2023
66 ARCHANAAJITH

Hybrid Topology
67 ARCHANAAJITH

Hybrid Topology
5/15/2023
68
Hybrid networks use a combination of any two or more
topologies in such a way that the resulting network does
not exhibit one of the standard topologies
ARCHANAAJITH

Hybrid Topology
5/15/2023
69 ARCHANAAJITH

Connecting devices
HUB
Switch
ARCHANAAJITH

Switch
 Network consists of a set of inter connected
nodes called switches
 From which information is transmitted from
source to destination through different routers.
 It operates at layer 2 of OSI model (Data Link
Layer)
72 ARCHANAAJITH

Switch
 Switches can be a valuable asset to networking.
 Switch can increase the capacity and speed of
your network.
 Switches occupy the same place in the network
as hubs.
 Unlike hubs, switches examine each packet and
process it accordingly rather than simply
repeating the signal to all ports.
73 ARCHANAAJITH

Network Switch
74 ARCHANAAJITH

Network Switch
75 ARCHANAAJITH

Switch
 Some switches have additional features,
including the ability to route packets.
 These switches are commonly known as layer-3
or multilayer switches.
 LAN switches come in two basic architectures,
 Cut-through and
 Store-and-forward.
76 ARCHANAAJITH

Switch
 Cut-through switches only examine the
destination address before forwarding it on to
its destination segment.
 A store-and-forward switch, on the other hand,
accepts and analyzes the entire packet before
forwarding it to its destination.
77 ARCHANAAJITH

Switches in a Network
79 ARCHANAAJITH

Switches in Network
80 ARCHANAAJITH
ARCHANAAJITH

Switches in Network
81 ARCHANAAJITH

Switching
 Determines when and how packets/messages
are forwarded through the network .
 Specifies the granularity and timing of packet
progress
 Relationship with flow control has a major
impact on performance of a Network
83 ARCHANAAJITH

Switching
 Switching can be classified in to
 Circuit switched Networks
 Packet switched Networks
 Datagram Network
 Virtual Circuit Networks
 Message switched Networks
86
Switched virtual circuit
Permanent virtual circuit
ARCHANAAJITH

Circuit Switching
87 ARCHANAAJITH

Circuit Switching
 It is a methodology of implementing a
telecommunications network in which two
network nodes establish a dedicated
communications channel (circuit).
 In circuit switching, most of the time line is idle
 Circuit switching gives fixed data rate
 Once circuit is established , that connection is the path
for transmission.
88 ARCHANAAJITH

Circuit Switching
 Circuit switching is also termed as connection
oriented networks
 It has three steps
 Connection Establishment
 Data Transfer
 Circuit Disconnects
91 ARCHANAAJITH

Circuit Switching
 In circuit switching, a caller must first establish
a connection to a called party before any
communication is possible.
 It maintain the connection to transfer
message
 The circuit is terminated when the connection
is closed.
92 ARCHANAAJITH

Circuit Switching
93 ARCHANAAJITH

Circuit Switching
94 ARCHANAAJITH

Circuit Switching
 Circuit switching uses any of the three technologies
1. Space division switches
2. Time division switches
3. Combination of both
95 ARCHANAAJITH

Space division switches
 Provide a separate physical connection between
inputs
& outputs (separated in space)
 Some of the space switches are
 Cross bar switch
 Crossbar switch: consists of N x N cross-points
( N: number of input lines = number of output
lines)
 Multi stage switch
96 ARCHANAAJITH

Cross Bar Switch
97 ARCHANAAJITH

Cross Bar Switch
98 ARCHANAAJITH

Multi Stage Switch/ Omega Switch
99 ARCHANAAJITH

Time Division Switch
100 ARCHANAAJITH

Time Division Switch
101
TDM with Switching using TSI
TSI=Time Slot Interchange
ARCHANAAJITH

Packet Switching
102 ARCHANAAJITH

Packet Switching
 Data are send as packets
 Packet size can be variable
 Packet contains data and header
103 ARCHANAAJITH

Packet Switching
 Network layer offer two services
 Connection oriented service
 A connection is called virtual circuit
 Connectionless service
 The independent packets are called Data grams
106 ARCHANAAJITH

Data gram Network
 Routes from source to destination are not worked out in
advance.
 Packets takes different routes.
 It does not maintain a table.
 It is the responsibility of transport layer to re order
the Data grams
107 ARCHANAAJITH

Data grams
108
A
B X
Y
4 3 2 1
4
3
2
1
1
3
3 1
3
1
4
2 4 4
4 3
2 1
ARCHANAAJITH

Virtual Circuit
 Only one route from source to destination
 When connection is established, it is used for all the traffic.
 When connection is released, the virtual circuit is terminated.
 Every router has to maintain a table.
109 ARCHANAAJITH

Switched Virtual Circuit (SVC)
 It is similar to dial-up lines
 A virtual circuit is created whenever it is needed.
110 ARCHANAAJITH

Switched Virtual Circuit (SVC)
111
A
B X
Y
ARCHANAAJITH

Permanent Virtual Circuit (PVC)
 Virtual circuit is provided between two user on a
continuous basis.
112 ARCHANAAJITH

Permanent Virtual Circuit
113
A
B X
Y
ARCHANAAJITH

Data gram Vs Virtual circuit Network
114
Parameter VC Datagram
Circuit setup Required Not required
Addressing Each packet contains a
short VC number
Each packet contains a source ,
destination address
Repairs Easy to repair Harder to repair
State
information
Table is required to hold
state information
Table is not required to hold state
information
Routing Route is fixed. (Static
routing)
Routed independently(dynamic
routing)
Congestion
control
Easy Difficult
ARCHANAAJITH

Message Switching
115 ARCHANAAJITH

Message switching
message switching is similar to packet
switching, where messages were routed
one hop at a time.
No physical path is established in advance
in between sender and receiver.
When the sender has a block of data to be
sent, it is stored in the first switching
office (i.e. router) then forwarded later at
one hop at a time.
116 ARCHANAAJITH

Message switching
117 ARCHANAAJITH

Layered Architecture
118 ARCHANAAJITH

A simple example for communication
We use the concept of layers in our daily life.
As an example, let us consider two friends who
communicate through postal mail.

simple example for communication
But 5 Steps are needed for proper delivery
ARCHANAAJITH

V. Writing letter in a paper ( Raw Data)
IV. Put signature ,Fold the letter and put the letter in a cover
(Adding Header1, Compression etc)
III. Seal the cover& Put signature (Provides security,
Header2)
II. Dropped the letter in to mail box after fixing stamp
(Adding Header3& trailer1)
I. Postman collects the letter to the post office (
TRANSMISSION THROUGH A MEDIUM)
121 ARCHANAAJITH

 Sorting the letter at the post office (ROUTING)
I. Postman collects the letter from post office to the mail box
(Transmitting data bits)
II. Letter was taken from mail box to Home (Removing
header3& Trailer)
III. Open the cover& signature (Removes Header2)
IV. Take the letter from the cover (Removing Header1)
V. Reading letter ( Raw Data)
122 ARCHANAAJITH

Network architecture
 Network architecture is the overall design of a
network
 The network design is divided into layers, each of
which has a function separate of the other layers
 Protocol stack- The vertical (top to bottom)
arrangement of the layers; Each layer is governed by
its own set of protocols

Virtual Communication Between layers
 Message is generated by 5th layer
 Layer 4 add header in front of message
 Header include control information to send the
message in the right order.
 Layer 3 breaks up the message in to small units
called packets
 Layer 2 add header and trailer to packets.
 Layer 1 transmits the raw data.

Issues in Layered Architecture
 Design Philosophy of Layered Architecture
 The complex task of communication is
broken into simpler sub-tasks or modules
 Each layer performs a subset of the required
communication functions
 Each layer relies on the next lower layer to
perform more primitive functions
 Changes in one layer should not affect the
changes in the other layers
 Helps in troubleshooting and identifying the
problem
ARCHANAAJITH

Design issues for layers
 Addressing
 Identify sender and receiver
 Direction of transmission
 Simplex, half duplex, full duplex
 Error control
 Error detection and correction algorithms
 Avoid loss of sequencing
 Sequence number
 Ability to receive long messages
 Disassemble , transmit, reassemble
 Use of multiplexing and de multiplexing
 Share the channel

Network Models
128 ARCHANAAJITH

Need for Network Models
• Network communication is an extremely
complex task.
• Layer architecture simplifies the network design.
• The complex task of communication is broken
into simpler sub-tasks or modules
• Need cooperative efforts from all nodes involved
ARCHANAAJITH

Need for Network Models
• A standard model helps to describe the task of a
networking product or service
• Also help in troubleshooting by providing a
frame of reference.
The network management is easier due to the
layered architecture.
.
ARCHANAAJITH

Need for Layered Architecture
• Each layer works with the layer below and
above it
• Each layer provides services to next layer
ARCHANAAJITH

Who define Network Model?
• Need non-profit making organizations
• ISO - International Standards Organization
IEEE - Institute of Electrical & Electronic
Engineers
ITU - International Telecommunication Union
ARCHANAAJITH

OSI Reference Model
The Open Systems Interconnection model is
a theoretical model that shows how
any two different systems can communicate
with each other.
ARCHANAAJITH

OSI Reference Model
The OSI model is now considered the primary Architectural
model for inter-computer communications.
The OSI model describes how information or data makes
its way from application programmes through a network
medium (such as wire) to another application programme
located on another network.
This separation into smaller more manageable functions is
known as layering.
OSI Model
ARCHANAAJITH

OSI Model
 To standardize the design of communication
system, the ISO created the OSI model
 ISO standard that covers all aspects of
network communications is the Open Systems
Interconnection (OSI) model.
 Contains Seven layers
 It describes the functions to be performed at
each layer
ARCHANAAJITH

OSI Model
 First introduced this model in the late 1970s.
 A layer model, Each layer performs a subset
of the required communication functions
 Changes in one layer should not require
changes in other layers
ARCHANAAJITH

ISO is the organization.
OSI is the model.
Important
ARCHANAAJITH

OSI Model
Application
Presentation
Session
Transport
Network
Data Link
Physical
ARCHANAAJITH

The OSI 7-layer Model
All
People
Seem
To
Need
Data
Processing
Away
Pizza
Sausage
Throw
Not
Do
Please
ARCHANAAJITH

Peer-to-Peer Process using OSI
ARCHANAAJITH

Relationship of OSI layers
Virtual
Communication
Physical
Communication
ARCHANAAJITH

Data exchange using the OSI model
ARCHANAAJITH

Flow of data in the OSI model
Bit stream  signal
Frames (node  node)
Packet (logical address)
Entire message
Synchronization points
Coding methods
User  network
ARCHANAAJITH

Protocols in a layered architecture
• Network communication is possible only if
machines speaking the same languages (protocols)
• Network communication is possible only if the
Protocol Stacks on two machines are the same
ARCHANAAJITH

Functions of Physical layer
147 ARCHANAAJITH

15 May 2023
149
OSI Model – Physical Layer
 This layer is the lowest layer in the OSI model.
 It helps in the transmission of data between two
machines that are communicating through a
physical medium, which can be optical fibres,
copper wire or wireless etc.
 Hardware Specification:
 The details of the physical cables, network interface
cards, wireless radios, etc are a part of this layer.

ARCHANAAJITH

OSI Model – Physical Layer
 Physical interface between devices
 Handles the transmission of bits over a
communications channel
 Choice of Wired / wireless medium
 Data is converted into signals
 Includes voltage levels, connectors, media
choice
 modulation techniques
 EIA/TIA-232, RJ45, NRZ.
ARCHANAAJITH

Functions of Physical Layer
 Make and Break physical connections.
 Define voltages and data rate
 Convert data bit in to electrical stream
 Decide mode of transmission
 Define physical topology
 Line configuration
ARCHANAAJITH

Medium used for Physical Connections

The physical layer is responsible for movements of
individual bits from one hop (node) to the next.
Note
ARCHANAAJITH

Functions of Data link layer
155 ARCHANAAJITH

OSI Model – Data Link Layer
• Means of activating, maintaining and
deactivating a reliable link
ARCHANAAJITH

Functions of Data Link Layer
 Framing
 Physical Addressing
 Flow Control
 Error Control
 Access control
 Synchronization.
ARCHANAAJITH

Access control in Data Link
Layer
 Sharing the access of the link
 Based on access control IEEE split the data
link layer in to two is called IEEE project 802
 Logical Link Control(LLC)
 Establish and maintain link
 Media Access control(MAC)
 Provides shared access and communicates with
network Interface Cards
 Establish a logical link between two computers
ARCHANAAJITH

Data Link Sub layers
Media Access
Control (MAC)
Logical Link
Control
(LLC)
802.3 802.4
802.5 802.12
802.2
802.1

The data link layer is responsible for moving
frames from one hop (node) to the next.
Note
ARCHANAAJITH

Functions of Network layer
161 ARCHANAAJITH

OSI Model – Network Layer
• Transport of information
• Responsible for creating,
maintaining and ending network
connections
• Routing
• Transfers a data packet from node to node
within the network.
 Examples :- IP, IPX, AppleTalk.
ARCHANAAJITH

15 May 2023
164
Functions of Network layer
 Routing of signals
 Divide outgoing message in to packets
 Act as network controller
 Logical Addressing
 Convert logical address to physical address
ARCHANA AJITH

The network layer is responsible for the delivery of
individual packets from the source host to the
destination host.
Note
ARCHANAAJITH

Functions of Transport
layer
166 ARCHANAAJITH

Transport Layer
 Transport
– Exchange of data between end systems
(end to end flow control)
– Error free
–Sequencing
– Quality of service
 Layer 4 protocols include TCP (Transmission
Control Protocol) and UDP (User Datagram
Protocol).
ARCHANAAJITH

Services offered by Layers
 Connection oriented Service
 Establish connection
 Use the connection
 Release the connection
 Connection less Service
 Similar to postal service
 Each message is routed independently
 Quality of service
 Reliable--- No Data Loss, Using ACK
 Un reliable
ARCHANAAJITH

15 May 2023
170
Functions of Transport layer
 Transmission is parallel or single path
 Multiplexing
 Segmentation and re assembly
 Service point addressing
 Connection control
ARCHANA AJITH

The transport layer is responsible for the delivery
of a message from one process to another.
Note
ARCHANAAJITH

Functions of Session layer
172 ARCHANAAJITH

OSI Model – Session Layer
 Session
– Control of dialogues between
applications
– Synchronization Points (backup points)
 Examples :- SQL, ASP(AppleTalk Session
Protocol), NETBIOS, RPC, PAP.
ARCHANAAJITH

15 May 2023
174
Functions of Session layer
 Controls logging off and logging on
 User identification
 Billing and session management

ARCHANA AJITH

The session layer is responsible for dialog control and
synchronization.
Note
ARCHANAAJITH

Functions of Presentation
layer
176 ARCHANAAJITH

OSI Model – Presentation Layer
– Translation
– Data compression
– Encryption
 Examples :- JPEG, MPEG, ASCII, EBCDIC,
HTML.
ARCHANAAJITH

The presentation layer is responsible for translation,
compression, and encryption.
Note
ARCHANAAJITH

Functions of Application
layer
179 ARCHANAAJITH

OSI Model – Application Layer
 Application
– Layer where the application using the
network resides.
– Common network applications include
 remote login
 file transfer
 e-mail
 web page browsing etc.
– Means for applications to access OSI
environment
ARCHANAAJITH

The application layer is responsible for providing
services to the user.
Note
ARCHANAAJITH

Summary of layers
ARCHANAAJITH

• To identify the language (protocol) of each layer,
identifier (header and trailer) are added to data
ARCHANAAJITH

TCP/IP Model
 It is used earlier by ARPANET
 Developed by research foundation by US
department of defense
 Later this architecture is known as TCP/IP model
 It has two protocols
 Transmission control protocol
 Message is divided in to packets
 Then Put in to IP packet
 Internet protocol
 Provide IP addressing
ARCHANAAJITH

TCP/IP Protocol Suit
 TCP/IP suite is the set of protocols that
implement the protocol stack on which the
Internet runs.
 It is sometimes called the Internet Model.
 This model consists of five ordered layers
 This model was developed prior to OSI model
ARCHANAAJITH

Internet layers
Internet
Data Link
Physical
ARCHANAAJITH

OSI vs TCP/IP
Application
Presentation
Session
Transport
Network
Data Link
Physical
ARCHANAAJITH

TCP/IP Model
 Networking concept can be explained with the
help of 4 layer protocol concept
 It is a variation of TCP/IP 5 layer model
ARCHANAAJITH

Variation of TCP/IP
Application
Presentation
Session
Transport
Network
Data Link
Physical
ARCHANAAJITH

TCP/IP protocol stack
Network Interface and Hardware
Internetwork
ARCHANAAJITH

Data flow in TCP/IP Model
ARCHANAAJITH

TCP/IP Protocol Architecture Model
ARCHANAAJITH

OSI vs TCP/IP
OSI TCP/IP
7 Layer 4/5 layer
Transport layer guarantees delivery
of packets
Transport layer does not
guarantees delivery of packets
Separate session layer No session Layer, Characteristics
are provided by transport layer
Separate presentation layer No presentation Layer,
Characteristics are provided by
application layer
Network layer offer connectionless
and connection oriented service
Network layer offer connectionless
service
Easy to replace the protocols Not easy to replace protocols
General Model TCP/IP cannot be used for any other
application

Some Protocols in TCP/IP Suite
ARCHANAAJITH

TCP/IP Frames
IP
Header
Frame
Check
Sequence
Ethernet
Header
Header contains source and
destination physical addresses;
Upper level (i.e. network)
protocol type
IP datagram is encapsulated in an Ethernet frame
Header contains source and
destination IP addresses;
Upper level (i.e. transport)
protocol type
ARCHANAAJITH

TCP/IP Services
 Two kinds of services: TCP & UDP.

 TCP—Transmission Control Protocol, reliable
connection oriented transfer of a byte stream.
 UDP—User Datagram Protocol, best-effort
connectionless transfer of individual messages.
ARCHANAAJITH

Network Classification/
Network configuration
202 ARCHANAAJITH

Network Classification
Networks may be classified according to a wide
variety of characteristics such as the
Transmission Technology
Scale
Medium used to transport the data
Topology
Organizational scope.
Communications protocol used
203 ARCHANA AJITH

Network Classifications
 Network categorization according the following are
important
 Transmission Technology
 Scaling/ According to physical size
According to Transmission technology
Broadcast Networks
Point to point Networks
204 ARCHANA AJITH

• Broadcast Networks
• Single communication channel shared by all the users
• Packets sent by any machine are received by all the
others (only one sender)
• Point to point Networks
• It consists of many connections between all machines
• It consists of dedicated links between each node
205 ARCHANAAJITH

• Broadcast Networks
• Point to point Networks
206 ARCHANAAJITH

Network Classification
according to scaling
207 ARCHANAAJITH

Main Categories of networks

208 ARCHANAAJITH

Main Categories of Network
Local area network (LAN)
 Links computers within a
building or group of buildings
 Uses direct cables, radio or
infrared signals
Metropolitan area network (MAN)
 Links computers within a major
metropolitan area
 Uses fiber optic cables
Wide area network
 Links computers separated by a
few miles or thousands of miles
 Uses long-distance transmission
media
209 ARCHANAAJITH

Network Scaling
210 ARCHANAAJITH

Network Scaling
211
Inter processor
distance
Processors are located
in
networks
0.1 m Same circuit board Data flow machine
1m Same system Multi computer
10m Same room LAN
100m Same building LAN
1km Same campus LAN
10km Same city MAN
100km Same country WAN
1000km Same continent WAN
10000km Same planet Internet
PAN
ARCHANAAJITH

Personal Area Networks (PAN)
• A PAN is a network that is used for communicating
among computers and computer devices (including
telephones) in close proximity of around a few meters
within a room.
• It can be used for communicating between the devices
themselves, or for connecting to a larger network such
as the internet.
• PAN’s can be
• Wired
• Wireless
•
5/15/2023
213
213 ARCHANAAJITH

5/15/2023
214
214 ARCHANA AJITH

 PAN’s can be wired with a computer bus such as a
universal serial bus
 USB (a serial bus standard for connecting devices to a
computer, where many devices can be connected
concurrently)
 PAN’s can also be wireless through the use of bluetooth
(a radio standard designed for low power consumption
for interconnecting computers and devices such as
telephones, printers or keyboards to the computer) or
IrDA (infrared data association) technologies
•
5/15/2023
215
215 ARCHANAAJITH

• Wireless PAN
5/15/2023
216
216 ARCHANAAJITH

Local area networks (LAN)
 A LAN is a network that is used for communicating among
computer devices, usually within an office building or group of
buildings or home
 LAN’s enable the sharing of resources such as files or hardware
devices that may be needed by multiple users
 Is limited in size, typically spanning a few hundred meters, and
no more than a mile
 Is fast, with speeds from 10 Mbps to 10 Gbps
 Requires little wiring, typically a single cable connecting to
each device
 Has lower cost compared to MAN’s or WAN’s
5/15/2023
218
218 ARCHANAAJITH

Metropolitan area network
 A metropolitan area network (MAN) is a computer
network in which two or more computers or
communicating devices or networks which are
geographically separated but in same
metropolitan city.
 A MAN is optimized for a larger geographical area
than a LAN
 A MAN typically covers an area of between 5 and 50
km diameter.
220 ARCHANAAJITH

Metropolitan area network
 Network in a City is call MAN
 A Metropolitan Area Network (MAN) is a network
that is utilized across multiple buildings
 It is larger than a LAN, but smaller than a WAN
 It is also used to mean the interconnection of
several LANs by bridging them together.
 This network is also referred to as a campus
network
222

Wide area network (WAN)
 A Wide Area Network is a network spanning a large
geographical area of around several hundred
miles to across the globe
 May be privately owned or leased
 Also called “enterprise networks” if they are
privately owned by a large company
 It can be leased through one or several carriers
(ISPs-Internet Service Providers) such as AT&T,
Sprint, Cable and Wireless
 Can be connected through cable, fiber or satellite
 Is typically slower and less reliable than a LAN
225

LAN STRUCTURE
228 ARCHANAAJITH

LAN
When you have several computers, it can be
convenient to connect them to each other to
create a local area network (LAN).
A physical network structure is composed mostly
of cables, switches and workstations.

229

230 ARCHANAAJITH

LAN Ethernet structure
 Ethernet LAN made up of several desktop
systems and a server attached to a coaxial cable.
5/15/2023
231
231

Repeaters to Build Multi segment LANs
5/15/2023
232
232

Bridges to Build Multi segment LANs
5/15/2023
233
233

 Users can access software, data and peripherals
 Require special hardware and software
 Computers connected to a LAN are called workstations or nodes
 Different types:
 Peer-to-peer
 Client-server
234

ARCHANAAJITH
• Client Server Model
• Client-server model is the one way computers
communicate via web
• Client –server is based on a centralized structure
• Examples: http web pages
• Peer- to- peer model
• Both computers can requesters and response
providers
• Each one is able to send and receive data directly
with one another
• De-centralised structure is called peer-to-peer
• Examples: video chat protocols like skype

Peer-to-peer Client-server
236

LAN Clients and Servers
In a client/server network
arrangement, network
services are located in a
dedicated computer whose
only function is to respond
to the requests of clients.
The server contains the file,
print, application, security,
and other services in a
central computer that is
continuously available to
respond to client requests.
237

 LAN’s can be either wired or wireless.
 Twisted pair, coax or fiber optic cable can be
used in wired LAN’s
 Nodes in a LAN are linked together with a certain
topology. These topologies include:
 Bus
 Ring
 Star
 Branching tree
5/15/2023
238
238

LAN topologies
Bus topology
 Topologies resolve the problem of contention or users
trying to access the LAN at the same time
 Collisions or corrupt data occurs when computers use
the network at the same time
 Called daisy chain
 Every workstation connected to a
single bus cable
 Resolves collisions through
contention management
Difficult to add workstations
Star topology
 Contains a hub or central wiring
concentrator
 Easy to add workstations
 Resolves collisions through
contention management
Ring topology
 All workstations attached in a circular arrangement
 A special unit of data called a token travels around the ring
 Workstations can only transmit data when it possesses a token
240

LAN Topologies
 Bus Topology
 Each node is connected one after the other (like christmas
lights)
 Nodes communicate with each other along the same path called
the backbone
Backbone
241

 Ring Topology
 The ring network is like a bus network, but the “end” of the
network is connected to the first node
 Nodes in the network use tokens to communicate with each other
Backbone
LAN Topologies
242 ARCHANAAJITH

 Star Topology
 Each node is connected to a device in the center of the network
called a hub
 The hub simply passes the signal arriving from any node to the
other nodes in the network
 The hub does not route the data
Hub
LAN Topologies
243 ARCHANAAJITH

 Branching Tree Topology
LAN Topologies
244 ARCHANAAJITH

Components in LAN
DEEPAK.P
245 ARCHANAAJITH

Components in a Local area networks
 A node is defined to be any device connected to the
network. This could be a computer, a printer, a router, etc.
 A Hub is a networking device that connects multiple
segments of the network together
 A Network Interface Card (NIC) is the circuit board that
has the networking logic implemented, and provides a plug
for the cable into the computer (unless wireless).
 In most cases, this is an Ethernet card inserted in a slot of
the computer’s motherboard
 Network Media provides the means through which data
from one NIC is transmitted to other NIC
 LAN – for transmiting electrical signals
 OFC – Light signals
 Air – Radio signls
5/15/2023
246
246

ARCHANAAJITH
• Connectors –
• LAN cables are connected to NIC using RJ45
connects.
• Provides connection points for network media
• The Network Operating System (NOS) is the
software (typically part of the operating system kernel)
that communicates with the NIC, and enables users to
share files and hardware and communicate with other
computers. Examples of NOS include: Windows XP,
Windows NT, Sun Solaris, Linux, etc..

Hardware and software requirement for
LAN
Hardware
 Network interface card (NIC)-
Inserted into computer’s
expansion slot
Software
 Operating system that
supports networking (Unix,
Linux, Windows, Mac OS)
 Additional system
software
ARCHANAAJITH

Hardware and software requirement for LAN
 A high speed, high capacity computer
 Contains the network operating system ( Novell
Netware, Windows NT, XP Server)
 Contains network versions of programs and large
data files
File server
ARCHANAAJITH

Advantage of LAN
 File transfers;
 Sharing of resources (internet connection
sharing, printer sharing, shared disks, etc.);
 Mobility (in the case of a wireless network);
 Discussion (mainly when the computers are
remote);
 Network games.
5/15/2023
250
250

LAN
 There are two main types of local network
architecture:
 Wired networks, based on the Ethernet
technology, which represent almost all local
area networks. Given that Ethernet networks
generally use RJ45 cables, people often talk of
RJ45 networks;
 Wireless networks, which generally use the WiFi
technology.
5/15/2023
251
251 ARCHANAAJITH

Multiple access
communications
252 ARCHANAAJITH

Multiple Access Communication
 The channel is employed to provide
communication media between a set of
geographically distributed terminals.
 Channel access method or multiple access
method allows several terminals connected to
the same multi-point transmission medium to
transmit over it and to share its capacity.
 Multiple access schemes are used to allow many
nodes to share the link simultaneously.
253 ARCHANAAJITH

Multiple Access Communication
 FDMA
 TDMA
 CDMA
 A channel-access scheme is also based on a
multiple access protocol and control
mechanism, also known as media access
control (MAC).
254 ARCHANAAJITH

Data Link Control
255 ARCHANAAJITH

256
Data Link Control( DLC)
 In the OSI networking model, Data Link Control
(DLC) is the service provided by the data link
layer.
 Network interface cards have a DLC address
that identifies each card.
 DLC identifier (DLCI) that uniquely identifies
the node on the network.
 DLC has 2 subsets : Logical Link Layer and
Media Access Layer
 For networks that conform to the IEEE 802
standards (e.g., Ethernet ), the DLC address
is usually called the Media Access Control
ARCHANAAJITH

Data Link Sub layers
DEEPAK.P
257
Media Access
Control (MAC)
Logical Link
Control
(LLC)
802.3 802.4
802.5 802.12
802.2
802.1
ARCHANAAJITH

ARCHANAAJITH
• LLC – upper subset of data link layer
• IEEE 802.2 standard describes the function of LLC and is
shared to varoius methods of accesing the medium as
defined by the IEEE 802.3 , .4 , .5

ARCHANAAJITH
RESPONSIBILITIES OF DATA LINK
LAYAER
• Framing
• Physical Addressing
• Error control
• Flow control
• Access control

ARCHANAAJITH
Framing
• Data received from the
network layer into manageble
unit is called a frame.
•

ARCHANAAJITH
• Error control is achieved by adding the trailer at the end of frame.
• Trailer contains control information
• It is responsible for ensuring that frames are received in-tact and error
• DLC calculates a checksum for each frame and is included in frame w
transmitted.
• When it reaches the destination it recalculates the checksum. If the new
calculated cheksum is differtent from the one we send, this means som
error occurs .
• Makes necessary steps to recover the original data

ARCHANAAJITH
• Character Count
• Flag bytes with byte stuffing
• Flag bytes with bit stuffing
Framing methods

Character Count
 Uses a field in the header to specify the no. of
bytes in the frame
 This helps DLC at destination to know how many
bytes are followed and where the end of frame is.


 Disadvantage : If the count is garbled by a
transmission error, the destination will loose
synchronization and will be unable to locate the
start of the next frame.
 Even if with checksum, the receiver knows that
the frame is bad there is no way to tell where the
next frame starts.
 Asking for retransmission doesn’t help either

ARCHANAAJITH
major disadvantage of this method as not all character codes
use 8-bit characters

Bit Stuffing
 Each frame begins and ends with a special bit
pattern, 01111110 called a flag byte.
 When five consecutive l's are encountered in the
data, it automatically stuffs a '0' bit into outgoing
bit stream.
 When the receiver sees five consecutive
incoming i bits, followed by a o bit, it automatically
destuffs (i.e., deletes) the 0 bit.

272
Logical Link Control( LLC)
Functions :
 Logical Addressing
 Provide Control Information
 Control the Data
ARCHANAAJITH

273
Media Access Control( MAC)
 Functions:
 Flow control
 Error Control
 Access control
 Synchronization
Link /Media control
ARCHANAAJITH

274
Link/ Media Control
 Flow Control
 Restrict the amount of data that the sender can
send
 Error Control
 Damaged frames
 Lost frames
 Lost Acknowledgement
ARCHANAAJITH

Performance Metrics and
Delays
 Transmission time (delay)
 Time taken to emit all bits into medium
 Propagation time (delay)
 Time for a bit to traverse the link
 Processing time (delay)
 time spent at the recipient or intermediate
node for processing
 Queuing time (delay)
 waiting time at the queue to be sent out

Model of Frame Transmission
transmission
time
propagation
time
ARCHANAAJITH

278
Flow Control
 Necessary when data is being sent faster
than it can be processed by receiver.
 If sender sends faster than recipient
processes, then buffer overflow occurs
 flow control prevents buffer overflow
 Flow control can be of two types
 Stop & Wait
 Sliding window

Stop and Wait Flow Control
 This flow control mechanism forces the sender
after transmitting a data frame to stop and wait
until the acknowledgement of the data-frame
sent is received.
1. Source transmits frame
2. Destination receives frame and replies with
acknowledgement (ACK)
3. Source waits for ACK before sending next
frame
4. Destination can stop flow by not sending ACK
5. Works well for large frames
6. Inefficient for smaller frames

Stop and Wait Flow Control
 However, generally large block of data split into
small frames
 Called “Fragmentation”
 Limited buffer size at receiver
 Errors detected sooner (when whole frame received)
 On error, retransmission of smaller frames is
needed
 Prevents one station occupying medium for long
periods
 Channel Utilization is higher when
 The transmission time is longer than the propagation
time
 Frame length is larger than the bit length of the link

Sliding Window Flow Control
 In this flow control mechanism both sender and
receiver agrees on the number of data-frames
after which the acknowledgement should be
sent.

Sliding Window Flow Control
 The problem of “Stop and Wait” is not able to send
multiple packets.
 Sending frame only after the ACK signal`
 There is waiting time and sometimes ack signal takes
more time to reach the source than prescribed. So the
next frame needs to wait long
 Sliding Window Protocol allows multiple frames to be
in transit
 Receiver has buffer of W (called window size) frames
 Transmitter can send up to W frames without ACK
 Each frame is numbered
 Sequence number bounded by size of the
sequence number field
 ACK includes number of next frame expected

Example of a Sliding Window Protocol
(W = 7)

Sliding Window Flow Control (W = 5)
ARCHANAAJITH

Access Control
286 ARCHANAAJITH

287
Access Control
 Access Control means controlling the link
when computers transmit.
 It is important in situations where more than
one computer wants to send data at the
same time over the same circuit.
 The two main MAC approaches are
 Controlled access
 Contention Based / Polling
ARCHANAAJITH

288
Controlled Access
 Controlled access works like a stop light,
controlling access to the shared resource
of the network circuit.

289
Contention Based Access
 Contention approaches, such as Ethernet,
allow all the computers to transmit data at
any time whenever the circuit is free(1st
come -1st server).
 Like two people in a group speaking at the
same time, their messages collide and have
to be resent.
 This system breaks down when two
computers attempt to transmit at the same
time, i.e, collisions can occur (more than

290
Contention Based Access
 Contention approaches to media access
control need to have a way to sort out
which computer is allowed to transmit first
after a collision occurs.
 A mechanism used for this is polling

291
Relative Performance
 Contention approaches tend to work better for
smaller networks with relatively low usage.
 Since usage is low, the probability of collisions
is also low, but when volume is high their
performance deteriorates.
 Controlled access tends to work better for
networks with high traffic volumes where the
probability of collisions is high and controlling
access means the network will be more efficiently
used.

Relative Performance of Controlled vs.
Contention based MAC protocols
ARCHANAAJITH

Multiple Access
 Broadcast link is called multi access channel.
 If two transmitter transmit at the same time , their
signal may interface or collide.
 A method is needed to share the broadcast link
and avoid collision is called medium access
control (MAC)

Multiple Access
 When no of stations uses a common link, we
have to use multiple access protocol.
 Thee techniques or protocols are mainly used to
deal with multiple access problem
 Random Access.
 Controlled Access.
 Channelization.
296

Multiple Access
297
Controlled access

Random Access Protocols
 Random Access
 There is no Control station.
 Each station has the right to use the common
medium.
 The will be an increased probability of collision.
 Random access protocols are
 ALOHA
 CSMA
 CSMA/CD
 CSMA/CA
298 ARCHANAAJITH

Controlled Access Protocols
 Controlled access
 There will be a Control station.
 Control station has the right to allocate the link to
the different users.
 The probability of collision will be some what lesser.
 Main Controlled access protocols are
 Reservation
 Round-Robin

 Round Robin
In Round Robin techniques, each and
every node is given the chance to
send or transmit by rotation.
Two types:
 Polling
 Token Passing

302
Polling
 Polling, on computer networks, involves a
server and client.
 With polling, the server periodically
contacts each client to see if it wants to
transmit.
 Clients transmit only after being asked by
the server if they want to send something.
ARCHANAAJITH

Polling
 Polling may be
 Centralized (often called hub polling)
 Decentralized(distributed)/Roll call.
 In roll call polling, each client is checked in order to
see if it wants to transmit.
 Clients can also be prioritized so that they are polled
more frequently.
 In a decentralized polling scheme, each station knows its
successor in the polling sequence and send the poll directly to
that station.
304 ARCHANAAJITH

306
Polling
 Permission to transmit on the network is
passed from station to station using a special
message called a poll.
 In hub polling (also called token passing)
one computer starts the poll, sending
message (if it has one) and then passes the
token on to the next computer.
 This continues in sequence until the token
reaches the first computer, which starts the
polling cycle all over again.
ARCHANAAJITH

Polling
 In hub polling, the polling order is maintained by a single
central station or hub.
 When a station finishes its turn transmitting, it sends a message
to the hub, which then forwards the poll to the next station in
the polling sequence.
308

Token Passing
309 ARCHANAAJITH

Token Passing
310 ARCHANAAJITH

Token Passing
311 ARCHANAAJITH

 Reservation
Centralized
 Clients was prioritized so that they are
polled more frequently.
Distributed
 Permission to access the link is carried out
using a special message called a poll.

Channelization
313 ARCHANAAJITH

Multiple Access Protocols
 Channelization
 Typical channelization methods include
 Frequency differentiation (FDMA)
 Time division multiplexing (TDMA)
 Code division multiple access (CDMA)

Random Access
315 ARCHANAAJITH

Random Access
 Random Access
 There is no Control station.
 Each station has the right to use the common
medium.
 The will be an increased probability of collision.
 Random access protocols are
 ALOHA
 CSMA
 CSMA/CD
 CSMA/CA
316 ARCHANAAJITH

Multiple Access
Multiple Access
Carrier Sense Multiple Access
CSMA/CD CSMA/CA

Multiple Access methods
 ALOHA used a simple procedure called multiple access
(MA)
 It was improved to develop Carrier Sense Multiple
Access (CSMA)
 Carrier Sense" describes the fact that a transmitter
uses feedback from a receiver that detects a carrier
wave before trying to send.
 OR
 That is, it tries to detect the presence of an encoded
signal from another station before attempting to
transmit.

Carrier Sense Networks
 A Network which adopts carrier sense is called
carrier sense networks
 CSMA evolves two methods
 CSMA/CD
 CSMA/CA
319 ARCHANAAJITH

ALOHA System
 It is invented by Norman Abramson in 1970
321
Central Computer
f1
f2
f2= Broadcast
f1= Random access
ARCHANAAJITH

ALOHA System
 Contention System
 Multiple user share a common link, leads to
conflicts are known as contention systems.
 ALOHA is a Contention system
 If a collision occurs, wait random amount of
time then retransmit; repeat until successful
 Receiver send ACK for data
 Detect collisions by timing out for ACK
322 ARCHANAAJITH

ALOHA System
 ALOHA has two version
 Pure ALOHA/ Un slotted
 Does not need time synchronization
 Slotted ALOHA
 Need time synchronization

Pure ALOHA
 It allows any station to broadcast at any time.
 If two signal collides, each station wait a
random time and tries again
 Collisions are easily detected
 When central station receives a frame it sends an
ACK on a different frequency.
 It is very simple

Pure ALOHA
Central station
Station
Station
Station
Station
F1
F2

Pure ALOHA System
328 DEEPAK.P

Slotted ALOHA
 Developed by Roberts in 1972
 Changing the protocol from continuous time
to slotted time
 One frame can be sent in each slots.
 All transmitters are synchronized so that all
transmissions start at the beginning of a slot

Slotted ALOHA
 Time is divided in to discrete intervals (T)
 Each interval corresponds to one frame
330
0 T 2T
ARCHANAAJITH

CSMA
 Link Utilization can be improved in CSMA
 It operates on the principle of Carrier sensing
 In this principle , a station listen to see the
presence of fames in the link.
 CSMA can be divided in to three
 Non Persistent
 1- persistent
 P- Persistent

CSMA
 Non Persistent
 Station check the link.
 If the station is busy, it has to wait for fixed interval
of time
 After this time , it again check the status of the
channel.

Channel ?
Idle
Busy
Wait randomly

CSMA
 1- persistent
 It continuously monitor the link until it is idle.
 It then transmits immediately.

337
Channel ?
Idle
Busy
ARCHANAAJITH

CSMA
 P- persistent
 All waiting stations are not allowed to transmit
simultaneously when the channel is idle.
 Only P=1/N station can transmit while others will wait.

338
Channel ?
Idle
Busy
Wait a slot
Channel ?
Prob. outcome?
>p
<p
idle
Busy
Use back off process
Station can transmit
ARCHANAAJITH

CSMA/CD
 Carrier Sense Multiple Access with Collision
Detection (CSMA/CD)
 It is widely used on LAN in MAC layer
 CSMA/CD protocol can be considered as a
refinement over the CSMA scheme.
 This refined scheme is known as Carrier Sensed
Multiple Access with Collision Detection (CSMA/CD)
or Listen-While-Talk.

CSMA/CD
 The nodes continue to monitor the channel while
transmitting a packet and immediately stop
transmission when collision is detected and it
transmits jamming signal for a brief duration to
ensure that all stations know that collision has
occurred.
 Collision can be detected by comparing TX data
with RX data in Ethernet

CSMA/CD
 Listen to channel while transmitting data
 If collision occurs, immediately stop sending,
back-off and retransmit
 Sending a jam signal to all transmitters
 Better performance than plain CSMA
 Examples: Ethernet, Wi-Fi
343 ARCHANAAJITH

Carrier sense comparison
345 ARCHANAAJITH

CSMA/CD
Frame Frame Frame Frame
Transmission
period
Contention
period
Contention
Slots
Idle Periods
 CSMA/CD can be in one of three states
 Contention, transmission, or idle.

 Pre amble(7Byte)-Alert receiver to coming Frame
 SFD-Start Frame de limiter(1)-Beginning of Frame
 DA-Destination Address(2 to 6)-Destination address of NIC
 SA-Source Address(2 to 6) -Source address of NIC
 L-Length of data field(2)-Length or type of PDU
 Frame Data (Variable)-Actual Data
 FCS/CRC-Frame check status(4)-Error correction
 PAD- Adding extra bit to adjust the frame size
CSMA/CD Frame format
PR SFD DA SA L DATA PAD FCS

CSMA/CA
 Sender send a request-to-send (RTS) frame to
receiver and indicates the time needed to complete
data transmission
 Receiver send clear-to-send (CTS) frame, indicates
time to complete data transmission and reserves
channel for the sender
 Sender transmits the data and receiver responds with
an ACK frame, ensuring reliable transmission
 RTS and CTS frames let other stations know of the
data transmission so that collision is avoided
 Used by 802.11 wireless LAN

CSMA/CA
 Unlike CSMA/CD (Carrier Sense Multiple
Access/Collision Detect) which deals with
transmissions after a collision has occurred,
CSMA/CA acts to prevent collisions before they
happen.
 CSMA/CA differs from CSMA/CD due to the nature of
the medium, the radio frequency spectrum.
 RTS-CTS-DATA-ACK to request medium
 Random back off after collision is detected

CSMA/CA
 The main difference is the collision avoidance :
on a wire, the transceiver has the ability to listen
before and while transmitting and so to detect
collisions.
 Collisions are avoided using three strategies
 Inter frame space (IFS)
 The contention window
 Acknowledgements

LAN standards
 LAN uses four architecture
 Ethernet
 Token Bus
 Token Ring
 Fiber Distributed Data Interface (FDDI)
 These standards are the part of IEEE’s Project 802

IEEE 802
 IEEE 802 refers to a family of IEEE standards dealing
with local area networks and metropolitan area
networks.
 This IEEE project covers the first two layers of the
OSI model and part of the third level.
 IEEE 802 splits the OSI Data Link Layer into two
sub-layers named
 Logical Link Control (LLC)
 Media Access Control (MAC)

IEEE 802
 More specifically, the IEEE 802 standards are
restricted to networks carrying variable-size
packets.
 LLC
 Upper sub layer
 It will take care of Logical address, Control
information and data.
 MAC
 Lower sub layer
 It contains Synchronization, Flag, Flow and Error
control specifications

IEEE 802
 IEEE 802 OSI Model
Other Layers
802.1 Internetworking
802.2 Logical link control
802.3
CSMA
802.4
Token Bus
802.5
Token ring
Physical
Data Link
Network
Other Network

Data Link
Layer
802.3
CSMA-CD
802.5
Token Ring
802.2 Logical Link Control
Physical
Layer
MAC
LLC
802.11
Wireless
LAN
Network Layer Network Layer
Physical
Layer
OSI
IEEE 802
Various Physical Layers
Other
LANs
Figure 6.11
IEEE 802 LAN standards

IEEE 802
 PDU (Protocol Data Unit)
 The data unit in LLC is called PDU
 PDU contains 4 fields
 Destination service access point (DSAP)
 Source Service Access point (SSAP)
 Control field
 Information field
DSAP Control Information
SSAP

IEEE 802 standards
 IEEE 802.1
 Management and Internetworking
 IEEE 802.2
 Logical Link Control(LLC)
 IEEE 802.3
 Ethernet (CSMA/CD)
 IEEE 802.4
 Token Bus

IEEE 802 standards
 IEEE 802.5
 Token Ring
 IEEE 802.6
 MAN Networks
 IEEE 802.7
 Broad Band LAN
 IEEE 802.8
 Fiber Optic LANS

IEEE 802 standards
 IEEE 802.9
 Integrated Data and Voice Networks
 IEEE 802.10
 Security
 IEEE 802.11
 Wireless Networks

IEEE 802 standards
 In LAN all the stations share common cable
 IEEE adopted 3 mechanism for media access
control
 CSMA/CD(IEEE 802.3)
 Token Bus (IEEE 802.4)
 Token Ring (IEEE 802.5)

IEEE 802.3(Ethernet)
 The IEEE 802.3 standard is based on the
ALOHA system
 IEEE standard 802.3 specifies the following
characteristics of Ethernet.
 The medium is normally base band co-axial
cable.
 Bandwidth is 10Mbps
 Cable segment length is 500m.

 It is a packet switching LAN technology.
 Most widely used LAN protocol.
 It uses CSMA/CD
 It defines two categories
 Base Band
 Broad band

Baseband &
Broadband LAN
366 ARCHANAAJITH

Base band LAN
 The two ways to allocate the capacity of
transmission media are with
 baseband and broadband transmissions.
 Baseband devotes the entire capacity of the
medium to one communication channel.
 The base band specifies a digital signal

Base band LAN
 Baseband LAN uses a single-carrier frequency
over a single channel.
 Most LANs function in baseband mode.
 Ethernet, Token Ring and Arcnet LANs use base
band transmission.

Broad band LAN
 Broadband enables two or more
communication channels to share the
bandwidth of the communications medium.
 Broadband LANs use frequency-division
multiplexing on a coaxial cable to establish a
communications network

Broad band Vs Base Band LAN
 Baseband transmission is bidirectional but
the broadband is unidirectional.
 No any frequency division multiplexing use in
baseband . where as frequency division
multiplexing use in broadband .
 In baseband signal travel short distance and
in broadband signal can travel long distance.
 Broad band specifies analog signal


808802.3
802.3
Base Band
10 Base5,10 base 2,10 base
T,10 base F
Broad Band
10 broad 36

 The first number (10,1,100) indicates Data rates
in MBPS
 The last number indicates cable length in
meters or type of cable.
 Ethernet uses coaxial cable as medium.
 A device called Transceiver is used to establish
connection between computer and cable.
Cable
Hosts
Transceiver

IEEE 802.3(Ethernet Generations)
 Standard Ethernet
 (10 Base 5{Thick Ethernet/Thicknet})
 (10 Base 2{Thin Ethernet})
 (10 Base T{Twisted Pair Ethernet})
 (10 Base F{Fiber Ethernet})
 Fast Ethernet
 Gigabit Ethernet
 10 Gigabit Ethernet

Standard Ethernet(10 Base 5)
 It uses bus topology
 LAN is divided in to segments
 Maximum segment length is 500 meters
 Total length cannot exceed 2500 meters(5 segments)
………..
Segment 1 Segment 5
2.5m 2.5m
500 m 500 m
2500 m

Standard Ethernet(10 Base 2)
 It uses bus topology
 It reduces cost , Installation is easy
 Maximum segment length is 200 meters
 Smaller capacity
N

Standard Ethernet(10 Base T)
 It uses Star topology
 It uses Un shielded Twisted Pair cable(UTP)
 Data rate is 10MBPS
 Maximum length(Hub to station) of 100 meters

Standard Ethernet(10 Base F)
 It uses Star topology
 It uses Fiber optic cables
 Data rate is 10MBPS
 Maximum length(Hub to station) of 2Km
Fiber optic cables

Ethernet Frame Format
Preamble
7 bytes
Length PDU
2 bytes
Data and
padding
0-46 bytes
Source address
6 bytes
SFD
1 byte
Destination Address
6 bytes
CRC
4 bytes
DA = 2 SA = 6 DATA
P L FCS

Ethernet Frame Format
• Preamble: For synchronization
• Des. Add: Destination address
• Sour. Add: Source address
• FCS: Frame Check Sequence --- Error control

Ethernet Address
 Ethernet addresses are 48 bits long.
 Ethernet addresses are governed by IEEE
and are usually imprinted on Ethernet cards
when the cards are manufactured.

Ethernet Address
00 00 E2 15 1A CA

Ring network
 A ring network is a network topology in which
each node connects to exactly two other
nodes, forming a single continuous pathway
for signals through each node
OR
 A ring network is a local area network (LAN) in
which the nodes (workstations or other devices)
are connected in a closed loop configuration.
 Because a ring topology provides only one
pathway between any two nodes, ring networks
may be disrupted by the failure of a single link.

Ring network
 A token ring is a widely-implemented kind of ring
network.
 A Token Ring network is a local area network (LAN)
in which all computers are connected in a ring or star
topology.
 A bit- or token-passing scheme is used in order to
prevent the collision of data between two computers
that want to send messages at the same time.

Token Ring network (IEEE 802.5)
 A token, which is a special bit pattern, travels around the
circle.
 To send a message, a computer catches the token, attaches
a message to it, and then lets it continue to travel around the
network.
 When its transmission is complete, the device passes the
token along to the next device in the topology.
 This ensures that there are no collisions because only one
machine can use the network at any given time.

Ring Interface unit

 In the example above, machine 1 wants to send some data
to machine 4, so it first has to capture the free Token.
 It then writes its data and the recipient's address onto the
Token
 The packet of data is then sent to machine 2 who reads the
address, realizes it is not its own, so passes it on to
machine 3.

 Machine 3 does the same and passes the Token on to
machine 4.
 This time it is the correct address and so number 4 reads
the message.
 It cannot, however, release a free Token on to the ring, it
must first send the message back to number 1 with an
acknowledgement to say that it has received the data

 The receipt is then sent ACK to machine 5 who checks the
address, realizes that it is not its own and so forwards it on
to the next machine in the ring, number 6.
 Machine 6 does the same and forwards the data to number
1, who sent the original message.
 Machine 1 recognizes the address, reads the
acknowledgement from number 4 and then releases the
free Token back on to the ring ready for the next machine
to use.
5/15/2023
392 ARCHANAAJITH

Token Ring Frame format
 Token ring network describes three frame format
 Data frame
 Token frame
 Abort frame
Data Frame
Pre ample D.A S.A Frame Data CRC ED FS
3 Bytes 6 Bytes 6 Bytes Up to 4500 4 Bytes 1 Bytes 1 Bytes

• Preamble:
• For synchronization
• It consists of 3 sub fields
• Each field has one byte long
• One flag in this field indicates that it is a data frame and not a token frame
or an abort frame
• Des. Add: Destination address
• It is 48 bits
• It gives the address of the NIC of the destination

• Sour. Add: Source address
• It is 48 bits
• It gives the address of the NIC of the Source
• Frame data– Actual data field
• CRC--- Error detection
• ED----End delimiter
• It represents the end of data
• FS: Frame status
• It identifies whether the data is received correctly

 Token Frame
 SD- Inform receiver that Frame is coming
 AC-Inform that arriving frame is Token
 ED-Inform to host about end of the token
Start Delimiter Access Control End Delimiter
1 Byte 1 Byte 1 Byte

 Abort Frame
 Sender used this frame to abort transmission
Start Delimiter End Delimiter
1 Byte 1 Byte

Scheduling
Approaches to MAC
400

Approaches to Media Sharing
Medium sharing techniques
Static
channelization
Dynamic medium
access control
Scheduling Random access
 Partition medium
 Dedicated allocation
to users
 Satellite
transmission
 Cellular Telephone
 Polling: take turns
 Request for slot in
transmission
schedule
 Token ring
 Wireless LANs
 Loose coordination
 Send, wait, retry if
necessary
 Aloha
 Ethernet
ARCHANAAJITH

Scheduling Approaches to MAC
 Multiple users share the communication channel
so a scheme (medium sharing technique) must
be devised to prevent collision of packets
 1. Reservation Systems
 2. Polling Systems
 3. Token Passing Systems
 4. Static Channelization: TDMA and FDMA

Reservation Systems
• Transmissions from stations are organized in
cycles that have variable length.
• Each cycle consists of a reservation interval
followed by the transmitted packets.

Reservation Systems
 A station uses its mini slot in the reservation
interval to broadcast its intention for transmission

Modification in Reservation
Systems
 Variable length frames be accommodated if
the reservation slot for a station contains
information on the frame length

Modification in Reservation Systems
 More than one frame can be transmitted by a
station by modifying the reservation slot to
indicate number of frames to be transmitted
per station

Network Connecting
Devices
407

Network Connecting Devices
408

 Repeaters and Hubs--- To increase the
coverable distance
 Bridges----- Traffic Management
 It has some filtering capacity
 Routers---- Routing to other networks
 Gateway---- Provides security
 Switches ---- Fast connecting
409

Connecting Devices and OSI Model
410 ARCHANAAJITH

411 ARCHANAAJITH

Repeaters
 A repeater is specific hardware designed to
overcome signal attenuation
 It usually has only two ports and is designed to
pure boost or amplify a signal.

Ethernet hubs and repeaters operate at the
Physical Layer of the OSI Reference model
415 ARCHANAAJITH

HUBS
 hub are very similar to repeaters and is
basically a multi port repeater.
 Repeater is usually used for the extension of
the length while hub is a simple connectivity
gadget that is used to broaden a network.

 The central connecting device in a computer
network is known as a hub.
418 ARCHANAAJITH

HUBS
 Hubs are also known as "multi-port repeaters" or
"active star networks”.
419 ARCHANAAJITH

Working of a HUBS
420 ARCHANAAJITH

HUB
 When data packets arrives at hub, it broadcast
them to all the LAN cards in a network.
 There are two types of hub
 Active hub--- Repeats or re generate signal
 Passive hub--- Used only for connection

Bridge
 A bridge is a network communication device that
is used to connect one segment of the network
with another that uses the same protocol.
 Bridges are fast devices for forwarding the
data but not as fast as the routers and
switches.
 A bridge when combined with the router,
known as a brouter.
 Bridges has now replaced the switches and
routers.

Bridges
 Bridges operate in the Data Link layer
 Bridges are two types
 Transparent Bridge
 Routing Bridge
 The duties of Transparent bridges are
 Filtering frames
 Forwarding
 Blocking
427

Transparent Bridges
429 ARCHANAAJITH

Transparent Bridges
 A transparent bridge is a common type of bridge
that observes incoming network traffic to identify
media access control (MAC) addresses.
 These bridges operate in a way that is
transparent to all the network's connected hosts.
 Transparent bridges are implemented primarily in
Ethernet networks.
430 ARCHANAAJITH

Transparent Bridges
 There are two types of Transparent Bridge
Modes:
 Store-and-Forward: Stores the entire frame and
verifies the CRC before forwarding the frame. If a
CRC error is detected, the frame is discarded.
 Cut-Through: Forwards the frame just after it
reads the destination MAC address without
performing a CRC check.
431 ARCHANAAJITH

Transparent Bridges
 Transparent bridges save and maintain the
source-route addresses of incoming frames by
listening to all the connected bridges and hosts.
 They use a transparent bridging algorithm to a
accomplish this. The algorithm has five parts:
 Learning
 Flooding
 Filtering
 Forwarding
 Avoiding loops
432 ARCHANAAJITH

Transparent Bridges
 Transparent bridges actively listen to traffic on
each segment on which it is attached.
 When a transparent bridge encounters a frame
that is to be forwarded to a destination MAC it
forwards it out a specific port that it has
associated with that MAC address.
433 ARCHANAAJITH

Transparent Bridges
 If a bridge does not 'know' that MAC address
(has no port associated with that MAC), it sends
the frame out all the other ports on the bridge.
 Frames are never forwarded out the port they
are received on.
434 ARCHANAAJITH

Source Route Bridges
435 ARCHANAAJITH

Source route Bridges
 The route through the LAN internet is determined
by the source (originator) of the traffic hence this
bridge is called as source routing bridge.
 The routing information field (RIF) in the LAN
frame header, contains the information of route
followed by the LAN network.
436 ARCHANAAJITH

Mixed-Media
Bridging
437 ARCHANAAJITH

Mixed Media Bridges
 Transparent bridges are found predominantly
in Ethernet networks, and source-route
bridges (SRBs) are found almost exclusively
in Token Ring networks.
 Both transparent bridges and SRBs are popular,
so it is reasonable to ask whether a method
exists to directly bridge between them.
438 ARCHANAAJITH

Mixed Media Bridges
439 ARCHANAAJITH

Switch
 A network switch (sometimes known as a switching
hub) is a computer networking device that is used to
connect devices together on a computer network.
 Switches are another fundamental part of many
networks because they speed things up.
 Switches allow different nodes (a network
connection point, typically a computer) of a network
to communicate directly with one another in a
smooth and efficient manner.
 A switch is considered more advanced than a hub
because a switch will only send a message to the
device that needs or requests it, rather than
broadcasting the same message out of each of its
ports.
441 ARCHANAAJITH

Switch
 A switch is a multi-port network bridge that
processes and forwards data at the data link layer
(layer 2) of the OSI model.
442 ARCHANAAJITH

Switch
 Like a hub, a switch connects multiple segments of a
network together, with one important difference.
Whereas a hub rebroadcasts anything it receives on
one port to all the others, a switch makes a direct
link between the transmitting device and receiving
device.
 Any party not involved in that communication will not
receive the transmission. The benefit of a switch
over a hub is that the switch increases performance
because it doesn’t suffer from the wasted bandwidth
of the extra transmissions.
443 ARCHANAAJITH

Switch
444 DEEPAK.P
ARCHANAAJITH

Switching Methods
446 ARCHANAAJITH

Comparison of Networking Devices
449 ARCHANAAJITH

Comparison of Networking Devices
450 ARCHANAAJITH

DEEPAK.P
Inter network
452 ARCHANAAJITH

Inter network
 Internetworking is the practice of connecting a
computer network with other networks through the
use of gateways that provide a common method of
routing information packets between the networks.
 The resulting system of interconnected networks is
called an internetwork.
 Internetworking is a combination of the words inter
("between") and networking;
 The most common example of internetworking is the
Internet
453 ARCHANAAJITH

Inter network
 Inter networking can be classified in to two
 Connection oriented or concatenated of virtual
circuit subnets
 Connectionless or Datagram
454 ARCHANAAJITH

Connection oriented
Virtual circuit
455 ARCHANAAJITH

virtual circuit
• A virtual network link is a link that does not consist
of a physical (wired or wireless) connection
between two computing devices but is implemented
using methods of network virtualization.
456 ARCHANAAJITH

concatenated of virtual circuit
457
B
A X.25
Subnet 1
Subnet 3
Host
ATM
M M
Subnet 2
SNA
Multi protocol router
(Gateway)
Routers
SNA-System Network Architecture
ARCHANAAJITH

virtual circuit Establishment
1. Subnet shows that the destination is remote
destination and builds a virtual circuit to the router
nearest to the destination.
2. It then constructs a virtual circuit from that router to
an external gateway (multi protocol router).
3. This gateway notes down the existence of this virtual
circuit in its table and builds another virtual circuit to
a router which is in the next subnet.
4. This process continues until the destination host has
been reached.
458 ARCHANAAJITH

virtual circuit Establishment
5. After building the virtual circuit, data packets begin to
flow along the path
459 ARCHANAAJITH

Advantage& Disadvantage virtual circuit
 Advantage
 Buffer can be reserved in advance
 Shorter header can be used
 Sequencing can be guaranteed
 Drawbacks
 There is no alternate path to avoid congestion
 Router failure creates big problems
460 ARCHANAAJITH

Connection less
461 ARCHANAAJITH

Datagram Internetworking
462
Path 2 B
A
Subnet 1
Subnet 3
Host
M M
Subnet 2
Multi protocol router
(Gateway)
Routers
M
M
Path 1
Datagram packets
Datagram packets
ARCHANAAJITH

 The packets that are forwarded across the Internet are
known as IP datagrams
 An IP datagram consists of a header and a payload
 The header contains information that allows Internet
routers to forward the datagram from the source host to
the destination host
463 ARCHANAAJITH

 Header contains all information needed to deliver
datagrams to destination computer
 Destination address
 Source address
 Identifier
 Other delivery information
 Router examines header of each datagram and
forwards datagram along path to destination
464 ARCHANAAJITH

Advantage& Disadvantage Datagram
 Advantage
 Higher Bandwidth
 Deal with congestion in a better way
 It is robust in Router failure
 Drawbacks
 No guarantee of packets
 Addressing is difficult
 Longer header is needed
465 ARCHANAAJITH

Tunneling
 It is used when source and destination networks of same
type are to be connected through a network of different
type.
467 ARCHANAAJITH

Learn Network Services, Topology and Social Relationships

Recommended

Recommended

More Related Content

Similar to Learn Network Services, Topology and Social Relationships

Similar to Learn Network Services, Topology and Social Relationships (20)

Recently uploaded

Recently uploaded (20)

Learn Network Services, Topology and Social Relationships