fundamentals of computer networks reference models

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Computer Networks

2. • Definition
• A computer network is a group of computer systems and other
computing hardware devices that are linked together through
communication channels to facilitate communication and
resource-sharing among a wide range of users.
• Computer networks are made up of wired or wireless
communication pathways that transmit data, voice and video
traffic using protocols to organize traffic.
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3. • A network must fulfil following criteria.
• Performance
• Reliability
• Security
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4. • Network Technologies
• The way networks are designed to communicate.
• Types of Network Technologies:
• Peer to Peer and Client/Server
• Peer To Peer Architecture
• A model in which all the computing devices within the network can
function as clients or servers as needed and there's no centralized
control over the network resources.
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●Peer to Peer technology

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●Client Server Architecture
– The Client-Server network model is widely used network
model. Here, Server is a powerful system that stores the data
or information in it and Client is the machine which access
the data on the server.

7. • Important Differences
• The key difference between Client-Server and
Peer-to-Peer network is that there is a dedicated
server and specific clients in the client-server
network model whereas, in peer-to-peer each
node can act as both server and client.
• In the client-server model, the server provides
services to the client. However, in peer-to-peer,
each peer can provide services and can also
request for the services.
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8. • Important Differences
• In the client-server model, sharing information is
more important whereas, in peer-to-peer model
connectivity between peers is more important.
• In the client-server model, data is stored on a
centralized server whereas, in peer-to-peer each
peer has its own data..
• The client-server model is more expensive to
implement than peer-to-peer.
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9. • Types of Networks- LAN, MAN and WAN
• 1 Local Area Network(LAN)
• LAN is a computer network that interconnects computers within a
limited area such as a residence, school, or office building.
• LAN can be built with relatively inexpensive hardware, such as hubs,
network adapters and Ethernet cables.
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10. • 2 Metropolitan Area Network(MAN)
• It can be considered as a larger LAN.
• Typically MAN spans over a city. A Metropolitan Area Network will have
many Local Area Networks Connected.
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11. • 3 Wide Area Network(WAN)
• A wide area network, or WAN, occupies a very large area, such as an
entire country or the entire world. A WAN can contain multiple smaller
networks, such as LANs or MANs.
• The Internet is the best-known example of a public WAN.
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●NETWORK TOPOLOGY
Topology is the Pattern in which nodes(computers and other
network devices) are connected to form a computer
network.
– Types of Network Topologies are given below.
● BUS,RING, STAR, MESH, Tree and HYBRID .
– BUS Topology
● In this topology, all the nodes (computers as well as
servers) are connected to a single cable (called bus), by
the help of interface connectors. This central cable is the
backbone of the network and is known as Bus. Every
node communicates with other devices through this Bus.

14. Bus Topology
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Advantages
● It is cost effective.
● Cable required is least compared to other
topologies.
● Used for small networks.
● It is easy to understand.
● Easy to expand joining two cables together.

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Disadvantages
● If the main bus encounters some problem, whole
network breaks down.
● It is not suitable for networks with heavy traffic.
● There is a limit on central cable length and number
of nodes that can be connected.
● Fault detection and troubleshooting is difficult.

17. • RING Topology
• Here all the nodes are
connected to each-other
forming a loop or RING.
• Each Node is connected
to nodes on either side,
and it communicates
with these two adjacent
neighbours. Data travels
around the network, in
one direction. Sending
and receiving of data
takes place by the help
of TOKEN.
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Advantages
●All data flows in one direction which reduces the chance of
packet collisions.
●Data can transfer between workstations at high speeds.
●Nodes can be added without impacting performance of the
network.
Disadvantages
●Troubleshooting is difficult in ring topology
●Adding or deleting the computers disturbs the network activity.
●Failure of one computer disturbs the whole network.

19. • STAR Topology
• STAR topology is one of the most
common network setups in which
all the nodes are connected to a
central network device(switch, hub
or computer). Here Every node has
its own dedicated connection to
the hub.
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Advantages
●The Network Device(hub/switch/router) can be upgraded
easily.
●Easy to troubleshoot
●Easy to setup and modify.
Disadvantages
●Cost of installation is high.
●If the switch fails then the whole network is disrupted
●More cable length is required

21. • MESH Topology
• It is a point-to-point
connection to other nodes or
devices. All the network nodes
are connected to each other.
• Mesh has n(n-1)/2 physical
channels to link n devices.
•
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Advantages
●Each connection can carry its own data load.
●It is robust
●Easy to troubleshoot
●Provides security and privacy.
Disadvantages
●Installation and configuration is difficult.
●Cabling cost is more.
●More cable length is required

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TREE Topology
In this Topology, all the computer are connected
like the branches of a tree. In Computer Networking, tree
topology is known as a combination of a Bus and Start network
topology. It is otherwise called star bus topology

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Advantages
●Easy to expand-(It is flexible and scalable)
●Easily manageable
●Failure of any of the node will not affect whole network.
Disadvantages
●If any problem happened for backbone cable, entire network will
be in trouble.
●Huge amount of Network Cabling is required. Management and
placement of large number of cables is really difficult.
●When more nodes are added, network performance may be
affected.

25. • Hybrid Topology
• It is a combination of two or more
topologies. Hybrid topology Inherits
the advantages and disadvantages of
the topologies included
• The combination of BUS, STAR,
RING or MESH topology constitute
HYBRID topology
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Advantages
●Reliable as Error detection and troubleshooting is easy
●It is an expandable network.
●Effective..
Disadvantages
●Complex Design.
●High Cost

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●Reference Models
ISO-OSI Reference model
Tcp/ip Reference model

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●ISO- OSI Reference Model
– ISO-International Standards Organization
– OSI- Open System Interconnection
– Introduced in 1984
– This model has 7 Layers.
● Application Layer
● Presentation Layer
● Session Layer
● Transport Layer
● Network Layer
● Data link Layer
● Physical Layer

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●Application Layer
– Used by Network Application.
– Protocols used for file transfer(ftp), web
browsing(http, https), email(smtp) etc.
●Presentation Layer
– Translation, Encryption and Compression of Data
●Session Layer
– Session Management, Authentication, Authorisation
●Transport Layer
– Segmentation, Flow control, Error control
– TCP and UDP

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●Network Layer
– Logical Addressing, routing
– Path determination
– Converts segments into packets
●Data Link Layer
– Physical addressing
– Collision prevention
– Converts packets to frames
●Physical Layer
– Responsible for transmission of raw bits over a
communication channel
– Converts data bits into signals
– Communication channel can be air(radio signals), optical
fibre, coaxial cable etc.

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●TCP/IP Reference Model
– Developed During 1960s by United States
department of defence(DoD)
– TCP-Transmission Control Protocol
– IP-Internet Protocol
– This model has 4 layers
● Application Layer
● Transport Layer
● Internet Layer
● Host to Network Layer/Link Layer

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Application Layer
Transport Layer
Internet Layer
Host to Network Layer/Link Layer
TCP/IP Reference Model

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●Application Layer
– Includes protocols used by most applications.
– HTTP, FTP, SMTP etc
●Transport Layer
– Establishes end to end connectivity
– Protocols in this layer provides error control,
segmentation, flow control etc.
– Message transmission is done either by UDP or
TCP.

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●Internet Layer
– This layer exchanges data packets across the
network.
– Primary protocol in this layer is the Internet
Protocol
– Functions of this layer includes packet delivery,
routing and congestion avoidance.
●Link layer/Host to network layer
– Defines how data is physically sent through the
network.
– Bits are converted to signals.

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DATA Transmission

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Modes of Data Transmission
#Transmission mode defines the direction of
flow of signals between two connected devices.
There are three modes of transmission
●Simplex
●Half Duplex
●Full Duplex

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●Simplex
– In simplex transmission mode, the communication
between sender and receiver occurs only in one
direction. The sender can only send the data and the
receiver can only receive the data. The receiver
cannot reply to the sender.
– Simplex is like a one way road.
– Eg:CPU-monitor communication
●Half Duplex
– The communication between sender and receiver
occurs in both the directions in a half duplex
transmission but, one at a time. The sender and
receiver both can send and receive the information but,
only one is allowed to send at a time.
– Eg: walkie-talkie

39. • Full Duplex
• In full duplex transmission
mode, the communication
between sender and
receiver can occur
simultaneously. The sender
and receiver can both
transmit and receive at the
same time.
• Eg: telephone
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