Physical
or Logical layout of structure called topology, in which all nodes are
connected. Network topology is the arrangement of the elements of a
communication network. The physical topology of LAN refers to the way in which
the stations are physically interconnected. Each topology has its own strengths
and weakness.
Feature
of network topology: 1. The topology should be flexible. You can increase or decrease
number of nodes in topology. 2. The cost of physical media and installation
should be minimum. 3. The network should not have any single point of complete
failures.
Types of Topologies
There are
5 types of topologies in computer network:
Star Topology
A star
topology consists of a number of devices connected by point-to-point
links to a central hub. Easy to control and traffic flow is simple. Data
travels from the sender to central hub and then to the receiver. A dedicated
link is provided to host and centralize hub. Centralized device may be hub or
switch.
Figure: Star Topology Structure
In a star
topology, the central hub acts like a server and the connecting nodes act like
clients. When the central node receives a packet from a connecting
node, it can pass the packet on to other nodes in the network. A star topology
is also known as a star network.
Figure: Star Topology Animation
Advantages
It is
easy to modify and new nodes to a star network without disturbing the rest of
the network.
Troubleshooting
techniques are easy.
Failures
of any node do not bring down the whole star network.
Disadvantages
If the
central hub fails, the whole network fails to operate.
Each
device requires its own cable segment.
Installation
can be moderately difficult, especially in the hierarchical network.
Physical
or Logical layout of structure called topology, in which all nodes are
connected. Network topology is the arrangement of the elements of a
communication network. The physical topology of LAN refers to the way in which
the stations are physically interconnected. Each topology has its own strengths
and weakness.
Feature
of network topology: 1. The topology should be flexible. You can increase or
decrease number of nodes in topology. 2. The cost of physical media and
installation should be minimum. 3. The network should not have any single point
of complete failures.
Types of Topologies
There are
5 types of topologies in computer network:
Bus Topology
A bus
topology is a network setup in which each computer and network
device are connected to a single cable or backbone. Bus topology also
called horizontal topology. In bus topology, multiple devices are connected one
by one, by means of connectors or drop cables. When one computer sends a signal
up (and down) the wire, all the computers on network receive the information,
but only one accepts the information (using address matching). The rest discard
the message.
Figure: Bus Topology Structure
The cable
to which the nodes connect is called a "backbone". A host on
a bus network is called a Station or workstation. Bus is passive
topology, because it requires termination. Cable cannot be left un-terminated
in a bus network. Terminators are required both ends of cable. Terminators were
the 50-ohm resistor that were connected to each end of cable.
Figure: Bus Topology Animation
In a bus
network, every station will receive all network traffic, and the traffic
generated by each station has equal transmission priority. For example, station
1 wants communicate to station 2. But after sending data by station 1, all
stations those are connected with bus will received data. In order for nodes to
transmit on the same bus simultaneously, they use carrier sense multiple
access (CSMA) protocol.
Advantages:
Easy to
use and easy to install.
Needs
fewer physical connectivity devices.
A
repeater can also be used to extend a bus topology.
Low cost.
Disadvantages:
Heavy
network traffic can slow a bus considerably.
It is
difficult to troubleshoot a bus topology.
Failure
of cable affects all devices on the network.
OSI Model
developed by ISO (International Organizations for Standardization). OSI stands
for Open System Interconnection. There are seven layers in this model. OSI
Model is developed after TCP/IP Model.
OSI model
provides following services: 1-Provides peer-to-peer logical services with
layer physical implementation. 2-Provides standards for communication between
system. 3-Define point of interconnection for the exchange of information
between system. 4-Each layer should perform a well-defined function.
Introduction of TCP/IP Model
The
internet architecture, which is also sometimes called the TCP/IP architecture
its two main protocols. It stands for Transmission
Control Protocol/Internet Protocol.
TCP/IP is
four-layer system. Layers of TCP/IP are Application layer, Transport layer,
Internet layer and Host to network layer. Host to network layer is
called physical and data-link layer in OSI model. Internet layer is called
network layer in OSI model. The application layer in TCP/IP model is
combination of application, presentation and session layer of OSI model.
TCP is connection-oriented protocol and IP is connectionless protocol. Application program
sends data to the transport layer protocols TCP and UDP. Routing of packet
takes place in internet layer. Transmitting IP datagram using host to network
protocol. TCP/IP model does not define any specific protocol in host to network
layer.
Comparison of OSI Model and TCP/IP Model
Figure: Comparison of OSI and TCP/IP Model
To learn more about Comaprison of OSI and TCP/IP Model, Click here
OSI Model
developed by ISO (International Organizations for Standardization). OSI stands
for Open System Interconnection. There are seven layers in this model. OSI
Model is developed after TCP/IP Model. (How to remember all layers in sequence - Watch the video)
Figure: OSI Reference Model
OSI model
provides following services: 1-Provides peer-to-peer logical services with
layer physical implementation. 2-Provides standards for communication between
system. 3-Define point of interconnection for the exchange of information
between system. 4-Each layer should perform a well-defined function.
Physical Layer
Physical
layer is the lowest layer of the OSI model. Physical layer co-ordinates the
function required to transmit a bit stream over a communication channel. The
physical layer is responsible for movements of individual bits from one hop
(node) to the next. It deals with electrical and mechanical specifications of
interface and transmission media. It also deals with procedures and functions
required for transmission. Carries
the bit stream over a physical media.
Function of Physical Layer:
Physical
characteristics of interfaces and media: The design issue of physical
layer considers the characteristics of interface between devices and
transmission media.
Representation
of bits: Physical layer encodes the bit stream into electrical or
optical signal.
Data
rate: The physical layer defines the duration of a bit which is
called as data rate or transmission rate.
Synchronization
of bits: The transmission rate and receiving rate must be same. This
is done by synchronizing clocks at sender and receiver.
Datalink Layer
The data
link layer is responsible for transmitting frames from one node to the next. It
transforms the physical layer to a reliable link making it an error free link
to upper layer. Data link layer is divided into two sub layers: LLC (Upper Layer), MAC
(Lower Layer).
LLC is responsible for Flow control, Error Control,
Access Control. MAC is responsible
for Physical addressing.
Function of Data Link Layer:
Framing: The
frames received from network layer is divided into manageable data units called
frames.
Physical
Addressing: When frames are to be sent to different LANs, the data link
layer adds a header to the frame to define sender to receiver.
Flow
Control: When the rate of the data transmitted and rate of data
reception by receiver is not same, some data may be lost. So, this layer
manages data flow.
Error
Control: Data link layer incorporates reliability to the physical
layer by adding mechanism to detect and retransmit damaged or lost frames.
Access
Control: When multiple devices are connected to same link, the data
link layer determines which device has control over link.
Network Layer
The
network layer is responsible for the delivery of packets from the source to
destination. It provides host to host delivery. In case of data link layer, packet delivers on the same network. If two different networksare connected then packet is concern with network layer.
Function of Network Layer:
Logical
Addressing: DLL implements physical addressing. When a packet
passes network boundary. An addressing system is needed to distinguish source
and destination, network layer performs this function. The network layer adds a
header to the packet of upper layer includes the logical addresses of sender
and receiver.
Routing: Network
layer route or switch the packets to its final destination in an internetwork.
Transport Layer
The
transport layer is responsible for delivery of message from one process to
another. The network does the host to destination delivery of individual
packets considering it as independent packet. But transport layer ensures that
the whole message arrives intact and in order with error control and process
control.
Function of Transport Layer:
Port
addressing: Computer performs several operations
simultaneously process-to-process delivery means specific process of one
computer must be delivered to specific process on other computer. The transport
layer header therefore includes port address. Network layer delivers packet to
the desired computer and transport layer, goes message to the correct process
on that computer.
Segmentation
and reassembly: Messages are divided into a segment; each
segment contains a sequence number which enables transport layer to reassemble
at destination.
Connection
Control: Transport layer performs connectionless or connection-oriented
services with the destination machine.
Flow
Control: Transport layer performs end-to-end flow control while data
link layer performs it across the link.
Error
Control: Error control at this layer is performed on end-to-end basis
rather than across the link. The transport layer ensures error free
transmission.
Session Layer
The session
layer is responsible for network dialog controller i.e., it establishes and
synchronizes the interaction between communication system.
Function of Session Layer:
Dialog
Control: Communication between two processes take place in either half
duplex or full-duplex mode. The session layer manages dialog control for this
communication.
Synchronization: Session
layer adds synchronization points into stream of data.
Presentation Layer
This
layer is concerned for data representation. The presentation layer deals with
syntax and semantics of the informing being exchanged. The presentation layer
is responsible for translation, compression, and encryption.
Function of Presentation Layer:
Translation: Different
computers use different encoding systems. The presentation layer maintains
interoperability between the two-encoding system.
Encryption: Encryption
is transforming sender information to non-readable format while transmission.
Decryption is reverse process.
Compression: Compression
is a technique of reducing number of bits required to represent the data.
Application Layer
Application
layer is nearest layer of user. The application layer is providing services to
the user. Application layer is responsible for accessing the network by user.
It provides user interfaces and other supporting services such as e-mail,
remote file access, file transfer, sharing database etc...
Function of Application Layer:
Network
virtual terminal: It is a software version of physical terminal that
allows a user to log onto a remote host.
File
Transfer, Access and Management (FTAM): FTAM allows user to access files
and remote hosts, to retrieve files and to manage files in remote computer.
Mail
Services: E-mail forwarding, storage are the services under this
category.
Summary of OSI Model
To learn more about OSI Reference Model, Click here
The
internet architecture, which is also sometimes called the TCP/IP architecture
its two main protocols. It stands for Transmission
Control Protocol/Internet Protocol.
TCP/IP is
four-layer system. Layers of TCP/IP are Application layer, Transport layer,
Internet layer and Host to network layer. Host to network layer is
called physical and data-link layer in OSI model. Internet layer is called
network layer in OSI model. The application layer in TCP/IP model is
combination of application, presentation and session layer of OSI model.
Figure: Prootcol and Services of TCP/IP Model
TCP is connection-oriented protocol and IP is connectionless protocol. Application program
sends data to the transport layer protocols TCP and UDP. Routing of packet
takes place in internet layer. Transmitting IP datagram using host to network
protocol. TCP/IP model does not define any specific protocol in host to network
layer.
Application Layer
Application
layer includes all process and services that use transport layer to deliver
data. The most widely known application protocols are: TELNET, File Transfer
Protocol (FTP), Simple Mail Transfer Protocol (SMTP) and Simple Network
Management Protocol (SNMP). TELENT is the Network Terminal Protocol, which
provides remote login over the network. FTP is used for interactive file
transfer. SMTP delivers the electronic mail.
Transport Layer
Application
program sends data to the transport layer protocols TCP and UDP. An application
is designed to choose either TCP or UDP based in the service it needs. Transport
layer provides process to process delivery in the network. TCP is reliable and connection-oriented
protocol. It delivers data without error from one PC to another PC. It converts
incoming bytes into discrete message. At the receiver side TCP reassembles the
received data or massage into bytes format. TCP also handles flow control. UDP
is a connection less protocol. Sometimes this type of protocol is used for fast
delivery. UDP cannot handle flow control or error checking.
Internet Layer
The
internet layer protocol (IP, IGMP, ICMP, ARP) handle machine to machine
communication. This layer protocols moves data from one host to another; even
if the host are on different networks. It attaches a header to datagram that
includes source address and the destination address, both of which are unique
internet addresses. It provides connection less method of delivering data from
one host to another. The primary protocol used to move data is the Internet
protocol (IP), which provides the following services.
Addressing:Determining the route to
deliver data to the destination host.
Fragmentation: breaking the messages into
pieces if an intervening network cannot handle a large message.
Host to Network Layer
This
layer is called network interface layer. All the physical media connected at
host to network layer. This layer is same as physical and data link layer of
OSI model. Host to Network layer cannot define any protocol, but provides services
based on switching and routing. Ex, ATM, Frame Relay, Token Ring. It is
responsible for accepting and transmitting IP datagram.
Computers
connected with network are known as end systems in network. The end system is
also known as Host.
For
Example, Workstations (PCs / Laptop), TVs and set top boxes, CCTV Cameras, Household
Applications, Mobile Phones.
Figure: End System in Computer Network
Categories of Host
Hosts can
be further divided into two categories: Client and Server.
Figure: Client and Server in Computer Network
Client Server Architecture:
Client:
The
individual workstation in network is called Client. Client send a request to
server, when client wants an access server. The software run at the client
machine is called as client program. Ex., Browser.
Server:
The
central computers which is more powerful than clients, no one access server
without authentication. Ex., File server, database server, print server. Server
provides services as per client request.
The
software run at the server machine is called as server program. Ex., Xampp,
File server.
