NETWORK TOPOLOGY
NETWORK is any connection of independent computers
that communicate with one other over a shared medium network. There may be two
or more computer. When computer joined in a network we can share files and
devices such as printers or CD-ROM drives. Different network at
multiple network location can also be connected to communicate with computers
of other networks. Today there is more access to more services in the
form of email , internet , and sharing of data base etc.
CATEGORIES OF NETWORK
A.PEEER TO PEER
PEER TO PEER or p2p computer network is one where all
the computers in the network are equal and there known as peers . usually each
computers serves as client/ server and there is no one assigned to be an
administrator for the entire network. They are developed suitably for small
organization. Security is not a such a big issue in this type of network.
It is based on computer power and bandwidth of the users in the network.
b. SERVER BASED
THIS uses the concept of client / server . in this
case work is distributed between client and server or one or more
machines . the work may involve database and management of application ,
such as spreadsheets , accounting , communication , and document management ,
network management and file storage . there may be many client or servers
depending on specific application. In this we can get maximum number of
utilization of machine and hardware .
BUS TOPOLOGIES
BUS topologies are multipoint electrical circuit that can be
implemented using coaxial cable , U T P , OR STP. Data communication is bi
directional ,with the attached devices transmitting in both direction.
This is employed frequently in the LAN with the distributed control. Messages
placed on the bus are transmitted to all nodes. Bus network are specified in
the IEEE 802.3 standard and generally have a maximum length of 2.5 km. Ethernet
is based on bus topology. A tree topology is variation of bus topology , with
multiple nodes branching off the trunk of the central bus. Examples
ETHERNET AND LOCAL TALK .
RING TOPOLOGY
In this topology information travels around the ring in only
one direction with each attached station or node serving as a repeater. Rings
generally are coaxial cable or fibre in nature operating at raw transmission
rates of 4, 6, or 100 mbps or or more . ring networks are specified in the IEEE
802.5 standard , token pass ring , ibm token ring and fddi are all based on
ring topologies.
STAR TOPOLOGIES
The distinguishing feature of star topology is that all
nodes are joined at a single point. Single point is called central node, hub or
switch to which all other devices are attached directly generally via UTP OR
STP.THIS topology is frequently used for networks in which control of the
network is located in the central node. if traffic is high between outlaying
nodes an undue switching burden is placed on the central node. The biggest
advantages of a star topology is that disruptive or failed station can be
isolated there by eliminating any negative effect it may have on lan
performance. The dis advantage is that all connectivity is provided through
central hub. And effects LAN entire. ATM is one example.
MESH TOPOLOGY
Mesh topology configures in such a way that every device on
the network is physically connected to every other device on the network. It
provides better reliability and performance in complexity and difficulty in
creating in mesh network consisting of three or more nodes on the
network.
HYBRID TOPOLOGY
IT includes combination of different topology and configures
a network including a star-bus hybrid, star ring network and mesh topology.
OSI REFERNCE MODEL
Open system interconnection was set us an international
standard for network architecture. The international organization for
standardization took the initiative in setting up OSI.OSI HAS two meanings
Protocols that are authorized by by iso
OSI basic reference model
Osi divides the required functions of the network
architecture into several layers and function of each layers.
ITS LAYERS
A.PHYSICAL LAYER
This layers describes the physical media over which the bit
stream is to be transmitted . It defines the electrical and mechanical
aspects of interfacing to a physical medium and transmitting data as well
as setting up maintaining and disconnecting physical links.
B. DATA LINK LAYER
It takes the bits that are received by the physical layer
and detects errors. This establishes error free communication path between
network nodes over the physical channel, frames messages from transmission, and
checks the integrity of received messages. It is responsible for reliable data
transfer across the physical links.
C.NETWORK LAYER
It is mainly responsible for providing routing services
across the internet. It also shields the upper layer from details about the
underlying network and the routing technology that might have been deployed to
connect different network together.
D.TRANSPORT LAYER
IT performs additional function such as data multiplexing
and de multiplexing. It divides the a transmitting message into packets and
reassembles it at the receiving end. It guarantees the orderely and reliable
delivery of data between end systems. Two protocols used in this TRANSMISSION
CONTROL PROTOCAL AND OSI TRANSPORT PROTOCOL.
E.SESSION LAYER
THE session layer is responsible for establishing
maintaining , arbitrating the dialogs between communicating application. It is
also responsible for the orderly recovery from failures by
implementing appropriate checking-point mechanisms.
Presentation layer
The presentation layer performs functions related to the
formatting and displaying of received data by terminals and printers. It is
concerned with the differences in the data syntax used by communicating
applications.
Application layer
This layer provides supports services for user and
application tasks. It determines how the user is using the data network. It
allows the user to use network. It defines the nature of task to be performed.
TCP/IP
IT DEFINES a suit of communications and application
protocol in layer structure ,with ieach layer handling distinct communication
services . it defines four layer model as consisting of application ,host to
host,internet, network access. It is based on osi reference model. Tcp
corredponding to fourth layer and ip operates at third layer of the osi mode.
Tcp-ip communication architecture
Application layer
(application specific processes)
Host to host layer
(host specific process)
Internet layer
(routing processes)
Network accsess layer
(network specific processes)
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