MODULE INETWORKING CONCEPTS
NETWORK MODELn/w is a combination of h/w,s/w that sends
data from one location to otherh/w consist of any physical equipment that
carries signals from one point of n/w to other
s/w consist of instruction set that make possible the services that use expect from a n/w
NETWORK MODELeg. Consider service provided by a
network like email sending from one point in world to other
It can be broken up to several task performed by separate s/w package and each s/w package uses services of other s/w package
At lowest layer a signal or a set of signals is sent from source computer to the destination computer
LAYERED TASKSWe use the concept of layers in our daily
life. As an example, let us consider two friends who communicate through postal mail. The process of sending a letter to a friend would be complex if there were no services available from the post office.
LAYERED TASKSTasks involved in sending a
letter
LAYERED TASKSIn fig there is sender,r eceiver, carrier
that transports letterHierarchy of tasks involved are
Higher layer. The sender writes the letter inserts the letter in an envelopewrites the sender and receiver
addressesand drops the letter in a mailbox.
LAYERED TASKSMiddle layer.
The letter is picked up by a letter carrier and delivered to the post office.
Lower layer. The letter is sorted at the post office; a
carrier transports the letter.
LAYERED TASKSOn the Way
The letter is then on its way to the recipient.
On the way to the recipient's local post office, the letter may actually go through a central office.
In addition, it may be transported by truck, train, airplane etc
LAYERED TASKSAt the Receiver Site
Lower layer. The carrier transports the letter to the
post office.Middle layer.
The letter is sorted and delivered to the recipient's mailbox.
Higher layer. The receiver picks up the letter, opens
the envelope, and reads it.
LAYERED TASKSHierarchy
There are three different activities at the sender site and another three activities at the receiver site.
The task of transporting the letter between the sender and the receiver is done by the carrier.
The tasks must be done in the order given in the hierarchy.
LAYERED TASKSAt the sender site, the letter must be
written and dropped in the mailbox before being picked up by the letter carrier and delivered to the post office.
At the receiver site, the letter must be dropped in the recipient mailbox before being picked up and read by the recipient.
LAYERED TASKSServices
Each layer at the sending site uses the services of the layer immediately above it
Sender at higher layer uses services of middle layer
Middle layer uses services of lower layer
Lower layer uses services of carrier