COMPUTER NETWORKS
O.S.I REFERENCE MODEL AND NETWORK
ARCHITECTURE
COMPUTER NETWORKS:-
A networks can be defined as when many computer and other devices are connected with each in such a way that it many be able to exchange the dates.Any devices in the networks can be considered as node and each node has a unique address .
Address are numeric quantities which is easy to use for computer but difficult to remember for human.
Computer Networks Criteria:-
Computer Networks is a system which allow communication among the computer connected in the networks. A network must be able to meet certain criteria.
The most important then are:-
1. Performance
2. Reliability
3. Security
1. Performance:-
Performance can be measured in many ways.
We can measure it in terms of transit time and response time.
(a) Transit time;-
It is defined as the amount of time required for a message to travel from one device.
(b) Response time;-
It is the time elapsed between enquiry and response time.
The other factory deciding the performance are as follow :-
1 Number of users.
2 Type of transmission medium.
3 Capability of connected hardware.
4 Efficient of software.
2. Reliability:-
The network reliability is important because it decides the frequency at which networks failure takes place. It also decide the time taken by the network to recover and its robustness in the catastrophe.
3. Security:-
The network security refers to protection of data from the unauthorised user or access.
ARPANET:-
ARPANET is basically called a WAN(Wide Area Network). It was developed by ARPA (Advanced Research Project Agency).
It was designed to service even a nuclear attack. The network of ARPANET was too vulnerable because the loss of even one line or switch would terminate all the conversation. ARPANET used the concept of packet switching network consisting of subnet and hosting computer.The subnet was a datagram subnet and each subnet consists of mini computers called IMPs. (Interface Message Processors). Each node of the network used to have an IMP and a host connected by a short wire .The host could send messages of up to 8063 bits.to its IMP which would break them into packets and forward them independently towards the destination.The subnet was first electronic store and forward type packed switched network.so each packet was stored before it was forward. The software for APRANET was split into two parts namely subnet and host.
ARPANET
INTERNET:-
Internet is a globally existing network of networks consisting of huge network of computers situated in the all the parts of the world. It starting growing exponentially with all the type of existing networks getting connected to internet .
All the computers are connected to internet are part of this huge network.The powers that a computer gets due to internet is amazing. It is now possible to send and receive.The data with in a few
