1. Identification of computers over a network:
A computer gets a data packet on a network, it can identify the senders address easily. It is similar to ours nails mail, each letter is stamped in sender’s post office as well as receiver’s post office.
(1) Media Access Control(MAC) address:
It is a unique 12 digit hexadecimal number(IMEI for mobile phones, it is a 15 digit decimal number) assigned to each NIC by its manufacturer. This address is known as MAC address and its permanent. It is of the form. MM:MM:MM:SS:SS:SS. The first MM:MM:MM contains the ID number of the adapter company and the second SS:SS:SS represents the serial number assigned to the adapter by the company.
(2) Internet Protocol (IP) address:
An IP address has 4 parts numeric address. Each parts contains 8 bits. By using 8 bits we can represent a decimal number between 0 to 255(2°=256 numbers). Each part is separated by dot. A total of 4*8=32 bits used. But nowadays 128 bits are used for IP address.
2. Network topologies:
Physical or logical arrangement of computers on a network is called structure or topology. It is the geometrical arrangement of computers in a network. The major topologies developed are star, bus, ring, tree and mesh.
(1) Star Topology:
A star topology has a server all other computers are connected to it. If computer A wants to transmit a message to computer B. Then computer A first transmit the message to the server then the server retransmits the message to the computer B.
That means all the messages are transmitted through the server. Advantages are add or remove workstations to a star network is easy and the failure of a workstation will not effect the other. The disadvantage is that if the server fails the entire network will fail.
(2) Bus Topology:
Here all the computers are attached to a single cable called bus. Here one computer transmits all other computers listen. Therefore it is called broadcast bus. The transmission from any station will travel in both the direction. The connected computers can hear the message and check whether it is for them or not.
Advantages are add or remove computer is very easy. It requires less cable length and the installation cost is less. Disadvantage is fault detection is very difficult because of no central computer.
(3) Ring Topology:
Here all the computers are connected in the shape of a ring and it is a closed loop. Here also there is no central computer. Here a computer transmits a message, which is tagged along with its destination computer’s address.
The message travels in one direction and each node check whether the message is for them. If not, it passes to the next node. It requires only short cable length. If a single node fails, at least a portion of the network will fail. To add a node is very difficult.
(4) Hybrid Topology:
It is a combination of any two or more network topologies. Tree topology and mesh topology can be considered as hybrid topology.
(a) Tree Topology:
The structure of a tree topology is the shape of an inverted tree with a central node and branches as nodes. It is a variation of bus topology. The data transmission takes place in the way as in bus topology. The disadvantage is that if one node fails, the entire portion will fail.
(b) Mesh Topology:
In this topology each node is connected to more than one node. It is just like a mesh (net). There are multiple paths between computers. If one path fails, we can transmit data through another path.
