HOW TO DETECT ERROR ! USING OSI MODEL - NETWORKING

⧭ In this post , I will discuss about how to detect error while sending message. Network layer send the data in the form of packet between sender and receiver.

➧ Suppose network layer send data in the form of packet such as:

1110  11110 111110 1111110 : packet

This packet is than received by DLL. It is responsibility of DLL that controlling the error and send the message to network layer of receiver end.

➧ For this error controlling DLL proceed following procedure such as:

Add even parity bit cheater for even no of 1's for this add 1 as extra bit in header. If there is even number of 1's in data than bit is not changed otherwise it will change to 0 and when DDL of receiver and receive the data, If header is 1 than the message is correct otherwise it is wrong that mean it will detect the error.

➧ The another method is using stuffing bit in header of message at receiver end.

If we have any message such as :

1110 11110 111110 11111110 than 

➧ We add 0111111110 in state and end of message like:

01111110  1110 11110 111110 1111110 01111110

In this procedure error will arise when continuous six 1's are come in data part than it will give error and can not detect it.

For successful / correctly transmitting data it is necessary that this additional header bits are not repeating in data part at sander end. If such type of problem arise than we stuffing bit.

➧ For understanding stuffing bit we take an example:

011111110 1110 11110 111110 1111110 01111110

here continuous / consecutive 1's are repeating in data part than for removing this we apply one technique such as :

we add '0' after even consecutive five 1's it will remove the possibility of coming continuous six 1's in data part.

➧ After adding '0' we get :

01111110  1110 11110 111110 011111010  011111110

This whole procedure is done at sander end.

After that it is a responsibility of receiver end that it can identify , that ever five 1's there will be a stuffed bit which is '0' here.

Than after identifying the stuffing bit ignore it.

Note : 

➧ If we have header such as 100001 than after every three 0's 1 is stuffed mean have stuffed bit is 1.

⧭ In the next post we will discuss about redundancy checker technique for detecting redundant bit  by using  CRC (Cyclic Redundancy Check).