What is Bit Map protocol in computer networks?

Bit map protocol is called collision free Protocol. In bitmap protocol, each contention period consists of exactly N slots. If any station has to send a frame, then it transmits a 1 bit in the respective slot.

Bitmap Algorithm

The algorithm of Bit Map protocol is explained below −

Step 1 − We use the bitmap or the bit vector which represents a finite set of distinct integers.

Step 2 − To sort the array of integers, initialization of the array size to the specified range is needed and then fill it with zeroes which is a default value in the program followed by setting the corresponding bit in the bitmap to 1 for each integer that was input.

Step 3 − Scanning the bitmap and printing the integers in a sorted order being the final step.

Explanation

The Bit Map protocol is diagrammatically represented as follows −

Here,

Step 1 − Each contention period has exactly N slots. If a station 0 has a frame to send then it transmits 1 bit during slot 0. In general station j may announce that it has a frame to send by inserting 1 bit into slot j.

Step 2 − After all N slots have passed, then each station gets an idea which station is ready to transmit, then the frames are transmitted in numerical order.

Step 3 − Because of mutual understanding there is no chance of collision.

Step 4 − After the last ready station is transmitted its frame, all stations can monitor, another N-bit contention period begins.

Step 5 − If a station becomes ready just after its bit slots have passed by, it must remain silent until the bitmap has come around again.

Step 6 − Protocols like this in which the desire to transmit is broadcast before the actual transmission are called as reservation protocols because they reserve channel ownership in advance and prevent collisions.

Basic Bitmap: Efficiency

• Channel efficiency/utilization: assume N slots, d bits per frame

Low load: ~ d/(d+N)
High load: ~ d/(d + 1)

• Mean delay

> (N-1)d/2 + N