Tag: Advantages and Disadvantages of Polling

Polling in Networking | Access Control Method

Computer Networks

Access Control in Networking-

 

Before you go through this article, make sure that you have gone through the previous article on Access Control.

 

We have discussed-

  • Access Control is a mechanism that controls the access of stations to the transmission link.
  • Broadcast links require the access control mechanism.
  • There are various access control methods-

 

 

  1. Time Division Multiplexing
  2. Polling
  3. CSMA / CD
  4. Token Passing
  5. Aloha

 

In this article, we will discuss about polling.

 

Polling-

 

In this access control method,

  • A polling is conducted in which all the stations willing to send data participates.
  • The polling algorithm chooses one of the stations to send the data.
  • The chosen station sends the data to the destination.
  • After the chosen station has sent the data, the cycle repeats.

 

Example-

 

 

Here-

  • Tpoll = Time taken for polling
  • Tsend = Time taken for sending the data = Transmission delay + Propagation delay = Tt + Tp

 

Efficiency-

 

Efficiency (η) = Useful Time / Total Time

 

  • Useful time = Transmission delay of data packet = Tt
  • Useless time = Time wasted during polling + Propagation delay of data packet = Tpoll + Tp

 

Thus,

 

 

Advantages-

 

  • Unlike in Time Division Multiplexing, no slot is ever wasted.
  • It leads to maximum efficiency and bandwidth utilization.

 

Disadvantages-

 

  • Time is wasted during polling.
  • Link sharing is not fair since each station has the equal probability of winning in each round.
  • Few stations might starve for sending the data.

 

Important Formulas-

 

  • Efficiency (η) = Tt / (Tpoll + Tt + Tp)
  • Effective Bandwidth / Bandwidth Utilization / Throughput = Efficiency(η) x Bandwidth
  • Maximum Available Effective Bandwidth = Total number of stations x Bandwidth requirement of 1 station

 

To gain better understanding about Polling Access Control Method,

Watch this Video Lecture

 

Next Article- CSMA / CD | Access Control Method

 

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