Difference between 1-Persistent and Non-Persistent CSMA
Last Updated :
22 Aug, 2024
Carrier Sense Multiple Access (CSMA) is a type of network protocol used in the organization of access to networks including Ethernet. Non-Persistent CSMA and 1-Persistent CSMA are two variations of CSMA that are often employed. The knowledge of the relative distinction between these two protocols is insightful when it comes to issues affecting the performance of a network; with regard to collision and throughput. The differences between 1-persistent and Non-Persistent CSMA together with their advantages, disadvantages, and applications will be discussed in this article.
What is a 1-persistent CSMA?
In 1-persistent CSMA, the station continuously senses the channel to check its state i.e., idle or busy so that it can transfer data. In case the channel is busy, the station will wait for the channel to become idle. When the station finds an idle channel, it transmits the frame to the channel without any delay with probability 1. Due to probability 1, it is called 1-persistent CSMA. The problem with this method is that there is a huge chance of collision, as two or more stations can find the channel in an idle state and transmit frames at the same time. At the time when a collision occurs, the station has to wait for a random time for the channel to be idle and to start again.
Advantages of 1-Persistent CSMA
- Simple and Straightforward Implementation: Automatic: The protocol is also easy to implement because the station transmits instantly when the channel is available.
- Lower Delay in Light Traffic: In low traffic, 1-Persistent CSMA this is because stations transmit as soon as the channel is idle and hence they spend little time waiting on the channel.
Disadvantages of 1-Persistent CSMA
- Higher Collision Rate: The protocol is rather assertive and as such more likely to collide with other networks, most especially if the network is busy.
- Inefficiency in Busy Networks: This can bring a problem of congestion and one can end up having to send the output for instant transmission even for continuous sensing.
What is Non-persistent CSMA?
In Non-persistent CSMA, station that has frames to send only senses for channel. In the case of an idle channel, it will send frames immediately to that channel. In case when channel is found busy, it will wait for a fixed amount of time and again sense for state of station to be idle or busy. In this method, station does not immediately sense for channel for only purpose of capturing it when it detects end of previous transmission. This method reduces the chances of a collision but reduces efficiency of network.
Advantages of Non-Persistent CSMA
- Lower Collision Rate: The random backoff time minimizes the chances of collision as opposed to the structured duty cycle and hence can be adopted where there many nodes on a network.
- Better Performance in Congested Networks: Non-Persistent CSMA takes a higher performance in the case of many stations competing for the same channel.
Disadvantages of Non-Persistent CSMA
- Increased Delay: The randomness of the waiting time results in longer time to wait in often in low traffic situations more than in fixed times scenarios.
- Complex Implementation: Random backoff and rechecking requirement adds complexity in the implementation of system.
Difference between 1-persistent and Non-persistent CSMA
| Basis | 1-persistent CSMA | Non-persistent CSMA |
|---|
| Carrier Sense | When channel is idle it will send with probability 1. | When channel is idle it will send frame. |
| Waiting | It will continuously sense channel for transmission of frames. | It will wait for random amount of time to check carrier. |
| Chance of Collision | In this method, there are highest number of collisions observed. | In this method, chance of collision are less than in 1-persistent. |
| Utilization | It's utilization is above ALOHA because frames are sent only when channel is found in idle state. | It's utilization is above 1-persistent because in this all stations constantly check for channel at same time. |
| Delay Low Load | It is small because frames are sent only in idle state. | It is longer than 1-persistent as it only checks randomly when channel is busy. |
| Delay High Load | It is high due to collision. | It is longer than 1-persistent because stations check randomly when channel is busy. |
Conclusion
As much as 1-Persistent and Non-Persistent CSMA protocols have respective advantages, they also have respective disadvantages. 1-Persistent CSMA – is more aggressive than others and we can use in the network scenarios when immediate transmission is required or when the traffic is low. On the other hand, Non-Persistent CSMA is ideal for the environment with a high trafficked tendency of nodes in which the avoidance of collisions is more important despite the offer of delay time. The usage of either of the two depends on the requirements of the particular network and the amount of traffic that is to be expected.