1持久性CSMA与非持久性CSMA的区别

先决条件–载波侦听多路访问(CSMA)
1. 1永久CSMA：
在1永久CSMA中，站点连续感测信道以检查其状态(即空闲或忙碌)，以便其可以传输数据。如果信道繁忙，站将等待信道变为空闲状态。当站发现空闲信道时，它将以概率1在没有任何延迟的情况下将帧发送到信道。由于概率1，它被称为1-persistent CSMA。这种方法的问题是冲突的机会很大，因为两个或多个站可以找到空闲状态的信道并同时发送帧。在发生冲突时，站点必须等待随机时间，信道空闲后才能重新开始。

图– 1 –持续的CSMA

2.非持久性CSMA：
在非持久CSMA中，具有帧的站仅发送信道感知。在空闲信道的情况下，它将立即将帧发送到该信道。如果发现信道繁忙，它将等待固定的时间，然后再次感觉到电台状态为空闲或繁忙。在这种方法中，当站检测到先前传输的结束时，它不会立即仅出于捕获信道的目的而立即感知信道。这种方法减少了冲突的机会，但降低了网络效率。

图–非持久性CSMA

1持久性CSMA与非持久性CSMA的区别：

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.