1持久CSMA和p持久CSMA之间的区别

先决条件–载波侦听多路访问(CSMA)
1. 1永久CSMA：
在1永久CSMA中，站点连续检测信道以检查其状态(即空闲或忙碌)，以便可以传输数据。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永久CSMA

2. p持久CSMA：
当一个信道具有时隙并且该时隙的持续时间等于或大于该信道的最大传播延迟时间时，使用p-persistent CSMA。当电台准备好发送帧时，它将感知信道。如果发现信道繁忙，电台将等待下一个时隙。但是，如果发现信道空闲，则站立即以概率p发送帧。因此，该站等待下一个时隙的开始的左概率，即等于1-p的q。如果还发现下一个时隙空闲，则站以概率p和q再次发送或等待。重复此过程，直到发送了一个帧或另一个站开始发送。

图– p永久CSMA

1-persistent CSMA和p-persistent CSMA之间的区别：

Basis	1-persistent CSMA	p-persistent CSMA
Carrier Sense	When channel is idle it will send with probability 1.	When channel is idle it will send with probability p.
Waiting	It will continuously sense channel for transmission of frames.	It will wait for next time slot for transmission of frames.
Chance of Collision	In this method, there are highest number of collisions observed.	In this method, there are less chances of collision 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 dependent on probability p.
Delay low load	It is small because frames are sent only in idle state.	It is large when probability p is small because station will not send always in idle state of channel.
Delay high load	It is high due to collision.	It is large when probability p of sending is small when channel is found in idle state.