非持久性和 p 持久性 CSMA 之间的区别

先决条件 – 载波侦听多路访问 (CSMA)

1. 非持久性 CSMA ：
在非持久 CSMA 中，具有要发送的帧的站点仅感知信道。在空闲通道的情况下，它将立即将帧发送到该通道。如果发现信道忙，它将等待固定的时间量并再次感知站的状态是空闲还是忙。在这种方法中，当站点检测到前一次传输结束时，它不会为了捕获信道而立即感知信道。这种方法减少了碰撞的机会，但降低了网络的效率。

图 –非持久性 CSMA

2. p 持久性 CSMA –
当信道具有时隙并且时隙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。当站准备好发送帧时，它将检测信道。如果发现信道忙，该站将等待下一个时隙。但是如果发现信道空闲，该站立即以概率 p 发送该帧。站因此等待左概率，即等于 1-p 的 q，以等待下一个时隙的开始。如果发现下一个时隙也空闲，则该站以概率 p 和 q 再次发送或等待。这个过程会一直重复，直到帧被传输或另一个站开始传输。

图 – p 持久性 CSMA

Non-persistent 和 p-persistent CSMA 的区别：

Parameter	Non-persistent CSMA	p-persistent CSMA
Carrier sense	When channel is idle, it will send frame.	When channel is idle, it will send with probability p.
Waiting	It will wait for a random amount of time to check the carrier.	It will wait for the next time-slot for the transmission of frames.
Chance of collision	In this method, chance of collisions are more than in p-persistent.	In this method, there are less chances of collision than in non-persistent.
Utilization	Its utilization is above 1-persistent because in this all the stations constantly check for the channel at the same time.	Its utilization depends upon the probability p.
Delay low load	It is longer than 1-persistent as it only checks randomly when the channel is busy.	It is large when the probability p is small because the station will not send always in the idle state of the channel.
Delay high load	It is high due to collision.	It is large when the probability p of sending is small when the channel is found in the idle state.