Carrier Sense Multiple Access

Hi to all,


What is Carrier Sense Multiple Access?
How it is helpful in CAN protocal.

CSMA/CA is Non-destructive. CSMA/CR: sender with lowest identifier (=highest priority) wins the arbitration, message is not destroyed.

In CAN if we start to detect the collision then there is more of time consumed, In order to make it l=consume less time and handle all data more efficiently, we use Collision avoidance technique. Using this technique compared to collision detection increases the execution time,

---------- Post added at 18:50 ---------- Previous post was at 18:49 ----------

In simple words Its cillision free data transfer

Hi Shivaram,

I Hered the following terms..

CSMA/CR : cillision Reselution
CSMA/CD : cillision Detection
CSMA/CA : cillision Avoidence

I think All these are for collision free data transfer only,May i Know is there any Difference among them.

you can find more information about CSMA/CA & CSMA/CD in data communication book by frozen

Canbus uses CSMA/CA : cillision Avoidence: the transmitter(s) waiting to transmit listens until the line is free (the CSMA part) then start to transmit - as data is transmitted 0's are dominant (if a 0 and a 1 are transmitted at the same time 0 appears on the bus) so if a transmitter transmit a 1 and sees 0 on the bus it aborts transmission (the CA part). Thus the message with the lowests (high priority) ID transmits first.
CSMA/CD : cillision Detection is used by Ethernet. the transmitter(s) waiting to transmit listens until the line is free (the CSMA part) then start to transmit - as they transmit they listen and if they 'hear' something other than their own signal (works on voltage level) they assume a collision (the CD part) and all transmissions abort.
Canbus is deterninistic network access (the worst case access time can be calculated) and etherenet is probablistic network access (access depends upon network traffic and there is only a probability of getting access and in an overloaded network may never happen). Deterministic is used for real time systems.