What does CSMA/CD mean?

Question

networking thing

Answer 1

Ron is correct. It stands for Carrier Sense Multiple Access with Collision Dectection. In the old days before Ethernet switches, when Ethernet Hubs were around or the coax Ethernet cables were used, then CSMA/CD was used. Now with Ethernet Switch, there is actually no CD (collision dection) required or used at all, as Ethernet Switches will store the entire packets from different ports and then send them out to the appropriate port in sequence without losing anything. In a coax cable Ethernet system (which is not used anymore) before sending a packet, the circuit will look for a carrier (the CS part) which means there is a packet being sent. If no one is sending, then I can start to send the packet. The MA (multiple access) means more than one can use the medium, i.e. not point-to-point as with a phone call. When I start to send the packet, I will also listen to corruption on my packet, this is the (CD) collision detection part.

Note that in Wireless LAN as in Wi-Fi, the multiple access method is CSMA/CA. "CA" being collision avoidance, I will wait for a predetermined time when I detect a carrier (CS) to let the other person to finish transmitting. The reason CA is used here verus CD is because the wireless does not allow me to listen at the same time while I am transmitting, thus CD is not possible.

When I detect a collision (CD) then there is a back-off time before I can re-transmit again. The back-off goes up exponentially on each subsequent collision detection of the same packet. Thus the old coax or hub based Ethernet can have significantly very low packet throughput when the channel get closer and closer to being full, i.e. when there is a lot of senders on the same network, then the actual throughput goes to zero or nothing gets through as in a grid lock.

Answer 2

carrier sense multiple access collision detect

Media-access mechanism wherein devices ready to transmit data first check the channel for a carrier. If no carrier is sensed for a specific period of time, a device can transmit. If two devices transmit at once, a collision occurs and is detected by all colliding devices. This collision subsequently delays retransmissions from those devices for some random length of time. CSMA/CD access is used by Ethernet and IEEE 802.3.

Answer 3

CS stands for cable select, it is a jumper setting on your CD rom drive. MA stands for Master, also a jumper setting.
You can set the jumpers on Master and Slave or cable select. You must boot from the one that is Master, or cable select. You cant boot from the slave. You can have two drives as cable select, but only one master, and only one slave. You cant have a single drive set to slave.