How does csmacd work on a lan

Another example of shared media is when the devices inside an Ethernet network are connected using hubs. When connected using hubs , all the devices in that Ethernet network logically share the same media. In a shared media, normally communication happen between devices using broadcasts.

These days we cannot find any Ethernet network , operating using shared media. In other words, devices are in listen-before-transmit carrier sense mode. When a device wants to place data on the wire for transmission, it will "sense" the wire to find whether there is a signal already on the wire. It senses or listens whether the shared channel for transmission is busy or not, and defers transmissions until the channel is free. The collision detection technology detects collisions by sensing transmissions from other stations.

On detection of a collision, the station stops transmitting, sends a jam signal, and then waits for a random time interval before retransmission. Host A detects that there are no other signals on the network and decides to send a packet. However, Host B also assumes that no other station is transmitting and sends a packet as well.

A collision occurs and it is detected by Host A and Host B. The sending stations send a jamming signal telling all hosts on the segment that a collision occured. To do this, the network must be split up. Switches or bridges are used for this — both work on the basis of MAC. Media access control works on the second i. It makes sense to form the sub networks in such a way that stations, which have to communicate with each other often, are next to each other.

This prevents bottlenecks on the bridges from canceling out the gain in speed. A distinction is made between half-duplex and full-duplex in network technology. Both models are related to the technology used. In the context of networks or other communication techniques, duplex basically describes the possibilities with regard to data transmission. Therefore, half-duplex only allows transmission in one direction at a time. With full-duplex, however, a station can send and receive at any time.

The former only allows transmission in one direction at any time. Dual-simplex, on the other hand, corresponds more to the principle of full-duplex, where both sending and receiving is possible.

In contrast to full-duplex, however, this is done in two different ways. This becomes tangible if you imagine the transmission channel as a single-lane road. If traffic comes simultaneously from both directions, it leads to a collision. Full-duplex , on the other hand, is always two-track.

Traffic can flow past each other from both directions. Therefore, Carrier Sense Multiple Access with Collision Detection is not required in networks that use full-duplex: collisions cannot occur. The duplex type is linked to the technical conditions and very specifically to the types of cable used. Networks connected to coaxial cables can only run in half-duplex mode. Full-duplex was only possible after twisted-pair and fiber optic cables were introduced.

The central problem here is the hidden station problem. This occurs when two stations do not recognize each other, but communicate simultaneously with a third station in the middle — which inevitably leads to collisions.