A transceiver serves two function; it is both a receiver and a transmitter which are combined together to form one unit and operate using the same circuitry. In some cases the circuitry will not be shared; in this case it is called a transmitter-receiver which was originally invented in the 1920s. Transceivers must combine a large portion of the handling circuitry that the transmitter and receiver share in order to be considered a transceiver and not a transmitter-receiver. If you are reading from an IEEE 802.3 document, then you will often see transceivers referred to as medium attachment units, or MAUs.



Medium attachment units can convert signals over either an Ethernet cable or an AUI signal. For the original 10base5 Ethernet, the medium attachment unit was often clamped directly to the Ethernet cable itself. Standards changed however with the advent of the 10base2. At this point the medium attachment unit was simply integrated within the card. Then in an effort to keep costs low, which was demanded by their consumer base, the entire Ethernet controller device was simply shrunken down into a single chip. Similar to a hub, a medium attachment unit shares much of the same characteristics, expect for the fact that an MAU allows a token to pass between the devices of different networks, even if the network utilizes physical Star topology. In modern Ethernet systems that are either hubbed or switch-based, the MAU and AUI devices are not used, except for in certain unordinary circumstances. They are replaced by the CAT5 cable. This cable connects directly into the Ethernet socket which can be found on the host or the router. Backwards capability exists with certain equipment which utilizes an external AUI interface. Medium attachment units can still be found on units with 10base2 and 10baseT connections.

Transceivers exist in various devices. They are most often used in computers, telephony, and radios. Computers often use transceivers in the guise of the previously discussed medium attachment units. These are often fiber-optic gigabit and 10 gigabit transceivers which are also known as: GBIC, SFP, XAUI, and XFP. Radio technology has made use of transceivers for a long time, although they will often be separate as transmitter-receivers. The Ham radio is a great example and they can be built using the operator's own equipment. Finally, there is telephony, which uses transceivers via a wired phone or a headset. One such example is the common cellular phone which is, in itself, a transceiver.

If you need to purchase transceivers from any major manufacturer – 3Com, HP, Extreme Networks, Linksys, Netgear, etc, you have two options – purchasing the transceiver directly from the manufacturer at a considerable premium, or purchasing from a memory and GBIC reseller at a considerable discount. If you decide to go the memory reseller route, finding a reliable memory reseller is important. Be sure to go with one with a complete line of GBIC, SFP and CWDM transceivers for your device, offers a warranty, and has technical advisors to help you with both making your transceiver purchase and operation of your transceivers.