The Difference in TDM and TDMA

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Time Division Multiplexing, or TDM, and Time Division Multiple Access, or TDMA, are forms of networking multiplexing -- a technology used for the analog or digital transmission of data packets. Both types of technologies transmit multiple streams of data from one device to another, but the way in which they perform this differs slightly.

Multiplexing

  • Multiplexing represents the transmission of multiple signals through one device and the subsequent reception of those signals. The key benefit to multiplexing is that it allows more information to be sent in a quicker time period. Note, however, that the receiver can only process the signals one by one. Plus, in analog multiplexing, the information is sent and received at the same time, whereas in digital multiplexing, there is a time period difference as per the large amount of traffic being generated.

Time Divison Multiplexing

  • In TDM, two more streams of data appear as if they are being transferred as sub-channels via one channel, while the truth is that they actually take turns on the single channel. What is known as the "time domain" is divided into time slots. The first byte of the first signal goes first in one time slot, and then the first byte of the second signal goes second in another time slot. The process continues until all the data has been transmitted.

Time Division Multiple Access

  • TDMA is a subset of TDM in which multiple transmitters are connected to a single receiver. It's commonly used in 2G and 3G cellular systems, as well as for high-speed local area networking over home wiring: electrical wiring, phone wiring and coaxial cable wiring. It's difficult to apply to mobile phones, however, because mobile phones often move around randomly with the caller, thus making it difficult for the transmitters to properly time their transmissions.

Primary Difference

  • TDMA offers a bit more flexibility. In TDM, telecommunications multiplexing time slots are dedicated to certain users, meaning other users cannot access them. An example of this includes digital ground telephone networks. With TDMA, time slots are freed after a user logs out of the system, thus allowing other people to access those same time slots. This is the case with the Global System for Mobile Communications, or GSM, network.

References

  • Data Communications & Computer Networks; A Business User's Approach; Curt M. White
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