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Digital Sense Multiple Access (DSMA)

Definition - What does Digital Sense Multiple Access (DSMA) mean?

Digital Sense Multiple Access (DSMA) refers to a protocol that is used in Cellular Digital Packet Data (CDPD) networks. DSMA's main objective is to support narrow-band data services.

DSMA transmits channels as well as decode status flags on the forward channel to imply if the reverse channel is occupied and also if the data block received just now on the reverse channel was decoded correctly with no errors.

By having information on the reverse channel, DSMA functions in a way much like slotted Carrier Sense Multiple Access/Collision Detection (CSMA/CD). Slotted non-persistent DSMA is used in the CDPD network.

Techopedia explains Digital Sense Multiple Access (DSMA)

CSMA/CD protocol is very popular among wired local area networks as it is straightforward and provides high throughput performance. At the same time, because of radio capturing effects, a wireless network user is unable to transmit and listen on the exact same radio channel concurrently, as needed by the CSMA/CD protocol.

In order to address this difficulty, the DSMA protocol transmits channel and decode status flags on the forward channel, that is, from base station to mobile unit. This is to signify the status of the reverse channel involved.

The channel as well as decode flags signifies if the reverse channel is idle or busy and also if the data block just received on the reverse channel was decoded aptly without any errors.

If the round-trip delay is long, the outdated channel busy or idle status and the decode status information on the forward channel trigger two impacts on the DSMA functionality:

  • Chance for high collision since other terminals have no idea of ongoing transmission on the reverse channel, thereby reducing the throughput.
  • Long delay in ending ongoing transmission in the event of a collision, thereby misusing bandwidth unnecessarily.
To overcome these flaws in DSMA protocol, an enhanced DSMA with Delayed Transmission (DSMA/DT) protocol is designed. This new protocol offers more efficiency, while retaining the simplicity of the DSMA protocol.

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