Bearer Capability

Bearer Capability is one of the Information Elements (fields) of the Q.931 SETUP message. It is used by the calling party to specify the kind of B channel that is being requested.

For example, if a Bearer Capability of Speech is specified, then the network is free to select a set of facilities that are able to provide this service (including, in this case, analogue trunks and routes involving echo cancellers or DCME).

If, on the other hand, a Bearer Capability of Unrestricted Digital Information[1] is specified, then the network is required to set up the call using only end-to-end digital facilities (without the use of robbed-bit signalling, echo cancellers, DCME nor A-law to mu-law conversion), or reject the call if no end-to-end digital circuit is available.

The Bearer Capability is augmented by the Higher Layer Compatibility (HLC) Information Elemen[2] (another field in the Q.931 SETUP message), which informs the network of the use that the caller intends to make of the channel.

References
  1. "Bearer Capability - Telecommunications on Cisco Certified Expert".
  2. "ETR 018 by European Telecommunications Standards Institute 1995" (PDF).


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