Bearer Capability in
telecommunications
Telecommunication, often used in its plural form or abbreviated as telecom, is the transmission of information over a distance using electronic means, typically through cables, radio waves, or other communication technologies. These means of ...
is one of the Information Elements (fields) of the
Q.931 SETUP message. It is used by the calling party to specify the type of
B channel
B channel (bearer) is a telecommunications term which refers to the ISDN channel in which the primary data or voice communication is carried. It has a bit rate of in full duplex.
The term is applied primarily in relation to the ISDN access in ...
being requested.
Description
For example, if a Bearer Capability of Speech is specified, the network is free to select a set of facilities that can provide this service (including, in this case, analogue trunks and routes involving
echo canceller
Echo suppression and echo cancellation are methods used in telephony to improve voice quality by preventing echo from being created or removing it after it is already present. In addition to improving subjective audio quality, echo suppression i ...
s or
DCME
Digital circuit multiplication equipment (DCME) was a type of voice compression equipment that is installed at both ends of a long-distance telecommunication link, typically a link via communications satellite or submarine communications cable. T ...
).
If, on the other hand, a Bearer Capability of Unrestricted Digital Information is specified, the network is required to set up the call using only end-to-end digital facilities (without the use of
robbed-bit signaling
In communications systems, robbed-bit signaling (RBS) is a scheme to provide maintenance and line signaling services on many T1 digital carrier circuits using channel-associated signaling (CAS). The T1 carrier circuit is a type of dedicated circu ...
, echo cancellers, DCME nor
A-law
An A-law algorithm is a standard companding algorithm, used in European 8-bit PCM digital communications systems to optimize, i.e. modify, the dynamic range of an analog signal for digitizing. It is one of the two companding algorithms in the ...
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 Element
(another field in the Q.931 SETUP message), which informs the network of the intended use of the channel by the caller.
References
External links
ITU-T Recommendation Q.931paragraph 4.5.5.
Integrated Services Digital Network
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