B channel

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 64 kbit/s in full duplex.

The term is applied primarily in relation to the ISDN access interfaces (PRA or PRI and BRA or BRI), since deeper in the PSTN network an ISDN bearer channel is essentially indistinguishable from any other bearer channel.

Apart from any transmission errors, the purpose of the network is to carry the contents of the B channel transparently between the endpoints of the call. Exceptions to this general principle include:

*If one or more trunks on the route between the endpoints employs Robbed Bit Signalling, this will result in frequent bit errors in the least-significant bit of bytes transported by the channel, effectively limiting the channel to 56 kbit/s.
*If the call has been established as a long-distance voice call, then echo cancellers may be being employed. While these improve the quality of the channel when it is used for voice communications, they render the channel essentially useless for data communications purposes (whether modulated or not).
*International voice calls may include A-law to μ-law conversion, which also impairs the channel when used for data communications purposes.
*Long-distance voice calls may also employ some form of voice compression, typically provided by equipment such as DCME.

In order to assure the usability of the channel for data communications, the following measures are at the disposal of users:
*ISDN terminal equipment can specify the required Bearer Capability when establishing the call.
*If the call is being set up as a voice call between modems, then a 2100 Hz answer tone sent in the backward direction during the initial seconds of the conversation phase of the call will result in any echo cancellers or echo suppressors being disabled for the remainder of the call.

ee also

*D channel

Wikimedia Foundation. 2010.

Look at other dictionaries:

  • Channel 4 programming — Channel 4, in common with the other main British stations broadcast on analogue, airs a highly comprehensive range of programming. It was established in 1982 with a specific intention of providing programming to groups of minority interests, not… …   Wikipedia

  • Channel 5 (UK) — Channel 5 Channel 5 logo Launched 30 March 1997 (1997 03 30) Owned by Northern Shell …   Wikipedia

  • Channel 5 (UK) programming — Channel 5 airs a wide variety of programming that coveres various genres and themes. Launched in 1997, the channel has always been seen to have less distinctive programming than their other terrestrial rivals at the BBC, ITV and Channel 4. The… …   Wikipedia

  • Channel Tunnel — Map of the Channel Tunnel Overview Location English Channel (Strait of Dover) Coordinates Folkestone …   Wikipedia

  • Channel S — Logo Launched 16 December 2004 Owned by Channel S Global Ltd. Picture format 4:3 (576i, SDTV) Slogan Working for the community Count …   Wikipedia

  • Channel Airways — IATA CW ICAO Callsign Founded 1946 Cease …   Wikipedia

  • Channel One (Russia) — Channel One Первый Канал Launched 9 March 1938 Owned by National Media Group (25%) Picture format 4:3/16:9 (576i, SDTV) …   Wikipedia

  • Channel One (UK TV channel) — Channel One Launched 1 October 2007 (2007 10 01) Closed 1 February 2011 (2011 02 01) Owned by …   Wikipedia

  • Channel 33 (Israel) — Channel 33 Launched February 1994 Owned by IBA Picture format 576i (PAL) 4:3 Country Israel Formerly cal …   Wikipedia

  • Channel 4's Comedy Gala (2010) — Genre Stand up comedy Format Live stage recording Starring Jo Brand …   Wikipedia

  • Channel Islands of California — Geography Location …   Wikipedia

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”

We are using cookies for the best presentation of our site. Continuing to use this site, you agree with this.