{{for, Indonesian television network formerly known as B-Channel, RTV (Indonesian TV network) 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 In telecommunications and computing, bit rate (bitrate or as a variable ''R'') is the number of bits that are conveyed or processed per unit of time. The bit rate is expressed in the unit bit per second (symbol: bit/s), often in conjunction ...

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 The public switched telephone network (PSTN) provides infrastructure and services for public telecommunication. The PSTN is the aggregate of the world's circuit-switched telephone networks that are operated by national, regional, or local teleph ...

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 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 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 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 two versions of the G.711 standard ...

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 Bearer Capability in telecommunications 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. Description For example, if a Bearer Capabil ...

when establishing the call. *If the call is being set up as a voice call between modems, then a 2100 Hz

answer tone Answer tone is a feature of wireline modems. The answer tone is the first signal sent by the answering modem after the billing delay. In its most basic form, it is a single continuous tone with a frequency of 2100 Hz (or 2225 Hz for Bell modes). ...

sent in the backward direction during the initial seconds of the conversation phase of the call will result in any echo cancellers or

echo suppressor 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 being disabled for the remainder of the call.

See also