B channel (bearer) is a

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 ...

term which refers to the

ISDN Integrated Services Digital Network (ISDN) is a set of communication standards for simultaneous digital transmission of voice, video, data, and other network services over the digitalised circuits of the public switched telephone network. ...

channel in which the primary

data Data ( , ) are a collection of discrete or continuous values that convey information, describing the quantity, quality, fact, statistics, other basic units of meaning, or simply sequences of symbols that may be further interpreted for ...

voice The human voice consists of sound made by a human being using the vocal tract, including talking, singing, laughing, crying, screaming, shouting, humming or yelling. The human voice frequency is specifically a part of human sound produ ...

communication Communication is commonly defined as the transmission of information. Its precise definition is disputed and there are disagreements about whether Intention, unintentional or failed transmissions are included and whether communication not onl ...

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 in

full duplex A duplex communication system is a point-to-point system composed of two or more connected parties or devices that can communicate with one another in both directions. Duplex systems are employed in many communications networks, either to allow ...

. 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) is the aggregate of the world's telephone networks that are operated by national, regional, or local telephony operators. It provides infrastructure and services for public telephony. The PSTN consists ...

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 employ robbed-bit signaling, this will result in frequent bit errors in the least-significant bit of bytes transported by the channel, effectively limiting the channel to . *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 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 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 type of B channel being requested. Description For example, if a Bearer Capability of Sp ...

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.

References

{{Reflist Integrated Services Digital Network ru:B-канал

See also

References