{{for, Indonesian television network formerly known as B-Channel, RTV (Indonesian TV network)
B channel (bearer) is a
telecommunications
Telecommunication is the transmission of information by various types of technologies over wire, radio, optical, or other electromagnetic systems. It has its origin in the desire of humans for communication over a distance greater than tha ...
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. Wor ...
data
In the pursuit of knowledge, data (; ) is a collection of discrete values that convey information, describing quantity, quality, fact, statistics, other basic units of meaning, or simply sequences of symbols that may be further interpret ...
communication
Communication (from la, communicare, meaning "to share" or "to be in relation with") is usually defined as the transmission of information. The term may also refer to the message communicated through such transmissions or the field of inqu ...
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 w ...
of 64 kbit/s 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) provides infrastructure and services for public telecommunication
Telecommunication is the transmission of information by various types of technologies over wire, radio, optical, or other el ...
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.