Basic rate interface
Encyclopedia
Basic Rate Interface is an Integrated Services Digital Network
(ISDN) configuration intended primarily for use in subscriber lines similar to those that have long been used for plain old telephone service
. BRI is in contrast to the Primary Rate Interface
(PRI) configuration which is also used in the access network
but uses more robust transmission lines to carry a higher bit rate
.
BRI is defined in the physical layer standard I.430
produced by the International Telecommunication Union
(ITU). The BRI configuration provides two 64 kbit/s bearer channels (B channel
s) and one 16 kbit/s data channel (D channel
). The B channels are used for voice
or user data
, and the D channel is used for any combination of data, control/signalling, and X.25
packet networking. The two B channels can be aggregated by channel bonding
providing a total data rate of 128 kbit/s. The BRI ISDN service is commonly installed for residential or small business service in many countries.
The I.430 protocol defines 48-bit packets comprising 16 bit
s from the B1 channel, 16 bits from B2 channel, 4 bits from the D channel, and 12 bits used for synchronization
purposes. These packets are sent at a rate of , giving the data rates listed above for a maximum possible throughput of .
BRI service is delivered via three types of physical interfaces. Signals are encoded by two modulation techniques, 2B1Q in North America, and 4B3T elsewhere.
coding is the standard used in North America. 2B1Q means that two bits are combined to form a single Quaternary line state (symbol). 2B1Q combines two bits at a time to be represented by one of four signal levels on the line. The signal rate, therefore, is 80 kilobaud
and the line rate 160 Kbit/s. It operates with a maximum frequency range (bandwidth) of .
2B1Q coding is defined in ANSI T1.601 and ETR 080, Annex A. It can operate at distances up to about 18,000 feet with loss up to . An internal termination impedance of 135 ohms is presented to the line at each end of the U-interface. Echo cancellation
techniques allow full-duplex operation on the line.
2B1Q transmission can be simply described as an amplitude modulation scheme for DC pulses.
is 3/4ths of the data rate (120 kbaud
).
4B3T is defined in ETR 080, Annex B and other national standards, like Germany's 1TR220. 4B3T can be transmitted reliably at up to over cable or up to over cable. An internal termination impedance of is presented to the line at each end of the U-interface. Echo cancellation techniques allow full-duplex operation on the line.
In 4B3T coding, there are three states presented to line: a positive pulse (+), a negative pulse (-), or a zero-state (no pulse: 0). An analogy here is that operation is similar to B8ZS or HDB3 in T1/E1 systems, except that there is an actual gain in the information rate by coding 16 possible binary states to one of 27 ternary states.
There are many ways to perform this conversion, but BRI standards define a code known as MMS43 (Modified Monitoring State 43).
One requirement for line transmission is that there should be no DC build-up
on the line, so there are some code substitutions based upon the transmission of the previous bits.
Integrated Services Digital Network
Integrated Services Digital Network is a set of communications standards for simultaneous digital transmission of voice, video, data, and other network services over the traditional circuits of the public switched telephone network...
(ISDN) configuration intended primarily for use in subscriber lines similar to those that have long been used for plain old telephone service
Plain old telephone service
Plain old telephone service is the voice-grade telephone service that remains the basic form of residential and small business service connection to the telephone network in many parts of the world....
. BRI is in contrast to the Primary Rate Interface
Primary rate interface
The Primary Rate Interface is a standardized telecommunications service level within the Integrated Services Digital Network specification for carrying multiple DS0 voice and data transmissions between a network and a user....
(PRI) configuration which is also used in the access network
Access network
An access network is that part of a telecommunications network which connects subscribers to their immediate service provider. It is contrasted with the core network, which connects local providers to each other...
but uses more robust transmission lines to carry a higher bit rate
Bit rate
In telecommunications and computing, bit rate is the number of bits that are conveyed or processed per unit of time....
.
BRI is defined in the physical layer standard I.430
I.430
The I.431/430 Networking standards are recommendations produced by the ITU. They are Layer 1 specifications for ISDN networks, using either an E1 or T1 circuit. The I.431 standard is known as the 'PRI Physical Layer' whereas the I.430 is known as the 'BRI Physical Layer'.-External links:* from the...
produced by the International Telecommunication Union
International Telecommunication Union
The International Telecommunication Union is the specialized agency of the United Nations which is responsible for information and communication technologies...
(ITU). The BRI configuration provides two 64 kbit/s bearer channels (B channel
B channel
B channel 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....
s) and one 16 kbit/s data channel (D channel
D channel
D channel is a telecommunications term which refers to the ISDN channel in which the control and signalling information is carried.The bit rate of the D channel of a basic rate interface is 16 kbit/s, whereas it amounts to 64 kbit/s on a primary rate interface.For DSS1 signalling, the D channel...
). The B channels are used for voice
Human voice
The human voice consists of sound made by a human being using the vocal folds for talking, singing, laughing, crying, screaming, etc. Its frequency ranges from about 60 to 7000 Hz. The human voice is specifically that part of human sound production in which the vocal folds are the primary...
or user data
Data
The term data refers to qualitative or quantitative attributes of a variable or set of variables. Data are typically the results of measurements and can be the basis of graphs, images, or observations of a set of variables. Data are often viewed as the lowest level of abstraction from which...
, and the D channel is used for any combination of data, control/signalling, and X.25
X.25
X.25 is an ITU-T standard protocol suite for packet switched wide area network communication. An X.25 WAN consists of packet-switching exchange nodes as the networking hardware, and leased lines, Plain old telephone service connections or ISDN connections as physical links...
packet networking. The two B channels can be aggregated by channel bonding
Channel bonding
Channel bonding is a computer networking arrangement in which two or more network interfaces on a host computer are combined for redundancy or increased throughput....
providing a total data rate of 128 kbit/s. The BRI ISDN service is commonly installed for residential or small business service in many countries.
The I.430 protocol defines 48-bit packets comprising 16 bit
Bit
A bit is the basic unit of information in computing and telecommunications; it is the amount of information stored by a digital device or other physical system that exists in one of two possible distinct states...
s from the B1 channel, 16 bits from B2 channel, 4 bits from the D channel, and 12 bits used for synchronization
Synchronization
Synchronization is timekeeping which requires the coordination of events to operate a system in unison. The familiar conductor of an orchestra serves to keep the orchestra in time....
purposes. These packets are sent at a rate of , giving the data rates listed above for a maximum possible throughput of .
BRI service is delivered via three types of physical interfaces. Signals are encoded by two modulation techniques, 2B1Q in North America, and 4B3T elsewhere.
Physical interfaces
ISDN technology standards define three main types of interfaces for Basic Rate Interface service:- The S/T InterfaceT-interfaceA T-interface is used for basic rate access in an Integrated Services Digital Network environment. It is a User–network interface reference point that is characterized by a four-wire, 144 kbit/s user rate....
(S0) uses four wires with a separate pair of wires for the uplinkUplinkA telecommunications link is generally one of several types of information transmission paths such as those provided by communication satellites to connect two points on earth.-Uplink:...
and another pair for the downlink. It is the most used of the three interfaces. - The Up InterfaceU interfaceU interface: For basic-rate access in an Integrated Services Digital Network environment, a user-to-network interface reference point that is characterized by the use of a 2-wire-loop transmission system that conveys information between the 4-wire user-to-network interface, i.e., the S/T...
uses one wire pair using the half duplex time-division multiplexingTime-division multiplexingTime-division multiplexing is a type of digital multiplexing in which two or more bit streams or signals are transferred apparently simultaneously as sub-channels in one communication channel, but are physically taking turns on the channel. The time domain is divided into several recurrent...
ping-pong protocol. It is used by many ISDN PABX systems. Depending of the applicable cable length, two varieties are implemented, UpN and Up0Up0-interfaceThe Up0-Interface is an integrated services digital network interface used in private networks. It derives from the UK0-Interface used in public networks....
. - The Uk0 interface uses one wire pair with echo cancellationEcho cancellation'The term echo cancellation is used in telephony to describe the process of removing echo from a voice communication in order to improve voice quality on a telephone call...
for the long last mileLast mileThe "last mile" or "last kilometer" is the final leg of delivering connectivity from a communications provider to a customer. The phrase is therefore often used by the telecommunications and cable television industries. The actual distance of this leg may be considerably more than a mile,...
cable between the telephone exchangeTelephone exchangeIn the field of telecommunications, a telephone exchange or telephone switch is a system of electronic components that connects telephone calls...
and the network terminatorNetwork termination 1Network Termination 1 : In Integrated Services Digital Networks , a functional grouping of customer-premises equipment that includes functions that may be regarded as belonging to OSI Layer 1, i.e., functions associated with ISDN electrical and physical terminations on the user premises.Note: The...
.
2B1Q line coding
2B1Q2B1Q
Two-binary, one-quaternary is a physical layer encoding used for Integrated Services Digital Network Basic Rate Interface implementations...
coding is the standard used in North America. 2B1Q means that two bits are combined to form a single Quaternary line state (symbol). 2B1Q combines two bits at a time to be represented by one of four signal levels on the line. The signal rate, therefore, is 80 kilobaud
Baud
In telecommunications and electronics, baud is synonymous to symbols per second or pulses per second. It is the unit of symbol rate, also known as baud rate or modulation rate; the number of distinct symbol changes made to the transmission medium per second in a digitally modulated signal or a...
and the line rate 160 Kbit/s. It operates with a maximum frequency range (bandwidth) of .
2B1Q coding is defined in ANSI T1.601 and ETR 080, Annex A. It can operate at distances up to about 18,000 feet with loss up to . An internal termination impedance of 135 ohms is presented to the line at each end of the U-interface. Echo cancellation
Echo cancellation
'The term echo cancellation is used in telephony to describe the process of removing echo from a voice communication in order to improve voice quality on a telephone call...
techniques allow full-duplex operation on the line.
2B1Q transmission can be simply described as an amplitude modulation scheme for DC pulses.
4B3T line coding
4B3T is a standard used in Europe and elsewhere in the world. 4B3T is a "block code" that uses Return-to-Zero states on the line. 4B3T converts each group of 4 data bits into 3 "ternary" line signal states (3 symbols). The symbol rateSymbol rate
In digital communications, symbol rate is the number of symbol changes made to the transmission medium per second using a digitally modulated signal or a line code. The Symbol rate is measured in baud or symbols/second. In the case of a line code, the symbol rate is the pulse rate in pulses/second...
is 3/4ths of the data rate (120 kbaud
Baud
In telecommunications and electronics, baud is synonymous to symbols per second or pulses per second. It is the unit of symbol rate, also known as baud rate or modulation rate; the number of distinct symbol changes made to the transmission medium per second in a digitally modulated signal or a...
).
4B3T is defined in ETR 080, Annex B and other national standards, like Germany's 1TR220. 4B3T can be transmitted reliably at up to over cable or up to over cable. An internal termination impedance of is presented to the line at each end of the U-interface. Echo cancellation techniques allow full-duplex operation on the line.
In 4B3T coding, there are three states presented to line: a positive pulse (+), a negative pulse (-), or a zero-state (no pulse: 0). An analogy here is that operation is similar to B8ZS or HDB3 in T1/E1 systems, except that there is an actual gain in the information rate by coding 16 possible binary states to one of 27 ternary states.
There are many ways to perform this conversion, but BRI standards define a code known as MMS43 (Modified Monitoring State 43).
One requirement for line transmission is that there should be no DC build-up
DC bias
When describing a periodic function in the frequency domain, the DC bias, DC component, DC offset, or DC coefficient is the mean value of the waveform...
on the line, so there are some code substitutions based upon the transmission of the previous bits.