Borscht: Hook Refers To When The Handset Is Idle and Waiting For A Signal Indicating That Someone Wants To
Borscht: Hook Refers To When The Handset Is Idle and Waiting For A Signal Indicating That Someone Wants To
Borscht: Hook Refers To When The Handset Is Idle and Waiting For A Signal Indicating That Someone Wants To
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BORSCHT
It is an acronym for the set of functions performed by a subscriber line interface circuit (SLIC) in
the line card of a telecommunication system. The letters represent the following functions battery
feed (B), over-voltage protection (O), ringing (R), signaling (S), coding (C), hybrid (H), and test
(T). An earlier or alternate version of the acronym is BORSHT, lacking the letter C for the
coding function.
SLIC
Subscriber-line interface cards (SLICs) provide the interface between the telephone-service
provider and the telephone handset in your home. They operate in two main modes: On-
hook refers to when the handset is idle and waiting for a signal indicating that someone wants to
make a connection, and off-hook refers to when the handset is active and the user is trying to
complete a connection.
LATA
ISDN
ISDN was first defined in the CCITT red book in 1988.The Integrated Services of Digital
Networking, in short ISDN is a telephone network based infrastructure that allows the
transmission of voice and data simultaneously at a high speed with greater efficiency. This is a
circuit switched telephone network system, which also provides access to Packet switched
networks.
The model of a practical ISDN is as shown below.
Voice calls
Facsimile
Videotext
Teletext
Electronic Mail
Database access
Data transmission and voice
Connection to internet
Electronic Fund transfer
Image and graphics exchange
Document storage and transfer
Audio and Video Conferencing
Automatic alarm services to fire stations, police, medical etc.
Types of ISDN
Among the types of several interfaces present, some of them contains channels such as the B-
Channels or Bearer Channels that are used to transmit voice and data simultaneously; the D-
Channels or Delta Channels that are used for signaling purpose to set up communication.
The ISDN has several kinds of access interfaces such as −
The Basic Rate Interface or Basic Rate Access, simply called the ISDN BRI Connection uses
the existing telephone infrastructure. The BRI configuration provides two data or bearer
channels at 64 Kbits/sec speed and one control or delta channel at 16 Kbits/sec. This is a
standard rate.
The ISDN BRI interface is commonly used by smaller organizations or home users or within a
local group, limiting a smaller area.
The Primary Rate Interface or Primary Rate Access, simply called the ISDN PRI connection is
used by enterprises and offices. The PRI configuration is based on T-carrier or T1 in the US,
Canada and Japan countries consisting of 23 data or bearer channels and one control or delta
channel, with 64kbps speed for a bandwidth of 1.544 M bits/sec. The PRI configuration is based
on E-carrier or E1 in Europe, Australia and few Asian countries consisting of 30 data or bearer
channels and two-control or delta channel with 64kbps speed for a bandwidth of 2.048 M
bits/sec.
The ISDN BRI interface is used by larger organizations or enterprises and for Internet Service
Providers.
Narrowband ISDN
The Narrowband Integrated Services Digital Network is called the N-ISDN. This can be
understood as a telecommunication that carries voice information in a narrow band of
frequencies. This is actually an attempt to digitize the analog voice information. This uses
64kbps circuit switching.
The narrowband ISDN is implemented to carry voice data, which uses lesser bandwidth, on a
limited number of frequencies.
Broadband ISDN
The Broadband Integrated Services Digital Network is called the B-ISDN. This integrates the
digital networking services and provides digital transmission over ordinary telephone wires, as
well as over other media. The CCITT defined it as, “Qualifying a service or system requiring
transmission channels capable of supporting rates greater than primary rates.”
The broadband ISDN speed is around 2 MBPS to 1 GBPS and the transmission is related to
ATM, i.e., Asynchronous Transfer Mode. The broadband ISDN communication is usually made
using the fiber optic cables.
As the speed is greater than 1.544 Mbps, the communications based on this are
called Broadband Communications. The broadband services provide a continuous flow of
information, which is distributed from a central source to an unlimited number of authorized
receivers connected to the network. Though a user can access this flow of information, he
cannot control it.
Advantages of ISDN
ISDN is a telephone network based infrastructure, which enables the transmission of both voice
and data simultaneously. There are many advantages of ISDN such as −
Disadvantages of ISDN
The disadvantage of ISDN is that it requires specialized digital services and is costlier.
However, the advent of ISDN has brought great advancement in communications. Multiple
transmissions with greater speed are being achieved with higher levels of accuracy.
Dedicated path
The dedicated line is a telecommunications path between two points that is available 24
hours a day for use by a designated user (individual or company). It is not shared in
common among multiple users as dial-up lines are.
In space division switching, a dedicated path is established between the calling and the called
subscribers for the entire duration of the call. In time division switching, sampled values of
speech signals are transferred at fixed intervals.
The time division switching may be analog or digital. In analog switching, the sampled voltage
levels are transmitted as they are whereas in binary switching, they are binary coded and
transmitted. If the coded values are transferred during the same time interval from input to
output, the technique is called Space Switching. If the values are stored and transferred to the
output at a late time interval, the technique is called as Time Switching.
The paths in a circuit are separated from each other, spatially in space division switching.
Though initially designed for analog networks, it is being used for both analog and digital
switching. A Crosspoint switch is mostly referred to as a space division switch because it moves
a bit stream from one circuit or bus to another.
The switching system where any channel of one of its incoming PCM highway is connected to
any channel of an outgoing PCM highway, where both of them are spatially separated is called
the Space Division Switching. The Crosspoint matrix connects the incoming and outgoing PCM
highways, where different channels of an incoming PCM frame may need to be switched by
different Crosspoints in order to reach different destinations.
Though the space division switching was developed for the analog environment, it has been
carried over to digital communication as well. This requires separate physical path for each
signal connection, and uses metallic or semiconductor gates.
Time Division Switching
Time division switching comes under digital switching techniques, where the Pulse Code
Modulated signals are mostly present at the input and the output ports. A digital Switching
system is one, where the inputs of any PCM highway can be connected to the outputs of any
PCM highway, to establish a call.
The incoming and outgoing signals when received and re-transmitted in a different time slot, is
called Time Division Switching. The digitized speech information is sliced into a sequence of
time intervals or slots. Additional voice circuit slots, corresponding to other users are inserted
into this bit stream of data. Hence, the data is sent in time frames.
The main difference between space division multiplexing and time division multiplexing is
sharing of Crosspoints. Crosspoints are not shared in space division switching, whereas they can
be shared in time division multiplexing, for shorter periods. This helps in reassigning the
Crosspoints and its associated circuitry for other connections as well.
The main difference between space division multiplexing and time division multiplexing
is sharing of Crosspoints. Crosspoints are not shared in space division switching,
whereas they can be shared in time division multiplexing, for shorter periods. This helps
in reassigning the Crosspoints and its associated circuitry for other connections as well.
This type of signaling is used to carry voice or data and pass control signals related to
a call or connection. There are different types of In-channel Signaling, as seen in the
above figure. The D.C. signaling is simple, cheap and reliable even for unamplified
audio circuits. However, for amplified audio circuits, low frequency A.C. signaling may
be adopted.
The Voice Frequency signaling is used when FDM (Frequency Division Multiplexing)
transmission systems are used, because low frequency signaling and D.C. signaling
cannot be provided. This Voice Frequency signaling may be In-band or Out-band.
In-band Signaling
In-band voice frequency uses the same frequency band as the voice, which is 300-
3400 Hz, which has to be protected against false operation by speech. One such
instant took place when a lady’s voice which has generated a tone at around 2600Hz
lasting for a duration of 100ms was detected as the line disconnect signal due to which
her calls were frequently being disconnected in the middle of her conversation. Such
problems precluded the in-band signaling during speech phase.
The advantages of In-band signaling are −
The control signals can be sent to every part where a speech signal can reach.
The control signals will be independent of the transmission systems as they are
carried along with the speech signals.
The Analog to digital and Digital to analog conversion processes will not affect
them.
Out-band Signaling
The out-band signaling uses frequencies which are above the voice band but below the
upper limit of 4000 Hz of the nominal voice channel spacing. The signaling is done
throughout the speech period and thus continuous supervision of the call is allowed.
Extra circuits are needed to handle the extremely narrow band width of this signaling,
due to which it is seldom used. Both of these in-band and out-band voice frequency
signaling techniques have limited information transmission capacity. In order to provide
enhanced facilities, common channel signaling is used.
The above figure shows an early model of the PBX system. The PBX is usually
operated and owned by the local office where the users are connected through it within
that limited area.
The parts of a PBX include −
A telephone trunk that contains many phone lines, which are terminated at PBX.
A computer that handles the incoming and outgoing calls of PBX along with
switching between different calls within the local loop.
The network of lines within the PBX.
A human operator console, which is optional.
Having all these along with the PBX equipment, the local branch exchange is built. The
PBX exchanges previously operated using the analog technology. However, these
exchanges operate on digital technology. The digital signals are converted to analog
for outside calls on the local loop using Plain Old Telephone Services (POTS).