3. ISDN INTRODUCTION
ISDN Full Form
I – INTEGRATED
S – SERVICE
D – DIGITAL
N - NETWORK
ISDN was Developed by International
Telecommunications Union (ITU-T) in
1976.
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The main purpose is to digitize the
telephone network to permit the
transmission of audio, video, and text
data over existing telephone lines.
Definition
ISDN is a set of protocols that combines
digital telephony and data transport
services.
The goal is to form a WAN that provides
universal End-to-End connectivity over
Digital Media.
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6. ISDN Services
Bearer services – provide the means to
transfer information (voice, data,
video) between users without the
network manipulating the content of
that information. Belongs to the first
3 layers of the OSI model.
Teleservices – the network my change
or process the contents of the data.
correspond to layers 4-7 of the OSI model
rely on the facilities of bearer services
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Supplementary services – provide
additional functionality to the bearer
services and tele-services
Ex. : reverse charging, call waiting, and
message handling
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10. Barrier(B) Channel
A Bearer Channel (B Channel) is
defined at a rate of 64 kbps.
It is the basic user channel and can
carry any type of digital information in
full duplex mode as long as the
required transmission rate does not
exceed 64 kbps.
It can be used to carry digital data,
digital voice and any other low data
rate information.
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Several transmission can be accommo-
dated at once if the signals are
multiplexed first.
Four kind of connections can be set up
over a B channel:
Circuit Switched
Packet switched
Frame mode
Semi-permanent
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12. Data(D) Channel
A data channel (D channel) carry
control signal for bearer channels.
This channel does not carry data and
can be either 16 or 64 kbps, depending
upon the user's need.
If we are using in-band signalling, the
same cable carries data as well as
control signals.
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If we are using out-of-band signaling
(as in ISDN), then two different
cables carry data and control
information.
Can also be used for packet switching
or low speed telemetry.
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14. Hybrid(H) Channel
A Hybrid channel (H-channel) is
provided for user information at
higher bit rates.
There are three types of H-Channels
depending on the data rates:
H0 with data rate of384 kbps
H11 with data rate of 1536 kbps
H12 with data rate of 1920 kbps
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Hybrid channels are used for high
data rate applications such as video,
teleconferencing and so on.
Can be used as a high-speed trunk.
Can also be subdivided as per user’s
own TDM scheme.
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16. User Interface of ISDN
User Interface
BRI
Basic Rate
Interface
PRI
Primary Rate
Interface
B-ISDN
Broadband-
ISDN
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17. Basic Rate Interface
Basic Rate Interface specifies a
digital pipe, consisting of two 64 Kbps
B channels and one 16 Kbps D channel
for a total of 144 Kbps (2B+D).
In addition, the BRI service itself
requires 48 Kbps operating overhead.
BRI therefore requires a digital pipe
of 192 Kbps.
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Conceptually, the BRI service is like a
large pipe that contains three smaller
pipes, two for the B channels and one
for the D channel. The remainder of the
space inside the large pipe carries the
overhead bits required for its operation
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Each B channel can be used for
separate applications Such as Internet
and Voice.
Allows individual B channels to be
aggregated together into a Multilink
channel.
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20. Primary Rate Interface
The usual Primary Rate Interface (PRI)
specifies a digital pipe with 23 B
channels and one 64 Kbps D channel for
signalling purpose.
Primary Rate Interface service consists
of a D channel and either 23 B Or 30 B
channels (depending on the country you
are in) .
In addition, the PRI service itself uses
8 kbps of overhead.
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Twenty three B channels of 64 Kbps
each, plus one D channel of 64 Kbps
equals 1.536 Mbps.
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Each B channel to be used for
separate applications including voice,
data and Internet.
Multiple B channels can be Multilinked
together.
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ISDN Primary Rate Interface service
provides digital access via a T1 line.
ISDN PRI service is used primarily by
large organizations with intensive
communications needs.
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24. Broadband-ISDN
Narrowband ISDN has been designed
to operate over the current
communications infrastructure, which
is heavily dependent on the copper
cable. BISDN however, relies mainly on
the evolution of fiber optics. According
to CCITT BISDN is best described as
'a service requiring transmission
channels capable of supporting rates
greater than the primary rate.
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25. Functional Grouping
Terminal Adapter (TA)
Converter device that converts standard
electrical signals into the form used by
ISDN - allows non-ISDN devices to
operate on an ISDN network.
Exchange Termination (ET)
This is the local phone company's logical
connection from your telephones to "the
phone network".
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Terminal Equipment type 1
Compatible with the ISDN network.
Ex.- Digital telephones, integrated
voice/data terminals, personal computers,
fax machine or videoconferencing machine.
Terminal Equipment type 2
Not compatible with the ISDN network.
Ex.- Analog telephone or modem, requires
a TA, Terminal workstation
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Network Termination type 1
This is the end of the line for the local
phone company, and the beginning of your
house's phone network.
Network Termination type 2
In most homes, this won't exist. If you
were a big company with your own private
telephone system, then this would be the
guts of that telephone system.
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Line Termination (LT)
This is the physical connection to the
phone company.
Defines the functions
of the connections
29. ISDN Reference Points
U - Two wire cable that connects the
customer’s equipment to the tele-
communications provider.
R - Point between non-ISDN
equipment (TE2) and the TA.
S - Four-wire cable from TE1 or TA to
the NT1 or NT2.
T - Point between NT1 and NT2.
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32. Simplified Layers of ISDN
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Mechanical and
electrical specs of
interfaces R, S, T, U
Encoding
Multiplexing
Power supply
33. Advantage of ISDN
Speed
BRI ISDN, using a channel aggregation
protocol such as BONDING or Multilink-
PPP, supports an uncompressed data
transfer speed of 128 kb/s, plus bandwidth
for overhead and signalling. PRI transfers
at an even higher speed of up to 1920 kb/s.
Multiple Devices
ISDN allows multiple devices to share a
single line. It is possible to combine many
different digital data sources and have the
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information routed to the proper destination.
Signaling/Fast Call Setup
Instead of the phone company sending a
ring voltage signal to ring the bell in your
phone ("In-Band signal"), it sends a digital
packet on a separate channel ("Out-of-
Band signal").
The Out-of-Band signal does not disturb
established connections, no bandwidth is
taken from the data channels, and call
setup time is very fast.
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35. Disadvantage of ISDN
BRI is slower than DSL and cable.
More expensive than DSL and cable.
Bottom line: ISDN, in its current
form, is no longer a “first-choice”
technology
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(a) Circuit switched
The user places a call and a current switched connection is established with another network user.
(b) Packet switched
The user is connected to a packet switching mode and data are exchanged with other users via X.25.
(c) Frame mode
The user is connected to a frame relay mode and data are exchanged with other users via LAPF.
(d) Semi-permanent
This is a connection to another user set up by prior arrangement and not requiring-a call establishment protocol.
It is equivalent to a leased line.
The quantity and bit capacity of channels in an ISDN line depends on the type of ISDN service implemented. ISDN currently offers the following two services:
1. BRI (Basic Rate Interface) – Consists of two 64 Kbps B channels, one 16 Kbps D channel, and 48 Kbps worth of framing and synchronization.
a) Available data bandwidth: 128 Kbps (2 times 64 Kbps)
b) User bandwidth: 144 Kbps (128 Kbps + a 16 Kbps D channel)
c) Total line capacity: 192 Kbps (144 Kbps + 48 Kbps framing)
Insider Information
The significance of the 64 Kbps B channels, which is the same as T1 channels, is the 64 Kbps is the telco standard for voice channels to ensure accurate reproduction of sound. The original purpose of T1 lines was to provide 24 voice lines – a T3 provides 28 times as many (672). If Voice over IP becomes common it will free up tremendous bandwidth because IP technologies compress voice data into 8 Kbps channels using technologies similar to those used on digital movies and music.
2. PRI – Primary Rate Interface. A PRI connection can assign 64 Kbps channels to both ISDN and analog modem connections
a) North America and Japan – PRI service has 23 64 Kbps B channels, one 64 Kbps D channel, and8 Kbps of synchronization and framing for a total bit rate of up to 1.544 Mbps (same as T1)
b) Europe, Australia, and other parts of the world – PRI service has 30 64 Kbps B channels, one 64 Kbps D channel, and 64 Kbps of framing and synchronization for a total bit rate of up to 2.048 Mbps (same as E1)
3. Both BRI and PRI allow each B channel to be used for separate applications. Example with BRI: the first B channel used for the Internet, while the second B channel is used for phone or FAX service
4. Both BRI and PRI allow individual B channels to be aggregated together into a single logical pipe to increase bandwidth (Multilinking).
The United States, Canada and Japan make use of a transmission structure based on 1.544 Mbps.
In Europe, Australia and other countries 2.048 Mbps is the standard rate. Both of these data rates are provided as
a Primary Rate Interface.
TA: Terminal Adaptor. This lets old, TE2 stuff talk to the ISDN network. It also adapts other kinds of equipment, like Ethernet interfaces, to ISDN.
TE1: Terminal Equipment type 1. This is the ISDN telephone, computer, ISDN FAX machine or whatever it is that you've hooked up to the ISDN phone line.
TE2: Terminal Equipment type 2. This is the old analog telephone, old-style fax machine, modem, or whatever you used to hook up to the analog phone line. It can also be other communications equipment that is handled by a TA (see below).
Network termination type 1 & 2 (NT1 and NT2) - A small connection box that physically connects the customer site to the Telco local loop, provides a four-wire connection to the customer site and a two-wire connection to the network (PRI – CSU/DSU).
NT1
Controls the physical & electrical termination of the ISDN at the user’s premises
Connects the user’s internal system to the digital subscriber loop
Organizes the data stream s from a connected subscriber into frames that can be sent over the digital pipe
Translates the frames received from the network into a format usable by the subscriber’s devices.
NT2 ( ex. Digital PBX, LAN)
Performs functions at the physical (multiplexing), data link (flow control), network layers (packetizing) of the OSI model
Provides intermediate signal processing between the data-generating devices and an NT1
Used primarily to interface between a multiuser system and an NT1 in a PRI.