2. An overview of ISDNAn overview of ISDN
ISDN was developed by ITU-T in 1970. It is a set
of protocols that combines digital telephony and
data transport services.
The goal of ISDN is to form a wide area network
(WAN) that provides universal end to end
connectivity over digital media.
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4. Continue…Continue…
The purpose of the ISDN is to provide fully
integrated digital services to users. These
services fall into three categories:
Bearer Services
Teleservices
Supplementary Services
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5. Bearer Services:-
. Bearer Services provide to transfer information
(voice, data, and video) between the network
manipulating the content of that information.
. Bearer services belong to the first three layers of
OSI model and are well defined in the ISDN
standard. They can be provided using circuit –
switched, packet – switched, frame – switched or
cell – switched networks.
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6. Teleservices :-
. In teleservicing the network may change or process
the content of the data.
. These services correspond to layers 4-7 of the OSI
model.
. Teleservices include telephony, telefax, videotex,
telex and teleconferencing.
. The ISDN defines these services by name, they
have not yet become standards.
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7. Supplementary Services :-
Supplementary services are those services that
provide additional functionality to the bearer
services and teleservices.
Example:- reverse charging, call waiting, and
message handling.
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10. Types of channels
. Bearer channels
. Data channels(Delta)
. Hybrid channels
Channel rates
Channel Data Rate(Kbps)
Bearer (B) 64
Data (D) 16, 64
Hybrid (H) 384, 1536, 1920
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11. B Channels :-
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.
128 Kbps
128 Kbps
B (64 Kbps)
B (64 Kbps)
Inverse Multiplexers
Inverse Multiplexing of B ChannelsInverse Multiplexing of B Channels
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12. D Channels :-
A data channel (D channel) can be either 16 or 64
Kbps, depending on the needs of the user.
The primary function of D channel is to carry
control signaling information for the B channels.
. Who is calling
. Type of call
. Calling what number
Can also be used for packet switching or low speed
telemetry.
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13. H Channels :-
Carry user information at higher bit rates 384 kb/s or
1536 kb/s or 1920 kb/s.
These rates suit H channels 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.
Uses include high speed data, fast facsimile, video,
high-quality audio.10/05/13 13
14. B Channel
(64 kbps)
D Channel
(16/64 kbps)
H Channel
(384/1536 kbps)
Digital voice Signalling (using
SS#7)
High-speed trunk
High-speed data (e.g.
packet and circuit
switched data)
Low- speed data,
(e.g. packet,
terminal,
videotex)
Very high speed
data
Other (e.g. fax, slow
video)
Other (e.g.
telemetry)
Other (e.g. fast
fax. Video)
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15. Advantages of ISDNAdvantages of ISDN
ISDN also provides more bandwidth than a
traditional 56 kbps dialup connection.
ISDN uses bearer channels, also called B channels,
as clear data paths.
Each B channel provides 64 kbps of bandwidth.
An ISDN connection with two B channels would
provide a total usable bandwidth of 128 kbps.
Each ISDN B channel can make a separate serial
connection to any other site in the ISDN network.
ISDN lines can be used in conjunction with PPP
encapsulation.
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16. Disadvantages of ISDNDisadvantages 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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18. ISDN standards define two main channel types
The bearer channel, or B channel, is defined as a
clear digital path of 64 kbps
The second channel type is called a delta channel,
or D channel.
– There can either be 16 kbps for the Basic Rate
Interface (BRI) or 64 kbps for the Primary Rate
Interface (PRI).
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19. Basic
ISDN Channel StructuresISDN Channel Structures
B
B
D
Primary
B
B
..
D
B
Basic Service:
Management rate: 192 kbps
Standard throughput: 144 kbps
Composition: B + B + D channels,
+ Synch & framing
Primary Service:
Rate: 1.544/2.048 Mbps
Composition: 2.048 Mbps: 30 B at 64 kbps each
2 D at 64 kbps
1.544 Mbps: 23 B at 64 kbps each
1 D at 64 kbps
Information:
Voice, Data
Signaling:
Overhead or
telemetry, etc.
PCM voice
channels
Signaling
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20. Basic Rate Interface (BRI)Basic Rate Interface (BRI)
• 2 B Channels
• 1 D Channel
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21. BRIBRI
• Two B channels of 64 Kbps each, plus 1 D channel
of 16 kbps, equal 144 kbps.
• In addition, the BRI services itself requires 48 kbps
of operating overhead.
• BRI therefore requires a digital pipe of 192 kbps.
• Conceptually, the BRI service is like a large pipe
that contains three smaller pipes, two for the B
channel and one for the D channel.
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22. Primary Rate Interface (PRI)Primary Rate Interface (PRI)
• More sophisticated service compared to BRI
• PRI service offers 23 B channels and 1 D channel
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23. PRIPRI
The usual primary rate interface(PRI) specifies a
digital pipe with 23 B channels and one 64 kbps D
channel.
In addition, the PRI service itself uses 8 kbps of
overhead.
The PRI services is like a large pipe containing
24 smaller pipes. 23 for B channels and 1 for D
channel.
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24. Functional GroupingFunctional Grouping
The devices that enable users to access the services of the BRI or
PRI are described by their functional duties and collected in func-
tional groupings.
Functional grouping is a model that can be implemented using
devices or equipment chosen by the subscriber.
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25. Network Termination 1(NT1) :-
A network termination 1(NT1) device controls the
physical and electrical termination of the ISDN at
the user’s premises and connects the user’s internal
system to the digital subscriber loop.
These functions are comparable to those define for
the OSI physical layer.
An NT1 organizes the data streams from a connected
subscriber into frames that can be sent over the digital
pipe, and translate the frames received from the
network.
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26. Network Termination 2(NT2) :-
A network termination 2(NT2) device performs at
the physical, data link and network layers of the
OSI model(layers 1, 2, 3).
An NT2 provides multiplexing (layer 1), flow
control (layer 2), and packetizing (layer 3).
NT2 can be implemented by a veriety of equipment
types. For example, a private branch exchange
(digital PBX).
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27. Terminal Equipment 1(TE1) :-
Terminal equipment 1(TE1) is any device that
supports the ISDN standards.
Example of TE1 are digital telephones, integrated
voice/data terminals, and digital facsimiles.
Terminal Equipment 2(TE2) :-
TE2 equipment is any non ISDN device, such as a
terminal, workstation, host computer, or regular
telephone.
Terminal Adapter(TA) :-
TA converts information received in non-ISDN Format
from a TE2 into a format capable of being carried by the10/05/13 27
34. ISDN and OSI modelISDN and OSI model
Layer1 - Physical
Layer2 - Data Link
Layer3 – Network
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35. ISDN Access Servers (2)ISDN Access Servers (2)
PPP Multilink
BACP (Bandwidth Allocation Control
Protocol)
Controlling the number of B-channels per
user
D-channel based callback
CLIP - Caller Line Identification
Presentation
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36. 56 k Technology56 k Technology
Access server
Modem
Telephone
switch
Telephone
switch
Telephone
switch
?
Access server
Modem
Modem
Digital line
Analog line
<= 33,6 kbps
<= 56 kbps
ISDN, E1,..
<= 33,6 kbps
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37. 56 k Prerequisites56 k Prerequisites
Only one analogue/digital conversion
– less noise and faster digital lines
Digital Access Server
Same technology in Access Server and in
dial-up modem
– 56K Flex from Lucent Technologies and Rockwell
– X2 from U.S. Robotics, Texas Instruments and Cirrus
Logic
– V.90 - ITU-T standard (to be confirmed in 9/98)
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38. 56 k Considerations56 k Considerations
56 k not reached in reality
– 45 kbps practical maximum
Cost for upgrading equipment to ITU-T
standard
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39. Using ISDN forUsing ISDN for
IP Data Networks (1)IP Data Networks (1)
Characteristics
– Speed
– Fast call setup
– Bandwidth on Demand
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40. Using ISDN forUsing ISDN for
IP Data Networks (2)IP Data Networks (2)
Modes of Usage
– Dial Up (LAN or host)
– Bandwidth on Demand
– Backup lines
– Permanent connections
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Samo za terminalski dostop za prilagajanje hitrosti na <COM port
Analog to digital conversions take more out of the signal than digital to analogue 70% modems to K56Flex X2 growing with 3Com For the standard wait 1 year
Aktivne kartice imajo svoj procesor in razbremenijo PC