Integrated Services Digital Network (ISDN)

Integrated Services Digital Network (ISDN)
Integrated
Services
Digital Network
(ISDN)
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Introduction to ISDN
• Developed by ITU-T (1976)
• it a protocol that combines digital telephony & data
transport services
• Idea: to digitize telephone network to transmit audio,
video & text over existing telephone line.
• Goal: to form a WAN that provides universal end-toend connectivity over digital media
• How: integrating all separate transmission services
into one without adding new links
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ISDN Services
• Purpose: to provide fully integrated digital services to users
Services
Bearer Services
TeleServices
Supplementary
Services
Bearer Services:
• provide services to transfer information (voice, audio,
data) between users without manipulating the content
• services: circuit switching, packet switching, frame
switching, cell switching
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ISDN Services
TeleServices:
• network may change/process the content of data
• OSI layer: 4-7
• rely on facilities of bearer services
• how: accommodate complex user needs without the user
having to be aware the details of the process
• services: telephony, telefax, teletext, telex, teleconferencing
Supplementary services:
• provide additional functionality to the Bearer services &
TeleServices
• example: reverse charging, call waiting, message handling
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ISDN Services
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ISDN Evolution
Voice Communication over Analog Network
Voice & Data Communication over Analog Network
Analog and Digital Services to Subscribers
Integrated Digital Network (IDN)
Integrated Services Digital Network (ISDN)
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Voice Communication over an
Analog Telephone Network
• entirely analog networks
• transmit analog information: voice
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Voice and Data Communication
over an Analog Telephone Network
• subscribers needed to exchange data as well as voice
• developed modem to allow digital exchange over analog lines
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Analog and Digital Services
over the Telephone Network
• to reduce cost and improve performing add digital
technology
• 3 types of customers: traditional customers, customers using
analog facilities, customers using digital services
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IDN
• combination of network available
• access using very-high speed paths - digital pipes
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ISDN
• fully digital services for sending data, voice, image, facsimile
• ISDN incorporates all communication connections in home
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into a single interface
Access to ISDN
• to allow flexibility, digital pipes are organized into
multiple channels with different sizes
Channel
Bearer (B)
Data (D)
Hybrid (H)
Data Rate (Kbps)
64
16, 64
384, 1536, 1920
B Channels
• basic user channel at rate 64 Kbps
• carry any types of digital information in full-duplex
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Access to ISDN
D Channels
• can be either 16 or 64 Kbps
• carry control signaling for B channels
method: common-channel (out-of-band) signaling
- a subscriber uses D channel to connect to network
- then uses B channel to send actual data
• acts like a telephone operator between user and network
H Channels
• data rates of 384 Kbps (H0), 1536 Kbps (H11), 1920 Kbps (H12)
• suit H channels for high data-rate application: video,
teleconferencing
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User Interface
• BRI
– Design to meet the needs of residential and small office customer
– No need to replace existing local-loop cable
– twisted pair can delivers analog as well as digital (but needs some
conditional)
• PRI
– Provide full-duplex transmission between as many as 23 source
and receiving nodes
– LAN uses PRI to connect to other LANs
– In Europe PRI includes 30 B-Channel and 2 D-Channel
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BRI
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PRI
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Functional Grouping
• User access ISDN base on functional duties and collected
in functional groupings.
• Model implementation chose by subscribers.
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NT1 (Network Termination 1)
• Control the physical and electrical termination at
user’s premises
• Connect the user’s internal system to digital
subscriber loop
• Organizes data streams into frames
• Translate the frames
• Synchronizes the timing of the contributing data
streams to the building of the outgoing frames
• No needs of multiplexing devices
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NT2 (Network Termination 2)
• Performs function at physical, data link dan
network layers.
• Provides multiplexing (layer 1), Flow control
(layer 2), Packetizing (layer 3)
• Still requires NT1
• Point-to-point connection between NT2 and NT1
• Interface between multi-user system and NT1 in a
PRI
• Examples PBX and LAN
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TE1 (Terminal Equipment 1)
• Same as DTE in other protocol
• Examples
– digital telephones,
– integrated voice/data terminal and
– digital facsimiles
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TE2 (Terminal Equipment 2)
• Provides backward compatibility with customer’s
existing equipment
• For non-ISDN devices such as
– Terminal
– Workstation
– Host computer
– Regular telephone
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TA (Terminal Adapter)
• Converts information received from nonISDN format from TE2 into a format
capable of being carried by the ISDN
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Reference Points
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ISDN Layers
• difficult to apply simple 7-layer architecture of OSI
• reason: ISDN specifies 2 different channel (B & D)
with different functionalities
• require different protocols from each other
• solution: ITU-T expand OSI model in 3 separate planes
• user plane
• control plane
• management plane
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ISDN Layers
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Simplified Layers of ISDN
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ISDN Layers
•
physical layer
• defined 2 ITU-T standard: I.430 (BRI), I.431 (PRI)
•
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define 4 primary aspect of BRI & PRI
1. Mechanical & electrical specification of interfaces
(R, S, T, U)
2. Encoding
3. Multiplexing channels for BRI/PRI digital pipes
4. Power supply
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BRI Interfaces
• BRI consists of 2 B channel and 1 D channel
BRI
2B + 1D
• connect to BRI using R, S and U interfaces
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BRI Interfaces
R interface
• connection between terminal adapter and non-ISDN terminals
• not defined by ISDN
• Subscriber can use any EIA standards (EIA-232,
EIA-499)
S interface
• interface between ISDN PBX and ISDN terminal
• ITU-T specifies the ISO standard: ISO8887
• calls for 4- (at least),6- or 8-wire connections (full
duplex)
• refer figure 16.14
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BRI Interfaces
(cont..) S Interface
3 methods supplying power:
1. From NT1
• battery/power outlet/ISDN center
• using wires c, d, e, f
2. From NT1
• but in two separate lines to relay
it to the TE
• using wires c, d, e, f, g, h
3. From TE to another TEs
• using wires a, b
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BRI Interfaces
U interface
• connection between ISDN and NT1
• ITU-T specifies a single-pair twisted-pair cable in
each direction
• encoding : two binary, one quaternary (2B1Q)
• uses 4 voltage level
• each level represent 2 bits (00, 01, 10, 11)
• reasons :
lowering baud rate
enabling more
efficient use of
available bandwidth
2B/1Q Encoding
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Figure 16-16
BRI Frame
• B channel is sampled twice for each frame (8 bit/sample)
• D channel is sampled 4 times for each frame (1 bit/sample)
• the rest reserved for overhead
• entire frame = 16 bits (B) + 16 bits (B) + 4 bits (D) + 12 bits (o/h)
= 48 bits
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BRI Topology
• supported by either bus or star topology
• main restriction for choosing topology distance of data
devices from NT1
• point-to-point connection each device 1000m from NT1
• multi-point connection max. length < 200m
• the restriction can ensure frame synchronization
• by clustering the devices, the length can be extended to 500m
• star topology link 1000m
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BRI
Topology
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PRI Interfaces
• consists of 23 B channels and 1 D channel
PRI
23B + 1D
• connect to PRI using R, S, T and U
• R and S standards are same in BRI
• T identical to S standard
• U same in BRI except PRI rate is 1.544 Mbps instead of
192 Kbps
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PRI Interfaces
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PRI Frame
• multiplexed of B and D channels using sync. TDM
• PRI frame samples each channel only once per frame
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Data Link Layer
• B channel using LAPB protocol
• D channel using LAPD protocol
• LAPD did few modifications to HDLC :
LAPD can be used either
acknowledged/unacknowledged format
addressing
LAPD Addressing
• 2 bytes long:
byte 1 contain SAPI (service access point identifier)
byte 2 contain TEI (terminal equipment identifier)
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LAPD Address Field
SAPI
TEI
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CR
(service access point identifier)
000000 – call control for network layer
000001 – call control for upper layer
010000 – packet communication
111111 – management
(terminal equipment identifier) (address complete (1) /address
incomplete (0))
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(command (0) /respond (1))
Network Layer Packet Format
• once connection established by D channel, B channel sends data
• network layer packet message
• a message is encapsulated in information field of LAPD I-frame
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Call Reference Field
• indicate the sequence number of the call
• mesg type identifies the purpose of the mesg
• 4 categories of mesg type:
• call establishment, call information, call clearing,
miscellaneous mesg.
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Information Elements
• carries specific details about connection required for call
establishment (addresses of sender/receiver, routing…)
• consists of one-byte (type 1, type 2) or more bytes
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Information Element Types
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Addressing in ISDN
• important part of information element
• 15 digits (country code, NC, subscriber number) define access
to a subscriber NT1
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Broadband ISDN
• originally designed, data rates of 64 Kbps to 1.544 Mbps
were sufficient
• these rates proved inadequate to support many applications
• several are beyond the capacities of both BRI and PRI
• refer figure 16.26
• solution : extending the ISDN to broadband ISDN (B-ISDN)
• Original ISDN known as narrowband ISDN (N-ISDN)
B-ISDN
• data rates in range 600 Mbps, almost 400 times faster
than PRI rate
• change from metal cable to fiber optic cable
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Bit Rates for Different Applications
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B-ISDN Services
Interactive services
• require 2-way exchanges between either 2 subscribers or
subscriber and service provider
• 3 types : conversational, messaging, retrieval
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B-ISDN Services
• conversational : support real-time exchanges
(telephony, video conferencing)
• Messaging : store-and-forward exchanges, bidirectional
(voice mail, data mail)
• retrieval : retrieve information from a central source
(on-line library)
Distributive Services
• unidirectional services send from provider to subscribers
• subscriber no need to request each time for a desired services
• without user control commercial TV program
• with user control pay TV
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B-ISDN Accesses
• 3 access methods for 3 level users needs
Symmetrical
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asymmetrical
symmetrical
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Future of ISDN
• N-ISDN was designed to replace the analog telephone
system with digital transmission
• considered a good solution because :
• minimum cost and the services satisfied by users
• new equipment appeared on market to use entire
bandwidth of ISDN line (192Kbps(BRI), 1.544Mbps(PRI))
• the protocol is flexible to be upgraded to higher data
rates using new technology and transmission media
• N-ISDN can be used as a forerunner for B-ISDN
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