digital services isdn (1)
DESCRIPTION
TRANSCRIPT
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CHAPTER CHAPTER
Digital Lines and the Digital Lines and the Integrated Service Integrated Service
Digital Network (ISDNDigital Network (ISDN))
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Chapter Objectives
• Define ISDN, its standards and the type of services offered
• Describe the two main types of services, namely BRI and PRI
• Give examples of ISDN links– Simple SOHO line, ISDN remote bridges
etc
• Briefly outline a few other features of ISDN
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Chapter Modules
• An overview of ISDN• Basic Rate Interchange (BRI)• Primary Rate Interchange (PRI)• A practical SOHO ISDN line• ISDN applications• Other features of ISDN
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MODULE
An Overview of ISDN
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ISDN Defined
• Known as the Integrated Services Digital Network– Data, audio, image and video
transmission
• It is a switched digital telecommunication line that can be delivered over regular copper wires– Possible to provide end-to-end digital
communications
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ISDN Application Examples• On/off ramp to the information super-
highway to communicate at speeds of 128 Kbps for a single ISDN line– Multiple ISDN lines can be combined together
to achieve higher communication speeds
• Home use– On/Off ramp to the Internet
• Business world– Provide remote access to LANs
.
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ISDN Standard
• There is a national ISDN standard known as the NI standard
• It is being implemented in phases• Current implementation is termed
as NI-1 to indicate that it is in phase 1 of the implementation process
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ISDN Connections
• Can be obtained from a local telephone company in the same way an analog connection is obtained
• Phone companies offer different types of ISDN connections
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ISDN Basic Characteristics
Signaling
Data
Data
DataD Channel16-64 Kbps
B Channels64 Kbps
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Inverse Multiplexing of B Channels
B (64 Kbps)
B (64 Kbps)
128 Kbps 128 Kbps
Inverse Multiplexers
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Bonding of B Channels or BOD (Bandwidth on
Demand)
B (64 Kbps)
B (64 Kbps)
64- 128 Kbps 64- 128 Kbps
Inverse Multiplexers with Dynamic Bonding
Channel Bonded on Demand
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ISDN Service Connections
• There are two different types of ISDN services that are widely available
• One is known as the Basic Rate Interface or BRI – Used for home or SOHO connection
• The other is known as the Primary Rate Interface or the – Used in large businesses
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World-wide Coverage
• U.K.• India • Germany• France• Australia• Japan• Canada• etc.
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In Summary
• ISDN is a switched digital network• Can be used for establishing a point-
to-point digital connection• BRI and PRI
– Number of B Channels vary in each case
• B channels can be combined together to achieve a higher communication speed
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END OF MODULEEND OF MODULE
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MODULE
Basic Rate Interface (BRI)
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BRI Characteristics
• 2 B Channels• 1 D Channel
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A Simple BRI Connection to a Microcomputer
NT 1
ISDN Terminal Adapter
Phone Computer
ISDN BRI Line
2B +DNetwork
Terminator
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Channels in BRI Service
• B channels are known as bearer channels– Carry information
• D channel is known as the Delta channel– Used for signaling purposes
• 2B + D channel service
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The B Channel
• 64k bps per channel• The two B channels can be inverse
multiplexed or boded together – Achieve a maximum aggregate
communication speed of 128 Kbps
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The D Channel
• 16 Kbps• Entire bandwidth is not used for
signaling purpose• Excess of 9.6 Kbps is available for
packet switched data transmission applications
• Excess bandwidth usage– Climate control, security alarm system etc.
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In Summary
• BRI is the basic ISDN service• Composed of 2 B channels and a D
channel• B Channels are circuit switched• D Channel is packet switched
– Excess capacity can be utilized for packet switched applications
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END OF MODULEEND OF MODULE
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MODULE
Primary Rate Interface (PRI)
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PRI Service
• More sophisticated service compared to BRI
• PRI service offers 23 B channels and 1 D channel
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Properties of B Channels in PRI
• Each B channel operates at a speed of 64K bps
• The B channels are used for carrying data
• B channels can be combined together to increase the aggregate communication speed
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Properties of D Channel in PRI
• Each D channel operates at a speed of 64 Kbps– Considerably faster than the D
channel in BRI
• 23 B channels share a D channel for signaling purpose
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PRI Channel Delivery
• PRI channels are delivered over a T1 line
• T1 speed– 1.544M bps
• Aggregate speed of PRI from all 23 B channels and the single D Channel is computed as follows:– 23 * 64 + 64 + xx = 1.544 Mbps
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Sample Services (PacBell)
• Centrex ISDN– For businesses that already have the
Pac Bell’s centrex phone system
• SDS-ISDN– BRI service offered for small businesses– Charges
• Per channel• Per minute
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Sample Services (ISDN)
• Home ISDN– Offers a BRI connection
• 2B + D
– Charges are cheaper especially during off-peak hour• Per channel• Per minute
• SDS-56– Single channel switched 56 Kbps digital
service
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Sample Cost Comparison
Service Month Inst. Usage
Cen-ISDN 31.65 220.75 Bus. MeasuredSDS-ISDN 26.04 190.75 Bus. MeasuredHome 24.50 159.75 8-5 Bus. MeasuredISDN Flat OtherwisePRI 220.00 750 Bus. MeasuredSDS- 56 45.00 500 Bus Measured
* Rebates may apply to Installation
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MODULE
Sample ISDN Applications
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Use of ISDN Adapters
Computer Computer Computer
ISDN AdapterISDN AdapterAnalog Modem
NT1 NT1
Pub. SwitchedNetwork
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Remote ISDN Access to a LAN
Computer
ISDN Adapter
NT1
ISDN Router
NT1
PSN
Ethernet
BRIBRI
RemoteISDNBridge
128K bps
28.8K bps to 56K bps
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Remote Access Over PRI
Computer
ISDN Adapter
NT1
ISDN Router
DSU/CSU
PSN
Ethernet
BRI PRI
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Important Features of the PRI Connection
• Communication links can be established between:– remote computers and this LAN– this LAN and remote locations– this LAN and other remote LANs
• Link is established using a powerful router
• A separate DSU/CSU unit is used as opposed to the NT1 network terminator used in the case of BRI
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Commercial Examples of ISDN Equipment
• ISDN adapter– 3Com Impact IQ
• ISDN routers – Ascend and Cisco are sample manufacturers– Ascend Pipeline 50 and Ascend Pipeline 100
are examples of such routers
• For the latest information on ISDN equipment access the manufacturers’ web sites
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ISDN Use in Video Conferencing
• Dynamic bandwidth allocation• Circuit switched• Symmetric bandwidth
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