Transcript ISDN - WordPress.com

Traditional Telephone Network VS
Integrated Digital Network
 Traditional Telephone Networks
 Separately designed and administrated transmission and
switching systems
 Demultiplexing and demodulating are necessary at each
switching center
 A repeated process results in an accommodation of noise as well
as cost
 Integration of transmission and switching systems
 Achievable when both systems are digital
 Using PCM modulation and TDM multiplexing
 Switching without decoding along the way
 Separate multiplex/demultiplex channel banks are not required
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Analog Communications w/o ISDN
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The Integrated Digital Network
Multiplex and modulate signals
Space-division
switch
Demultiplex and demodulate signals
Analog telephone network
PCM: pulse-code modulation
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Digital Communications with ISDN
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The Integrated Digital Network (cont’d)
 The IDN will combine the coverage of the
geographically extensive telephone network with
the data carrying capacity of digital data
networks in a structure called the “integrated
services digital network (ISDN)”
“integrated” refers to the simultaneous carrying of
digitized voice and a variety of data traffic on the
same digital transmission links and by the same
digital exchanges
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Principles of ISDN
1. Support of voice and non-voice applications using a
limited set of standardized facilities
 Defines the purpose of ISDN and the means of achieving it
2. Support for switched and non-switched applications
 Both circuit-switched and packet-switched connections
 Support non-switched services in the form of dedicated lines
3. Reliance on 64-kbps connections
 Fundamental block of ISDN
 64 kbps were chosen because it was the standard rate for
digitized voice
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Principles of ISDN (cont’d)
4. Intelligence in the network

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Sophisticated serviced beyond simple setup a circuit-switched call
Sophisticated network management and maintenance capabilities
Use of SS7 ( (common channel) signaling system number 7) and
intelligent switching nodes in the network
SS7 is a set of telephony signaling protocols which are used to set up
the vast majority of the world's public switched telephone network
telephone calls.
5. Layered protocol architecture
 User access to ISDN protocol is a layered architecture that can be
mapped to OSI model
 Standards can be developed independently for various layers and
functions
6. Variety of configurations
 More than one physical configuration is possible for implementing
ISDN
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The User Interface
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The User Interface (cont’d)
 User has access to ISDN via a local interface to a digital
“pipe”.
 Pipes of various sizes are available to satisfy different
needs
 Pipe to the user’s promises has a fixed capacity but the
traffic on the pipe may be a variable mix up to the
capacity limit
 ISDN requires control signals to instruct how to sort out
the time-multiplexed data and provide the required
services
 Control signals are multiplexed onto the same digital
pipe
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The User Interface (cont’d)
 Recommendation from I.410: more than one size of pipe
is needed
 A single terminal (e.g. a residential telephone)
 Multiple terminals (e.g. a residential telephone, PC, and alarm
system)
 A network of devices attached to a LAN or PBX (ISDN
gateway)
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The User Interface (cont’d)
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Benefits
 The principle benefits of ISDN to the customer
can be expressed in terms of cost savings and
flexibility
 Integrated voice and data means that the user
does not have to buy multiple services to meet
multiple needs
Access charges to a single line only
Purchasing services based on actual needs
Product diversity, low price, and wide availability of
equipment
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ISDN Architecture
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ISDN Architecture (cont’d)
 Physical interface provides a standardized means of
attaching to the network
 The interface supports a basic service consisting of
three time-multiplexed channels, two at 64 kbps and one
at 16 kbps
 In addition, there is a primary service that provide
multiple 64-kbps channels
 An interface is defined between the customer’s terminal
equipment (TE) and a device on the customer’s
premises, known as a network termination (NT)
 The subscriber loop is the physical path from the
subscriber’s NT to the ISDN central office
 Must support full-duplex digital transmission for both basic and
primary data rates
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Outline
 ISDN Overview
 ISDN Interfaces and Functions
 ISDN Standard
 Transmission Structure
 ISDN Model
 Reference Points and Functional Groupings
 Access Configurations
 ISDN Switch Types
 ISDN Tutorial
 Network Diagram
 Type of Equipment
 Configuring your ISDN Line and Equipment
 Wiring your Location for ISDN
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ISDN Standard
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Transmission Structure
 Digital pipe between central office and ISDN subscriber
carry a number of communication channels, varies from
user to user
 The transmission structure of access links includes
channels of:
 B channel: 64 kbps
 D channel: 16 or 64 kbps
 H channel: 384 (H0), 1536 (H11), or 1920 (H12) kbps
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B Channel
 A user channel, carrying digital data, PCM-encoded
digital voice, or a mixture of lower-rate traffic at a fraction
of 64 kbps
 The information is carried in frame format, using either
high-level data link control (HDLC) or PPP as the Layer
2 protocol. PPP is more robust than HDLC because it
provides a mechanism for authentication and negotiation
of compatible link and protocol configuration.
NETE0510: Communication Media and Data
Communications
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D Channel
 Carry common-channel signaling (CCS) information to
control circuit-switched calls
 Traffic over the D channel employs the Link Access
Procedure on the D Channel (LAPD) protocol. LAPD is a
data link layer protocol based on HDLC.
 May be used for packet switching or low speed (e.g. 100
bps) telemetry (data transfer over media) when no
signaling information is waiting
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ISDN Channel Functions
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H Channel
 Provides user information transmission at higher data
rates
 Use the channel as a high-speed trunk or subdivide it
based on TDM
 Examples: fast fax, video, high-speed data, high quality
audio
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Basic and Primary Channel Structures
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ISDN Model
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ISDN Protocols at the user-network
interface
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ISDN Physical Layer
 Each ISDN BRI frame contains two sub-frames each containing the
following:
 8 bits from the B1 channel, 8 bits from the B2 channel, 2 bits from the D
channel, and 6 bits of overhead
 So, each BRI frame contains 48 bits
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ISDN Physical Layer (cont’d)
 The overhead bits of an ISDN sub-frame are used as
follows:
 Framing bit — Provides synchronization
 Load balancing bit- Adjusts the average bit value
 Echo of previous D channel bits — Used for contention
resolution when several terminals on a passive bus contend
for a channel
 Activation bit — Activates devices
 Spare bit — Unassigned
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ISDN Physical Layer (cont’d)
 4,000 frames are transmitted per second.
 Each B channel, B1and B2, has a capacity of 8 * 4000 * 2
= 64 kbps, while channel D has a capacity of 2 * 4000 * 2 =
16 kbps.
 This accounts for 144 kbps (B1 + B2 + D) of the total ISDN
BRI physical interface bit rate of 192 kbps.
 The remainder of the data rate are the overhead bits that
are required for transmission: 6 * 4000 * 2 = 48 kbps.
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ISDN Data-link Layer
SAPI identifies the portal at which LAPD services are provided to Layer 3
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ISDN Data-link Layer (cont’d)
 Layer 2 of the ISDN signaling channel is LAPD. LAPD is
similar to HDLC. LAPD is used across the D channel to
ensure that control and signaling information is received
and flows properly.
 The LAPD flag and control fields are identical to those of
HDLC.
 The LAPD address field is 2 bytes long.
 The first address field byte contains the service access point
identifier (SAPI), which identifies the portal at which LAPD
services are provided to Layer 3. The command/response bit
(C/R) indicates whether the frame contains a command or a
response.
 The second byte contains the terminal endpoint identifier (TEI).
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ISDN Layer 3:
Q.931 Messaging Call Setup
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(Q.931 Messaging Call Setup)
NETE0510: Communication Media and Data
Communications
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Reference Points and Functional
Groupings
ITU-T approach for actual user’s physical
configuration
Functional grouping: certain arrangements
of physical equipment or combination of
equipment
NT1, NT2, TE1, TE2, TA
Reference points: conceptual points of
separation of group function
R, S, T, U
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Functional Groupings
 NT1 (Network Termination 1)
Includes functions similar to OSI layer 1
May be controlled by ISDN provider (a boundary to
network)
Isolate the user from the transmission technology of
subscriber loop
Supports multiple channels (e.g. 2B+D) using TDM
Might support multiple devices in a multidrop
arrangement
 E.g. a residential interface might include a telephone, PC,
and alarm system, all attached to a single NT1 interface
via a multidrop line
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Functional Groupings (cont’d)
 NT2 (Network Termination 2)
 An intelligent device that may include up to OSI layer 3
 Perform switching and concentration functions
 Switching: the construction of a private network using semipermanent circuit among a number of sites
 Concentration: multiple devices, attached to a digital PBX,
LAN, or terminal controller, may transmit data across ISDN
 E.g. digital PBX, a terminal controller, LAN
 Digital PBX provides NT2 functions at layers 1, 2, and 3
 A simple terminal controller provides layers 1 and 2
 A simple Time Division MUX provides layer 1
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Functional Groupings (cont’d)
 TE1 (Terminal Equipment type 1)
 Devices that support the standard ISDN interface
 E.g. digital telephone, integrated voice/data terminal, digital
fax
 TE2 (Terminal Equipment type 2)
 The existing non-ISDN equipment
 E.g. physical interface RS-232, host computer with X.25
 Requires a terminal adaptor (TA) to plug into an ISDN
interface
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Functional Groupings (cont’d)
 TA (Terminal Adaptor)
Converts standard electrical signals into the form used
by ISDN
Needed for connection with TE2 devices
The ISDN TA can be either a standalone device or a
board inside the TE2
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Reference Points and Functional
Groupings
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Reference Points
 Reference point R (connect TE2-TA)
 Provides a non-ISDN interface between user equipment that is
non-ISDN compatible and adaptor equipment
 Comply with X or V series ITU-T recommendation
 Reference point S (connect TE1-NT2, TA-NT2)
 The interface of individual ISDN terminals
 Separate user terminal from network communications functions
 Reference point T (connect NT2-NT1)
 A minimal ISDN network termination at CPE
 Separate network’s provider equipment from the user’s one
 Reference point U (connect NT1-provider)
 Describes full-duplex data signal on the subscriber line
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Access Configurations
 Based on definitions of functional grouping and
reference points, several possible configurations
for ISDN user-network interface have been
proposed by ITU-T
The most straightforward configuration is that one or
more pieces of equipment correspond to each functional
grouping:
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Access Configurations (cont’d)
 In second case, the line termination function is combined
with other ISDN interface functions
 ISDN provider may provide the NT1 function e.g. NT1
may be integrated into a PBX
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Access Configurations (cont’d)
 In the third case, NT2 and TE functions are combined
 A host that supports users, but also acts as a packet
switch in a private packet-switching network that uses
ISDN for trunking
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Access Configurations (cont’d)
 Final case: an ISDN subscriber device can connect
directly to the subscriber loop terminator or into a PBX or
LAN using the same interface specifications and thus
ensuring portability
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Examples of implementation of NT1 and
NT2 functions
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Examples of implementation of NT1 and
NT2 functions
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NT1 equipment
NT1 circuit card
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ISDN Switch Type
 Routers must be configured to
identify the type of switch with
which they will communicate.
 Available ISDN switch types
vary, depending in part on the
country. As a consequence of
various implementations of
Q.931, the D channel signaling
protocol used on ISDN
switches varies from vendor to
vendor.
 Each switch type operates
slightly differently, and has a
specific set of call setup
requirements.
 Before the router can be
connected to an ISDN service,
it must be configured for the
switch type used at the CO.
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ISDN Switch Type (cont’d)
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Network Diagram
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Types of Equipment
Network Termination Device 1 (NT1)
 The NT1 is a simple device that serves as an interface
between the ISDN BRI line and your other ISDN
equipment.
 It converts the physical wiring interface delivered by
Southwestern Bell to the wiring interface needed by your
ISDN equipment, and also provides a testing point for
troubleshooting.
 Many ISDN terminal adapters and some ISDN routers
have the NT1 function built-in. This makes for an easier
installation and also reduces the total cost of your ISDN
setup. However, a separate NT1 is more flexible in that it
can support multiple ISDN devices.
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Types of Equipment (cont’d)
ISDN Routers
 Perform a function similar to that of a standard router.
 Using an ISDN router, multiple computers on a LAN can
share a single ISDN BRI connection.
 Because ISDN routers use Ethernet connections, they
can take full advantage of ISDN's speed.
 Many of the most popular ISDN routers also support
analog voice, modem, or fax applications, as well as
sophisticated network management capabilities.
 ISDN routers are typically more than twice as expensive
as TAs, but they are often worth the money since they
allow multiple computers on a small LAN to leverage
your ISDN investment.
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Physical Interfaces
 U-Interface
 The U-interface is the 2-wire interface your phone company
delivers for connection to the NT1.
 Many of the newer ISDN networking devices, e.g. the 3Com
Impact, include a built-in internal NT1 and power supply, so they
can connect directly to the U-interface.
 Manufacturers may describe this feature as a "built-in NT1 " or
simply as a U-Interface ISDN TA.
 S/T Interface
 The S/T-interface is the 4-wire interface between the NT1 and
the ISDN networking equipment such as an ISDN TA or router.
 An S/T interface is used when the NT1 is a separate device.
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Physical Interfaces (cont’d)
 Other interfaces
The interface between your ISDN networking equipment
and your computer is usually one of the standard
industry interfaces.
For example, an External TA will use the computer's
serial COM port such as RS232.
ISDN routers will use a standard Ethernet connection,
either directly to a computer's NIC card or via an
intermediary Ethernet hub.
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Configuring your ISDN Line and
Equipment
Switch Type
ISDN Phone Number (Directory Number)
SPID (Service Profile Identifier)
TID (Terminal Identifier)
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Switch Types
 The "engines" of the ISDN phone network are the
complex network switches which deliver the service.
There are two dominant switches that provide ISDN:
Lucent Technology's 5ESS and Northern Telecom's
DMS100.
 While those two switches provide the same basic
features and functionality, they differ in how they interact
with your ISDN equipment.
 It is important that you find out which switch type and
which software version will be providing you with
ISDN service, so you can order your ISDN service and
set your ISDN networking equipment parameters
correctly.
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Switch Types (cont’d)
 In Southwestern Bell Internet Services territory,
the possible switches and software versions are:
Lucent Technology (formerly a part of AT&T) 5ESS - NI2
(National ISDN version 2) and/or AT&T custom ISDN
software
Northern Telecom DMS100 - Custom ISDN software
Northern Telecom DMS100 - NI1 (National ISDN version
1) software
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ISDN Phone Number
 Your ISDN phone line will be assigned a phone number
just like a standard phone line.
 However, depending on which kind of switch you are
served from and how you are going to use the ISDN
service, you may get one phone number per ISDN line or
one phone number for each ISDN B-channel.
 It is important for you to define how you plan to use your
ISDN line so Southwestern Bell can assign the correct
number of phone numbers.
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ISDN Phone Number (cont’d)
 DMS100
 A DMS switch always assumes a multipoint configuration.
 If you are served from a DMS-100 switch, you should receive
two phone numbers, one for each B-channel.
 5ESS
 If you receive your ISDN service from a 5ESS switch, you need
to choose either a "point-to-point" or "multipoint" configuration.
 If you only intend to connect a single device/application to your
ISDN line, then you only need the point-to-point configuration.
 With the point-to-point configuration you are assigned a single
phone number per ISDN line (not one for each B-channel).
 If you intend to connect multiple devices/applications, then you
need the multipoint configuration.
 With multipoint configuration you are assigned a phone number
for each device connected.
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SPIDs
 The ISDN carrier provides a SPID to identify the line
configuration of the ISDN service.
 SPIDs are a series of characters (that can look like
phone numbers with extra digits) that identify you to the
switch at the CO. After you're identified, the switch links
the services you ordered to the connection.
 However, depending on which kind of switch you are
served from and how you are going to use the ISDN
service, you may not need a SPID or you may need a
SPID for each B-channel, or each device.
 It is important for you to define how you plan to use your
ISDN line so Southwestern Bell can assign the correct
number of SPIDs.
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SPIDs
 DMS100
You should receive two SPIDs, one for each B-channel.
 5ESS
Need to choose either a "point-to-point" or "multipoint"
configuration.
If you only intend to connect a single device/application
to your ISDN line, then you only need the point-to-point
configuration and you are not assigned any SPIDs.
If you intend to connect multiple devices/applications,
then you need the multipoint configuration.
With the multipoint configuration you are assigned a
SPID for each device connected.
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TID
 Specific to a National ISDN-1 BRI line from a DMS100
switch, is the need for a terminal identifier (TID).
 The TID is comprised of two additional digits used in
conjunction with the SPID when initializing devices.
 The TID is intended for use on all non-initializing
terminals.
 All terminals in use today are initializing terminals, and
most do not require a specific TID.
 To minimize confusion, it is recommended that you use
"00" on each terminal device, no matter how many
terminal devices there are.
 For further clarification, you should check with your ISDN
equipment vendor for their recommendation.
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Wiring your Location for ISDN: Inside
Wiring
 By regulation, Southwestern Bell ISDN service ends at
what is called the demarcation point ("demarc") usually
just outside your residence or in an apartment building
basement.
 You are responsible for the wiring from the demarcation
point to your ISDN equipment including the wall jacks.
 You will want your ISDN phone jacks close to your ISDN
equipment for the best performance.
 You can choose to have Southwestern Bell install and
maintain this "inside wiring" for an additional charge, or
you can use an electrical contractor.
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Wiring your Location for ISDN: Inside
Wiring (cont’d)
 While some homes and offices may need to be re-wired
for ISDN, most will not.
 The copper twisted pair wiring that currently provides
standard analog phone service can be successfully used
for ISDN.
 However, with the increasingly popularity of multiple lines
you may not have spare wiring available for your ISDN
service. Therefore, additional cabling may be necessary.
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Wiring your Location for ISDN: ISDN
Phone Jacks
 RJ11
 This is the standard analog phone jack, and is used to deliver 2wire service.
 The phone company will often install this jack for ISDN unless
otherwise requested.
 However, some NT1s required the wider RJ45 or SJA11C jack.
 The 3Com Impact phone cable has an RJ11 plug on one end to
connect to a RJ 11 wall jack.
 RJ45
 Slightly wider than the RJ11, and has 8 pins but can still be used
to deliver 2-wire service such as ISDN BRI.
 Again, some NT1s require this jack and their associated
connecting cable with the RJ45 plug will not fit into an RJ11 jack.
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Wiring your Location for ISDN: ISDN
Phone Jacks (cont’d)
 SJA11
 This is identical to the RJ45 jack, but is a non-regulated
product and therefore is significantly less expensive than the
RJ45.
 Specifically request this jack when ordering your ISDN
service.
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