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ISDN

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Completion of Call to Busy Subscriber - Like Camp-on and still under study, ... Outgoing Call Barring - Disable outgoing service. ISDN User-Network Interfaces ... – PowerPoint PPT presentation

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Title: ISDN


1
ISDN
  • Integrated Services Digital Networks

2
ISDN Teleservices
  • Telephony
  • Teletex
  • Telefax 4
  • Mixed Mode
  • Videotex
  • Telex
  • Telephony 7 kHz
  • Teleaction

3
Supplementary Services(1)
  • Direct Dialing In
  • Multiple Subscriber Number
  • Calling Line Identification Presentation
  • Calling Line Identification Restriction
  • Connected Line Identification Presentation
  • Connected Line Identification Restriction
  • Malicious Call Identification
  • Sub-addressing
  • Call Transfer
  • Call Forwarding Busy
  • Call Forwarding No Reply
  • Call Forwarding Unconditional
  • Call Deflection
  • Line Hunting
  • Explicit Call Transfer
  • Call Waiting
  • Call Hold

4
Supplementary Services(2)
  • Completion of Call to Busy Subscriber - Like
    Camp-on and still under study, probably because
    given ISDN's abilities you need not literally
    camp-on. If you ask for the service, you could
    hang up and be called back when the called number
    becomes available
  • Terminal Portability- Authorizing the use of
    Suspend and Resume to provide a portability
    service
  • Conference Calling
  • Three Party - You can hold one party and call a
    third party, switch back and forth between the
    two, release either party, or join all three
    people in a conference.
  • Closed User Group - Similar to existing data
    network services of the same name. Users may
    belong to more than one group. Access may be
    limited to incoming or outgoing, and incoming or
    outgoing calls may be barred
  • Private Numbering Plan - This service is still
    under study and is not described. Presumably it
    is an attempt to provide users with a sort of
    overlay numbering plan in ISDN.
  • Multilevel Precedence Preemption - Precedence
    assigns a priority level to calls. Preemption
    allows calls of higher priority to preempt
    resources, i.e., B-channels, from lower priority
    calls
  • Priority Service - Able too set priorities on
    calls
  • Outgoing Call Barring - Disable outgoing service

5
ISDN User-Network Interfaces
  • Basic Rate Interface (144 kbit/s)
  • The Basic Rate Interface (BRI) for ISDN consists
    of two 64 kbit/s B-Channels and a single 16 kbit/
    s D-Channel. The B-Channels are for information
    transfer only. The D-Channel is primarily for
    signaling the network, but may also be for
    packet-mode and telemetry information transfer.
    This interface connects to the user premises over
    a single twisted pair loop.
  • Primary Rate Interface
  • The Primary Rate Interface (PRI) for ISDN
    consists of 23 - 64 kbit/s B-Channels and a
    single 64 kbit/s D-Channel in North America and
    Japan, countries who follow what is known in the
    ITU-T as m-law. In the rest of the world there
    are 30 - 64 kbit/s B-Channels and one 64 kbit/s
    D-Channel these countries follow what is known
    in the ITU-T as A-law. Both m-law and A-law have
    to do with the Pulse Code Modulation (PCM)
    techniques. This interface connects to the user
    premises over two twisted pairs. The D-Channel of
    the PRI can serve other PRIs belonging to the
    same user. This means that a user with two PRIs
    could use all 24 channels on the second interface
    for B Channels.
  • Broadband ISDN
  • Broadband ISDN (B-ISDN) is under development
    within the ITU-T, and has achieved significant
    agreement since the 1988. There is one
    Recommendation, I.121, which covers the basics,
    but there is still more work to be done. I.121
    states that the user interface should be
    standardized at two rates, one of 155.52 Mbit/s
    and the other of 622.08 Mbit/s. Asynchronous
    Transfer Mode (ATM), a form of asynchronous time
    division multiplexing is the target method. The
    Synchronous Optical Network (SONET) and
    Synchronous Digital Hierarchy (SDH) fiber optic
    systems are accepted as a transmission media.
  • Present
  • Basic Rate Interface - 2BD
  • Primary Rate Interface - 23BD (m-law)
  • - 30BD (A-law)
  • Broadband ISDN - 155.52 622.08 Mbit/s

6
The ISDN Reference Configuration (1)
  • NT1 - a single (physical) layer device that
    terminates the loop technology and provides the
    user interface.
  • NT2 - a three layer (physical, data-link,
    network) device that provides many user
    interfaces and is capable of interconnecting
    (switching) B-Channels between those devices.
  • TE1 - a terminal device that is fully capable of
    interoperating with ISDN.
  • TE2 - an existing terminal device, designed for
    existing protocols. It is not capable of directly
    interoperating with ISDN.
  • TA - an adaptive device designed to permit TE2s
    to inter-operate with ISDN.

7
The ISDN Reference Configuration (2)
  • The circled numbers in the lower diagram indicate
    the level of service observed at each reference
    point and also at the human/machine interface of
    TE1 and TE2.
  • 1 2 - ISDN bearer service
  • 4 - other ITU-T standardized services
    according to
  • V or X series Recommendations,
  • 3 5 - ISDN teleservices
  • R - a reference point representing existing
    interfaces such as X.25, V.24, EIA-232-D, V.35, a
    PC internal bus, etc. It operates at rates up to
    56 kbit/s. Note that the combination of a TA and
    TE2 is equivalent to a TE1.
  • S - a reference point generally supporting two
    B-Channels at 64 kbit/s and one D Channel at 16
    kbit/s operating at 192 kbit/s, the Basic Rate
    Interface (BRI). When attached to an NT2 this
    could be a Primary Rate Interface (PRI) operating
    at 1544 or 2048 kbit/s.
  • T - a reference point supporting 2 B-Channels
    and 1 D-Channel at 192 kbit/s (BRI), 23
    B-Channels and 1 D-Channel at 1.544 Mbit/s (PRI),
    and 30 B-Channels and 1 D-Channel at 2.048 Mbit/s
    (PRI). Note that in the BRI case, T and S are
    equivalent.
  • U - a reference point supporting the same three
    cases as T, but with the loop technology that, in
    the BRI case, is different from the T reference
    point technology. Due to the Federal
    Communications Commission ruling, it is also an
    interface. The distinction between reference
    points and interfaces is that reference points
    are not necessarily visible. If the NT1 and NT2
    functions were combined, there would not be a
    visible reference point T. Concerning the boxes,
    not all installations would necessarily have all
    the functions depicted by the boxes.

8
The ISDN Reference Configuration (3)
  • The network domain involves the ISDN switches and
    the inter-office trunking contained within the
    dashed box.
  • The signaling system involves the Signal Transfer
    Points (STP) and associated trunks that are
    contained within the dotted box.
  • The user domain involves the basic and primary
    rate interfaces and the line cards and exchange
    termination portion of the ISDN switch.
  • In actual fact, no portion of the ISDN switch can
    really be said to be part of the user domain, but
    what is being discussed here is that portion of
    ISDN directly observable by the users.
  • All of these component parts must work together
    to provide the services that put the S in ISDN.
    For example, a user sends signaling messages (of
    the Recommendation Q.931 format) over the D
    Channel into the ISDN switch. Inside the switch,
    the Q.931 messages are converted into ISDN user
    part formats and sent to the STP. At the called
    ISDN switch, these ISDN user part messages are
    converted back to Q.931 format for delivery to
    the called user. To the users, it may seem that
    the D-Channel is end-to-end, but in fact the
    D-Channel terminates at the first (or serving)
    switch.
  • It may seem that it would have been better to
    simply extend SS7 directly to the user
    interface, and this was considered at one time
    for PABX. However, SS7 is designed for
    inter-office use and is specifically geared for
    network operator functions. Recommendation Q.931
    signaling is designed for user-to-network
    interaction and is better suited to the user
    interface.
  • When the signaling is complete, an inter-office
    trunk of the appropriate type is assigned to the
    user's call. The user does not know which
    specific trunk is assigned and really does not
    care. All that is of interest is that a trunk is
    assigned and that it is of the correct type and
    functionality.
  • 3 distinct domains, which while they are
    logically separated from each other, work
    cooperatively for the ISDN service.

9
The Physical Layer of ISDN
  • deals in 48 bit synchronized frames.
  • provides basic time division multiplexing to
    derive the two B-Channels and the D-Channel (in
    both BRI and PRI) and what might be called "data
    sense multiple access with collision resolution"
    to share the D-Channel equitably among several
    terminal devices.
  • 2 Physical Layer protocols
  • on the user side of the network-terminating
    device (NT1)
  • on the network side (for BRI).
  • reduces the terminal-network interfaces to just
    two
  • The network carries voice data video
  • The ITU-T is continuing work on a Broadband ISDN
    that will create at least one more interface, and
    possibly two. Broadband ISDN has user-network
    interface (UNI) data rate of 155 Mbit/s user to
    network, and a rate of 600 Mbit/s network to
    user. Work by the ATM Forum has defined other UNI
    rates as well as Network - Network Interface
    (NNI) and even a Private Network Network
    Interface (PNNI).

10
Wiring Scenarios (S/T) (1)
  • point-to-point scenario of a single Terminal
    Equipment (TE) attached to the Network
    Termination (NT).
  • wiring length may be up to 1 km with a max cable
    attenuation of 6db at 96 kHz.
  • wiring scenario is very similar to the current
    analog telephone network customer premises
    wiring. Prior to the advent of the telephone plug
    and jack most households were simply wired from
    the protector to the single telephone set. Even
    today, PABXs are wired from the network
    termination point directly to a single PABX
    trunk.

11
Wiring Scenarios (S/T) (2)
  • short passive bus, expected to be a very popular
    configuration.
  • allows attachment of up to 8 terminal devices to
    a single network-terminating device.
  • the wiring length is approximately 100-200 meters
    with the TEs connected at random points along the
    cable. The 100 meter length applies to low
    impedance cable (Zc75 ohms) and the 200 meter
    length applies to high impedance cable (Zc150
    ohms).
  • This multidrop scenario could apply to a private
    residence, being not much different than the
    current situation in households that have
    multiple jack appearances. However, it is more
    likely to apply in the business environment. A
    passive bus arrangement in a corporate employee's
    workspace, providing connection for telephone,
    personal computer, facsimile machine, etc. will
    soon be the norm

12
Wiring Scenarios (S/T) (3)
  • extended passive bus, similar to the short form,
    but designed for inter-building arrangements.
    This would most likely be on the terminal side of
    PABXs that serve corporations that have
    multi-building campus-like environments. This
    configuration extends from 100 to 1000 meters.

- rather than random positioning, the terminal
devices must be clustered in the last 25 to 50
meters of the cable - It states that the number
of TEs connected to the cable is to be determined
by individual administrations. This far-end
clustering is quite logical, as well as
electrically necessary, since the greater part of
the cable length would be in the run from the
PABX to the connected building.
13
An ISDN Residence
14
The Primary Rate Interface (PRI)
  • differs depending the location of ISDN.
  • In North America and Japan, a 1.544 Mbit/s (the
    m-law rate) digital rate is used as the first
    step up from the 64 kbit/s channel rate.
  • In much of the rest of the world, a 2.048 Mbit/s
    (the A-law rate) digital rate is used.
  • 1 D-Channel per PRI
  • associate 2 or 3 PRIs using the D-Channel of 1
    interface to serve the group. This affects the
    H11 rate (1536 kbit/s) in the m-law case, since
    to use a single PRI at the H11 rate effectively
    removes the signaling channel. T1.408 has an H10
    rate of 1472 kbit/s that would leave the
    D-Channel intact on a single PRI. The H0 rates
    are similarly affected, where a single PRI may
    support 4 H0 channels at 384 kbit/s each without
    a D-Channel, or only 3 H0 Channels and a
    D-Channel. The specification did not state it,
    but you would presumably also have 5 B-Channels
    available as well as the 3 H0 Channels.
  • The 2.048 Mbit/s rate has always set aside 1
    channel (Channel 1) for synchronization and
    timing, and 1 channel (Channel 16) for signaling.
    They have no problems with the H12 rate, since it
    always leaves the D-Channel in place. This use
    would seem to be an instance of common channel
    signaling, but it is still referred to as channel
    associated signaling.

15
Broadband ISDN
  • ITU-T is still working upon the definition of
    B-ISDN as it has become more commonly known. Some
    Recommendations have been published for B-ISDN,
    but the package is not yet complete. However,
    from the modest beginnings in the 1988 where
    there were basically 3 or 4 Recommendations to
    1990 when some 13 or 14 existed there are now in
    excess of 40. Many view B-ISDN as superceding
    regular ISDN, or Narrowband ISDN as it has been
    termed.
  • This view is of course expressed in the journals
    and press because they serve the business sector
    and have little or no concern for the general
    public. There are several suggested reasons why
    B-ISDN should feed the residential market as
    well however, they have yet to prove-in despite
    numerous trials and not insignificant investment.
    These applications have many unsolved problems
    beyond that of a broadband delivery system.
  • Some parts of B-ISDN are already functional, such
    as the Synchronous Optical Network (SONET)
    physical layer. Some experiments have been
    conducted with other aspects of broadband
    networking.

16
Broadband ISDN Services
  • Broadband ISDN is the elevation of the ISDN
    user-network interface to much higher transfer
    rates, rates in the order of 51.84 to 2488.32
    Mbit/s. It is also the adaptation of a
    synchronous interface to an asynchronous
    interface. This is not intended to confuse you
    with the technology underlying B-ISDN, but to
    point out that B-ISDN to the end user will appear
    as bandwidth on demand in whatever quantities are
    needed - up to the maximum rate of the interface.
  • User-Network Interface is proposed to be
  • full-duplex 155.52 Mbit/s,
  • asymmetrical full-duplex 622.08 Mbit/s in and
    155.52 Mbit/s out,
  • full-duplex 622.08 Mbit/s.
  • However, B-ISDN is more than a simple increase in
    bandwidth. B-ISDN is also the evolution of new
    service types for the network. These services are
    currently envisaged as falling into two broad
    categories interactive services, and
    distribution services.
  • Interactive services are further categorized as
  • conversational services
  • messaging services
  • retrieval services
  • Distribution services have been separated on the
    basis of user presentation control.

17
Interactive services
  • Conversational services
  • Generally described as bi-directional dialog
    communication with real-time information transfer
    requiring high bandwidth, e.g., video-telephony,
    video conferencing and high-speed data transfer.
    Proposed transmission of medical data (x-ray, CAT
    scan, etc.) for remote diagnosis requires
    considerable bandwidth since loss data
    compression simply cannot be used.
  • Messaging services
  • Generally described as offering user-to-user
    communication via store-and-forward mailbox or
    message handling units, e.g., electronic mail.
    These are not, as is the case with conversational
    services, real-time applications. Both users need
    not be present simultaneously so that demands on
    network are lesser.
  • Retrieval services
  • Generally described as a means for retrieving
    information stored in information centers which
    are provided for public use, e.g., video-on
    demand, distance learning, access to databases
    and multimedia information.
  • Distribution without user presentation control
  • Generally described as a broadcast service
    providing a continuous flow of information to an
    unlimited number of authorized receivers.
    However, these authorized receivers do not have
    the ability to control the time at which the
    information flow, or any specific part of that
    flow, will start, e.g., elevator music, the movie
    channel, content distribution to CATV systems.
  • Distribution with user presentation control
  • Generally described as similar to the above
    service, however, the information flow is defined
    as being a cyclical sequence of information
    frames (movies). The user will have the ability
    to individually access the cyclical flow, with
    control over the start and order of presentation.
    In this way, the user will always be able to
    start at the beginning. The MPEG-2 video
    compression standards contain methods for a user
    to pause, fast forward, fast reverse, etc.,
    making it indistinguishable from a discrete VCR.

18
B-ISDN Reference Configurations
  • strong similarity between the B-ISDN Reference
  • Configuration and the ISDN Reference
    Configuration except for the notation. In B-ISDN
    the S / T Reference Points have a B subscript to
    denote that this is broadband. Similarly, the
    functionality boxes have a B prefix for the same
    reason. The R Reference Point does not carry a B
    subscript since it is not part of B-ISDN
  • new reference point (W) has appeared along with a
    new function (MA), for Media Adapters. The draft
    recommendation specifically notes that in Figure
    2 there should be a connection between the two
    MAs that is shown by the dashed line for the case
    of ring configurations.
  • The MA function is described as accommodating the
    specific topology of a distributed B-NT2. The
    interface at W may include topology dependent
    elements it may be a non-standardized interface
    or it may in some implementations be identical to
    the interface at SB. This looks rather like the
    IEEE 802.6 Metropolitan Area Network topology.
  • Figure 2 is described as a generic configuration
    whereas Figure 3 is described as a physical
    configuration.
  • One does wonder, given the explanation of a TE2
    as a terminal device that pre-dated ISDN, just
    what a B-TE2 is supposed to be? This could be a
    television set with a B-TA in the form of a
    set-top box, similar to the Cable-TV
    de-scramblers of today, given that distribution
    of television broadcast signals is perceived as
    one of the B-ISDN services.

19
B-ISDN Protocol Reference Model
  • The Physical Layer is divided into 2 sublayers
  • The PM (Physical Medium) sublayer only includes
    media dependent functions. For example, the
    Recommendations now define the use of coaxial
    cable for the 155.52 Mbit/s rate at distances of
    100 to 200 meters, or optical fiber for distances
    of 800 to 2000 meters. For the 622.08 Mbit/s only
    optical fiber is to be used.
  • The TC (Transmission Convergence) sublayer
    performs all functions necessary to transform a
    flow of cells (the ATM unit of transmission) into
    a flow of data units, e.g., cells or STS-n
    frames, which can be transmitted and received
    over a physical medium. The Service Data Unit
    (SDU) across the boundary between the Physical
    Layer and the ATM Layer is a flow of valid cells.
    The ATM Layer is independent of the physical
    media.
  • The TC sublayer is responsible for generation and
    recovery of frames, e.g., STS-n frames. It
    prepares the cell flow and delineates it so that
    the receiving system can recover cell boundaries
    as defined in Recommendation I.432 (B-ISDN
    Physical Layer specification). The HEC (Header
    Error Control) is concerned with generating or
    validating header check sequences. Any cell whose
    header shows in error is discarded if the error
    cannot be corrected. Finally, cell rate
    decoupling concerns the insertion or removal of
    idle cells from the cell stream.
  • The ATM layer is not sublayered. Its first
    function is to demultiplex (or multiplex) cells
    into virtual paths and virtual channels according
    to the header information. Headers are extracted
    (or generated) only at termination points based
    upon information from higher layers, e.g.,
    translation from VPI/VCI to Service Access Points
    (SAP). If generic flow control is applied it is
    done here.
  • The ATM Adaptation Layer is divided into the SAR
    and CS sublayers. The AAL exists because in an
    ideal situation B-ISDN ATM would use variable
    sized cells (packets?) depending upon the nature
    of the information flow. However, the underlying
    physical medium in B-ISDN is either the
    Synchronous Optical Network (SONET) or the
    Synchronous Digital Hierarchy (SDH), which
    operate with a fixed 53-octet cell size.
  • The Segmentation and Reassembly function either
    packs small information units into SONET/SDH
    cells or spreads larger information units across
    one or more SDH cells.
  • The Convergence (CS) sublayer functions depend
    upon which of five types of AAL service is being
    offered, but generally consists of timing
    extraction and error correction.
  • CS Convergence Sublayer
  • SAR Segmentation And Reassembly
  • SSCF Service Specific Coordinating Function
  • SSCOP Service Specific Connection Oriented
    Peer-to-peer protocol
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