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