Aspects of ISDN

1
Aspects of ISDN

• CSI5171 Network Architecture, Services, protocol
  and standards
• A presentation by
• Razzaqul Haider

2
Introduction

• ISDN stands for Integrated services Digital
  network
• It provides end-to-end digital connectivity for
  voice and non-voice services
• ISDN provides all the services through a single
  interface
• Use out-of-band signaling
• Protocol used by ISDN is layered protocol

3
ISDN Architecture
USER
ISDN
USER

• Fig.1 ISDN architecture
• ISDN offers 8 main switching and functional
  capabilities

4
ISDN Capabilities

• Local Connection related function
• 64 kbps circuit switched capabilities
• 64 kbps circuit non-switched capabilities
• Packet switching capabilities
• Switched capabilities gt 64kbps
• Non-Switched capabilities gt 64kbps
• Frame mode functional entities
• CCS capabilities (SS7)

5
Channels and Access Interface

• Two types of channels
• D-channel (Data channel) usually carries signals
  _at_ 16 Kbps or 64 Kbps also can carry packet data
• B-channel (Bearer channel) carry information for
  user services _at_ 64 Kbps

• Two access interfaces
• BRI (Basic Rate Interface) 2B D (16 Kbps)
  intended for home use
• PRI (Primary Rate Interface)23BD (64Kbps) in
  North America 30BD in Europe intended for
  business use

6
ISDN Reference Configuration
SS7
TE1 Terminal Equipment Type 1 TE2 Terminal
Equipment Type 2 TA Terminal Adapter NT1
Network Termination 1 NT2 Network Termination 2
LE Local Exchange LT Local Termination ET
Exchange Termination
7
ISDN Reference Configuration (contd)

• ISDN recommendation describes several functional
  device types as shown
• Each device talks to the neighbouring device(s),
  using certain communication protocol.
• Each of these device interfaces is called a
  reference point and denoted by R, S, T, U and V.

8
Signaling Protocol
B-ch
USER
Other Net node
SS7
ISDN Switch
D-ch
Voice, data
B-ch

• Two types of signaling protocols
• user- network interface protocol through
  D-channel known as DSS1 (Digital subscriber
  System 1) defined in three layers and
• Networking (interswitch) protocol CCS signaling
  by SS7, specifically ISDN User Part (ISUP) of
  SS7, defined in 7 layers

9
Protocol Architecture

• DSS1 protocol is defined in 3 layers

• SS7 protocol architecture

TCAP
ISUP
Basic Suppl. Services Services Q.931
messages
SCCP
LAPD
MTP
I.430/I.431
10
D-channel protocol

• Used to establish, maintain and terminate network
  connections
• Provide procedures for invocation and operation
  of supplementary services

11
ISDN User Part

• ISUP is an upper layer application supported by
  SS7
• ISUP provides the signaling functions required to
  support basic bearer services and supplementary
  services
• ISUP uses either SCCP, which in turn uses MTP, or
  it uses MTP directly for message transfer
• ISUP basic call control is divided into three
  parts call set-up, the data/conversation phase
  and call clear down

12
ISDN User Part (contd)

• Two signaling methods link-by-link, end-to-end
• ISUP Signaling Capabilities are of two class
  Internationally applicable class and National use
  class
• ISUP end-to-end signaling
• Capability to transfer information of end point
  significance
• Typically used between all originating and
  terminating local exchanges

13
ISUP end-to-end signaling

• Used to request or to respond to requests for a
  basic call, to invoke a supplementary or to
  transfer user-to-user information transparently
  through the network
• Two methods of end-to-end signaling SCCP method
  of end-to-end signaling and pass-along method of
  end-to-end signaling
• Pass-along signaling is done without requiring
  the service of SCCP.
• Pass-along method usually used when information
  to be transferred relates to an existing call for
  which a physical connection between the same two
  exchanges has been established

14
Basic Call Setup
15
Basic Call Release
16
Basic Call Setup/release

• User initiates call by Q.931 SETUP message on the
  D-channel
• Upon receiving the SETUP message OLE launch an
  ISUP IAM message to the Transit eXchange (TX),
  TXs generate IAM until it reaches Terminating
  local Exchange (TLE)
• IAM contains originating point code, destination
  point code, Circuit identification code, etc.
• Finally, the destination exchange sends a SETUP
  message to the called party on the Dchannel
• Called party terminal equipment generates an
  ALERTING message
• TLE then sends ISUP message ACM to the OLE
  through TX
• After called party answers the call, TE sends
  Q.931 CONNECT message on the D channel, which
  causes the TLE to send an ISUP message called ANM

17
Basic Call Setup/release (contd)

• ANM message at OLE generates CONNECT message to
  the calling party TE
• Connection is established between the end users
  through B-channels at the originating and
  terminating access interfaces and network trunks
  between the OLE and TLE.
• Call termination initiated my the message
  DISCONNECT from the terminal Equipment
• the OLE sends an ISUP release message (REL) to
  release the trunk circuit between the switches
• Upon receiving the REL, the destination switch
  disconnects the trunk from the called party's
  line, sets the trunk state to idle, and transmits
  an ISUP release complete message (RLC) to the
  originating switch to acknowledge the release of
  the remote end of the trunk circuit

18
Supplementary Services

• ISDN supplementary services offer capabilities to
  customers that can be dynamically controlled and
  accessed via their CPE.
• Some services have local significance and
  available from the local switch, e.g. conference
  call, call waiting, etc.
• While others have end to end significance and
  availability depend on the capability of the
  switch to communicate with other switches through
  ISUP, e.g. number identification, User to user
  signaling, etc.
• Users control the both type of services through
  signaling capabilities of the D-channel

19
Supplementary Services (contd)

• Category of supplementary services
• Number identification services DDI, MSN, CLIP,
  CLIR, COLP, COLR, MCID
• Call offering services CT, TP, CFU, CFB, CFNR,
  CD, ECT, LH
• Call completion services CW, HOLD, CCBS
• Multiparty CONF, 3TPY
• Community of interest CUG, PNP, MLPP
• Charging services AOC, CRED, RC
• Additional transfer information services UUS

20
Conclusion

• ISDN architecture and capabilities
• ISDN protocols
• Channels and Access Interface
• ISDN reference configuration
• ISUP signaling
• Message sequence flow for basic call set-up
• Supplementary services