1. CSI5171: Network Architecture, Services, protocol and standards
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. Fig.1: ISDN architecture
USER
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 > 64kbps
Non-Switched capabilities > 64kbps
Frame mode functional entities
CCS capabilities (SS7)

5. Channels and Access Interface
Two types of channels
D-channel (Data channel): usually carries 16 Kbps or 64 Kbps; also can carry packet data
B-channel (Bearer channel): carry information for user 64 Kbps
Two access interfaces
BRI (Basic Rate Interface): 2B + D (16 Kbps); intended for home use
PRI (Primary Rate Interface):23B+D (64Kbps) in North America; 30B+D 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 (cont’d)
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 Two types of signaling protocols B-ch USER SS7
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 (cont’d)
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 (cont’d)
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 (cont’d)
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