Aspects of ISDN
CSI5171: Network Architecture,
Services, protocol and standards
A presentation by:
Razzaqul Haider
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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
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ISDN Architecture
USER
ISDN
USER
Fig.1: ISDN architecture
ISDN offers 8 main switching and functional
capabilities
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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)
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Channels and Access Interface
• Two types of channels
– D-channel (Data channel): usually carries signals @ 16
Kbps or 64 Kbps; also can carry packet data
– B-channel (Bearer channel): carry information for user
services @ 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
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ISDN Reference Configuration
LE
T
S
TE1
NT2
R
TE2
U
V
LT
ET
NT1
NT1
SS7
NT1
TA
Fig. 2: ISDN devices and common reference configurations
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
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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.
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Signaling Protocol
Other
Net
node
SS7
Voice, data
ISDN
Switch
B-ch
D-ch
B-ch
U
S
E
R
• 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,
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defined in 7 layers
Protocol Architecture
• DSS1 protocol
is defined in 3
layers
• SS7 protocol architecture
TCAP
Basic
Suppl.
Services Services
ISUP
SCCP
Q.931 messages
LAPD
MTP
I.430/I.431
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D-channel protocol
• Used to establish, maintain and terminate
network connections
• Provide procedures for invocation and
operation of supplementary services
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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
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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
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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-toend 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
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Basic Call Setup
Calling
Party
Originating
Ex.
Transit
Ex.
Transit
Ex.
Destination
Ex.
Called
Party
SETUP
IAM
IAM
IAM
SETUP
CP
CP
ALERTING
ACM
ACM
ACM
ANM
CONNECT
ANM
ALERTING
CONNECT
ANM
CONNECT
CONNECT
ACK
ACK
ON going connection
Q.931
ISUP
Q.931
Fig.5: Circuit-mode basic Call setup
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Basic Call Release
Calling
Party
Originating
Ex.
DISCONNECT
Transit
Ex.
REL
RLC
RELEASE
Transit
Ex.
REL
RLC
Destination
Ex.
REL
RLC
Called
Party
DISCONNECT
RELEASE
RELEASE
RELEASE
COMPLETE
COMPLETE
Q.931
ISUP
Q.931
Fig. 6: Circuit-mode basic Call Release
IAM: Initial Address Message ACM: Address Complete
Message ANM: Answer Message
REL: Release RLC: Release Complete
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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
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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
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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
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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
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Conclusion
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•
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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
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