SIP / ISUP interconnection

Gonzalo Camarillo
Gonzalo.Camarillo@ericsson.com

ASRL
Advanced Signalling Research Lab.
Gonzalo Camarillo Fall ‘99 VON
Atlanta September 28th, 1999 VON protocols - SIP Advanced Signalling Research Lab.
 Telephone Services
•GSTN (General Switched Telephone Network)
•IP Telephony

IP Telephony GSTN
Gonzalo Camarillo Fall ‘99 VON
Atlanta September 28th, 1999 VON protocols - SIP Advanced Signalling Research Lab.
 Contents

• Brief SS7 introduction (architecture)

• Gateway architecture ( SG, MGC, MG )
• ISUP - SIP interworking issues and proposed
solutions

Gonzalo Camarillo Fall ‘99 VON

Atlanta September 28th, 1999 VON protocols - SIP Advanced Signalling Research Lab.
 Different architectures
GSTN architecture:
Intelligence in the network
Dumb terminals

SIP architecture:
Move the intelligence to the edge

Gonzalo Camarillo Fall ‘99 VON

Atlanta September 28th, 1999 VON protocols - SIP Advanced Signalling Research Lab.
 Signalling in GSTN
Signalling in the network (between switches)
User to network signalling

DSS 1 ISUP DSS 1

Gonzalo Camarillo Fall ‘99 VON

Atlanta September 28th, 1999 VON protocols - SIP Advanced Signalling Research Lab.
 DSS-1
Q. 931
Protocol between the user and the network
Much simpler than ISUP.

Q. 921
Handles the transport of the messages

Gonzalo Camarillo Fall ‘99 VON

Atlanta September 28th, 1999 VON protocols - SIP Advanced Signalling Research Lab.
 Signalling in GSTN
SS7 (System Signalling No. 7)
Level

TCAP ISUP TUP

4

SCCP

3
2 MTP
1

Gonzalo Camarillo Fall ‘99 VON

Atlanta September 28th, 1999 VON protocols - SIP Advanced Signalling Research Lab.
 General ISUP<->SIP Conversion
Voice Stream
Signalling
SG

SIP Server
STP ISUP/MTP
ISUP/IP
SIP

SIP
MGC
IP network

SS7 MGCP SIP

MG SIP Client
DSS 1

E1/T1 RTP

Gonzalo Camarillo Fall ‘99 VON

Atlanta September 28th, 1999 VON protocols - SIP Advanced Signalling Research Lab.
 Architecture of the distributed gateway
ISUP
Signalling Gateway
IP side
ISUP/IP
GSTN side
SIP
Media Gateway Controller

MGCP

Voice stream Voice stream

Media Gateway

Gonzalo Camarillo Fall ‘99 VON

Atlanta September 28th, 1999 VON protocols - SIP Advanced Signalling Research Lab.
 Signalling Gateway
Function:
• To find the appropriate media gateway controller
Signalling GW
ISUP

ISUP/IP
ISUP/IP
ISUP/IP ISUP/IP

MGC MGC MGC MGC

MGCP SIP MGCP SIP MGCP SIP MGCP SIP

Gonzalo Camarillo Fall ‘99 VON

Atlanta September 28th, 1999 VON protocols - SIP Advanced Signalling Research Lab.
 Media Gateway
Mapping between different voice formats

Control
Protocol

GSTN RTP

Gonzalo Camarillo Fall ‘99 VON

Atlanta September 28th, 1999 VON protocols - SIP Advanced Signalling Research Lab.
 Media Gateway Controller for
distributed
Media Gateways

Functions
• Actual mapping between protocols (ISUP-SIP)
• Control the Media Gateway/s
• Authentication, Authorization and Accounting (AAA)

Gonzalo Camarillo Fall ‘99 VON

Atlanta September 28th, 1999 VON protocols - SIP Advanced Signalling Research Lab.
 Experiences implementing
ISUP to SIP mapping

• Different flavours of ISUP (message flow)

• Overlap signalling (SAMs)
• In band announcements and ring-back tone
• ISUP transparency
• Billing in forwarding situations
• Tracing calls (malicious, SOS)

Gonzalo Camarillo Fall ‘99 VON

Atlanta September 28th, 1999 VON protocols - SIP Advanced Signalling Research Lab.
 Different message flows
ITU ISUP message exchange during a call
Local Local
Exchange Exchange
IAM
ACM
CPG
ANM

Voice Transfer
REL
RLC

ANSI ISUP: CPG before ACM

Gonzalo Camarillo Fall ‘99 VON
Atlanta September 28th, 1999 VON protocols - SIP Advanced Signalling Research Lab.
 Overlap signalling (SAMs)
European phone numbers does not have a fixed length.
Example:
+358 9 299 1
Finland Helsinki Ericsson Front desk

+358 9 299 3371

Finland Helsinki Ericsson Camarillo’s

The ingress gateway cannot know when the number is

complete.
Gonzalo Camarillo Fall ‘99 VON
Atlanta September 28th, 1999 VON protocols - SIP Advanced Signalling Research Lab.
 Proposed solution

Ingress gateway waits for SAMs with more digits

a certain amount of time.

• Timer = 0
Heavy signalling traffic may be generated

• Timer = 5 secs ( inter-digit timeout)

User is not that patient

Gonzalo Camarillo Fall ‘99 VON

Atlanta September 28th, 1999 VON protocols - SIP Advanced Signalling Research Lab.
 In-band announcements and
ring-back tones
•‘Your call is being forwarded to an automatic voice mail’
• Ring-back tone
• Busy tone
Proposed solution: 183 SIP response
MG SIP Client
DSS 1

E1/T1 RTP

Gonzalo Camarillo Fall ‘99 VON

Atlanta September 28th, 1999 VON protocols - SIP Advanced Signalling Research Lab.
 ISUP transparency
Voice Stream (SIP bridging)
SG SG
Signalling

ISUP/MTP ISUP/MTP
ISUP/IP ISUP/IP
SIP

STP MGC MGC STP

IP network
MGCP MGCP

E1/T1 RTP E1/T1

MG MG

Gonzalo Camarillo Fall ‘99 VON

Atlanta September 28th, 1999 VON protocols - SIP Advanced Signalling Research Lab.
 ISUP transparecy
( SIP bridging)

ISUP messages in SIP bodies (MIME),

SIP INFO method, reliable 1xx responses ...

Trusted parties, confidentiality, ISUP flavours...

Gonzalo Camarillo Fall ‘99 VON

Atlanta September 28th, 1999 VON protocols - SIP Advanced Signalling Research Lab.
 Billing
scenarious

Isabel calls from Spain to my GSM mobile:

+358 40 702 35 35 (Finland’s international prefix)

Isabel pays the call leg Spain-Finland

I pay the call leg Finland-Atlanta

SIP is end to end … where are the call legs??

Gonzalo Camarillo Fall ‘99 VON

Atlanta September 28th, 1999 VON protocols - SIP Advanced Signalling Research Lab.
 Tracing calls

• SOS services ( physically closest center )

• Malicious calls

An IP address or a SIP URL do not give any useful

information for catching the “bad guys”.

Gonzalo Camarillo Fall ‘99 VON

Atlanta September 28th, 1999 VON protocols - SIP Advanced Signalling Research Lab.
 Further information
IETF internet drafts ( www.ietf.org )
• draft-ietf-sigtran-mime-isup-00.txt
• draft-ietf-mmusic-sip-multipart-00.txt
• draft-zimmerer-mmusic-sip-isup-mime-00.txt
• draft-ietf-mmusic-sip-info-method-01.txt
• draft-ietf-mmusic-sip-100rel-00.txt
• draft-roach-mmusic-sip-provisional-media-00.txt
• draft-donovan-mmusic-183-00.txt
• draft-roach-mmusic-sip-pstn-require-header-00.txt
• draf-zimmerer-mmusic-sip-bcp-t-00.txt
• draft-roach-sip-isup-parameters-00.txt
• draft-camarillo-mmusic-sip-isup-bcp.txt
Gonzalo Camarillo Fall ‘99 VON
Atlanta September 28th, 1999 VON protocols - SIP Advanced Signalling Research Lab.