Advanced Signalling Research Lab. Fall ‘99 VON VON protocols - SIP Gonzalo Camarillo Atlanta September 28th, 1999 Gonzalo Camarillo [email protected]

Gonzalo CamarilloAtlanta September 28th, 1999 Advanced Signalling Research Lab.

Fall ‘99 VONVON protocols - SIP

Gonzalo [email protected]

ASRL

Advanced Signalling Research Lab.

SIP / ISUP interconnection



Telephone Services

•GSTN (General Switched Telephone Network)

•IP Telephony

IP Telephony GSTN



• Brief SS7 introduction (architecture)

• Gateway architecture ( SG, MGC, MG )

Contents

• ISUP - SIP interworking issues and proposed solutions



Different architectures

GSTN architecture:Intelligence in the networkDumb terminals

SIP architecture:Move the intelligence to the edge



DSS 1 ISUP DSS 1

Signalling in GSTN

Signalling in the network (between switches)User to network signalling



DSS-1

Q. 931Protocol between the user and the networkMuch simpler than ISUP.

Q. 921Handles the transport of the messages



Signalling in GSTNSS7 (System Signalling No. 7)

MTP

ISUP TUPTCAP

SCCP

Level

4

3

2

1



General ISUP<->SIP Conversion

SG

SIP Client

SIP ServerSTP ISUP/MTP

E1/T1

SIP

SS7

Voice Stream

Signalling

MG

RTP

MGCP SIP

SIP

IP network

ISUP/IP

MGC

DSS 1



Architecture of the distributed gateway

Signalling Gateway

Media Gateway Controller

Media Gateway

GSTN side

IP side

Voice stream Voice stream

ISUP

SIP

MGCP

ISUP/IP



Signalling Gateway

• To find the appropriate media gateway controller

Function:

Signalling GW

ISUP/IP

ISUP/IPISUP/IP

ISUP/IP

ISUP

SIPMGCPSIPMGCPSIPMGCPSIPMGCP

MGC MGC MGC MGC



Media Gateway

Mapping between different voice formats

ControlProtocol

GSTN RTP



Media Gateway Controller for distributed

Media Gateways

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

Functions



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)



ITU ISUP message exchange during a call

LocalExchange

IAM

ACM

RLC

CPG

ANM

REL

Voice Transfer

LocalExchange

Different message flows

ANSI ISUP: CPG before ACM



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.



Proposed solution

Ingress gateway waits for SAMs with more digitsa certain amount of time.

• Timer = 0 Heavy signalling traffic may be generated

• Timer = 5 secs ( inter-digit timeout) User is not that patient



In-band announcements and ring-back tones

•‘Your call is being forwarded to an automatic voice mail’• Ring-back tone• Busy tone

SIP Client

E1/T1

MG

RTP

DSS 1

Proposed solution: 183 SIP response



ISUP transparency(SIP bridging)

IP network

ISUP/MTP

E1/T1

Voice Stream

Signalling

STP

SIP

RTP

ISUP/MTP

E1/T1

STP

SGSG

MGMG

MGC MGC

MGCP MGCP

ISUP/IP ISUP/IP



ISUP transparecy( SIP bridging)

ISUP messages in SIP bodies (MIME),SIP INFO method, reliable 1xx responses ...

Trusted parties, confidentiality, ISUP flavours...



Billingscenarious

Isabel calls from Spain to my GSM mobile:+358 40 702 35 35 (Finland’s international prefix)

Isabel pays the call leg Spain-FinlandI pay the call leg Finland-Atlanta

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



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”.



Further information

• 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

IETF internet drafts ( www.ietf.org )

Documents

Advanced Signalling Research Lab. Fall ‘99 VON VON protocols - SIP Gonzalo Camarillo Atlanta September 28th, 1999 Gonzalo Camarillo [email protected]