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SIP / ISUP interconnection. Gonzalo Camarillo. [email protected] ASRL Advanced Signalling Research Lab. Telephone Services. GSTN (General Switched Telephone Network). IP Telephony. IP Telephony. GSTN. Contents. Brief SS7 introduction (architecture).

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Presentation Transcript
slide1
SIP / ISUP interconnection

Gonzalo Camarillo

[email protected]

ASRL

Advanced Signalling Research Lab.

slide2
Telephone Services
  • GSTN (General Switched Telephone Network)
  • IP Telephony

IP Telephony

GSTN

slide3
Contents
  • Brief SS7 introduction (architecture)
  • Gateway architecture ( SG, MGC, MG )
  • ISUP - SIP interworking issues and proposed

solutions

slide4
Different architectures

GSTN architecture:

Intelligence in the network

Dumb terminals

SIP architecture:

Move the intelligence to the edge

slide5
Signalling in GSTN

Signalling in the network (between switches)

User to network signalling

DSS 1

ISUP

DSS 1

slide6
DSS-1

Q. 931

Protocol between the user and the network

Much simpler than ISUP.

Q. 921

Handles the transport of the messages

slide7
Signalling in GSTN

SS7 (System Signalling No. 7)

slide8
General ISUP<->SIP Conversion

Voice Stream

Signalling

SG

SIP Server

ISUP/MTP

STP

ISUP/IP

SIP

SIP

MGC

IP network

SIP

MGCP

SS7

SIP Client

MG

DSS 1

E1/T1

RTP

slide9
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

slide10
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

slide11
Media Gateway

Mapping between different voice formats

Control

Protocol

GSTN

RTP

slide12
Media Gateway Controller for distributedMedia Gateways

Functions

  • Actual mapping between protocols (ISUP-SIP)
  • Control the Media Gateway/s
  • Authentication, Authorization and Accounting (AAA)
slide13
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)
slide14
Different message flows

ITU ISUP message exchange during a call

ANSI ISUP: CPG before ACM

slide15
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.

slide16
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
slide17
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

SIP Client

MG

DSS 1

E1/T1

RTP

slide18
IP network

ISUP transparency(SIP bridging)

Voice Stream

SG

SG

Signalling

ISUP/MTP

ISUP/MTP

ISUP/IP

ISUP/IP

SIP

MGC

MGC

STP

STP

MGCP

MGCP

E1/T1

RTP

E1/T1

MG

MG

slide19
ISUP transparecy( SIP bridging)

ISUP messages in SIP bodies (MIME),

SIP INFO method, reliable 1xx responses ...

Trusted parties, confidentiality, ISUP flavours...

slide20
Billingscenarious

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??

slide21
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”.

slide22
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
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