Gonzalo Camarillo

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SIP / ISUP interconnection
Gonzalo Camarillo
Gonzalo.Camarillo_at_ericsson.com
ASRL Advanced Signalling Research Lab.
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Telephone Services

• GSTN (General Switched Telephone Network)

• IP Telephony

IP Telephony
GSTN
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Contents

• Brief SS7 introduction (architecture)

• Gateway architecture ( SG, MGC, MG )

• ISUP - SIP interworking issues and proposed

solutions
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Different architectures
GSTN architecture Intelligence in the
network Dumb terminals SIP architecture Move
the intelligence to the edge
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Signalling in GSTN
Signalling in the network (between switches) User
to network signalling
DSS 1
ISUP
DSS 1
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DSS-1
Q. 931 Protocol between the user and the
network Much simpler than ISUP. Q. 921 Handles
the transport of the messages
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Signalling in GSTN
SS7 (System Signalling No. 7)
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General ISUPlt-gtSIP 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
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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
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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
SIP
MGCP
SIP
MGCP
SIP
MGCP
SIP
MGCP
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Media Gateway
Mapping between different voice formats
Control Protocol
GSTN
RTP
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Media Gateway Controller for distributedMedia
Gateways
Functions

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

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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)

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Different message flows
ITU ISUP message exchange during a call
ANSI ISUP CPG before ACM
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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 Camarillos
The ingress gateway cannot know when the number
is complete.
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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

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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
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ISUP transparency(SIP bridging)
Voice Stream
SG
SG
Signalling
ISUP/MTP
ISUP/MTP
ISUP/IP
ISUP/IP
SIP
STP
MGC
MGC
STP
MGCP
MGCP
E1/T1
RTP
E1/T1
MG
MG
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ISUP transparecy( SIP bridging)
ISUP messages in SIP bodies (MIME), SIP INFO
method, reliable 1xx responses ...
Trusted parties, confidentiality, ISUP flavours...
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Billingscenarious
Isabel calls from Spain to my GSM mobile 358 40
702 35 35 (Finlands 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??
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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.
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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