FINAL DRAFT—CISCO CONFIDENTIAL
SIP Overlap Signaling Feature ModuleSIP
Overlap Signaling Feature Module
Document Release History
Publication Date
Comments
August 5, 2008
Initial version of the document.
Feature History
Release
Modification
9.7(3)
This feature was introduced on the Cisco PGW 2200 Softswitch.
This document describes the SIP Overlap Signaling Feature Module feature in the following sections.
•
Feature Description, page 1
•
Provisioning, page 5
•
Software Changes for this Feature, page 7
•
Glossary, page 8
•
Obtaining Documentation and Submitting a Service Request, page 9
Feature Description
This feature supports SIP overlap signaling between the Cisco PSTN Gateway Softswitch (Cisco PGW
2200) and the Cisco BTS 10200 Softswitch products using a derivative of
draft-zhang-sipping-overlap-01, a method for overlap signaling in SIP.
Both the Cisco PGW 2200 and the Cisco BTS 10200 support the sending and receiving of overlap dialed
digits over SIP. The Cisco PGW 2200 also supports the sending/receiving of overlap digits over the SS7
network.
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SIP Overlap Signaling Feature Module
Feature Description
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Operating Modes
This feature is designed to work with only the interworking and B2BUA operation modes. The mode of
operation is not determined until seizure of the terminating side.
If you select proxy mode before sending is complete on the originating call side, the call is forced into
B2BUA mode to ensure that the call continues to signal correctly.
Interworking and B2BUA modes support overlap signaling, with the behavior of the terminating call side
based on the setting of the TOverlap property.
For B2BUA mode it is possible for the originating side to work in overlap mode while the terminating
side works in en-block mode, thus allowing conversion of overlap to en-block signaling
Call Flows
This feature uses a 184 “Ready For More Digits” response instead of a 183 'Session Progress' to avoid
any ambiguity about when to send ACM.
Because the sending of a 183 might cause ACM to be returned, you can send a 184 to prevent any
confusion about when to send ACM. Do not map the 184 to ACM, 184 is considered purely an enabler
for subsequent INFO messages to be forwarded containing the remaining address digits if overlap is
supported.
To improve the call flow, an additional specialized parameter “overlap” is attached to the username in
the request line to explicitly indicate that subsequent address digits can be received. This parameter can
then be used as a trigger for sending a 184.
The “overlap' username parameter is used instead of a SIP: URI parameter, so that a tel: URI can also
use the same mechanism. The absence of this parameter in the request line indicates that the number
should be assumed to be a complete and normal en-block working.
Example 1:
INVITE sip:1234;overlap@host SIP/2.0
Example 2:
INVITE tel:1234;overlap SIP/2.0
The absence of this parameter in the request line indicates that the number should be assumed to be
complete and normal en-block working.
Figure 1 shows the call flow difference.
SIP Overlap Signaling Feature Module
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SIP Overlap Signaling Feature Module
Feature Description
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Figure 1
PSTN
Call Flow Difference
Originating
Server
Terminating
Server
PSTN
IAM
INVITE
SAM1
IAM
184
SAM2
PRACK
200(PRACK)
INFO
SAM1
200(INFO)
SAM3
INFO
SAM2
200(INFO)
INFO
SAM3
281178
200(INFO)
Example 3:
Figure 2 shows the call flow for both sides enabled for overlap, SIP to SS7.
OOverlap=1
TOverlap=1
OMinDigits=0
OMaxDigits=20
TMinDigits=
TMaxDigits= 20
SIP Overlap Signaling Feature Module
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SIP Overlap Signaling Feature Module
Feature Description
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Figure 2
Overlap to Overlap SIP to SS7
OCC
INVITE
F1
100 Trying
F2
184 (INVITE)
F4
PRACK
F5
200 (PRACK)
F6
INFO
F7
200 (INFO)
F9
INFO
F10
200 (INFO)
F12
INFO
F13
200 (INFO)
F15
184 (INVITE)
F17
PRACK
F18
200 (PRACK)
F19
F21
LCallNext
LCallNext
LCallLast
LAddressAck
LAnswer
LCallPart
LCallNext
LCallNext
LCallNext
LAddressAck
LAnswer
TCC
IAM
F3
SAM
F8
SAM
F11
SAM
F14
ACM
F16
ANM
F20
281168
200 (INVITE)
LCallPart
LCM
Prerequisites
The Cisco PGW 2200 must be running Cisco Media Gateway Controller (MGC) software Release 9.7(3)
or later. Prerequisites for this release can be found in the Release Notes for the Cisco Media Gateway
Controller Software Release 9.7(3) at
http://www.cisco.com/en/US/partner/docs/voice_ip_comm/pgw/9/release/note/rn973.html
Restrictions or Limitations
•
The Cisco PGW 2200 and the Cisco BTS 10200 must comply with the BTS 10200 support for
Overlap Dialing when the Cisco BTS 10200 and Cisco PGW 2200 are connected over SIP.
•
Ensure that INVITE requests that require a Cisco PGW 2200-specific 184 Response do not fork.
Related Features and Technology
•
The Cisco BTS 10200 Overlap Dialing feature is related to this feature.
•
The SIP Early-Dialog Offer/Answer Using PRACK/180/183 feature is related to this feature.
SIP Overlap Signaling Feature Module
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SIP Overlap Signaling Feature Module
Provisioning
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Related Documents
This document contains information that is strictly related to this feature. The documents that contain
additional information related to the Cisco PGW 2200 are at
http://www.cisco.com/en/US/products/hw/vcallcon/ps2027/tsd_products_support_series_home.html
Provisioning
To enable the SIP Overlap Signaling feature, follow the instructions provided in the following sections.
OOverlap/ TOverlap
Example 1
Use these commands to enable the OOverlap or TOverlap properties.
mml> prov-add:trnkgrpprop:name=''478'',ooverlap=''1''
MGC-01 - Media Gateway Controller 2008-06-22 21:06:30.672 CDT
M COMPLD
''trnkgrpprop:
WARNING: Restart is needed to activate property(s): OOVERLAP ''
;
sh-mustang mml> prov-ed:trnkgrpprop:name=''479'',ooverlap=''1'',toverlap=''1''
MGC-01 - Media Gateway Controller 2008-06-22 21:11:33.377 CDT
M COMPLD
''trnkgrpprop:
WARNING: Restart is needed to activate property(s): OOVERLAP ''
;
Example 2
For the Cisco PGW 2200, if the OCC side trunkgroup is 666 and TCC side is 444, configure on both
sides to control the Overlap.
mml>prov-sta::srcver=''active'',dstver=''P_5_3'',confirm
M COMPLD
mml>prov-ed:trnkgrpprop:name=''444'',toverlap=''1'',tmindigits=''0'',tmaxdigits=''20'',sup
port183=''3'',supportreliable100=''SUPPORTED''
M COMPLD
''trnkgrpprop''
;
mml>prov-cpy::
M COMPLD
''PROV-CPY''
mml>prov-ed:trnkgrpprop:name=''666'',ooverlap=''1'',omindigits=''0'',omaxdigits=''20'',sup
port183=''3'',supportreliable100=''SUPPORTED''
M COMPLD
''trnkgrpprop''
;
SIP Overlap Signaling Feature Module
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SIP Overlap Signaling Feature Module
Provisioning
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mml>prov-cpy::
M COMPLD
''PROV-CPY''
OMaxDigits/OMinDigits/TMaxDigits/TMinDigits
Use these commands to change the OMaxDigits/OMinDigits/TMaxDigits/TMinDigits properties.
mml> prov-add:trnkgrpprop:name=''478'',omaxdigits=''10''
MGC-01 - Media Gateway Controller 2008-06-22 21:13:28.993 CDT
M COMPLD
''trnkgrpprop:
WARNING: Restart is needed to activate property(s): OMAXDIGITS ''
;
mml>
prov-ed:trnkgrpprop:name=''479'',omaxdigits=''10'',omindigits=''5'',tmaxdigits=''20'',tmin
digits=''10''
M
MGC-01 - Media Gateway Controller 2008-06-22 21:14:27.038 CDT
COMPLD
''trnkgrpprop:
WARNING: Restart is needed to activate property(s): OMAXDIGITS OMINDIGITS ''
;
OverlapDigitTime
Use these commands to change the OverlapDigitTime property.
mml> prov-ed:trnkgrpprop:name=''1701'',overlapdigittime=''30''
M
MGC-01 - Media Gateway Controller 2008-06-22 21:15:52.725 CDT
COMPLD
''trnkgrpprop''
;
Disable the SIP Overlap
Use the following commands to disable the SIP overlap.
mml> prov-ed:trnkgrpprop:name=''478'',ooverlap=''0''
M
MGC-01 - Media Gateway Controller 2008-06-22 21:17:20.809 CDT
COMPLD
''trnkgrpprop:
WARNING: Restart is needed to activate property(s): OOVERLAP ''
;
mml> prov-dlt:trnkgrpprop:name=''478'',''ooverlap'',''toverlap''
M
MGC-01 - Media Gateway Controller 2008-06-22 21:18:04.673 CDT
COMPLD
''trnkgrpprop''
;
SIP Overlap Signaling Feature Module
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SIP Overlap Signaling Feature Module
Software Changes for this Feature
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Software Changes for this Feature
Properties
There are no new properties associated with this feature, however, a number of existing properties are
used to control overlap behavior. Some existing trunk group properties must be configured against SIP
trunk groups.
OMaxDigits/OMinDigits/TMaxDigits/TMinDigits
The existing properties, OMinDigits, OMaxDigits, TMinDigits, and TMaxDigits are used to control
overlapping behavior. Both call sides may allow overlap behavior but the conditions for overlap may be
different on both call sides.
The following summarizes the behavior of these properties. These settings affect call behaviors of the
SIP overlap in the same way as all other existing interworking scenarios.
OMinDigits
If a stop digit '#' is received on the originating call side but the number of digits in total received on the
originating side is less than OMinDigits, the call is released with Address Incomplete.
OMaxDigits
If the call is in overlap and a subsequent digit is received not containing a stop digit and if the number
of digits received is greater than OMaxDigits, the Cisco PGW 2200 sends out the number of OMaxDigits
digits to the TCC side.
TMinDigits
If the number of digits to be sent to the terminating side is less than TMinDigits, the call is terminated
with AddressIncomplete.
TMaxDigits
If the number of digits to be sent to the terminating side exceeds the value of TMaxDigits, the digit string
is truncated to the length of TMaxDigits.
OOverlap/TOverlap
The existing properties TOverlap and OOverlap are changed to allow configuration against SIP trunks.
•
If an INVITE is received with a username parameter ';overlap', and OOverlap is not set to 1 (overlap
supported), the call is terminated with 484 'Address Incomplete'.
•
On the terminating call side, a check is made on receipt of LCallPart to see if the TOverlap is set to
1 (overlap supported). If this is true, and based on the settings of TMinDigits, an INVITE is created
that includes the ';overlap' parameter in the INVITE. Subsequent INFO messages are created on
receipt of LCallNext, LCallLast.
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SIP Overlap Signaling Feature Module
Glossary
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•
If TOverlap is set to 0 (en-block), LCM waits until Cisco PGW 2200 analysis determines that the
number is complete before creating the terminating call side and sending LCall to the terminating
call side.
OverlapDigitTime
The existing property OverlapDigitTime is used to set the value of OverlapDigitsTimer used for timing
inter-digit pause.
If the originating call-side is in overlap, LCM will start the existing timer OverlapDigitsTimer based on
the property setting of the existing property OverlapDigitTime. This times the inter-digit pause waiting
for more digits. Failure to receive more digits within this time results in a release of the call. On the
originating call-side 484 'Address Incomplete' is returned, and, if applicable on the terminating side, a
CANCEL is generated.
When digit lengths are undetermined, this timer sets the amount of time it will wait before assuming no
further digits will be dialed. Use of an explicit stop digit in the overlap signaling allows the call to reset
the timer and continue call processing without waiting before timer expiry, thus speeding up connection
times.
Glossary
Table 1
Expansions
Acronym
Expansion
B2BUA
Back to Back User Agent
BCF
Border Control Function (IMS function)
BGCF
Border Gateway Control Function (IMS function)
CBGF
Core Border Gateway Control Function (IMS function)
CDR
Call Detail Record
CLI
Calling Line Identity
CPC
Calling Party Category
DBR
Domain Based Routing
DNS
Domain Name System
DTMF
Dual Tone Multi-Frequency
DRP
Domain Routing Policy
GA
Generic Analysis (PGW analysis and routing module)
I-CSCF
Interrogating Call Session Control Function
IMS
IP Multimedia System
LI
Lawful Intercept
LCM
LightSpeed Call Model (PGW call control module aka UCM)
LNP
Local Number Portability
MGCF
Media Gateway Control Function
MGCP
Media Gateway Control Protocol
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Obtaining Documentation and Submitting a Service Request
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Table 1
Expansions
Acronym
Expansion
MGW
Media Gateway
NANP
North American Numbering Plan
P-CSCF
Proxy Call Session Control Function (IMS component)
PN
Presentation Number
POL
PGW Provisioning object Library
RN
Redirecting Number
S-CSCF
Serving Call Session Control Function (IMS component)
SIP
Session Initiation Protocol
TMR
Transmission Medium Requirements
TNS
Transit Network Selection
UCM
Universal Call Model (PGW call control module aka LCM)
URI
Universal Resource Identifier
URL
Universal Resource Locator
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Obtaining Documentation and Submitting a Service Request
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