SIP to MGCP T.38 Fax Fallback to Pass-Through
and Voice
Document Release History
Publication Date
Comments
February 13, 2006
Initial version of the document.
Feature History
Release
Modification
9.5(2)
This feature was introduced on the Cisco PGW 2200 Release 9.5(2)
This document describes the SIP to MGCP T.38 Fax Fallback to Pass-Through and Voice feature on the
Media Gateway Controller (PGW) 2200.
This feature is described in the following sections:
•
Feature Overview, page 2
•
Supported Platforms, page 3
•
Supported Standards, MIBs, and RFCs, page 3
•
Prerequisites for Using This Feature, page 3
•
XECfgParm.dat Configuration Tasks, page 5
•
Monitoring and Maintaining the Feature, page 5
•
Configuration Examples, page 9
•
Reference Information, page 10
•
Obtaining Documentation, Obtaining Support, and Security Guidelines, page 11
•
Glossary, page 11
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© 2007 Cisco Systems, Inc. All rights reserved.
SIP to MGCP T.38 Fax Fallback to Pass-Through and Voice
Feature Overview
Feature Overview
The SIP to MGCP T.38 Fax Fallback to Pass-Through and Voice feature provides support on the Cisco
PGW 2200 to allow a FAX call in pass-through mode (that is, upspeed CODEC). For example, in the
event of a T.38 fax setup failure due to lack of T.38 fax support on a SIP endpoint, such as the Cisco SIP
Analog Telephone Adaptor (ATA).
This feature provides the following two capabilities:
Note
•
When the PGW 2200 receives a T.38 Fax start indication from an MGCP gateway, it initiates
Re-Invite with Session Description Protocol (SDP) indicating T.38 attributes to the SIP endpoint,
which returns a 488 message because the endpoint does not support T.38. The PGW 2200 modifies
the connection at the MGCP gateway to up speed to G.711 (for example, “L:
e:off,a:PCMA,fxr/fx:off,s:off”) if the audio channel is not set for G.711A. Thus the upspeed
capability applies to both SIP-initiated fax or SS7/ISDN-side initiated fax calls.
•
If the T.38 fax is successful, the call configuration falls back to voice with the original audio
CODEC after the fax is finished, if the original call event was a voice call.
This feature does not support HSI.
Benefits
This feature provides the following benefits:
Up-speed CODEC to Pass-through
The PGW 2200 can be configured on a system-wide basis to upspeed the CODEC in pass-through mode
when T.38 is not supported by a SIP endpoint. See “XECfgParm.dat Configuration Tasks” section on
page 5,
If the SIP endpoint does not support upspeed CODEC either, the call reverts to voice and the fax may fail.
Fallback to Voice
If the T.38 fax is successful, the call configuration falls back to voice with the original audio CODEC
after the fax is finished, if the original call event was a voice call.
Generate CDRs for Upspeed Attempts
The PGW 2200 updates the tag 4081 in the call data record (CDR) when up-speed is attempted.
Related Documents
This document contains information that is related strictly to this feature. The documents that contain
additional information related to the Cisco PGW 2200 are listed below:
•
Release Notes for Cisco Media Gateway Controller Software Release 9.5(2)
•
Cisco Media Gateway Controller Hardware Installation Guide
•
Regulatory Compliance and Safety Information for the Cisco Media Gateway Controller
•
Cisco Media Gateway Controller Software Release 9 Installation and Configuration Guide
•
Cisco Media Gateway Controller Software Release 9 Provisioning Guide
SIP to MGCP T.38 Fax Fallback to Pass-Through and Voice
2
SIP to MGCP T.38 Fax Fallback to Pass-Through and Voice
Supported Platforms
•
Cisco Media Gateway Controller Software Release 9 Dial Plan Guide
•
Cisco Media Gateway Controller Software Release 9 MML Command Reference
•
Cisco Media Gateway Controller Software Release 9 Messages Reference Guide
•
Cisco Media Gateway Controller Software Release 9 Billing Interface Guide
•
Cisco Media Gateway Controller Software Release 9 Management Information Base Guide
•
Cisco Media Gateway Controller Software Release 9 Operations, Maintenance, and
Troubleshooting Guide
Supported Platforms
The hardware platforms supported for the Cisco MGC software are described in the Cisco Media
Gateway Controller Hardware Installation Guide.
Supported Standards, MIBs, and RFCs
Standards
No new or modified standards are supported by this feature.
MIBs
No new or modified MIBs are supported by this feature.
For more information on the MIBs used in the Cisco MGC software, refer to the Cisco Media Gateway
Controller Release 9 Management Information Base Guide.
RFCs
No new or modified RFCs are supported by this feature.
For more information on the MIBs used in the Cisco MGC software, refer to the Cisco Media Gateway
Controller Release 9 Management Information Base Guide.
Prerequisites for Using This Feature
You must have Cisco Media Gateway Controller (MGC) software Release 9.5(2). Prerequisites for this
release can be found in the Release Notes for the Cisco Media Gateway Controller Software Release
9.5(2).
Up-speed to CODEC to Pass-through Operation
This section provides a procedure for the PGW 2200 to up-speed the voice call into fax pass-through
mode (G.711 a/ulaw) if only one call leg supports call agent controlled T.38 Fax.
If the call is started as fax call, then up-speed CODEC selection is not needed.
If both call legs support call agent controlled T.38 fax, the PGW 2200 can successfully switch the call
to T.38 mode, then CODEC up-speed is not needed.
SIP to MGCP T.38 Fax Fallback to Pass-Through and Voice
3
SIP to MGCP T.38 Fax Fallback to Pass-Through and Voice
Prerequisites for Using This Feature
If neither side of the call supports T.38 fax, the gateways at both ends of the call up-speed without PGW
2200 involvement.
The PGW 2200 uses the following logic to select G711 CODEC if a T.38 fax fails:
•
Note
You must define the up-speed CODECs in XECfgParm.dat, by the *.FaxUpspeedCodecPreference
parameter. You can define the first CODEC upspeed preference and second CODEC upspeed
preference. If the second CODEC preference is not defined, then the first CODEC preference
becomes the mandatory upspeed CODEC. The valid upspeed CODECs are G711alaw and
G711ulaw. If neither CODEC is defined in XECfgparm.dat, it is an indication that Operator does
not want the PGW 2200 to use upspeed method of fax pass-through and want to rely on end-device
to auto-upspeed to G711.
The valid upspeed CODEC preferences are G711alaw and G711ulaw.
•
If the original call was established using G.711 and the T.38 CODEC switch fails, no further action
is required as call is already in upspeed CODEC mode. If the original voice call was established with
a different CODEC, continue to next bullet.
•
The PGW 2200 proposes up-speed CODECs to the MGCP gateway in the following order: first
CODEC preference, then second CODEC preference.
•
The PGW 2200 must request to turn off of silence suppression, echo cancellation, and T.38 fax tone
detection along with upspeed CODEC. So a typical Local Connection Option may look like:
L: e:off,a:PCMU;PCMA,fxr/fx:off,s:off
•
If the first device does not support either the first CODEC preference or the second CODEC
preference upspeed CODEC, skip to the next main bullet. If the first device supports at least one of
the proposed CODECs, the device notifies the PGW 2200 of its CODEC selection in the form of
SDP.
Note
Cisco IOS or VXSM gateways support both G711 alaw and ulaw. So it is expected that the
gateway will notify the PGW 2200 regarding its support of both CODECs).
The PGW 2200 would then transmit the first device SDP to the other call leg:
– If the device at the other end of the call also supports at least one of the CODECs contained in
the SDP from the first device, the call is up-speeded for pass-through fax.
– If device at the other end of the call does not support any of the CODECs in SDP from the first
device, device rejects the upspeed proposal. The PGW 2200 sends a new proposal to the first
device to go back to its original voice CODEC so the call can return to voice mode and the fax
transmission fails.
•
If the first device does not support G.711 at all, it rejects the proposal and the call remains in voice
mode.
Note
Since IOS and the VXSM gateways always support G711, this condition will not arise if the
first device is an IOS/VXSM MGCP gateway).
SIP to MGCP T.38 Fax Fallback to Pass-Through and Voice
4
SIP to MGCP T.38 Fax Fallback to Pass-Through and Voice
XECfgParm.dat Configuration Tasks
XECfgParm.dat Configuration Tasks
This section contains the steps necessary for configuration of the Cisco MGC software to support this
feature. If you are installing and configuring the Cisco MGC software on your system for the first time,
use the procedures in the Cisco Media Gateway Controller Software Release 9 Installation and
Configuration Guide, coming back to this section once you encounter the
*.FaxUpspeedCodecPreference parameter in the XECfgParm.dat file. If you are upgrading your Cisco
MGC software, be sure to start with the procedure in the “Upgrading” section on page 5. That procedure
refers you here at the appropriate time.
Note
You need to configure the *.FaxUpspeedCodecPreference parameter.
Caution
Configuration of the Cisco MGC software requires that the system software be shut down. In a simplex
system, calls cannot be processed during system shutdown. In a continuous service system, your system
loses the ability to maintain calls during a critical event if the system software on one of the
PGW 2200 hosts is shut down.
Caution
Do not modify the other XECfgParm.dat parameters.
To configure the fax upspeed preference, perform the following steps:
Step 1
If you have not already done so, open the /opt/CiscoMGC/etc/XECfgParm.dat file on the active and
standby Cisco PGW 2200 hosts using a text editor, such as vi.
Step 2
If you have not already done so, ensure that the pom.dataSync parameter is set to false on the active and
standby Cisco PGW 2200 hosts.
Step 3
Search for the *.FaxUpspeedCodecPreference parameter and enter the CODEC preference on the active
and standby Cisco PGW 2200 hosts. See “XECfgParm.dat Parameters” section on page 10 for parameter
values.
Step 4
If you are upgrading your Cisco MGC software, save your changes, close the text editor, and return to
where you left off in the “Upgrading” section on page 5.
If you are installing and configuring your Cisco MGC software for the first time, return to the Cisco
Media Gateway Controller Software Release 9 Installation and Configuration Guide and continue from
where you left off.
Monitoring and Maintaining the Feature
The following section contains the procedures required for proper monitoring and maintenance of this
feature:
•
Daily Tasks, page 6
For more information on operational tasks for the rest of the Cisco MGC software, refer to the Cisco
Media Gateway Controller Software Release 9 Operations, Maintenance, and Troubleshooting Guide
SIP to MGCP T.38 Fax Fallback to Pass-Through and Voice
5
SIP to MGCP T.38 Fax Fallback to Pass-Through and Voice
Monitoring and Maintaining the Feature
Daily Tasks
The following section detail the procedures you should perform on a daily basis on the Cisco PGW 2200.
These procedures use Man-Machine Language (MML) and UNIX commands. These procedures can also
be performed using the optional Cisco MGC Node Manager (MNM) application. For more information
on using the Cisco MNM to operate the Cisco PGW 2200, refer to the Cisco Media Gateway Controller
Node Manager User’s Guide.
The tasks you should perform on a daily basis are found in the following sections:
•
Verifying the Platform State of the Cisco PGW 2200 Hosts, page 6
•
Verifying That Processes Are Running, page 7
Verifying the Platform State of the Cisco PGW 2200 Hosts
You can determine which of your Cisco PGW 2200 hosts is the active Cisco PGW 2200 and which is the
standby Cisco PGW 2200. If your system uses a Cisco PGW 2200 in a simplex configuration, the single
Cisco PGW 2200 host is always active. To do this, complete the following steps:
Step 1
Log in to one of the Cisco MGCs, start an MML session, and enter the following command to determine
its platform state:
rtrv-ne
The system should return a message, similar to the following, if it is currently the active Cisco
PGW 2200:
M
Media Gateway Controller 2004-03-29 14:15:22
RTRV
"Type:"MGC””
"Hardware platform:sun4u sparc SUNW,Ultra-5_10"
"Vendor:"Cisco Systems, Inc.""
"Location:Media Gateway Controller"
"Version:"9.1(5)""
"Platform State:ACTIVE"
The valid values for the Platform State field are ACTIVE, STANDBY, or OOS.
Step 2
Log in to the other Cisco PGW 2200, start an MML session, and enter the following command to
determine its platform state:
rtrv-ne
The system should return a message that indicates that it is in either the active or standby platform state.
If the Cisco PGW 2200 hosts have changed their platform state, determine why the switchover occurred
by searching the contents of the active system log file.
Under normal operations, one Cisco PGW 2200 host should be active and the other Cisco PGW 2200
host should be standby.
If the platform state of either Cisco PGW 2200 host is OOS, check the alarms as described in the Cisco
Media Gateway Controller Software Release 9 Messages Reference Guide, and take the actions
necessary to correct the condition that caused the associated alarm(s). The alarms that require you to take
corrective action and their associated actions can be found in the “Troubleshooting with System Logs”
section on page 4. A complete listing of alarms can be found in the Cisco Media Gateway Controller
Software Release 9 Messages Reference Guide.
If the platform state of both Cisco PGW 2200 hosts is active, proceed to Step 4.
SIP to MGCP T.38 Fax Fallback to Pass-Through and Voice
6
SIP to MGCP T.38 Fax Fallback to Pass-Through and Voice
Monitoring and Maintaining the Feature
Step 3
Verify that the active configuration has not changed by entering the following UNIX commands:
cd /opt/CiscoMGC/etc
ls -l
The system returns a response similar to the following:
total 35350
-rw-r--r-1 mgcusr mgcgrp
38240 May 8 10:46 02.trigger
-rw-rw-r-1 mgcusr
mgcgrp
20488 Oct 10 2004 64eisup.bat
lrwxrwxrwx
1 mgcusr
mgcgrp
43 Aug 1 18:55 active_link ->
/opt/CiscoMGC/etc/CONFIG_LIB/CFG_pol-addipl
-rw-rw-rw1 mgcusr
mgcgrp
30907 Jul 24 15:29 alarmCats.dat
-rw-rw-rw1 mgcusr
mgcgrp
2064 Jun 4 10:57 alarmTable.dat
-rw-rw-rw1 mgcusr
mgcgrp
0 Jun 4 10:57 auxSigPath.dat
Identify the active_link file. The listing indicates which configuration is currently active. The active
configuration in the example is CFG_pol-addipl.
If the configuration has changed, you may want to compare the active configuration to the previous
configuration.
Step 4
Contact the Cisco Technical Assistance Center (TAC) for assistance. Refer to the “Obtaining
Documentation, Obtaining Support, and Security Guidelines” section on page 11 for more information
on contacting the Cisco TAC.
Verifying That Processes Are Running
To verify that the processes on your Cisco PGW 2200 are running, perform the following steps:
Step 1
Log in to the active Cisco PGW 2200, start an MML session, and enter the following command:
rtrv-softw:all
The system returns a response similar to the following:
Media Gateway Controller - MGC-04 2004-04-05 08:06:03
M RTRV
"CFM-01:RUNNING ACTIVE"
"ALM-01:RUNNING ACTIVE"
"MM-01:RUNNING ACTIVE"
"AMDMPR-01:RUNNING ACTIVE"
"CDRDMPR-01:RUNNING ACTIVE"
"DSKM-01:RUNNING IN N/A STATE"
"MMDB-01:RUNNING IN N/A STATE"
"POM-01:RUNNING ACTIVE"
"MEASAGT:RUNNING ACTIVE"
"OPERSAGT:RUNNING ACTIVE"
"PROVSAGT:RUNNING ACTIVE"
"MGCP-1:RUNNING IN N/A STATE"
"Replic-01:RUNNING ACTIVE"
"ENG-01:RUNNING ACTIVE"
"IOCM-01:RUNNING ACTIVE"
"TCAP-01:RUNNING IN N/A STATE"
"FOD-01:RUNNING IN N/A STATE"
"EISUP-1:RUNNING IN N/A STATE"
"SS7-A-1:RUNNING IN N/A STATE"
SIP to MGCP T.38 Fax Fallback to Pass-Through and Voice
7
SIP to MGCP T.38 Fax Fallback to Pass-Through and Voice
Monitoring and Maintaining the Feature
If this MML command is entered on the standby Cisco PGW 2200, the state of the processes is
either RUNNING STANDBY or RUNNING IN N/A STATE.
Note
Step 2
If any of the processes are initializing, wait a few moments and repeat Step 1. If that process is still
initializing, contact the Cisco TAC for assistance. Refer to the “Obtaining Documentation, Obtaining
Support, and Security Guidelines” section on page 11 for more information on contacting the Cisco
TAC.
If any of the processes are stopped, contact the Cisco TAC for assistance. Refer to the “Obtaining
Documentation, Obtaining Support, and Security Guidelines” section on page 11 for more information
on contacting the Cisco TAC.
Understanding Processes
The Cisco MGC software contains processes and process groups that perform various functions. These
functions include managing the I/O channels; generating alarms, call detail records (CDRs), and logs;
and performing signal conversion. All these processes are managed by the process manager process of
the Cisco MGC software.
Three different monitoring levels are offered:
•
Active process—Controlled and monitored directly by the process manager.
•
Passive process—Does not communicate with the process manager.
•
Monitoring process—Periodically runs an executable or script and sets or clears an alarm based on
the return code. This type of process can monitor other processes or tasks that can be checked
programmatically. Some examples are the amount of available disk space, system daemon existence,
and established process dependency.
Table 1 shows the system processes and process groups controlled by the process manager.
Table 1
Group
Processes Controlled by the Process Manager
Process
ENGG-01
Description
Engine Group
Replic-01
Replicator controller. It is an active process. If it should go down,
it causes a critical out-of-service alarm.
ENG-01
Call engine. It is an active process. If it should go down, the system
cannot process calls. Its failure causes a critical out-of-service
alarm.
IOSG-01
I/O Subsystem Group
IOCC-01
I/O channel controller. It is a passive process. If it should go down,
it causes a critical out-of-service alarm.
IOCC-02
I/O channel controller. It is a passive process. If it should go down,
it causes a critical out-of-service alarm.
IOCM-01
I/O channel manager. It is a passive process. If it should go down,
it causes a major out-of-service alarm.
TCAP-01
TCAP and SCCP protocol handler. It is a passive process. If it
should go down, it causes a major out-of-service alarm.
SIP to MGCP T.38 Fax Fallback to Pass-Through and Voice
8
SIP to MGCP T.38 Fax Fallback to Pass-Through and Voice
Configuration Examples
Table 1
Group
Processes Controlled by the Process Manager (continued)
Process
XEG-01
Description
Execution Environment Group
CFM-01
Configuration manager. It is an active process. If it should go
down, it causes a major out-of-service alarm.
ALM-01
Alarm manager. It is an active process. If it should go down, it
causes a major out-of-service alarm.
AMDMPR-01
Alarm and measurement dumper. It is an active process. If it should
go down, it causes a major out-of-service alarm.
MM-01
Measurement manager. It is an active process. If it should go down,
it causes a major out-of-service alarm.
CDRDMPR-01 CDR dumper. It is an active process. If it should go down, it causes
a major out-of-service alarm.
MMDB-01
TimesTen database. It is a passive process. If it should go down, it
causes a minor out-of-service alarm.
POM-01
Provisioning object manager. It is an active process. If it should go
down, it causes a major out-of-service alarm.
FTG-01
Failover Group
FOD-01
PFMG-01
Failover controller. It is a monitoring process. If it should go down,
it causes a minor out-of-service alarm.
Platform Monitoring Group
DSKM-01
SNMPG-01
Disk space monitor. This shell script monitors disk space and trims
back older files in case the current amount of free space is below a
specified threshold. This is a monitoring process. If it should go
down, it causes a minor out-of-service alarm.
SNMP Group
MEASAGT
Measurements SNMP agent. This is an active process. If it should
go down, this is a major out-of-service alarm.
OPERSAGT
Operational SNMP Agent. This is an active process. If it should go
down, this is a major out-of-service alarm.
Configuration Examples
This section provides a configuration example for the XECfgParm.dat parameters associated with this
feature. Additional configuration examples for the Cisco MGC software can be found in the Cisco Media
Gateway Controller Software Release 9 Installation and Configuration Guide.
Note
Configuration of XECfgParm.dat parameters for this feature is required.
*.FaxUpspeedCodecPreference
SIP to MGCP T.38 Fax Fallback to Pass-Through and Voice
9
SIP to MGCP T.38 Fax Fallback to Pass-Through and Voice
Reference Information
Reference Information
The following sections contain reference material related to this feature. Information is included on the
following areas:
•
XECfgParm.dat Parameters, page 10
•
Billing Interface, page 10
XECfgParm.dat Parameters
The XECfgParm.dat file configuration parameters added for this feature are in the table below. For
information on the other XECfgParm.dat parameters, refer to the Cisco Media Gateway Controller
Software Release 9 Installation and Configuration Guide.
Configuration Parameter
Definition
*.FaxUpspeedCodecPreference
You must statically define the upspeed CODECs in
XECfgParm.dat. You can define the first preference and the
second preference upspeed CODEC. If the second
preference is not defined, the first preference becomes the
mandatory CODEC. The valid upspeed CODECs are
G711alaw and G711ulaw.
Valid value: null (default) - the PGW 2200 does not upspeed
the CODEC if the T.38 fails,
G711alaw - up-speeds to G.711A-law if T.38 fails,
G711ulaw - up-speeds to G.711 U-law if T.38 fails,
G711alaw;G711ulaw - the PGW 2200 first choice is A-law
and the second choice is U-law for upspeed CODEC
selection
G711ulaw;G711alaw - the first choice is G.711 U-law and
the second choice is G.711 A-law for upspeed CODEC
selection
Billing Interface
This section identifies the call detail record (CDR) data modified for this feature by adding data values
2 through 4. For billing interface information for the rest of the Cisco MGC software, refer to the Cisco
Media Gateway Controller Software Release 9 Billing Interface Guide.
SIP to MGCP T.38 Fax Fallback to Pass-Through and Voice
10
SIP to MGCP T.38 Fax Fallback to Pass-Through and Voice
Obtaining Documentation, Obtaining Support, and Security Guidelines
T.38 Fax Call (Tag: 4081)
Table 2
T.38 Fax Call Description Form
Name: T.38 Fax Call
Tag: 4081
Source: MDL
Description/Purpose: Indicates that the call was a fax call negotiated using T.38.
Format: IA5
Length in Octets: 1
Data Value:
0 = No T.38 fax
1 = T.38 fax
2 = T.38 fax fail and up-speed CODEC is used for pass-through fax
3 = T.38 fax fail and no up-speed CODEC is used for pass-through fax
Extended Data Value: No extended value.
General Information: The data for this CDR is assigned by SCP and transparently passed to CDR.
MGC Release: Release 9.3(2) and later.
Added data values 2-4 in Release 9.5(2).
Answered
(1010)
Deselected
(1020)
Aborted
(1030)
Release
(1040)
Interrupted
(1050)
Ongoing
(1060)
Maintenance
(1070)
External DB End of Call
(1080)
(1110)
Y
Y
N
N
Y
Y
Y
Y
N
Obtaining Documentation, Obtaining Support, and Security
Guidelines
For information on obtaining documentation, obtaining support, providing documentation feedback,
security guidelines, and also recommended aliases and general Cisco documents, see the monthly What's
New in Cisco Product Documentation, which also lists all new and revised Cisco technical
documentation at
http://www.cisco.com/en/US/docs/general/whatsnew/whatsnew.html
Glossary
Table 3 contains expansions of acronyms and technical terms used in this feature module.
Table 3
Acronyms and Expansions
Acronym
Expansion
ATA
analog telephone adaptor
CDR
call data record
MGC
Cisco Media Gateway Controller
MGCP
Media Gateway Control Protocol
PGW
PSTN Gateway
SIP to MGCP T.38 Fax Fallback to Pass-Through and Voice
11
SIP to MGCP T.38 Fax Fallback to Pass-Through and Voice
Glossary
Table 3
Acronyms and Expansions
Acronym
Expansion
SDP
Session Description Protocol
SIP
Session Initiation Protocol
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SIP to MGCP T.38 Fax Fallback to Pass-Through and Voice
12