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SIP to MGCP T.38 Fax Fallback to Pass-Through and Voice

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SIP to MGCP T.38 Fax Fallback to Pass-Through and Voice

Feature Overview

Benefits

Related Documents

Supported Platforms

Supported Standards, MIBs, and RFCs

Prerequisites for Using This Feature

Up-speed to CODEC to Pass-through Operation

XECfgParm.dat Configuration Tasks

Monitoring and Maintaining the Feature

Daily Tasks

Verifying the Platform State of the Cisco PGW 2200 Hosts

Verifying That Processes Are Running

Configuration Examples

Reference Information

XECfgParm.dat Parameters

Billing Interface

T.38 Fax Call (Tag: 4081)

Obtaining Documentation, Obtaining Support, and Security Guidelines

Glossary


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

•Supported Platforms

•Supported Standards, MIBs, and RFCs

•Prerequisites for Using This Feature

•XECfgParm.dat Configuration Tasks

•Monitoring and Maintaining the Feature

•Configuration Examples

•Reference Information

•Obtaining Documentation, Obtaining Support, and Security Guidelines

•Glossary

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:

•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.

Note 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,

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

•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.

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:

•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.

Note 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).

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 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

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

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

•Verifying That Processes Are Running

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: 

   Media Gateway Controller 2004-03-29 14:15:22

M  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.

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-rw-   1 mgcusr   mgcgrp     30907 Jul 24 15:29 alarmCats.dat

-rw-rw-rw-   1 mgcusr   mgcgrp      2064 Jun  4 10:57 alarmTable.dat

-rw-rw-rw-   1 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 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"

Note 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.

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 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 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 Processes Controlled by the Process Manager 

Group
Process
Description
ENGG-01
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.

XEG-01
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

Failover controller. It is a monitoring process. If it should go down, it causes a minor out-of-service alarm.

PFMG-01
Platform Monitoring Group
 

DSKM-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.

SNMPG-01
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

Reference Information

The following sections contain reference material related to this feature. Information is included on the following areas:

•XECfgParm.dat Parameters

•Billing Interface

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.

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 (1080)

End of Call (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

SDP

Session Description Protocol

SIP

Session Initiation Protocol



Any Internet Protocol (IP) addresses used in this document are not intended to be actual addresses. Any examples, command display output, and figures included in the document are shown for illustrative purposes only. Any use of actual IP addresses in illustrative content is unintentional and coincidental.