Configuring T.38 Fax Relay

Configuring T.38 Fax Relay
Configuring T.38 Fax Relay
Last Updated: December 4, 2012
This chapter describes configuration for T.38 fax relay on an IP network. T.38 is an ITU standard that
defines how fax communications are packetized and transported over IP networks. T.38 fax relay includes
the following features:
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Fax Relay Packet Loss Concealment
MGCP Based Fax (T.38) and DTMF Relay
SIP T.38 Fax Relay
T.38 Fax Relay for T.37/T.38 Fax Gateway
T.38 Fax Relay for VoIP H.323
SG3 Fax Support on Cisco Time Division Multiplexing-Internet Protocol (TDM-IP) Voice Gateways
and Cisco Unified Border Element (Cisco UBE) platforms
History for the Fax Relay Packet Loss Concealment Feature
Release
Modification
12.1(3)T
This feature was introduced.
12.1(5)XM
This feature was implemented on the Cisco
AS5800.
12.1(5)XM2
This feature was implemented on the Cisco AS5350
and Cisco AS5400.
12.2(2)XB1
This feature was implemented on the Cisco
AS5850.
12.2(11)T
This feature was integrated into this release and
implemented on the Cisco AS5350, Cisco AS5400,
Cisco AS5800, and Cisco AS5850.
Americas Headquarters:
Cisco Systems, Inc., 170 West Tasman Drive, San Jose, CA 95134-1706 USA
Configuring T.38 Fax Relay
History for the MGCP Based Fax (T.38) and DTMF Relay Feature
Release
Modification
12.2(2)XB
This feature was introduced.
12.2(8)T
This feature was integrated into this release and
implemented on the Cisco 2600 series, Cisco 3600
series, and Cisco 7200 series.
12.2(11)T
This feature was implemented on the Cisco
AS5300, Cisco AS5350, Cisco AS5400, and Cisco
AS5800.
12.2(11)T2
The gateway force keyword pair was introduced.
12.2(15)T
This feature was implemented on the Cisco 1751
and Cisco 1760.
12.4T
The mgcp fax t38 inhibit command was no longer
configured by default for MGCP gateways that use
the auto-configuration function.
12.4(4)T
The mgcp fax-relay sg3-to-g3 command was
integrated into Cisco IOS release 12.4(4)T
History for the H.323 and SIP T.38 Fax Relay Feature
Release
Modification
12.2(13)T
This feature was introduced.
12.4(4)T
The fax-relay sg3-to-g3 command was integrated
into Cisco IOS release 12.4(4)T
History for the T.38 Fax Relay for T.37/T.38 Fax Gateway Feature
Release
Modification
12.1(3)X1
This feature was introduced.
History for the SG3 Fax Support Cisco TDM-IP Voice Gateways and Cisco UBE Platforms Feature
Release
Modification
15.1(1)T
This feature was introduced.
Finding Support Information for Platforms and Cisco IOS Software Images
Your software release may not support all the features documented in this chapter. For the latest feature
information and caveats, see the release notes for your platform and software release.
Use Cisco Feature Navigator to find information about platform support and Cisco IOS and Catalyst OS
software image support. To access Cisco Feature Navigator, go to http://www.cisco.com/go/cfn . An
account on Cisco.com is not required.
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H.323 and SIP T.38 Fax Relay
Finding Feature Information
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Finding Feature Information, page 3
Prerequisites for Configuring T.38 Fax Relay, page 3
Restrictions for Configuring T.38 Fax Relay, page 4
Information About T.38 Fax Relay, page 5
How to Configure H.323 and SIP T.38 Fax Relay, page 12
How to Configure MGCP T.38 Fax Relay, page 18
Configuration Examples for T.38 Fax Relay, page 23
Finding Feature Information
Your software release may not support all the features documented in this module. For the latest caveats
and feature information, see Bug Search Tool and the release notes for your platform and software release.
To find information about the features documented in this module, and to see a list of the releases in which
each feature is supported, see the feature information table at the end of this module.
Use Cisco Feature Navigator to find information about platform support and Cisco software image support.
To access Cisco Feature Navigator, go to www.cisco.com/go/cfn. An account on Cisco.com is not required.
Prerequisites for Configuring T.38 Fax Relay
Before you configure T.38 fax relay, perform the following tasks:
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H.323 and SIP T.38 Fax Relay, page 3
MGCP T.38 Fax Relay, page 3
SG3 Fax Support on Cisco TDM-IP Voice Gateways and Cisco UBE platforms, page 4
H.323 and SIP T.38 Fax Relay
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Ensure that your platform is supported.
Install a software release that supports fax relay.
Install appropriate hardware and memory for your platform.
Establish a working H.323 or SIP network for voice calls. T.38 fax relay interoperability requires H.
323 Version 2.
Complete voice interoperability testing with third-party gateways and gatekeepers.
To disable fax relay ECM on the AS5xxx series of voice gateways using Nextport DSP models, ensure
that you have system processing engine (SPE) firmware version 2.8.3.8 or a higher version.
MGCP T.38 Fax Relay
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Install a software release that supports T.38 fax relay
Install appropriate hardware and memory for your platform.
Identify endpoints and configure the MGCP application as described in the appropriate section of
theCisco IOS MGCP and Related Protocols Configuration Guide .
Complete voice interoperability testing with third-party gateways and gatekeepers.
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SG3 Fax Support on Cisco TDM-IP Voice Gateways and Cisco UBE platforms
Restrictions for Configuring T.38 Fax Relay
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Ensure that you have adequate memory in the gateway. Although 96 to 128 MB of RAM is
recommended, the memory requirement is dependent on the platform and the anticipated number of
calls to be made through the system.
SG3 Fax Support on Cisco TDM-IP Voice Gateways and Cisco UBE platforms
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Working familiarity with Cisco IOS command-line interface and basic configuration procedures for
voice gateway networks.
You should be familiar with the configuration information in the Universal Voice Transcoding
Support for IP-to-IP Gateways document.
Restrictions for Configuring T.38 Fax Relay
The restrictions for configuring T.38 fax relay are as follows:
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H.323 T.38 Fax Relay, page 4
SIP T.38 Fax Relay, page 4
SG3 Fax Support on Cisco TDM-IP Voice Gateways and Cisco UBE Platforms, page 5
MGCP T.38 Fax Relay, page 5
H.323 T.38 Fax Relay
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The transport protocols specified in the ITU-T recommendation for T.38 are Transmission Control
Protocol (TCP) and User Datagram Protocol (UDP). However, for T.38 fax relay on Cisco gateways,
only UDP is supported for the transport layer.
Some third-party gateways and gatekeepers may not be compatible with Cisco voice gateways for T.
38 fax relay because different manufacturers can select certain parts of H.323 and T.38 to implement
into their gateways and gatekeepers. Voice interoperability testing with these third-party gateways and
gatekeepers should be performed to make sure that T.38 fax relay can be successful.
T.38 fax relay is not supported on Cisco MC3810 series concentrators with Voice Compression
Modules (VCMs).
T.38 fax relay is not supported by Multimedia Conference Manager (MCM) H.323 proxy in Cisco IOS
Release 12.1(3)T.
If the fax rate disable command is configured on a dial peer, neither the originating nor the
terminating gateway can enter into Cisco fax relay mode, T.38 fax relay mode, or fax pass-through
mode. The fax rate disable command disables fax transfer support.
SIP T.38 Fax Relay
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The transport protocols specified in the ITU-T recommendation for T.38 are Transmission Control
Protocol (TCP) and User Datagram Protocol (UDP). However, for T.38 fax relay on Cisco gateways,
only UDP is supported for the transport layer.
If SIP T.38 fax relay is not supported by both gateways, the T.38 negotiation fails and the call reverts
to an audio codec.
T.38 fax relay requires a 64-kbps transmission rate, the same amount of bandwidth as a voice call with
the G.711 codec.
SG3 Fax Support on Cisco TDM-IP Voice Gateways and Cisco UBE Platforms
Information About T.38 Fax Relay
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Fax Calling Tones (CNG) are optional and are not used to initiate a switch to T.38 mode. Instead,
Called Station Identifier (CED) tones or preamble flags are used.
SIP fax relay does not rely on named signaling events (NSEs) to signal a switch to T.38 mode.
Standard RFC 2543 and RFC 2327 SIP and SDP signaling are used instead.
If the fax rate disable command is configured on a dial peer, neither the originating nor the
terminating gateway can enter into Cisco fax relay mode, T.38 fax relay mode, or fax pass-through
mode. The fax rate disable command disables fax transfer support.
SG3 Fax Support on Cisco TDM-IP Voice Gateways and Cisco UBE Platforms
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SG3 fax capability is not supported for Cisco Fax Relay.
For T.38 fax sessions to operate at SG3 speeds, all the endpoints involved must support T.38 Version 3
(v3) configuration and have negotiated T.38 v3. If all endpoints are not configured for SG3/V.34
speeds, then the slowest speed in the topology is the one supported by all endpoints.
SG3 fax support on TDM-IP gateways is available in H.323 and SIP configurations.
MGCP T.38 Fax Relay
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Only UDP is supported for the transport layer.
The gateway does not dynamically issue a call admission control (CAC) request to increase the
bandwidth allocated for a call when the call is switched from voice to fax. A best-effort support of
bandwidth requirements for the call is supported.
Information About T.38 Fax Relay
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Methods for Fax Relay, page 5
T.38 Fax Relay Functions, page 6
T.38 Fax Relay Call Control, page 6
SG3 Fax Support on Cisco TDM-IP Voice Gateways and Cisco UBE Platforms, page 8
Fax CM Message Tone Suppression, page 11
Methods for Fax Relay
Cisco provides two methods for fax relay; Cisco fax relay and T.38 fax relay.
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Cisco fax relay, a Cisco-proprietary method, is the default on most platforms if a fax method is not
explicitly configured.
T.38 fax relay is a method based on the ITU-T T.38 standard.T.38 fax relay is real-time fax
transmission; that is, two fax machines communicating with each other as if there were a direct phone
line between them. Fax relay is configured by using a few additional commands on gateway dial peers
that have already been defined and configured for voice over IP calls.
T.38 fax relay is described in this chapter. Cisco fax relay is described in the “Configuring Cisco Fax
Relay” chapter.
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T.38 Fax Relay Functions
H.323 and SIP T.38 Fax Relay
T.38 Fax Relay Functions
T.38 fax gateways provide the following functions:
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Demodulation of incoming T.30 fax signals at the transmitting gateway (T.30 is the standard
procedure for fax transmission in the PSTN.)
Translation of T.30 fax signals into T.38 Internet Fax Protocol (IFP) packets
Exchange of IFP packets between the transmitting and receiving T.38 gateways
Translation of T.38 IFP packets back into T.30 signals at the receiving gateway
T.38 Fax Relay Call Control
The T.38 fax relay feature can be configured for H.323, Session Initiation Protocol (SIP), Media Gateway
Control Protocol (MGCP), and Skinny Client Control Protocol (SCCP) call control protocols. For H.323
and SIP networks, the only configuration tasks that differ are configuration of VoIP dial peers.
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H.323 and SIP T.38 Fax Relay, page 6
H.323 and SIP T.38 Fax Relay
This section describes the capabilities available with H.323 and SIP T.38 fax relay.
Fax Relay Packet Loss Concealment
High-end fax machines with the memory to store page data often are able to use Error Correction Mode
(ECM) for error-free page transmission. When ECM is enabled, a fax page is transmitted in a series of
blocks that contain frames with packets of data. After receiving the data for a complete page, a receiving
fax machine notifies the transmitting fax machine of any frames with errors. The transmitting fax machine
then retransmits the specified frames. This process is repeated until all frames are received without errors.
If the receiving fax machine is unable to receive an error-free page, the fax transmission may fail and one
of the fax machines may disconnect. On networks that have a packet loss rate greater than 2 per cent, fax
transmissions routinely fail when ECM is enabled because of ECM’s low tolerance for packet loss.
The fax relay packet loss concealment feature allows you to control whether ECM is enabled or disabled
for fax transmissions on a VoIP dial peer. By disabling ECM on networks with a large amount of packet
loss, you ensure that more fax transmissions are completed, although they may not be totally error-free.
When ECM is disabled, a fax page is transmitted using high-speed modulation in its raw encoded format.
When detecting line errors with ECM disabled, the receiving fax machine has three options (in order of
increasing severity):
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Respond to page reception with the ReTrain Positive command. This response causes the transmitting
fax to go through the training check process before transmitting the next page.
Respond to the page reception with the ReTrain Negative command. This response causes the
transmitting fax to go through the Training Check Frame (TCF) process with a lower modulation
scheme.
Disconnect immediately.
Fax relay ECM is enabled by default. To disable ECM, you use the fax-relay ecm disable command on the
VoIP dial peer. After this command is configured, the gateway’s Digital Signal Processor (DSP) fax-relay
firmware modifies the T.30 Digital Information Signal (DIS) message. This modification is performed on
DIS signals in both directions, so that ECM is disabled even when only one gateway is configured to
disable ECM.
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T.38 Fax Relay Call Control
H.323 and SIP T.38 Fax Relay
Disabling of ECM is recommended for dial peers handling fax relay traffic on known lossy networks,
especially those with a packet loss rate of 2 percent or greater. The debug fax relay t30 command provides
information about the E.164 destination and T.30 messages associated with fax transmissions. Note than an
excessive number of simultaneous debug operations can degrade performance.
H.323 or SIP T.38 Fax Relay Fallback
You can specify a fallback fax method for the gateway to attempt if H.323 or SIP T.38 fax relay cannot be
successfully initiated between gateways. A failure to switch to T.38 fax relay can occur if you are
interworking with a network that does not support T.38 fax relay. The following are the fallback options:
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Cisco fax relay.
Fax pass-through using a G.711 codec.
No fallback. The fax is transmitted using the existing voice codec. If modem pass-through has been
configured, the fax is transferred through named signaling event (NSE) pass-through.
H.323 or SIP Support of Resource Reservation Protocol for T.38 Fax Relay
H.323 or SIP gateways that are configured for T.38 fax relay allow Resource Reservation Protocol (RSVP)
bandwidth adjustments when the original voice call is configured to use RSVP. When the original voice
codec is restored at the end of the fax session, the original RSVP bandwidth is restored as well. When
current bandwidth is unavailable, the fax proceeds at a best-effort rate without RSVP and with no
performance guarantees. RSVP bandwidth adjustments for fax transmissions are made as follows:
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T.38 fax relay--RSVP bandwidth is adjusted to 80 kbps
Fax pass-through--RSVP bandwidth is adjusted to 96 kbps
H.323 Support for Call Admission Control
H.323 call admission control (CAC) adjustments are allowed in the case of fax relay and fax pass-through.
An H.323 gateway that uses a gatekeeper requests the following bandwidths from the gatekeeper when
codec changes are necessary:
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T.38 fax relay--Bandwidth of 80 kbps
Fax pass-through--Bandwidth of 96 kbps
If the gatekeeper accepts the bandwidth changes, the session is permitted to continue over the fax codec (G.
711). If the gatekeeper rejects the bandwidth increase, the fax codec is terminated and the gateway uses the
configured fax protocol fallback or the original voice codec, in which case the fax transfer fails.
H.323 or SIP Support for NSEs with T.38 Fax Relay
Use the fax protocol command to specify that a gateway should use NSEs for fax signaling. This option
allows interoperability with MGCP gateways as well as other H.323 and SIP gateways. The use of NSEs
and their payload type is negotiated in Session Description Protocol (SDP) messages. Because NSEs are
passed in the media stream, they avoid the signaling delays that can be introduced by MGCP call agents.
The addition of the NSE capability to Cisco SIP and H.323 gateways addresses these delays and improves
interoperability between MGCP, SIP, and H.323 products.
If NSEs are specified and NSE use is not successfully negotiated between gateways, T.38 fax relay
signaled through the protocol stack is attempted. If protocol-stack T.38 fax relay also fails, the configured
fallback fax transfer protocol is used.
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SG3 Fax Support on Cisco TDM-IP Voice Gateways and Cisco UBE Platforms
H.323 and SIP T.38 Fax Relay
H.323 or SIP T.38 Fax Relay Interworking with Cisco MGCP Gateways
Specify that gateways must use T.38 fax relay and NSEs even though those gateways may be unable to
negotiate those attributes by themselves at the time of call setup. This may happen during negotiations for
fax attributes between H.323 or SIP gateways and MGCP gateways.
Both gateways must be configured to use T.38 fax relay and NSEs. On an H.323 or SIP gateway, use the
fax protocol t38 nse force command. On an MGCP gateway, use the mgcp fax t38 gateway force
command.
SG3 Fax Support on Cisco TDM-IP Voice Gateways and Cisco UBE Platforms
This feature provides support for V.34 fax relay based on the ITU Specification T.38 version 3 (04/2007)
and for fax pass-through at SG3 speed. Prior to Cisco IOS Release 15.1(1)T, SG3-to-SG3 calls would fail
because the V.34 modulation was not supported. A fallback solution allowed SG3-to-SG3 connections to
be made, but the transmission speed was set to G3 levels.
For T.38 fax sessions to operate at SG3 speeds, all the endpoints involved must support T.38 Version 3 (v3)
configuration and have negotiated T.38 v3. For example:
Originating Gateway(T.38 v3)--IP-(T.38 v3)Cisco UBE or TDM-IP GW(T.38 v3)-IP--Terminating
Gateway(T.38 v3)
In this context, all currently supported TDM-IP gateways and Cisco UBE T.38 flows (H.323-H.323, H.323SIP and SIP-SIP) are supported in Release 15.1(1)T. However, in topologies where at least one endpoint
has a T.38 v0 configuration, the TDM-IP gateway or Cisco UBE configuration must be T.38 v0 (the lowest
common version). Any other combination of T.38 v3 or v0 configuration involved in the Cisco UBE
topologies is not supported.
When two endpoints are involved in negotiating the T.38 parameter, the mandatory parameter is the
"FaxVersion." That is, when one of the endpoints supports Version 0 (v0), the resulting session operates as
a v0 session. As long as Cisco UBE is configured for the lowest common version of the traffic expected,
calls are completed successfully.
The information for supported calls is summarized in the tables below.
Table 1
Emitting End
Receiving End
Resulting Session
v0
v0
v0
v0
v3
v0
v3
v0
v0
v3
v3
v3
Table 2
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Supported Call Flows with Mixed Endpoints at v0 and v3 Speeds
Supported Call Flows with Mixed Endpoints and Cisco UBE
Emitting End
Cisco UBE
Receiving End
Resulting Session
v0
v0
v0
v0
v0
v0
v3
v0
SG3 Fax Support on Cisco TDM-IP Voice Gateways and Cisco UBE Platforms
MGCP T.38 Fax Relay
Emitting End
Cisco UBE
Receiving End
Resulting Session
v3
v0
v0
v0
v3
v3
v3
v3
Beginning in Cisco IOS Release 15.1(1)T, full SG3 fax support is enabled on Cisco TDM-IP voice
gateways and Cisco UBE platforms. To enable this feature, complete the procedures in the How to
Configure H.323 and SIP Fax Pass-Through section of the Configuring Fax Pass-Through chapter of the
Cisco IOS Fax, Modem, and Text Support over IP Configuration Guide, Release 15.1 and the procedures in
the How to Configure H.323 and SIP T.38 Fax Relay, page 12.
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MGCP T.38 Fax Relay, page 9
SCCP and T.38 Fax Relay, page 11
MGCP T.38 Fax Relay
When MGCP-based fax relay is disabled, MGCP networks use passthrough for fax relay transmission.
However, when MGCP-based fax relay is enabled, ITU-T T.38 support is added, providing a standardized
method of supporting reliable fax transmission in the MGCP network. With MGCP-based fax relay,
interworking is allowed between the T.38 application that already exists on Cisco gateways and the MGCP
applications on call agents (CAs).
MGCP-based fax relay provides two modes of implementation: gateway-controlled mode and CAcontrolled mode. In gateway-controlled mode, a gateway advertises its capabilities using Session
Description Protocol (SDP) messages during the establishment of a call, using the call-control protocol that
was used to establish the call. After the call is established, the connected gateways negotiate the actual
switch from voice to T.38 fax relay by exchanging named signaling event (NSE) or named telephony event
(NTE) messages embedded in the RTP stream. That transmission is transparent to the CA, which knows
only about the voice call. Gateway-controlled mode allows you to use MGCP-based fax relay (T.38)
without upgrading the CA software to support the capability.
In CA-controlled mode, the gateways rely on the MGCP CA to direct the T.38 fax relay call flow.
Gateway-Controlled MGCP T.38 Fax Relay
In gateway-controlled mode, the gateways do not need instruction from the CA to switch to T.38 mode.
This mode should be used if the CA has not been upgraded to support T.38 and MGCP interworking or if
the CA does not want to manage fax calls.
Gateway-controlled mode can also be used to bypass the message delay overhead caused by CA handling;
for example, to meet time requirements for switchover to T.38 mode. If the CA does not specify a mode to
the gateway, the gateway defaults to gateway-controlled mode.
In gateway-controlled mode, the gateways exchange NSEs that provide the following services:
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Instruct the peer gateway to switch to T.38 for the call.
Either acknowledge the switch and a readiness to accept packets or indicate that a gateway cannot
accept T.38 packets.
MGCP-based fax relay in gateway-controlled mode uses the following call flow:
1 An incoming call is initially established as a voice call.
2 The gateways advertise capabilities in an SDP exchange during connection establishment.
3 If both gateways do not support T.38, fax passthrough is used for fax transmission. If both gateways do
support T.38, they attempt to switch to T.38 upon fax tone detection. The existing audio channel is used
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SG3 Fax Support on Cisco TDM-IP Voice Gateways and Cisco UBE Platforms
MGCP T.38 Fax Relay
for T.38 fax relay, and the existing connection port is reused to minimize delay. If failure occurs at
some point during the switch to T.38, the call reverts to the original settings that it had as a voice call. If
this failure occurs, a fallback to fax passthrough is not supported.
4 Upon completion of the fax image transfer, the connection remains established and reverts to a voice
call using the previously designated codec, unless the CA instructs the gateway to do otherwise. If the
CA has been configured to control fax relay, the CA instructs the gateway on processing the call with
the fx: extension of the local connection option (LCO).
CA-Controlled MGCP T.38 Fax Relay
CA-controlled MGCP T.38 fax relay enables T.38 fax relay interworking between H.323 gateways and
MGCP gateways and between two MGCP gateways under the control of a call agent. In Cisco IOS Release
12.3(1) and later releases, the feature has been modified. The new method supersedes previous methods for
CA-controlled fax relay and introduces the following gateway capabilities to enable this functionality:
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Note
Ability to accept the MGCP FXR package, to receive the fxr prefix in commands from the call agent,
and to send the fxr prefix in notifications to the call agent.
Ability to accept a new port when switching from voice to fax transmission during a call. This new
ability allows successful T.38 CA-controlled fax between H.323 and MGCP gateways for those
occasions in which the H.323 gateway assigns a new port when changing the call type from voice to
fax. New ports are assigned in H.323 gateways using Cisco IOS images from Release 12.2(2)T to
Release 12.2(7.5)T. Note that gateways in MGCP-to-MGCP fax calls simply reuse the same port. CAcontrolled T.38 fax relay enables MGCP gateways to handle both situations, either switching to a new
port or reusing the same port, as directed by the call agent.
The CA-controlled mode described in this document makes obsolete the previous method that was
described in Media Gateway Control Protocol-Based Fax (T.38) and Dual Tone Multifrequency (IETF
RFC 2833) Relay . The previous CA-controlled mode for T.38 fax relay used the ca parameter to
communicate with the call agent, and the ca parameter is no longer supported as of Cisco IOS Release
12.3(1). The previous method has been superseded by the CA-controlled mode described in this document.
Note that the gateway (GW)-controlled mode that is described in the previous document remains supported
and is the same as the GW-controlled mode that is described in this document.
The sequence for T.38 CA-controlled fax is as follows:
1 The MGCP call agent determines that CA-controlled mode is necessary for fax relay because the far
end of the connection is an H.323 gateway or other entity incapable of directly negotiating T.38 with
the Cisco IOS MGCP gateway.
2 The call agent establishes a voice call with the local MGCP gateway and specifies that any subsequent
fax transmissions should take place using T.38 fax relay in CA-controlled mode. The call agent includes
an "fxr/fx:t38" or "fxr/fx:t38-loose" parameter in the Local Connection Options parameter of the Create
Connection (CRCX) command that it sends to the MGCP gateway. The term "loose" indicates that a
description of T.38 capabilities is not required in the resulting Session Description Protocol (SDP)
message.
3 When the voice call is established between the gateways, the call agent asks the MGCP gateway to
notify it of any T.38 events with an "R: fxr/t38" requested event parameter in a Notification
Request(RQNT) or Modify Connection (MDCX) command. If the MGCP gateway detects fax
transmission during this call, it generates a Notify (NTFY) command with an "O: fxr/t38(start)"
observed event parameter and sends it to the call agent.
4 The call agent responds with an MDCX containing one or both of the following:
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"a:image/t38" descriptor in the Local Connection Options parameter
Fax CM Message Tone Suppression
SCCP and T.38 Fax Relay
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"m=image port udptl t38" line in the included SDP message
Note that port is replaced in the MDCX with the actual port number for the fax transmission. This port
number can be the same as or different from the port number negotiated earlier when the voice call was
established. T.38 CA-controlled fax supports either using the same port or switching to a new port for fax.
Note that if the MGCP gateway does not detect fax first, it may receive the same MDCX prior to sending a
NTFY.
1 When the fax transmission is complete, the MGCP gateway sends the call agent a NTFY command with
an "O: fxr/t38(stop)" parameter. The call agent then has the option of either sending another MDCX to
return to voice or using a Delete Connection (DLCX) command to terminate the call.
MGCP T.38 Fax Relay Interworking with Cisco H.323 and SIP Gateways
Some MGCP call agents do not properly pass those portions of Session Description Protocol (SDP)
messages that advertise T.38 and NSE capabilities. As a result, gateways that are controlled by these call
agents are unable to use NSEs to signal T.38 fax relay to other gateways that use NSEs. As of Cisco IOS
Release 12.2(13)T, you can configure gateways to use T.38 fax relay and NSEs even though those
gateways may be unable to negotiate those attributes by themselves at the time of call setup.
The mgcp fax t38 gateway force command provides a way to ensure gateway-controlled T.38 fax relay
between an MGCP gateway and another gateway. The other gateway in the negotiation can be an H.323,
Session Initiation Protocol (SIP), or MGCP gateway. Both gateways must be configured to use NSEs to
signal T.38 fax relay mode switchover. On H.323 and SIP gateways, use the fax protocol t38 nse force
command to specify the use of NSEs for T.38 fax relay. On MGCP gateways, use the mgcp fax t38
gateway force command.
NSEs are the Cisco-proprietary version of named telephony events (NTEs), which are defined in IETF RFC
2833. NSEs and NTEs are used to communicate telephony signaling events that are normally indicated by
the presence of tones, such as dual-tone multifrequency (DTMF) or fax transmissions. NSEs and NTEs do
not transmit audible signaling tones across the network, but instead work by sending a binary code that is
later used to recreate a tone. NSEs use different values to represent events and tones than NTEs use.
NSEs and NTEs are passed in the media stream. They consist of Real-Time Transport Protocol (RTP)
packets that have the same source and destination IP addresses and User Datagram Protocol (UDP) ports as
the rest of the media stream. However, NSE and NTE packets use different RTP payload types than the rest
of the media stream so that they can stand apart from the audio packets in the stream. NSEs are normally
sent with RTP payload type 100.
SCCP and T.38 Fax Relay
For information about this capability, refer to the Configuring DTMF Relay, Fax Relay and Modem Relay
chapter in the Supplementary Services Features for FXS Ports on Cisco IOS Voice Gateways Configuration
Guide.
Fax CM Message Tone Suppression
Super Group 3 (SG3) is a new generation of fax machines that support speeds of up to 33.6 kbps through
V.34 half duplex (HD) modulation and V.8 signaling.
SG3 V.8 fax CM message tone suppression enables SG3 fax machines to scale down without end-user
interaction and without using the extra bandwidth required by modem pass-through and allows SG3 fax
machines to interoperate over a fax-relay network at G3 speeds by blocking the SG3 V.8 CM message, or
fax tone, from reaching the called fax machine. This causes the called fax machine to time out on the
ANSam tone and scale down to G3 speeds by initiating V.21 negotiations.
11
Configuring One or More Individual VoIP Dial Peers for T.38 Fax Relay
How to Configure H.323 and SIP T.38 Fax Relay
SG3 V.8 fax CM message tone suppression supports both one-gateway and two-gateway solutions:
•
•
With a one-gateway solution, the gateway on one end of the call can be configured to suppress the
SG3 V.8 fax CM message independently of the gateway on the other end of the call. The one-gateway
solution suppresses the fax CM tone on both TDM and IP interfaces (TI C5510 DSPs only), and can
interoperate with third-party gateways when the fax CM tone suppression gateway is the originating
gateway.
With a two-gateway solution, the gateways on both ends of the call must have this feature enabled.
The two-gateway solution suppresses the fax CM tone only on the TDM interface (TI C5421 and TI
C549 DSPs). Both gateways must support this feature to interoperate at G3 speeds, or the fax tone
suppression gateway must be the originating gateway.
How to Configure H.323 and SIP T.38 Fax Relay
There are two ways to configure T.38 fax relay on VoIP gateways:
Note
Beginning in Cisco IOS Release 15.1(1)T, you can configure SG3 Fax Support when you enter the fax
protocol t38 command. This is described in the following sections.
Note
Fax relay parameters that are set for an individual dial peer under the dial-peer voice command take
precedence over global settings made under the voice service voip command.
•
•
Configuring One or More Individual VoIP Dial Peers for T.38 Fax Relay, page 12
Configuring T.38 Fax Relay on VoIP Dial Peers Globally, page 15
Configuring One or More Individual VoIP Dial Peers for T.38 Fax Relay
Use the following tasks to configure T.38 Fax Relay for an individual VoIP dial peer.
SUMMARY STEPS
1. enable
2. configure terminal
3. dial-peer voice tag voip
4. dtmf-relay h245-signal
5. fax protocol t38 [nse [force]] [version {0 | 3}] [ls-redundancy value [hs-redundancy value]]
[fallback {cisco | none| pass-through {g711ulaw| g711alaw}}]
6. fax rate {12000 | 14400 | 2400 | 4800 | 7200 | 9600 | disable | voice} [bytes rate]
7. fax-relay ecm disable
8. fax-relay sg3-to-g3 system
9. session protocol sipv2
12
Configuring One or More Individual VoIP Dial Peers for T.38 Fax Relay
How to Configure H.323 and SIP T.38 Fax Relay
DETAILED STEPS
Command or Action
Step 1 enable
Purpose
Enables privileged EXEC mode.
•
Enter your password if prompted.
Example:
Router> enable
Step 2 configure terminal
Enters global configuration mode.
Example:
Router# configure terminal
Step 3 dial-peer voice tag voip
Enters dial-peer configuration mode and defines a dial peer that directs traffic to or
from a packet network.
Example:
•
Router(config)# dial-peer
voice 25 voip
•
Step 4 dtmf-relay h245-signal
Example:
Router(config-dial-peer)# dtmfrelay h245-signal
tag --Dial-peer identifier that consists of one or more digits. Range: 1 to
2147483647.
voip --Calls from this dial peer use voice encapsulation on the packet
network.
Specifies how an H.323 or Session Initiation Protocol (SIP) gateway relays dual
tone multifrequency (DTMF) tones between telephony interfaces and an IP
network.
•
h245-signal --(Optional) Forwards DTMF tones by using the H.245 signal
User Input Indication method. Supports tones from 0 to 9, *, #, and from A to
D.
13
Configuring One or More Individual VoIP Dial Peers for T.38 Fax Relay
How to Configure H.323 and SIP T.38 Fax Relay
Command or Action
Step 5 fax protocol t38 [nse [force]]
[version {0 | 3}] [ls-redundancy
value [hs-redundancy value]]
[fallback {cisco | none| passthrough {g711ulaw| g711alaw}}]
Purpose
Specifies the global default ITU-T T.38 standard fax protocol to be used for all
VoIP dial peers.
•
•
Example:
Router(config-dial-peer)# fax
protocol t38 version 3
•
nse --(Optional) Uses Named Signaling Events (NSEs) to switch to T.38 fax
relay.
force --(Optional) Unconditionally, uses Cisco NSE to switch to T.38 fax
relay. This option allows T.38 fax relay to be used between Cisco H.323 or
Session Initiation Protocol (SIP) gateways and Media Gateway Control
Protocol (MGCP) gateways.
version --(Optional) Specifies a version for configuring fax speed:
◦
◦
0--Configures version 0, which uses T.38 version 0 (1998, G3 faxing)
3--Configures version 3, which uses T.38 version 3 (2004, V.34 or SG3
faxing)
Note The version 0| 3 option was added in Cisco IOS Release 15.1(1)T to enable
SG3 fax support.
•
•
ls-redundancy value --(Optional) Specifies the number of redundant T.38 fax
packets to be sent for the low-speed V.21-based T.30 fax machine protocol.
Range varies by platform from 0 (no redundancy) to 5 or 7. The default is 0.
hs-redundancy value --(Optional) Specifies the number of redundant T.38
fax packets to be sent for high-speed V.17, V.27, and V.29 T.4 or T.6 fax
machine image data. Range varies by platform from 0 (no redundancy) to 2 or
3. The default is 0.
Note Setting the hs-redundancy parameter to a value greater than 0 causes a
significant increase in the network bandwidth consumed by the fax call.
•
•
fallback --(Optional) A fallback mode is used to transfer a fax across a VoIP
network if T.38 fax relay could not be successfully negotiated at the time of
the fax transfer.
cisco --(Optional) Cisco-proprietary fax protocol.
Note Do not use the cisco keyword for the fallback option if you specified
version 3 for SG3 fax transmission.
•
•
none --(Optional) No fax pass-through or T.38 fax relay is attempted. All
special fax handling is disabled, except for modem pass-through if configured
with the modem pass-through command.
pass-through --(Optional) The fax stream uses one of the following highbandwidth codecs:
◦
◦
14
g711ulaw--Uses the G.711 u-law codec.
g711alaw--Uses the G.711 a-law codec.
Configuring T.38 Fax Relay on VoIP Dial Peers Globally
How to Configure H.323 and SIP T.38 Fax Relay
Command or Action
Purpose
Step 6 fax rate {12000 | 14400 | 2400 | 4800 (Optional) Selects the fax transmission speed to be attempted when this dial peer
| 7200 | 9600 | disable | voice} [bytes is used.
rate]
• 12000 , 14400, 2400, 4800, 7200, 9600--Maximum bits-per-second speed.
• bytes rate --(Optional) Fax packetization rate, in ms. Range: 20 to 48.
Default: 20. For T.38 fax relay, this keyword-argument pair is valid only on
Example:
Cisco 5350, Cisco 5400, and Cisco 5850 routers. For other routers, the
Router(config-dial-peer)# fax
packetization rate for T.38 fax relay is fixed at 40 ms and cannot be changed
rate 14400
with this keyword-argument pair.
• disable --Disables fax relay transmission capability.
• voice --Highest possible transmission speed allowed by the voice rate. For
example, if the voice codec is G.711, fax transmission occurs at up to 14400
bps because 14400 bps is less than the 64-kbps voice rate. If the voice codec
is G.729 (8 kbps), the fax transmission speed is 7200 bps. This is the default.
Step 7 fax-relay ecm disable
(Optional) Disables fax-relay ECM.
Note To enable ECM, use the no form of this command.
Note If you are using Cisco IOS Release 15.1(1)T and enabling SG3 fax support,
Example:
do not enter this command.
Router(config-dial-peer)# faxrelay ecm disable
Step 8 fax-relay sg3-to-g3 system
Specifies that for SIP and H.323 signaling types, V.8 fax CM message suppression
is enabled on the specific dial peer. Enabled by default.
•
Example:
Router(config-dial-peer)# faxrelay sg3-to-g3 system
Step 9 session protocol sipv2
system --Uses the protocol set under the voice-service configuration mode.
Note If you are using Cisco IOS Release 15.1(1)T and enabling SG3 fax support,
do not enter this command.
(Optional) Specifies the IETF SIP session protocol for calls between the local and
remote routers using the packet network.
Note This command is required for SIP calls.
Example:
Router(config-dial-peer)#
session protocol sipv2
Configuring T.38 Fax Relay on VoIP Dial Peers Globally
Use the following steps to configure T.38 fax relay globally for previously defined VoIP dial peers.
Alternately, you can configure fax relay for individual VoIP dial peers. See the Configuring One or More
Individual VoIP Dial Peers for T.38 Fax Relay, page 12.
Note
Fax relay parameters that are set for an individual dial peer under the dial-peer voice command take
precedence over global settings made under the voice service voip command.
15
Configuring T.38 Fax Relay on VoIP Dial Peers Globally
How to Configure H.323 and SIP T.38 Fax Relay
SUMMARY STEPS
1. enable
2. configure terminal
3. voice service voip
4. fax protocol t38 [nse [force]] [version{0 | 3}] [ls-redundancy value [hs-redundancy value]]
[fallback {cisco | none | pass-through {g711ulaw | g711alaw}}]
5. fax-relay sg3-to-g3
DETAILED STEPS
Command or Action
Step 1 enable
Purpose
Enables privileged EXEC mode.
•
Enter your password if prompted.
Example:
Router> enable
Step 2 configure terminal
Enters global configuration mode.
Example:
Router# configure terminal
Step 3 voice service voip
Example:
Router(config)# voice service voip
16
Enters voice-service configuration mode.
Configuring T.38 Fax Relay on VoIP Dial Peers Globally
How to Configure H.323 and SIP T.38 Fax Relay
Command or Action
Purpose
Step 4 fax protocol t38 [nse [force]] [version{0 | Specifies the global default ITU-T T.38 standard fax protocol to be used for
3}] [ls-redundancy value [hs-redundancy all VoIP dial peers.
value]] [fallback {cisco | none | pass• nse --(Optional) Uses Named Signaling Events (NSEs) to switch to T.38
through {g711ulaw | g711alaw}}]
fax relay.
• force --(Optional) Unconditionally, uses Cisco NSE to switch to T.38
fax relay. This option allows T.38 fax relay to be used between Cisco H.
Example:
323 or Session Initiation Protocol (SIP) gateways and Media Gateway
Router(config-voi-srv)# fax
Control Protocol (MGCP) gateways.
protocol t38 version 3
• version --(Optional) Specifies a version for configuring fax speed:
◦
◦
0--Configures version 0, which uses T.38 version 0 (1998, G3
faxing)
3--Configures version 3, which uses T.38 version 3 (2004, V.34 or
SG3 faxing)
Note The version 0| 3 option was added in Cisco IOS Release 15.1(1)T to
enable SG3 fax support.
•
•
ls-redundancy value --(Optional) Specifies the number of redundant T.
38 fax packets to be sent for the low-speed V.21-based T.30 fax
machine protocol. Range varies by platform from 0 (no redundancy) to
5 or 7. The default is 0.
hs-redundancy value --(Optional) Specifies the number of redundant T.
38 fax packets to be sent for high-speed V.17, V.27, and V.29 T.4 or T.6
fax machine image data. Range varies by platform from 0 (no
redundancy) to 2 or 3. The default is 0.
Note Setting the hs-redundancy parameter to a value greater than 0 causes
a significant increase in the network bandwidth consumed by the fax
call.
•
•
fallback --(Optional) A fallback mode is used to transfer a fax across a
VoIP network if T.38 fax relay could not be successfully negotiated at
the time of the fax transfer.
cisco --(Optional) Cisco-proprietary fax protocol.
Note Do not use the cisco keyword for the fallback option if you specified
version 3 for SG3 fax transmission.
•
•
none --(Optional) No fax pass-through or T.38 fax relay is attempted.
All special fax handling is disabled, except for modem pass-through if
configured with the modem pass-through command.
pass-through --(Optional) The fax stream uses one of the following
high-bandwidth codecs:
◦
◦
g711ulaw--Uses the G.711 u-law codec.
g711alaw--Uses the G.711 a-law codec.
17
Configuring T.38 Fax Relay on VoIP Dial Peers Globally
Troubleshooting Tips for H.323 or SIP T.38 Fax Relay
Command or Action
Purpose
Step 5 fax-relay sg3-to-g3
Specifies that for SIP and H.323 signaling types, V.8 fax CM message
suppression is enabled for all dial peers on the digital signal processor (DSP)
firmware. Enabled by default.
Example:
Note If you are using Cisco IOS Release 15.1(1)T and enabling SG3 fax
Router(config-voi-serv)# fax-relay
sg3-to-g3
•
support, do not enter this command.
Troubleshooting Tips for H.323 or SIP T.38 Fax Relay, page 18
Troubleshooting Tips for H.323 or SIP T.38 Fax Relay
To troubleshoot T.38 fax relay, perform the following steps:
•
•
•
•
•
•
•
•
Ensure that you can make a voice call.
Ensure that the desired fax protocol was set using the fax protocol command on both the originating
and terminating gateways.
Ensure that the fax protocol is configured as T.38 at the global configuration level or at the dial-peer
configuration level for both the originating and terminating gateways.
Use the show call active voice command to display information for the active call table.
Use the show call history fax command to display recent call history for faxes.
Use the show dial-peer voice command to display configuration information for dial peers.
For H.323 gateways, use the debug cch323 all command to enable all H.323 debugging capabilities,
or use one of the following commands to debug problems while making the call:
◦ debug cch323 error
◦ debug cch323 h225
◦ debug cch323 h245
◦ debug cch323 RAS
◦ debug cch323 session
◦ debug voip ccapi inout
◦ debug vtsp session
For SIP gateways, use the debug ccsip all command to enable all SIP debugging capabilities, or use
one of the following SIP debug commands:
◦
◦
◦
◦
◦
◦
◦
debug ccsip calls
debug ccsip error
debug ccsip eventsfor T.38 fax relay
debug ccsip info
debug ccsip media
debug ccsip messages
debug ccsip states
How to Configure MGCP T.38 Fax Relay
Cisco supports two modes of MGCP T.38 fax relay:
18
Configuring Gateway-Controlled MGCP T.38 Fax Relay
How to Configure MGCP T.38 Fax Relay
•
In gateway-controlled mode, a call agent uses the fx: extension of the local connection option (LCO)
to instruct a gateway about how to process a call. Gateways do not need instruction from the call agent
to switch to T.38 mode.
In call-agent (CA)-controlled mode, the call agent can instruct the gateway to switch to T.38 for a call.
In Cisco IOS Release 12.3(1) and later releases, CA-controlled mode enables T.38 fax relay
interworking between H.323 gateways and MGCP gateways and between two MGCP gateways under
the control of a call agent.
•
Select one of the following MGCP T.38 fax relay configuration tasks:
•
•
•
Configuring Gateway-Controlled MGCP T.38 Fax Relay, page 19
Configuring CA-Controlled MGCP T.38 Fax Relay, page 21
Troubleshooting Tips for MGCP T.38 Fax Relay, page 22
Configuring Gateway-Controlled MGCP T.38 Fax Relay
Use the following steps to configure gateway-controlled MGCP T.38 fax relay.
SUMMARY STEPS
1. enable
2. configure terminal
3. mgcp fax t38 {ecm | gateway force| hs_redundancy value | inhibit | ls_redundancy value | nsf word}
4. mgcp tse payload value
5. mgcp timer nse-response t38 timer
6. mgcp fax rate {2400 | 4800 | 7200 | 9600 | 12000 | 14400 | voice
7. mgcp fax-relay sg3-to-g3
DETAILED STEPS
Command or Action
Step 1 enable
Purpose
Enables privileged EXEC mode.
•
Enter your password if prompted.
Example:
Router> enable
Step 2 configure terminal
Enters global configuration mode.
Example:
Router# configure terminal
19
Configuring Gateway-Controlled MGCP T.38 Fax Relay
How to Configure MGCP T.38 Fax Relay
Command or Action
Step 3 mgcp fax t38 {ecm | gateway force|
hs_redundancy value | inhibit |
ls_redundancy value | nsf word}
Purpose
(Optional) Configures MGCP T.38 fax relay parameters.
•
•
Example:
Router(config)# mgcp fax t38
ls_redundancy 2
•
•
ecm --Enables Error Correction Mode (ECM) for the gateway. By default,
ECM is not enabled.
gateway force --Forces gateway-controlled T.38 fax relay using Ciscoproprietary named signaling events (NSEs) even if the capability to use T.38
and NSEs cannot be negotiated by the MGCP call agent at call setup time.
By default, force is not enabled.
hs_redundancy value --Number of redundant T.38 fax packets to send for
high-speed V.17, V.27, and V.29 T.4 or T.6 fax machine image data. Range:
0 (no redundancy) to 2. The default is 0.
ls_redundancy value --Number of redundant T.38 fax packets to send for
low-speed V.21-based T.30 fax machine protocol. Range: 0 (no redundancy)
to 5. The default is 0.
Note Setting the hs_redundancy parameter greater than 0 causes a significant
increase in network bandwidth consumed by a fax call.
•
inhibit --Disables MGCP-based T.38 fax relay on the gateway. By default,
T.38 is enabled.
Note If the MGCP gateway uses the auto-configuration function, the mgcp fax
t38 inhibitcommand is automatically configured on the gateway each time
a new configuration is downloaded. Beginning with Cisco IOS Software
Release 12.4T, the auto-configuration of this command is removed. For
MGCP gateways running Cisco IOS version 12.4T or later, you must
manually configure the mgcp fax t38 inhibitcommand to use T.38 fax
relay.
•
nsf --Overrides the non-standard facilities (NSF) code with the code provided
in the word argument. NSFs are capabilities that fax manufacturers have built
into fax machines to distinguish their products from others. By default, the
NSF code is not overridden.
◦
Step 4 mgcp tse payload value
Example:
Router(config)# mgcp tse
payload 106
20
word--Two-digit country code and four-digit manufacturer code, in
hexadecimal.
(Required) Enables inband telephony signaling events (TSEs) and specifies the
payload value to be used during fax and modem pass-through and network
continuity tests.
•
value --TSE payload value. The range is 98 to 119. The default is 100.
Configuring CA-Controlled MGCP T.38 Fax Relay
How to Configure MGCP T.38 Fax Relay
Command or Action
Step 5 mgcp timer nse-response t38 timer
Purpose
Configures how a gateway detects the Real-Time Transport Protocol (RTP)
stream host.
•
Example:
Router(config)# mgcp timer nseresponse t38 250
Step 6 mgcp fax rate {2400 | 4800 | 7200 |
9600 | 12000 | 14400 | voice
Example:
Router(config)# mgcp fax rate
9600
nse-response t38 timer --Timeout period, in milliseconds, for awaiting T.38
named signaling event (NSE) responses from a peer gateway. Range is from
100 to 3000. The default is 200.
(Optional) Establishes the maximum fax rate for MGCP T.38 sessions.
•
•
2400 , 4800, 7200, 9600, 14400--Maximum bits-per-second speed.
voice --Highest possible transmission speed allowed by the voice rate. For
example, if the voice codec is G.711, fax transmission occurs at up to 14400
bps because 14400 bps is less than the 64-kbps voice rate. If the voice codec
is G.729 (8 kbps), the fax transmission speed is 7200 bps. This is the default.
Note MGCP normally limits the maximum fax rate on a voice port to the
bandwidth of the configured voice codec. This ensures that the fax session
does not exceed the bandwidth initially authorized for the voice call. In
some cases an administrator may desire to exceed the voice bandwidth
when the call switches to fax in order to offer the best possible fax rate. The
mgcp fax rate command allows you to override this limitation.
Note When the MGCP fax rate is set to the highest possible transmission speed
allowed by the voice codec (mgcp fax rate voice), all MGCP endpoints
limit T.38 fax calls to this speed.
Note The values for this command apply only to the fax transmission speed and
do not affect the quality of the fax itself.
Step 7 mgcp fax-relay sg3-to-g3
Specifies that for MGCP signaling types, V.8 fax CM message suppression is
enabled on the digital signal processor (DSP) firmware.
Example:
Router(config)# mgcp fax-relay
sg3-to-g3
Configuring CA-Controlled MGCP T.38 Fax Relay
Use the following steps to configure CA-controlled MGCP T.38 fax relay.
SUMMARY STEPS
1. enable
2. configure terminal
3. no mgcp fax t38 inhibit
4. mgcp package-capability fxr-package
5. mgcp default-package fxr-package
21
Troubleshooting Tips for MGCP T.38 Fax Relay
How to Configure MGCP T.38 Fax Relay
DETAILED STEPS
Command or Action
Step 1 enable
Purpose
Enables privileged EXEC mode.
•
Enter your password if prompted.
Example:
Router> enable
Step 2 configure terminal
Enters global configuration mode.
Example:
Router# configure terminal
Step 3 no mgcp fax t38 inhibit
(Optional) Enables T.38 fax relay on the gateway if it has been previously
disabled.
Note T.38 fax relay is enabled on the gateway by default. The command is
Example:
Router(config)# no mgcp fax t38
inhibit
included here to illustrate how you would enable T.38 if it were
disabled by a previous command.
Note If the MGCP gateway uses the auto-configuration function, the mgcp
fax t38 inhibitcommand is automatically configured on the gateway
each time a new configuration is downloaded. Beginning with Cisco
IOS Software Release 12.4T, the auto-configuration of this command
is removed. For MGCP gateways running Cisco IOS version 12.4T or
later, you must manually configure the mgcp fax t38
inhibitcommand to use T.38 fax relay.
Step 4 mgcp package-capability fxr-package
(Optional) Specifies an MGCP package capability type for a media gateway.
•
fxr-package --FXR package for fax transmissions.
Example:
Router(config)# mgcp packagecapability fxr-package
Step 5 mgcp default-package fxr-package
(Optional) Configures the default package capability type for the media
gateway.
•
Example:
fxr-package --FXR package for fax transmissions.
Router(config)# mgcp defaultpackage fxr-package
Troubleshooting Tips for MGCP T.38 Fax Relay
Use the following steps to troubleshoot MGCP T.38 fax relay:
•
•
22
Ensure that you have a working MGCP network and that you can make a voice call.
Ensure that T.38 fax relay for MGCP is configured on both the originating and terminating gateways.
H.323 T.38 Fax Relay with ECM Enabled Example
Configuration Examples for T.38 Fax Relay
•
Use the following commands during the call:
◦
◦
◦
The show mgcp [connection | endpoint | statistics] command displays information about MGCP
calls.
The show voice call summary command indicates, during a T.38 fax transmission, a change of
state from S_CONNECT to S_FAX in the VTSP STATE column and a change from the codec
name to a numeric fax rate in the CODEC column (for example, g711u changes to 14400).
The debug mgcp packets command displays the MGCP side of the call flow.
For CA-controlled T.38 fax relay, you can verify the MGCP side of the call flow by using the debug mgcp
packets command. You should see the following output:
•
•
•
•
CRCX from the call agent with "fxr/fx:t38-loose" or "fxr/fx:t38" parameter
RQNT from the call agent with "R: fxr/t38" parameter
NTFY from the gateway with "O: fxr/t38(start)" parameter (optionally)
MDCX from the call agent with either "m=image" in the SDP message, or "a:image/t38" in the Local
Connection Options message, or both.
For CA-controlled T.38 fax relay, you should see the following messages in the output from a show voice
call summary command on the MGCP gateway during a T.38 fax transmission:
•
•
Change of state from S_CONNECT to S_FAX in the VTSP STATE column
Change from codec name to numeric fax rate (such as "g711u" to 14400") in the CODEC column
Configuration Examples for T.38 Fax Relay
•
•
•
•
•
H.323 T.38 Fax Relay with ECM Enabled Example, page 23
T.38 Fax Relay with ECM Disabled on Dial Peer Example, page 24
Gateway-Controlled MGCP T.38 Fax Relay Example, page 24
CA-Controlled MGCP T.38 Fax Relay Example, page 24
SG3 Fax Support on the Cisco TDM-IP Voice Gateways and Cisco UBE Platforms Example,
page 26
H.323 T.38 Fax Relay with ECM Enabled Example
This example configuration shows T.38 fax relay in an H.323 network with ECM enabled:
.
.
.
voice service voip
fax protocol t38
.
.
.
interface Ethernet0/0
ip address 10.0.47.47 255.255.0.0
h323-gateway voip interface
h323-gateway voip id ipaddr 10.0.47.36 1719
h323-gateway voip h323-id 36402
.
.
.
dial-peer voice 14151 voip
! Uses t38 fax from voice service voip.
destination-pattern 14151..
session target ras
23
T.38 Fax Relay with ECM Disabled on Dial Peer Example
Configuration Examples for T.38 Fax Relay
dial-peer voice 14152 voip
destination-pattern 14152..
session target ras
fax protocol cisco
gateway
end
! Uses Cisco fax for a specific dial peer.
T.38 Fax Relay with ECM Disabled on Dial Peer Example
This example shows ECM disabled on dial peer 50:
.
.
.
dial-peer voice 100 pots
destination-pattern 5550919
port 2/0:D
prefix 5550
!
dial-peer voice 50 voip
incoming called-number 5550919
codec g711ulaw
fax-relay ecm disable
fax rate 9600
fax protocol t38 ls-redundancy 0 hs-redundancy 0
.
.
.
Gateway-Controlled MGCP T.38 Fax Relay Example
The following example shows a configuration for gateway-controlled T.38 fax in an MGCP network. This
configuration uses the defaults for the mgcp fax t38 command and the mgcp timer nse-response t38
commands, so they do not appear in the running configuration presented in the example.
.
.
.
!
mgcp
mgcp call-agent 192.168.195.147 2427 service-type mgcp version 0.1
mgcp dtmf-relay voip codec all mode nse
mgcp modem passthrough voip mode ca
mgcp package-capability dtmf-package
mgcp default-package mo-package
mgcp tse payload 110
no mgcp timer receive-rtcp
mgcp timer net-nse-rsp 300
.
.
.
CA-Controlled MGCP T.38 Fax Relay Example
This example configuration shows CA-controlled MGCP T.38 fax relay.
!
version 12.2
service timestamps debug datetime msec
service timestamps log datetime msec
no service password-encryption
!
hostname tyler
!
boot system tftp project/c2600-is-mz.0711 192.168.222.10
24
CA-Controlled MGCP T.38 Fax Relay Example
Configuration Examples for T.38 Fax Relay
no logging buffered
no logging rate-limit
enable password mary
!
ip subnet-zero
!
!
no ip domain lookup
ip domain name abctrading.com
ip host jackson 192.168.184.144
ip host lincoln 192.168.222.10
ip name-server 192.168.12.13
ip name-server 192.168.12.134
ip name-server 192.168.222.72
!
!
no voice hpi capture buffer
no voice hpi capture destination
!
mrcp client session history duration 0
mrcp client session history records 0
fax interface-type fax-mail
mta receive maximum-recipients 0
!
!
interface FastEthernet0/0
ip address 192.168.191.132 255.255.255.0
duplex auto
speed auto
!
interface FastEthernet0/1
no ip address
shutdown
duplex auto
speed auto
!
ip classless
ip route 0.0.0.0 0.0.0.0 172.16.184.1
ip route 192.168.0.0 255.255.0.0 192.168.184.1
ip http server
ip http port 1111
ip pim bidir-enable
!
!
access-list 101 permit tcp any any
access-list 101 permit udp host 192.168.184.144 any
access-list 101 permit udp host 192.168.222.10 any
access-list 102 permit ip any any
access-list 111 permit udp host 192.168.184.144 any
access-list 111 permit udp host 192.168.191.132 any
access-list 111 permit icmp any any
!
snmp-server packetsize 4096
snmp-server enable traps tty
call rsvp-sync
!
voice-port 1/0/0
!
voice-port 1/0/1
!
voice-port 1/1/0
!
voice-port 1/1/1
!
mgcp
mgcp call-agent 192.168.184.144 3562 service-type mgcp version 0.1
mgcp dtmf-relay voip codec all mode nse
mgcp tse payload 102
no mgcp timer receive-rtcp
!
mgcp profile default
!
dial-peer cor custom
25
SG3 Fax Support on the Cisco TDM-IP Voice Gateways and Cisco UBE Platforms Example
!
!
dial-peer voice 110 pots
application mgcpapp
port 1/1/0
!
dial-peer voice 111 pots
application mgcpapp
port 1/1/1
!
!
line con 0
exec-timeout 0 0
line aux 0
exec-timeout 0 0
line vty 0 4
exec-timeout 0 0
password lab
login
line vty 5 15
exec-timeout 0 0
password lab
login
!
end
SG3 Fax Support on the Cisco TDM-IP Voice Gateways and Cisco UBE
Platforms Example
The following example shows fax protocol T.38 version 3 enabled to provide SG3 fax support:
!
voice service voip
fax protocol t38 version 3 ls-redundancy 0 hs-redundancy 0 fallback cisco
!
!
interface FastEthernet0/0
ip address 1.2.103.1 255.255.0.0
!
!
!
dial-peer voice 100 voip
destination-pattern 1.....
session target ipv4:1.2.103.3
dtmf-relay h245-signal
fax protocol t38 version 3 ls-redundancy 0 hs-redundancy 0 fallback cisco
!
dial-peer voice 200 voip
destination-pattern 2.....
session protocol sipv2
session target ipv4:1.2.103.3
dtmf-relay rtp-nte
fax protocol pass-through g711ulaw
!
dial-peer voice 6789 voip
destination-pattern 6789
session target ipv4:1.2.102.2
dtmf-relay rtp-nte
fax protocol pass-through g711ulaw
!
!
sip-ua
Cisco and the Cisco logo are trademarks or registered trademarks of Cisco and/or its affiliates in the U.S.
and other countries. To view a list of Cisco trademarks, go to this URL: www.cisco.com/go/trademarks.
26
SG3 Fax Support on the Cisco TDM-IP Voice Gateways and Cisco UBE Platforms Example
Third-party trademarks mentioned are the property of their respective owners. The use of the word partner
does not imply a partnership relationship between Cisco and any other company. (1110R)
Any Internet Protocol (IP) addresses and phone numbers used in this document are not intended to be
actual addresses and phone numbers. Any examples, command display output, network topology diagrams,
and other figures included in the document are shown for illustrative purposes only. Any use of actual IP
addresses or phone numbers in illustrative content is unintentional and coincidental.
© 2012 Cisco Systems, Inc. All rights reserved.
27
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