Product Support Notice © 2011 Avaya Inc. All Rights Reserved.
PSN # PSN003460u
Original publication date: 17-Oct-11. This is Issue #01, published date:
17-Oct-11.
Severity/risk level Medium Urgency Optional
Name of problem Configuring FAX over IP in CS 1000: An Overview
Products affected
Communications Server 1000M and Communications Server 1000E
Problem description
Introduction
Fax support is a commonly used value addition feature on CS 1000. The CS 1000 provides Fax support on both Analog or PSTN and
over VoIP environments.
The CS 1000 supports Standard facsimile operations in an analog or PSTN environment adhering to the ITU published T.30
specification. For complete info on T.30 specification please visit [URL unfurl="true"]http://www.itu.int/rec/T-REC-T.30/e[/URL]
Modern Fax machines typically support two different standards for data transmission rates. The data rates supported by the Group 3
T.30 compliant machines using V.17 are 14400, 12000, 9600 and 7200 bps. The data rate supported by the Super Group 3 compliant
machines using V.34bis is 33600 bps. This bulletin will provide the recommended settings to optimize the system configuration for
both fax and modem support
In VoIP environment it is supported on both SIP as well as H.323. On SIP, T.38 UDP fax is supported. The switchover procedure in
T.38 ANNEX D (D.2.2.4) is used on SIP to establish a fax channel. On H.323, CS 1000 Virtual Trunks support the voice-to-fax
switchover protocol for T.38 fax, by using the mode select signaling. For complete info on T.38 specification please visit
[URL unfurl="true"]http://www.itu.int/rec/T-REC-T.38/e[/URL]
This document is an up-issue to the Nortel bulletin DTR-2007-0280-Global, which describes the Fax over IP support in CS 1000 in
release 5.5 and prior.
Minimum Vintage Loadware Recommendation
Avaya recommends the following MGC loadware as a minimum lineup for best Fax over IP performance:
MGCCBD05
DSP1AB06
DSP2AB06
DSP3AB06
DSP4AB06
DSP5AB06
CS 1000 Fax over IP Support
NOTE: This next section covers protocols and procedures for faxing that apply to Releases 5.0 and newer.
The Virtual Trunk/IP Trunk (ITG) transfers T.30 protocol (G3 Fax) implementations over the IP network. Near real-time operational
mode is supported where two T.30 facsimile terminals are able to engage in a document transmission in which the T.30 protocol is
preserved.
H.323 Virtual Trunks
H.323 Virtual trunks supports the voice-to-fax switchover protocol for T.38 fax, by using the mode select signaling.
First, a voice call is established. When the DSP detects the fax tone, H.245 signaling is exchanged to request the far end node to
change from voice mode to T.38 mode. The existing voice channels are closed and new channels for T.38 are opened. The fax call
then proceeds.
The CS 1000 systems comply with H.323 version 3 with the version 4 extensions necessary for voice-to-fax switchover.
This version standardizes the procedures in switching from voice mode to fax mode.
© 2011 Avaya Inc. All Rights Reserved. Page 2
Note: Some third-party H.323 gateways can use different implementations of protocols to switch from voice to fax. Using
a third-party gateway requires fax interoperability testing of the system. This can be accomplished through participation in the Avaya
DevConnect program ([URL unfurl="true"]www.avaya.com/devconnect)[/URL] by the third party gateway manufacturer.
SIP Virtual Trunks
T.38 UDP fax is supported. The switchover procedure in T.38 ANNEX D (D.2.2.4) is used to establish a fax channel.
A SIP INVITE is made to the called party requesting a voice connection using the basic call setup flow. A voice connection is then
established. Upon the detection of the fax tone (V.21) at the terminating end, the voice channel is replaced by a fax channel using the
offer/answer SDP exchange.
Recommended settings for Best FoIP Performance
The use of the T.38 codec will provide the best Fax performance and success rate on the CS1000 system and is the recommended
codec for all Fax communication. To configure a system to guarantee that this codec is selected for all fax calls requires configuration
changes to the EM Voice Gateway General settings, the EM Voice Gateway T.38 codec settings, the analog stations class of service
and the Fax machine configuration.
If V.34 Fax over G.711 pass-through codec must be used due to a limitation on the ability to reduce the maximum transmission rates
for a V.34 fax machine, the optimum configuration settings are slightly different and will be described in the CS1000 Fax over IP
Configuration setting for V.34 and Modems section below.
CS 1000 Fax over IP Configuration Setting for T.38 (Recommended Settings for all Fax)
Element Manager Configuration Parameters
The CS 1000 uses Element Manager to configure parameters for VoIP and T.38 Fax transmission. The following parameters must be
configured for successful FoIP communications. Additionally, disabling unused voice codecs should be considered a best practice.
V.21 Fax Tone Detection
This option must be checked in order to detect a Fax call and process it as data via T.38. Failing to check this option will cause the Fax
call to traverse the network over a voice codec. The Fax quality and speed may suffer, or the fax may completely fail due to excessive
loss of data.
Modem/Fax Passthrough
This option is configured per gateway and must be selected in order to properly detect modems. When selected, the gateway will
detect and process the modem call as over a G.711 codec that has been optimized for modem passthrough. Failing to check this
option in a gateway with modems will force the calls to traverse the network over a non-optimized voice codec and the modem calls
will fail.
Fax Maximum Rate
This option determines the maximum rate supported via T.38. Currently 14,400 is the highest level supported on Avaya T.38 fax calls.
Fax TCF Method
This option determines where the Training Check function will negotiate with the far end fax machine. Method 2 is the recommended
setting since this transmits the TCF information to the far end fax machine to complete the negotiation. Method 1 uses a local
negotiation and has a lowers the probability of a successful fax transmission.
Fax Playout Nominal Delay
The jitter buffer parameters directly affect end-to-end delay. Lowering the Fax playout settings decreases one-way delay, but there is
less waiting time for voice packets that arrive late.
Note: The default setting for this parameter is 100ms. Complex FAX environments often require this setting to be much lower. Please
consult your Avaya Design and Engineering team for further assistance in determining the optimal setting for Fax Playout Nominal
Delay in your specific network environment.
Fax No Activity Timeout
This timer designates how long the V.21 Fax Tone Detector will look for a fax tone on a specific call. Once this timer has expired, and
no fax tone is detected, the call is switched back to a voice call over the original codec.
Fax Packet Size
© 2011 Avaya Inc. All Rights Reserved. Page 3
Each CODEC can use a specific packet size for the data packets transmitted. This parameter sets the packet size for Fax T.38 data
packets. Avaya recommends that the network be engineered and set to the default of 30 ms.
Settings for each of these prompts are shown below
Analog Station Provisioning for T.38
Fax devices are provisioned as analog devices on the CS 1000. There are two specific options that are required in a Fax over IP
environment in order to detect and pass Fax traffic on T.38
DTN class of service is required for standard DTMF Touch Tone detection.
FAXA designates this device as a Fax device to the system that allows for proper CODEC usage over an IP or ISDN network.
TN 006 0 00 00..............................Terminal Number
© 2011 Avaya Inc. All Rights Reserved. Page 4
TYPE 500 .....................................Analog Station Type
DN 3500.........................................Extension Number
CLS DTN ......................................Digitone (DTMF)
CLS FAXA ....................................Fax Class of Service
CLS MPTD……………………….Will force T.38 codec selection when FAX V.21 preamble is detected
Fax Machine Provisioning for T.38
Error Correction Method (ECM)…………………………….Disable ECM on fax machines
Max Transfer Rate …………………………………………...Limit this to 14400 bps
Negotiation Timeout………………………………………….Set to 4000 ms
© 2011 Avaya Inc. All Rights Reserved. Page 5
CS1000 Fax over IP Configuration setting for V.34 and Modems
Note that these settings can be used in conjunction with the T.38 settings described above to create a system that supports both T.38
Faxes, modems, and point-of-sale terminals. Please pay particular attention to the Analog station CLS of service differences and Fax
machine provisioning differences. Additionally, disabling unused voice codecs should be considered a best practice.
This option should only be used for V.34 Fax machines that are not falling back to T.38 gracefully or cannot be modified to restrict
their maximum data rate to V.17 (14400bps) speeds. The preferred and recommended settings for all fax communications is T.38 as
documented n the previous section.
Element Manager Configuration Parameters
The CS 1000 uses Element Manager to configure parameters for VoIP and T.38 Fax transmission. The following parameters must be
configured for successful FoIP communications using Modem Pass through.
Modem/Fax Passthrough
This option is configured per gateway and must be selected in order to properly detect modems or V.34 fax machines that do not allow
their maximum data rate to be reduced to 14,400bps. When selected, the gateway will detect and process the V.34 Fax and modem
call as over a G.711 codec that has been optimized for modem passthrough. Failing to check this option in a gateway with modems
will force the calls to traverse the network over a non-optimized voice codec and the modem/V.34 Fax calls will fail.
Analog Station Provisioning for V.34 Fax and Modem
Fax devices are provisioned as analog devices on the CS 1000. There are two specific options that are required in a Fax over IP
environment in order to detect and pass Fax traffic over an optimized G.711 codec.
DTN class of service is required for standard DTMF Touch Tone detection.
MPTA designates this device as a modem or V.34 Fax device to the system that allows for proper CODEC usage over an IP or ISDN
network.
TN 006 0 00 00..............................Terminal Number
TYPE 500 .....................................Analog Station Type
DN 3500.........................................Extension Number
CLS DTN ......................................Digitone (DTMF)
CLS FAXD ....................................Fax Class of Service
CLS MPTA……………………….Will use the G.711 codec with optimizations when V.34 modem tones are detected
Note: the MPTA feature is only supported when a Mindspeed DSP is used.
Fax Machine Provisioning for V.34 Fax
Error Correction Method (ECM)…………………………….Enable ECM on fax machines
Negotiation Timeout…………………………………………Set to 4000 ms
© 2011 Avaya Inc. All Rights Reserved. Page 6
DSP and codec selection Behavior
The tables below describe the Codec vs Fax/Modem baud rates supported on both Mind Speed and Telogy DSPs. Note that CLS
MPTA must be configured on units with where modems need to be supported. In addition, MPTA is only supported on Mindspeed
DSPs:
Table 1: Mindspeed DSP Solution (NTDW62, NTDW64, NTDW65, NTDW78, NTDW56, NTDW59, NTDW20)
Codec EM Modem
Detect
EM V.21
Fax Detect
Switch to
T.38
Switch to
Pass-thru
V.34 Fax V.17 Fax
14400
Modem
G.729a N/A N/A V.21 Never Negotiate
down to
14400 over
T.38
T.38 Not Supported
G.723.1 N/A N/A V.21 Never Negotiate
down to
14400 over
T.38
T.38 Not Supported
G.711 On On V.21 ANS,
ANSam
V.34 Speed
via MPT
T.38 V.34
Supported via
MPT
G.711 On Off Never V.21,
ANS,CNG,
ANSam
V.34 Speed
via MPT
Via FPT V.34
Supported via
MPT
G.711 Off On V.21 Never Negotiate
down to
14400 over
T.38
T.38 Not Supported
G.711 Off Off Never Never Best Effort
over G.711
Best Effort
over G.711
Not Supported
Table 2: Telogy DSPs (NTVQ01)
Codec EM Modem
Detect
EM V.21 Fax
Detect
Switch to T.38 V.34 Fax V.17, Fax
14400
Modem
G.729a N/A N/A V.21 Not Supported T.38 Not Supported
G.723.1 N/A N/A V.21 Not Supported T.38 Not Supported
G.711 N/A On V.21 Not Supported T.38 Not Supported
G.711 N/A Off Never Not Supported Best Effort over
G.711
Not Supported
© 2011 Avaya Inc. All Rights Reserved. Page 7
Recommendations
Once a VoIP Fax network is deployed, verification of the initial installation must be performed to make certain the application is
functioning correctly.
The ITU has published for sale under their T.22 specification specific images for use in testing fax transmissions. Avaya recommends
that customers utilize these standard images in all testing to ensure consistent results.
Customers wishing to obtain full size copies of these images should contact the ITU directly.
Network QoS
QoS is a significant factor in FoIP networks. Since T.38 FoIP technology is significantly affected by the overall packet loss, latency
and jitter experienced on a fax call, a network experiencing a degradation of QoS will also experience a degradation of successful
FoIP transmissions. Fax quality starts to degrade when packet loss exceeds 2%. Avaya recommends that fax services be supported
with Virtual Trunk/ IP Trunk 3.0 (or later) operating at the Excellent or Good QoS level used for Voice over IP.
CS 1000 QoS Measurement Tools
These tools are used in the post-installation, day-to-day activities of maintaining an acceptable QoS level for the VoIP network.
Passive tools are used to monitor and report on real-time VoIP traffic metrics gathered from network devices that already collect and
gather RMON information.
To adequately assess the data network on an on-going basis, other more intrusive tools are used to generate synthetic VoIP traffic. The
more intrusive tools are similar to those used to perform pre-sales network assessments.
Avaya recommends customers use a mechanism that provides notification of QoS policy breaches through email, alarm, or page.
CS 1000 Support for FAX Models
Avaya utilizes various test equipment as well as actual Fax machines from various vendors to establish proper Fax inter-working.
It should be noted that some Fax machine manufacturers do not entirely adhere to the published ITU T.30 fax recommendation.
Because of this, fax inter-working cannot be guaranteed 100%.
CS 1000 Support for Modem/Other Models
Avaya utilizes various test equipment as well as actual modems from various vendors to establish data communications. Avaya
recommends all modems be hard-modems (e.g. physical modem or point-of-sale terminal) as opposed soft-modems due to the
superior echo cancellation capabilities of hard-modems.
Resolution
Not Applicable
Workaround or alternative remediation
Not Applicable
Remarks
This bulletin replaces and obsoletes Nortel bulletin number DTR-2007-0280-Global
© 2011 Avaya Inc. All Rights Reserved. Page 8
Patch Notes
Backup before applying the patch
Not Applicable
Download
Not Applicable
Patch install instructions Service-interrupting?
Not Applicable No
Verification
Not Applicable
Failure
Not Applicable
Patch uninstall instructions
Not Applicable
Security Notes
The information in this section concerns the security risk, if any, represented by the topic of this PSN.
Security risks
Not Applicable
Avaya Security Vulnerability Classification
Not Susceptible
Mitigation
Not Applicable
For additional support, contact your Authorized Service Provider. Depending on your coverage entitlements, additional
support may incur charges. Support is provided per your warranty or service contract terms unless otherwise specified.
Avaya Support Contact Telephone
U.S. Remote Technical Services – Enterprise 800-242-2121
U.S. Remote Technical Services – Small Medium Enterprise 800-628-2888
U.S. Remote Technical Services – BusinessPartners for Enterprise Product 877-295-0099
BusinessPartners for Small Medium Product Please contact your distributor.
Canada 800-387-4268
Caribbean and Latin America 786-331-0860
Europe, Middle East, and Africa 36-1238-8334
Asia Pacific 65-6872-8686
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