Working Examples of T.30 Debugs

Introduction

This document provides two traces: a Cisco IOS® Software debug and a fax analyzer trace. The Cisco IOS debugs work on the Cisco 3660 in Cisco IOS Software Release 12.2(5.8)T and later. Debug formats for this command were improved in later Cisco IOS Software releases, possibly 12.2(7a) and 12.2(5.8)T.

Before You Begin

Conventions

For more information on document conventions, see the Cisco Technical Tips Conventions.

Prerequisites

There are no specific prerequisites for this document.

Components Used

The information in this document is based primarily on Cisco IOS Software Release 12.2(5), although most of the information should also be useful for other Cisco IOS Software releases.

The information presented in this document was created from devices in a specific lab environment. All of the devices used in this document started with a cleared (default) configuration. If you are working in a live network, ensure that you understand the potential impact of any command before using it.

Working Example of the debug fax relay t30 all Command

Originating Router

3660A
Oct 25 14:33:02.001: 6/0:1:8 3698358 fr-entered (10ms)
Oct 25 14:33:03.193: 6/0:1:8 3699550 fr-msg-tx NSF
Oct 25 14:33:03.433: 6/0:1:8 3699790 fr-msg-tx CSI
Oct 25 14:33:04.125: 6/0:1:8 3700480 fr-msg-tx DIS
Oct 25 14:33:05.905: 6/0:1:8 3702260 fr-msg-det TSI
Oct 25 14:33:06.701: 6/0:1:8 3703060 fr-msg-det DCS
Oct 25 14:33:11.201: 6/0:1:8 3707560 fr-msg-tx CFR
Oct 25 14:35:47.261: 6/0:1:8 3863620 fr-msg-det EOP
Oct 25 14:35:49.601: 6/0:1:8 3865960 fr-msg-tx MCF
Oct 25 14:35:51.157: 6/0:1:8 3867510 fr-msg-det DCN
Oct 25 14:35:53.304: 6/0:1:8 3869660 fr-end-dcn

Terminating Router

Oct 25 10:33:01.801: 6/0:1 (8) 3183322 fr-entered (10ms)
Oct 25 10:33:02.885: 6/0:1 (8) 3184410 fr-msg-det NSF
Oct 25 10:33:03.125: 6/0:1 (8) 3184650 fr-msg-det CSI
Oct 25 10:33:03.817: 6/0:1 (8) 3185340 fr-msg-det DIS
Oct 25 10:33:06.205: 6/0:1 (8) 3187730 fr-msg-tx TSI
Oct 25 10:33:07.009: 6/0:1 (8) 3188530 fr-msg-tx DCS
Oct 25 10:33:10.897: 6/0:1 (8) 3192420 fr-msg-det CFR
Oct 25 10:35:47.565: 6/0:1 (8) 3349090 fr-msg-tx EOP
Oct 25 10:35:49.293: 6/0:1 (8) 3350820 fr-msg-det MCF
Oct 25 10:35:51.469: 6/0:1 (8) 3352990 fr-msg-tx DCN
Oct 25 10:35:53.457: 6/0:1 (8) 3354980 fr-end cause unknown 0x1

Working Example of an ECM-mode Fax Analyzer Trace

It is important to know the following information:

• Phase in which the fax transmission error occurred.

• Whether the router or fax machines terminated the connection, and if it was a fax machine, which one.

• What fax protocol events took place prior to the connection being terminated.

An example of the fax analyzer trace for a successful ECM-mode transmission (but with a high error rate) may look like the following:

=====================================================================
#   Phase                   dBm   Elapse Duration Optimum   Size Type
---------------------------------------------------------------------
 0 >> Dialed digits          0.0   -7.909   4.220   0.000     32 DTMF
 1 >> quiet                 --     -3.689   3.689   0.000      0
 2 << Answer Tone          -19.0    0.000   2.938   2.650      0 Tone
 3 << quiet-mod chg    ***  --      2.938   0.153   0.060      0
 4 << NSF, CSI, DIS    *   -17.8    3.091   4.079   3.040    126 FSK
 5 << quiet                 --      7.170   0.558   0.060      0
 6 >> TSI, DCS         *   -13.8    7.728   2.104   1.813     74 FSK
 7 >> quiet-mod chg         --      9.832   0.088   0.060      0
 8 >> V.29 9600 TRAIN  *   -11.3    9.920   1.843   1.655   1853 9600
 9 >> quiet                 --     11.763   1.555   0.060      0
10 << FTT              *   -17.7   13.318   1.437   1.013     50 FSK
11 << quiet            *    --     14.755   0.589   0.060      0
12 >> TSI, DCS         *   -13.8   15.344   2.107   1.813     74 FSK
13 >> quiet-mod chg         --     17.451   0.091   0.060      0
14 >> V.29 7200 TRAIN  *   -11.4   17.542   1.843   1.655   1389 7200
15 >> quiet                 --     19.385   2.078   0.060      0
16 << CFR              *   -18.1   21.463   1.438   1.013     50 FSK
17 << quiet            *    --     22.901   0.626   0.060      0
18 >> V.29 7200 DATA   *   -11.5   23.527  16.390   0.000  14004 7200
19 >> quiet-mod chg         --     39.917   0.069   0.060    256
20 >> PPS-EOP          *** -13.8   39.986   1.353   1.120     43 FSK
21 >> quiet            *    --     41.339   1.853   0.060      0
22 << PPR              *   -17.9   43.192   2.454   1.866     87 FSK
23 << quiet                 --     45.646   0.636   0.060      0
24 >> V.29 7200 DATA   *   -11.2   46.282   1.148   0.000    783 7200
25 >> quiet-mod chg         --     47.430   0.062   0.060    256
26 >> PPS-EOP              -13.8   47.492   1.354   1.120     44 FSK
27 >> quiet            *    --     48.846   1.849   0.060      0
28 << RNR              *   -17.8   50.695   1.437   1.013     50 FSK
29 << quiet                 --     52.132   0.583   0.060      0
30 >> RR                   -13.8   52.715   1.235  15.210     43 FSK
31 >> quiet            *    --     53.950   1.995   0.060      0
32 << MCF              *   -17.8   55.945   1.456   1.013     50 FSK
33 << quiet            *    --     57.401   0.596   0.060      0
34 >> DCN                  -13.8   57.997   1.791   1.013     43 FSK
35 >> Call end         *     0.0   59.788   0.000   0.000      0

1. The exchange of DIS/DCS (CSI,DIS / TSI,DCS) messages:

   • DIS is the initial message stating the capabilities of the answering end. The accompanying CSI frame has the phone number.

   • DCS defines the transmit parameters and starts an image transfer sequence. The accompanying TSI frame has the phone number.

2. The fax machines go into training mode and can attempt more than once to agree on a transmission speed. For instance, the fax machines may first train to a speed of 9600 bps, fail, and then train to a speed of 7200 bps.

In the fax trace output above, the transmission starts with:

1. The exchange of DIS/DCS (CSI,DIS / TSI,DCS) messages:

   • DIS is the initial message stating the capabilities of the answering end. The accompanying CSI frame has the phone number.

   • DCS defines the transmit parameters and starts an image transfer sequence. The accompanying TSI frame has the phone number.

2. The fax machines go into training mode and can attempt more than once to agree on a transmission speed. For instance, the fax machines may first train to a speed of 9600 bps, fail, and then train to a speed of 7200 bps.

3. Successful training is followed by a CFR message.

4. Transmission starts following the CFR message.

5. If there is a high number of errors, a good fax analyzer will detect them.

   Also, if ECM mode is enabled, there will be a high number of retransmissions and partial page request (PPR) messages. When the terminating fax machine considers the error rate too high, it will terminate the connection.

6. MCF is the normal response to an end-of-image message sequence by the receiving end. It indicates that the image was received with less than five percent of lines in error. It is normally followed by the DCN (disconnect) message.

7. If there is no MCF message, the transmission was not completed successfully. It may suggest a high error rate caused by one of the following:

   • Digital line errors (clocking, cabling)

   • VoIP packet loss (queueing, prioritization, fragmentation, compression)

   • Hardware fault

   • Cisco IOS/DSPW incompatibility (rarely occurs)

8. If the DIS or DCS messages are retransmitted several times, it may be that they are not passed across the VoX connection correctly or only passed in one direction—a software or configuration problem.

9. If training repeats multiple times, each time at a lower speed and then the transmission fails, it may be that the fax codec was not loaded and the voice gateways handle the fax transmission as a normal voice conversation, again a configuration or software issue.

Related Information

• Voice - Configuring Fax Relay with VoIP ( T.38)
• Voice and Unified Communications Product Support
• Troubleshooting Cisco IP Telephony
• Technical Support - Cisco Systems