Debugging T30 Fax Messaging
The most frequently used tool for troubleshooting fax relay problems is the IOS command debug fax relay t30 all-level-1. This command displays the T.30 messaging that is passing through the Cisco voice gateway from the perspective of the gateway's DSP. Output that is equivalent to this IOS command can be found on Cisco non-IOS gateways using the procedures discussed at the end of this section.
Before using this command, you should have already determined that the Cisco voice gateways are properly switching over to either T.38 or Cisco fax relay. Otherwise, this debug command might not provide any output. The command debug fax relay t30 all-level-1 should be used only for troubleshooting post-switchover T.38 and Cisco fax relay problems.
Before looking at the output from debug fax relay t30 all-level-1, it is important to understand the direction of the debug messages. Figure 12-20 illustrates how the T.30 debug messages are tagged from a directional perspective by the DSP.
Figure 12-20 Directional Notation of T.30 Messages as Shown in debug fax relay t30 all-level-1
fr-msg-tx
T.30 Message Transmitted by DSP
fr-msg-det
Fax T.30 Message Received by DSP Voice
Machine Gateway
As diagrammed in Figure 12-20, all the messages that are output from debug fax relay t30 all-level-1 are shown from the DSP's point of view as it faces the telephony leg or the gateway's physical voice port. A T.30 message preceded by fr-msg-tx signifies an outgoing message from the DSP, and an fr-msg-det means that a message has been detected by the DSP in the inbound direction.
Example 12-66 shows the output from the command debug fax relay t30 all-level-1 for a two-page fax transaction. All of these T.30 message types were discussed earlier in the book, so see the pertinent sections in Chapter 2 for more information about a specific message listed in the debug output.
Example 12-66 debug fax relay t30 all-level-1 Command Output for a Two Page Fax Transaction
Example 12-66 shows the output from the command debug fax relay t30 all-level-1 for a two-page fax transaction. All of these T.30 message types were discussed earlier in the book, so see the pertinent sections in Chapter 2 for more information about a specific message listed in the debug output.
Example 12-66 debug fax relay t30 all-level-1 Command Output for a Two Page Fax Transaction
|
Apr |
26 12:15:22.578: 0/0/0 |
(39) |
653761544 |
fr |
entered=10(ms) |
|
|
timestamp=653762364 |
fr |
msg |
det CSI |
|||
|
timestamp=653763164 |
fr |
msg |
det NSF |
|||
|
timestamp=653763964 |
fr |
msg |
det DIS |
|||
|
timestamp=653766374 |
fr |
msg |
tx TSI |
|||
|
timestamp=653767174 |
fr |
msg |
tx DCS |
|||
|
timestamp=653772244 |
fr |
msg |
det CFR |
|||
|
timestamp=653824474 |
fr |
msg |
tx MPS |
|||
|
timestamp=653826014 |
fr |
msg |
det MCF |
|||
|
timestamp=653851074 |
fr |
msg |
tx EOP |
|||
|
timestamp=653852634 |
fr |
msg |
det MCF |
|||
|
timestamp=653854804 |
fr |
msg |
tx DCN |
|||
|
Apr |
26 12:16:56.170: 0/0/0 |
(39) |
653855134 |
fr |
end-dcn |
|
The output from the command debug fax relay t30 all-level-1 contains a lot of information in just a few lines. Immediately, you can tell the direction of the call. The CSI, NSF, and DIS messages are always sent by the terminating fax device. In the case of Example 12-66, these messages are marked fr-msg-det, which means that they are incoming into the telephony port of this gateway. Subsequently, you now know that this is the terminating gateway.
The debug output in Example 12-66 tells you that this was a non-ECM fax call. When the ECM feature is not enabled, MPS messages signal the end of pages and EOP signals that no additional pages remain to be sent. The output for an ECM fax call is shown next in Example 12-67.
In addition, you can see that following the MPS and EOP messages, MCF messages are returned. This indicates that pages were successfully exchanged between the two fax devices. At the end of the debug, there is a graceful disconnect ending with the DCN message. Basically, Example 12-66 epitomizes a typical, successful non-ECM fax call.
TIP The output from the IOS command debug fax relay t30 all-level-1 displays only the low-
speed T.30 messages. High-speed messaging such as trainings and page transmissions are not shown. Therefore, if you see a CFR message in the debug output, you can deduce that the training was sent and came through without any problems despite not being able to see the high-speed TCF message. If you see an MCF message, you know that page information was successfully received.
When an ECM fax call takes place, the output from the command debug fax relay t30 all-level-1 contains some minor changes. Because ECM breaks pages down into sections or partial pages, each section is followed by a Partial Page Sent (PPS) message. If PPS messages are seen in the output of debug fax relay t30 all-level-1, you know that an ECM call has occurred. Example 12-67 highlights the output from the command debug fax relay t30 all-level-1 for a two-page ECM fax call.
Example 12-67 debug fax relay t30 all-level-1 Command Output for a Two-Page ECM Fax Transaction
|
Apr |
26 12:11:31.930: 0/0/0 |
(37) |
653530902 |
fr |
entered=10(ms) |
|
|
timestamp=653531692 |
fr |
msg |
det CSI |
|||
|
timestamp=653532492 |
fr |
msg |
det NSF |
|||
|
timestamp=653533292 |
fr |
msg |
det DIS |
|||
|
timestamp=653535722 |
fr |
msg |
tx TSI |
|||
|
timestamp=653536522 |
fr |
msg |
tx DCS |
|||
|
timestamp=653541592 |
fr |
msg |
det CFR |
|||
|
timestamp=653585622 |
fr |
msg |
tx PPS |
|||
|
timestamp=653587272 |
fr |
msg |
det MCF |
|||
|
timestamp=653600032 |
fr |
msg |
tx PPS |
|||
|
timestamp=653601692 |
fr |
msg |
det MCF |
|||
|
timestamp=653614262 |
fr |
msg |
tx PPS |
|||
|
timestamp=653615932 |
fr |
msg |
det MCF |
|||
|
timestamp=653618102 |
fr |
msg |
tx DCN |
|||
|
Apr |
26 12:12:59.474: 0/0/0 |
(37) |
653618442 |
fr |
end-dcn |
|
The command debug fax relay t30 all-level-1 is also useful in diagnosing a number of different fax problems. For example, Example 12-68 highlights a common fax problem involving repeated Failure to Train (FTT) messages. Example 12-68 debug fax relay t30 all-level-1 Command Output Illustrating Corrupted Training Sequences
|
*Jul 17 08:07:34.397: |
3/0 (342) 7397896 |
fr |
entered=10(ms) |
||
|
timestamp=7405782 |
fr |
msg |
det NSF |
||
|
timestamp=7406932 |
fr |
msg |
det CSI |
||
|
timestamp=7407622 |
fr |
msg |
det DIS |
||
|
timestamp=7410702 |
fr |
msg |
tx TSI |
||
|
timestamp=7411842 |
fr |
msg |
tx DCS |
||
|
timestamp=7415832 |
fr |
msg |
det FTT |
||
|
timestamp=7419122 |
fr |
msg |
tx DCS |
||
|
timestamp=7423112 |
fr |
msg |
det FTT |
||
|
timestamp=7426382 |
fr |
msg |
tx DCS |
||
|
timestamp=7430362 |
fr |
msg |
det FTT |
||
|
timestamp=7433642 |
fr |
msg |
tx DCS |
||
|
timestamp=7437642 |
fr |
msg |
det FTT |
||
|
*Jul 17 08:08:24.123: |
3/0 (342) 7447632 |
fr |
end cause unknown 0x4 |
||
Example 12-68 shows a problem where the fax training is getting corrupted and then rejected by the terminating fax machine. The most common cause of a problem such as this is physical errors such as slips on one of the telephony legs of the call.
TIP When using the command debug fax relay t30 all-level-1 on voice gateways with many simultaneous fax relay calls occurring, the output can be confusing to read because all the fax messaging for all calls will be displayed together. In these situations, run the debug command for only the specific called or calling number that you are interested in with the commands debug fax relay t30 called-number or debug fax relay t30 calling-number.
Another example of the variety of problems that can be seen with the debug fax relay t30 all-level-1 command is shown in Example 12-69. Here you can see that messages from the terminating fax machine are being repeated because there is never a response from the originating fax machine.
Example 12-69 debug fax relay t30 all-level-1 Command Output Showing Messages Only from the Terminating Fax Machine
*Apr 23 13:52:43.509: 0/1/1:23 211162261 fr-entered=10(ms) timestamp=211166931 fr-msg-tx CSI timestamp=211167561 fr-msg-tx DIS timestamp=211172031 fr-msg-tx CSI timestamp=211172651 fr-msg-tx DIS timestamp=211177121 fr-msg-tx CSI
Example 12-69 debug fax relay t30 all-level-1 Command Output Showing Messages Only from the Terminating Fax Machine (Continued)
|
timestamp= |
=211177751 |
fr- |
msg- |
tx |
DIS |
|
timestamp= |
=211182211 |
fr- |
msg- |
tx |
CSI |
|
timestamp= |
=211182841 |
fr- |
msg- |
tx |
DIS |
|
timestamp= |
=211187311 |
fr- |
msg- |
tx |
CSI |
|
timestamp= |
=211187931 |
fr- |
msg- |
tx |
DIS |
|
timestamp= |
=211192341 |
fr- |
msg- |
tx |
CSI |
|
timestamp= |
=211192971 |
fr- |
msg- |
tx |
DIS |
|
timestamp= |
=211197371 |
fr- |
msg- |
tx |
CSI |
|
timestamp= |
=211198001 |
fr- |
msg- |
tx |
DIS |
timestamp=211202401 fr-msg-tx DCN
timestamp=211202401 fr-msg-tx DCN
In Example 12-69, the CSI and DIS messages from the terminating fax machine are being transmitted to the originating fax machine. However, there is never a response detected by this originating voice gateway from the originating fax machine.
In the case of the debug output shown in Example 12-69, the reason that this voice gateway is not detecting any messages from the originating fax machine is because of a levels problem. The incoming fax messages from the originating fax machine are too loud and are not understood by the originating voice gateway's DSP.
Although not all levels problems present themselves in this manner, too strong of a signal level can make fax messages unreadable by the voice gateway's DSP. In the case of Example 12-69, adding a decibel drop between the originating fax machine and the originating gateway resolved this issue. For more information about signal levels and loss planning for faxes and modems, refer back to the section "Loss Planning" in this chapter.
TIP Additional fax problems can be diagnosed from the output of the debug fax relay t30 all-
level-1 command. One problem involves an NSF/NSS scenario where fax devices may try to engage in proprietary transactions that break fax relay. Example 12-72 highlights the debugs seen with this issue in the section "NSF/NSS" later in this chapter. Another problem that can be diagnosed with the debug fax relay t30 all-level-1 command is too much delay between the fax endpoints. See Example 12-73 in the section "Handling High Delay" later in this chapter to view sample debug output of this issue.
Non-IOS gateways such as the 6608 and VG248 are also able to display the same information as the IOS command debug fax relay t30 all-level-1. On the 6608 Catalyst blade, the Dick Tracy troubleshooting utility must be used to set the appropriate traces. For more information about the Dick Tracy utility, see the 6608 portion of the "Telephony Troubleshooting" section earlier in this chapter.
The following settings should be used in Dick Tracy for debugging Cisco fax relay calls: 6 set mask 0x323 and 6 set fr-debug 24 1. These settings provide key DSP information and the T.30 messaging. The T.30 messaging shown with these commands is practically identical to the output from the debug fax relay t30 all-level-1 command on IOS voice gateways. Example 12-70 highlights just the T.30 messages obtained from the 6 set mask 0x323 and 6 set fr-debug 24 1 settings using the Dick Tracy utility.
Example 12-70 6608 Dick Tracy 6 set mask 0x323 and 6 set fr-debug 241 Command Output Showing T.30 Messages
|
22 |
06 |
37 |
110 |
(FAX) |
DSP<0> |
Chan<2> |
-> |
2135480 |
fr |
msg |
tx |
NSF |
|
22 |
06 |
38 |
090 |
(FAX) |
DSP<0> |
Chan<2> |
-> |
2136460 |
fr |
msg |
tx |
CSI |
|
22 |
06 |
38 |
790 |
(FAX) |
DSP<0> |
Chan<2> |
-> |
2137160 |
fr |
msg |
tx |
DIS |
|
22 |
06 |
41 |
920 |
(FAX) |
DSP<0> |
Chan<2> |
-> |
2140290 |
fr |
msg |
det |
TSI |
|
22 |
06 |
42 |
640 |
(FAX) |
DSP<0> |
Chan<2> |
-> |
2141010 |
fr |
msg |
det |
DCS |
|
22 |
06 |
47 |
160 |
(FAX) |
DSP<0> |
Chan<2> |
-> |
2145530 |
fr |
msg |
tx |
FTT |
|
22 |
06 |
50 |
120 |
(FAX) |
DSP<0> |
Chan<2> |
-> |
2148490 |
fr |
msg |
det |
TSI |
|
22 |
06 |
50 |
840 |
(FAX) |
DSP<0> |
Chan<2> |
-> |
2149210 |
fr |
msg |
det |
DCS |
|
22 |
06 |
55 |
570 |
(FAX) |
DSP<0> |
Chan<2> |
-> |
2153940 |
fr |
msg |
tx |
CFR |
|
22 |
06 |
58 |
570 |
(FAX) |
DSP<0> |
Chan<2> |
-> |
2153940 |
fr |
msg |
det |
EOP |
|
22 |
07 |
02 |
480 |
(FAX) |
DSP<0> |
Chan<2> |
-> |
2184870 |
fr |
msg |
tx |
MCF |
|
22 |
07 |
05 |
450 |
(FAX) |
DSP<0> |
Chan<2> |
-> |
2187840 |
fr |
msg |
det |
DCN |
In Example 12-70, you can see that Dick Tracy uses the same directional notation for the directions of the T.30 messages as the IOS command debug fax relay t30 all-level-1. Messages coming into the DSP on the T1 or E1 port are coded as fr-msg-det, and outbound messages are shown as fr-msg-tx. In addition, the DSP number and channel number are shown as DSP<0> and Chan<2>, respectively. If a number of fax calls are occurring simultaneously, this extra information allows you to accurately follow the debug messages for a specific DSP and channel.
Example 12-70 also displays how Cisco voice gateways keep the bandwidth consumed by the fax call less than that of the voice codec that is used to initially establish the VoIP call. In this case, the voice codec is G.729, which consumes 8000 bps of bandwidth. Cisco voice gateways by default will then enforce a V.29 modulation, which includes both 9600 bps and 7200 bps speeds.
The originating fax device will always start with the fastest speed within a modulation type. So, a 9600 bps training is sent; but to force the originating fax machine to train down to the 7200 bps speed, the Cisco voice gateway corrupts the 9600 bps training sequence. This is the reason for the FTT in Example 12-70. The next training sequence is at 7200 bps, which the voice gateway allows to pass untouched, and it is confirmed with a CFR.
For the VG248 non-IOS gateway, you can view the T.30 fax messaging by setting the DSP logging level to trace mode. In addition to the T.30 messages, this DSP trace captures other information, too. For the sake of brevity, only the T.30 messages from the DSP trace are shown in Example 12-71.
Example 12-71 VG248 DSP Trace Showing T.30 Messages
|
11 |
23 |
09 |
25 |
14 |
I |
FaxRelay13 |
2591101559 |
fr |
entered (10 ms |
|
|
21 |
23 |
09 |
26 |
13 |
I |
FaxRelay13 |
2591102420 |
fr |
msg |
det CSI |
|
26 |
23 |
09 |
27 |
14 |
I |
FaxRelay13 |
2591103220 |
fr |
msg |
det DIS |
|
45 |
23 |
09 |
29 |
13 |
I |
FaxRelay13 |
2591105850 |
fr |
msg |
tx TSI |
|
54 |
23 |
09 |
30 |
14 |
I |
FaxRelay13 |
2591106650 |
fr |
msg |
tx DCS |
101 23:09:35 14 I FaxRelay13 2591111730 fr-msg-det CFR
148 23:10:24 15 I FaxRelay13 2591160460 fr-msg-tx EOP
172 23:10:25 14 I FaxRelay13 2591162010 fr-msg-det MCF
194 23:10:28 15 I FaxRelay13 2591164580 fr-msg-tx DCN
205 23:10:28 14 I FaxRelay13 2591164920 fr-end 1
101 23:09:35 14 I FaxRelay13 2591111730 fr-msg-det CFR
148 23:10:24 15 I FaxRelay13 2591160460 fr-msg-tx EOP
172 23:10:25 14 I FaxRelay13 2591162010 fr-msg-det MCF
194 23:10:28 15 I FaxRelay13 2591164580 fr-msg-tx DCN
205 23:10:28 14 I FaxRelay13 2591164920 fr-end 1
Example 12-71 shows how the VG248 provides the same output as the 6608 and the IOS gateways with regard to viewing the T.30 messages. This uniformity between platforms ensures that if you know how to read the T.30 messages on one platform you can understand the messages on the other Cisco voice gateways, too.
Post a comment