Interdigit Timeout with Legacy PBX via PRI

Unanswered Question
Oct 9th, 2007

As mentioned in a previous conversation, we've got a Cisco 2821 ISR running CME 4.0(2) which is connected to an Alcatel 4200 legacy PBX. The ISR is a gateway to the PSTN so the Legacy PBX sits behind it, connected via an E1 link (Primary Rate Interface).

In order for the Legacy PBX to reach the PSTN, it adds a prefix ("5432") to each call placed. The ISR then uses this prefix to match an outgoing dial-peer. This configuration has been tested and works fine.

The only snag is that there's a HUGE delay between the last digit being received from the Legacy PBX and the ISR actually placing the call.

On the Serial interface to the legacy PBX we need to run "isdn overlap-received" because the Legacy PBX sends the digits one by one. I've got the "interdigit timeout" on all concerned voice-ports set to 3 seconds. I've also tried playing around with several ISDN timers but no results.

I've tried changing the timeout values but I still get roughly a 15 second delay between the last digit being received and the actual call being placed.

I have this problem too.
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Paolo Bevilacqua Tue, 10/09/2007 - 08:30

Hi,

the issue is related to the need for overlap dialing. If you can configure the outgoing DPs to not use T at least for most calls (this is possible for most countries despite contrary appearance), that should trigger a faster call, because you can configure "isdn sending-complete" on the port connected to PSTN.

Not to mention that you should be able to use # from any phone to indicate end of called number.

However, I would like to see a q931 trace and config, because ultimately, certain timers should kick in anyway.

jaimeatnok Tue, 10/09/2007 - 08:44

I thought "isdn overlap-receiving" might have something to do with it...

I'll post a debug tomorrow morning because at the moment its pretty hectic (many calls in and out) to make any sense of the logs.

Paolo Bevilacqua Tue, 10/09/2007 - 09:34

Ok. The ISDN timer that you want to play with to control interdigit timeout is T302. Please make sure you run an update IOS release like 12.4(11)XJ4 because ISDN bugs are still frequent in IOS.

jaimeatnok Wed, 10/10/2007 - 01:45

I've had a look at the Serial port and the current IOS (12.4(11)T2) doesn't have a T302 timer:

router(config-if)#isdn timer ?

T-Activate Specify Timer T-Activate in milliseconds.

T200 Specify Timer T200 in milliseconds.

T203 Specify Timer T203 in milliseconds.

T301 Specify Timer T301 in milliseconds.

T303 Specify Timer T303 in milliseconds.

T306 Specify Timer T306 in milliseconds.

T309 Specify Timer T309 in milliseconds or 0 to Disable.

T310 Specify Timer T310 in milliseconds.

T321 Specify Timer T321 in milliseconds or 0 to Disable.

T3OOS Specify Timer T3OOS in milliseconds.

I have however run an "debug isdn q931" with "qsig decode" which I've attached to this post.

After point "040559", there's a 10 second delay before the rest of the output is shown.

PS: I've masked the calling number for privacy reasons.

Paolo Bevilacqua Wed, 10/10/2007 - 01:55

Jaime,

I had forgot this, please configure T302 as a parameter for "isdn overlap-receiving". I suggest a value of like 3500.

The interaction with the Portoguese switch is interesting. I will save your trace as certain messages are not seen frequently.

jaimeatnok Wed, 10/10/2007 - 03:01

I'll try this command during the customer's lunch hour as it will cause the least disruption.

For reference, the PSTN is connected to "Serial 0/2/1:15" and the Legacy PBX (Alcatel 4200E) is connected to "Serial 0/3/0:15".

As you can see, the Legacy PBX sends out the digits one by one (thus the need for "overlap-receiving").

Is the interaction with the PSTN different from most other countries? I must admit that I've never seen a log trace from any other ISDN<->PSTN interaction!

Paolo Bevilacqua Wed, 10/10/2007 - 03:22

For sure you need to command on the interface connected to the PBX. It doesn't cause any disruption.

If the PRI has DID, you might need the command on the PSTN interface as well. Try calling from outside, from an analog line. You might see the overlap in there as well.

It is normal that the PBX dials in overlap. Most PBXs outside the US do that. The idea is that it makes calling faster, because the PSTN will send alerting as soon it has accumulated enough digits to route the call.

If you want to make the calling even faster, try configuring DPs without T.

For example, if you know that all cellphones number have fixed length, you can configure an additional DP for them.

You trace has some message that is not widely used, eg advice of charge, reject for facilities, etc.

jaimeatnok Thu, 10/11/2007 - 02:43

I've applied the "isdn overlap-receiving T302 3500" command to the Serial port and according to the person at the customer's premisis, the waiting time seems to have been reduced to about 6 seconds.

Strangely enough, the user reports that no audiable "ringing" tone is heard before the call is established.

I asked him to test this for other phone numbers (mobile and land-line) and this happens for all calls.

Is there a way to insert some sort of "comfort" tone whilst the call is waiting to be established?

Paolo Bevilacqua Thu, 10/11/2007 - 04:44

If you still has switchtype qsig, reconfigure as net5.

If still no ringback tone, under interface going to PBX, configure;

progress_ind setup enable 3

and

progress_ind setup enable 8

You can further reduce T302 timer and interdigit timeout (it seems like they sum up) to reduce post-dial delay.

jaimeatnok Thu, 10/11/2007 - 08:41

Hi,

I've configured the "progress_ind" under the "dial-peer" going into the PBX and from the PBX to the PSTN but still no ringback tone.

Paolo Bevilacqua Thu, 10/11/2007 - 08:58

Hi,

can you take again the trace with "debug isdn q931" and "debug vtsp tone" ?

I would also strongly recommend that you upgrade to either 12.4(11)XJ4 or 12.4(11)T3 before you do this.

jaimeatnok Thu, 10/11/2007 - 09:23

Will do but I'll upgrade to a newer IOS revision before taking the debug.

I'll let you know sometime next week as I'll be doing this on-site!

jaimeatnok Tue, 10/16/2007 - 06:37

Hi,

I don't know if this is related but of all the incoming MSNs, two are forwarded to ISDN FAX machines which are in turn connected to the Legacy PBX.

I've tried sending a few faxes (incoming from the PSTN to the ISR, which is forwarded to the Legacy PBX) and they all get cut off around the 30 second mark. It will just about work with a 1 page long FAX but for 2+ pages they always get cut off.

I've run a debug and it seems the ISR is re-negotiating the bearer capability which arrives as "unrestricted digital". I've tried forcing the bearer-cap to "speech" or "3100hz" under both voice-ports but the incoming faxes still get cut off.

Any thoughts?

Paolo Bevilacqua Tue, 10/16/2007 - 06:52

Hi,

can you send "show controllers e1" and if you have any network-clock commands. You you don't and have E1 slips, that is the reason fax are failing.

jaimeatnok Tue, 10/16/2007 - 06:55

Hi,

I haven't got any network-clock commands, should I configure these for the E1 port connected to the PSTN and the Legacy PBX? I do know that for data E1, one end must be clock-master and the other end clock-slave.

The output of "sh controllers e1" is:

E1 0/2/1 is up.

Applique type is Channelized E1 - balanced

Description: PSTN

No alarms detected.

alarm-trigger is not set

Version info Firmware: 20060711, FPGA: 13, spm_count = 0

Framing is CRC4, Line Code is HDB3, Clock Source is Line.

CRC Threshold is 320. Reported from firmware is 320.

Data in current interval (318 seconds elapsed):

0 Line Code Violations, 0 Path Code Violations

10 Slip Secs, 0 Fr Loss Secs, 0 Line Err Secs, 0 Degraded Mins

10 Errored Secs, 0 Bursty Err Secs, 0 Severely Err Secs, 0 Unavail Secs

Total Data (last 9 15 minute intervals):

0 Line Code Violations, 0 Path Code Violations,

244 Slip Secs, 0 Fr Loss Secs, 0 Line Err Secs, 0 Degraded Mins,

244 Errored Secs, 0 Bursty Err Secs, 0 Severely Err Secs, 0 Unavail Secs

E1 0/3/0 is up.

Applique type is Channelized E1 - balanced

Description: PRI_ALCATEL_4200

No alarms detected.

alarm-trigger is not set

Version info Firmware: 20060711, FPGA: 13, spm_count = 0

Framing is CRC4, Line Code is HDB3, Clock Source is Line.

CRC Threshold is 320. Reported from firmware is 320.

Data in current interval (318 seconds elapsed):

0 Line Code Violations, 0 Path Code Violations

10 Slip Secs, 0 Fr Loss Secs, 0 Line Err Secs, 0 Degraded Mins

10 Errored Secs, 0 Bursty Err Secs, 0 Severely Err Secs, 0 Unavail Secs

Total Data (last 9 15 minute intervals):

0 Line Code Violations, 0 Path Code Violations,

272 Slip Secs, 0 Fr Loss Secs, 0 Line Err Secs, 0 Degraded Mins,

272 Errored Secs, 0 Bursty Err Secs, 0 Severely Err Secs, 0 Unavail Secs

Paolo Bevilacqua Tue, 10/16/2007 - 07:08

Hi,

please configure

network-clock-participate wic 2

network-clock-participate wic 3

network-clock-select 1 e1 0/2/1

this should eliminate the slips.

But I think you also need to provide clock to PBX, so configure clock source internal under controller E1 0/3/0.

jaimeatnok Tue, 10/16/2007 - 07:49

Hi,

This seems to have cleared up the problem, thanks!

RE the IOS upgrade, I'm waiting for Cisco to register the SmartNET package as there seems to be a problem with registering the end user's address so the whole process is being taken care of by Cisco's helpdesk.

I'll let you know after I've upgraded the IOS.

Paolo Bevilacqua Tue, 10/16/2007 - 07:59

Glad to know it helped.

you need to insist with cisco to get the registration done, sometime their system doesn't work and you have to call many times.

jaimeatnok Fri, 11/02/2007 - 04:30

Finally the SmartNET has been registered and I'm furiously searching the Cisco IOS Software Download to make heads or tails out of the never ending list of IOS versions!

At the moment we've got:

- CME 4.0.2(3)

- IOS 12.4(13r)T

We want to upgrade to:

- CME 4.2

- A higher IOS revision but as far as I can see, CME 4.2 is supported only in 12.4(11)XW2 or XW3

It seems that by upgrading to CME 4.2, I'll have to go down an IOS revision....can this be right?

Paolo Bevilacqua Fri, 11/02/2007 - 06:13

You would actually loose only the features that are in 12.4(13)T but not in 12.4(11)T. For telephony, that means none.

If you really want CME 4.2, your only choice is 12.4(11)XW4.

jaimeatnok Fri, 11/02/2007 - 07:04

Yes, I thought so...for the 2821 its actually XW3 as XW4 seems to be for the UC520 and an 17xx series routers.

Where could I find some sort of changelog of telephony features for IOS versions? Navigating the IOS upgrade portal is sometimes frustrating as the information is very patchy.

Paolo Bevilacqua Fri, 11/02/2007 - 07:19

You are right, XW4 has been released for the 1861 only for now.

The changelog you want is the IOS release notes. It lists the new features as bugs fixed.

jaimeatnok Wed, 11/07/2007 - 03:26

Hi,

Yesterday I upgraded the software on the ISR 2821 to the following:

- IOS 12.4(11)T2 to 12.4(15)T1

- CME 4.0.3 to 4.1(0)

However, calls from the Legacy PBX to IP phones are still received without a Caller ID...

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