[cisco-voip] Special considerations for IAD or PRInetwork-emulation on Cisco hardware...

[Jeff Anderson]

I have looked over all of the interfaces for slips and errors and everything
looks clean. We are the ISP for the customer so I have access to both the
CPE side and the PE side. In this scenario the the data T1 on the IAD
recieves clock from the line. The IAD PRI is set to clock source internal.
The PBX is set to clock source line.

If there is a method to picking IOS, I havent learned it. Our requirements
for these devices are pretty basic. Any ipvoice feature set should meet our
requirements.. Does anyone have a preferred IOS version for voice or
specifically 2431 IAD's.

Thanks,

Jeff
On Wed, May 6, 2009 at 4:23 PM, Jason Aarons (US) <
jason.aarons at us.didata.com> wrote:

>  All your questions are around layer1, a show controller or show
> service-module would indicate if clocking or timing or other layer1 issues.
> You have to look at both sides. Your side may be clean but the other side
> dirty.
>
>
>
> Usually a TTC T-Berd with Y-Cable in the middle would help with analysis.
> You can even listen in to troubleshoot.  You can rent T-Berd for a month for
> less than $250 from Renfro Test Equipment (Google).
>
>
>
> Other answers inline
>
>
>
> *From:* cisco-voip-bounces at puck.nether.net [mailto:
> cisco-voip-bounces at puck.nether.net] *On Behalf Of *Jeff Anderson
> *Sent:* Wednesday, May 06, 2009 5:00 PM
> *To:* cisco-voip at puck.nether.net
> *Subject:* [cisco-voip] Special considerations for IAD or
> PRInetwork-emulation on Cisco hardware...
>
>
>
> I have a couple of customers who are experiencing poor audio using an IAD
> to connect their PBX to our h.323 PSTN GW.
>
>
>
> Basic Layout.
>
>
>
> Customer PBX PRI > IAD PRI (Network-emulate) converted to VoIP > MPLS
> enabled T1 > Core > AS5850 (VoIP converted to TDM) > PSTN.
>
>
>
> The customer reports that poor audio is experienced inbound into their PBX.
> They say their outbound audio is okay. This doesnt happen on every call but
> we do have more than one customer reporting the issue.
>
>
>
> The audio can be described anywhere from echo, cutting out or distorted
> audio. The problem has also been reported by users who have 38xx series
> gateways so i dont think the problem is IAD specific. The AS5850 is a shared
> device used by many different customers, the majority of which connect using
> Cisco IP phones and this demographic of customers are not reporting the
> problem.
>
>
>
> I have done packet captures on the AS5850 and there is no packet loss
> reported, the packets arrive in sequence and the jitter is very low.
>
>
>
> In my testing, I have found double-talk to cause the far end audio (AS5850)
> to cut-out. All the packets arrive but they contain a payload value of 7F.
> Some improvement can be made to this condition by disabling non-linear
> progression.
>
>
>
>
>
>
>
> My questions for the community are related to experiences or lessons
> learned from using PRI network emulate.
>
>
>
> Can there be too many echo cancellers in the call flow? (i.e. Customer PBX
> UC500 with Cisco PRI, IAD PRI, AS5850 PRI all with echo cancellers)
>
>  They are usually local link significant. Bad DSP micro code can cause the
> issues you are reporting. I’ve done PCM captures that were good yet the DSP
> turned out to be bad.
>
>
>
> Does the cable length command have any bearing on voice quality?
>
> I haven’t seen the cable length command fix quality issues
>
>
>
> Are there any special commands i should enter when connecting back to back
> wth a T1 cable (echo-cancel coverage, nlp, etc)?
>
> Who is clocking? Network vs user side? Clock slips, line code violations,
> etc  would create the problems you describe
>
>
>
> Is a 2 pair sheilded T1 cable necessary for the PRI back to back connection
> of less than 20 ft?
>
> I always use shielded T1, who knows when EMF will be present? A 1 ft cable
> wrapped around a ballast would be bad..
>
>
>
>
>
> Any insight or suggestions would be greatly appreciated.
>
>
>
> Thanks,
>
>
>
> Jeff
>
>
>
>
>
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