Call quality problems, please help troubleshoot

Hello: I’m new to this forum and new to Asterisk. We have implemented an Asterisk based IP PBX sold to us through an IP PBX vendor. We continue to have terrible call quality. To date, we have been unable to locate the source of the problem/s in order to correct them. I would truly appreciate any feedback emailed to me, etc. from someone willing to read the following summarization of our configuration and offer any advice:

We have the following:
T1 1.5Mbs up/down with a newer Cisco rack mount T1 router. T1 provider shows zero packet loss/drop on their end when viewing their reports.

Dratek Vigor 3300 series VOIP router; we’ve tried both enabling and disabling the Qos function of this router/firewall.

IP PBX server with Pentium 4 CPU, 1Gb RAM and Digium TDM400 analog PCI card. Inbound calls come in through the analog PCI card or SIP lines depending on inbound DID #. All outbound calls are VOIP through a SIP provider (SIP lines purchased through IP PBX vendor).

Polycom 601 hard phones and Counterpath softphones (quality issues same on both)

IP PBX vendor says problem is with T1 provider and T1 provider says problem is with our configuration.

I realize their is certainly more information necessary for anyone to help offer a diagnosis so I apologize in advance for not being more descriptive or helpful in providing such info. emails, etc would be appreciated.

Please help with any advice. Thank you.


You need to break this down.

Is call quality OK on th elan phone to phone.
are calls in on the TDM400 OK ?
Is the problem on both incoming and outgoing calls over sip

Oh and what is the vigor doing if the T1 terminates on a Cisco ?


Thank you for the quick response.

Pardon my ignorance, but by “elan” I assume you mean extension to extension. We have four physical locations (one of which has the IP PBX). When dialing extension to extension within the location of the IP PBX or from an outside location extension to an in-IP PBX-office extension, call quality is degrated. Our quality issues occur when our bandwidth exceeds on average, 400kbs (we’ve never come close to maxing out bandwidth on our 1.5 T1); at any rate, yes, quality is also bad on extension to extension if our bandwidth is over the 350-400kps mark.

The TDM400 is used only as the location with the IP PBX and our published DID line is connected to the TDM400. Only inbound calls from that server location are handled through the TDM 400. Yes, inbound calls coming in from the TDM400 are bad.

Yes, problems on both incoming and outgoing SIP calls

Vigor was recommended to us by vendor. T1 Cisco router is “wide open” providing no firewall or Qos. We purchased our data only T1 through a telecom provider that specializes in providing integrated voice/data T1. Obviously we didn’t purchase any communication services through the T1 provider (IP PBX for that) but the T1 provider was willing to sell us a data only T1. That’s why no Qos through the Cisco.

I hope that helps a bit more. The location with the server is not a heavy bandwidth user. If there is only one or two simultaneous calls…no quality issues; but if 4-5+ calls at the same time (max we’d ever have at once would be less than 10.

Also, we purchased and had enabled G729 codec for all lines in the hope of flying under the mysterious ceiling of that 350-400kbs in which call quality degrades dramatically…no change by doing this.

To describe the actual quality problems: some echo, rarely jitter, mainly dead/dropped sections of conversations (heard by both callers on either end of the conversation) lasting as long as 1-2 seconds at a time.


If [quote]The TDM400 is used only as the location with the IP PBX and our published DID line is connected to the TDM400. Only inbound calls from that server location are handled through the TDM 400. Yes, inbound calls coming in from the TDM400 are bad. [/quote] these are calls to users on the same site as the PBX then the PBX is the issue.

What is the hardware ? and what does “show translation” say.


Are you saying that since DID calls from the one analog line that we have running through the TDM400 card into our server which are only calls answered by the one of our four locations (all other three locations are SIP and not related/do not utilize the analog line going into the TDM400 card) is an INDICATOR that because of the bad call quality on those specific calls, our PBX is the problem in relation to ALL calls (even calls having nothing to do with PSTN inbound through the TDM400 such as SIP?)

I hope I’m explaining things correctly. Only one phone number at one specific location which is used by clients calling inbound to that office (which also happens to house our IP PBX with the TDM400) - that one phone number/line is the analog line. All outbound calls, all calls from location to location/extension to extension are SIP. All calls when traffic reaches that 350-400kbs bandwidth level are of unacceptable broken quality.


If all your traffic as you have explained goes out over the T1 via the IPPBX and unless you are allowing the traffic to reinvite (which I doubt) and all locations extensions are of the IPPBX then is safe to say that the problem is with the IPPBX or its lan segment.

The T1 is out of the equation as a Local call from the server to a phone on the lan has the problem.

You dont say what lan you have or hardware o the server. but I assume you have a managed layer2 switch so you may get some stats from that.