'iax2 show netstats' sometimes gives negative figures


We run an Asterisk PBX for a client who we think has horrible quality networking up to their floor as the amount of lost packets and jitter means that they are constantly having dropped calls. In aid of this we have enabled the IAX jitter buffer, however sometimes when running ‘iax2 show netstats’ at the CLI, we get negative figures for the ‘lost packets’:

ipbx*CLI> iax2 show netstats
                                -------- LOCAL ---------------------  -------- REMOTE --------------------
Channel                    RTT  Jit  Del  Lost   %  Drop  OOO  Kpkts  Jit  Del  Lost   %  Drop  OOO  Kpkts
IAX2/vt-foo-6          1000    9   62 -3231   0     0    6      4    0    0     0   0     0    0      0

This figure rapidly then increases until the call drops. Does anyone know why this might be giving a negative figure, and is it meaningful? The ‘RTT’ figure is almost always 1000 too, which is weird.

Thanks for your time.

EDIT Sorry I just realised how messy the pasted code is… basically what it’s saying is ‘Lost’ (under the ‘LOCAL’ header) is -3231.

UPDATE 11/06/08 By running some decent cabling downstairs, we discovered the packet loss was indeed due to shoddy cabling to their floor. However, this genuine packet loss manifested itself as positive packet loss (up to 15%) resulting in very bad voice quality.
In aid of this we had previously purchased some G729 channels and activated the IAX jitter buffer which solved the voice quality issues in absence of decent cabling, however it resulted in what the client was describing as “dropped calls”. HOWEVER…

On further inspection the calls weren’t being dropped, Asterisk would just inexplicably stop sending it’s RTP stream to the UA (confirmed with packet trace) which meant the client couldn’t hear the person at the other end, although audio in the other direction was fine and the call remained up. When this happened, the “Lost” packet reading would shoot into the negatives and keep rising until the point where the client got frustrated and hung up.

We still don’t know what is causing Asterisk to do this (anyone???) but it has only been a problem since we activated the jitter buffer and so I have disabled this along with G729 in the hope that our decent cabling will solve the voice quality issues by itself. Will know whether or not this solves the problem by tomorrow evening… does anyone know of any bugs in the 1.4.19 jitter buffer, or is there any information I can provide to help nail this down?