Calls dropping


I have a system in, pure voip. No analogue / ISDN lines.

There are 5 people in the office and they make and receive around 100-200 calls a day.

However, about 1-5 times a day, a call is dropped. It might be incoming, it might be outgoing.

Where can I begin to troubleshoot this?

Could it be resources? The reason I ask is because it is running on a relatively low spec ‘green PC’.

Asterisk 1.4.13 / GSM Codec
Celeron 215 @ 1.33GHz / 512Kb Cache / CPU MHz 1333.468
512Mb RAM
Swap 0K used.

I just looked at ‘top’ for a few minutes and it peaked at %CPU = 4.0 and %MEM = 2.0

Feedback appreciated.

It is more likely to be network and most likely to be the Internet connection. What sort of connection do you have for voice to the Internet and is it dedicated or shared with other data access? What sort Router do you have? Does it support QoS? Does your network switch support QoS?

Hi Lee,

Thanks for your help. Client has a cable internet connection which is 4mb down / 512k up. I am sure it is shared but do not know the contention ratio. This is also shared as their standard internet connection for approx 5 PC’s.

They are using a Draytek Vigor 2800 router with 80% of the bandwith allocated to traffic to and from the Asterisk server.

Call quality is fine, but calls drop too frequently.

Any help appreciated

** I edited upstream speed as it between 512kb and 768kb

Do they have a network switch capable of supporting QoS? How does the Draytek handle the bandwidth commitment? Is it simply by IP address or does it use DSCP (ToS byte)? If it’s a cable connection then it might only be 50:1 which would not be good for call drops, etc. Are you using G.729 for your connections to the service provider on the Internet?

Hi Lee,

I have configured the QOS settings on the Draytek using IP addresses only. Anything to or from Asterisk and anything to or from the ITSP server is prioritised. The router does support other QOS configs, should I be learning how to use them :smile:

I am using gsm codec on LAN and WAN which is only a little bigger than g729 isn’t it.

I must say, I don’t understand why call quality is fine, then the call drops. I thought a degradation of quality would be experienced first and ultimately a drop but that isn’t whats happening.

Can you recommend any troubleshooting steps?


Are the links IAX or SIP ?



Are the links IAX or SIP ?


IAX (Gradwell).


IAX relies on timing, and if the timing sliips then the call will drop. run the iax debug, also zttest. But on a “poor” link you wil get drops if the lag or timing is out


OK Thanks Ian, so the reason I have not seen this before could be because in other systems I have always had a card present to provide timing? (Do Sangoma cards control timing like Digium cards?).

With no card, there is no reliable timing source and this could contribute to the calls dropping?

I guess a possible solution be to change to SIP for my Gradwell trunks?

Thanks for your help.

I have used IAX provided by Gradwell and had similar problem. I switched to SIP and the majority of problems disappeared.

I will try SIP and let you guys know how I get on.

Thanks for your help.