Cisco VOIP Phones dropping External calls

I have a Cisco phone system that was recently installed.  Everything seems to be working fine, but we are having issues with the system randomly dropping external calls.  The call still shows as active but no audio can be heard.  I've got a Gateway router 2821 model that handles all of the call routing, and Cisco Call manager 6.1.1.300-2.  VOIP to VOIP internal calls seem to be fine, and outgoing external calls seem to  not have a problem, but incoming external calls are pretty hit an miss.   Any suggestions?
breckdahlinAsked:
Who is Participating?

[Product update] Infrastructure Analysis Tool is now available with Business Accounts.Learn More

x
I wear a lot of hats...

"The solutions and answers provided on Experts Exchange have been extremely helpful to me over the last few years. I wear a lot of hats - Developer, Database Administrator, Help Desk, etc., so I know a lot of things but not a lot about one thing. Experts Exchange gives me answers from people who do know a lot about one thing, in a easy to use platform." -Todd S.

michofreihaCommented:
it seems a firewall issue...
breckdahlinAuthor Commented:
I thought it might be that as well, but the voice PRI is connected driectly to the router.  Our pix is not an issue with voice data
michofreihaCommented:
can you check if inbound leg is reachcing your firewall and how it treats it?
Powerful Yet Easy-to-Use Network Monitoring

Identify excessive bandwidth utilization or unexpected application traffic with SolarWinds Bandwidth Analyzer Pack.

breckdahlinAuthor Commented:
The calls come directly into the router from the CO.  There are 3 PRI's that are directly connected to the voice gateway router (2821) and from there are sent to Call manager.  the firewall is not in play in this instance
lrmooreCommented:
Is your gateway h.323 or mgcp?
What codec are you using between call manager and the router?
breckdahlinAuthor Commented:
The gateway is H.323

the codec is
codec preference 1 g711ulaw
 codec preference 2 g729r8
lrmooreCommented:
What version Call Manager? Try resetting the h323 gateway in CM?
breckdahlinAuthor Commented:
Cisco Call manager 6.1.1.300-2

I will reset the gateway after close of business today, and let you know
greekstonesCommented:
Hi there

this is a Codec issue. are the phones in the same location?

regards
breckdahlinAuthor Commented:
yes all of the phones are in the same location.

Experts Exchange Solution brought to you by

Your issues matter to us.

Facing a tech roadblock? Get the help and guidance you need from experienced professionals who care. Ask your question anytime, anywhere, with no hassle.

Start your 7-day free trial
It's more than this solution.Get answers and train to solve all your tech problems - anytime, anywhere.Try it for free Edge Out The Competitionfor your dream job with proven skills and certifications.Get started today Stand Outas the employee with proven skills.Start learning today for free Move Your Career Forwardwith certification training in the latest technologies.Start your trial today
Voice Over IP

From novice to tech pro — start learning today.