no sound out of the PSTN...

Answered Question
Feb 10th, 2009
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I am calling an external number through a CIPC softphone that is connected to CME. The CME has a dial-peer that goes to an AS5300 gateway. The gateway makes the call out of the PSTN and rings the phone. When I pick up the phone there is dead air. Where should I start to troubleshoot? TIA.

Correct Answer by Nicholas Matthews about 8 years 4 months ago

A number of things:

1) Firewall

2) ACL

3) Routing problems

4) Odds and Ends of routing commands - ip verify unicast reverse source, no ip classless, no ip routing

5) Bad DSP

6) Bad b-channel

7) Errors in the RTP protocol

8) NAT errors

9) VPN ACLs

10) Gateway bugs



-nick

Correct Answer by paolo bevilacqua about 8 years 4 months ago

Do you have a firewall between CIPC and CME, or between routers ?

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Correct Answer
paolo bevilacqua Tue, 02/10/2009 - 08:37
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Do you have a firewall between CIPC and CME, or between routers ?

snickered Tue, 02/10/2009 - 08:51
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Thanks for your reply. Yes, I have access-lists. I didn't even think of that for some reason. Which ports are necessary for sound to travel properly?

snickered Tue, 02/10/2009 - 10:39
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I am suspecting a routing issue. I need a little more information. When I establish a call from my CIPC is the RTP stream going to the gateway directly or is it going to the CME which is redirecting it to the gateway?

Nicholas Matthews Tue, 02/10/2009 - 10:42
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If your CME is using a VOIP protocol to reach another gateway (H323/SIP), then your media will be terminated on CME.


You can check this on your computer fairly easily by installing wireshark.


For hard phones you can go to the website of the phone and it will tell you, but CIPC is on your PC so it's different.



-nick

paolo bevilacqua Tue, 02/10/2009 - 11:00
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Also CIPC has web server that gives you information.

snickered Tue, 02/10/2009 - 11:05
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Do you happen to know which port it listens on? I only show two ports open with TCPView. 56583 which is connected to CME at port 2000 and 58932 UDP which definitely isn't a webserver.

paolo bevilacqua Tue, 02/10/2009 - 11:07
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RTP ports are negotiated dynamically.

Browse to phone address or press ? twice rapidly to get informations about RTP.

snickered Tue, 02/10/2009 - 11:13
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I am talking about the web server that CIPC has. How do I access that?

snickered Tue, 02/10/2009 - 11:34
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I have verified connection between CME and the gateway connected to the PSTN. I setup an access-list on the CME interface:

permit ip host ip.add.of.gw host ip.add.of.cme


and I put an access-list on the gateway:

permit ip host ip.add.of.cme host ip.add.of.gw


The counters go up on both of them. Also, I can ping between the two without issue. Is there something beyond firewall issues that would cause no sound?

Correct Answer
Nicholas Matthews Tue, 02/10/2009 - 12:14
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A number of things:

1) Firewall

2) ACL

3) Routing problems

4) Odds and Ends of routing commands - ip verify unicast reverse source, no ip classless, no ip routing

5) Bad DSP

6) Bad b-channel

7) Errors in the RTP protocol

8) NAT errors

9) VPN ACLs

10) Gateway bugs



-nick

snickered Tue, 02/10/2009 - 13:51
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Alright... it was definitely a combination of firewalls and ACLs. Thanks for your help fellas.

paolo bevilacqua Tue, 02/10/2009 - 13:53
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You are welcome. Thanks for the nice rating and good luck!

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