One way audio in ATA 186

Unanswered Question
May 29th, 2008
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I am trying to resolve a client issue where the client complained that he is not able to send/recieve fax connected to ATA186.

I connected an analog phone to the ATA port to make calls and found it to be one-way. The ATA side can recieve audio and the other side cannot.

The network is flat, with one 3560 POE switch. All the devices (CM, VG, ATA, IP Phones, PIX) connect to the same switch. All the devices are in the same VLAN. All devices use PIX firewall as the default gateway.

I tested a call from an IP Phone to the ATA, both connected to the same switch. I am attaching the sniffer trace of the call taken simultaneously from the switch ports of the ATA and Phone. I find a confusing thing in the sniffer trace, the RTP packets leaving the ATA are marked to a destination MAC address not matching that of the IP Phone. I dont understand how this change happened. It seems that the packets dont reach the IP phone because of this change. Any help on what could have initiated the change would be helpful.


1. The ARP cache was cleared already, we even changed the switch.

2. We changed the ATA.

3. The destination MAC address to which the packets are sent remain the same even when the ATA is called from a different IP Phone, or a PSTN Phone.



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singhcisco Fri, 05/30/2008 - 11:34
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Make sure the following parameters on ATA are set correctly.

DialTone :: 2,31537,30830,1490,1859,1,0,0,0,1000,0

BusyTone :: 2,30466,28958,1246,1583,0,4000,4000,0,0,0

ReorderTone :: 2,30466,28958,1246,1583,0,2000,2000,0,0,0,0,0,0,0,0,0

RingbackTone :: 2,30830,30466,793,862,0,8000,24000,0,0,0

AlertTone :: 1,30467,0,5970,0,0,2400,800,6400,0,0

CallWaitTone :: 1,30831,0,5493,0,0,2400,2400,4800,0,0

RingCadence :: 2,4,25

abdul ilyas Fri, 05/30/2008 - 12:21
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any chance of ARP poisoning is going over the network? I mean any host on the network doing ARP spoofing in between?? and what the status of mac table on the switch?

aprasanna Fri, 06/06/2008 - 19:00
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Solved the problem by diabling proxy arp at the inside interface of the pix firewall.


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