SIP Media Negotiation Failed

[Bigblue886]

Hello,
I have a few Cisco SPA112 ATA units connecting to our 3300 for our fax machines. I configured the ATA's and the 3300 per Mitel's knowledge base article regarding the configuration of the ATA's and I am having issues where either the call will fail midway through or incoming calls will not come in at all. I checked the logs and there are several entries for the fax lines "Media Negotiation failed on call from 3793 to 55512345 (transport or codec mismatch)" I've double checked the configurations and everything appears to be right. Any ideas?

[scottbunby]

Hi Bigblue886
Did you ever get to the bottom of this?

Thanks

Scott

[Dogbreath]

Have you checked the RTP Packet Size on the ATA? I found that SPA112 defaults to 30ms, MCD and our usual SIP trunk provider defaults to 20ms. This led to inbound calls working but outbound not, until I corrected the ptime on the ATA to match. I spent ages going nowhere with CoR and CoS until a packet capture led me to the answer.