Error with unsuported format

Hello, i have a small problem with next error:

[Aug 1 10:33:15] NOTICE[16760]: rtp.c:1288 ast_rtp_read: Unknown RTP codec 100 received from ‘’

This problem is with my FAX machine. I’m using LINKSYS SPA 2102.

Please help, how to resolve this error.

Best regards!

Make sure that your linksys phone isn’t trying to use the g.729 codec. Make sure you configure the phone to use one of the codecs you’ve allowed in your sip.conf file.

you are trying to use a fax machine on a ATA? The results may vary on that, there is a special codec you have to use. This may help or at least give you a starting point


Ok it looks as if your fax is trying to use t30 you need to diable this in the ATA and make sure it only uses g711 or t38 passthough if enabled,