Distorted audio with Yealink Phones and alaw g711a

If you have been searching for a reason why some of the latest Yealink phones have really bad audio when you are using g.711a or a-law codec. Here is the solution you are looking for.

Yealink have got the SIP  rtpmaps the wrong way round for a-law and also u-law.

Correct Mapping:

g.711a  [alaw] is mapped to rtpmap:8

g.711u  [ulaw] mapped to rtpmap:0

Yealink Mapping:

g.711a  [alaw] is mapped to rtpmap:0

g.711u  [ulaw] mapped to rtpmap:8

To correct this you have to use a auto-provision  file and specify the correct mapping in the y0000000xx.cfg file

#######################################################################################
## Audio Codec ##
#######################################################################################

account.1.codec.1.enable = 1
account.1.codec.1.payload_type = PCMA
account.1.codec.1.priority = 1
account.1.codec.1.rtpmap = 8

account.1.codec.2.enable = 1
account.1.codec.2.payload_type = PCMU
account.1.codec.2.priority = 2
account.1.codec.2.rtpmap = 0

Hope that helps someone