"rtp.c unknown rtp codec 126 received from" error in asterisk

We have received an error while trying to forward a TDM call to a softphone like XLite through Asterisk. After a lot of struggle, we have figured out the answer as below,

1. Turn off your firewall settings (both Asterisk server)
2. Use the same audio codec you are using in the asterisk.
3. Configure your softphone in asterisk sip.conf as below,

  

[101]

type=friend
username=101
secret=101
host=dynamic
context=init ;my context name. give yours if you want to.
nat=yes
disallow=all
allow=GSM
allow=alaw
allow=ulaw

 4. Make sure that you are using the same codec in your softphone preferably GSM.
 5. It worked like a charm.

Thank you!