Revtel direct SIP
From aa-asterisk.org.uk wiki
If you have your Revtel setting on clueless set to 'Direct' you will need to allow the following IP's for SIP or for RTP:
For SIP
213.166.5.129 213.166.5.130 213.166.5.131 213.166.5.135 87.238.72.151 87.238.72.153 87.238.72.154
For RTP
RTP can originate from any of the IP's in the following ranges:
213.166.5.128/26 87.238.72.128/26 87.238.74.128/26
