You may encounter FAX issues when you convert PRI to SIP. Few steps to troubleshoot FAX related issues
1- From
CUCM/ ATA side we need to
make sure T.38 FAX Relay is selected
2- ATA following should be selected
3- CUBE Side
voice service voip
fax protocol t38 version 0 ls-redundancy 0 hs-redundancy 0 fallback pass-through g711ulaw
no fax-relay sg3-to-g3
4- Dial peer add following commands
fax-relay ecm disable
fax-relay sg3-to-g3
fax rate 14400
fax nsf 000000
5- Make sure on CUCM Region is properly configured. If ATA and CUBE are in two different Region, Make this two region codec is properly added.
6 - CUBE you could enable following debugs to see what's happening for fax inbound and outbound
debug ccsip messages
debug voice ccapi inout
debug fax relay t30 all-level-1