We are using SIP Carrier for ourside line that supports FAX T.38 option.
The FAX T.38 option is activated per standard in officeserv and MGI/OAS Card.

We tried to send several faxes but it does not work very well. I don't know if Officeserve is using the T.38 standard.

The question is: how does officeserv know that we are sending a fax or when to switch over to T.38. I didn't find any setting.

Thank you

Jonas

The system and your sip provider should auto negotiate t.38 when they detect fax tones.
You may need to use g711 for your codec rather than g729

Fax over ip I found to be unreliable. We always converted them to vfax (email based send/receive) if the carrier supported it.