ECM or not ECM

[a.trueland1]

I have a voice gateway VG320 used for faxing over a SIP provider circuit. I am using fax pass-through.  Should I disable ECM and fax-rate for better reliability?  Having some issues with some faxing to going through.

Current dial-peer:

dial-peer voice 4 voip
 description 7 digit calls
 translation-profile outgoing 1
 destination-pattern 9[2-9]......
 session protocol sipv2
 session target ipv4:10.x.x.x
 dtmf-relay rtp-nte
 codec g711ulaw
 fax protocol pass-through g711ulaw
 no vad

voice service voip
 no ip address trusted authenticate
 allow-connections h323 to h323
 allow-connections h323 to sip
 allow-connections sip to h323
 allow-connections sip to sip
 fax protocol pass-through g711ulaw
 sip
  registrar server expires max 1200 min 300
  early-offer forced

[Brandon Buffin]

I don't think disabling ECM will help as it is only relevant to fax relay. Essentially fax passthrough allows the fax call to be passed through as a normal voice call. The problem is fax is very sensitive to delay, jitter, etc. Any dropped/out of order packets will cause the fax call to fail. I've seen a number of problems with fax over SIP. I have not seen a solution that solves them completely. If possible, my recommendation is to remove fax from the SIP scenario by moving the fax lines to POTS/PRI.

Brandon

[a.trueland1]

Thank You.  I do miss POTs lines for Faxing. Unfortunately my organization is strict with no POTs lines for this configuration.  All of our medical faxing is going over this voice gateway.  I am constantly chasing down offices that don't get full faxes delivered.

I understand ECM gets negotiated between the faxes in-band for pass-through.  So  disabling ECM has no affect on this is that correct?

[Brandon Buffin]

Yes, that is correct.

[a.trueland1]

Thank You.