Source note · Fax and T.38 in cloud calling
In CUBE fax call flows the terminating gateway detects the V.21 preamble and triggers switchover to T.38 with a SIP ReINVITE (or H.323 RequestMode) which CUBE must permit.
Checked 2026-09-24
- Vendor
- Cisco
- Product
- Cisco Unified Border Element
- Subsystem
- fax interworking
- Deployment
- on-premises
- Region
- not restricted
- Release range
- IOS 15.x era (2013 tech note)
- Checked
- 2026-09-24
Sources
- CUBE Third-Party Interoperability Fax Guidelines — Cisco · tier 2 current vendor documentation · CUBE Fax Call Flows section
Cite this note
APA
WarmTransfer. (2026, September 24). Fax and T.38 in cloud calling: source note fax-t38-cube-v21-reinvite-switchover. WarmTransfer. https://warmtransfer.net/knowledge/claims/fax-t38-cube-v21-reinvite-switchover
BibTeX
@misc{warmtransfer-claim-fax-t38-cube-v21-reinvite-switchover,
title = {Fax and T.38 in cloud calling: source note fax-t38-cube-v21-reinvite-switchover},
author = {{WarmTransfer}},
year = {2026},
url = {https://warmtransfer.net/knowledge/claims/fax-t38-cube-v21-reinvite-switchover},
note = {Source note fax-t38-cube-v21-reinvite-switchover, checked 2026-09-24}
}