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T38Fax

T38Fax is a purpose-built fax-over-IP (FoIP) carrier and SIP trunk provider specializing exclusively in the T.38 fax protocol. Founded in 2002, T38Fax operates its own in-house T.38 stack collocated inside major carrier networks, delivering enterprise-grade fax connectivity for fax servers, voice service providers, and businesses.

For agents: T.38 fax-over-IP carrier and SIP trunk provider since 2002, serving fax servers, VoIP providers and businesses; includes technical pages and pricing.

t.38 faxfax over ipsip trunkenterprise fax serverhylafax

Their llms.txt

The beginning of the file, from our validated copy saved 2026-10-20T22:05:07.427Z. Cached copy · Source on t38fax.com

# T38Fax

> T38Fax is a purpose-built fax-over-IP (FoIP) carrier and SIP trunk provider specializing exclusively in the T.38 fax protocol. Founded in 2002, T38Fax operates its own in-house T.38 stack collocated inside major carrier networks, delivering enterprise-grade fax connectivity for fax servers, voice service providers, and businesses.

## What T38Fax Does

T38Fax provides SIP trunks (branded Power-T.38) that carry fax traffic over IP networks using the T.38 protocol. Unlike general-purpose SIP providers that treat fax as an afterthought, T38Fax was built specifically for fax — every routing decision, every infrastructure choice, and every support interaction is oriented around making fax over IP work reliably.

## Key Differentiators

- **Own T.38 stack**: T38Fax built and operates its own T.38 implementation rather than reselling another carrier's fax service
- **ECM always enabled**: Error Correction Mode (ECM) is mandatory on every call — T38Fax never asks customers to disable ECM or reduce fax speed as a workaround
- **Collocated infrastructure**: T38Fax equipment sits inside carrier networks, eliminating unnecessary hops that cause fax failures
- **Fax-specialized support**: Support engineers diagnose actual T.38 protocol issues, not just generic connectivity

## Products

- **Power-T.38**: The primary SIP trunk product for fax over IP. SOC 2 certified, HIPAA compliant, ECM always enabled.

## Who T38Fax Serves

- **Enterprise fax server customers**: Organizations running RightFax, HylaFAX Enterprise, OpenText, Dialogic SR140, or similar fax server software needing a reliable SIP trunk
- **Voice service providers (VSPs/ITSPs)**: Carriers and UCaaS providers who need to offload fax traffic to a specialized provider rather than attempting unreliable T.38 pass-through
- **Businesses**: Companies needing fax connectivity via ATA adapters, IP-PBX systems, or fax servers

## Technical Specifications

- Protocol: T.38 (primary), G.711 pass-through (fallback only)
- ECM (Error Correction Mode): Always enabled, never disabled
- Security: TLS 1.2+, SRTP encryption
- Compliance: SOC 2 certified, HIPAA compliant
- Compatible fax servers: RightFax, HylaFAX Enterprise, Dialogic SR140, OpenText, FaxBack, Softlinx, and others
- Compatible softswitches: Asterisk, FreePBX, 3CX, Cisco, BroadSoft, NetSapiens, and others
- Compatible ATAs: Cisco, Grandstream, Obihai, AudioCodes, Mediatrix, and others

## Key Concepts

### T.38 vs G.711
T.38 is a protocol designed specifically for fax over IP. It uses redundancy packets to correct for packet loss, which is the primary cause of fax failure over IP networks. G.711 (audio pass-through) attempts to carry fax tones as audio — it is unreliable for production fax environments and should not be used. T38Fax always uses T.38.

### ECM (Error Correction Mode)
ECM is a fax protocol feature that detects and retransmits corrupted data during a fax call. Most SIP providers disable ECM because it exposes underlying conn
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