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ATA Fax Setup Guide

Cisco ATA Fax Machine Configuration

Configure Cisco ATA adapters for fax machines with T.38 support. This guide covers ATA 190, ATA 191, SPA112, SPA122, SPA232D, and similar models.

Important: Fax configuration is different from voice. Incorrect settings will cause fax failures. Follow this guide exactly.
Fax vs Voice

Why Is Fax Configuration Different?

Fax machines are sensitive to the audio processing that improves voice quality. For reliable faxing, we disable these features.

Voice Configuration

  • Echo cancellation: Enabled
  • Call waiting: Enabled
  • Jitter buffer: Medium
  • NAT keep-alive: Optional

Fax Configuration

  • Echo cancellation: Disabled
  • Call waiting: Disabled
  • Jitter buffer: High
  • T.38 fax: Enabled
  • Modem passthrough: Enabled
Setup Options

Choose Your Setup Method

Option 1: Auto-Provisioning (Recommended)

Fax configuration is complex. We recommend letting us provision your ATA with the correct fax settings.

Steps:
  1. Find the MAC address on your ATA
  2. Tell us it's for a fax machine
  3. We'll create a fax-optimized configuration
  4. Set the Profile Rule and reboot
Profile Rule:
<Profile_Rule>http://provisioning.voipplus.net/SIP$MA.xml</Profile_Rule>

Option 2: Manual Configuration

Configure manually using the detailed settings below. Follow exactly for reliable faxing.

You'll need:
  • ATA's IP address
  • Your VoipPlus SIP credentials
  • Patience—fax settings are detailed
Fax Configuration

Required Fax Settings

Access the ATA web interface and navigate to the Line 1 tab. Apply these settings exactly.

Proxy and Registration

Setting Value
Proxy sip.voipplus.net:5060
Register yes
Register Expires 300
SIP Port 5080 (different from voice!)
SIP Transport UDP
Restrict Source IP yes

Subscriber Information

Setting Value
User ID Your fax SIP username (provided by VoipPlus)
Password Your fax SIP password (provided by VoipPlus)

NAT Settings

Setting Value
NAT Mapping Enable no
NAT Keep Alive Enable no

Audio Configuration

Setting Value
Network Jitter Level high
Jitter Buffer Adjustment no
Echo Cancellation Enable no Critical for fax!

T.38 Fax Settings (Critical)

Setting Value
Modem Line yes
FAX Passthru Method ReINVITE
FAX Enable T38 yes
FAX T38 Redundancy 3
FAX T38 ECM Enable yes
FAX Tone Detect Mode callee only

Call Features (Disable for Fax)

Setting Value
Call Waiting Service no Would interrupt fax!
Three Way Call Service no
Fax Tips

Improving Fax Reliability

Use a Dedicated Line

Don't share the fax ATA port with voice calls. Fax needs dedicated configuration that will cause poor voice quality.

Reduce Fax Speed

If faxes fail, try setting your fax machine to 9600 bps instead of 14400 bps. Slower speeds are more reliable over VoIP.

Use ECM Mode

Error Correction Mode (ECM) on your fax machine helps recover from transmission errors. Keep it enabled.

Stable Internet Required

Fax is less tolerant of network issues than voice. Packet loss or jitter will cause fax failures. A stable connection is essential.

Consider eFax

For occasional faxing, email-based fax (eFax) is more reliable than analog fax over VoIP. Ask us about eFax options.

Fax Over VoIP Limitations

Even with perfect configuration, fax over VoIP is less reliable than traditional phone lines. Success rates of 90-95% are typical.

Troubleshooting

Common Fax Problems

Problem Possible Cause Solution
Fax fails partway through Network jitter or packet loss Check internet stability. Increase T38 Redundancy to 5.
Fax connects but sends blank pages T.38 negotiation issue Verify FAX Enable T38 is set to Yes.
No fax tone detected Echo cancellation interfering Confirm Echo Cancellation is set to No.
Receiving faxes fails FAX Tone Detect Mode wrong Set FAX Tone Detect Mode to "callee only".
Intermittent failures Speed too high Lower fax machine speed to 9600 bps.

Need Help With Fax Setup?

Fax configuration can be tricky. Send us your ATA's MAC address and we'll set it up correctly via provisioning.

Call 1-847-984-1184 Contact Support