Note the caveats:

Fax works via G.711 passthrough, not T.38. Hence, the success of fax is sensitive to the network/bandwidth condition.
The configuration on the ATA for fax is specially for fax (e.g. echo cancellation is off), so if you need to do voice call, you need to use the 2nd RJ-11 port and a different SIP line/trunk.

Here are the steps you follow to configure the ATA to use fax via Hoiio SIP:
1. Go to the configuration page > "Quick Setup"
2. Enter the following information:
  • Proxy:
  • User ID: SIP ID (e.g. sip1234567)
  • Password: SIP password we provide


3. Go to "Voice" and select "SIP"
4. Enable "STUN" and set the "STUN server" as:


5. Go to "Line 1" and enable "NAT Mapping" and "NAT Keep Alive"

6.   Under "Network Settings", set "Network Jitter Level" as "High"
7.   Set "Jitter Buffer Adjustment" as "No" and submit


8.   On the next page, enter the following information:
  • Proxy:
  • Outbound Proxy:
  • Use Outbound Proxy: Yes
  • Register: Yes
  • Call Waiting Serv: No
  • Three Way Call Serv: No



9. Submit and go to the next page
10. Enter the following information:
  • Preferred Codec: G711a
  • Use Pref Coded Only: Yes
  • Silence Supp Enable: No
  • Echo Cancel Enable: No
  • Fax Passthru Codec: G711a


11.   Submit and complete the configuration

**To make outgoing calls, follow this standard: <country code> + <area code> + <destination>. For example, if you are calling a Singapore number 1234 5678, key in: 65 1234 5678 and call.

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