After connecting up the ATA as the analog gateway device, and making sure that adequate bandwidth exists, you may want to take advantage of some of the configuration changes that will help ensure the best possible result when faxing. *Ensure that your device is running the latest firmware.
- Select Voice in the Menu Bar, and then select either Line1 or Line 2 depending on which line you have used for your fax, then select Network. Set the Network Jitter Level to very high and the Jitter Buffer Adjustment to no.
- Next, in the Supplementary Service Subscription section, select the following settings; Call Waiting Serv to no and the Three Way Call Serv to no.
- Navigate to the Audio Configuration section and enter the following settings to support T.38 Fax Preferred Codec; G.711u (USA) or G.711a (rest of the world). Select Use pref. codec only as yes, Silence Supp Enable as no, Echo Canc Enable as no,and FAX Passthru Method as ReINVITE.
- Click Submit to save your settings
- Since you are are using the Cisco media gateway for PSTN termination; then disable T.38 (fax relay) and enable fax using modem passthrough. For example:
modem passthrough nse payload-type 110 codec g711ulaw. Next set fax rate to disable, and fax protocol pass-through to g711ulaw
Note: If a T.38 call cannot be set-up, then the call automatically reverts to G.711
fallback. - Verify that your fax machine BAUD rate is set to a speed between 7200 and 14400. We suggest 9600. Try to fax as a test and make sure it completes.
- Voice -> SIP
- RTP Packet Size: 0.020
- Voice -> Line 1 [or 2]
| Preferred Codec | G711u | Second Preferred Codec | G711u |
| Third Preferred Codec | G711u | Use Pref Codec Only | yes |
| Silence Supp Enable | no | Silence Threshold | medium |
| G729a Enable | yes | Echo Canc Enable | no |
| G723 Enable | yes | Echo Canc Adapt Enable | no |
| G726-16 Enable | yes | Echo Supp Enable | no |
| G726-24 Enable | yes | FAX CED Detect Enable | yes |
| G726-32 Enable | yes | FAX CNG Detect Enable | yes |
| G726-40 Enable | yes | FAX Passthru Codec | G711u |
| DTMF Process INFO | yes | FAX Codec Symmetric | yes |
| DTMF Process AVT | Yes | FAX Passthru Method | ReINVITE |
| DTMF Tx Method | Auto | DTMF Tx Mode | Strict |
| DTMF Tx Strict Hold Off Time | 90 | FAX Process NSE | yes |
| Hook Flash Tx Method | None | FAX Disable ECAN | yes |
| Release Unused Codec | yes | FAX Enable T38 | yes |
| FAX T38 Redundancy | 1 | FAX Tone Detect Mode | caller or callee |
In addition to above, you will want to use the following settings:
- Source: cisco manual
On the Same Line Tab:
- Network Jitter Buffer: very high
- Jitter buffer adjustment: disable
- Call Waiting: no
- 3 Way Calling: no
- Echo Canceller: no
- Silence Suppression: no
- Preferred Codec: G.711
- Use Pref. codec Only: Yes
