SPA 112 Data Modem

[PDaltSCADA]

Can anyone suggest how to configure a SPA-112 to optimize for a data modem? (Not Fax)

I have a project that requires the connection of a data modem through a SPA-112 but I have been unable to get the modem to communicate over the ATA connection. I have tested the devices that will be using this connection over two POTS lines and there are no issues. When the initiating modem calls the device connected to the SPA-112 the two modems begin the sync process but fail to negotiate a connection.  Any suggestions to get this system working will be greatly appreciated. 

My current SPA-112 settings are optimized for fax. 

Default settings for all except:

Network Jitter Level: Very High

Jitter Buffer Adjustment: No

Call waiting serv: No

Three way call serv: No

Preferred Codec: G.711u

Use Pre Codec Only: Yes

Silence Supp Enable: No

Echo Canc Enable: No

FAX Passthru Method: ReINVITE

The calling device is a US Robotics Courier 56K Modem. 

The answering device connected to the SPA is a Multi‐Tech 5600ZDX

[Dan Lukes]

You should note that classic analog phone line with 'just lowest standard quality' can carry 9600Bd data only. Line needs to be better than lowest required quality (end-to-end measurement) to be suitable to carry higher speed.

Even with VoIP the end-to-end parameters are very important. Jitter, reliability of IP packet delivery (again - end-to-end) affects resulting speed. Every transcoding on the path harm.

Your settings looks good assuming you are connected in either USA, Japan or one of other few countries using G.711u in public telephony. Use G.711a otherwise.

You didn't mentioned  value of RTP Packet Size - I recommend you to use the 0.010 if your provider can honor your preference, otherwise use the same value your provider is using.

But even best settings may not allow you to connect at high speeds.

Follow either AT Commands for the MT5600/MT5656 Series Products or 56K Softmodem Command Reference - USRobotics (search for +MS command) to limit modulations used to transmit data. I'm sure neither V.90 nor V.92 protocol will work. V.34 may work, but I don't expect it will work reliably. V.32 bis or even just V.32 should work reliably for you. Assuming your IP connectivity is reliable and end-to-end latency is low and stable.

[PDaltSCADA]

Dan, 

Thank you for the reply and I apologize for the late response. We knew this was going to be a long shot. Latency at our location ended up being too high and the connection not stable enough for this setup. We were unable to get a consistent reliable connection. The project will end up going in a different direction. 

Thanks for your time and expertise. 

 PD

[Dan Lukes]

Unfortunately, even 'why it will not work for you' may be best answer available. Glad to hear it has been considered helpful.