SBC w/ Encryption + FXS Gateway + Outbound Faxing?

[mujin1]

Hi,

I haven't tried this myself but I am using SBC with encryption.
I am just wondering if anyone has tried to use a FXS gateway for fax sending with this configuration before. Is so which model did you use?

Thank you.
Carl

 

[eddv123]

Hi Carl,

Note: This is not a supported setup and would recommend you use a VPN connection.

With that being said, I have successfully setup Grandstream, Patton, Mediatrix and beroNet gateways via the SBC by simply changing the configuration files PBX address to that of the SBC - but this was for standard FXS endpoints only.

Setting up remote FAX can be a real issue and I would suggest you save the headache and just opt for an online FAX service (unless your customer desires this for business/legal reasons).

As far as encryption is concerned I guess you mean using encryption across the SBC - this is an added security layer, and security and encryption is another benefit you would get if you used the VPN option anyway.

The only way I have heard of (not deployed myself) of getting this working is by using G.711 Pass-through (not T.38) for FAX directly on an extension (the old school FXS way) on the PBX but even if you did get this working you would not get the encryption you desired.

 

[cobaltit]

Do note that the encryption provided by the SBC is nothing compared to the encryption you would get via VPN. It's a basically a slight obfuscation of the traffic so it's not recognizable as SIP.

More specific to the OPs question is no I don't make a habit of setting up unsupported scenarios since I like my customers. That being said the ATA is of little relevance to your question. The SBC doesn't mangle the SIP traffic so any ATA that works well will work well and any ATA that doesn't won't in any configuration.

 

[eddv123]

The main issue that you will have using FAX with a remote SBC or STUN (which you would not get with a VPN) is that it will add more conversions in the path between the FAX machine(s) this is normally the route cause of any issue you get with FoIP (FAX over IP).

For example, a slow SIP response caused by the sheer amount of protocol conversion can (for example) result in T.38 re-INVITE failure (if using T.38 and not G.711).

As standard to fix such an issue you can look at your network and attempt standard VoIP delay troubleshooting techniques. Try and reduce jitter, bandwidth and packet loss – employ some QoS techniques into the network possibly.

G.711 would give you more of a chance as I said in my previous post however here are some points to note about this:

· Simple protocol.
· Real time.
· G711 is like a VoIP call.
· Uses RTP and RTCP.
· Faster than T.38 with SG3.
· Sensitive to delay, jitter and packet loss.
· Likes to eat bandwidth.
· Only codec option cannot compress.
· Can secure with SRTP.


Code issues (if using G.711) G711 is the only codec that works in pass through mode as it is non-compressing. V.21 Fax messages only run at 300bps so in theory a low bitrate codec such as G.729 could carry them also.

 

[mujin1]

Hi Everyone,

Thanks for the response. Its pretty clear now.

Best Regards,
Carl

 

[accentlogic]

Hi Everyone,

Thanks for the response. Its pretty clear now.

Best Regards,
Carl

Another option you might look at is fax over HTTPS. It won't go through 3CX at all, but works great. Several 3CX SIP providers offer these, including SIP.US, SIPTRUNK.COM, and Vitelity. They use an AudioCodes MP-202 ATA and enable your fax machine to send and receive faxes - plus you can use the web portal and maintain compliance, or email to send/receive if you don't need secure fax.

 

[cobaltit]

We also provide HTTPS fax and it saves a lot of headache over supporting ATAs, even with T38.