Dumb question on fax server ext 888

Discussion in '3CX Phone System - General' started by FGCUHank, Feb 4, 2011.

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  1. FGCUHank

    FGCUHank New Member

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    We have a licensed, not free, version of 3cx in the office and I was looking at setting up the inbound fax server. Just on a whim I dialed 888 from my desk phone and, according to the management console, was connected to 888.

    Dumb question is should I have heard the old traditional fax screech sounds or is the whole game different with T.38?

    Lastly, if someone has this setup and would recommend a US provider I would be grateful. I have voip.ms and voipvoip as sip trunk providers but neither provide T.38

    Just looking to have one inbound fax line.

    Thanks
     
  2. abc123

    abc123 Active Member

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    No you wont hear the tones.

    G711/G729 audio is different to t38 so it will be deathly silent. Which also means you cannot answer a call on your phone and then forward it to a fax machine

    I wont go into full details but briefly the way it works is
    A call comes in to your fax number (no one knows at this point it is a fax) as a normal call
    It is routed by your provider to 3cx
    3cx looks at the invite and determines by your inbound rules that it is going to the fax server and that you are using t38
    3cx sends a reinvite back and tells the provider (not the caller) to use t38 for this session
    the provider switches to t38 and the fax does its stuff.

    When you try to dial from your extension to 888 then the same thing happens. Only now your phone has been told to switch to t38 and the fax tones are being sent using that protocol. Your phone does not understand t38 and does not even bother to decipher the tones - hence silence.

    Now if you had a t38 fax number routing to the inbound fax server you could dial it from your cell phone and you would hear the tones.

    For the USA we use Broadvox for our phones and they do T38. We have also heard Nexvortex support T38 too.
     
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  3. FGCUHank

    FGCUHank New Member

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    Thank you for the reply Mark, it clears it up.

    I have a call into Nexvortex and will inquiry with Broadvox.

    Am I correct in assuming that once you have the provider, such as Broadvox, then I could send outbound with a device connected to an FXO gateway that routed the call across that provider?

    All the best.
    Hank
     
  4. abc123

    abc123 Active Member

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    With some providers yes - others no. We are a Broadvox Authorized agent so contact us if you want a lot more details.

    We use Broadvox to send faxes and receive them (in fact we have one of our customers with 24+ inbound fax numbers with Broadvox and 3cx).

    To send a fax with 3cx (and I will probably have Brian or Michael email me for this lol) you need to set up a device like the SPA2102 or 3102. I have no problems with these but 3cx are no longer providing outbound fax devices and i dont think they support it (I cannot speak for them but i dont think they want to work with faxes until it gets more stable).

    I connect the 2102 or 3102 (these are my preferred choices there are others that work too) as a fax machine in 3cx NOT an extension. in V9 there are fax machines in the left menu where you can add more. I dont do anything else and it works nicely. Occasionally we have a small problem and need to resend.

    They used to (and I have it installed) also have a fax device set up to work with 3cx and MS Fax Server on Windows Server where you can fax from your pc etc. but it is not there any longer. I liked it and mine works. But i guess as they provided it, people expected support which they could not do so they dropped it.

    You can also use a 2102 or 3102 directly to the t38 provider. You register the provider just the same as you would register an extension but you use the provider information and bypass 3cx. There are more problems this way. And companies like broadvox dont like you using the same registration information from two ip/port combinations so will drop off. Others may like it so wont be a problem.
     
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  5. igor.snezhko

    igor.snezhko Active Member

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    Interesting... Another dumb question ;-).

    Why the T.38 provider or PSTN Gateway cannot switch "on the fly" from T.30 (i.e. "tones") to T.38?

    That way you can answer normal call first, but when calling party press "Send" on it's old FAX Machine, you can transfer this call to 3CX 888 FAX.

    Theoretically, gateway or provider should recognize that fax tone and "switch" on T.38 (if settings allow this).

    But at real word I cannot implement this behavior :cry:
     
  6. abc123

    abc123 Active Member

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    Because (as I mentioned in the reply above) there needs to be a re invite sent for t38 protocol.

    Once the initial call comes in on an invite and 3cx sees it as a normal call to a normal extension then the extension rings and answers the provider and 3cx are no longer looking at invites they are dealing with the call. And end of transmission signal stating the other end has ended it.

    So there is no way a re invite is able to be sent halfway through a call to switch to another protocol.

    It is similar to transferring a call to another extension or external number. the voip provider is not aware of this nor is another invite sent. 3cx takes the incoming call then sends an invite to the other number. If it is external the call comes in and then goes out - not bypassing 3cx but going through it (you have to be aware of this as it ties up CCS lines both internal and external).

    So once a call is in progress it sticks to the protocol. transferring voice to voice is easy but not voice to t38 halfway through.

    Follow me?
     
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  7. igor.snezhko

    igor.snezhko Active Member

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    Yes!

    I slightly changed my post, because it was incorrect.

    The idea, that a gateway, not 3CX, choosing a protocol for a FAX. In all gateways I have seen, I can set a protocol type manually. (T.30, T.30 Native, T.30 Bypass, T.38. T.38 Native).

    So, why this gateway cannot switch on T.30 automatically, if 3CX Fax server report, that it can support it?

    So a gateway FXO port will switch on T.38 "on the fly"!
     
  8. abc123

    abc123 Active Member

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    Ahh but if I am correct in what you are saying...

    an analog gateway is doing the changing. Well it isnt negotiating with anyone as it has a direct connection to the phone on the other end. An analog signal is coming to the gateway and the gateway fxo is changing how it sends information. It answers the call and then based on the tone it receives it decides if it is a fax tone and so sends the fax on to the pbx. It negotiates a t38 wth 3cx immediately on invite not switching through (though t30 and t38 are similar).

    But 3cx never gets a tone. It cannot connect to an analog line directly and "listen". It is only ever given sip headers not waveforms. So it has to go by what is in the header. and then the invite is ok (200 status) it cannot change.

    If you look at an audio call, the invite may come from one ip (the voip provider) but the data (RTP) goes somewhere totally different (usually a PSTN gateway on a carrier) so no more changes to the sip header as it is not in the loop.
     
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  9. igor.snezhko

    igor.snezhko Active Member

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    I understand you. But 3CX not "oblige" to listen a tone. The PSTN gateway have to listen a tone and "switch" protocol on the fly.
    I don't know this mechanics in deep, but on my opinion, some solution that push Gateway from T.30 to T.38 should exist.
    For example, when call go to 888, 3CX should (forcible) reestablish a session with new protocol. Then FXO port should switch on T.38 also.

    Maybe I am wrong, though...
     
  10. igor.snezhko

    igor.snezhko Active Member

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    I write all this, because 100% of my clients become very disappointed when I say them, that they cannot transfer caller, that want to send a fax, to 3CX Fax.

    It is common, that secretary first answer a voice call, and than start to receive a FAX from this person. 3CX allow this, but only using FAX device with АТА gateway.
     
  11. abc123

    abc123 Active Member

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    3cx doesnt have a tone to listen to. Not they dont have to but they dont have one. The PSTN gateway does listen to the tone because it has an analog signal coming in down a POTS.

    3cx is not directly connected to the PSTN, it is either connected via a gateway or via a voip provider. So the VOIP Provider has a gateway (large) connected to the PSTN which does the tone listening.

    I can understand your problem but it cannot change to t38 based on your scenario of secretary answering the call. It should be feasible though to route it to an ATA connected to a fax machine. It isnt perfect but it should still work, just not t38 to the fax server itself.

    I am not sure how your customers are set up there, but can they not get a dedicated telephone number (DID) for a voip provider? Here in the USA i can add DIDs for $1 per month to my account. I dont need to increase my concurrent calls. Then i route the new number to the fax server. It is a cheap solution for dedicated fax (Which is why some of my customers have over 20 fax numbers on their system).
     
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  12. igor.snezhko

    igor.snezhko Active Member

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    Yes, you are right. I also recommend to add a DID number. This is no problem here.

    The BIG problem, that our people got accustomed to send a fax directly from a conversation. It is not common to direct a caller to another number just for FAX sending.

    It is common rule, that employee simply "transfer" that caller to FAX and press START. NO conversation interruption!

    So, after 3CX installation, a client say "Ok, now I want to test a 3CX FAX. I will transfer it to 888, rigth?" I say, no, it is not working that way :). But client say "Opps, my old PBX always did it! I need a solution!"... etc, etc... :x
     
  13. abc123

    abc123 Active Member

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    Well we can set up another fax machine on 3cx and use something like the SPA2102 and forward it to that ext (889) and it should work that way. That would be similar to their old pbx too.
     
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  14. igor.snezhko

    igor.snezhko Active Member

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    Yes, it is possible. But users want "unified communications", that all faxes should be it digital form. So, АТА adapter is not a best solution, unfortunately.
     
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