Fax on PAP2 with HP LJ 2840 = Resolved

I have conected the HP LaserJet 2840 all-in-one fax machine to the LinkSys PAP2 and I can’t recive faxes. I can send faxes without problem.
When the incoming fax rings, th HP 2840 do not pick-up it, even if I press button “start fax”.
If I connect a modem-fax in this extension I can send and recieve.

any Idea?

Thank you.

i think this is probably a laserjet fax problem more than it is a voip problem.

that said, on the pap2 look into the ring waveform pattern and ring intensity… DON’T play with them too much or you might fry devices attached to the pap2…

Hello IronHelix,

I think that is a problem between a PAP2 and HP 2840, because I conected another fax machine - Panasonic Panafax UF-332 and… it dosn’t recive faxes too. In diference with HP 2840 if I pick up manualy and press buton to recive fax manualy the Panafax UF-332 recive it ok.
I try too with a notebook with modem-fax incorporated and the faxes are recived without problem. Everythink conected on the same port of PAP2.

I think that there is some parameter on PAP2 that have to change to be operete with the fax machines. Or, maybe to change some parameter on the fax machines to operate with PAP2. Is the same cuestion, because the HP 2840 and Panafax UF-332 in another enviroment like simple analog line works fine!

There the cuestion es wich parameter is? Why the faxes not pick up?
I’m looking for a detailed manual (not this in web-site of LinkSys, I need more detaliled) that this parameters like "FAX CED Detect " , “FAX CNG Detect” and more are explaned. Or maybe the cuestion is about the polarity.

Thank you

I still think it has to do with ringing.

if the laserjet fax detects the call and answers (sending a fax tone) then it’s not a ringing related problem, ignore that. I think this is the problem, you say that other things can answer and recieve the fax, yet the laserjet fax does not answer the call. That has nothing to do with faxing or not, that means that either the laserjet doesn’t know the line is ringing (in other words your pap2 ring settings are off) or the laserjet doesn’t know that it’s supposed to answer the line (in which case you need to reconfigure your laserjet fax).

The pap2 doesn’t know if you’re sending a fax or not (or care for that matter) until the call is established, and that doesn’t happen until the fax picks up. So it’s not a fax specific issue. I have a feeling that if you call the number of the pap2 (with a phone) that it won’t answer that either. (if it does then ringing probably isnt your problem…).

Hello IronHelix,
When I connect a phone to the HP 2840 (there is 2 jack - one for the line and one for an external phone) the phone rings. But the HP 2840 does not respond. While the phone is ringing I press the button of the HP 2840 “recive fax” and I can listen the fax tone on the speker of HP 2840 - piip…piip…piip. But HP 2840 not start to recieve. When I connet a Panafax IU-332, it not pick-up too, but when I press the button - recieve fax, it start to recive and the fax comming ok.
With 2 modem that I try the fax are recivied fine, automaticaly. The Panafax IU-332 works in another enviroment fine. The HP 2840 is new machine.

In the configurationa of PAP2 are this parameters, that I think could be setting:

FAX Codec Symmetric: yesno
FAX Passthru Method: None
DTMF Tx Method: InBand
Hook Flash Tx Method: None
FAX CED Detect Enable: yesno
FAX CNG Detect Enable: yesno
FAX Passthru Codec: G711uG711a
FAX Codec Symmetric: yesno
FAX Passthru Method: NoneNSEReINVITE
FAX Process NSE: yesno
FAX Disable ECAN:

Thank you.

P.S. When I pick-up the ringing phone connected to HP2840 I can do conversation.

As IronHelix said, it is a ringing detect problem, not a fax problem. You see, there are some specifications for ring detect and another parameters (this have to be bettwen some limits). Try to use HP fax on a standard telecom line, you’ll see that you can receive faxes without problem.

Or try to answer manually the phone attached to HP fax, then press Start. You should receive the fax.

To fix this, you have to increase some parameters in Linksys (ringing voltage). But, as IronHelix said, be very carefull, other way you can fry your HP or other fax.

Hello, I resolved the ring problem changing the ring frecuency from 25Hz (default) to 35. Seems that the fax machine detects the rings from a range 32-37Hz. Now HP2840 pick-ups the call and start to recieve faxes.

But there is another problem:
When the fax reception starts, the bouth faxes starts negotiate a fax velocity and they going down from 14.400 bps to 2.400 bps. At 2.400 pbs the fax starts but don’t works very well. Some faxes are recieved, some are truncated and some are terminated without recivieng with “connection error”.

Any idea? Any parameter in PAP2 to correct this issue?

Thano you.


Another option would to get an SPA-2100 or SPA-2102 with the T.38 Codec it should help the faxing process, even though faxing isn’t very reliable as is.

Finaly this issue was resolved this way:

  1. I log like admin with advanced view.
  2. Menu “Regional” - “Ring and Call Waiting Tone Spec” I changed “Ring Frequency:” from 25 to 35 - then the fax pick-ups calls.
  3. Menu “Line 1” - “Audio Configuration” ?:
    Silence Supp Enable = no
    Silence Threshold = medium
    Echo Canc Enable = no
    Echo Canc Adapt Enable = no
    Echo Supp Enable = no
    FAX CED Detect Enable = no
    FAX CNG Detect Enable = no
    FAX Passthru Codec = G711a
    FAX Passthru Method = NSE
    FAX Process NSE = yes
    FAX Disable ECAN = no

Preferred Codec = G711a
Use Pref Codec Only = no - i think this resolve my problem
G729a Enable = yes
G723 Enable = yes
G726-16 Enable = yes
G726-24 Enable = yes
G726-30 Enable = yes
G726-40 Enable = yes
FAX Codec Symmetric = yes
DTMF Tx Method = auto
Hook Flash Tx Method = none
Release Unused Codec = yes

Thanks everbody who helps.

Thank you !

I was having the same issue with my Officejet 6110xi and sipura spa-1001

I think the

Silence Supp Enable = no
Echo Supp Enable = no

Where the main issues

Once agian thank you !

For me, at first time I put every parameter like described above, except “Use Pref Codec Only” (was = yes) and I can’t recived faxes. When I change it to “no” then every fax comming in fine.