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Fax Transmissions over PRI? 3
- Thread starter Werthit
- Start date
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3
- #2
dagwoodsystems
Programmer
I'd be more than happy to comment myself, but your question seems a bit leading...especially since you advertise yourself as a vendor.
Are you truly interested in the feedback from techs with field experience, or will you use someone's response to springboard into marketing conversation about a product that you represent?
No harm...no foul. Just asking for clarification
Tim Alberstein
Are you truly interested in the feedback from techs with field experience, or will you use someone's response to springboard into marketing conversation about a product that you represent?
No harm...no foul. Just asking for clarification
Tim Alberstein
- Thread starter
- #3
I suppose that's a valid question these days, when there are those who will try anything to make a sales call, ethical or not.
I'm a vendor, I'm a technician. I know about all about the WIN 440CT series. I am learning VoIP, and the question is to learn from other technicians. I'm also growing an existing Partner ACS customer to a Merlin Magix 4.0 and learning that as I go; clear programming instructions are hard to find!
I'm a vendor, I'm a technician. I know about all about the WIN 440CT series. I am learning VoIP, and the question is to learn from other technicians. I'm also growing an existing Partner ACS customer to a Merlin Magix 4.0 and learning that as I go; clear programming instructions are hard to find!
dagwoodsystems
Programmer
I guess the common term today is FoIP (for fax over IP), but "common" may be inaccurate as it doesn't seem to be widely used. Officially, it's known as ITU Recommendation T.38. Wikipedia has a very readable article about it here.
I'm sure you've heard the term "voice compression" if you've hung out with us weirdo voice guys for any length of time. The idea is to either 1) save bandwidth or 2) put more voice traffic through the same size pipe. It's accomplished by removing some number of sampled bits in the speech, and then process the remaining bits through any number of algorithms to "smooth it out" or clean it up. Many people's ears can't detect a lightly compressed voice call, but nearly every algorithm introduces some artifact or character that a good ear can pick up. Note that a true toll quality phone call requires 64kb/s (that's 64 x 1000 in the phone world, not 64 x 1024 as in the computer world).
Do some compresses or VoIP calls "sound" toll quality? Absolutely. You might want to read about perceived quality and MOS scoring along those lines. But here's the thing, while a human ear/brain can tolerate a couple of missing bits in a phone calls, machines like modems and faxes cannot because each and every bit is meaningful.
There have been a few ways to solve the problem of sending lossless data across compression connections--the most popular of which is (drum roll) don't bother. At least that's what I most often see. But there are plenty of boxes out there that "listen for CNG tone" (fax machine's CalliNG tone used during the handshake prior to transmission) and, if detected, momentarily turns off compression for THAT call so that it can have the full and proper bandwidth to complete the call.
In my experience, CNG detection works pretty well. It's not flawless by any means, but it's gotten better over time. One thing that I have NOT seen is someone developing chipsets to detect modem calls. I suppose that's because fax machines still hold sway in most businesses today while modems largely do not.
But around the late 1990's, a bunch of talk about sending fax calls through the Internet began to pop up. The solution? Redesign the fax machine itself! We'll stick an Ethernet port on the back of it, change the standards in which it's data is sent, popularize it so that everybody makes and buys one and Voila! Problem solved.
A variant of that idea is to continue using standard old-fashioned fax machines, but have them make and receive calls through a FoIP gateway. These gateways basically have a split personality in that they speak the language of both PSTN (regular phone lines) as well as manage an IP uplink. It also does the job of converting the in/oubound transmission between the two interfaces.
Does that help? That and a $1.25 might get you some scalding hot coffee made from overcooked, burnt smelling coffee beans. But that's another topic....
Tim Alberstein
I'm sure you've heard the term "voice compression" if you've hung out with us weirdo voice guys for any length of time. The idea is to either 1) save bandwidth or 2) put more voice traffic through the same size pipe. It's accomplished by removing some number of sampled bits in the speech, and then process the remaining bits through any number of algorithms to "smooth it out" or clean it up. Many people's ears can't detect a lightly compressed voice call, but nearly every algorithm introduces some artifact or character that a good ear can pick up. Note that a true toll quality phone call requires 64kb/s (that's 64 x 1000 in the phone world, not 64 x 1024 as in the computer world).
Do some compresses or VoIP calls "sound" toll quality? Absolutely. You might want to read about perceived quality and MOS scoring along those lines. But here's the thing, while a human ear/brain can tolerate a couple of missing bits in a phone calls, machines like modems and faxes cannot because each and every bit is meaningful.
There have been a few ways to solve the problem of sending lossless data across compression connections--the most popular of which is (drum roll) don't bother. At least that's what I most often see. But there are plenty of boxes out there that "listen for CNG tone" (fax machine's CalliNG tone used during the handshake prior to transmission) and, if detected, momentarily turns off compression for THAT call so that it can have the full and proper bandwidth to complete the call.
In my experience, CNG detection works pretty well. It's not flawless by any means, but it's gotten better over time. One thing that I have NOT seen is someone developing chipsets to detect modem calls. I suppose that's because fax machines still hold sway in most businesses today while modems largely do not.
But around the late 1990's, a bunch of talk about sending fax calls through the Internet began to pop up. The solution? Redesign the fax machine itself! We'll stick an Ethernet port on the back of it, change the standards in which it's data is sent, popularize it so that everybody makes and buys one and Voila! Problem solved.
A variant of that idea is to continue using standard old-fashioned fax machines, but have them make and receive calls through a FoIP gateway. These gateways basically have a split personality in that they speak the language of both PSTN (regular phone lines) as well as manage an IP uplink. It also does the job of converting the in/oubound transmission between the two interfaces.
Does that help? That and a $1.25 might get you some scalding hot coffee made from overcooked, burnt smelling coffee beans. But that's another topic....
Tim Alberstein
Werthit,
What does PRI have to do with VOIP for faxes on a MAGIX? From your post content the title does nor make any sense!
Tim,
That was an excellent explanation, and I just realized one thing I have noticed at times, when you hear some modems answer, you get CNG, then it switches to the modem handshake sequence. Is that by design or does it work for fax only transmissions?
....JIM....
What does PRI have to do with VOIP for faxes on a MAGIX? From your post content the title does nor make any sense!
Tim,
That was an excellent explanation, and I just realized one thing I have noticed at times, when you hear some modems answer, you get CNG, then it switches to the modem handshake sequence. Is that by design or does it work for fax only transmissions?
....JIM....
dagwoodsystems
Programmer
Thank you for the recognition CarGoSki, it's very much appreciated.
@Jim: The link between VoIP and PRI? With these IADs and softswitches come weird things like "fractional PRI"--a beast that didn't exist when I was first introduced to ISDN. But it seems that some providers offer some limited number of voice channels (let's say 11), provision 12 of them for Internet traffic and of course keep the 24th as the D-Channel.
But what if you decide that 768k is too slow for your Internet needs? Once inside the IAD, each voice channel can be compressed so that additional bandwidth can be allocated for Internet traffic. Ding ding ding! Compression on a PRI circuit. On top of all that, I've noticed that some providers will either convert the traffic to VoIP or may at least use IP as a transport mechanism somewhere along the way. I don't know if the original poster was aware of all that or not, but it sounded to me like he might be considering a product like the one I described above. And in those conversations, the topic of modems and faxes is invariably brought up.
I used to sell Codex and Motorola "corporate grade" modems and was always excited about the cool new things that each generation brought to the table. But I've been out of that loop for a while and haven't kept up on the latest (I kind of got disinterested when computer manufacturers introduced those crappy "soft modems" that are often built into laptops and such). I wouldn't be surprised if some clever company built a modem that can slip in a synthetic CNG tone to trigger G.711 codec on the DSP.
To my recollection, every carrier that I've spoken to about their bundled products readily confessed that modems (particularly the one's in credit card machines and postage meters) are not supported, yet fax almost always seems to be. The exception for IAD installations seems to be when the provider hands off loop start lines. In that case, they will configure individual ports for faxes, modems and such to have full bandwidth--thus avoiding fax/modem detection process altogether.
Tim Alberstein
@Jim: The link between VoIP and PRI? With these IADs and softswitches come weird things like "fractional PRI"--a beast that didn't exist when I was first introduced to ISDN. But it seems that some providers offer some limited number of voice channels (let's say 11), provision 12 of them for Internet traffic and of course keep the 24th as the D-Channel.
But what if you decide that 768k is too slow for your Internet needs? Once inside the IAD, each voice channel can be compressed so that additional bandwidth can be allocated for Internet traffic. Ding ding ding! Compression on a PRI circuit. On top of all that, I've noticed that some providers will either convert the traffic to VoIP or may at least use IP as a transport mechanism somewhere along the way. I don't know if the original poster was aware of all that or not, but it sounded to me like he might be considering a product like the one I described above. And in those conversations, the topic of modems and faxes is invariably brought up.
I used to sell Codex and Motorola "corporate grade" modems and was always excited about the cool new things that each generation brought to the table. But I've been out of that loop for a while and haven't kept up on the latest (I kind of got disinterested when computer manufacturers introduced those crappy "soft modems" that are often built into laptops and such). I wouldn't be surprised if some clever company built a modem that can slip in a synthetic CNG tone to trigger G.711 codec on the DSP.
To my recollection, every carrier that I've spoken to about their bundled products readily confessed that modems (particularly the one's in credit card machines and postage meters) are not supported, yet fax almost always seems to be. The exception for IAD installations seems to be when the provider hands off loop start lines. In that case, they will configure individual ports for faxes, modems and such to have full bandwidth--thus avoiding fax/modem detection process altogether.
Tim Alberstein
- Thread starter
- #8
Thanks for the informative feedback! Jim: the VOIP question has nothing to do with Merlin Magix. Tim: appears that local businesses are following your sage advice: "don't bother" (with FoIP). I agree; my client that I'm assembling now, turns out, is using some dial-up modems in his business as well; so we'll just stick with good ol' POTS.
I will visit with our ISP, and see what they have to say as well. Have a star.
Werth
I will visit with our ISP, and see what they have to say as well. Have a star.
Werth
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