Author Topic: Contentious and rambling Analog multiplexing for connecting PABX to Central Office discussion  (Read 3939 times)

bellsystem

  • Guest
I asked the following question on Stack Exchange but was told it was off-topic: https://networkengineering.stackexchange.com/questions/42193/pbx-co-trunks-analog-multiplexing-analog-version-of-pri

It's sort of technical in nature which is I presume why it was put on hold.

Does anyone know if they can maintain an analog connection between the central office and their house/business using just 1 cable, like PRI,  but with analog channels instead of digital? Is there a name for this type of technology to distinguish it from PRI?

I want the call quality and reliability of having as many separate landlines coming into the building as I needed outside lines, but the convenience that one large cable coming in offers - in addition to one cable, Direct Inward Dialing and Direct Outward Dialing are my primary concerns.

Nobody on the site I posted to was helpful, so thanks in advance to anyone who can help me out with this!


===========================================
EDIT: text copied from "other site" and pasted here for posterity


"PBX CO Trunks: Analog multiplexing (analog version of PRI)? [on hold]

I've been doing more research into PBXs, specifically trunk connection methods. My understanding is that there are 3 primary options:

    Separate telephone lines for each trunk line
    Primary Rate Interface (PRI)
    Session Initiation Protocol (SIP)

I'm trying to figure out what the best way would be to connect an analog-only PBX to the central office. I've already ruled SIP/VoIP out as being considerably inferior, from a quality and reliability perspective especially. PRI is preferable to SIP, but my understanding is that PRI uses TDM/digital transmission which would not be acceptable.

- - - - - - - - - - - - - - - - - - - - - - - - - -
Premise:

    Transmission must be analog, not digital, for call quality and reliability - the call quality should be basically the same as that with a separate standalone landline connection.

    Digits should be dialed immediately. I know many systems "hold" digits and then analyze the digits dialed using a "dial plan". Internally, this might be of some used. But if "9" is dialed for an outside line, I want the PBX to grab an outside line for the station and step out of the picture. The digits should be sent to the central office then as they are dialed, not all at the end (again, as with a separate, standalone landline connection).

    Going along with my second point, all central office connections, whether they are individual cables or one large one with separate analog channels, would have to be identical. Because the circuit will be grabbed as soon as "9" is dialed, all "features" (i.e. ability to make Long Distance/International calls) would have to be the same for each line/channel, since it would be impossible for the actual intended number to be analyzed. Basically, the call should be being routed as it is being dialed, not after.

    There's extreme controversy it seems regarding 9-1-1 and 9 9-1-1 going around (the linked petition will be impossible to force for systems such as the one I desire). I know that 9-1-1 will not be doing anything because to the central office, it looks like 1-1 has been dialed which could have easily been a switchhook mishap (I assume this is why 1-1 is not rerouted to 9-1-1). The PBX will be in a home environment (not a public system) and since I, most of the time, will be its only user, I will know to dial 9911 instead of 911 anyways. 911 should NOT connect to anything.

    I don't believe nesting PBXs will be a problem. I am going to buy a PBX that will support at least 50 stations, but one of the "stations" will end up being a corded switchboard PBX (PMBX or Private Manual Branch Exchange), and other "stations" may be other sub-PBXs that are PABXs, like the main one. Is there any way to use features like Direct Inward Dial from telephone stations to PBXs nested further down in the tree?
- - - - - - - - - - - - - - - - - - - - - - - - - -

I'm trying to figure out which networking technologies would best meet most, if not all, of my requirements. My guess is it would be some technology that lies between separate regular landlines and PRI, if there is one. The PBXs that will actually be used are arbitrary and irrelevant, but they will all be analog and have no digital support.

I believe something along the lines of an early 1970s analog PABX would end up being used (as is described here), but I am interested in what transmission technologies concerning the trunk lines should be used.

Is there a sort of medium between separate analog lines and PRI? I'm looking for a medium that will retain an analog transmission between the PBX and the Central Office, but the switching technology itself can obviously be digital (as all PABXs are). Is there any way to maintain an analog connection between the central office and the PBX without running separate regular landlines for each trunk? Analog will be needed to support good call quality for regular analog rotary and pushbutton phones, fax machines, and modems (including dial-up). I want whatever trunk technology is used to function like a standalone line without actually being 4 or 6 separate standalone lines. Costs aside, my primary concern with having standalone lines will be direct inward dialing as well as direct outward dialing. Even if there are 50 stations, there are only a few numbers I'd want to have DID and DOD for - otherwise, I want only ONE telephone number - and NOT as many numbers as there are trunks (this might be appropriate for a Key Telephone System but not a PBX), since I want one number to be used for Caller ID from any non DOD phone, which I don't think standalone lines would support.

If my internal extensions range from 1000 to 1500, the numbers I need supported for DID/DOD would be 1000 as well as a few other numbers between 1000 and 1200. I don't want to have to purchase a whole block of 200 "numbers" if that can be avoided (unless there is no additional cost).

I am estimating between 4 and 6 trunks will be required. Costs are not a concern, although since this will be installed in a home environment with 1 bill-payer, ideally they should be low.

Summary:

    No digital transmission (i.e. packet switching)
    Analog multiplexing is possible so multiplexing is fine if each individual circuit is analog.
    Routing as calls are dialed, not after
    Compatibility with DID and DOD

CLARIFICATION: I'm not asking anything about a PBX at all. I'm inquiring about the protocols used, specifically PRI, and if an analog variant of PRI (possibly a predecessor to PRI) exists."

« Last Edit: June 26, 2017, 10:24:07 PM by TelePlay »

unbeldi

  • Guest
I think you should summarize and post your questions here and not refer to another site.

I also think you should talk more about the eventual goal. Is this for some kind of commercial service or for pleasure ?
Connecting a PBX to a central office is not a goal, the benefit of that is the goal, I presume.

What kind of PBX are you connecting?  What kind of interfaces are available on that?

Analog trunks are rapidly coming out of style, have been for some time and the traditional DID service is not usually available anymore.  What many people, especially the VoIP folks today mean with DID is a different service.

How many simultaneous calls are anticipated ?   This determines the number of analog trunks you need.   Nobody does analog multiplexing via carrier systems anymore, except the cable company's coax systems.

The most prominent analog multiplex system was probably AT&T's L-carrier system, dead for decades.

Does anyone know if they can maintain an analog connection between the central office and their house/business using just 1 cable, like PRI,  but with analog channels instead of digital? Is there a name for this type of technology to distinguish it from PRI?

Who is "THEY" ?
PRI is not an analog channel, it is ISDN over T1 carrier, or E1 carrier in most other places in the world, except the US and Japan.
CAS T1 service is almost extinct and is also not analog.


Quote
I want the call quality and reliability of having as many separate landlines coming into the building as I needed outside lines, but the convenience that one large cable coming in offers - in addition to one cable, Direct Inward Dialing and Direct Outward Dialing are my primary concerns.

The best quality today comes via VoIP, it can provide a much larger bandwidth than 3.5 kHz, but you need the right kind of PBX for that too.
« Last Edit: June 27, 2017, 07:49:31 AM by unbeldi »

unbeldi

  • Guest
    Transmission must be analog, not digital, for call quality and reliability - the call quality should be basically the same as that with a separate standalone landline connection.
Call quality on analog systems is only best over very short distances when the entire voice path is metallic.  Ever since the T carrier was introduced this is rarely the case anymore, as virtually every communication is sampled 8000 times per second.

Quote
    Digits should be dialed immediately. I know many systems "hold" digits and then analyze the digits dialed using a "dial plan". Internally, this might be of some used. But if "9" is dialed for an outside line, I want the PBX to grab an outside line for the station and step out of the picture. The digits should be sent to the central office then as they are dialed, not all at the end (again, as with a separate, standalone landline connection).
This is a function of the terminal equipment, not the trunk or communication channel.  What kind of PBX are you using ?


Quote
    Going along with my second point, all central office connections, whether they are individual cables or one large one with separate analog channels, would have to be identical. Because the circuit will be grabbed as soon as "9" is dialed, all "features" (i.e. ability to make Long Distance/International calls) would have to be the same for each line/channel, since it would be impossible for the actual intended number to be analyzed. Basically, the call should be being routed as it is being dialed, not after.

    There's extreme controversy it seems regarding 9-1-1 and 9 9-1-1 going around (the linked petition will be impossible to force for systems such as the one I desire). I know that 9-1-1 will not be doing anything because to the central office, it looks like 1-1 has been dialed which could have easily been a switchhook mishap (I assume this is why 1-1 is not rerouted to 9-1-1). The PBX will be in a home environment (not a public system) and since I, most of the time, will be its only user, I will know to dial 9911 instead of 911 anyways. 911 should NOT connect to anything.
You will have to design your own PBX system and design the dialing plan according to your needs.  Any old commercial system, that has such features, as selecting outgoing CO trunks, can hardly be customized. You will have to use it the way it was built.

Quote
    I don't believe nesting PBXs will be a problem. I am going to buy a PBX that will support at least 50 stations, but one of the "stations" will end up being a corded switchboard PBX (PMBX or Private Manual Branch Exchange), and other "stations" may be other sub-PBXs that are PABXs, like the main one. Is there any way to use features like Direct Inward Dial from telephone stations to PBXs nested further down in the tree?
Never heard the term PMBX, at least I don't recall.    I am not sure how a single station can make a meaningful PBX.

The term 'PBX' has no technical significance in terms of capabilities or technical features.  It only labels a telephone system as being capable of operating as a private branch of the public switched telephone network. It is a local switching center and only calls to the "outside" are passed to the PSTN. How those connections exactly are made is entirely different matter.   A PABX was typically a PBX in which the stations could dial other stations, or possibly dial a trunk connection, without attendant involvement.   But, as technology progressed into digital electronics, PABXs after perhaps the early 1980s, were simply called PBX, because nobody would buy a manual PBX anymore.


Quote
I'm trying to figure out which networking technologies would best meet most, if not all, of my requirements. My guess is it would be some technology that lies between separate regular landlines and PRI, if there is one. The PBXs that will actually be used are arbitrary and irrelevant, but they will all be analog and have no digital support.
Without digital support, you can only use standard POTS lines. Perhaps DID trunks are available somewhere still, but it is probably a long shot.  Most of them were provisioned with interoffice trunk facilities, I believe, which probably have all been replaced by fiber optics by now.


Quote
Is there a sort of medium between separate analog lines and PRI? I'm looking for a medium that will retain an analog transmission between the PBX and the Central Office, but the switching technology itself can obviously be digital (as all PABXs are).
I really don't understand what a middle ground (medium?) between analog and digital would be.  It can only be one or the other.
Analog carrier systems don't exist anymore in telephony, AFAIK.


Quote
Is there any way to maintain an analog connection between the central office and the PBX without running separate regular landlines for each trunk? Analog will be needed to support good call quality for regular analog rotary and pushbutton phones, fax machines, and modems (including dial-up). I want whatever trunk technology is used to function like a standalone line without actually being 4 or 6 separate standalone lines. Costs aside, my primary concern with having standalone lines will be direct inward dialing as well as direct outward dialing. Even if there are 50 stations, there are only a few numbers I'd want to have DID and DOD for - otherwise, I want only ONE telephone number - and NOT as many numbers as there are trunks (this might be appropriate for a Key Telephone System but not a PBX), since I want one number to be used for Caller ID from any non DOD phone, which I don't think standalone lines would support.

A common solution has been to use a SIP or MGCP media gateway with the required number of analog ports, and direct calls to the PSTN via these ports.  Media gateways, for example by AudioCodes or Mediatrix, were/are very popular to convert old PBXes with only analog facilities to use efficient trunking via IP networks.
This has been the recommended upgrade path even for vendors such as Lucent and Avaya, who both in fact certified AudioCodes gateways for such use. These are available in small boxes of 2, 4, 8, and 24 ports, but higher density carrier-grade equipment is available and very expensive.
Another possibility is the use of channel banks, such as by Adtran or Carrier Access.  In particular, I like the Carrier Access ADIT-600 boxes, because they have a VoIP access card that speaks the MGCP protocol for which I have written a protocol driver for Asterisk that works well.  The ADIT-600 provides me with 40 ports with local loop characteristics comparable to a standard POTS line.


Quote
If my internal extensions range from 1000 to 1500, the numbers I need supported for DID/DOD would be 1000 as well as a few other numbers between 1000 and 1200. I don't want to have to purchase a whole block of 200 "numbers" if that can be avoided (unless there is no additional cost).

I am estimating between 4 and 6 trunks will be required. Costs are not a concern, although since this will be installed in a home environment with 1 bill-payer, ideally they should be low.

Summary:

    No digital transmission (i.e. packet switching)
    Analog multiplexing is possible so multiplexing is fine if each individual circuit is analog.
    Routing as calls are dialed, not after
    Compatibility with DID and DOD

CLARIFICATION: I'm not asking anything about a PBX at all. I'm inquiring about the protocols used, specifically PRI, and if an analog variant of PRI (possibly a predecessor to PRI) exists."
Your equipment determines what kind of connectivity you need.  I would recommend building your private network first with the equipment you like and then look for outside access.  Start with a cheap SIP service that allows multiple calls, and an ATA, most likely it will be totally sufficient.

The idea of routing as digits are dialed went out the door long time ago, direct control was abandoned in the 1920s already in Panel offices. It is implemented in your equipment, not the network.   PS:   However, using MGCP digits can be transmitted one-by-one across an IP network. This does open some conveniences for switching to simulate old technology.  It is commonly deemed inefficient today, since the overhead for transmitting a single digit far exceeds (by factors of 100s) the payload of sending a single digit.  Nevertheless, MGCP was designed with a  decomposed network model by telecom people (Bellcore) with the traditional PSTN in mind.


« Last Edit: June 27, 2017, 02:23:54 PM by unbeldi »

bellsystem

  • Guest
The best quality is not with VoIP. The folks on networkengineering at StackExchange tried to convince me that digital was superior to analog too.
I'm definitely NOT using SIP. If I had to choose between PRI and SIP, I would choose PRI.

The PBX that would be used is completely arbitrary. This is something I would implement in about 10 years.

I would definitely want completely analog circuits WITHIN the PABX for sure. No reason to compromise on that there, since switching would be local.

I would have between 50 and 100 stations, in a private home environment. There might be a few other PABXs and PMBXs that are "stations" for this main PABX, and other phones would be connected to those nested PBXs.

I wouldn't need more than 4 to 6 outside lines - probably 10 is a maximum. This wouldn't be where I'm living now (Wisconsin) - it would be somewhere else, perhaps Montana.

The only reason I'd rather not have standalone analog landline connections for outside lines would be because EACH of the telephone lines would have their OWN number and there would be NO support for Direct Inward Dialing and Direct Outward Dialing. I'm not entirely sure by what is meant by "most people who refer to DID and DOD mean something else" - not sure what that something else might be but please enlighten me. I'm pretty sure I mean DID and DOD.

Let me explain:

For example's sake, Montana's area code is 406. So say I own a block of numbers in an exchange. Say (406) 255-XXXX. The XXXXs I want would be 1000 to 1500, let's say.

The main number I'd list in the telephone directory would be 1000, and it would have an auto-attendant. The numbers 1003, 1005, 1010, 1015, 1020, 1110, 1115, 1120, and a couple of numbers are numbers on which I'd WANT DID/DOD. So if I called (406) 255-1015, it would reach extension 1015. When these numbers dial out, their actual extension will be used for Caller ID (i.e. (406) 255-1015 if a call was made outside from that number).

But take extensions 1011 or 1111. These would NOT be DID/DOD, and these extensions CANNOT be reached DIRECTLY from the outside world. If an outside call is made using these numbers, the main number - 1000 - is used for Caller ID since there is no DOD - i.e. the caller ID for a call made from extension 1011 or 1111 would be (406) 255-1000

I have seen environments like this using VoIP/SIP - i.e. the secretary's number might be 2505 and the principal is 2510 and these numbers have DID/DOD, but calls can't be made to classroom phones from the outside, and calls made from classroom phones show up as 2500, not their internal extension number.

Hopefully I've explained well enough that you can get the general gist of it.

I want to use a medium to connect the main PBX to the Central Office that is as reliable and good-quality as individual analog, copper local loop landlines coming in.
But I don't want telephone NUMBERS for each Central Office line - they should all be equal in terms of what they can do, if that makes sense. A call to any number should be able to use any trunk, and the trunk itself will NOT have a number. Meaning the only number I'd "really" have would be (406) 255-1000, but there would be, say SIX "channels" or "lines" or whatever for that number meaning there can be 6 concurrent calls to that number, and with DID, the call will automatically go the appropriate extension - or the auto-attendant if 1000 is the actual number dialed.

Hope that makes more sense. I don't think the DID/DOD functionality I described can be accomplished with a bunch of individual standalone landlines, which is why I am looking for a single-cable solution that will support it. But that means going digital, which is not really a sacrifice I think I should have to make. SIP and VoIP are definitely not options and I will never use SIP/VoIP.

unbeldi

  • Guest
Well, sounds like you assume that you know more than the people you are asking advice from.
What is this objection against the standards of modern telephony based on, if not experience ?


Alex G. Bell

  • Guest
But that means going digital, which is not really a sacrifice I think I should have to make. SIP and VoIP are definitely not options and I will never use SIP/VoIP.
I have bad news for you.  Verizon is sending letters to large numbers of customers who have and have had for decades analog copper POTS service from them.  The letters inform them that within the coming year the copper outside plant will be retired and the customer must make an appointment to have a VoIP terminal adapter installed to continue service at the existing monthly rates.  This is not an attempt to raise monthly charges.

If Vz is doing this other ILECs surely are going to be doing it soon too if they aren't already.  The handwriting is on the wall.  Your choice will soon be to have VoIP service of some kind, cellular, or no service at all.  Take your choice.  Even if you get analog service installed you will be forced to migrate it.  Whether you like it or not, this is what's happening.

bellsystem

  • Guest
You can either give in or fight. I'm not a puppet that AT&T or Verizon can control. And it's not just me - see www.savelandlines.org

Anyways, I don't want to debate whether landlines are going away or not. I'd just like to know what options are available based on what I outlined. Even if what I'm looking for is deprecated, I'd still like to learn about it. Maybe I'll build my own central office :)

Alex G. Bell

  • Guest
The best quality is not with VoIP. The folks on networkengineering at StackExchange tried to convince me that digital was superior to analog too.
Well actually this is not so.  Polycom makes a series of SIP telephone sets which have much better than 3KHz BW and sound much better than a conventional telephone set.  Of course this benefit only accrues when two such sets are used end-to-end.

Carbon transmitters used in conventional passive telephone sets have very high inherent intermodulation distortion, so even an electret mike in a 3KHz circuit is vastly more natural sounding.

Alex G. Bell

  • Guest
You can either give in or fight. I'm not a puppet that AT&T or Verizon can control. And it's not just me - see www.savelandlines.org

Anyways, I don't want to debate whether landlines are going away or not. I'd just like to know what options are available based on what I outlined. Even if what I'm looking for is deprecated, I'd still like to learn about it. Maybe I'll build my own central office :)
You can build your own internal network.  Lots of people have.  You cannot create or recreate the network which serves the rest of the world beyond the confines of your property or your immediate contiguous neighbors.

unbeldi

  • Guest
Well actually this is not so.  Polycom makes a series of SIP telephone sets which have much better than 3KHz BW and sound much better than a conventional telephone set.  Of course this benefit only accrues when two such sets are used end-to-end.

Carbon transmitters used in conventional passive telephone sets have very high inherent intermodulation distortion, so even an electret mike in a 3KHz circuit is vastly more natural sounding.

AGB's advice is valid and correct.  High-bandwidth coders are becoming routine on VoIP systems today, especially within local networks.   But even on international calls to Europe I have routinely far better voice quality today using a commercial SIP network provider than I ever had with traditional circuit-switched telephony. 

bellsystem

  • Guest
Okay, I'm done debating voice quality. The reality is VoIP does not support many of the things analog lines do - like dial-up, DSL, fax machines, alarm systems, pacemakers, etc. Landlines are extremely versatile and can be used for many different purposes. Plus pulse dialing is supported, which, considering we're on classicrotaryphones.com, is very important!

Does anyone know what options I have for the scenario I have described? SIP and VoIP are out of the question. PRI would be my last resort.

Thank you all for your input!

unbeldi

  • Guest
You can either give in or fight. I'm not a puppet that AT&T or Verizon can control. And it's not just me - see www.savelandlines.org

Anyways, I don't want to debate whether landlines are going away or not. I'd just like to know what options are available based on what I outlined. Even if what I'm looking for is deprecated, I'd still like to learn about it. Maybe I'll build my own central office :)

Well, have you read the nonsense on this page:  https://savelandlines.org/the-issues/  ?

Alex G. Bell

  • Guest
Okay, I'm done debating voice quality. The reality is VoIP does not support many of the things analog lines do - like dial-up, DSL, fax machines, alarm systems, pacemakers, etc. Landlines are extremely versatile and can be used for many different purposes. Plus pulse dialing is supported, which, considering we're on classicrotaryphones.com, is very important!

Does anyone know what options I have for the scenario I have described? SIP and VoIP are out of the question. PRI would be my last resort.

Thank you all for your input!
Oh, I'd say your options are approximately zero (give or take).  Since you don't have control over equipment deployed in the CO at the other end of the wished for transmission channel unless you establish yourself as a CLEC and rent co-location cage space, you are limited to those transmission methods chosen for deployment by the ILECs.  That topic has already been explored here pretty thoroughly.

A friend who has had a T1 delivering 6 true DID trunks and 800 PSTN numbers to him by a CLEC for the last 15 or so years is ready to bail and migrate to VoIP because of the ever mounting costs.  So if you're willing to "settle" for a PRI I trust that means you have deep pockets and cost is no object: a few hundred dollars/month is an acceptable cost.
« Last Edit: June 27, 2017, 03:25:26 PM by Alex G. Bell »

unbeldi

  • Guest
Okay, I'm done debating voice quality. The reality is VoIP does not support many of the things analog lines do - like dial-up, DSL, fax machines, alarm systems, pacemakers, etc. Landlines are extremely versatile and can be used for many different purposes. Plus pulse dialing is supported, which, considering we're on classicrotaryphones.com, is very important!

Does anyone know what options I have for the scenario I have described? SIP and VoIP are out of the question. PRI would be my last resort.

Thank you all for your input!

PRI is perhaps the last resort today.  But its days are numbered too. A high percentage of the business market has migrated to VoIP already.  In Europe the ISDN providers are terminating service arrangements already too.

The reality is that VoIP provides everything needed for modern communications, and that includes terminal adapters that provide a local loop as good as from a central office, only cheaper.

DSL is a digital transmission system over analog circuits, not needed anymore.  Fax machines work as well today over VoIP infrastructure, as before, but frankly why is it needed anymore ?
Land lines are extremely non-versatile in reality.  What other purposes might they be used for other than for analog telephone calls ?
Pulse dialing can be easily supported with cheap hardware.  Using pulse dialing on the network is completely unnecessary, especially as you are proposing to build some kind of local network with PBXes anyways.   PRI does not transmit pulse dialing either.

Being an activist for old technology is a waste of time.  Nobody listen to that stuff, and the market place moves forward.  It would be better to spend that time on mobilizing for better, modern, and more reliable infrastructure of the power grid, of transport systems, and such.  Why can't the power lines be as reliable today as dial tone has been for many decades.

bellsystem

  • Guest
VoIP does not work in a power outage. That is enough said. It isn't progress to me to move from something that will work indefinitely, like in the 1965 Blackout, to something that will shut off when it may be most needed. And dial tone is only getting less reliable as we move away from analog and copper. I'll take reliable over all the "cool digital features" any day.

Well, pulse dialing transmission to the Central Office is a must-have. So I guess PRI won't work for me really at all. I'm surprised even rotary telephone enthusiasts have no objection to the stuff that's happening right now. I'd at least thought that some people had avoided being brainwashed by corporate spokespeople...

Fax machines are necessary for legal documents. And if I want to fax something to someone, I have every right to do so. Back in the days of the Bell System, the telephone company worked for us. I'm disgusted how things work these days and how telecommunications corporations no longer look out for what their customers really need or want.

PS - power line faliures are common because of CASCADING failures, which is how many failures happen. That does not happen with telephone wires.
« Last Edit: June 27, 2017, 03:51:38 PM by bellsystem »