TIPS low voltage POTS lines

[newtoast]

Hello,
First time post, so please excuse any issues.

I have a Sangoma A200 with two A200-O FXO modules providing 4 FXO ports to connect to 4 POTS lines provided by Comcast business service. System info below.

PIAF Installed Version = 2.0.6.5 under *HARDWARE*
FreePBX Version = 2.11.0.38
Running Asterisk Version = 11.10.0
Asterisk Source Version = 11.10.0
Dahdi Source Version = 2.9.0
Libpri Source Version = 1.4.14
IP Address = X.X.X.X on eth0
Operating System = CentOS release 6.5 (Final)
Kernel Version = 2.6.32-431.1.2.0.1.el6.i686 - 32 Bit

I am running this on a SuperMicro SYS-5015A-EHF-D525 with 4GB RAM and 120GB SSD.

I successfully tested placing and receiving calls on each of the 4 phones lines using a simple touch tone phone.

I plugged the phone lines into the 4 FXO ports and quickly noticed that only 2 of the 4 were working with the phone system to place and receive calls. I switched the phones lines to different FXO ports, and the same phone lines that worked before continued to work on the new FXO ports. And the phone lines that didn't work before continued to not work on the new FXO ports.

This leads me to believe it's the phone lines and I have a Comcast tech coming on Wed, but expect a difficult time if all they do is test each line like I did with a basic phone and they say it's working and lay the blame on the phone system.

One thing I am seeing is that the voltage on each POTS line shows something interesting depending on whether it is working or not. When I run the command below on each port, I see a common trait for the working versus non-working lines.

wanpipemon -i w1g1 -c astats -m 1

For the lines that are working the voltage is 51-52 Volts. For the lines not working, the voltage is 48 Volts, maybe 49, but never reaching 50. When I switch the phone lines to different FXO ports, similar voltage values follow the lines.

I saw that this appears to be within acceptable values for on hook from the Sangoma wiki.

FX0 legend:

Voltage (V)Connection
0 to 1No line detected
6 to 12Off hook
45 to 55On hook

The software configuration to use all the FXO ports are the same and so I don't think it's a configuration issue.

One last thing. When I try and receive a call on one of the non-working lines when it's connected to the phone system, it causes the corresponding port LED on the Comcast phone equipment to blink and if I immediately take the phone line out of the FXO port and plug it into the regular phone, when I pick up the phone, I don't hear a dial tone, but some random clicking and static. After a while (10-15 mins) the phone line returns to normal and I can pickup the regular phone and get a dial tone and place and receive calls again.

Has anyone seen a similar issue? Could it possibly be some type of setting to make it work better with a larger acceptable voltage range?

Any help or info is appreciated.

 

[rossiv]

Have you tried to swap the modules around in the card? Shouldn't make a difference since you said that if you move the lines themselves around that they continue to work, but stranger things have happened.

(Also, thanks for the very detailed post. It makes things a lot easier for us to help.)

 

[newtoast]

Thanks for the info. rossiv, great idea about swapping the two modules on the A200.

Does anyone know if this can be done after powering everything off without re-installing any software? I read online someone saying to install PIAF without the A200 card in and only install after all the software was installed as it caused problems otherwise. So that's what I did when I installed the SW. I'm not sure if somehow the config is tied to the modules and the exact slots they're currently in, like a MAC address equivalent in the FXO world.

If no one has done this, I'm willing to give it a shot. I guess worst case is to install everything over again.

Thanks.

 

[james]

1. "Phone modems" generally suck and are usually complete crap. You should see if you can get a new one. (Not a refurbished, reissued) In my expierience the failure rates on these things are astronomical.
2. You will probably need to replace it again. See 3rd part of 1.
3. If you can get it to work with a $9.99 Wal-Mart phone then it works as far as they are concerned. All other testing doesn't matter and it is automatticaly your equipment's fault.

Voltages:
Idle line should be around 48vDC @~20-50mA
In use will vary maybe 3-10vDC @~20-50mA
Ring 100-120vAC
Hangup ~500ms < 1vDC

All voltages depend on the base voltage/current

Phones should generally be ~200 ohms on hook and ~600 ohms off hook.

 

[snarpatroid]

Years ago I worked as an operator and spent a fair chunk of time with the engineers at BT so picked up a thing or two.

I think Ross's suggestion is the best first suggestion.

Otherwise 48v is the accepted voltage, if anything the 51v is slightly over but within tolerances. You could try reversing the line polarity (if you have an engineer's handset available these usually have a green or red LED to demonstrate polarity). Analogue equipment is polarity neutral, digital equipment can sometimes be picky. Easy way to change polarity (but this may be against your provider's terms of service so proceed with caution) is to cross over the two cables coming from the exchange in the back of the phone socket. Or you could simply cut into a spare cable between the socket and module and physically cross the cables over (sometimes tricky as this cable can be really thin to work with).

I don't know Comcast's setup but briefly looking online they refer to cloud systems and I'd imagine from this statement it'll be IP routed calls all the way (here in the UK we started with Strowger, went to electrical relays, through the 80's had 'System X' and 'System Y' with concentrators, these days it's all 21st century network (21CN) which is IP routing at the exchange end. It's cheap. The only time I would have expected you to hear static was on your equivalent of our System X/Y services with a time break recall (flash recall) service, or an open trunk on a Strowger or the electrical AXE10 equivalent. These days to hear static on an IP based line indicates a clear fault to me, I'd expect at least a 'howler' to remind a person they've left a phone off hook.

As a final test you could always chain four analogue phones to one line, see if they all ring and if you can make and receive manual calls with an analogue phone. A line should be able to hold four phones, if yours cannot then again it's a line fault.

 

[snarpatroid]

1. "Phone modems" generally suck and are usually complete crap. You should see if you can get a new one. (Not a refurbished, reissued) In my expierience the failure rates on these things are astronomical.
2. You will probably need to replace it again. See 3rd part of 1.
3. If you can get it to work with a $9.99 Wal-Mart phone then it works as far as they are concerned. All other testing doesn't matter and it is automatticaly your equipment's fault.

Voltages:
Idle line should be around 48vDC @~20-50mA
In use will vary maybe 3-10vDC @~20-50mA
Ring 100-120vAC
Hangup ~500ms < 1vDC

All voltages depend on the base voltage/current

Phones should generally be ~200 ohms on hook and ~600 ohms off hook.

Spot on, the other thing I'd be wary about is getting an engineer out to check the service without doing every possible test I could locally first as with a lot of telco's the engineer is chargeable if no fault is found.

 

[briankelly63]

This should be working....

When you say "I plugged the phone lines into the 4 FXO ports" how did you do that? Have you got the telco lines on the correct modular connector pins? Checked the modular cables? use a linemans test set, meter or phone and check the pins themselves with tiny screwdrivers or pins. 48v is fine. You can also check ringing voltage. Most cards or ATA's can be adjusted for different voltage ranges. I think this is a simple problem vs. a complicated one.

 

[rossiv]

I don't know Comcast's setup but briefly looking online they refer to cloud systems and I'd imagine from this statement it'll be IP routed calls all the way (here in the UK we started with Strowger, went to electrical relays, through the 80's had 'System X' and 'System Y' with concentrators, these days it's all 21st century network (21CN) which is IP routing at the exchange end. I

Generally if it's Comcast, it's an EMTA (cable modem + phone ports) that routes calls over Comcast's network. Something like this.

I've also seen (for higher line counts) Cisco IAD2400 media gateways used that spit out either a PRI over T1 or 24 channels of analog by way of an amphenol connector to a 66 block. Definitely know TWC Bus. Class uses these for their PRI over Fiber.

 

[newtoast]

Thanks again for all the follow up. Great community here with lots of knowledgeable folks.

Lots of great info , so I'll try and address each one.

I tried swapping the two A200-O FXO modules on the Sangoma A200 card and the same results. Still only the same 2 of the 4 lines work.

The Comcast phone modem device is very similar to the one rossiv described from ARRIS. Mine is Model TM604G/CT with coax in from Comast and 4 RJ11 phone ports out.

I am using phone cables provided with the Sangoma card to connect the Comcast phone modem to the FXO ports. They have RJ11/6 plugs on one end and then the narrower RJ11/4 plugs to plug into the narrower FXO ports on the Sangoma card.

I swapped the phone cables among the working lines and non-working lines and same result, so I don't believe there is an issue with the cables.

I am not sure I want to mess with the polarity as it sounds a bit risky.

I did request a new phone modem to be swapped out by the tech when they visit tomorrow.

I agree to check everything I can before the tech visit. Is there anything else I can check or try out?

If I get a chance, I will try chaining 4 phones together as snarpatroid suggests.

Everyone's help is much appreciated.

 

[snarpatroid]

If you have EMTA then a lot of info we have suggested is redundant. Basically I'd start by getting Comcast to try swapping out a new unit and go from there, all the info about line voltages and polarity is irrelevant since you'll be IP from that terminal over their network. I was going on basis you had a physical analogue socket on the wall. The chaining of phones I suggested earlier also won't highlight line problems on an EMTA in the same way it would with a traditional POTS.

If Comcast are coming out tomorrow I wouldn't spend any more time worrying until you've got them to swap out your EMTA then we can try more tests once this happens.

 

[newtoast]

Ok, thanks for the clarification. I hope I'm able to resolve with the tech visit and will update the post with details.

 

[newtoast]

Ok, things are now working. The Comcast tech came and ran some tests and identified the possible problem. I'll describe the changes I made to get it working below.

First a quick summary of what's causing problems.

For the 4 POTS line ports on the back on the EMTA, the tech described how ports 1 and 3 actually provide two phones lines. Port 1 has one line on the inner pair of wires and then also the same line as port 2 on its outer pair of wires. So as below. The Xs shows which of the 4 wires are used for a specific line.


PORT 1 PORT 2 PORT 3 PORT 4
------ ------ ------ ------
line 1 line 2 line 3 line 4
|XX| |XX| |XX| |XX|
line 2 line 4
X||X X||X

The tech said this is to accommodate multi-line phones.

The modular phone cables that came with the Sangoma card has the 6P4c connector on one end (what I commonly thought was a regular RJ11 phone plug that has 6 pins in the plug, but only the middle 4 are used since using a 4 wire cable) and then the narrower 4P4C connector on the other end which is what fits into the ports on the Sangoma card. It's a 4 wire cable so the 4 middle pins of the 6P4C connector go through to all 4 pins of the 4P4C connector.

Since all 4 wires are being used between the EMTA and the Sangoma card for each port, when dialing lines 2 or 4, it is also coming through on the cables plugged into ports 1 and 3, respectively. Somehow this causing the phone system and/or EMTA grief and was causing the problems that I was experiencing on just those 2 of the 4 lines.

So what I needed to do was isolate just the middle two pins from especially ports 1 and 3 so that only one line was actually going from the EMTA to the phone system.

I didn't want to splice into the Sangoma cables and I also couldn't find any 4P4C plugs to make new cables. So I bought two modular splitters (one plug with two ports) and rewired the insides so that (a) only 2 wires from the plug feed each of the ports and (b) the second port has the outside plug wires connected to the middle pins of the port.

So now with my modified splitters plugged into ports 1 and 3 of the EMTA, I have a port for each line where just the middle wires are active. I used the Sangoma provided cables to connect the splitter ports to the phone system and now everything works.

I am not sure if I had provided more info, that this would have been something easily identified by someone. I hope this can help someone else out there. If there is any more info I can add to make this more helpful, please let me know.

Thanks again for everyone's input.

 

[newtoast]

I just noticed the representation of the ports to lines did not come through well in my last post, so here it is more clearly.

Port 1 - line 1 |XX|, line 2 X||X
Port 2 - line 2 |XX|
Port 3 - line 3 |XX|, line 4 X||X
Port 3 - line 4 |XX|

 

[snarpatroid]

Makes perfect sense, thanks for the follow up you're right it may help someone else in the future. Pleased it has been rectified.

 

[briankelly63]

Ok I think I get the award for closest answer in my previous post ("Have you got the telco lines on the correct modular connector pins?"). Glad you got it up and running!!

 

[benhadad]

I have the same comcast setup hooked to an old nortel pbx that I am trying to ditch. Anyway as i read the post i was saying to my self, I wonder if the tech told him each physical line has 2 on it. In fact if you look closes you will see the back of the emta is labeled as such.

I did wonder why you chose the Sangoma A200 verse another solution? If you had your choice would you have used a stand alone unit instead of a PCI solution?

To the general group is there a solution to use the TOUCHSTONE MULTILINE E-MTA TM608
[http://www.arrisi.com/products/product.asp?id=75] directly with asterisk?

I know it is a packetcable setup and I saw this posting before - http://docsis.org/node/244, http://docsis.org/node/1122 but not sure how to setup this unit. Is it that comcast control the setup and wont let me see it?

[https://issues.asterisk.org/jira/browse/ASTERISK-12278].