Gateway recommendation

Hello everyone,

I’m a little bit new to VoIP. I have previously setup E1 to FreePBX server, but now I need another thing.

We have Multiline ISDN from our telephony provider in Switzerland, technically they provide us with 3 phone numbers (from which one is used as FAX number) each with 2 lines.

Here is a picture:
ISDN from provider goes to switch, from which one is out for internet and one for phones. The green one is the phone line.
2 nearby lines are for first number (rj-11 and rj-45). This is the same number, one goes to analog phone and another to IP phone, 2 other rj-11s are 2 remaining phone numbers.

We have FreePBX server in another country and I want to route those numbers from Switzerland to FreePBX. So I need a gateway, but I can’t understand exactly what gateway I need: ISDN Gateway or FXO Gateway. I mean is there a ISDN gateway, to which I will connect green line (from provider) and I will have 3 phone numbers available as SIP Trunk or do I need FXO Gateway with 3 ports? Also do you have any recommendations for gateway brand.

Thanks in advance.

ISDN is too broad.


If you are voip trunking you don’t need any additional hardware.

The problem is that I don’t know exactly is it BRI or PRI. I couldn’t find any specific details on provider’s website other than the type of connection is ISDN.

As you can see in image below their router gives me access to 3 different phone numbers that their service provide, so I guess it is PRI cause as far as I know BRI has only 2 channels so they can’t give me 3 phone numbers with one line (physical line), or is it possible that I don’t know?
I’m also inclined to think that it is PRI cause I can order additional phone numbers from them with that one physical line.

I don’t really understand what you mean by voip trunking. If you mean that ITSP (provider) can do trunking and provide me trunk configuration details, than I can’t do voip trunking cause, they don’t provide such service, they only provide all-in-one solution (IP-PBX also on their side) and GUI for it.

What other details I need to find out is it BRI or PRI? Is it possible to do without any gateway? If not, what gateway can you recommend?

I really appreciate the help of the community.

That’s a euro bri cuzt it has three b’s

Ok, thanks, now that I know that it is Euro BRI, any recommendations for gateway?
Also if I find provider that will allow me to port the numbers to him/her and provide me SIP Trunking services, I won’t need gateway, right?

Thanks in advance.

I think Switzerland ISDN is slightly different from the Italian one here, but from what I understand , thet device is a Network Termination for service provider , it translate the signal coming from the outside (the green cable, here is called the “U” interface) to one ISDN BRI S-bus (the one you call the VoIP phone but I think it’s not, it should be an ISDN phone) and three analogue PSTN line

Since I don’t know the swiss standard and don’t know if any “swiss ISDN user interface to VoIP gateway” exist, I suggest to use a common ISDN BRI VoIP gateway such Mediatrix 4400 series I use succesfully with no problem.
Simply connect the “S” output to the Mediatrix and the Mediatrix ethernet to eth. switch/FreePBX and do the routing.

Check: The TWO connectors you indicates with arrow as 1st phone number (one to ip and one to analogue phone) should instead go both to TWO ISDN devices as those are marked as “S” bus, that is the BRI interface and the ports are connected in parallel inside the board.

Also if you note that device name, it is called "ISDN NT1+2a/b"
so 1 BRI (in parallel) plus two a/b pstn interfaces

Frankly that is some crazy shit. I have been searching for an hour. I have never heard of a BRI with 3 B channels. Perhaps that device is a hybrid ATA ISDN TA.

Here are the Digium Euro ISDN BRI interfaces. They only support 2 channels per BRI.

Here is an explanation of what he has:

That said in 15+ years doing telecom I have never seen ISDN-NT as far as I am aware.

Actually I have seen many NT-1’s Cisco routers had S/T interfaces in the day. The idea being they only had to make one WIC then the NT-1 would handle the layer 1 conversion of the regional ISDN variant.

That being said BRI is 2B+D that has two B interfaces. The device the user sent a picture of has a third B channel. I just don’t get it.

The OP has won the stump the experts award.

What country was the OP in again?

I see only a two S0 ports (the S0 Bus) and 2 a/b (analog) ports, it’s a quite normal ISDN NT (like we have in Italy, called ISDN “NT1 Plus” in comparison with normal “NT1” which has no a/b ports at all): it looks like an ISDN BRI (2B+D) with 2 additional a/b (analog) ports for use with analog phone terminals or G3 FAX machines.

We should not confuse the number of “line numbers” a line could have with the number of concurrent communication channels it can offers to user.

The ISDN NT BRI (Basic Rate Interface or BRA, Basic Rate Access) is a 2B+D (S0 Bus) so it offers only 2 concurrent communication channels (PRI in Europe is 30B+D so it’s a 30 channels) but it could have up to 8 public “line numbers” associated with them (because in a “Point to Multi-Point” PMP Multi-Number configuration you could connect up to 8 ISDN terminals through the S0 bus and assign each ISDN Terminal with a public “line number”).

IMHO, it is a classical Euro ISDN NT1 2B+D PMP Multi-Number with 3 “line numbers” associated; probably it was configured to permanently link some of those numbers to each a/b port and S0 Bus, that’s for convenience (so user knows that a public line number is permanently associated, let me say, with the first a/b port for FAX, as example and the other could be for voice services).

The two a/b ports (a1/b1 and a2/b2) are only provided as an S0 “interface mirroring” (better: basically the ISDN NT Plus has an analog TA internally that converts S0 to analog a/b) of the 2B ISDN channels…so, despite the number of NT ports we see on the pictured device, the user could perform only (and always) two concurrent calls at time no matter using which port.

you are definitely OK with a very clear explanation, it is a NT1plus (where plus is referred to the added analogue circuit ports)
And yes, it is a 2B+D
James, the european ISDN is a little bit different from NorthAmerican one (is ISDN still used in NA ???) and yes, we like to make things more difficult so we have ISDN-NT to translate the “U” interface (the copper pair coming from provider) to 4wire S/T customer interface.

Thanks to everybody for your input. I wish I had more technical knowledge on everything stated, but unfortunately I’m more software side guy (I’m programmer and I’m fine with everything (Linux, Asterisk) except hardware side of telecommunication).

I’ve found out that the 1st phone number is connected with one analogue phone and one ISDN phone (not IP Phone), here is the ISDN Phone:

Overall picture is the following. We have following service from Swisscom:
Yes, we actually can have up to 10 phone numbers and 2 simultaneous lines with 64kbit/s each. In the below image you can see full picture of what we have:
I - Line from socket goes to a little switch II, from which we one line out for internet (to router) and another (the green one) for phones. The green connects to the device you’ve seen above III (one that they’ve provided) and we have 3 analogue lines out and one ISDN line to ISDN phone (IV).

I have done some investigation to find SIP trunk provider that we will port our current phone numbers to. And it turns that it’s very difficult to find provider that will port Swiss phone numbers and will have flat rates (it’s more economical in our business model to use flat rates with bulk minute packages to EU countries than per minute rates). ports numbers, but their porting for 3 numbers will cost more or near the price of the gateway I think and they have only per minute rates. I have contacted some other SIP trunk providers but haven’t got answer from all of them still. We are ok with the rates Swisscom charges, so the final question (if I don’t find appropriate SIP Trunk Provider) is what gateway to choose, to do the trunking on our side and still have all 3 phone numbers? Will Mediatrix 4400 work with that configuration? (I have actually used Mediatrix 3000 series before with E1/PRI configuration in another country).

Like Germany you’re using ADSL over ISDN , so both components are carried by a single copper pair to the wall outlet , next by mean of splitter on photo II two signals are divided but ISDN one needs a further translation to BRI and/or a/b interfaces by mean of network terminal in photo III

So I think a Mediatrix 4400 ( the ones we usually use due to low cost and ease of configuration) should be a good choice, you can configure as many telephone number as you want (three in your case , max 8 here in Italy for a single BRI channels pair as Parnassus said)
Just configure per number call routing and let it managed by FreePBX
You can use Digium BRI cards as suggested by Skyking if your FreePBX is running on a classic PCI motherboard PC (I never tried them)

You still say you have three analogue line out from device in photo III , I think not …
Please check again those cables exiting the ports marked as “S” (the ones you marked with “1st phone number” arrow :
One goes to ATON isdn phone and the other one ???

You can find manual here:

The first two ports are “S” BRI interfaces, not analogue.

That makes sense. So the third analog port has a SPID assigned to it for the extra phone numbers? It decodes the DNIS and directs calls?

It has no third analog port
It has two 4-wire “S” output that are in parallel inside the board (it’s an “S” bus, you can also make a 4 wire parallel bus out of those RJ45 ports)

Also , there is a “S” to 2_analogue_ports converter inside the “NTBA” board to provide pots output for analogue machine

The service provider can assign up to 10 numbers (8 in Italy)
All of these number are available on the two RJ45 S ports , the BRI device connected will be instructed which number to answer
The two analogue a/b port instead will be instructed by NTBA configuration which of these numbers to answer by making the port ring.
Pratically this way:

Great description. Here it is (Euro ISDN BRI 2B+D digital channels with integrated TA for analog - a1/b1 and a2/b2 - user ports).

I think this TU could be very uncommon in North and South America (and not only there…): basically in USA they should have T1 lines (similar to european E1 or S2m ISDN PRI 30B+D) but definitely not Euro ISDN lines…and, yes, in this case Euro stands for Euro(pe)!

Actually BRI’S were widely available as 128k 2B+D configuration. Most ISDN routers would drop the.bonded B channel and rebond when voice call was over.

The cool thing is most dial up providers used PRI’s for access servers so you could sign up for a dial up connection and end up with full period 128k,

That was a big deal in 1997.

I think if you use a S/T interface with existing TA you should be in good shape.

(actually 144k was possible bonding all three channels over some hardware, my son was the hero of the neighborhood for online gaming parties, we still have a few “Talent” in the Hollywood Hills that use ISDN BRI for voice-overs from their swanky home studios to the radio stations. Apart from that, ISDN BRI is pretty well dead here with project Bravo extending pstn/dsl over fiber into the “boonie” neighborhoods )