Building an analog -> SIP adapter

Hello, I was going to buy a standalone analog -> SIP adapter device, but I’m wondering if I could build it into my router instead. My router is a desktop system running Gentoo Linux. Can I do this, and if so, what hardware and software is required?

If you want to use an existing Linux box you can install a Digium TDM400 with a single FXO module (for a phone line connection) or an FXS module (for an analogue telephone) and then install Asterisk on it. However, this is likely to be more expensive that buying an ATA device to do the same job.

If you buy an ATA I would recommend a Sipura SPA-2000 if you want to plug in an analogue phone or an SPA-3000 if you want to plug in a phone and have a phone line connected. The SPA-3000 is particularly good because you can set the FXO port up as a lifeline connection for the phone or a trunk from an Asterisk box.

My goal is to allow a postage meter to dial an 800 number to download postage. Can I use a normal PCI modem to connect the meter to the router instead of the Digium card you mentioned?

The point of building the adapter into the router is to avoid having to configure and run a standalone adapter’s software. Is there any way to control a standalone adapter with software on the router?

I’m being told the Digium cards won’t work without a lot of custom coding since I’ll be outsourcing the PBX.

uhh, it sounds like you want an ATA like a linksys pap2. an ata (analog telephony adapter) is just a box that has ethernet (speaks SIP) on one end and one or more FXS ports on the other. So you could plug your meter into the ATA, and when the meter dialed it would go out via whatever SIP service you have the ATA configured for.

unless i am misunderstanding you…

This is the first time I’ve looked into voip stuff at all so I’m probably making no sense.

I want my postage meter to be able to dial the Pitney-Bowes 1-800 number to download postage. I’d like this to happen via voip so I don’t have to get a POTS line. My buddy is starting a voip service which includes a remotely hosted PBX and I’d like to use that so I don’t have to figure out how to set one up myself. I have a desktop router running Gentoo.

What do I need to do to make this happen?

IronHelix is right. Yes, asterisk will do it for you, and then some. If you ONLY want it for the postage metre tho, and not for any other phone calls, then you’re looking at a fair amount of overkill, imho. You’d be better off with something like a Cisco ATA-186, or whatever is common now (linksys has a few out, as do a myriad of other providers - same hardware as what Vonage ships you). They’re Analogue Telephone Adapters that do part of what Asterisk can do, in a much more simplified manner. You’d need about $150 worth of hardware (to let you turn the VOIP traffic into an analogue telephone line), plus the computer, plus the software and configuration time, in order to set up a voip/analogue adapter out of Asterisk. The ATA’s give you a telephone jack inside, and connect you to a remote VOIP server on the outside. Quick and easy.

Now, if you’re wanting to make phone calls as well, then Asterisk is gonna be a better bet for you. Just my $0.02 tho.

How does this look? It’s a Grandstream HandyTone 386. … 170496.htm

Does anyone know if the two FXS ports can be configured separately so I could connect and use the postage meter with one and a normal phone with the other?

My router is currently set up for wireless only, but could I pop a normal ethernet adapter in there and connect the Grandstream to it via a crossover ethernet cable?

Would all of this allow me to use the hosted PBX voip service?

Tho I’ve not worked with that model directly, every other box I’ve seen which has two FXS ports on it configures them independently of each other - you could have one port with Vonage, and another with Packet8 for instance, but you can use them at the same time, even if they’re with different providers or the same provider. So yes, that should do exactly what you need.

Read the specs carefully about what the Grandstream needs for its ethernet handoff - if it’s auto mdi-x/mdi-ii sensing (or if the router’s NIC is as well), it won’t matter. You’ll also want to make sure your router can do QOS if you intend on making voice calls regularly, otherwise you may get some quality loss if you’re passing high traffic at the same time.

Should I be reading the specs on the ethernet handoff carefully to determine if I need a crossover cable or not? Can you tell me a little more about what you mean there?

The router should be ok for QOS. It’s a desktop running Linux.

I made that sound a little more important than I think it will be in reality. Try setting it up with the crossover cable. If it works, go with it. If the link lights don’t turn on, try a straight-thru cable. Generally, if it doesn’t light up, its either not plugged in or using the wrong cable. A lot of newer NIC’s are autosensing as well, so it will pick up whether or not you’re using a crossover cable, and what environment you’re in (so you can use a crossover cable to connect to a switch, and it will adjust accordingly - something that wouldn’t work otherwise). Anyway, way off topic here. You shouldn’t have much trouble with it.

You may also want to make sure you configure port forwarding correctly as well, since your setup sounds suspiciously like you’ll be running the ATA behind a NAT device. That being said, it may not be required at all. I used a Cisco ATA-186 with Vonage a few years ago, and it was literally plug and play, no network config required. I’ve also done setups for devices that required the ports to be forwarded, so it’s touch and go. Good luck! I’d like to hear how it works out!

I actually don’t have a crossover cable and I’d rather not buy one. You think it might work with a normal cable? My NIC is really old.


I have got a similar problem: the office has got an asterisk with isdn trunk lines, and voip phones. Our postage thing comes with a stand-alone modem, so possible options were to add one analog port to the asterisk, or get an ATA. I chose a PA168 based one running IAX

Installation was a bit of fun, though: the manual explains how to do some initial configuration from the connected phone … and in the end I had to borrow an analog phone to get the beast running


Is that an ATA or did you add an analog port to the PBX?


it is an ATA -the one I got has 1 FXO and 1 FXS. I chose it because it supports IAX as an option.
It turns out to be cheaper than a single-port analog card, btw


From what I understand the original poster to say he wants to dial a modem connection to download some data (Pitney Bowes postage credit).

All I have heard and read so far suggests that doing this over a VoIP connection might just barely succeed as long as he uses a alaw or ulaw (i.e. non-compressed) codecs; but that generally it is not very reliable.

Any comments on that?


Wolf Paul