There are two different approaches available:
1. Hardware
What you want is a remote SIP gateway. These are boxes which have FXS/FXO/E&M ports in some combination on one side and and an ethernet port on the other. Most of these boxes were originally designed to run H.323 and had SIP firmware added at a later stage.
An example is http://www.ovislink.com.tw/voip400.htm.
Ovislink have 4 and 8 port units. Each takes a 4-port (or two 4-port units for the 8 port model) adapters. These can be either four FXS or four FXO or four E&M adapters.
Ovislink also have a 2-port model http://www.ovislink.com.tw/voip220rs.htm which seems to have better SIP support.
These boxes were originally designed to run H.323. Since SIP has become popular Ovislink added a SIP frontend component to their firmware. This has the effect that you have to configure *both* the H.323 component *and* the SIP component to get the box going. It does work, but it can be a pain to configure (try reading the fairly comprhensive manual two or three time and then having two or three goes at it before it all works). Read the user manual (http://www.ovislinkcorp.com/Manuals/VoIP800-400%20manual.pdf), the separate SIP guide (http://www.ovislinkcorp.com/Manuals/SIP_Guide.pdf) and the VOIP command reference (http://www.ovislinkcorp.com/Manuals/VoIPReference.pdf) to figure out whether they do what you want.
These boxes can be rediculously cheap on occasion. I've seen new Ovislink 8-port gateways on eBay for US$200-300 form time to time. Otherwise, I believe that they have distributors in the US/Europe/Australia.
The main problem with using the Ovislink gateways is making sure that they have the correct approvals. For instance I found that I couldn't use one here in Australia because they lack A-tick approval (and I'm not about to spend the $50K needed to get them tested). They *appear* to have FCC and CE approval, but they would not be the first manufacturer to print approval numbers on the case when the approvals did not actually exist. I'd check before I'd use one - using non type-approved equipment can attract very large fines.
In general, these boxes are reasonably reliable, or at least reliable as say an ADSL modem/router. If the location was really remote you could place a second box at the loaction and a PSTN switch to switch the lines. Hopefully there would be someone on the premises who could unplug the PSTN line from box-A and connect them to box-B if necessary.
2. Telco/Service Provider
I don't use the Ovislink box myself, although I did evaluate them. After I hit the lack of approvals roadblock I mention above, I took a very different and much simpler approach.
I found a telco who would do call collection for me. They had Cisco routers in each telephone district in Australia. Incoming calls on my numbers were sent to their routers which sent them directly to my gateway.
Now admittedly this was for a much larger application than you are talking about (60 "lines" - actually telephone numbers) are involved. The biggest problem was that the telco would only deliver the calls using H.323 (since most business PABX's use H.323 rather than SIP), so I had to build a H.32-to-SIP gateway using asterisk (which was a pain to get going - asterisk's H.323 support is ideosyncratic).
On one hand the telco approach was cheaper (a monthly charge rather than having to buy and house a number of routers). On the other hand it is an ongoing charge. From memory, the hardware cost represented about 30-40 months of telco charges.
The compelling reasons for choosing the telco approach are (a) simplicity - its a lot simpler to have one gateway rather than a number of different PSTN gateways in remote locations; (b) reliability - the telco has around $175M is Cisco kit, if something breaks they have a redundent backup standing by.
I hope this gives you a few pointers.
regards Matthew
Date: Fri, 31 Dec 2004 18:22:03 +1100
From: David Uzzell <[EMAIL PROTECTED]>
Subject: [Asterisk-Users] FXO to IAX on ethernet. or FXO to SIP on Ethernet
To: Asterisk Users Mailing List - Non-Commercial Discussion
<asterisk-users@lists.digium.com>
Now I have searched around and not seen anything to do this.
I want to in remote locations were we need to have single or 2 PSTN lines for in dial as little hardware as possible and as stable as possible so that they will operate without user intervention.
What I want to do is be able to take a single PSTN line in and go out through adsl for the Inet link.
These would be in VERY remote locations like smaller towns so they would need to be simple, stable and require little to no user intervention after they are installed.
Does anyone know of any hardware that will do this or a way that this
could be done or ??????
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