Simple to Complex VOIP questions. Part 1...

Posted on 2005-04-22
Last Modified: 2010-04-12
Hi Guys,

I am a networking guy who's fairly competent but terribly new to VOIP, and yet I'm left in charge of providing voip solutions to several of our customers. I sort of need a crash course on the different aspects of voip and I would need answers to some questions I will be asking on the coming days. Each question will be worth 500 points and I believe there'll be several ranging from simple to complex issues.

 On this first one, I'll be asking the most simple question:

I have 2 offices with broadband DSL connections to the internet (1mbit up, 256 k down.). These offices are in different countries but the connections are pretty reliable.

I want to connect only one phone from office A to another phone located in office B.
I want to dial, say, 8888 on the phone in office A, and the phone in office B will ring. I want to dial, say, 9999 on the phone in Office B and the one in Office A should ring.

I have a DSL modem / firewall doing NAT connected to dumb 100mbit switches in each office. I can do port forwarding etc. that's no problem. I can get faster DSL connections as well if needs be.
I believe I will be needing a device in each office to connect the dedicated phone to, and this device will in turn be connected to the 100mbit switch and will access the internet to reach the other device over the DSL modem / firewall. But there may be other solutions that I do not know of?
I will be waiting for your suggestions.

Deep Regards
Question by:egeiyioglu
    LVL 15

    Assisted Solution

    Hi egeiyioglu,
    Your best bet is to take a look at - it has loads of excellent information that you'll find useful.

    It's also worth taking a look at Asterisk.  This is an open-source PBX system, which has many advanced features.  You can get info on this at and

    Right, to your question.  Do you mind what the phones at each end actually are?
    You can you an IP phone (either software of a bit of kit on your desk) to do this - see the options at

    Alternatively, you can use an Analogue Telephone Adapter (ATA) to connect a "standard" phone to your network connection.  A list of options are at

    The exact way that you'd do this will depend on precisely what you want to achieve longer-term, what level of sophistication you need and what your budget is.

    Do you have a VPN between the two sites?  The data that travels between the phones would generally be unencrypted, so routing the traffic through a VPN is a good idea.

    You shouldn't have a problem with bandwidth at each site, however the fact that they're in different countries could cause problems with latency.

    VoIP traffic is very sensative to packet loss, latency and jitter - you need to minimise this as much as possible, otherwise you get poor call quality.  Where possible, you would implement routers that can prioritise traffic.  More info on QoS at
    It's also worth visiting to get a feel for what to expect.

    Sorry that the post contains loads of links and not "this is the right way to do it".  As with many things, there is no "right" way - you just need to choose the most suitable way for you.

    Does that help?  Please let me know if you have any questions.
    LVL 8

    Assisted Solution

    I agree that Asterisk is a good way of going. This can be done in a very simple matter. At I have an article called Building your own PBX with Asterisk that will get you started. If you are just trying to call from phone to phone, this will be VERY simple and you can have this up and running within an hour. You can use the Asterisk@Home package ( for a pretty automated install. You would then only need to setup the two extensions. As scampgb  said, you then either need SIP phones or ATA's (again Geek Gazette has several reviews).

    The fine tuning aspect will be to play with the codecs available on your phone or ATA and set the default to a low bandwidth codec in order to minimize problems with latency.
    LVL 1

    Author Comment


    Do I realllly need an intermediary like Asterisk? Can't I simply do it with just 2 analog phones and an ATA device?
    I only want connectivity between 2 phones in 2 locations, nothing else.
    LVL 1

    Author Comment

    Dear KeeryG,

    I read the how-to guide. I understand how to setup the two offices using this system, but I don't see how dialing 8888 from Office A will get you Office B and vice versa.

    I'd also like a simpler solution without a server in between if possible.
    LVL 8

    Expert Comment

    Using Asterisk 8888 is the extension to a phone at Office A and 9999 is an extension to a phone at Office B, both phones point to the Asterisk server. Pick up The phone in Office A and dial 9999 and the phone in Office B rings. Very simple to setup. Without a server of some kind you could use the same phones but use a service such as Free World Dialup ( Each phone would have its own account and would use FWD to dial each other.

    You DO have to have something in between whether it is a server or service. An ATA by itself has to have something to connect to.
    LVL 15

    Accepted Solution

    Actually, it is possible do to direct IP-to-IP calls, without using a server in between.

    It's a bit of a hassle though, as you need to "dial" the full IP of the other ATA.
    Apparently the HandyTone 286 will let you do this, but I've not tried it myself.  See page 10 of the user manual at

    You should investigate other ATAs though, as you'll probably find one with an "address book" feature that will make this process simpler.

    Note that both ATAs must be able to communicate with each other without having to use NAT or have any firewalls in the way.  This would work if you had a private VPN between the sites, for example.


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