[Liverpool] SIP Providers

[Sebastian Arcus]

Hi,

On 18/08/11 14:34, Liam Craddock wrote:
> Afternoon all,
>
> I want to setup a SIP phone at home instead of getting a BT line. I have
> a Cisco 7940g phone which has a SIP firmware image I can flash on. I
> want to to talk directly to the sip provider, no go through any
> intermediate hardware.(Sebastian, any reason why this wouldn't work?)

This could work, with some caveats. On the plus side, it saves you 
having an Asterisk server to configure. On the minus side, it gives you 
less flexibility in configuration and specially troubleshooting. Your 
phone will not support as many options and codecs as Asterisk - no 
matter what model you use.

Also, as the others have pointed out, most phones have limited ability 
to pass through NAT's both ways. STUN, ICE and open ports all can help 
here - depending what the phone supports. Although I use the 7940g's 
that you gave me - I haven't investigated NAT traversal with them - as I 
never needed it. However, open incoming ports add some question marks on 
the security front - but you can help by limiting source ports to your 
provider's IP address(es) at firewall level - to at least mitigate the 
potential for DoS or worse. You will have to research in this case if 
your provider does use a limited number of specific IP addresses. Some 
providers do, others don't.

You will also struggle (or find it impossible) to run multiple phone 
sets on the same line (in different parts of the house) - depending on 
the provider's settings - if that is something to be desired.

But the above doesn't necessarely mean it is impossible. I would say 
that phone sets aimed more squarely at consumers (such as some DECT sip 
phones or some soft phones such as X-lite) seem to be better equipped in 
the NAT traversal department then phones aimed at business - which are 
expected to be inside a NAT - talking to a voip server on the local 
network. But that is merely a general observation.

Also, if you use Asterisk you will be able to use IAX trunks. They don't 
use two different port (sets) like SIP - so they are more straight 
forward to pass through firewall. But, generally, you can't use IAX 
directly with a phone - although there was one IAX hardware phone if I 
remember correctly - and one or two soft phones.

>
> My question is, what sip providers would people suggest? It'll be low
> call volumes, possibly one or two calls a week, and probably most
> incoming. I'll need an external number and I don't really mind if its
> local or not. Do sip providers generally charge for incoming calls?

There are plenty of providers out there. I would say, specially for 
tests, it is hard to beat somebody like sipgate.co.uk. You get a free 
incoming local phone number (0151 etc.), and pay-as-you-go for outgoing 
calls. They didn't have any setup costs last time I checked, and no 
monthly cost. Even if you use them for initial testing - and then move 
on to some contract based offering. I've managed to set them up on 
Asterisk for incoming and outgoing without opening ports in the firewall.

I have also used gradwell.com - and found them good. They were doing two 
types of SIP trunks - an enterprise one which absolutely required 
incoming ports open - and one designed to be used on its own (without 
Asterisk) - which I believe might have worked without opening ports.

I would be curious about using voipon.co.uk as VoIP providers. I've 
never used them for phone calls, but I bought quite a bit of VoIP 
hardware over the years from them - and been very pleased with it.

>
> I also want to configure the devices and test them before committing to
> anything, do providers let you do this?

Again - a pay-as-you-go provider would come in handy here. If they also 
provide an incoming phone number - like sipgate do (and others I 
believe) - it can be useful for testing both incoming and outgoing.

Sebastian