FreePBX on a hosted public box

Hi All,

How many IP Handsets do you think could connect from one ADSL connection via NAT to a public hosted FreePBX box? Just one? Would it be best to create an OpenVPN connection to the FreePBX etc. for serveral IP phones? We normally deploy these all in house.

Thanks for any advice.

you have to love open ended questions…

To answer that you need to know a few things.

  1. bandwidth cap’s (or better yet actual limits if you are far, far away from the Central office) for inbound and outbound on the adsl.
  2. amount of bandwidth already used by all other normal internet processes and there upper limit that they use.
  3. the codec you are planning on using.
  4. Can you do QOS or not (with QOS you can control which side get’s priority over the other so you can reserve a set amount for use)

Once you have all those pieces of information take say 80% of the smaller bandwidth (normally the outbound), look up the bandwidth requirements for the codec(s) and do the calculations.

Sorry I can’t give you a hard and fast number.

FYI: ADSL distance is very important as from my house on ADSL I’m lucky if I could do 2 calls using ulaw, but a mile up the street at a friends house you could do 4. That’s why I dropped the local telco service and went with Cable until they can deliver a fiber loop to me in another year or two.

Sorry, I didn’t mean to ask about bandwidth, but merely from a NAT point of view. For example, SIP and RTP will need to be port forwarded to only one handset right? So you could only have one handset behind a natted router?

A handset with a good firewall should allow through more then one through without a issue (i.e. SIP aware). If you “have to” setup port forwarding to make a handset work then yes you would be limited to 1.

A handset registers to a server so it makes outbound connections.

Sure, I know it makes outbound connections, but rtp 10000-20000 ports and 5060 need to come back in, so if using a SIP aware router, more than one handset behind NAT with the server on a public will work?


With good phones and a decent router you do not need to forward any ports to phones.
I have boxes with MANY Polycoms / GS phones behind decent routers (Linksys RV082)
I NEVER forward ports for phones… unless the router was crap and I could not get the customer to replace it.

OK, thanks. Need to get new routers then!