Hosted VoIP

I am shopping for hosted VoIP and have this dilemma:

- Hosted VoIP over existing internet data connection
- Dedicated T1 in each office for VoIP only

besides looking for to reduce cost and deal with less providers I would also prefer to reduce the equipment on site (while with the first option I will need a router in each location for the VoIP only) and really like the idea of utilizing existing data bandwidth for the VoIP service while few consulting companies told me they would not recommend that.

What are your thoughts or experience with this?
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Let me break this down to make it clearer. From what i have read.

1. 3 offices
2. Average of 20 people per office (assuming already there will be 20 phone or end points per office)
3. There is A 20 Mbps existing Internet line.

Okay to help you further I would need to ask certain questions. I do hope you can bear with me.

1.  Of the 20 people per office would it be safe to say that all of them will be on the phone at the same time?  (this is a very hard question to answer. And can only be answered by you since your boots on the ground so to say).  

2.  Assuming that the 20Mbps existing line is only with the Main office are there existing internet lines for the other 2 offices?  Or all 3 offices already have 20Mbps lines each?

3. What is the current average and max utilization of the 20Mbps line on peak hours?

To explain further  there are a lot of ways to make 20 concurrent Voip calls fit into a small internet pipe. The chief is using narrow band codecs.

The normal standard codec for voip is G.711 which has a base of 64kbps however in reality this is not exactly what goes out your internet pipe.  There are some overheads to this number depending on what transport is used (Layer  2).  This size can range from 80kbps to 87kbps.  However in comparison G.729 is declared at only 8kbps plus overhead it would range from 26kbps to 32kbps.

This means that on a T1 line (1.5Mbps) using G.711 you can only fit about 17 concurrent calls.  With G.729 you would fit 46 concurrent calls.  However the only draw back of using G.729 is that you need an endpoint with a G.729 licence.  Normally all Hardware phones is capable of this unless its stated otherwise.  The other draw back the Hosted service you are looking at should have G.729 fully supported (i.e licensed) not just pass through.

Ref for voip codecs:
Check out Ring Central.

    T1 is not much bandwidth these days.  How many end points per "office".   Do you plan on limiting the T1 to VoIP only or are they shared spans ?  

    Other big consideration is how much inter-phone traffic do you have.  As calls between two users in the same building will take twice the bandwidth if you go totally hosted.

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CozumelAuthor Commented:
3 offices, and I have a maximum of 20 people in 1 office. T1 should be enough as per my calculations but I would like to avoid having separate connection for voice only, while this is what most consultants recommend.
Well a T1 is 24 channels (calls) in TDM analog mode, and depending on the CODEC will equate to about the same in VoIP.   So 20 people and a little email will bury a T1 almost immediately.  

For these type installs I have had good luck with Comcast Cable business band installs...

But I much prefer a local PBX in each facility with IAX2 channels between the facilities.

CozumelAuthor Commented:
T1s will be for voice only, email and everything else will continue to be used over my 20Mbps internet connection. I am advised to get one T1 for the voice only - which for me doesn't make sense.
If you have a 20Mbps pipe and really want to outsource this I would do a Hosted solution with RentPBX or one of the many other services and you should be alright.  You can always add the T1 latter if call volume or other factors change.

Might want to use the tool winmtr to response times to the hosted facilities.

Just watch the loading and QOS internal.  

CozumelAuthor Commented:
We ended up with shoretelsky, so far, so good. T1 in each office is enough, just a few dropped calls. Their messenger sucks, and SF adapter doesn't work for our SF edition but the saving is great, no more PRIs and AT&T bills - it's like a dream!
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