[asterisk-users] Phone system layout suggestions

[Bill Andersen]

I am thinking about a change to our company's phone "layout" and would like
to get comments from people who have done something similar.

Currently, we have 3 locations - each with their own Asterisk PBX.  The
corporate office has a PRI.  Each remote location has a SIP provider for
5 channels of SIP going to their own PBX.  Interoffice calls use the PSTN.
Most inbound calls come to the headquarters via a toll free number.

We are adding another remote office and are planning a MPLS network to
connect all locations for DATA.  As we really want a "centralized"
switchboard
anyway, I thought with QoS and an MPLS, I could eliminate the remote PBXs
(and not have to buy another for the new locations) by simply using the MPLS
to
tie everything together.  See below.

/--------------------\
|  CORP HEADQUARTERS |----> PRI (23 Channels, 100 DIDs)
|  Asterisk PBX      |
|  30 Polycom 501s   |
\--------------------/
          |
          | < 3Mbps MPLS (2 T1s)
          |
/--------------------\
|  MPLS "Cloud"      |
\--------------------/
  |       |       |
  |       |       \---SIP over MPLS 1.5Mbps T1---Branch Office 1  (5 Polycom
501s)
  |       |
  |       \-----------SIP over MPLS 1.5Mbps T1---Branch Office 2  (5 Polycom
501s)
  |
  \-------------------SIP over MPLS 1.5Mpbs T1---Branch Office 3  (3 Polycom
501s)


Question 1: I've never had an MPLS network with QoS.  Will the call quality
            "Really" be as good as AT&T assures me it will be with QoS?
Assuming
            we never have more than 5 calls going over the MPS from a
branch?

Question 2: MPLS are pretty reliable, but last mile connections can be cut,
hardware
            can fail at AT&T or whatever.  Is this putting too many eggs in
one
            basket?  If I lose the headquarters T1s (MPLS or PRI), everyone
is
            down.  Would "You" do it this way?

Question 3: (OT) For those who have used an MPLS.  How much better
throughput for
            DATA (NOT VoIP) should I see compared to using the Internet?
I'm mostly
            just curious here and realize it is hard to compare, but when I
do any
            type of file transfer between office right now, I use FTP over
the Internet
            and both ends have a T1.  Assuming an MPLS on each end, what is
your
            experience when comparing average "throughput" compared to an
Internet
            transfer.  Just a guess of what you've seen.  (i.e. Yes, you'll
see
            a big difference, maybe a little better or couldn't really see
that
            big of a difference)

Thanks for your input.

Bill