[Asterisk-Users] System Design

Thu Mar 9 09:04:51 MST 2006

> The DSL speed at the remote office is 1.5 to 6.0 Down and 384 to 608 up.
> The DSL does have a static IP address and it's pretty rock solid in
> regards to stability.

Curious, why the huge range in numbers?  I have 1.5mb/s down and
512kb/s up, it's always been that.  Or do you mean you have 6.0mb/s
down and 608kb/s up, but in testing sometimes the actual speed tests
lower?  Anyways, just curious.  If you could keep the upload at 608
that'd be great.  384 is a tad on the low side, but even handling
uncompressed calls you could handle 3-4 calls.  Using compression will
help out a lot, especially if you're using that link for non-voip
purposes.  You'll definitely need some kind of qos.  I'd go with
another box, preferably one that doesn't require cooling and has no
hard drive.  I'm just picky, but I hate having multiple points of
failure.  Another server thrown in could have a fan fail (either
locking it up or burning up the processor) or have the hard drive fail
(and your whole network is brought down until you take the qos server
out of the way).  That's another reason I run qos on the asterisk box
(I'm cheap, and it's one less possible point of failure, and one less
thing to plug into my ups).  I'm guessing you're going to run some
kind of nat?  Whatever you run the nat server on, have that handle qos
too.  Actually, throw on a decent firewall too.  Any low-end cpu
should be able to handle the load no problem, heck a 486 would do
(again, personally I'd look at a newer cpu that needs no fan to keep
cool, feel free to put one on it, but you'll know if it konks out your
network is a-ok).

> Would the remote office * need a couple of POTS lines to make those
> local calls?

It all depends.  How many local calls do you plan on making at a time?
 If generally you need four total incoming/outgoing calls via a local
line (that's incoming and outgoing combined, not separate), but will
very rarely need say, 5-6 or more, it may be cheaper to just get four
lines and any time a fifth call needs to go out, make it as a
long-distance call.  1.1cents/minute for a few calls will be cheaper
than paying for that fifth or sixth line.  Even if you have enough
pstn lines to handle all local calls, I'd still have it setup to
automatically let them make the call as a long-distance call, never
know when that important call needs to be made.  You can do the same
for incoming calls btw, get a feature called "Call Forward Busy" and
do NOT get call-waiting on the line.  When someone calls in, and the
line's busy, it'll forward to another number you have via voip
(whether it's a local number, or a toll-free number, doesn't matter). 
Now on those incoming calls, you may get the callerid of the original
caller, or the callerid of your regular line (since in effect it's
calling your other number, forwarding it on).  In fact, you can get
this to simulate your own PRI with just a few cheap PSTN lines.  It'd
be setup something like this:

555-1000:  If busy, forward to 555-1001
555-1001:  If busy, forward to 555-1002
555-1002:  If busy, forward to 555-1003
555-1003:  If busy, forward to 555-1004
555:1004:  If busy, forward to 555-2000 (a voip number)
555-2000:  Unlimited inbound calls

Actually, you may want 555-1000 to immediately forward to 555-2000, if
bandwidth isn't a concern and the number you're forwarding to is a
local call.  In my case, there's no local voip providers and I have to
forward to a toll-free number, so I would want to keep the calls on
the pstn line.  Other than the possible caller-id issue (callerid may
be of your own pstn line, or of the caller), this setup should work
fine.

> Once again thanks for all of your replies!  They are definitely clearing
> things up for me.
>
>  - Jason
>
> -----Original Message-----
> From: asterisk-users-bounces at lists.digium.com
> [mailto:asterisk-users-bounces at lists.digium.com] On Behalf Of Joseph
> Tanner
> Sent: Wednesday, March 08, 2006 6:54 PM
> To: Asterisk Users Mailing List - Non-Commercial Discussion
> Subject: Re: [Asterisk-Users] System Design
>
> Lot of questions, lots of variables, but I'll touch base on a few
> things.
>
> 5-10 concurrent calls is hardly anything.  A plain T1 will more than
> handle that, even at ulaw or alaw (non)compression.  Throw in a decent
> codec, and 10 calls won't even put a dent in your T1.  Heck, it'd handle
> all 20 users in your main office, and the 5 users in your remote office
> with G729, no problem.
>
> How reliable is the remote office's DSL connection?  I'd make sure you
> have a static ip for it (dynamic ips are just slightly problematic,
> especially if you have slightly flaky service, coupled with a slightly
> flaky modem).  If it's reliable, then just keep that.  What's the
> connection speed?  Need to know the upload and download.  If it's ADSL,
> then the upload will be a fraction of the download, and will be the
> limiting factor.
>
> Since I don't know your specific setup, I can't tell you specifically
> what to do.  I'll make some guesses though.  Keep DSL.  No need to use
> VPN just for asterisk.  Make sure each end has a static ip (dynamic ip
> will work, but is harder to setup and more prone to errors).  Have each
> asterisk box register to the other.  For normal incoming and outgoing
> calls, just have the asterisk box at that particular location handle it
> (no need for the remote office to connect to the main office's asterisk
> box, then call out via iax or sip for a long-distance phone call).  You
> can create "local" extensions that when dialed, will ring a person on
> the other asterisk box.  I.e., a user at the main office can dial 2001,
> and get a user at the remote office.  If you deal with call queues you
> can group users from both offices together, no problem.
>
> A T1 or a point to point connection at the remote office would work, but
> is probably unecessary.  If their DSL connection is flaky and
> unreliable, then start looking at both options.  I'd probably go with
> whichever is cheapest, be sure to factor in equipment costs (you can
> generally lease equipment with a T1 line, but not with a point to point
> connection).
>
> As far as server specs, if all it's going to run is asterisk, then
> that's overkill even if it was handling all the calls.  If you think you
> need that much server but are on a budget, then get one setup for dual
> processors but with just one installed, and less ram but that has room
> to add more.  If budget's not a problem, I say go for it!  That system
> should last you for quite a while.
>
> As for QOS, sorry I can't help you there.  You could get a cheap router
> that has QOS built-in, or run a separate low-end server just for QOS.
> Personally my asterisk box also serves as my nat server, so I just run
> QOS directly on it.  It's probably not something you want to do in an
> office environment, but it's better than no QOS at all.
> Hopefully someone else will give you some good advice on QOS equipment.
>
> Joseph Tanner
>
> On 3/7/06, Jason Adams <jadams at sumosystems.net> wrote:
> >
> > Hey Everyone,
> >
> > We are in the works of planning a new * installation for our company.
>
> > We have 20 users in our main office and 5 users in a remote office a
> > couple of states away.  Our call volume for the main office will be
> > anywhere from 5-10 concurrent calls.  The remote office will have
> > about 3 heavy users with two users making calls occasionally.
> >
> > Right now we have an existing PBX.  We have a T-1/PRI coming into the
> > main office and a DSL connection at the remote office.  We have a
> > Cisco 2610/PIX
> > 501 at the main office a cheesy linksys router at the remote site.
> >
> > We are planning on purchasing new Cisco IP phones for everyone.
> >
> > My main question is this:  What type of hardware/network design would
> > be best for this situation?  Would a full T-1 at the remote site work
> > with a VPN between the offices?  Or would a higher bandwidth DSL work
> with a VPN?
> > Or should we move to a Point-to-Point connection?  What type of
> > hardware would be best for the end-to-end communication in regards to
> > QoS?  I know the PIX 501 doesn't support it.
> > Would it be best to have two * servers in each office or for that call
>
> > volume at the remote office does it make sense?  I was thinking of a
> > Dell Power Edge server with 4GB of ram and a dual processor.. is that
> enough?
> >
> > Sorry for all the questions!
> >
> >
> >
> >  - Jason
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