[Asterisk-Users] Softswitch

Fri Nov 7 22:12:37 MST 2003

On Fri, 2003-11-07 at 23:30, Darren Martz wrote:
> Thanks Brian, and thanks again for the included definitions <grin> - that
> helped too. Your comments are really helping clear many questions.
> 
> I suppose our intensions are to become an IXC.
> 
> So if my local carrier is sporting old technology, they'll provide TDM
> services. So if I understood you correctly, the "in-band signaling" is
> typically SS7, and the alternative is typically PRI? Sounds like one carrier
> more of the call management tasks and the other is a more finished product -
> and you pay more for each PRI channel right?
> 
SS7 is out-of-band signalling.  Any time the signalling is carried over
a different channel than the voice its called out-of-band.  If the
signalling is carried on the same channel as the voice its called
in-band signalling.  SS7 allows things like early-abandon and other
advanced carrier features.  Its also more efficient when you're talking
about hundreds/thousands of voice bearer channels.  The last CLEC
network I ran (Denver, CO) had a couple hundred T1s worth of interswitch
trunking to the various USWest (LEC) COs.  When you add up a D channel
per PRI we would have lost a lot of capacity.  You can use a D channel
across a number of PRIs in a trunk group, but SS7 is the standard for
interconnection.  

I'm not familiar with Canadian interconnection agreements or telecom
pricing.  You'd have to look at the requirements to be an IXC there.

> I know our local carrier recently upgraded the entire LD infrustructure to a
> Nortel VOIP solution (Telus in Canada). Perhaps they could provide VOIP
> channels as you indicated instead of TDM services. FYI: Telus spans across
> the entire Canada, and are a major carrier. They are also a major pain to
> deal with, and I'm not sure they'd be willing to sell a VOIP package.
> 
Gee, a LEC that is a pain to deal with? No, say it isn't so. <G> I've
sat on the cell phone talking to a USWest tech who was supposedly at a
fiber-optic-terminal (FOT) working on a down T1 that we had already
escalated a couple times (down for over 8 hours).  Then I told him to
look to his left and he'd see me waving.  He was in the drive-thru line
at a McDonalds.

> Hmmm.... if our target is to manage a maximum of 2000 concurrent calls (for
> arguement sake), I suppose a softswitch is overkill. Although I did notice
> that companies like MetaSwitch operate as small as 400 lines.
> 
Do you mean 2K concurrent calls across your network or dropping 2K
concurrent calls at a single location?  Again, Canada may be very
different than the US in how calls are originated/terminated.  Here the
IXCs pick up and drop off calls to the LEC at a switch known as a "LATA
(local access telecommunications area) Tandem".  (Anyone know the exact
number of LATAs or the US?)  If you want ot handle calls between Dallas,
Texas and Denver, Colorado (for example), you would take the call from
Southwestern Bell at the Dallas LATA tandem, route it through your
network according to the NPA/NXX and hand it off to USWest at the Denver
LATA tandem.  That means the call occupies 2 hand-off channels (1
Dallas, 1 Denver) and a single voice channel of bandwidth across your
network.

2K concurrent calls on the network may not be a problem.  2K calls
originating/terminating on the same * box might.  I'm a telco heavy just
getting started with *.  I try to do my part by answering the telco
questions I see on the list.

> So if our only option was a TDM based solution, and we used Asterisk as our
> "softswitch", what signaling would be ideal to keep the cost at a minimum? I
> don't recall Asterisk supporting SS7. Besides I read the Telco's only allow
> SS7 products they have tested and certified.
> 
I think the most preferable solution would be PRI.  I can't say for sure
though without knowing more about what you are trying to accomplish.
That may get a little close to your business plan for an email list
though.  Generally, PRI gives more detailed and complete signalling data
than other types.  Its probably a legal issue more than anything else. 
There may be regulations in Canada that require you to do SS7 if you're
legally classed as an IXC.  I don't know.

> I wonder what would happen if the carrier provided VOIP channels. I suppose
> it would still use T1s, but with what form of signaling?
> 
Again, not really enough information to answer.  Even if Telus has a
VoIP core network they are almost certainly handing off to customers
with TDM services.  Its a regulatory issue as much as a technical one.

If they were handing off packet switched VoIP interfaces I'm guessing
you would see a LAN type interface.  The hand-off to the customer would
(hopefully) be 100Mbps Ethernet and the LEC would charge by the
bandwidth back to the equivalent of the tandem.  Other charge models
might work too.  Thats a whole different side of the business.  It could
just as easily be IP over ATM or some other bearer service.

Fell free to contact me off-list if you like.

			THX/BDH

> Cheers,
> Darren
> 
> > Subject: Re: [Asterisk-Users] Softswitch
> > From: Brian D Heaton <bdheaton at c4i2.com>
> > To: asterisk-users at lists.digium.com
> > Organization: bdheaton at c4i2.com
> > Date: Fri, 07 Nov 2003 21:26:49 -0500
> > Reply-To: asterisk-users at lists.digium.com
> >
> > Darren,
> >
> > The answer (unfortunately) is "sort of" and "it depends"
> >
> > ----- Definitions -----
> > LEC = Local Exchange Carrier
> > CLEC = Competitive LEC
> > IXC = Interexchange Carrier (LD company)
> > -----------------------
> >
> >
> > In most cases a traditional phone company is going to want to hand off
> > TDM (circuit switched) services to you.  This is true whether you are a
> > normal business or a CLEC/IXC.  If you are a CLEC with SS7 connectivity
> > (and an assigned point code) they will hand off T1s and do the
> > signalling out of band over the SS7 connections.  In-band signalling is
> > possible, but not common anymore. I know that in the late-90s in
> > SouthWestern Bell land they often wanted to hand off calls from their
> > 1AESS switches in MF format rather than SS7.
> >
> > A typical business would be handed either in-band signalled T1s or
> > PRIs.  I don't know of any cases where private enterprises have gotten
> > their own point codes and SS7 connectivity, but someone else may have an
> > example.
> >
> > In the market now are firms which offer the end-user individual or
> > business VoIP origination/termination of both local and LD calls.  While
> > the customer of these firms sees a VoIP interface I would bet that the
> > hand-off to the terminating LEC is still done via TDM circuits.  This
> > may change in the future as the IXCs complete their transitions to VoIP
> > internal trunking networks.  I don't expect the LECs to change rapidly
> > though.  Their cost-recovery and depreciation models are based on their
> > switches lasting a loooooooong time.  If anyone has an example of a
> > traditional US LEC offering VoIP hand-off and termination I'd love to
> > hear about it.  I just haven't heard of a real-world example yet.
> >
> > Depending on the size of the deployment, a softswitch may be the way to
> > go for hand-off to a LEC.  Given the size of typical carrier grade
> > softswitches though, I'd think that is something you'd only be looking
> > at if you were a very large enterprise or some type of carrier.  The
> > size of the enterprise and the mix of traffic would determine where the
> > crossover is between a softswitch and another solution.  Actually, you
> > could make a case that * is a softswitch.  Really you're just talking
> > about scale here.
> >
> > The big question is when does a * server run out of gas? If you have 4
> > quad-PRI boards in a system you can provision 368 trunks via PRIs.
> > Depending on the average length of call that is quite a bit of
> > trunking.  I've seen CLEC trunk-groups to the access tandem that were
> > smaller than that.
> >
> > Hopefully this answers some of your questions.....
> >
> > THX/BDH
> >
> >
> 
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