[Asterisk-Users] Softswitch

[Brian D Heaton]

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
 

On Fri, 2003-11-07 at 20:05, Darren Martz wrote:
> Pardon my ignorance, but I was hoping someone could clear up something for
> me.
> 
> - For a few POTS lines, digium has a single port card for that, or a T1 card
> to a channel bank.
> - For 10 or more lines, digium has a T1 or E1 card for that too based on PRI
> channels
> - For 100's to 1000's of lines, I suspect a soft-switch is in order???
> 
> A traditional phone company will sell:
> - POTS lines for small quantities
> - PRI channels over one or more T1 lines
> - ??? for 100's to 1000's of lines???
> 
> Unlike PRI channels, we are all able to get better than 64k using a variety
> of different codecs. So how is it possible to get more out of a link/bridge
> (pardon my lack of proper technical terms) to the public phone systems?? If
> a codec can drop a channel down to 8k, then a single T1 should be capable of
> supporting nearly 184 concurrent calls right??
> 
> I suspect this is where a softswitch comes in, but it is not clear to me. Do
> you call up a phone company and ask for a block of T1's using SS7
> signalling, or MGCP, and plug it into a softswitch?? If that is even
> partialy correct, does that decrease the cost (HERE IS THE KEY) for access
> to public lines? I'm sure the softswitch (again assuming I'm partially
> right) costs around $100k.
> 
> Asterisks shows support for MGCP channels, does that help in this fuzzy
> scenario?
> 
> Perhaps I am way off, but I do hope someone can clarify some of these things
> for me, or at least get a laugh at my quesions and wording <grin>
> 
> Cheer,
> Darren
> 
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