[asterisk-users] OT - Avantages of ISDN PtP and PtmP

[Tzafrir Cohen]

On Mon, Sep 29, 2008 at 01:26:10PM +0200, Olivier wrote:
> Hi,
> 
> Reading  http://www.asteriskguru.com/tutorials/bri.html , it seems PtP is
> the way to connect businesses but if you read
> http://public.swbell.net/ISDN/connect.html you would think the opposite.
> 
> Can anyone elaborate a bit PtP or PtmP respective advantages ?

With analog phone lines you can have multiple handsets share the same
physical line. That is: multiple FXSs and one FXS. Only one talk at a
time.

PtMP is an attempt to preserve that feature: multiple CPE units can
share the same physical connection to a network unit. Only up to two
talks at a time. 

Another nice feature of analog handsets is that they are powered from
the FXS. Likewise BRI phones can be powered from the network unit.

Those two features are quite nice when your equipment is a simple phone.
They are mostly useless for a PBX: your PBX will have an independent
power source anyway. And will most likely want to handle all the line by
itself.

The problem is that those features come with a price tag of complexity.
For instance, many providers want to save power and hence drop the (even
layer 1) connection to a ptmp bri cpe unit because it is probably an
isdn phone that takes some precious power (some 25V, IIRC). As a result,
your PBX cannot really tell if the red alert it has is faked or not.

-- 
               Tzafrir Cohen
icq#16849755              jabber:tzafrir.cohen at xorcom.com
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http://www.xorcom.com  iax:guest at local.xorcom.com/tzafrir