On Sun, Nov 04, 2001 at 02:53:16PM +0000, Padraig Brady wrote:
> Niall O Broin wrote:
> > ADSL over ISDN provides the 2B+D of an ISDN line AND the ADSL digital
> > channel. To my knowledge, this is available in parts of Spain and is the de
> > facto means of getting ADSL in Germany - in fact, you have to fight quite
> > hard with Deutsche Telekom to get them to give you "plain" ADSL.
and of course when you use ADSL over ISDN you get the advanced telephony
features of features of ISDN which of course you don't have with ADSL over
POTS. Another issue is that ADSL over ISDN is actually theoretically a worse
ADSL than ADSL over POTS because some of the available bandwidth has to be
used for ISDN. As the theoretical max. bandwidth of xDSL is 15Mb/s, way more
than that provided by telcos for marketing reasons, this theoretical
disadvantage is not actually a problem.
> > provided over an ADSL channel, but I've no idea if it's been done.
>> Primary rate ISDN was designed to work over the existing "level 1" links,
Indeed - I was merely speculating on the possibility of provisioning PRI
over ADSL now that that would be technically possible, 2 wire links being
cheaper than 4 wire or fiber.
> T1 in the states/japan which is 1.544Mb/s and E1 elsewhere 2.048Mb/s.
>> T1 rate is (24*64)+(8 for framing). Hence the user rate for T1 ISDN is
> 23*64Kb/s = 1.472Mb/s. E1 is 32*64Kb/s, 1 slot is used for signalling
> and another for framing. So the ISDN user has 30*64Kb/s = 1.92Mb/s.
To add to the confusion BRI in the U.S. is provided with B channels of
56Kb/s and 64Kb/s depending on where you are.
> Note also that for both basic rate and primary rate ISDN the D channel
> is *always on*, and only a very small % of it is used for call
> signalling. There was a service in the US that basically did IP across
> this (16Kb/s always on can be seriously useful!), and you could then
> dialup incramentally for 144Kb/s (64 + 64 + 16).
I remember looking into this years ago. It's a great idea but rarely used.
I remember reading something in Germany which stated that to attempt to use
the D channel for signalling other than telco signalling was forbidden.
BTW a useful link for an explanation of ADSL over ISDN is at
http://www.orckit.com/fr_newsa.html?/adsl_white_paper.html. It's from a
vendor but it's quite good and has some more good links.
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