Optus cable modems, US school net access: Broadband bob
Mon, 11 Nov 1996 23:49:07 +0000
Jan Whitaker <email@example.com> wrote:
> Thanks for that Robin. I also received word through a vendor that Optus
> is NOT going to go for the ISDN market as they feel it to be old
> technology . Can anyone else support this?
Optus does provide ISDN connections - usually primary rate I guess -
for business customers which it serves directly via fibre in CBD
areas. This enables customers to connect their ISDN PABX systems to
Optus' Nortel DMS 100 (?) exchanges. This has been going on for some
However this is only for places where Optus has SDH (Synchronous
Digital Hierarchy - direct digital at 155 or 620 Mbps) fibre. This
is not the HFC fibre system.
As noted in my Australian Communications article in August, ADC can
(or will be able to) supply a BR-ISDN (Basic Rate ISDN 2 x 64 kbps +
16 kbps for control) version of their home interface unit, and I
think Motorola could do this as well. ADC can do PR-ISDN (30 x 64
kbps = 64 kbps for control) as well.
I don't know of any plans by Optus Vision to use these.
I would expect that this LANCity announcement is a disappointment to
ADC and partner NetComm who would have liked to supply Optus Vision
with HFC data "cable modem" technology.
I would expect Optus Vision to be providing POTS telephony and a
full-on LanCity based cable modem service via their HFC system. With
these, why would you want Basic Rate ISDN? There may be a need to
connect business customer's PABXs with PR-ISDN via HFC. I think the
ADC equipment would be capable of doing that, but it is not the
"main-game" as they say in the classics.
Broadband Bob mentions "LCP" cable modems. See:
These use QPSK for downstream as well as upstream. This means
relatively low spectral efficiency (10 megabits per second in a 6 MHz
RF bandwidth) compared to other systems with QAM 32 or QAM 64.
However, I don't see this as a problem, since the bandwidth will be
efficiently managed on demand millisecond to millisecond, between
multiple cable modems.
Cable modems are far from being standardised, so don't think that
the cable modem you buy for Optus Vision will ever work on another
system such as Telstra's. The rate of technology development is far
too rapid at present to expect these things to be standardised in
the near future. By then there will be large installed bases of
(potentially incompatible) equipment on the Telstra and Optus Vision
networks. I don't think it is worth waiting for such
standardisation - the best thing is to get this stuff installed ASAP
and start using it creatively and productively.
. Robin Whittle .
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