Re: Is the cable system insecure?

Nonapeptide@xxxxxxxxx wrote:

So, if I'm understanding correctly, as I sit here and look at my
modem, its receiving downstream transmissions that are headed for me
and every other cable modem subscriber in my area. The modem is
selectively choosing to ignore all but the transmissions that are
addressed to it (I'm supposing that it's filtering by IP address?). My
mind's eye is picturing all downstream content that is intended for me
being split to all nodes on my local last mile, but only being
accepted by my modem. Is that correct?

Yes, although the RF network has its own addressing scheme, it doesn't
use IP addresses. Most cable systems allow multiple IPs behind a single
modem (although there may be an additional charge).

Also, (again, if I understand correctly) each transmission that I send
hits some kind of local aggregator (multiplexer?) which then, in hub-
like fashion, repeats the transmission to every port, which includes
every neighbor that has a cable modem as well as the upstream
connection to the head end? Eek! Seems like a waste of bandwidth for
the provider. Each last mile area of a cable provider's service is
essentially a big MAN sized collision domain?

No. The transmissions that you send go to the local node over coax that
is shared with your neighbors, so they receive those transmissions but
the node itself only retransmits (over fiber) to the head-end so people
attached to other nodes don't see the transmissions. And the upstream
bandwidth is divided into specific time slots that are, for the most
part, preassigned to specific cable modems, so there are no collisions
except for the few slots that are left open for contention.

Any word on what type of encryption cable providers use?

The packet data is encrypted using either 56- or 40-bit DES. The DES
keys are managed using RSA public-key encryption.

-Larry Jones

Even though we're both talking english, we're not speaking the same language.
-- Calvin
.

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