Subject: Multiple CPE interfaces on a CM

From: "Bob Himlin" <[email-masked]>
Date: Wed, 23 Dec 1998 10:40:21 -0800

In reviewing the CMCI specification, it seems clear that at least one
configuration of CM is assumed not to exist, specifically the CM with
multiple types of CPE interfaces.  Examples of such CMs would include a CM
with a USB and an Ethernet interface (such as many that were on display at
the Western Cable show), or an internal PCI-based modem with an Ethernet
interface.  The Cable Device MIB also seems not to account for such devices
in its filtering rules, as was mentioned previously by Guenter Roeck on the
IPCDN mailing list.

I have a question as to the expected bridging behavior of such a modem
between its CPE interfaces (i.e. USB or PCI port to/from Ethernet port).
Assuming that the CMCI specification and MIBs eventually allow for such a
CM, is it sufficient for the CM to only forward data from its CPE interfaces
to/from the RFI?  The consequences of this approach would be that the only
way communication between the CPE devices attached to the Ethernet port and
what I'll call the "primary" CPE could occur is through the CM & CMTS over
the RFI.  This traffic would be filtered according to the CD MIB filters
configured inside the CM and/or CMTS.  This means it is likely that some
IP-level communication would be possible, but things such as Windows
Networking would definitely not work.

Do MSOs or other vendors have an opinion on this?  For instance, if a
customer was given an internal modem with an F connector and an RJ-45
connector, would they not assume that the CM is a combo modem/Ethernet card
for the PC, and expect that they can Windows-network their other on-site PCs
with the PC containing the CM?  The same question applies to a USB/Ethernet
modem.

Just some food for thought.
Bob Himlin, TurboNet Communications
15932 Bernardo Center Drive
San Diego, CA 92127
(619) 451-1061 x116; Fax 451-1775