Re: demo stream, filter questions

["Karsten Siebert" <Karsten.Siebert@sv-gmbh.de>]

One word on IP multicast:

RFC1112 is used to set the DSM-CC section MAC address filter. The
transmitter fills the section header MAC bytes accordingly, when sending to
an IP multicast group. If a host at the receive site joins a group the
receiver listens to IGMP messages and sets the filter.

The more different IP multicast groups you are going to join, the more
section filters are set (often max. per receiver equals 32). But you can
set, how many filter bytes are valid and you could ignore some (which at the
other hand would give the filter less strength and more other packets would
pass to the next level (IP)).

Sometimes receiver manufacturers just enable a 12 bytes filter option (which
really includes all the DSM-CC header bytes), you can ignore specific bytes
(for instance the scrambling bytes).

Unfortunately today no relationship between PID setting and section filter
setting exists. A couple of years ago we introduced a so called auto mode
(last two bytes of MAC address & 0x1fff -> PID). In case you join a group,
the entire chain from IP over MAC filter to PID filter will bet set. Works
well, but this approach is very static and a better approach is to introduce
additional service information for MAC addresses (as proposed for instance
by A92 (ATSC)).


Karsten