[linux-dvb] Re: IP over DVB receiver cards for Linux

["Felix Domke" <tmbinc@gmx.net>]

> Do you really think, this is a problem? Normally, SAT-providers state
> their bandwidth in kBit/s and not MByte/s. So I believe you won't hardly
> be able to exploit the bandwidth within your card with IP-Networking.
> The bottelneck of SAT-IP-Networking is the shared bandwidth on the
> transponder and not the hardware on the DVB-card.
But these 1.5MB/s are the *theoretical* bandwidth. I think the card doesn't
offer any busmastering (correct me if i'm wrong), so when you read from the
card, say, 200kb, you need
200k/1.5M = ~130ms. In these 130ms you cannot do anything else, so you have
a VERY HIGH cpu load with higher bandwiths. It get's critical if you want to
do timeshifting and stuff (ok, that's not your concern). It's like an IDE
harddisk which does about 2MB/s without DMA. Are you willing to use this to
record movies? Movies are ~500kb/s. But it won't work very well.

Some multicasts on EON (or other) have bandwidths of up to 8MBit/s, and then
it really gets hot. I know that some PCI-cards (not the Siemens ones) had a
problem here and thus couldn't be used for this.

> I have no personal experience with the full featured cards, but I know
> people using T-DSL via Satellite from Deutsche Telekom with such cards
> and they are getting equal transmission rates like I have with my budget
> card.
Off course. It *WILL* work. But for myself, i'd like to experiment with all
streams i find on the transponders, especially the multicast stuff. And, as
said, for this, the bandwidth provided by some cards isn't just enough. In
contrast, the bandwidth provided by the Nova is always enough. So i strongly
recommend these Cards for everyone who doesn't want to watch TV.
(Additionally, the delivery of the full, unmodified, unfiltered TS is an
unique feature of this cards.) And they are cheaper.

felix




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