[Udpcast] Content system

Fernando Rodriguez frod at aitelecom.net
Thu Sep 18 23:06:09 CEST 2008


Alain,

I also wanted to know because on your satellite example you set the  
interface to dvb0 i have some cards dvb cards and lnb.

Im going to get a php programer to make the scheduling.

Thanks


On Sep 18, 2008, at 3:16 PM, Alain Knaff wrote:

> Fernando Rodriguez wrote:
>> Hello, i want to know if udpcast will be able to transmit different
>> files to different multicast addresses at the same time.
>
> Yes, you can start several instances of udpcast simultaneously. You  
> only
> need to make sure that each instance uses a different port base (-P
> parameter).
>
>> Also if it is plausible to make a web interface to handle scheduling
>> of the files that are going to be sent over udpcast, so remote
>> recievers are able to get the files they where requested, this will  
>> be
>> like on demand content delivery.
>
> You could make a cgi script that would start udpcast in the background
> as requested.
>
>> to do this all clocks from the remote sides have to be in sync with
>> the master content node, and the remote content node or client should
>> be able to parse a file to see the content that udpcast will  
>> transmit.
>
> You could have one udpcast responsible for transmitting the
> announcement, which would be saved to a file on the receiver, to be
> parsed by the GUI frontend. Then, the actual content would be
> transmitted by separate instances, either on-demand, or continuously  
> as
> a carousel.
>
>> Also i need to know what is the best fec algorithm for one way
>> satellite comunicacion.
>
> It all depends on the quality of the link, and the power of your
> receivers. You want to play with the 3 parameters   stripes x  
> redundancy
> / stripesize .
>
> A higher ratio redundancy / stripesize can protect against higher loss
> rates. However, it also makes the transmission larger.
>
> Larger number of stripes protects against clustered losses (so, if  
> your
> link is likely to lose many packets in a row, use a high number of
> stripes). However, a higher number of stripes leads to higher memory
> requirements.
>
> A bigger stripesize also helps against clustered losses, at the cost  
> of
> memory and computation time.
>
> You need to play a little bit with the parameters to find the best fit
> for your transmission link and receiver hardware.
>
> The way it works is that each stripe is an independant FEC group. Each
> stripe is made up of stripesize (n) data packets plus a number of
> redundancy packets (k). As long as at least n packets are received  
> (i.e.
> less than k packets lost), no matter whether they are original data
> packets, or redundancy packets, everything in the FEC group (stripe)  
> can
> be reconstructed.
>
> During transmission, s stripes (FEC groups) are active  
> simultaneously, a
> packet of each being transmitted in a round-robin fashion (i.e.  
> first a
> packet of stripe 1, then one stripe 2, etc. until the last stripe is
> reached, after which the second packet of stripe 1 will be  
> transmitted).
> This interleaving is meant to protect against clustered losses, so  
> that
> if for instance 10 packets in a row are lost, they won't all fall  
> within
> the same FEC group.
>
>>
>> Fernando Rodriguez
>> frod at aitelecom.net
>
> Alain

Fernando Rodriguez
frod at aitelecom.net






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