Re: [AVT] Comments on draft-boyaci-avt-app-sharing-00

[Omer Boyaci <boyaci at cs.columbia.edu>]

Hi Cullen,

Thanks for your comments. I want to mention some more issues with the  
VNC.

1) VNC uses a client-pull mechanism which results in poor performance  
in high RTT situations.
    Our proposal uses a server-push mechanism.

2) VNC uses the same encoding for all updates.
     This new system may use different encodings for updates in the  
same session.
     For example, if the user plays a movie, our implementation  
detects that and uses Theora or MJPEG just for this movie region.

3) VNC uses a separate compressor for each connected user. This  
results high CPU usage if more than one person connects.
     Also due to this compressor issue, one can not use these  
encodings in a multicast session (decompressor needs all the packets).
     TeleTeachingTool uses Hextile encoding (which means uncompressed  
data and bandwidth inefficiency) to overcome this limitation.

     Our proposed system compresses each update only once. The  
compressed updates are stored with metadata such as the top-left  
coordinates, width and height.
     Then ready-to-go updates are transmitted to participants. For  
low bandwidth clients, the system skips some updates if they are  
overwritten by the following updates.

-Omer Boyaci


On Nov 14, 2008, at 8:52 PM, Cullen Jennings wrote:

> I like the idea of an applications share protocol that can be set up  
> over SIP and glad to see this submission.
>
> Few comments
>
> At a high level, why not just standardize something like VNC. It  
> seems like this would be better than inventing something new.
>
> I also wondered about why run it over RTP vs just be it's own  
> protocol. It was not clear that RTP was a good match.
>
> Some more small details ... you might want to look at how X deals  
> with mouse and keyboard events - particularly compression of mouse  
> motion.
>
> Make sure that you have some way for the protocol to send a CTRL-ALT- 
> DEL to the far side without the user actually having to  
> simultaneously press CTRL, ALT and DEL.
>
> You probably want your PLI to be able to specify a partial rectangle  
> to update.
>
> Cullen in my individual contributor roll
>
> _______________________________________________
> Audio/Video Transport Working Group
> avt at ietf.org
> https://www.ietf.org/mailman/listinfo/avt

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