[Live-devel] minimum inter-packet delay

[Dong Hoon Van Uytsel]

On Fri, 2007-07-06 at 01:22 -0700, Ross Finlayson wrote:
> >I have a linux application send uncompressed frames using the liveMedia
> >library; with wireshark I'm measuring 17 microseconds between successive
> >packets (sized 1490 bytes, of the same image frame) being sent, which
> >boils down to instantaneous bandwidth consumption of 700 Mb/s. In this
> >configuration, several packets are lost at some receivers. I've already
> >tried increasing the UDP sending and receiving buffers - but this
> >doesn't solve the packet loss.
> >
> >A temporary work-around seems to increase the interpacket gap to 30
> >microseconds by inserting a few fprintf()s in sendPacket() in
> >RTPInterface.cpp. However, isn't there a cleaner solution to specify the
> >minimum inter-packet gap in liveMedia?
> 
> Are you setting the "fDurationInMicroseconds" variable correctly in 
> whatever source object(s) feed into your "RTPSink" (or 
> "BasicUDPSink") object?  It's that variable that determines the 
> (average) inter-packet gap.

yes, I think so (40000 us ; 25 fps). the _average_ inter-packet gap is
what you would expect, but in effect the packets are not spaced evenly
in time; they are sent in bursts.
> 
> However, what is your data's bitrate *supposed* to be?  If it really 
> is supposed to be 700 Mbps, then you're not going to be able to 
> increase the average inter-packet delay - it is what it is.

the average data's bitrate is supposed to be 130Mbs. but the bitrate
during "bursts" is 700Mbs (and zero in between), as measured with
ethereal. it seems something in the network seems to have difficulties
with this.

> Note that becuase the "LIVE555 Streaming Media" code is 
> single-threaded code that simply reads sequentially from a socket, 
> any packet loss that you see cannot be the fault of this code. 
> Instead, it must be either actual network packet loss, or data loss 
> (e.g., overflowing buffers) within your OS.

yes, it may be due to the switch or its configuration I'm using (D-Link
DGS-1216T). i'll look into it further. thanks for your suggestions!

Dong Hoon