[streaming] Multicast errors: discontinuity at reception

[Sebastien Chaumontet]

Hi,

Problem with multicast (as broadcast) over wireless is that it is not reliable:
In the unicast world, wireless is retransmitting lost packets.
With broadcast or multicast on wireless (downstream way: from AP to
clients) if packets are lost they are not retransmitted.

An other behavior is that multicast is used as the rate of the lowest
client associated with the AP. ie: if all your clients on the AP are
using 11Mb/s except one at 1Mb/s, multicast and broadcast will be sent
at 1Mb/s.

Regards
Seb

On Mon, Mar 3, 2008 at 2:53 PM, Javier Gálvez Guerrero
<dulceangustia at gmail.com> wrote:
> Hi,
>
> I am trying to stream multicast videos through a hybrid wireless-wired
> network and I am having some problems at wireless clients. I have checked
> with differents devices and even with different networks (laboratory and
> home), but the results are the same: "ts warning: discontinuity received 0xX
> instead of 0xX (pid = 68 or 69)" messages, so having some video and audio
> interruptions and poor frame decoding results.
>
> I stream from a VLC server (through VLM, VLC 0.8.6d), Ubuntu Linux 32 bits
> based, running in a laptop. It serves RTSP VOD videos and UDP multicast,
> both configured with VLM telnet interface. It streams via 802.11g at 54 Mbps
> to a Cisco Aironet 1200 series access point, connected to a switch with many
> other computers. Then I have two clients: a desktop and a laptop. The
> desktop is wired and it receives both VOD and the multicast streams
> perfectly, but the laptop, connected to the network with 802.11g receives
> VOD with no problems but the multicast stream with many discontinuity
> errors. If I connect the laptop to the wired network the multicast streams
> are received with no problems.
>
> I configure the scheduled multicast streaming:
>
> > new test broadcast enabled
> > setup test input /media/sda2/diptv/server/contents/test.mpg
> > setup test output #standard{mux=ts,access=udp,dst=239.255.1.5:60101}
>  > new test_tv schedule enabled
> > setup test_tv date 2008/02/28-14:50:00
> > setup test_tv append control test play
>
> I have tried with different videos, different wireless receivers, different
> 802.11g channels and transmission rates (and many other access point
> features), streaming from a wired and wireless server, with a WIFI
> Conceptronic router or a D-Link DWL700 access point instead the Cisco
> Aironet 1200 and receiving in a Linux or WinXP client with the same results,
> the raw of discontinuity errors at receiver. I have also tried increasing
> the buffer size of VLC for UDP muxer with no effect.
>
> I have launched Wireshark protocol analyzer to track the udp packets on the
> wired desktop and on the wireless laptop and the difference are some random
> missing packets on the wireless laptop network interface, obvious losses.
>
> So what I would like to know is if somebody has faced this problem with
> multicast streaming in a wireless environment and, if it has been finally
> solved, how to do it. If the solution is a different access point I would
> like to know which ones have worked properly with this issue.
>
>
> Thanks a lot.
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