#2724 NORM Untriag: Wireless multicast more unreliable than expected.

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#2724: Wireless multicast more unreliable than expected.
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 Reporter:  dwmw2     |       Owner:  marcelo  
     Type:  defect    |      Status:  new      
 Priority:  normal    |   Milestone:  Untriaged
Component:  wireless  |     Version:           
 Keywords:            |    Verified:  0        
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 In the mtd-utils.git tree there are utilities for transmitting and
 receiving a file over UDP packets.

 We can send at fairly high rates by using unicast, but as soon as we
 switch to multicast it gets _massively_ unreliable at any rate above about
 80KiB/s.

 This seems more lossy than we might expect just because of the lack of
 link-layer acks, and causes a problem for us because it isn't fast enough
 for sending NAND images.

 To test...
 {{{
 $ git-clone git://git.infradead.org/mtd-utils.git
 $ make recv_image serve_image

 ... then on one machine run...

 $ ./recv_image <IPaddr> <port> /dev/null

  ...and on another machine...

 $ ip -6 addr add ff0f::114 dev eth0
 $ ip -4 add 224.0.0.0/4 dev eth0
 $ dd if=/dev/zero of=testfile bs=131072 count=20
 $ ./serve_image <IPaddr> <port> testfile 131072 80
 }}}

 That'll send the test file across the network to the IP address you
 selected, at 80KiB/s. If you use a unicast address you can send at much
 higher rates. If you use a multicast address like ff0f::114 or
 239.255.0.1, you'll see _many_ missing packets if you go above 80KiB/s.

-- 
Ticket URL: <http://dev.laptop.org/ticket/2724>
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