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UDP RTP TS til UDP TS



Hej

Jeg har en pæn MPEG-2 TS datastrøm, der sendes enkapsuleret i RTP-pakker enkapsuleret i UDP over IP. Hver pakke i TS-strømmen er 188 bytes lang.

Det jeg ønsker er, at læse UDP-strømmen, re-order RTP-pakkerne (de har nemlig et sekvensnummer), smide RTP-headeren væk og sende TS-pakkerne ud igen i UDP.

Her er et tcpdump af RTP-pakkestrømmen.

17:39:45.464813 IP 80.137.32.61.32877 > 239.255.0.1.50000: UDP, length: 1328
17:39:45.465130 IP 80.137.32.61.32877 > 239.255.0.1.50000: UDP, length: 1328
17:39:45.465430 IP 80.137.32.61.32877 > 239.255.0.1.50000: UDP, length: 1328
17:39:45.465671 IP 80.137.32.61.32877 > 239.255.0.1.50000: UDP, length: 1328
17:39:45.465989 IP 80.137.32.61.32877 > 239.255.0.1.50000: UDP, length: 1328

Så der er 7 TS pakker i hver UDP-pakke. Jeg bruger nu programmet rtpdump til at modtage RTP-pakkerne og ville gerne sende data videre med f.eks. nc.

  $ rtpdump 239.255.0.1 50000 | nc -u -b 239.255.0.2 50002

Det virker af mange grunde ikke. Men hvorfor? Her er et output fra tcpdump

17:58:17.032824 IP 80.137.32.61.32886 > 239.255.0.2.50002: UDP, length: 7896
17:58:17.046779 IP 80.137.32.61.32886 > 239.255.0.2.50002: UDP, length: 1316
17:58:17.047005 IP 80.137.32.61.32886 > 239.255.0.2.50002: UDP, length: 1316
17:58:17.047335 IP 80.137.32.61.32886 > 239.255.0.2.50002: UDP, length: 1316
17:58:17.053008 IP 80.137.32.61.32886 > 239.255.0.2.50002: UDP, length: 3948

Hvis det skulle virke, skulle jeg kunne angive til nc, at den skal pakke data ned i udp-pakker med N x 188 bytes, og det kan man vist ikke. Noget andet mystisk er, at data sendes i pakker større end 1500 bytes. Ifconfig viser, at MTU er 1500 bytes

eth0      Link encap:Ethernet  HWaddr 00:0D:61:44:AA:C5
          inet addr:80.137.32.61  Bcast:80.137.32.127  Mask:255.255.255.128
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1

Hvorfor viser tcpdump så, at der sendes en UDP-pakke med 7896 bytes ?

Findes der et udp-sendingsprogram, der kan læse fra stdin i kvanter af 188 bytes og sende dem ud på netværket, f.eks. 7 x 188 bytes af gangen ?

mvh.

--PMM

 
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