Voice over IP with multicast failed

Hello,we are trying to build a voice over ip network with netos51 and multicast. The receiver can switch without problems between the channels. When several senders sending data to the network (at least 2) the activated channel in the receiver is audible but disturbed. Stops the second sender with data transmission the audio signal is perfect. All data are completely received but never the less we hear a distortion. The application runs in a thread: status = tx_thread_create(&mythread, “multicast program”, my_entry_function, 0x1234, (VOID *) 0x400000, 1000, 15, 15, TX_NO_TIME_SLICE, TX_AUTO_START); Is it a buffer or time problem? Who can help us in this case? Kind Regards Matthias

Some idea’s: 1. The hash table is only 64 bits wide. That means that more than one multicast address can be mapped to the same filter bit. If all senders use the same destination port number you may receive multiple streams on the same socket! You could filter out streams if you give each stream sender an ID in the stream header (search for “RTP”). 2. The Net+ARM 50 MAC/DMA combination sometimes looses back-to-back receive packets. With TCP this is corrected by the protocol but not on the multicast UDP stream. You will need FEC (forward error correction), as on most networks. It should be possible: we currently have 35 Mbps multicast being send or received by a single NET+ARM50 in multicast mode (3 video, 3 audio, 6 data). But we rewrote the complete ethernet driver, UDP stack and we use FEC. Regards, Arie de Muynck

Ok, thanks for your support! We will use OS Version 6 - that’s easier to handle. Matthias

Hello Voiceman and all the VoIP-Cracks! Did you implement the VoIP-Stack on your own, or are there any open implementations? In our application, VoIP would be a supplement and I’m about to find out if it is worth to implement a standard like H232 or prehaps it’s easier to implement a proprietary solution. I’d be glad about any ideas or hints about this. - stefan