If you change the "Set time" in the node "Play movie" you can restart the video playback. In the composition I attach I restart by clicking on the window.
I have some work with IP cameras and I use some apps to capture the stream and then pass it to syphon.
There are cameras that have the option to choose between two protocols: http and rtps. There are also different codecs for streaming: MJPEG, H.264, ...
If you use the HTTP protocol and MJPEG encoding, there are two applications you can use to convert the stream to a syphon feed.
If you use the RTSP protocol you can use:
I hope it can be of help.