According to one VMS manufacturer, to simultaneously feed the recording server and viewing clients, either the devices (cameras or encoders) must support dual streams (one unicast and at least one multicast) or the system would require proxy server(s) to convert a single unicast stream from the device to multiple streams: unicast for recording and multicast for viewing. They do not recommend feeding only a multicast stream from the device because of the difficulties encountered in troubleshooting multicast streams if there are problems.
I had never heard of the need for proxy servers but the manufacturer claims that they would add substantially to the cost of a system of our size. The same manufacturer also states that their own cameras are able to deliver (up to 8, I think) simultaneous streams due to the design of the cameras.
We tested a number of IP cameras during VMS system evaluations and the ones we liked best, Axis' P3354/64/84, were unable to deliver more than one 30fps stream at 720p/1280x960. Axis has confirmed that shortcoming. The documentation they sent us graphs resolution and frame rate versus number of streams. The only way they can deliver even two 30fps streams is to throttle back the resolution to <= 800x600.
That was also true of other third party IP cameras we tested. That leaves us "stuck" using only the VMS manufacturer's cameras or spending additional money on proxy servers or finding another camera(s) capable of delivering multiple 30fps streams at HD resolution.
Our budget would require sacrificing important features if we had to purchase proxy servers but we are concerned that if we don't, we would be basically sacrificing our ability to choose other IP cameras.
Any comments or suggestions?