Multicast and portnumber(s)

In CCTV, multicast is a method of sending one video stream to a group of interested receivers in a single transmission. It is a form of point-to-multipoint communication to reduce the bandwith in the IP-network.

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One stream is send to the first switch as point-to-point. In the switch the stream is copied and paste to all requesting receivers. In multicast the switch is the point-to-multipoint device, not the camera or the encoder. For multicast the address range to use is, 224.0.0.0 - 239.255.255.255

You can also use the standard unicast. In unicast for each requesting receiver a seperate stream over the IP connection runs towards the first switch. The disadvantage of unicast is that with each additional stream the bandwith increases.

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The advantage of multicast is, there is no increase of the bandwith.
However this is only valid if all receivers use the same portnumber. If  X different port numbers are used, the number of video streams send from the transmitter (camera or encoder) are also X. And the total bandwidth grows to X-times the bandwidth of one videostream.
With multicast you often can set a port number in the transmitter. This is no more than a default (suggestion or advise). If in the receiver another portnumber is used than the default from the transmitter, than this other portnumber will be used.