D-Link DCS-6517 User Manual page 54

Configuration
Unicast video transmission delivers a stream through point-to-point transmission.
Multicast, on the other hand, sends a stream to the multicast group address and
allows multiple clients to acquire the stream at the same time by requesting a copy
from the multicast group address. Therefore, enabling multicast can effectively save
network bandwidth.
An IP Multicast group address is used to send and receive content. Sources use
this group address as the destination address while sending their data packets.
Receivers use this group address to inform the network that they are interested in
receiving packets sent to that group.
The ports can be changed to values between 1025 and 65535. The multicast RTP
port must be an even number, and the multicast RTCP port number is the multicast
RTP port number plus one, and thus is always odd. When the multicast RTP port
changes, the multicast RTCP port will change accordingly.
Multicast TTL [1~255]: The multicast TTL (Time To Live) is the value that tells the
router the range a packet can be forwarded.
Click the items to display the detailed configuration information. Select the Always
multicast option to enable multicast for stream 1 ~ 4.
D-Link DCS-6517 User Manual 54