User manual

Page 55
C h a p t e r 10
10 Appendix: Multicasting,
Multi-Unicasting, Port Numbers
Multicasting
The A-80 can be used in a multicasting setting. The network switches and other devices used
must be carefully configured for, and capable of, handling multicasting and its associated
protocols (most notably IGMP v2). If not, broadcasting will occur, which can put a very heavy
load on the network. This is a phenomenon inherent to multicasting and the facilities of network
devices, not of the A-80 itself, although it is compounded by the density of the UDP streams
used.
To define a multicast group, a source unit should be assigned a valid multicasting ('destination')
TX stream address and the destination units should get this same address as source. The group
vanishes when the source is disabled, but the source will not automatically be disabled when the
last remaining destination is cancelled and will keep transmitting at least towards the nearest
switch. Additionally, it is possible to have the multicast group units send unsolicited membership
reports, keeping it alive even if only one - any - unit of the group is still active.
Multi-unicasting
Alternatively, the A-80 features 'multi-unicasting', i.e. sending out up to max. 10 RTSP or 3 MX
audio streams per input, and 3 contact closure streams per input. If the bit rates selected are
moderate, it may be more convenient to use this mechanism instead of multicasting, even
though the network gets more signal to carry from the encoder.
When such a destination is removed, the source also stops sending the corresponding stream. If
the input channel of a destination is disabled without disabling the source, source transmission
will be throttled, but not disabled (this behavior is selectable through the FloodGuard settings
discussed in the section on FloodGuard. The source downsizes the stream by sending empty UDP
packets until a wake-up call is received. The empty packets, of course, carry the relevant IP/port
information.
Port numbers
A valid UDP port number in a Siqura A-, C-, S-, and V-series system is an unsigned 16-bit integer
between 1024 and 65536. Generally, you do not need to select other than the default receiver
port numbers as given in the MIB (Management Information Base). If you want to change these
receiver port numbers for some reason, use even numbers. A given receiver port number N is
associated with the port number N+1, through which control information is returned to the
source.
Eligible port numbers in general are within the range indicated above, with some exceptions.
Those within the 3000-10000 range are reserved and/or hard-coded, or may become reserved,
so only 10000-65535 are generally safe. Default port numbers (used by receivers) are shown in
the following table.