Selecting a switch
6
· G&D ControlCenter-IP 2.0
Selecting a switch
Computer modules (
IP-CPU
) send the video stream to user modules (
IP-CON
) using
multicast
.
Multicast transmission allows users with »Target multi access« rights to connect to a
computer to which
another
user is already connected.
Requirements of network switches
The following requirements apply to the network:
Gigabit Ethernet:
User and computer modules are connected to the network using 1
GBit network connections (in accordance with IEEE 802.3ab).
Multicast:
The computer modules (
IP-CPU
) transmit the video stream via multicast.
The switch manages the multicast groups and maintains multicast tables.
IGMP:
The
Internet Group Management Protocol
(IGMP) was designed for organising
multicast groups. The user modules (
IP-CON
) use the protocol (min.
IGMPv2
) to
notify the switch which multicast group they want to join or which they want to
leave.
IGMP snooping:
IGMP snooping
is the interception of IGMP network traffic through
a network switch. By listening to the IGMP conversation, the switches can deter-
mine which of their
own
hosts have requested a multicast stream. Only these hosts
are supplied with the required multicast stream.
IGMP Snooping Querier:
An IGMP snooping querier (function of the switch) regu-
larly asks all subscribers of a multicast group whether they still want to receive
this group (IGMP query). The answers (IGMP reports) are identified and evalu-
ated by all local switches.
IMPORTANT:
The multicast streams are controlled by the network switches and
enable efficient distribution of the streams to multiple receivers at the same time.
IMPORTANT:
Without
IGMP snooping
, the switch floods all ports with the multi-
cast stream so that potential users can receive the stream.
Since the multicast stream of a single computer module already uses the
full
GBit,
packet loss occurs if a port receives more than one multicast stream at the same
time.
NOTE:
Ports that do not regularly confirm their subscription to the respective
multicast groups
no longer
receive their packets.
If
no
querier is available, a switch disables the port after reaching the timeout of a
member port for receiving multicast packets.
Summary of Contents for ControlCenter-IP 2.0
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