3
Network AV Infrastructure Prerequisites
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Dynamic multicast router port
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Forwarding unknown multicast to multicast router ports only
Any network switch should have a backplane capacity of at least (2 x 1000-Mbps x N) where N is the number of ports on the
switch passing the video traffic. For example, a 24-port switch where all available ports may be used to pass video traffic should
have a (2 x 1000 x 24) = 48Gbps backplane. One channel of encoder video can be sent or received from each port in this switch
example although full bandwidth may not be used at any one time.
The maximum distance between devices is 100m (328ft) over CAT 5e (or better) cable. This distance can be extended in
increments of 100m (328ft) by using a gigabit switch as a repeater between devices. Copper to fiber adapters can extend the
maximum distance between devices up to 10km through the use of fiber.
Since different brands and models of switches perform differently when handling multicast IP packets, functional verification
and pressure testing are also recommended in any installation. Switches that perform well in smaller installations may not
work well in larger installations. Recommended configuration settings may vary based on your switch.
Visionary Solutions offers sample switch configuration files, optimized for Network AV, for certain switch brands/models for
testing purposes. Contact
to obtain the files.
S
WITCH
G
UIDELINES
1.
Enable IGMP querying and snooping (set IGMP Version to IGMP V2 if the switch is capable)
. To enable the transmission of
a source to multiple destinations, MV4 devices make use of multicast. The default behavior of a layer-2 switch is to
broadcast those packets, which means that every packet will be transmitted to all possible destinations. IGMP snooping
checks IGMP packets passing through the network, picks out the group registration, and configures multicasting
accordingly. A layer-2 switch supporting IGMP Snooping can passively snoop on IGMP Query, Report, and Leave (IGMP
version 2) packets transferred between IP multicast routers/switches and IP multicast hosts to determine the IP multicast
group membership. This is why any network switch used with MV4 must support IGMP Snooping. Our end points use IGMP
protocol to assign the end points into multicast groups and the router uses IGMP snooping to efficiently route multicast
packets only to the receivers that want to receive them.
IGMP Snooping is used to identify multicast IP packets, assign IP packets into multicast groups so that the router only sends
to devices that want to receive the packets, establish membership in a multicast group, and register a router to receive
designated multicast traffic. Multicast filtering is achieved by dynamic group control management. Many switches have the
IGMP Snooping feature disabled by default and manual configuration is required. Often, checking the
Enable IGMP
Snooping
option is the only setting needed to enable IGMP Snooping. Implementing IGMP Snooping is vendor specific and
additional configuration is often needed.
IGMP Snooping Querier is used to send out group membership queries on a timed interval, retrieve IGMP membership
reports from active members, and update the group membership tables. The Leave Group packet is sent when a device wants
to leave a group.
Because multicasting video traffic can flood a network and significantly reduce the flow of traffic, it is important to ensure
that your network infrastructure and backbone switches support IGMP Snooping so that your core network is able to ignore
the traffic streams multicasting can generate. By default, all multicast traffic should be blocked until requested by a multicast
group member. Without IGMP Querying/Snooping, multicast traffic is treated in the same manner as a broadcast
transmission, which forwards packets to all ports on the network. With IGMP Querying/Snooping, multicast traffic is only
forwarded to ports that are members of that multicast group. IGMP Snooping generates no additional network traffic,
which significantly reduces the multicast traffic passing through your switch.
Note
: Some switches require that the routing table be pre-loaded so that the switch does not have to interrogate each IP
packet to determine its destination. Static routing can be used to route multicast traffic. Protocols similar to Generic Routing
Encapsulation (GRE) can be used to encapsulate multicast packets in unicast wrappers for point-to-point transmission
between switches, and when the packets arrive at the destination IP address, the unicast wrapper is removed.
2.
Enable Fast Leave
. The switch may also support IGMP Snooping Fast Leave, which shortens the time takes for a device to
leave a group and be made available to join to a different group. A switch can be informed that a device wants to leave a
multicast channel by sending it a IGMP Leave Group packet. Once received, the time it takes for the switch to apply the new
configuration may vary from one switch to another. Most switches have a Fast Leave configuration option. When enabled,
Fast Leave speeds up the time needed for a port assigned to one multicast group to leave the group and join a different
multicast group. This significantly reduces the video switching time. Always enable the Fast Leave option when it is
available.
