User guide
7
Conguring switches and ALIFs
The correct conguration of each switch can have a signicant impact on overall
performance, so in this section we’ll take a look at the various issues. The precise
conguration details for each switch vary with make and model, so please also
check the Switch setups section where a selection of specic conguration details
are made available for a limited number of common switches.
Enable IGMP snooping
IGMP snooping is an essential and effective tool to prevent multicast data from
ooding the switches within a subnet. Ensure that IGMP snooping is enabled on
every switch.
Ensure that the IGMP Fast-Leave option is enabled on all switches that have ALIF
units connected directly to them. This will allow the switches to respond quicker
to changes in multicast arrangements.
As an alternative to IGMP, some Cisco switches also support a proprietary
standard called CGMP (Cisco Group Management Protocol) which is not directly
compatible with IGMP but achieves a similar outcome. CGMP sends multicast
group messages at layer 2 and so switches can natively read these without
needing to perform IGMP snooping. The use of CGMP is only possible if all of the
switches within your network are Cisco units that support this standard.
Enable Jumbo frames (Jumbo packets)
For the majority of video resolutions that are transmitted by ALIF units, standard
Ethernet frame sizes are used to transfer video data quickly and efciently.
However, certain video resolutions cause issues which require ALIF units to
instead output Jumbo frames in order to correctly convey the necessary data. To
efciently handle these enlarged frames, the switches within the subnet need to
have their Jumbo frames options enabled.
If any of the computers attached to your ALIF transmitters are using/or will use
any resolution that uses 2048 horizontal pixels (e.g. 2048 x 1152), ensure that
Jumbo frames are enabled on all of the switches within the subnet.
Enable Spanning Tree Protocol
Multiple and redundant links between switches are important for both transfer
speeds and network resilience. However, unless carefully managed, such multiple
links can cause bridge loops to occur and that is what the Spanning Tree Protocol
(STP) is designed to prevent. However, that’s not the end of the story because
STP can cause a new issue. It temporarily blocks newly found network links for
tens of seconds to ascertain their function, often causing problematic timeouts.
This also causes a problem for device discovery when using AIM, whereby ALIF
units cannot be correctly congured. Therefore, it is important to enable STP on
every switch and also enable a technique known as portfast on every switch port
that is not a link to another switch.