8. Appendix
VINX-1x0-HDMI Extenders – User's Manual
48
Managed Switch Properties in Details
IGMPv2
IGMPv2 is version 2 of the Internet Group Management Protocol. This
protocol is used by end-point devices to signal their interest in receiving
a specific multicast content via subscribing to the multicast group
corresponding to the content. Using IGMPv2 packets, the end-point
devices can send a leave message to indicate that they are no longer
interested in receiving the stream of the multicast group. Moreover, a
multicast capable router can periodically poll the end-point devices on
its interfaces which multicast streams they are interested to receive.
The answer to such a query is called a membership report. IGMPv2
must be supported by the managed switch.
IGMP Snooping
IGMP snooping is a feature which allows the switch to monitor
IGMP traffic when enabled. The information collected from the IGMP
packets is used by the managed switch to determine which interfaces
the multicast traffic should be forwarded to. In other words, IGMP
snooping is used to converse bandwidth by allowing the switch to root
multicast traffic to those interfaces where it is really required.
IGMP Fast Leave
IGMP fast leave (or immediate leave), when configured, reduces
the amount of time it takes for the managed switch to stop sending
multicast traffic (corresponding to a multicast group defined by a
multicast address) to an interface, where all end-point devices that
used to be interested in a stream have sent a IGMP leave message.
Without fast leave being enabled the managed switch would first send
out a query message and then would stop forwarding when no end-
points answered within a pre-specified time interval. If fast leave is
enabled, the switch stops forwarding the traffic without sending a
query message.
IGMP Querier
In order for IGMP snooping to work properly, IGMP messages must
traverse in the subnet between managed switches. However, if there
is no multicast capable router present periodically sending out query
messages and receiving answers to those queries, IGMP messages
are usually not forwarded upstream from one switch to another. By
enabling the IGMP querier feature in a managed switch, the managed
switch will act like a router and periodically query the devices in the
subnet (even other managed switches) to send their membership
reports. From those report all the listening switches with IGMP
snooping enabled will be able to determine where multicast traffic
should be rooted to.
Multicast Filtering
Some control information from VINX devices is transmitted via
multicast packets. However, these packets are not registered during
certain startup intervals or not registered at all. In order for all VINX
devices in the subnet to receive such control information, multicast
filtering must be set up, so that unregistered groups are forwarded to
all interfaces on the managed switch.
Jumbo/Giant Frames
Ethernet frames consist of a header and a payload. Since the header
has a fixed length (20 or 26 bytes) the bigger the payload, the higher
the useful bandwidth is. Similarly, the higher the useful bandwidth,
the better the picture quality of the encoded video stream will be. To
maximize picture quality, the Ethernet frame size (and consequently,
the payload) should be as high as possible. In a normal Ethernet
frame, the payload can be at most 1500 bytes. An Ethernet jumbo
frame, however, can carry up to 9000 bytes of payload. Since the goal
of the transmission is to provide the best possible picture quality in
all circumstances, the VINX Encoder device produces Ethernet jumbo
frames. Thus, the handling of jumbo frames has to be enabled in the
managed switches.
