Extron Electronics VN-Matrix 200 Series - Manual (Page 102)

Understanding
Network
Performance
This section describes features of the network.
Network Characteristics
There are a number of characteristics of networks that have to be taken into account
when transmitting image data.
When a conventional analog or digital video signal is sent from a source to a display, the
image is transmitted in real time with negligible delay (or “latency”). The signal itself is
continuous with (even in the case of a digital signal) very little redundancy in the signal
(the great majority of the signal is image data, so little bandwidth is “wasted”). In general,
the signal is not subject to any unpredictable degradation.
Data Packets/Frames
If a digital image stream is sent across a network, it must be “packetized.” The network
itself is indifferent to the nature of data, and simply treats all digital information in a
standard way. Before it can be sent over a network, the data must be reformatted into
packets called “IEEE MAC frames”.
Preamble
Number
of bytes
Synchronizes internal
clock generator
Indicates type of payload
8 6 6 2 4 3 or 8 Variable
Destination
Address Source
Address Length
of
Data C
R
C IEEE802.2 Header
Optionally with
snap extensions Data
46 - 1500 bytes
at 10 MHz
Figure 53. IEEE802.3 Media Access Control frame
Some points arise from this:
• The data carried within a frame/packet is limited to the MTU (maximum transmission
unit) of the network, typically 1500 bytes.
• The data must include any additional overhead arising from the protocol being used
(UDP or TCP/IP).
The MTU is the largest physical packet size (measured in bytes) that a network can
transmit. Any messages larger than the MTU are divided into smaller packets before being
sent.
VN-Matrix 200 Series • Understanding Network Performance 97