User's Manual

Document Number: 0100SM1401 Issue: 12-16

Compression

The radio can apply compression to the payload of an IP packet, prior to transmitting it over the air. It can take upto 2 ms for

the payload to be run through the compressor. Generally, once the payload has run through the compressor, the payload

becomes smaller in size, reducing the amount of packets required to be transmitted, therefore, reducing over-all latency.

In some circumstance, the payload data can be ‘un-compressable’, meaning, once the payload has been run through the

compressor, the payload is mostly the same size it was to begin with. This results in no reduced packet size being sent over

the air, therfore, the time it took to run the payload through the comrpessor, will be added to the over-all latency. As this is

only approximatley 2 ms, it can be considered neglegable when compared with the over-all latency of the radio link.

The default and reccommended setting for compression is “Low”.

Ethernet Filtering

Ethernet filtering provides an easy to configure Layer 2 filtering mechanism, which can help prevent unnecessary Ethernet traffic

and increasing channel loading. There are various different addressing methodologies that can be filtered, which include:

Unicast:

Unicast is an addressing methodology that delivers messages to a single network destination

identified by a unique address.

Multicast:

Multicast is an addressing methodology that delivers messages to a group of destination addresses

simultaneously in a single transmission. Spanning tree messages are an example of multicast

messages.

Broadcast:

Broadcast is an addressing methodology that delivers messages to every device on a network. The

broadcast address of a device is calculated from the subnet mask. If all devices within a network use a

common network mask, the broadcast address will also be common.

Although typical SCADA applications only require Unicast & ARP data, the filtering mechanism provides the option to allow:

• All Ethernet traffic

• ARP + Unicast + Multicast (Although Spanning tree messages are multicast messages, they are also filtered out unless

the user is allowing all Ethernet traffic to pass. This also helps to prevent unnecessary channel loading.)

• ARP + Unicast (ARP is primarily used by networks to identify which physical devices own which IP addresses, Enabled

by default).

• Unicast only (Only used when a MAC address table is statically assigned).

• Or allow traffic from a single MAC address only.

Part D – Feature Detail