Comtech EF Data DMD1050 - Manual (Page 175)

DMD1050 Satellite Modem Board Ethernet Data Interface
MN-DMD1050 F–9
Revision 9
F.8.1 Normal QOS
When Normal QOS is selected, the determination of traffic priority and queuing is based on
information contained in the packet. This type of QOS is the default on the original Ethernet
Bridge and is typically what most users require. Normal QOS uses the following packet
information:
When a packet contains an IEEE802.3ac Tag (this tag is optional), the EEI uses the IEEE802.1p
priority information embedded in the Tag.
When a packet does not contain the optional Tag, priority is determined using the
IPv4 Type of Service / Differentiated Service field
or
IPv6 Traffic Class field
F.8.2 Port Based QOS
When Port Based QOS is selected, the EEI ignores and QOS information embedded in the
headers and instead priority and queuing is based on the port on which the traffic arrives. This
type of QOS is typically used when the operator wants to control bandwidth allocation based
upon ports. However, it can also be used to create a FIFO like operation where the data is
transmitted in the exact order it is received. With Port Based QOS, Port 1 has the highest priority
and Port 4 on the standard 10/100 EEI .
F.8.3 Fair Weighted Queuing
A fair weighted priority scheme allows higher priority traffic to move quickly through the system,
while at the same time insuring that lower priority traffic isn't stalled indefinitely. Fair weighted
queues are the default on the original Ethernet Bridge. When Fair Weighted queuing is selected,
packets will be transmitted at a rate of 8, 4, 2, and 1 from the highest to lowest priority queues
respectively.
F.8.4 Strict Priority Queuing
A strict priority scheme means that the highest priority traffic will always be transmitted first,
even if it means that the lower priority traffic is stalled indefinitely. When Strict Priority queuing
is selected, packets in the highest priority queue will be transmitted until that queue is empty. At
that time, packets from the next highest priority queue will be transmitted until it is either empty
or a higher priority packet arrives. If a higher priority packet arrives before a lower priority
queue is empty, it will immediately go to the head of the line and be the next packet transmitted.
Care needs to be taken when selecting this option as it is entirely possible that data in a lower
priority queue might never be transmitted.