Advanced Configuration Features
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Horizon Compact Release 1.01.00 Wireless Ethernet Product User Manual – Volume 2
3.3.2 CoS Committed Information Rate (CIR)
The Horizon Compact system allows the user to assign a percentage of the maximum bandwidth
available to the data flowing in each of the four QoS Queues. Its purpose is to ensure that each Queue
gets at least a portion of the bandwidth and does not get “starved” of bandwidth resulting in no bandwidth
being allocated. If CIR was not available:
• QUEUE 4 would get most of its packets through
• QUEUE 3 would get a large percentage of its packets through
• QUEUE 2 would get some of its packets through
• QUEUE 1 would get very few of its packets through
• The “Scheduler” algorithm then progresses as follows:
o QUEUE 4,
o back to QUEUE 4 then to QUEUE 3,
o QUEUE 4 then QUEUE 3 then QUEUE 2,
o QUEUE 4 then QUEUE 3 then QUEUE 2 then QUEUE 1
The scheduler uses it’s algorithm to search for and deliver traffic in each of the Queues, but it also checks
that the CIR rate has been met, and has not been exceeded. If the CIR rate has reached its maximum,
then the scheduler moves on to the next Queue according to its algorithm. For example:
• The Scheduler checks QUEUE 4 for packets.
• If there is a packet AND the CIR threshold has not been met, then service the Queue.
• If the CIR threshold has been exceeded, then jump to QUEUE 3 without processing the packet (in
order to ensure that QUEUE 3 is allocated its CIR bandwidth)
Each Queue can have different maximum bandwidths or information rates assigned to them but the total
CIR cannot exceed 100%. For example:
• Assuming a 200 Mbps system:
• With Queue 1 assigned a CIR of 10% (20Mbps) or 25% (50Mbps)
• With Queue 2 assigned a CIR of 20% (40Mbps) or 25% (50Mbps)
• With Queue 2 assigned a CIR of 30% (60Mbps) or 25% (50Mbps)
• With Queue 2 assigned a CIR of 40% (80Mbps) or 25% (50Mbps)
=100%(200Mbps) 100%(200Mbps)
NOTE: See also section
3.3.4 Expedite Queuing
3.3.3 CoS Queue Committed Burst Size
Since IP traffic is “bursty” in nature, the Horizon Compact provides a feature, called CoS Queue
Committed Burst Size (CBS) to handle Ethernet bursts. The Horizon Compact system contains a data
buffer that is used to accommodate bursts of traffic in excess of the user allocated amount as specified
through the CIR setting for each Queue. The buffer is used for traffic bursts only and is functional when
802.1P is enabled on the Horizon Compact system.
The CoS Queue CBS defines the percentage of the total amount of burst buffer that the Queue is
allocated. There is a total of 100 Mbits of buffer allocated to CoS Queues. Each Queue can be allocated
a percentage of this memory. The default allocation for all four Queues is 25%. Each Queue can be
allocated a percentage of the total memory space available for CoS Queues and the total percentage
equals 100%. The CoS Queue CBS function will “smooth out” the output and transmit at the Queue’s
CIR by flushing the burst buffer allocation.
The CoS Queue CBS operates as a FIFO for each individual queue. Burst traffic will be handled as an
extension of the CIR and therefore will be inserted, or interjected, into the Queue as it arrives. This may
have the effect of creating a short delay for subsequent traffic arriving at that Queue if the subsequent
traffic is at that Queue’s CIR level. Conversely, if the burst is followed by traffic that is less than the CIR
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