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488
BigIron RX Series Configuration Guide
53-1002253-01
Determining packet drop priority using WRED
18
How WRED Operates
The graph in
Figure 88
describes the interaction of the previously described variables in the
operation of WRED. When a packet arrives at a switch, the average queue size (q-size) is calculated
(note that this is not the statistical average queue size - (refer to
“Calculating avg-q-size”
on
page 488). If q-size as calculated is below the configured Min. Average Queue Size, then the packet
is accepted. If the average queue size is above the configured Max. Average Queue Size threshold,
the packet is dropped. If the Average Queue size falls between the Min. Average Queue Size and
the Max. Average Queue Size, packets are dropped according to the calculated probability
described in
“Calculating packets that are dropped”
on page 488.
FIGURE 88
WRED operation graph
Calculating avg-q-size
The algorithm first calculates the avg-q-size through the following equation.
avg-q-size = ( (1 - Wq) * Statistical Average-Q-Size) + (Wq * Current-Q-Size)
The Wq value is instrumental to the calculation and can be:
•
equal to the statistical average queue size (Wq == 0), or
•
equal to the current queue size (Wq == 1) or
•
be between 0 and 1 (0 < Wq < 1).
Lower Wq values cause the avg-q-size to lean towards the statistical average queue size, reducing
WRED's sensitivity to the current state of the queue and thus reduce WRED's effectiveness. On the
other hand, higher Wq values cause the avg-q-size to lean towards the instantaneous queue size,
which exposes WRED to any change in the instantaneous queue size and thus may cause WRED to
overreact in cases of bursts. Thus, the value of Wq should be carefully chosen according to the
application at hand.
Calculating packets that are dropped
The Pdrop value, as calculated in the following equation, is the probability that a packet will be
dropped in a congested switch.
Pmax
Min. Average
Queue Size
Max. Average
Queue Size
Содержание BigIron RX Series
Страница 100: ...24 BigIron RX Series Configuration Guide 53 1002253 01 Logging on through the Web Management Interface 2 ...
Страница 192: ...116 BigIron RX Series Configuration Guide 53 1002253 01 Configuring authentication method lists 4 ...
Страница 228: ...152 BigIron RX Series Configuration Guide 53 1002253 01 Enabling WAN PHY mode support 6 ...
Страница 312: ...236 BigIron RX Series Configuration Guide 53 1002253 01 Displaying IP information 7 ...
Страница 356: ...280 BigIron RX Series Configuration Guide 53 1002253 01 Resetting LLDP statistics 9 ...
Страница 402: ...326 BigIron RX Series Configuration Guide 53 1002253 01 Transparent firewall mode 11 ...
Страница 432: ...356 BigIron RX Series Configuration Guide 53 1002253 01 SuperSpan 12 ...
Страница 500: ...424 BigIron RX Series Configuration Guide 53 1002253 01 MRP CLI example 14 ...
Страница 580: ...504 BigIron RX Series Configuration Guide 53 1002253 01 Configuring multicast traffic engineering 18 ...
Страница 591: ...BigIron RX Series Configuration Guide 515 53 1002253 01 Displaying traffic reduction 19 ...
Страница 592: ...516 BigIron RX Series Configuration Guide 53 1002253 01 Displaying traffic reduction 19 ...
Страница 598: ...522 BigIron RX Series Configuration Guide 53 1002253 01 Viewing Layer 2 ACLs 20 ...
Страница 656: ...580 BigIron RX Series Configuration Guide 53 1002253 01 Trunk formation 22 ...
Страница 754: ...678 BigIron RX Series Configuration Guide 53 1002253 01 Displaying RIP filters 24 ...
Страница 814: ...738 BigIron RX Series Configuration Guide 53 1002253 01 Displaying OSPF information 25 ...
Страница 932: ...856 BigIron RX Series Configuration Guide 53 1002253 01 Generalized TTL security mechanism support 26 ...
Страница 980: ...904 BigIron RX Series Configuration Guide 53 1002253 01 Clearing IS IS information 28 ...
Страница 1000: ...924 BigIron RX Series Configuration Guide 53 1002253 01 Using secure copy 30 ...
Страница 1088: ...1012 BigIron RX Series Configuration Guide 53 1002253 01 IP source guard 35 ...
Страница 1108: ...1032 BigIron RX Series Configuration Guide 53 1002253 01 Reading CDP packets 37 ...
Страница 1126: ...1050 BigIron RX Series Configuration Guide 53 1002253 01 Clearing sFlow statistics 39 ...
Страница 1140: ...1064 BigIron RX Series Configuration Guide 53 1002253 01 802 1s Multiple Spanning Tree Protocol 40 ...
Страница 1324: ...1248 BigIron RX Series Configuration Guide 53 1002253 01 Displaying OSPFv3 information 48 ...
Страница 1363: ...BigIron RX Series Configuration Guide 1287 53 1002253 01 Continuous System Monitor 51 ...
Страница 1364: ...1288 BigIron RX Series Configuration Guide 53 1002253 01 Continuous System Monitor 51 ...
Страница 1404: ...1328 BigIron RX Series Configuration Guide 53 1002253 01 Commands That Require a Reload D ...
Страница 1458: ...1382 BigIron RX Series Configuration Guide 53 1002253 01 VSRP E ...