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SonicOS Enhanced 4.0 Administrator Guide
e. Record class credit as remaining credit.
f. If remaining credit is greater than or equal to average rate, process the ACK packet and
deduct average rate from remaining credit.
g. Repeat g until remaining credit is not enough or the ingress ACK queue is empty.
h. Repeat steps f through h for the next rule queue in the ring.
i. Repeat steps f through i for the next lowest priority ring.
Example of Inbound Bandwidth Management
Consider a class with GBW = 5 Kbps, MBW = 10 Kbps and Link BW = 100 Kbps. In terms of
bytes per second we have GBW=640, excess BW = (MBW - GBW) = 640 and link BW = 12800.
a. Class credit starts with 640. In row 2, 1300 bytes are received for this class in the
previous time slice. Since it is more than the class credit, debt = 20 (1300-GBW-excess
BW). For the current time slice class credit = 620 (GBW - debt), debt = 0 and link BW
= 12780 since 20 bytes of debt is already used up from GBW for the class.
b. Row 2a shows an egress ACK for the class. Since class credit is less than the rate this
packet is queued in the appropriate ingress queue. And it will not be processed until
class credit is at least equal to the rate.
c. In the following time slices, class credit gets accumulated until it matches the rate.
Hence, after two time slices class credit becomes 1900 (620 + 640 + 640). The queued
ACK packet is process from the ingress pool at this point.
In row 2a, an ACK packet is received that needs to be sent to the TCP source on the WAN zone.
Sending this ACK immediately would have caused the TCP source to send more packets
immediately. By queuing the ACK and sending it only after the class credit reaches the average
rate, we have reduced the TCP’s sending rate; i.e. by doing this we have slowed down the
ingress rate.
BWM with WAN load balancing
BWM with WAN load balancing works in the following manner:
a. If two interfaces are configured as WAN and load balancing is NOT enabled, BWM is
only applied to the primary WAN interface.
b. If two interfaces are configured as WAN and load balancing is enabled:
• For Active/Passive Failover, BWM is done only on the active WAN interface.
• For Round Robin and Ratio options, link capacity is the sum of available BW for
primary and secondary WAN interface and BWM is done on both interfaces.
• For Spill Over option, link capacity is Primary’s available BW and BWM is done on
primary interface before the spill over occurs. And after the spill over occurs, the
secondary interface’s capacity is used and BWM is done on the secondary WAN
interface.
No. Ingress Egress Credit Debt Rate Link BW #Acks
1. 0 0 640 0 0 12800 0
2. 1300 0 620 0 1300 12780 0
2a. 0 40 620 0 1300 12780 1
3. 0 0 1260 0 1300 12800 1
4. 0 0 1900 0 1300 12800 0