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Firewall Settings > QoS Mapping
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SonicOS 5.8.1 Administrator Guide
Process ACKs
This algorithm is used to update the BW parameters per class according to the amount of BW
usage in the previous time slice. Amount of BW usage is given by the total number of bytes
received for the class in the previous time slice. The algorithm is also used to process the
packets from the ingress module queues according to the available credit for the class.
Credit-Based Processing
A class will be in debt when its BW usage is more than the GBW for a particular time slice. All
the egress ACKs for the class are then queued until the debt is reduced to zero. At each
successive time slice, debt is deducted by GBW and if link BW is left, (MBW – GBW) is also
deducted.
Compute BW usage in the previous time slice:
a. Compute average ingress rate using the amount of BW usage by the class.
b. If the BW usage is more than the class credit, record the difference as debt. If link BW
is left over, deduct (MBW - GBW) from debt.
c. Compute the class and link credit for the current time slice:
• If the class is in debt, deduct GBW from debt and also from link’s credit, indicating
that the class has already used up its GBW for the current time slice.
• If class is not in debt and there are packets arriving for this class, accumulate link
credit; i.e. add GBW to credit at each time slice.
• Class is marked as over utilizing if debt is nonzero.
d. Process packets from ingress pool from highest priority to lowest priority.
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.
i. Repeat steps f through i for the next lowest priority.
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.
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