MC-MLPPP on the 7705 SAR supports scheduling based on multi-class implementation. Instead of the standard profiled queue-type scheduling, an MC-MLPPP encapsulated access port performs class-based traffic servicing. The four MC-MLPPP classes are scheduled in a strict priority fashion, as shown in Table: MC-MLPPP Class Priorities.
MC-MLPPP Class |
Priority |
|---|---|
0 |
Priority over all other classes |
1 |
Priority over classes 2 and 3 |
2 |
Priority over class 3 |
3 |
No priority |
For example, if a packet is sent to an MC-MLPPP class 3 queue and all other queues are empty, the 7705 SAR fragments the packet according to the configured fragment size and begins sending the fragments. If a new packet arrives at an MC-MLPPP class 2 queue while the class 3 fragment is still being serviced, the 7705 SAR finishes sending any fragments of the class 3 packet that are on the wire, then holds back the remaining fragments in order to service the higher-priority packet.
The fragments of the first packet remain at the top of the class 3 queue. For packets of the same class, MC-MLPPP class queues operate on a first-in, first-out basis.
The user configures the required number of MLPPP classes to use on a bundle. The forwarding class of the packet, as determined by the ingress QoS classification, is used to determine the MLPPP class for the packet. The mapping of forwarding class to MLPPP class is a function of the user-configurable number of MLPPP classes. The mapping for 4-class, 3-class, and 2-class MLPPP bundles is shown in Table: Packet Forwarding Class to MC-MLPPP Class Mapping .
FC ID |
FC Name |
MLPPP Class 4-class Bundle |
MLPPP Class 3-class Bundle |
MLPPP Class 2-class Bundle |
|---|---|---|---|---|
7 |
NC |
0 |
0 |
0 |
6 |
H1 |
0 |
0 |
0 |
5 |
EF |
1 |
1 |
1 |
4 |
H2 |
1 |
1 |
1 |
3 |
L1 |
2 |
2 |
1 |
2 |
AF |
2 |
2 |
1 |
1 |
L2 |
3 |
2 |
1 |
0 |
BE |
3 |
2 |
1 |
If one or more forwarding classes are mapped to a queue, the scheduling priority of the queue is based on the lowest forwarding class mapped to it. For example, if forwarding classes 0 and 7 are mapped to a queue, the queue is serviced by MC-MLPPP class 3 in a 4-class bundle model.