User guide

EDA System Services

1/1551-HSC 901 35/3 Uen C 2005-12-02

Queue 1

Weight

Queue 2

Weight

Queue 3

Weight

Queue 4

Weight

One

Round

Figure 44 Deficit Round Robin

• Modified Deficit Round Robin (MDRR) - The highest prioritized queue

(queue 1) is processed first and next the remaining queues are

processed by weight as for Deficit Round Robin. The weights are fully

operator configurable. Note that when MDRR is used, queue 1 has no

weight since there is strict priority between queue 1 and all the other

queues (meaning that queue 1 will always be emptied when serviced).

Queue 1

Queue 2

Weight

Queue 3

Weight

Queue 4

Weight

One

Round

Figure 45 Modified Deficit Round Robin

DRR and MDRR weight is given in Bytes per round. The weight defines the

number of bytes that can be sent from a specific queue in one round. This

way the relative bandwidth of a CoS flow with relations to other QoS flows

can be defined. When a queue is serviced, an Ethernet frame is the

smallest unit (whichever size the actual frame has) that can be sent. If the

frame waiting in the queue is larger in size than the weight for the specific

queue (for example if the frame is 1500 bytes and the weight is 1000 bytes)

then the frame will not be sent in the first round. The unused bytes that

could have been sent in this round will be summed to the bytes in the next

round. At that time the allowed bytes will be 2000, and therefore the frame