D-Link DGS-1250 User Manual - Page 150

DGS-1250 Series Gigabit Ethernet Smart Managed Switch Web UI Reference Guide Port Scheduler Method This window is used to display and configure the port scheduler method settings. To view the following window, click QoS > Basic Settings > Port Scheduler Method, as shown below: Figure 7-2 Port Scheduler Method Window The fields that can be configured are described below: Parameter From Port - To Port Scheduler Method Description Select the range of ports that will be used for this configuration here. Select the scheduler method that will be applied to the specified port(s). Options to choose from are: • SP (Strict Priority) - Specifies that all queues use strict priority scheduling. It provides strict priority access to the queues from the highest CoS queue to the lowest. • RR (Round-Robin) - Specifies that all queues use round-robin scheduling. It provides fair access to service a single packet at each queue before moving on to the next one. • WRR (Weighted Round-Robin) - Specifies to transmit permitted packets into the transmit queue in a round robin order. Initially, each queue sets its weight to a configurable weighting. Every time a packet from a higher priority CoS queue is sent, the corresponding weight is subtracted by 1 and the packet in the next lower CoS queue will be serviced. When the weight of a CoS queue reaches zero, the queue will not be serviced until its weight is replenished. When weights of all CoS queues reach 0, the weights get replenished at a time. This is the default option. • WDRR (Weighted Deficit Round-Robin) - Specifies to serve an accumulated set of backlogged credits in the transmit queue in a round robin order. Initially, each queue sets its credit counter to a configurable quantum value. Every time a packet from a CoS queue is sent, the size of the packet is subtracted from the corresponding credit counter and the service right is turned over to the next lower CoS queue. When the credit counter drops below 0, the queue is no longer serviced until its credits are replenished. When the credit counters of all CoS queues reaches 0, the credit counters will be replenished at that time. All packets are serviced until their credit counter is zero or negative and the last packet is transmitted completely. When this condition happens, the credits are replenished. When the credits are replenished, a quantum of credits are added to each CoS queue credit counter. The quantum for each CoS queue may be different based on the user configuration. To set a CoS queue in the SP mode, any higher priority CoS queue must also be in the strict priority mode. 141