Congestion management technique comparison
Breaking through the single congestion management policy of FIFO for traditional IP devices, the device provides all the congestion management techniques described above to offer powerful QoS capabilities, meeting different QoS requirements of different applications.
Table 3: Congestion management technique comparison
Type | Number of queues | Advantages | Disadvantages |
|---|
FIFO | 1 | No need to configure, easy to use. Easy to operate, low delay.
| All packets are treated equally. The available bandwidth, delay and drop probability are determined by the arrival order of packets. No restriction on traffic from connectionless protocols (protocols without any flow control mechanism, UDP, for example), resulting in bandwidth loss for traffic of connection-oriented protocols (TCP, for example). No delay guarantee for time-sensitive real-time applications, such as VoIP.
|
PQ | 4 | Absolute bandwidth and delay guarantees for real-time and mission-critical applications, such as VoIP. | Need to configure, low processing speed. If no restriction is imposed on bandwidth assigned to high-priority packets, low-priority packets might fail to get bandwidth.
|
CQ | 16 | | Need to configure, low processing speed. |
WFQ | Configurable | Easy to configure. Bandwidth guarantee for packets from cooperative (interactive) sources (such as TCP packets). Reduced jitter. Reduced delay for interactive applications with a small amount of data. Bandwidth assignment based on traffic priority. Automatic bandwidth reassignment to increase bandwidth for each class when the number of traffic classes decreases.
| The processing speed is faster than PQ and CQ but slower than FIFO. |
CBQ | Configurable (0 to 64) | Flexible traffic classification based on various rules and differentiated queue scheduling mechanisms for EF, AF and BE services. Highly precise bandwidth guarantee and queue scheduling on the basis of AF service weights for various AF services. Absolutely preferential queue scheduling for the EF service to meet the delay requirement of real-time data. Overcomes the disadvantage of PQ that some low-priority queues are not serviced by restricting the high-priority traffic. WFQ scheduling for best-effort traffic (the default class).
| The system overheads are large. |
If the burst traffic is too heavy, increase the queue length to make queue scheduling more accurate.