3Com 10014299 manual Selecting Congestion Management Policies

Selecting Congestion Management Policies 681

For the interface with the lower rate, customizing the queue for it can guarantee that the data flows passing through this interface may also obtain the network services to certain extent.

Weighted Fair Queuing Weighted Fair Queuing (WFQ) provides a dynamic and fair queuing mode, which distinguishes the traffic based on the priority/weight and decides the bandwidth size of each session according to the session situation. Thus, it guarantees that all communications can be fairly treated according to the weight allocated to them. The foundation based on which WFQ classifies the traffic includes the source address, destination address, source port number, destination port number, and protocol type.

Selecting Congestion 3Com routers implement the four congestion management policies (FIFO, PQ, CQ Management Policies and WFQ) discussed previously, in the Ethernet interface and serial interface

(encapsulated PPP, FR, HDLC), which may satisfy the requirements for various service qualities to a certain extent.

FIFO implements the no priority policy of the data packet in user data communication, which is not needed to determine the priority or type of the communication. However, when using the FIFO policy, some low priority data in abnormal operation may consume most of available bandwidths and occupy the entire queue, which causes the delay of the burst data source, and the important communication may be thereby discarded.

PQ can assure some communication transmission with higher priority. That is, the strict priority sequence is conducted at the cost of transmission failure of data packets with lower priority. For example, the packets in the lower priority queue may not be transmitted in the worst case where the available bandwidth is very limited and emergency communication occurs frequently.

CQ reserves a certain percent of available bandwidth for each type of specified traffic, so that the interface running at a low rate can obtain network service even if congestion occurs. The size of this queue is determined by deciding the total number of the data packets configured in the queue to control access to the bandwidth.

WFQ uses the fair queuing algorithm to dynamically divide the communications into messages. The message is a part of a session. With the use of WFQ, the interactive communication with a small capacity can obtain the fair allocation of the bandwidth, as the same as the communication with a large capacity (such as file transmission).

Table 719 compares between the four different policies: