3Com 3032 Configuration Manual

Also see for 3036: Release note Command reference guide Supplementary guide Manual Datasheet

3Com 3032 Configuration Manual Manual pdf 685 page image

Selecting Congestion Management Policies 681For the interface with the lower rate, customizing the queue for it can guaranteethat the data flows passing through this interface may also obtain the networkservices to certain extent.Weighted Fair Queuing Weighted Fair Queuing (WFQ) provides a dynamic and fair queuing mode, whichdistinguishes the traffic based on the priority/weight and decides the bandwidthsize of each session according to the session situation. Thus, it guarantees that allcommunications can be fairly treated according to the weight allocated to them.The foundation based on which WFQ classifies the traffic includes the sourceaddress, destination address, source port number, destination port number, andprotocol type.Selecting CongestionManagement Policies3Com routers implement the four congestion management policies (FIFO, PQ, CQand WFQ) discussed previously, in the Ethernet interface and serial interface(encapsulated PPP, FR, HDLC), which may satisfy the requirements for variousservice qualities to a certain extent.FIFO implements the no priority policy of the data packet in user datacommunication, which is not needed to determine the priority or type of thecommunication. However, when using the FIFO policy, some low priority data inabnormal operation may consume most of available bandwidths and occupy theentire queue, which causes the delay of the burst data source, and the importantcommunication may be thereby discarded.PQ can assure some communication transmission with higher priority. That is, thestrict priority sequence is conducted at the cost of transmission failure of datapackets with lower priority. For example, the packets in the lower priority queuemay not be transmitted in the worst case where the available bandwidth is verylimited and emergency communication occurs frequently.CQ reserves a certain percent of available bandwidth for each type of specifiedtraffic, so that the interface running at a low rate can obtain network service evenif congestion occurs. The size of this queue is determined by deciding the totalnumber of the data packets configured in the queue to control access to thebandwidth.WFQ uses the fair queuing algorithm to dynamically divide the communicationsinto messages. The message is a part of a session. With the use of WFQ, theinteractive communication with a small capacity can obtain the fair allocation ofthe bandwidth, as the same as the communication with a large capacity (such asfile transmission).Table 719 compares between the four different policies: