1-4CongestionmanagementThe S5600 series support SP and WRRqueue scheduling algorithms and supportthe following three queue schedulingmodes:z SPz WRRz SP+WRRFor information about SPand WRR, refer to QueueScheduling.Introduction to QoS FunctionsTraffic ClassificationTraffic here refers to service traffic; that is, all the packets passing the switch.Traffic classification means identifying packets that conform to certain characteristicsaccording to certain rules. It is the foundation for providing differentiated services.In traffic classification, the priority bit in the type of service (ToS) field in IP packet headercan be used to identify packets of different priorities. The network administrator can alsodefine traffic classification policies to identify packets by the combination of sourceaddress, destination address, MAC address, IP protocol or the port number of anapplication. Normally, traffic classification is done by checking the information carried inpacket header. Packet payload is rarely adopted for traffic classification. The identifyingrule is unlimited in range. It can be a quintuplet consisting of source address, source portnumber, protocol number, destination address, and destination port number. It can also besimply a network segment.Priority Trust ModeIntroduction to precedence types1) IP precedence, ToS precedence, and DSCP precedenceFigure 1-2 DS field and ToS byteThe ToS field in an IP header contains eight bits numbered 0 through 7, among which,z The first three bits indicate IP precedence in the range 0 to 7.z Bit 3 to bit 6 indicate ToS precedence in the range of 0 to 15.z In RFC2474, the ToS field in IP packet header is also known as DS field. The first sixbits (bit 0 through bit 5) of the DS field indicate differentiated service codepoint (DSCP)in the range of 0 to 63, and the last two bits (bit 6 and bit 7) are reserved.
