3Com 2928 User Guide - Page 465

z Expedited Forwarding (EF) class: In this class, packets are forwarded regardless of link share of other traffic. The class is suitable for preferential services requiring low delay, low packet loss, low jitter, and high bandwidth. z Assured forwarding (AF) class: This class is divided into four subclasses (AF 1 to AF 4), each containing three drop priorities for more granular classification. The QoS level of the AF class is lower than that of the EF class. z Class selector (CS) class: This class is derived from the IP ToS field and includes eight subclasses; z Best effort (BE) class: This class is a special CS class that does not provide any assurance. AF traffic exceeding the limit is degraded to the BE class. Currently, all IP network traffic belongs to this class by default. Table 2-2 Description on DSCP values DSCP value (decimal) 46 10 12 14 18 20 22 26 28 30 34 36 38 8 16 24 32 40 48 56 0 DSCP value (binary) 101110 001010 001100 001110 010010 010100 010110 011010 011100 011110 100010 100100 100110 001000 010000 011000 100000 101000 110000 111000 000000 Description ef af11 af12 af13 af21 af22 af23 af31 af32 af33 af41 af42 af43 cs1 cs2 cs3 cs4 cs5 cs6 cs7 be (default) 2) 802.1p precedence 802.1p precedence lies in Layer 2 packet headers and is applicable to occasions where Layer 3 header analysis is not needed and QoS must be assured at Layer 2. 2-5