In IP network, there are three kinds of bearing in the IPv4 packet QoS priority tag, respectively based on the second floor of cosine fields (IEEE802.1 p) priority, based on IP layer IP ToS priority and priority fields based on IP layer DSCP (Differentiated Services Codepoint) field, the priority of each priority are defined as follows:

(1) IEEE802.1 p priority======& gt; 2 layer Qos (ISL& Dot1Q)

It is located in the Ethernet frame with labels on the second floor of cosine fields, with a VLAN ID is used, place in the byte is as follows:



IEEE802.1 p priority: 3 - (P2 - P0)

Unused (CU) : 1 -

VLAN ID: 12 bit (V11 - where V0)

IEEE802.1 p priority value has eight (0 to 7), the lowest priority 0, 7, the highest priority message is divided into three conditions: take priority and a VLAN ID tag message, the priority value is its own value; Only take priority tag message, the VLAN ID is 0, the priority value is itself to bring value; Without tag message, generally the default priority value is 0, also can be changed to specify new priority,

(2) IP priority=============="layer 3 IP header one type of service

It consists of the types of service in IP packet header (ToS) bytes of the three, its position in bytes are as follows:

P1 P2 P0 T3 T2T1 T0 CU

Among them: IP priority: 3 - (P2 - P0)

The types of services (ToS) : 4 bit (T3 - T0)

Unused (CU) : 1 -

8 P priority value (0 to 7), the lowest priority 0, 7, the highest priority by default, IP priority 6 and 7 for network communication control use, not recommended users, ToS field type of service failed to its widespread use in the existing IP network,

(3) the DSCP priority=============="layer 3 second service type of the IP header is

It is composed of six of the IP packet header, using the ToS bytes, so after using DSCP is also known as the bytes DSCP bytes, its position in bytes are as follows:

DS5 DS4DS3 DS2 DS1 DS0 CU CU

Among them: DSCP priority: 6 bit (DS5 - DS0)

Unused (CU) : 2 bit

DSCP priority value. There are 64 (0-63), the lowest priority 0, 63, the highest priority in fact is a superset of IP priority field DSCP field, the definition of DSCP field backwards compatible with IP priority fields, the current definition of DSCP have default DSCP, value is 0; Class selectors DSCP, defined as backwards compatible with IP priority, value of,16,24,32,40,48,56 (8); Accelerate forward (EF), general services for low latency, recommended value for 46 (101110); Determine the forwarding (AF), defines the four service level, each service level has three descent, so use 12 DSCP values (,12,14 (10), (18,20,22), (26,28,30),,36,38) (34),