Section 2
2-7
GigaFast
Port based priority
!
802.1p based priority
When 802.1p tag priority is applied, the EE2400-SS can recognize the
802.1Q VLAN tag frames and extract the 3-bit User_Priority information
from the VLAN tag. The RTL8326 set the threshold of User_Priority as 3.
Therefore, VLAN tagged frames with User_Priority value = 4~7 will be
treated as high priority frames, and treat other User_Priority values (0~3)
as low priority frames (following 802.1p standard).
!
Differentiated Service based priority
When TCP/IP's TOS/DiffServ (DS) based priority is applied, the EE2400-
SS can recognize TCP/IP Differentiated Services Codepoint (DSCP)
priority information from the DS-field defined on RFC2474. The DS field
byte for IPv4 is the Type-of-Service (TOS) octet, and for IPv6, it is the
Traffic-Class octet. The recommended DiffServ Codepoints is defined in
RFC2597 to classify the traffic into different service classes. The EE2400-
SS can extract the Codepoint value of the DS-field from Ipv4 and IPv6
packets, and identify the priority of the incoming IP packet following the
definitions listed bellow:
High priority: whose DS-field =
(EF,expected forwarding:) 101110;
(AF, Assured Forwarding:) 001010; 010010; 011010; 100010
(Network Control:) 11x000.
Low priority: whose DS-field = others values.
The VLAN tagged frame and 6-bit DS-filed in IPv4 and IPv6 frame format
are shown below:
802.1Q VLAN tag frame format:
6 bytes
6 bytes
2 bytes
3 bits
5bits
DA
SA
81-00
User-Priority
----
( 0~3:Low-pri; 4~7: High-pri )
