342-86400-498PS
Issue 1.2
April 2012
Page 96
Copyright
GE Multilin Inc. 2010-2012
Priority
In general, Ethernet frames ingressing paddleboard access ports (“add” frames)
may or may not carry
source priority
information. The source priority can be
used to properly prioritize frames when they are passed through the switches.
If present, the source priority is carried in the frame's 802.1p/Q priority field (3
bits) and/or in the TOS field (6 bits) of the encapsulated IP frame (see Appendix
C) and it can range from 0 to 7, where 7 is the highest and 0 is the lowest priority.
If the frame does not carry Source Priority information or its use is purposely
suppressed, a user-defined Default Priority (configured per port) will be taken as
the frame‟s source priority.
Note:
In the case of a “nested 802.1Q frame” (QinQ) the relevant 802.1p/Q
priority field is the one carried in the last nesting level (i.e. the one carried in the
802.1Q tag that is received first in the series of up to 28 nested 802.1Q tags).
Each access port on the paddleboard can detect ingressing “mission critical”
frames based on the user-specified EtherType code (e.g. 88b8 for GOOSE
messages) and treat them as “super-priority” frames regardless of their source
priority. These mission critical frames will be switched through the highest
priority queues in the ETHER-1000 system. This feature guarantees that the
selected mission critical traffic type is transported with the highest priority
possible.
48
The “LAN” switch (i.e. the Marvell switch chip residing on the paddleboard) has 4
priority queues. The ingressing frames with source priorities 0/1, 2/3, and 4/5 are
mapped into the three lower priority queues, respectively, while the top-priority
queue is used for the ingressing frames with source priorities 6 and 7 and
segregated EtherType frames.
When passed from the paddleboard to the ETHER-
1000 unit (i.e. the “WAN”
switch), each “add” frame is assigned a
mapping priority
(0 to 7) based on the
Mapping Priority setting for its ingressing paddleboard port. Specifically, the
mapping priority assigned to a frame can be:
7 (applicable to segregated EtherType frames);
Equal to its source priority (for frames with source priority lesser than 7) or
equal to its source priority decremented by one (for frames with source
priority 7);
Forced to “Priority N” (N=0,1…6).
48
When ETHER-100 units are used in the same ETHER system, caution shall be exercised as
these unit‟s do not support this feature.
