GE T1000, Technical Manual

Page: 93 / 302

GE Reason Switches Chapter 4
– Functions
REASON SWITCHES-TM-EN-3 93
Figure 54: CoS classification as shown in IEC 61850-90-4 Technical Report, section D.2.6
R
EASON
S
WITCHES HAVE SUPPORT TO PRIORITIZATION USING
C
O
S
BITS
,
WHICH IS PERFORMED IN
EIGHT DIFFERENT QUEUES
,
ONE FOR EACH
C
O
S
PRIORITY ALLOWED
. T
HE SWITCH WILL PRIORITIZE
FORWARDING TRAFFIC FROM HIGHER
C
O
S
QUEUES BEFORE FORWARDING OTHER TRAFFIC
. A
S
THERE ARE EIGHT QUEUES
,
THE
C
O
S 7
QUEUE WILL BE THE FIRST TO BE EMPTY
,
THEN
C
O
S 6
QUEUE
WILL BE FORWARDED AND SO ON
.
The queue description given below is known as a strict priority queue. By default, Reason Switches operate in the Strict Priority
Queue mode. If a given LAN needs to dynamically prioritize traffic which there is higher classes transmission, but no stop on
transmission in the lower classes traffic, then the port shaping or WRED functions can be used.
One important point using CoS bits is that traffic prioritization will be linked to the
VID (VLAN ID) of the frame. Thus, this QoS mechanism will prioritize traffic from
one VLAN over another. As there is traffic prioritization related to the VLAN, this
mechanism assumes that data at the given VLAN must be prioritized.
IED equipment, in power system communication, must allow the usage of VLAN mechanisms and traffic prioritization at least to
digital (GOOSE), analogue (Sampled Values) and synchronization (PTP) packet messages separately, as they are mapped directly
at the data-link layer. Thus, QoS mechanism with CoS bits would be enough to guarantee prioritization for these messages, as
the VLAN ID can be mapped directly to message type.
IED equipment, in power system communication, should send packets containing VLAN and priority information. This way, as
they send packets classified to determined CoS, the switch will by default queue the packet in CoS defined queue. If all IED are
correctly configured to send GOOSE, Sampled Values and PTP messages, the switch will classify the packets by default, with no
need for QoS configurations.
If core networking equipment has some philosophy on traffic prioritization of CoS
values that is different from the edge equipment, it is possible to re-map the
frames to a given CoS at the switch. There are several applications there is a
need to change incoming frame CoS to adapt it to the network. Thus, incoming
frame from a given CoS will be stored in another CoS queue, and forwarded with
the new CoS values.
If application requires the switching equipment to be able to inspect the type of
traffic to prioritize them, it is possible to map messages to a determined CoS