GE T1000, Technical Manual

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Chapter 4
– Functions
GE Reason Switches
96 REASON SWITCHES-TM-EN-3
CoS bits value DSCP bits value
5 40 – 46
6 48
7 56
If core networking equipment has some philosophy on DSCP values that is different
from the edge equipment, it is possible to re-map the frames to a given DSCP at the
switch. There are several applications where there is a need to change incoming
frame DSCP to adapt it to the network. Thus, incoming frame from a given DSCP will
be marked as a new DSCP value and will be forwarded with this new DSCP value.
10.4 GE Reason Switches QoS Capabilities
GE Reason Switches allow the user to apply QoS in network applications at layer 2
protocols. For layer 3 applications, DSCP-based QoS is also supported. There are two
types of QoS allowed when using Reason Switches:

CoS values QoS;
o
Direct CoS value at 802.1Q frames;
o
Protocol Mapping to CoS;
o
DSCP mapping to CoS.

DSCP values QoS.
As shown in the previous sections, VLAN tagged frames always carry information of
packet prioritization. Thus, quality of service is guaranteed to higher priority VLAN
identification over lower values, as each CoS value has a specific queue at
forwarding decision.
If IED equipment sends priority information correctly at the frames that are sent throughout the network, then Reason Switches
will perform its QoS functions without need to configuration, as default configuration ensures that CoS value is queued correctly.
This means also to IP communication sending DSCP bits value, which is informing the IP network equipment its priority over the
network. Thus, if there is no legacy equipment without CoS capabilities, configuration might not be necessary. In addition, strict
priority is generally enough to ensure QoS services. Thus, using weighted queues or WRED congestion detected should be clearly
understood before using, as these mechanisms increase network complexity.
QoS configuration is applied when legacy equipment is connected as it does not allow prioritization itself. Besides, strict priority
can be changed to weighted queues, or early congestion detection can be obtained over IP protocols with WRED function when
network simulations show that network performance can be increased without increasing network bandwidth
.
By default, ports are classified to queue 802.1Q non-compliant packets at CoS
priority number 0 (best-effort service) and uses CoS information from incoming
802.1Q frames to queue at the given CoS value queue. Besides, tag classification can
be enabled to change which queue will be used by incoming data with CoS
information. Each port has independently classification, enabling the user to remark
CoS value independently at each port. At packet egress processing, it is possible to
remark the CoS value at the packets from a given queue, thus enabling incoming
data to be re-mapped with another CoS value as illustrated in the figure bellow.