Figure 59: Cos Queues And Remarking Functions - GE T1000 Technical Manual

GE Reason Switches
REASON SWITCHES-TM-EN-3

Figure 59: CoS queues and remarking functions

Besides, it is possible to configure port incoming traffic to guarantee class of service
by limiting bandwidth at a given port, thus saving processing at ports which hosts
such IED or low priority networks are connected. This function is called Queue
Policing. In addition a flow control can be used to send paused frames instead of
discarding them. This function is called Port Policing at Reason Switches.
By default, Reason Switches queues are scheduled and forwarded as strict priority
mode, that is, only if higher CoS queues are empty a given CoS queue will start
forwarding traffic. This ensures that higher priority queues will always forward traffic
before lower ones. Besides, it is possible to change the egress schedule queues and
port behaviour to forward traffic based in average traffic, to guarantee that average
traffic at a given queue or port will be reliable. These functions are allowed only for 0
to 5 priorities CoS queues, and are divided in Port Scheduler and Port Shaping
functions. CoS 6 and CoS 7 priorities queues operate only in strict priority mode.
Port scheduler functions allow the user to set a weight value to prioritize some of
them based on average calculations. Thus, at instantaneous point of view there will
be some transmission of lower queues traffic, but the average traffic of higher CoS
queues will be higher and based on its weight at the transmission. To limit bandwidth
at a given port, based on the weight and configurations at port scheduler, there is
the Port Shaping function. When using strict priority mode, port and queue policing
would perform these functions.
If IP packets that traffic in the switch carry information of priority at DSCP bits, the
switch can process higher priority IP packets to ensure less delay at transmission of
them over lower priorities packets. By default, this function is disabled.
If enabled, DSCP-based QoS will perform its functions much like CoS bits do, been
also possible to enable DSCP independently at each port of the switch, classify each
priority in a specific queue for forwarding decisions and then translate the incoming
DSCP value to another before egressing the packet, as shown below.
Chapter 4 – Functions
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