H3C S7500 Series Ethernet Switches Operation Manual
Operation Manual – QoS
H3C S7500 Series Ethernet Switches Chapter 1
QoS Configuration
1-11
In the RED algorithm, an upper limit and a lower limit are set for each queue, and it is
stipulated that:
z When the queue length is smaller than the lower limit, no packet is dropped.
z When the queue length is bigger than the upper limit, all received packets all
dropped.
z When the queue length is in the range of the upper limit and the lower limit, the
received packets are dropped at random. In this case, a number is assigned to
each received packet and then compared with the drop probability of the current
queue. If the assigned number is bigger than the drop probability, the received
packet is dropped. The longer a queue is, the higher the drop probability is.
However, there is a maximum drop probability.
In the RED algorithm, packets are dropped at random so that global TCP
synchronization is avoided. When packets in a TCP connection are dropped and sent
at a low rate, packets in other TCP connections are still sent at a high rate. In this way,
packets in a part of TCP connections are sent at a high rate in any case. Thus, the
utilization rate of bandwidth is improved.
1.2 QoS Supported by the S7500 Series Ethernet Switches
Table 1-4 QoS features supported by the S7500 series Ethernet switches and related
commands
QoS Specification Related command
Priority mapping
Support only the
802.1p-priority-to-
local-queue
mapping
qos cos-local-precedence-map
Port priority Supported
priority priority-level
Priority according to which
a packet is put into an
output queue
Supported
priority-trust
TP
Supported
traffic-limit
Priority marking Supported
traffic-priority
Redirect Supported
traffic-redirect
Queue scheduling
Support SP, RR
and WRR
queue-scheduler
Rate limiting Supported
line-rate
Guaranteed bandwidth Supported
traffic-bandwidth
Congestion avoidance RED operation
traffic-red
Traffic statistics
Supported
traffic-statistic
Inbound CAR Supported inboundcar { enable | disable }