System Description
H3C S3600 Series Ethernet Switches
Chapter 3 Software Features
3-9
3.6 QoS
Quality of service (QoS) provides differentiated network services to accommodate to
various demands.
3.6.1 Traffic Classification
Traffic classification is to classify packets to facilitate the subsequent packet processing
conducted by a switch
.
In traffic classification, a rule is specified for discriminating packets compliant with some
characteristics. Classification rules can be very simple; for example, packets can be
sorted by the priority defined in the type of service (ToS) field in the IP header. They can
also be very complex; for example, packets can be sorted by any combination of MAC
address, IP protocol type, source (host or network) address, destination (host or
network) address, and even application port number, which involve the layers of data
link, network, and transport.
3.6.2 Traffic Policing/Traffic Assurance
Traffic policing polices the traffic matching a traffic classification rule on the port where
the packets are received, so that the traffic can effectively use the assigned network
resources such as bandwidth.
Traffic policing mainly functions to limit the speed of an input port and thereby monitor
the traffic that enters its connected network.
When packets arrive at the port at a speed
exceeds the assigned bandwidth, they are either dropped or assigned a new
preference.
Bandwidth assurance refers to assuring the minimum bandwidth for a special traffic so
that it can satisfy such QoS requirements as packet loss rate, delay, jitter even when
network congestion occurs.
3.6.3 Port Flow Control
Port flow control is used for congestion management. Congestion occurs when the
network cannot reach the committed or negotiated performance specifications (such as
speed).
When congestion occurs, the switch transmits a pause frame to the corresponding
connection and notifies the peer to pause for a period of time before transmitting data
again, so as to reduce the incoming traffic on the network. The port control takes effect
on all traffic.
