User Manual

Configuration Examples
343
S3300 Smart Managed Pro Switch
Differentiated Services
Standard IP-based networks are designed to provide best effort data delivery service. Best
effort service implies that the network deliver the data in a timely fashion, although there is no
guarantee that it will. During times of congestion, packets can be delayed, sent sporadically,
or dropped. For typical Internet applications, such as e-mail and file transfer, a slight
degradation in service is acceptable and in many cases unnoticeable. However, any
degradation of service has undesirable effects on applications with strict timing requirements,
such as voice or multimedia.
Quality of Service (QoS) can provide consistent, predictable data delivery by distinguishing
between packets that have strict timing requirements from those that are more tolerant of
delay. Packets with strict timing requirements are given special treatment in a QoS-capable
network. With this in mind, all elements of the network must be QoS-capable. If one node is
unable to meet the necessary timing requirements, this creates a deficiency in the network
path and the performance of the entire packet flow is compromised.
There are two basic types of QoS:
• Integrated Services. Network resources are apportioned based on request and are
reserved (resource reservation) according to network management policy (RSVP, for
example).
• Differentiated Services. Network resources are apportioned based on traffic
classification and priority, giving preferential treatment to data with strict timing
requirements.
The switch supports DiffServ.
The DiffServ feature contains a number of conceptual QoS building blocks you can use to
construct a differentiated service network. Use these same blocks in different ways to build
other types of QoS architectures.
There are 3 key QoS building blocks needed to configure DiffServ:
• Class
• Policy
• Service (i.e., the assignment of a policy to a directional interface)
Class
You can classify incoming packets at layers 2, 3, and 4 by inspecting the following
information for a packet:
• Source/destination MAC address
• EtherType
• Class of Service (802.1p priority) value (first/only VLAN tag)
• VLAN ID range (first/only VLAN tag)
• IP Service Type octet (also known as: ToS bits, Precedence value, DSCP value)