User Manual

24-Port and 48-Port Gigabit Ethernet PoE+ Smart Switches with 4 SFP Ports
Configuration Examples User Manual521
Differentiated Services (DiffServ)
Standard IP-based networks are designed to provide best effort data delivery service. Best
effort service implies that the network delivers the data in a timely fashion, although there is
no guarantee that it does. During times of congestion, packets might be delayed, sent
sporadically, or dropped. For typical Internet applications, such as email and file transfer, a
slight degradation in service is acceptable and in many cases unnoticeable. However, any
degradation of service can negatively affect applications with strict timing requirements, such
as voice or multimedia.
Quality of Service (QoS) can provide consistent, predictable data delivery by distinguishing
between packets with 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
cannot meet the necessary timing requirements, this creates a deficiency in the network path
and the performance of the entire packet flow is compromised.
Two basic types of QoS are supported:
•
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 traf
fic
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 that you can use
to construct a differentiated service network. Use these same blocks in different ways to build
other types of QoS architectures.
You must configure three key QoS building blocks for DiffServ:
• Class
• Policy
• Service (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
• EtherT
ype
• Class of Service (802.1p priority) value (first/only VLAN tag)
• VLAN ID range (first/only VLAN tag)