Netgear GS728TPP Manuel d'utilisateur télécharger pdf (Page 259)

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GS752TP, GS728TP, and GS728TPP Gigabit Smart Switches

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 will. 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 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. For this reason, 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 support 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 various ways to build

other types of QoS architectures.

There are three key QoS building blocks needed to configure DiffServ:

• Class

• Policy

• Service (that is, 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 and destination MAC addresses

• EtherType

• Class of Service (802.1 p priority) value (first or only VLAN tag)

• VLAN ID range (first or only VLAN tag)

• IP service type octet (also known as: ToS bits, precedence value, DSCP value)

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Netgear GS728TPP Manuel d'utilisateur Page 259