NETGEAR S3300-28X (GS728TX) 24x1GE - Инструкция по эксплуатации - Страница 343

 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)