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19
TRENDnet User’s Guide
TEG-7080ES
QoS (Quality of Service)
When a port on an Ethernet switch becomes oversubscribed, its egress queues contain
more packets than the port can handle in a timely manner. In this situation, the port
may be forced to delay the transmission of some packets, resulting in the delay of
packets reaching their destinations. A port may be forced to delay transmission of
packets while it handles other traffic, and, in some situations, some packets destined to
be forwarded to an oversubscribed port from other switch ports may be discarded.
Minor delays are often of no consequence to a network or its performance. But there
are applications, referred to as delay or time sensitive applications, which can be
impacted by packet delays. Voice transmission and video conferences are two examples.
If packets carrying data in either of these cases are delayed from reaching their
destination, the audio or video quality may suffer. This is where Class of Service (CoS) is
of value. It allows you to manage the flow of traffic through a switch by having the
switch ports give higher priority to some packets, such as delay sensitive traffic, over
other packets. This is referred to as prioritizing traffic.
Set IEEE 802.1P settings
Bridge > QoS > IEEE 802.1P QoS
1. Log into your switch
management page (see “
Access your switch management page
on page 7).
2. Click on
Bridge
and click on
QoS
.
3. By default, the
QoS Mode setting
is set to
IEEE 802.1P QoS
.
4.
Review the fixed
IEEE 802.1P QoS
settings. These
Traffic Classes
are fixed to their
respective queues (Queue 0, Queue 1, Queue, 2, Queue 3) and cannot be changed.
o
IEEE 802.1p sets a 3-bit value in the MAC header to indicate prioritization.
This 3-bit value provides priority levels ranging from 0 to 7 (i.e., a total of 8
levels), with level 7 representing the highest priority. This permits packets
to cluster and form different traffic classes. Thus, when network
congestion occurs, those packets that have higher priorities will receive
preferential treatment while low priority packets will be kept on hold.
6. Change the
Scheduling Method Settings
to define the hierarchy and parameters for
the QoS Mode application. Click
Apply
to save the settings.
•
Weighted Round Robin
- The port transmits a set number of packets from each
queue, in a round robin fashion, so that each has a chance to transmit traffic.
•
All-High-Before-Low
- The port transmits all packets out of higher priority
queues before transmitting any from the lower priority queues.
7. Click
Apply
to save configuration changes to the NV-RAM to ensure that if the switch
is rebooted or power cycled, the configuration changes will still be applied.