Understanding Ieee 802.1P Priority; Qos; The Advantages Of Qos - D-Link DES-3010F Manual

QoS

Port Bandwidth
802.1p Default Priority
802.1p User Priority
QoS Scheduling Mechanism
QoS Output Scheduling
QoS
The Switch supports 802.1p priority queuing Quality of Service. The following section discusses the implementation of
QoS (Quality of Service) and benefits of using 802.1p priority queuing.

Understanding IEEE 802.1p Priority

Priority tagging is a function defined by the IEEE 802.1p standard designed to provide a means of managing traffic on a
network where many different types of data may be transmitted simultaneously. It is intended to alleviate problems
associated with the delivery of time critical data over congested networks. The quality of applications that are dependent on
such time critical data, such as video conferencing, can be severely and adversely affected by even very small delays in
transmission.
Network devices that are in compliance with the IEEE 802.1p standard have the ability to recognize the priority level of
data packets. These devices can also assign a priority label or tag to packets. Compliant devices can also strip priority tags
from packets. This priority tag determines the packet's degree of expeditiousness and determines the queue to which it will
be assigned.
Priority tags are given values from 0 to 7 with 0 being assigned to the lowest priority data and 7 assigned to the highest.
The highest priority tag 7 is generally only used for data associated with video or audio applications, which are sensitive to
even slight delays, or for data from specified end users whose data transmissions warrant special consideration.
The Switch allows you to further tailor how priority tagged data packets are handled on your network. Using queues to
manage priority tagged data allows you to specify its relative priority to suit the needs of your network. There may be
circumstances where it would be advantageous to group two or more differently tagged packets into the same queue.
Generally, however, it is recommended that the highest priority queue, Queue 3, be reserved for data packets with a
priority value of 7. Packets that have not been given any priority value are placed in Queue 0 and thus given the lowest
priority for delivery.
A weighted round robin system is employed on the Switch to determine the rate at which the queues are emptied of
packets. The ratio used for clearing the queues is 4:1. This means that the highest priority queue, Queue 3, will clear 4
packets for every 1 packet cleared from Queue 0.
Remember, the priority queue settings on the Switch are for all ports, and all devices connected to the Switch will be
affected. This priority queuing system will be especially beneficial if your network employs switches with the capability of
assigning priority tags.

The Advantages of QoS

QoS is an implementation of the IEEE 802.1p standard that allows network administrators a method of reserving
bandwidth for important functions that require a large bandwidth or have a high priority, such as VoIP (voice-over Internet
Protocol), web browsing applications, file server applications or video conferencing. Not only can a larger bandwidth be
created, but other less critical traffic can be limited, so excessive bandwidth can be saved. The Switch has separate
hardware queues on every physical port to which packets from various applications can be mapped to, and, in turn
prioritized. View the following map to see how the Switch implements basic 802.1P priority queuing.
DES-3010F/G / DES-3018 / DES-3026 Fast Ethernet Switch Manual
Section 8
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