Configuring Quality Of Service - D-Link DGS-3100 User Manual

DGS-3100 Series Gigabit Stackable Managed Switch User Manual
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CONFIGURING QUALITY OF SERVICE

Configuring 1p
Priority tagging is an IEEE 802.1p defined standard function designed to provide a means of managing traffic on networks
where many different types of data are transmitted simultaneously. It is intended to alleviate problems associated with the
delivery of time-critical data over congested networks. The quality of applications dependent on such data, such as video
conferencing, can be severely and adversely affected by even very small delays in transmission.
IEEE 802.1p standard-compliant network devices recognize the priority level of data packets and can assign priority labels
or tags to packets, as well as strip priority tags from packets. The priority tag determines the packet's degree of
expeditiousness and the queue to which it is assigned.
Priority tags are assigned values from 0 to 7, with 0 being assigned to the lowest priority data, and 7 to the highest.
Generally, tag 7 is used for data associated with video or audio applications, sensitive to even slight delays, or for data from
specified end users whose data transmissions warrant special consideration.
The switch enables increased definition for handling priority tagged data packets on the network. Using queues to manage
priority tagged data enables user-specification for the data's relative priority to suit the needs of the network. Circumstances
can arise where it is advantageous to group two or more different tagged packets into the same queue. Generally, however, it
is recommended that the highest priority queue, Queue 1, be reserved for the data packets with a priority value of 7.
1) Classes not Queues should be used when explaining traffic handling techniques.
2) The ratio is Class0:Class1:Class2:Class3 = 1:2:4:8
A Weighted Round Robin system is employed on the switch to determine the rate 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 1, clears four packets for
every packet which cleared from Queue 0.
It is important that the priority queue settings on the switch are for all ports, and all devices connected to the switch are
affected. The priority queuing system is especially beneficial for networks that employ priority tag assignment capable
switches.
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 a larger bandwidth can be created, but
also a 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 DGS-3100 series implements 802.1P priority queuing.
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