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xStack DGS/DXS-3300 Series Layer 3 Stackable Gigabit Ethernet Switch User Manual
QoS
The xStack DGS/DXS-3300 Switch Series 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.
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 xStack DGS/DXS-3300 Switch Series implements basic 802.1P
priority queuing.
Figure 6- 45. An Example of the Default QoS Mapping on the Switch
The picture above shows the default priority setting for the Switch. Class-6 has the highest priority of the seven priority
classes of service on the Switch. In order to implement QoS, the user is required to instruct the Switch to examine the
header of a packet to see if it has the proper identifying tag. Then the user may forward these tagged packets to designated
classes of service on the Switch where they will be emptied, based on priority.
For example, lets say a user wishes to have a video conference between two remotely set computers. The administrator can
add priority tags to the video packets being sent out, utilizing the Access Profile commands. Then, on the receiving end,
the administrator instructs the Switch to examine packets for this tag, acquires the tagged packets and maps them to a class
queue on the Switch. Then in turn, the administrator will set a priority for this queue so that will be emptied before any
other packet is forwarded. This results in the end user receiving all packets sent as quickly as possible, thus prioritizing the
queue and allowing for an uninterrupted stream of packets, which optimizes the use of bandwidth available for the video
conference.
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