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DES-3500 Series Layer 2 Stackable Fast Ethernet Managed Switch User Manual
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QoS
The DES-3500 Series switches 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.
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
DES-3500 Series switches implements 802.1P priority queuing.
Figure 6- 51. Mapping QoS on the Switch
The picture above shows the default priority setting for the Switch. Class-3 has the highest priority of the four priority queues 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 tagged. Then the user may forward these tagged packets to designated queues 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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