D-Link xStack DGS-3400 Series User Manual - Qos

xStack DGS-3400 Series Layer 2 Gigabit Ethernet Managed Switch 

QoS 

The xStack DGS-3400 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-3400 switch series implements basic 802.1P priority queuing. 

Figure 7- 44. 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, let’s 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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