D-Link DGS-1008D Product Manual - Page 9

D-Link DGS -1008D Unmanaged Gigabit Ethernet Switch 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. "The DUT support strict mode for 802.1p QoS. The untagged pkt will follow the priority 0 to work (i.e. class 1)." Understanding QoS The Switch has four priority queues. These priority queues are labeled as 3, the high queue to 0, the lowest queue. The eight priority tags, specified in IEEE 802.1p are mapped to the Switch's priority tags as follows: • Priority 0 is assigned to the Switch's Q1 queue. • Priority 1 is assigned to the Switch's Q0 queue. • Priority 2 is assigned to the Switch' s Q0 queue. • Priority 3 is assigned to the Switch's Q1 queue. • Priority 4 is assigned to the Switch's Q2 queue. • Priority 5 is assigned to the Switch's Q2 queue. • Priority 6 is assigned to the Switch's Q3 queue. • Priority 7 is assigned to the Switch's Q3 queue. The Switch uses strict priority for Scheduling. Strict priority-based scheduling, any packets residing in the higher priority queues are trans mitted first. Switching Technology Another key development pushing the limits of Et hernet technology is in the field of switching technology. A switch bridges Ethernet packets at the MAC address level of the Ethernet protocol transmitting among connected Ethernet or fast Ethernet LAN segments. Switching is a cost-effective way of increasing the total network capacity available to users on a local area network. A switch increases capacity and decreases network loading by making it possible for a local area network to be divided into different s egments that do not compete with each other for network transmission capacity, decreasing the load on each segment. The switch acts as a high-speed selective bridge between the individual segments. Traffic that needs to go from one segment to another (from one port to another) is automatically forwarded by the switch, without interfering with any other segments (ports). This allows the total network capacity to be multiplied, while still maintaining the same network cabling and adapter cards. For Fast Ethernet or Gigabit Ethernet networks, a Switch is an effective way of eliminating problems of chaining hubs beyond the "two-repeater limit." A Switch can be used to split parts of the network into di fferent collision domains, for example, making it possible to expand your Fast Ethernet network beyond the 205 -meter network diameter limit for 100BASE-TX networks. Switches supporting both traditional 10Mbps Ethernet and 100Mbps Fast Ethernet are also ideal for bridging between existing 10Mbps networks and new 100Mbps networks. Switching LAN technology is a marked improvement over the previous generation of network bridges, which were characterized by higher latencies. Routers have also been used to segment local area networks, but the cost of a router and the setup and maint enance required make routers relatively impractical. Today's Switches are an ideal solution to most kinds of local area network congestion problems. 2 2