My TN Connection

With the introduction of new technologies such as Voice over IP and digital video, network managers and administrators have a tough time keeping up with ever-increasing bandwidth requirements. These new technologies are brought with historically high expectations for reliability and quality. Today’s networks must be able to treat these services as high priority. These traditionally “best effort” Local Area Network protocols (Ethernet) face a difficult time handling these High Priority requirements. Quality of Service (QoS) is a method to better handling these new challenges; increasing reliability and quality.

Quality of Service (QoS)
Network administrators have two major types of Quality of Service (QoS) techniques available. They can attempt to negotiate, reserve and hard-set capacity for certain types of service (hard QoS), or just prioritize data without reserving any “capacity setting” (soft QoS). This post will provide information on 802.1p which is a signaling technique for prioritizing network traffic at the data-link/MAC sublayer (OSI Reference Model Layer 2).

The 802.1p header includes a three-bit field for prioritization, which allows packets to be grouped into various traffic classes. The IEEE 802.1p compliant switches pick up on this tag (the packet contains a 32-bit tag header located after a destination and source address header), read it, and put the packet in the appropriate priority queue. No bandwidth is reserved nor requested by this technique.

There are eight levels (0-7) of priority and consequently eight queues that could be created (see Figure 1). Level Seven represents the highest priority. This will be assigned for mission-critical applications. Level 6 & 5 are designed for delay-sensitive applications such as interactive video and voice. Levels four and below, are suitable for regular enterprise data transfer, as well as streaming video. Level zero is assigned for a traffic that can tolerate all the drawbacks of a best-effort protocol.

Figure 1

You can see in (Figure 2) that the switch will analyze the packet based in the “P” tag and will place it in the appropriate priority Queue for sending. An adjustable algorithm in the switch is used to choose how many packets are being sent from each queue before the packets in the lower priority queue are sent.

Figure 2
“P” tag will determine what order the packets will be sent through.

As you can see 802.1p is a useful item when you need to prioritize traffic within your LAN. The good news is that almost all managed Ethernet switches are able to handle 802.1p today. You can view Transition Networks’ line of managed Ethernet switches here.

For more information on Quality of Service (QoS) and 802.1p please see the Transition Networks white paper for QoS.

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