Hard Quality of Service (QoS) - 10 : Variable Bit Rate (VBR)
The concept of QoS is covered in detail in the following 3 playlists:
1 - #QoS - Explains how the quality of service (QoS) provides different levels of priority to traffic crossing the network. Discusses the need for and advantages of QoS.
• 42 : QoS - Fundamentals of Communications
2 - #Hard QoS - Discusses the advantages and disadvantages of hard QoS, which provides guaranteed levels of service to network traffic.
• 43 : Hard QoS - Fundamentals of Communicat...
3 - #Soft QoS - Discusses the advantages and disadvantages of soft QoS, which provides priority levels (rather than guarantees) to network traffic.
• 44 : Soft QoS - Fundamentals of Communicat...
The next traffic category is variable bit rate or VBR, and, once again, the name identifies the type of traffic it supports. The VBR traffic class is defined to support traffic that does not send data at a constant rate. An example that falls into the VBR category is compressed video.
Let's take a minute to see how video traffic is communicated across a network link. In the past, everything in the video was transmitted across the link. This required a lot of bandwidth, and was an inefficient way to do things. Today, video compression typically only sends what changed in the scenes. This means, if I am being recorded, and I am standing very still, the network only needs to support a small amount of traffic-but when I move, the bandwidth requirements increase.
So, I need a traffic category that allows me to vary the amount of data I send at different times. The VBR traffic category allows me to define an average amount of bandwidth, and also the maximum amount of bandwidth I might need in a "burst" when requirements are high. The switch discards traffic that is sent in excess of the maximum level. Video and multimedia traffic typically use a VBR traffic class. VBR traffic is always a lower priority than CBR traffic on the network.