Class-based queuing(CBQ) allows a bit more control than PRIQ. In CBQ, each class gets a percentage of bandwidth, after being grouped by classes. It divides traffic into a hierarchy of classes and thus allows you to classify traffic into a hierarchy. Criteria for prioritization can include protocol, the application being used, the IP address of the sender, and many other factors. It operates at the IP network layer (Layer 3). An additional appeal of CBQ is that it is in the public domain.

Each class is assigned a bandwidth limit, and packets within the class are processed until the bandwidth limit for the class is reached. This tends to ensure that even low-priority packets get some bandwidth. The first goal of CBQ is quantitative bandwidth sharing, but a secondary goal is that when some class is not using its allocated bandwidth, the distribution of excess bandwidth should not be arbitrary. Rather, the distribution of such bandwidth should follow a set of guidelines.

As a simple example of PRIQ and CBQ in practice, consider a company in which the ISP guarantees 150 Mbps of download bandwidth and 50 Mbps of upload bandwidth and four networks: developers, engineering, sales, and DMZ. We want two-thirds of the download bandwidth and half the upload bandwidth to go to the developers and engineering networks. We also want 60% of this share of the bandwidth to go to the developers network. This means that developers should get 60 Mbps of download bandwidth and 15 Mbps of upload bandwidth; engineering should get 40 Mbps of download bandwidth and 10 Mbps of upload bandwidth; the rest is allocated to sales and DMZ. 

With PRIQ, we have no way of guaranteeing a fixed share of bandwidth to developers and engineering. We could assign higher priority levels to developers and engineering, so that developers have a higher priority than engineering, which in turn has a higher priority than sales and DMZ. However, this could result in sales and DMZ ultimately being starved of bandwidth, as a packet from either DEVELOPER or engineering will always win out over one from sales or DMZ.

With CBQ, however, each subnet could be assigned a percentage of bandwidth. Even better, CBQ can be hierarchical, so that developers and engineering share a percentage of bandwidth, with engineering being assigned a greater portion of their shared bandwidth.