One of the things I insist on is learning the theory or concepts behind the technologies, rather than just learning how to configure the technology. This is often more difficult than it seems, though, because it’s hard to find (and often read) the documents that describe the technology — they’re often written in a language different from that of normal humans (even engineers), and cast asides and make references few people can understand. This is one of the neat things about IETF documents: while many of them are, in fact, bare descriptions of a packet format, a processing mechanism, or something similar, you can often find sets of RFCs and drafts that not only provide a solid overview of an entire area, but even give you a good set of reading material to dig deeper into the topic.
One such case is quality of service (QoS). Henceforth, a short list of documents published by the IETF that will help you understand QoS.
- A Framework for QoS-based Routing in the Internet: Describes some basic problems in QoS routing. While this isn’t strictly a QoS focused document (it’s really routing focused), it does describe the problems involved in routing based on QoS well.
- Architecture for Differentiated Services: This document describes the DSCP fields in the IP header, including classifiers and conditioners.
- Next Steps for the IP QoS Architecture: Provides a broad overview of the set of problems that need to be addressed by any given system of QoS.
- Analysis of Existing Quality-of-Service Signaling Protocols: While this is supposed to be a pretty specific examination of the existing QoS signaling protocols, it actually turns out to be a nice overview of problems and potential solutions in signaling QoS.
- Considerations of Provider-to-Provider Agreements for Internet-Scale Quality of Service: Just about any RFC or draft with “considerations” in the title is generally worth reading, and this one is no exception. Here you’ll find a good explanation of the various problems involved in cross-domain QoS.
- Comcast’s Protocol-Agnostic Congestion Management System: Sometimes providers and operators will publish documents through the IETF describing how they’ve built a particular part of their network. This is one such document describing the QoS implementation of one provider. This type of document is well worth reading as it provides a model and ideas towards implementing QoS in all networks.
- On Queuing, Marking, and Dropping: And, from time to time, someone working in a particular area will write up and publish a summary of research and thinking draft. This one covers different queuing methods, and the positive and negative aspects of each one. This is a fantastic document, well worth reading.
- The Effect of Encrypted Traffic on the QoS Mechanisms in Cellular Networks: Sometimes you can learn a good bit by looking at the intersection of two different technologies — in this case, encryption and QoS.
This reading list should give you a good start on understanding the world of QoS — particularly if you dive into the references section and try to “back read” the documents referenced by each one.