Table of Contents

GSoC2013: net80211 rate control API - 802.11n extensions

Project description

There is a simplistic rate control API in net80211 of FreeBSD, which lack the support of 802.11n features. 802.11n brought a 10x maximum net data rate compared to its predecessor, but, unfortunately, the hard-won rate up can be easily wasted if rate control hasn't been properly performed. This project will extend the net80211 rate control API of FreeBSD to be 802.11n aware and be able to support multiple rate attempts. With the extended API, wireless throughput can be further imrpoved.

Deliverables

An 802.11n features aware net80211 rate control API.

A summary of the feature improvements are listed below:

  1. Multiple Rate Attempts Support: The current rate control API of net80211 in FreeBSD is quite straightforward. The way of performing rate control is just selecting the “best” rate found by rate adaptation algorithms. Rather than just selecting the “best” rate, the rate control API should be able to do some real “control” works. It should be able to support multiple rate attempts which ath(4) hardware support.
  1. 802.11n Features Support: The rate control API should be extended to support 802.11n features including MCS rates, 20/40MHz wide channels, short-gi, stbc, ldpc. 802.11n APs and STAs need to negotiate capabilities like the type of RF modulation, coding rate and channel width. They also must agree upon the guard interval and number of spatial streams to be used. The 802.11n standard defines Modulation and Coding Scheme (MCS) a simple integer assigned to index 77 possible permutations of the factors that determine data rate. The standard also added support for short guard interval (short-gi), which provides an 11% increase in data rate. The rate control API of net80211 in FreeBSD should support these features to perform better rate control operations in 802.11n environment.
  1. Statistics API: An interface for exposing the global, per-vap and per-device rate control statistics should be added to the rate control API of net80211 in FreeBSD. This is pretty a useful feature for developers, academic researchers and, of course, end-users.
  1. 802.11n Aggregation Support: Frame aggregation is a feature of 802.11n that increases throughput by sending two or more data frames in a single transmission. Instead of having one frame be transmitted and received at a time, with A-MPDU, multiple subframes can be aggregated for one transmission and sender can be told of which subframes were successfully received. The current rate control API of net80211 in FreeBSD only works well for non-aggregate frames as it would be called each for a rate lookup and a single frame completion. With 802.11n aggregation, the rate control API should be extended to perform a single rate lookup for an aggregate, which would containing multiple frames.

Milestones

Test Plan

All 4 parts of the code need testing. I will set up the testing environment, which includes 2 machines (at least one of them with a supported WNIC) and an AP. The machine with WNIC will run the to-be-tested code. The other machine acts as corresponding node which generating or receiving test related network traffic. The AP does its routine work. As for functionality tests, I will test each of the above-mentioned functions. Because the API implemented could heavily relay on the driver, the performance tests of the API seemed trivial but I will talk about it later with my mentor.

Code