As specified in the AF document, there are four AF classes and each class has three drop precedences within each class.
The bandwidth and priorities assigned to the classes
|AF class 1||1 Mbit||5|
|AF class 2||3 Mbit||4|
|AF Class 3||4 Mbit||3|
|AF Class 4||1500Kbit||2|
I conducted some simple throughput tests. I hacked into ttcp to include a TOS option.
Two flows carrying AF3 and AF4 were run simultaneously:
AF3 throughput - 3.965340
AF4 throughput - 1.465146 Mb/sec
Three flows carrying AF2, AF3 and AF4:
AF2 throughput -
AF3 throughput - 2.753034 Mb/sec
AF4 throughput - 1.451708 Mb/sec
Four flows carrying AF1, AF2, AF3 and AF4:
AF1 throughput - 0.975126
AF2 throughput - 2.143372 Mb/sec
AF3 throughput - 2.340236 Mb/sec
AF4 throughput - 1.441672 Mb/sec
This clearly shows the way priorities are given in AF.
Three flows within the same class with different drop precedences.
Within AF 1:
Drop Precedence 1 - 0.332679 Mb/sec
Drop Precedence 2 - 0.311464 Mb/sec
Drop Precedence 3 - 0.300651 Mb/sec
Drop Precedence 1 - 1.504594 Mb/sec
Drop Precedence 2 - 1.306159 Mb/sec
Drop Precedence 3 - 1.206719 Mb/sec
With Best Effort Service:
All four classes with an additional best effort traffic..
AF1 throughput - 0.983084
AF2 throughput - 2.162563 Mb/sec
AF3 throughput - 2.306572 Mb/sec
AF4 throughput - 1.457024 Mb/sec
Best effort - 0.000000 Mb/sec