Comet<----------------->Testbed16
 

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
 
 

	Bandwidth	Priority
AF class 1	1 Mbit	5
AF class 2	3 Mbit	4
AF Class 3	4 Mbit	3
AF Class 4	1500Kbit	2
Best Effort	500Kbit	6

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 Mb/sec
AF4 throughput - 1.465146 Mb/sec

Three flows carrying AF2, AF3 and AF4:

AF2 throughput - 2.548395 Mb/sec
AF3 throughput - 2.753034 Mb/sec
AF4 throughput - 1.451708 Mb/sec

Four flows carrying AF1, AF2, AF3 and AF4:

AF1 throughput - 0.975126 Mb/sec
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

Within AF3:
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 Mb/sec
AF2 throughput -  2.162563 Mb/sec
AF3 throughput -  2.306572 Mb/sec
AF4 throughput -  1.457024 Mb/sec
Best effort            -  0.000000 Mb/sec