[altq 47] altq-diffserv

[Geoffrey CRISTALLO <geoffrey.cristallo@alcatel.be>]

Hi,

I wanted to test atq with diffserv, in the following configuration:

 ___
| R1|fxp1
|___|\
      \
       \ ___ fxp3   fxp2 ___
    fxp1| R2|___________| R3|
        |___|           |___|
       /fxp2
 ___  /
| R4|/ 
|___|fxp1

Both R1 and R4 send Traffic to R3 via R2, which is the congested node.
R4 sends "EF" traffic to R2 (with TOS byte = 0xb8)
R1 sends "BE" traffic to R2 (with TOS byte = 0x0)

On R2, I use the following script:

# cbq config file for R2 
# to test diffserv... 
interface fxp3 bandwidth 80M cbq
class cbq fxp3 "RootClass" NULL pbandwidth 100  
# default class
# -------------
class cbq fxp3 "DefaultClass" "RootClass" pbandwidth 98 default
#
# BE class
# --------
class cbq fxp3 "BestEffort" "DefaultClass" pbandwidth 25 borrow 
        filter fxp3 "BestEffort" 0 0 0 0 6 tos 0x0 tosmask 0xfc
#
# EF class
# -------- 
class cbq fxp3 "ExpFwd" "DefaultClass" pbandwidth 50 borrow
        filter fxp3 "ExpFwd" 0 0 0 0 6 tos 0xb8 tosmask 0xfc 

I give EF traffic at least 50% of the bandwidth (40 Mbit/s) and BE at
least 25% (20 Mbit/s).

Since I allow EF and BE to borrow the rest of the bandwidth (20 Mbit/s)
from their parent class ("DefaultClass"), I expected that

EF would receive: 40 + (40/60)*20 = 53.3 Mbit/s
BE would receive: 20 + (20/60)*20 = 26.7 Mbit/s

This would be the case with a fair queue.

But the value I measured with netperf were the following: 48Mbit/s for
EF and 29 Mbit/s for BE. So we can see that EF receives less than what I
expected and BE receives more. Is it the normal behavior ?

-----
With a bandwidth of 100 Mbit/s on fxp3 and the same allocation for the
two classes, i got:

EF: measured: 55.4 Mbit/s 
    Theoretical: 50+(50/75)*25 = 66.7 Mbit/s
BE: measured: 39.6 Mbit/s 
    Theoretical: 25+(25/75)*25 = 33.3 Mbit/s 

So, this confirms the previous results...

------

Does anybody see any reason/explanation for that behaviour ???

Many thanks in advance

--Geoffrey



------------------------------------------
Geoffrey CRISTALLO
Alcatel Telecom, Corporate Research Center 
Francis Wellesplein, 1        
2018 Antwerp
Belgium
      
phone: +32 3 240 82 97

mailto:geoffrey.cristallo@alcatel.be
------------------------------------------