Re: Traffic shaper TOS and DSCP bits

Hello again,

On Fri., Apr 16, 2010, Michael SIERCHIO wrote:
>Michael wrote:
>> Referring to the page '/firewall_shaper_edit.php', there are
>> several choices for 'IP Type of Service':
>> 
>>   lowdelay
>>   throughput
>>   reliability
>>   mincost
>>   congestion
>> 
>> It seems that recent RFCs [1] have outdated the classical TOS
>> semantics used by the most recent M0n0wall release. I'm trying
>> to match DSCP class selector 5 (CS5) and am confused about the
>> mapping to the older TOS bits. A document [2] on such mapping
>> helps a little.
>
>Have you looked at actual traffic to see if these bits are being
>used according to the newer semantics?
>
Okay, now I've finally looked at the actual traffic and:

  Yes the bits are being set according to my wishes (CS5/EF.)

After I verified that I can manipulate how they are set, I decoded
them according to both the DSCP RFC and the older TOS semantics.
CS5 is 101000 while EF is 101110:

          *** CS5 ***                        *** EF ***
  Precedence-bits  Other-bits       Precedence-bits  Other-bits
  101              000              101              110

The 'other-bits' correspond to 'lowdelay, throughput, ?' but it
is the 'precedence-bits' which best describe these traffic types.
Namely, precedence 101 describes the packet as 'CRITIC/ECP'.

This leads to the question:

  Of the remaining bits 'reliability, mincost, congestion,'
  which relate to the precedence-bits associated with DSCP
  class selector 5 (namely 101 or CRITIC/ECP)?

>This information is useful for routing, esp. fragmented packets,
>but is of very little importance to controlling bandwidth
>utilization to and from your endpoint users.
>
One endpoint user is sending low priority FTP traffic while
another user is sending high priority RTP traffic. If I can
mark the traffic in question properly, then these DSCP markings
should indeed be useful for controlling bandwidth utilization in
the m0n0wall router. Do you agree?

Regards,
Michael