[Asterisk-Users] 802.1p , precedence and TOS

[Eugenio De Vena]

Hello everyone, I have some doubt on the QoS matter and I hope that someone
could
bring me some light.
I see my 3Com 3300 switch supports 802.1p priorization ,
I see through Microsoft network monitor that the packet coming from my SIP
phones
have in IP header  a field which is marked "Precedence" and when the packet
is sent from
phone to asterisk the value is "CRITICAL/EXP" , when the packet is sent back
from asterisk
to phone the value is "Normal". To correct this I set the value "Tos" in
sip.conf to 160 and now
the packet sent back from asterisk to phone is marked "CRITICAL/EXP" too.
Fine.
Under the field "Precedence" there is a value called "Type of Service" (
TOS ) and the values is
"Normal" both ways.

Googling around I see that 802.1p is a Layer2 and not Layer3 specification
so it must work at MAC level,
so I think that these field which are contained into the IP header are not
considered  by my switch and are just ignored.
The Ip precedence field I think would be considered when routed by a QoS
router ( which is not my case ).

Questions:
1) How can I set the 802.1p precedence field from Snom and asterisk?
2) Which is the differences between the IP Precedence field and TOS field?

Thanks Everyone
Eugenio