[Asterisk-Users] 802.1p , precedence and TOS

[Eugenio De Vena]

Thanks for your kind help, I understand ip precedence and that's ok. I also
found on Snom phones how to mark 802.1p ( which is what I need now ). On
the 3Com 3300 802.1p is enabled and correctly priorized . The only thing I 
miss
is how to tell asterisk to originate rtp packet marked with 802.1p tag ( at 
layer 2 )
Any idea?

----- Original Message ----- 
From: "SCollins" <smjjscollins at comcast.net>
To: "Asterisk Users Mailing List - Non-Commercial Discussion" 
<asterisk-users at lists.digium.com>
Sent: Tuesday, April 19, 2005 8:45 PM
Subject: Re: [Asterisk-Users] 802.1p , precedence and TOS


> 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?
>
> IP Precednce and ToS are synonymous. There is a 3-bit ToS field in the IP 
> header that allows for 8 levels of classification of IP traffic - these 
> are known as the IP precedence bits.
>
> 802.1p or CoS (Class of Service) is a Layer 2 Prioitization protocol. 
> 802.1p uses a 3-bit prioitization field, in an 802.1q TAG,to define 8 
> priority levels.  To obtain the correct Layer 2 CoS on your 3300 I believe 
> you need to set the prioritization on the IP phone, using 802.1q and then 
> setting the prioritization, and then configure the clasifiers and profiles 
> on the 3Com 3300 so that it will remark the packets on ingress.  The CoS 
> traffic classification will need to be configured on ALL Switches in your 
> network for the 802.1p prioritzation of the Voice traffic.
>
> Most layer 3 Switches support both ToS and CoS and will re-mark the 802.1p 
> Prioritization into the ToS field in the IP header, so that if the traffic 
> is being routed, between VLANs for example, the traffic will maintain it's 
> priority.
>
>
> Hope this helps.
>
> Sean
>
>
> On Tue, 19 Apr 2005 15:28:43 +0200, Eugenio De Vena <edevena at gsy.it> 
> wrote:
>
>> 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
>>
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