[asterisk-users] QOS/DSCP for IAX?

[Dave Fullerton]

Yea, kinda, sorta. The DSCP is six bits, which occupy six of the 8 bits 
in what is/was the type of service byte in an IP packet. Three of the 6 
DSCP bits reside over the old precedence field and three reside over the 
old low delay, high throughput and high reliability fields (those three 
often referred to as TOS). The DSCP code points are designed to be 
backwards compatible with the PRECEDENCE portion of the old tos. The low 
delay, high throughput and high reliability bits have been redefined and 
no longer are backwards compatible. When doing my research I found some 
web sites displayed the tos byte in different bit-orders (cisco with 
precedence first, wikipedia with precedence last). It was confusing as heck.

I also have some old equipment that does not understand DSCP/Diffserv. 
What I ended up doing was making asterisk and phones use the dscp code 
points and my old router software queue packets based on what it sees in 
the precedence field. Works like a charm.

Good luck.

-Dave


Michelle Dupuis wrote:
> That link is great thanks.
> 
>>From what I read elsewhere, ToS is just the first 3 bits which should be
> honored by DSCP (first 5 bits)- even old equip should be DSCP
> "compatible"...or I need to do more reading :)
> 
> -----Original Message-----
> From: asterisk-users-bounces at lists.digium.com
> [mailto:asterisk-users-bounces at lists.digium.com] On Behalf Of Dave Fullerton
> Sent: Thursday, October 01, 2009 3:01 PM
> To: Asterisk Users List
> Subject: Re: [asterisk-users] QOS/DSCP for IAX?
> 
> Michelle Dupuis wrote:
>> I actually see the TOS setting in iax.conf, but the default (commented 
>> out) is EF - which doesn't even match a valid bit combination 
>> according to voip-info wiki
>>  
>> If this is the right place, what TOS value are people using 
>> succesfully over an ADSL connection?
>>
>>   _____
>>
>> From: asterisk-users-bounces at lists.digium.com
>> [mailto:asterisk-users-bounces at lists.digium.com] On Behalf Of Michelle 
>> Dupuis
>> Sent: Thursday, October 01, 2009 2:27 PM
>> To: Asterisk Users List
>> Subject: [asterisk-users] QOS/DSCP for IAX?
>>
>>
>> Is it possible to set QOS/COS/DSCP on IAX packets?  I see some 
>> parameters in sip.conf but not iax.conf
>>  
>> Thanks
> 
> Yes the tos setting is the right place and EF is an acceptable value. EF is
> the differentiated services code point (or dscp) for expedited forwarding.
> The sample sip.conf defaults tos_audio to EF as well. The iax.conf wiki page
> only shows the old type of service values which are considered deprecated.
> Look at this page for more info on diffserv:
> 
> http://www.voip-info.org/wiki/view/DiffServ
> 
> As for what to use, well, that depends on whether your upstream provider
> even honors what you set. They may use the old type of service values, they
> may use dscp or they may ignore what you put there entirely.
> 
> -Dave
> 
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