[asterisk-users] switch QOS requirements

[Benny Amorsen]

"Al lists" <asteriskal at gmail.com> writes:

> Theoretically, setting TOS value ( these days called DSCP) wont change
> anything in switch behavior, unless you are using Layer 3 switches.
> What makes a difference in a switch is COS bits, and i'm not sure how
> asterisk sets that.

Sadly Asterisk still calls DSCP TOS, so I stuck with Asterisk
nomenclature.

Modern switches can translate DSCP into COS (lossily) and many do so
automatically. With most switches, sending DSCP set to EF will give
the traffic priority. Signalling (SIP) is usually set to class AF21;
Cisco recommends that CS3 is used instead. Either should work fine
with the default setup on many LAN switches.

> I guess to be safe, you would need to create 2 VLANS and in the switch
> define on VLAN  as a high priority VLAN.

That certainly works too. It's just a pain if you use the built-in
switches available in most phones. You need to manually tell them to
use a different VLAN, or use Cisco-switches with CDP. Most phone
manufacturers don't support LLDP for voice VLAN discovery yet.


/Benny