[Asterisk-Users] Re: Mission-Critical Deployments

[Rich Adamson]

> >> 2. What do we need to do for our data network to make VOIP reliable?
> >>    QoS, basic traffic prioritization on the switch, vlan, ???
> >>
> >
> > If you are not running a bandwidth hungy network, then you might be
> > able to work with just one vlan, if you don't want to take the chance,
> > then yes you need: QOS, and VLANs.

Vlan's are certainly not a tool used to improve performance, and in many
cases, will cause more issues then what they solve. Part of the reason for
that is that there isn't any realistic way to manage switch-to-switch
trunks when multiple vlans traverse it. Eg, If the offered instantanous
traffic is greater then the port speed, packets will be dropped. Identifying
the root-cause of such issues is no where near as easy as one might
believe.

QoS on a switch will have zero impact _unless_ the offered traffic is
greater then the port speed, or, port speed differences (eg, traffic
from 100 meg ports heading outbound on a 10 meg port). Not likely
to be the case in environments outside larger corporate networks.

> Can you elaborate a bit on that?  I've never used VLANS, nor QoS on the
> switch level.  Do we really get more reliability by using both, or would
> QoS alone be enough?

QoS would be enough "if" your existing traffic is congested. Congestion
can be seen in the form of dropped packets on individual switch ports.
If you're not dropping any packets, then QoS will not do any good at
all on the switch.