Any sort of QoS frob that is implemented for VoIP
(or any other traffic for that matter) _must_ be
truly honored end-to-end, and at every intermediate
hop in between, for it to be "guaranteed" -- otherwise
when traffic that you may designate as "higher quality"
is handed off to another administrative domain that
does not honor your traffic classifications, all bets
are off.
If you do not "own" the end-to-end network
infrastructure, there is no way to guarantee any
preferential handling of any particular subset of
traffic.
- ferg (who has been down this QoS road a few times before)
So, set your Rate-Limiting of SIP traffic to 1 packet per second for the
network that YOU control and then offer your VoIP subscribers a different
QOS profile at a higher cost.
Bingo, problem solved. The economy will work itself out.
In fact this just happened to me here in Bangkok; I was doing some
tests of streaming audio during which I was moved administratively
from one ADSL domain to another. Streaming audio became unuseable with
many packet discards apparently due to jitter running up to a
second. (The utility at <http://testyourvoip.com> proved invaluable: it
uses Java to install a simulated VoIP client and runs a broad suite
of tests.) Behind-the-scenes discussions have revealed the provider's
experience that a short time after it brought the service online,
its bandwidth was overwhelmed by a small minority of users
downloading videos etc. The solution was silently to throttle
the throughput. (Same operator nightmare experienced at many
institutions of "higher" education where the "students" use the
ethernet jack in their dormrooms, intended for research purposes,
to download sex videos.)
If you do not "own" the end-to-end network
infrastructure, there is no way to guarantee any
preferential handling of any particular subset of
traffic.
There is a way to guarantee end-to-end QoS even
if you don't own all networks along the way. That
is for a 3rd party organization to impose a contractual
requirement. Aside from the very common scenario where
a large customer contracts with 2 ISPs, there are some
3rd parties which require such QoS in order to "certify"
an ISP. In Europe, the automotive industry does this.
Maybe the ANX does similar? Maybe one of the ANX
certified service providers could do a talk about their
experiences?
If a group of ISP's want to create a trade association
for end-to-end QoS guarantees, they are free to do this.
Perhaps the shift to VoIP will even make this
economically viable. In any case, this issue should
make for an interesting panel discussion if NANOG
does a VoIP track/theme.