VOIP and QOS across local network and the Internet

Neal Rauhauser neal at lists.rauhauser.net
Tue May 15 22:07:00 UTC 2007

  I've thought long and hard about this, mostly from the perspective of 
regional ILECs too small to implement MPLS.

  QoS should be sold in 80k 'channel' increments. You, the carrier, 
don't care what the customer is marking as DSCP EF, you just accept and 
accelerate the first 80k x number of channels, then treat the rest as 
best effort. There should be a cost here as you have various management 
tasks - its not fire and forget like best effort service.

  Your interior must prioritize the DSCP EF marked traffic ... but you 
open up the capacity engineering worm on your network. Can you easily 
predict maximums along paths and ensure they'll never be topped? Do you 
have queueing on all routers and switches that is rigged to support the 

  The return path is *always* the problem. Sure, they can mark, you can 
accept, but how does the return sound? Do ISPs honor QoS markings across 
their network? Not the ones I touch, because they've often got public IP 
and private voice data riding in the same 802.1Q trunk, even though they 
may hit separate routers.

   Its a big puzzle and the prize goes to whom ever figures out how to 
do it nice and neat in both directions. The big prize is, of course, 
declining voice profits as voice transitions to being just another 
internet app with no need for the regulated, media gateway & TDM telco 
world. At the end of the day the only phone companies left standing are 
going to be those who provide wireless phones, as there is significant 
capital investment required in such a plant. The wireline voice carriers 
are all going to slowly spiral into being nothing but ISPs.

> Hello all,
> We're getting an increasing amount of pressure from VOIP providers
> colocated with us and from VOIP end-users to prioritize traffic on our
> network.  From a network administrator's point of view, I am sensing that
> this is the proverbial can of worms, and I'm hesitant to open it.  I
> thought perhaps I could just do a quick survey, both of what people do on
> their individual networks, and of what they know about others.
> - Do you offer QOS services across your network for VOIP or other types of
> traffic?
> - Do you do this on a per-customer basis, or is it done globally?
> - If per customer, are there charges involved?
> - Are there any major carriers that give preference to VOIP traffic?  
> I've heard rumors that Global Crossing does.  I've also heard rumors that
> almost all of them do.  I've also heard that almost none do.
> - For those that offer QOS services for VOIP, is traffic classification
> done by TCP layer protocol and port number?
> - It's hard for me to imagine major carriers implementing any kind of
> standardized classification.  For instance, if most carriers agree that
> UDP traffic destined for ports Y through Z is VOIP and should thus be
> treated in a more time-sensitive manner, what's to prevent the newest
> version of BitTorrent to take advantage of this by fitting it's traffic to
> that profile?  One of the things that makes VOIP so frustrating to the
> telcos - data is data is data - seems to bite VOIP in the ass here.  Is my
> thinking correct?  Or maybe traffic classification is happening at a
> higher layer?
> I can only imagine this issue growing larger.  With streaming audio and
> video well-established, VOIP at the dawn of major acceptance, and Internet
> TV, movies, and other real-time dependent applications on the near
> horizon, it's looming large.
> I know aspects of this have been brought up before, notably the whole "the
> Internet core can't take it" conversation.  I'm hoping my questions are a
> little more specific.  (However, I do find the aforementioned threads
> quite fascinating, for the record.)
> Thanks,
> Rick Kunkel

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