I had an inquiry from a potential customer yesterday asking if we could monitor their QoS. I was a bit miffed as to what to tell them. At first, the question struck me as if they’d asked if we can monitor electrons on their power grid. In other words, it was a legitimate question in a sense, but of what use would it be to monitor QoS? I then asked him why he had implemented QoS in the first place. How did he know he needed it?
After inquiring a bit deeper, I also found out this customer was using extensive VPNs to remote offices over DSL internet circuits. His WAN traffic from the remote offices was sharing links with regular Internet data traffic, and all of it was traversing the public Internet. Then it hit me – he did not realize his QoS mechanisms were useless outside of his internal network.
Where there is one customer with confusion there are usually others. Hence, I’ve put together a quick fact sheet on QoS over an Internet link. Below, you’ll find five quick facts that should help clarify QoS and answer the primary question of “is it possible over the Internet?”.
If your QoS mechanism involves modifying packets with special instructions (ToS bits) on how it should be treated, it will only work on links where you control both ends of the circuit and everything in between.
Most Internet congestion is caused by incoming traffic. For data originating at your facility, you can certainly have your local router give priority to it on its way out, but you cannot set QoS bits on traffic coming into your network (We assume from a third party). Regulating outgoing traffic with ToS bits will not have any effect on incoming traffic.
Your public Internet provider will not treat ToS bits with any form of priority (The exception would be a contracted MPLS type network). Yes, they could, but if they did then everybody would game the system to get an advantage and they would not have much meaning anyway.
The next two facts address our initial question — Is QoS over the Internet possible? The answer is, yes, QoS on an Internet link is possible. We have spent the better part of seven years practicing this art form and it is not rocket science, but it does require a philosophical shift in thinking to get your arms around it.
We call it “equalizing,” or behavior-based shaping, and it involves monitoring incoming and outgoing streams on your Internet link. Priority or QoS is nothing more than favoring one stream’s packets over another stream’s. You can accomplish priority QoS on incoming streams by queuing (slowing down) one stream over another without relying on ToS bits.
Surprisingly, behavior-based methods such as those used by our NetEqualizer do provide a level QoS for VoIP on the public Internet. Although you can’t tell the Internet to send your VoIP packets faster, most people don’t realize the problem with congested VoIP is due to the fact that their VoIP packets are getting crowded out by large downloads. Often, the offending downloads are initiated by their own employees or users. A good behavior-based shaper will be able to favor VoIP streams over less essential data streams without any reliance on the sending party adhering to a QoS scheme.
For more information, check out Using NetEqualizer To Ensure Clean Clear VOIP.