The Internet is Not a Pipe and Bandwidth is Bad
Neil Davies, Co-Founder, Predictable Network Solutions
Neil will present a significant advance in applied mathematics and its application to queuing
algorithms and packet scheduling. He will describe a new way for understanding packet flows and
their statistical properties. It allows networks to be run at full capacity, and the budget of loss and
delay to be dynamically assigned to packet flows. Each packet flow can be given a statistically
assured quality of delivery. This can be achieved at a fraction of the cost and complexity of today's
circuit-based paradigm for managing "bandwidth" - a concept that is fatally flawed.
From the dawn of the telephony era, communications service providers have been selling circuits
as their primary product. Even today, we buy packet-based connectivity using a circuit metaphor
of "pipes" with "bandwidth". We use a variety of techniques like MPLS and VLANS to sub-divide
physical carrying capacity by quantity and quality -- creating "virtual pipes".
Within each (virtual) pipe, we effectively treat all traffic as being a first-class passenger, whether that
treatment is appropriate or not. Our naive approach to QoS is to always create more pipes carrying
first-class traffic.
If we ran physical trucks like we run networks, we'd carry gravel in refrigerated containers, because
that's what fresh tomatoes need. We would manage QoS by reserving lanes on motorways for
different types of freight. The only answer to lack of capacity, or tomatoes perishing in transit as they
get stuck behind gravel trucks, would be to build more roads. Freight carriers would be bankrupted by
waste, and infrastructure providers overwhelmed by the cost of inefficient resource utilisation.
The underlying problem is that we continue to propagate circuit thinking onto packet networks where
it is not appropriate. This approach causes two problems. Firstly it leaves us with networks that
are nearly empty (to preserve "quality"), such as for emulating circuit telephony over IP. Secondly,
networks fail to deliver the appropriate value to the user (to utilise "quantity"), as many Skype users
will attest when a video call breaks up. The result is an industry and ecosystem that is out of balance,
since the current mental models we employ do not match the reality of the networks we have built.
The question is how to match supply and demand better, not just over the next microsecond, but over
the next month. The answer is to understand that the Internet is not a grid of pipes moving information
indiscriminately, it is a method of focused delivery of that information.
It is the properties of that delivery, not the information itself that are the primary driver for good quality
user experience. Communications service providers need to become data logistics providers. Think
of it as the difference between a shipping line and FedEx. FedEx doesn't sell portions of ships, it sells
promises of delivery.
This advance in thinking and technology allows us to jointly optimise quantity and quality of packet
delivery for the first time. It will have far reaching consequences across the communications industry
both in terms of user experience and efficiency. For example, properly managing delay eliminates
buffer bloat. Many existing technologies will be made redundant, but the opportunity for innovation is
vast.
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Martin Geddes
