FEATURE ARTICLE: Getting a handle on p2p
By P2PNet.net

But, "add the rapid and accelerating uptake of mass-market broadband IP access, and the result is rampaging bandwidth consumption that is threatening to choke the Internet on an uncontrolled diet of file-sharing traffic, much of it of dubious legality," says a new report by Heavy Reading chief technologist Geoff Bennett.

Called Controlling P2P Traffic and published by Light Reading and Boardwatch, "Welcome to the world of mass-market P2P media file sharing - the first killer application of the broadband age," it says.

"It's both popular and bandwidth intensive. What more could an ISP want? Yet how much are they making out of it? Zilch, pretty much, because it is all part of an undifferentiated traffic stream (and mostly offnet, to boot). And what is it costing them? An arm and a leg as new capacity fills up, congestion grows, and P2P non-enthusiasts (they exist) complain more loudly about falling service quality as their traffic gets squeezed out."

On some networks, more than 90% of traffic is p2p at times and worse, "ISPs may not even realize how much P2P traffic they have, as standard methods of analyzing traffic by looking at TCP ports are frequently fooled by P2P applications using random ports or those usually assigned to other applications," says the report.

But, it goes on, p2p doesn't have to be the first ISP-killer application - "the hyphen is important".

In fact, because it's a highly efficient and resilient way to distribute content over IP, it makes a lot of sense from both an engineering and business viewpoint to think of ways of exploiting these virtues and, "it can be done, but only by making the network more intelligent and application-aware.

"Current network architectures just aren't designed to cope with P2P traffic patterns or even to distinguish them. Yet, with the right tools and application management platforms, P2P traffic can be identified, classified, controlled - and eventually built into revenue generating services."

p2p background
Already, three distinct generations of p2p technology have emerged, says Bennett's report.

In the beginning was Napster, a centralized system. Then came Gnutella, "which distributed everything (files and file-location database) to avoid the legal issues of Napster". The third generation is a hybrid of the first two with New Gnutella, FastTrack, KaZaA, and Grokster as current examples.

And, "In KaZaA, for example, some of the nodes become supernodes, which hold the lists of files and the locations of the clients from which they can be downloaded. The term 'client' here is in the context of the control plane of KaZaA, where ordinary nodes only have control connections to supernodes, and the supernodes form their own higher-level mesh of connections."

It's Terabytes Now
P2p apps are the most downloaded and p2p now accounts for 50% to 70% of all Internet traffic, Controlling P2P Traffic goes on and although KaZaA leads worldwide, Winny leads in Japan, with runners-up eDonkey and WinMX. Newcomers on the scene include Piolet and BitTorrent: "So in network terms P2P is big - and it is creating big problems for carriers and service providers."

It seems to trap service providers between falling revenues on one side and rising capacity investment costs on the other - effectively giving an ugly negative return on investment.

"Provider survival is going to depend on abuse control and the meaningful offering of tiered levels of service for different types of application," Bennett states. "To do this, providers must look much more closely at their network usage and how it can be managed."

What's happening to traffic
P2p appl "have some very striking - and somewhat unexpected - effects on aggregate network traffic flows. Critically important is that upstream and downstream flows are pretty much symmetrical. In other words, the aggregate volume of traffic downstream over a period is similar to the volume sent upstream."

This matters, says the report, because mass-market broadband access networks such as residential DSL are based on the idea that downstream traffic will dominate, as it does with browsing and streaming media and, ""The whole assumption of ADSL is that it can steal some of the upstream spectrum without damaging application performance. But if flows are symmetrical, this argument flies out the window.

"At the level of a single subscriber doing a P2P download, the traffic is, of course, asymmetric because there is a small customer file sent upstream, followed by a larger file being transferred downstream. So the download traffic by itself looks just like the client/server model of the Web. But, because subscribers are sharing files as peers, at any given time a home PC may be a client or a server, so this combination of different subscribers uploading and downloading at the same time makes the aggregate traffic for file sharing symmetrical.

And P2P traffic is always on, meaning a lot of file sharing occurs in the background - "probably even when some subscribers are sleeping, having left their PCs switched on.

"Another critical fact is that bandwidth for standard interactive applications is most needed during peak hours, as this is when most customers are active and form their perceptions of service quality. To have interactive bandwidth and Web traffic competing with huge quantities of P2P traffic during these hours is a recipe for trouble."

Traffic and Applications
So P2P users are creating a vast wall of bytes that's hitting the Net. For example, the report continues, Ellacoya Networks measured 37 terabytes in total over 35 days behind one 12,000-subscriber cable-modem termination system alone, "utterly dwarfing the other application categories".

And yet, it's estimated that although p2p users can account for only about a quarter of online users at a time (although this proportion is increasing), they can be 'hogging' more than 90% of the bandwidth and, "The upshot is that the popularity of P2P traffic is causing network-capacity issues for providers, not only because of total amount of traffic, but also from its unique nature compared to traditional applications, such as browsing and email."

P2p wasn't planned from the service-provider viewpoint, and now they're actively looking at a solution to try to address these issues, says the report.

"However," it says, "this isn't easy, because P2P applications have some pretty weird characteristics compared to the applications and protocols service providers are used to dealing with. They tend to be nonstandard or proprietary, and are often developed by hackers with the deliberate intention of fighting back against efforts made to control them. So they can use port hops to random port numbers, including those assigned to other applications, and some are now moving to using an encrypted mode (for example, Winny, which uses random port selection as well)."

'Combatting' P2P
Controlling P2P Traffic says there are various possible solutions, "and the good news is that these can be deployed together in certain combinations".

Keep cranking up the bandwidth.

"This is fine to a very limited extent, but P2P tends to expand to fill the bandwidth available and drives a lot of off-net bandwidth, which is expensive for service providers. And they don't get any extra revenue from their customers who are running P2P traffic."

So, why not just shut down P2P?

"There are several reasons why this isn't going to happen. Service providers could potentially be sued by the P2P companies, for instance. But probably the biggest reason is that the first ISP that blocks KaZaA will lose a huge number of customers overnight; these are the applications that are driving the rollout of residential broadband. However, there's a special case with the enterprise network. Here the CIO really must get a grip over nonbusiness P2P traffic and shut it down. CIOs have a solid legal position, and the Recording Industry Association of America (RIAA) has threatened to sue companies that allow their networks to be used for the downloading of copyright-infringing files." [Our emphasis]

What about capping?

"In practice, such caps go down like a lead balloon with customers. In the U.K., NTL Inc. had only to mention that it was thinking of applying bandwidth caps to receive a wave of complaints from users."

Or what about prioritizing traffic to throttle back P2P volumes?

This, says the report, can be hard with conventional IP filters because P2P traffic tends to masquerade as other traffic.

Another option is to cache content, but, "Of course, caching makes sense only if the frequency distribution of downloaded files is heavily skewed, but this seems to be so. It turns out that a big chunk of P2P traffic comes from a tiny proportion of files - there are definitely top-100 lists for both music and movie files.

"The issue with caching may well be its legality. ISPs are currently safe from prosecution by the RIAA because they aren't responsible for the nature of traffic that passes through their network. However, if they use caches, they are technically storing illegal material. The legal position has yet to be settled."

The final option is the most elegant, says Bennett: "apply traffic management and service control to the P2P traffic. This puts control back in the hands of the service provider, which can now create tiered services or apply priorities as desired.

Service Control
Service control and optimizing the network for peer-to-peer traffic is a two-step process.

"The first step is to gain a much better, or more granular, view of the traffic on the network. The goal is to develop a clearer view of what applications are running on the network, and to analyze this information to understand traffic patterns - for example, by time of day, or whether traffic is off-net or on-net traffic - and even to identify some of the top users of P2P.

"The second step is to control the amount of P2P traffic on the network, taking into account the other applications that are running and the service provider's overall objectives for the network. So the provider might decide to halve the bandwidth currently being used by P2P and instead use the freed-up capacity to improve the service experience for other applications - and also to introduce new revenue-generating services."

In particular, "upstream file-sharing bandwidth control is very effective at reducing bandwidth and goes undetected by an ISP's paying subscribers, as typically over 93 percent of traffic is served off-net to nonsubscribers."

How and Where to Control P2P
Service providers can control P2P bandwidth, "on an aggregate or on a per-protocol basis, or control upstream only, or control downstream only," the report goes on. "They can apply control in both directions and at different rates. And control can be applied to an entire group of subscribers, or just to subgroups or even individual subscribers. And all these options can be combined in various ways, and applied differently at different times during the day."

But, it states, there's a further angle to service control and traffic management that potentially goes far beyond P2P congestion control and capacity optimization: differentiated services.

P2P Differentiated Services
"By implementing service control in the network, service providers are adding a layer of intelligence to make the network smarter," Bennett says at the coinclusion of his report.

"Being able to identify P2P applications and optimize the network clears the ground for the next stage of providing differentiated services.

They can create new application-based plans, which is a new way of thinking for them. Traditionally, providers have concentrated on speed tiers through, for example, Gold, Silver, and Bronze services offering decreasing bandwidths. But application-based plans could involve tiers such as:
Basic Internet (email and Web) + Basic P2P (limited shared bandwidth)
Basic Internet + Premium P2P (channels for specific applications, such as gaming)

Further, providers can think in terms of driving the consumption of legal content by providing new services - for example, by faster downloads and integrated billing with content distribution partners and, "Apple iTunes is a specific example of this opportunity.

"Each download of a $0.99 iTunes track is treated as a separate transaction and attracts a standard credit-card fee to Apple of 1.735% + $0.20 (about $0.22). Financially, this is not very efficient, both for Apple and the content providers. Apple could, of course, improve matters by grouping transactions, but service providers historically have been masters at billing efficiently for small amounts. So collecting payments efficiently for content providers could become an important new revenue stream for the service providers."

But to make this transformation possible, providers need a new piece of kit: a service-management platform that has to perform four tasks:

* Accurate identification and classification of traffic on a per-application and per-subscriber basis
* Real-time control over classified traffic - for example, bandwidth shaping or application blocking
* Adaptation to changes in protocol encoding and rapid support for new applications because of the rapid turnaround needed for supporting emerging P2P applications
* Support for high-speed network rates and large subscriber capacity, which means classifying, analyzing, controlling, and reporting at gigabit line rates

"Once service-management platforms are installed, service providers can transform their broadband networks into efficient, intelligent, application-aware distribution networks," the report concludes. "And this presents a real opportunity to turn P2P into a legitimate application to everyone's benefit.

"P2P is undoubtedly the killer application that broadband has been waiting for, but so far the commercial opportunity has been missing. The people who are effectively funding the P2P revolution at the moment are unfortunately the copyright owners. But one very positive thing that has come out of P2P is that it is a very efficient and very resilient distribution-network architecture.

"So there is a real opportunity here for broadband service providers to take P2P as a serious business proposition for content distribution. And there is growing evidence - witness iTunes - that subscribers are willing to pay for legal content if it is reasonably priced and easy to obtain. Providers would receive carriage fees for the content they carry, while offering faster downloads as a premium channel. By integrating download transactions onto a cable or broadband bill they could eliminate transaction fees - one of the bugbears of distribution. And they would be exploiting the high subscriber penetration of Tier 1 operators."

(Saturday 03 January 2004)

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