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At the end of 2006, there were an estimated 280 million
broadband subscribers worldwide (ref. DSL Forum). This massive infrastructure
has enabled the rapid creation of new markets such as VoIP, Digital Music
Distribution, Online Gaming, Video Sharing, and IPTV, which in turn have led to
a need for home networks that connect multiple users and a number of different
technologies to the Internet. Home networks—originally architected simply to
support web browsing via Internet connection sharing—are falling behind in their ability to support these new usage scenarios.
One of the biggest challenges faced by these networks is
that different applications present different requirements. They vary not just
in their overall bandwidth needs, but also in their relative tolerance for
packet loss, delay and jitter while maintaining a high-quality user experience.
When multiple applications with such disparate requirements run on the same network, problems can and will occur.
When we talk about "media" in this context, we are referring
to network applications that require special treatment to guarantee a good user
experience as network conditions vary. Table 1 shows a representative sample of
a number of typical network applications, their bandwidth usage, and their
relative tolerance for the variable loss and delay common in multi-application networks.
|Network Traffic||Bandwidth Required||Sensitivity to Delay or Packet Loss|
|Online games (Client)||10 ~30 Kbps||High|
|Online Games (Host)||10 ~ 30Kbps x # of players||High|
|Audio Chat||64K ~ 256Kbps||High|
|Audio + Video Chat||128K ~ 1Mbps||High|
|Voice over IP||110Kbps (G.711)||High|
|Internet Radio||80kbps ~ 256Kbps||Medium|
|Standard Definition Video||1Mbps ~ 10Mbps||High|
|High Definition Video||6Mbps ~ 25Mbps||High|
|Place Shifting (e.g.SlingBox )||Adaptive 100Kbps ~ 3Mbps||Medium|
|P2P File Transfers||Adapts to internet connection||Low|
|Bursts to internet connection||Low|
Table 1: Internet Application Requirements
Usage problems start cropping up, of course, when
applications use more bandwidth than is available on the network, but problems
also arise quickly when applications designed to move data from point A to B in
the shortest amount of time (e-mail, file transfers, and so on) compete with those that are more sensitive to delay and packet loss (“media”).
The challenge is creating a media-optimized network: How can these issues be minimized, or even eliminated entirely?
The consumer’s dilemma
Despite what some of the marketing might lead one to
believe, just buying another router with a bigger number on the box does not
necessarily guarantee a good user experience. As Table 1 shows, many
applications do not require all that much bandwidth per se. The real challenge
is that each of several of these applications does rely on the network to behave as if it were the only application running.
In fact, this concept is not especially new. Quality of
service (QoS) schemes, used to separate different application streams within a
network, have existed in service provider and large corporate networks for many
years. What the consumer may not realize, however, is that while a number of
newer home networking devices may claim to implement these same QoS schemes,
these technologies were designed for large networks actively managed by IT professionals.
In such larger environments, a manager manipulates QoS
parameters to create a network that maintains necessary quality of experience
(QoE) across a pre-defined set of applications. Such networks are typically
designed such that all of the equipment meets certain minimum interoperable QoS
requirements so that the most critical application(s) can be reliably deployed.
At the same time, other traffic on the network is closely controlled. Any large enterprise that deploys VoIP, for instance, will generally go through a
deliberate process—first planning, then user trials—to ensure that the
network is capable of carrying this new voice traffic reliably and without interference.
Compare this to the typical home setup, where the consumer
simply piles in new equipment and software as the need arises. One day the only
application is web browsing, and the next thing you know the network is
delivering the latest online game and streaming soap opera episodes over a P2P file sharing service (such as the recently announced BBC iPlayer).
plays havoc with an unmanaged network. Bandwidth-hungry file sharing freely
competes with delay-sensitive media traffic. Common user complaints include
dropped (or poor quality) Voice Over IP calls, game lag, and pixilation or stuttering of video streams.
But no problem, just call the network manager, right? Wait,
you are the network manager! Well, some growing number of consumers are really
very tech savvy. Find the IP address and port numbers for your VoIP service,
then prioritize that over everything else in the router if it supports rule
based QoS. Wait, what about the XBOX? That needs to be high priority, too.
Next, you download a game demo and it, too, messes with your VoIP call. Toss in
that P2P application—they typically use all kinds of random ports—and what do you do with that?
If that’s not enough, consider that usage patterns in a home
vary dramatically through the course of the day. A home office by day—tons of
e-mail and VoIP calls—becomes a conduit for IM video, online games, and YouTube in the evening when the kids get home from school.
What consumer wants to constantly tinker like this with the
home network, day to day, hour to hour? In reality, rule-based QoS just wasn’t
designed for the emerging media-rich and preferably low-maintenance (or even install and forget!) home-networking environment.
A number of initiatives have sought to ensure that consumer
networking equipment meets some minimum requirements for networking media in
the home. Most notable are the certifications developed by the Wi-Fi Alliance,
in particular the Wireless Multi Media (WMM) certification, and the work done
by the Windows Rally team at Microsoft, which gave us the “Works with Vista” and “Certified for Vista” logos.
The good news is that if you see these logos on a networking
box, you know that it has had to pass a specific, well-defined set of tests. In
particular, devices carrying these logos will correctly interpret QoS tags attached to packets by an application and prioritize them appropriately.
home networking gear, the Microsoft Vista logos also require added
functionality that lets a Windows Vista-based PC interrogate the network to
find out how much bandwidth is available between two points, then make that
bandwidth available to Vista applications via Vista’s “qWave” application interfaces.
The common drawback to relying on tags within the data,
however, is that it remains quite difficult to make sure that all of your
network components actually pay attention to the tags and avoid removing them.
And along with some of these routers and other networking devices, many older
PC networking cards and drivers are also tag-unaware, often stripping the QoS
tags so that a packet appropriately tagged by a software application may still leave the PC minus the tag.
To be effective, tagging demands predicable end-to-end
network behavior. If you have media on a Windows Vista PC that travels through
a “Works with Vista” router to an XBOX or Windows Media Extender, your chances
of everything working as you expect are greatly increased. If you connect an
old Ethernet switch somewhere in the path then all bets are off. It was
probably designed before all of the QoS requirements and standards were fully put in place.
Another drawback to tagging is that it is largely limited to
traffic originating within your home network. Most of the content we’re
interested in, of course, resides out on the Internet. Unless these media are
coming directly from a tagging-compliant, subscription-based service from your broadband provider, it will all arrive without a tag.
Service providers generally strip tags from traffic that originates outside their own networks because they need to manage the amount of bandwidth available for their own premium content. Stream a video from the Internet? Play an online game? Data from those applications will be untagged and thus ignored even by a fully implemented home network tag-based QoS scheme.
At Ubicom, we have been advocating an approach to these
issues that adds a level of intelligence to networking devices to allow them to
dynamically adjust to the physical network environment and the application
usage at any given instant. And this is done wholly within the network device
itself. There is no need to rely on vulnerable, static, tag-based QoS information.
Such media-aware networks don’t try to follow a pre-defined set of
rules for behavior since, as noted before, any set of rules that was
appropriate at lunchtime may well be completely useless in the evening. Not
only that, but in a home environment, the software running on the network
changes from day to day and week to week. A media-aware network employs a more
active and dynamic approach, optimizing the performance of whatever applications are actually currently utilizing the network.
This concept is probably most easily explained by looking at some specific examples of applications, such as online gaming over the Internet and media streaming within the home network.
Returning to Table 1, one can see that most applications
currently deployed on the Internet were, in fact, designed to work within its
bandwidth constraints. Most broadband connections provide an uplink bandwidth of a few
hundred kilobits per second so most applications either stay within that limit or adapt to use as much bandwidth as available.
Consider a simple case where an online game starts up during
a voice call (for instance, via an instant messaging client such as Skype). As
the game starts, it does a bulk transfer of information, for example to
transfer map information to the client. The Internet connection is instantly congested, and the voice call either degrades or drops completely.
be fixed by setting a QoS rule that says Skype is higher priority than game
traffic (though on most products this is easier said than done). But later that
evening, someone uses Skype again to make a video call or transfer a file. Once
again, the available bandwidth is saturated, only now it’s the game that begins to lag.
If you consider the many permutations of this type of
interaction across many different applications, it is essentially impossible to
come up with a set of static QoS rules to ensure a great quality experience for every application and every user in the home.
A media-aware network, on the other hand, simply adapts the relative priority of these traffic streams on the fly to ensure that both the game and voice calls proceed uninterrupted.
For traffic originating within the home network itself, the
problems differ slightly. Here, a number of emerging applications have simply
been waiting for the installation of high bandwidth networks before they could
become entirely practical and widely deployed, the most interesting example
being video streaming, especially now that game consoles are becoming media players.
Moving video is, of course, very bandwidth intensive. Just how much bandwidth can a user reasonably expect to see in a home network?
Wired Ethernet is certainly an option in the home and
available very cost effectively, even at gigabit speeds today. The main problem
is getting the wire from the router to the “Entertainment Island” underneath
the television. If that’s not practical, wireless or power-line networking can bridge the gap.
With multiple tens of megabits of throughput, the better performing wireless and powerline products are more than capable of supporting streaming video, as always with the caveat that it can be prioritized appropriately on the wireless network.
As discussed above, relying on legacy equipment to deliver QoS tagging for all of this traffic can be hit-or-miss at best. On the other hand, media-aware networking products are available to deliver optimal performance for applications such as YouTube, Joost, Skype, Vonage and Netflix Online.
The “media-aware” network accounts for the mix of applications and the
bandwidth required by each. Media are dynamically identified, each separate
stream is appropriately prioritized, and all data moves efficiently throughout the network.
As consumers rely more and more on digital media at home for
work, play and communications, it is essential that they understand the role of
their home network in making sure that they can continue to get the most out of digital living.
Keith Morris leads Ubicom’s product marketing, business development and customer engineering activities. Prior to Ubicom, he served as Senior Director of Product Management and
Marketing at Applied Microcircuits Corporation (AMCC) and Director of Marketing
at MMC Networks. Keith has more than 18 years of experience in the semiconductor industry and has also held positions in engineering and management at Fujitsu and GEC/Plessey. He can be reached at [email protected].