(Accedian Networks') EtherNEWS Blog

My previous post about traffic micro-bursting explained the adverse impact these transient bandwidth spikes have on business-critical Ethernet and IP/MPLS access links supporting financial trading and other time-sensitive applications. But just like it’s hard to leave your work at the office, micro-bursting has followed us home – and that’s bad news for ISPs, telcos and cable MSOs serving up residential broadband.

In a presentation at the SCTE Conference on Emerging Technologies recently held in Washington, DC, Carol Ansley, the Director of IP Engineering at Arris showed how streaming video delivery from popular sites has changed dramatically over the last several months. Crying wolf? Yes – but justifiably so – a big one just arrived!

 These graphs she captured from a cable modem accessing a “leading video streaming site” shows just how quickly and significantly download traffic profiles are changing. In the first graph a video is being slowly (peak 1.5Mbps) and steadily being loaded into a browser. In the second graph, recorded less than a year later, the same video is being delivered in occasional micro-bursts approaching 30 Mbps (20x greater peak bandwidth)!

Carol pointed out that despite numerous inquiries to service providers and the video content sites themselves, no one could clearly explain why videos are now being delivered in short, sharp bursts compared to the steady flows from less than a year ago. What is clear, however, is that with video traffic increasing at a rapid rate, servers, content delivery networks, cloud-computing and caching resources are straining to keep up.

And this could explain what we’re seeing.

Servers using preemptive multitasking – a technique where equal slices of processing time are allocated to each thread – are handling so many flows concurrently that the time-slice dedicated to each end user is becoming ever shorter. This would result in micro-bursts as servers attempt to keep up with thousands of downloads by shooting out streaming data as fast as possible within the short time allocated to each end-user.

The cause may be open for speculation, but whatever the reason, there’s no sign of download patterns returning to the moderate flows of the past. Increasingly online videos are encoded in HD formats, and selection is growing to include more feature-length films and complete TV shows as all camps from CNN to Google compete for the almighty surfer’s attention.

This is definitely a problem if you’re a broadband provider. Quality of Service and network performance are going to take a big hit very soon if this goes unchecked. As more and more users download videos, there’s a greater chance that not only will link capacity to each home not support these data rates, the aggregated micro-bursts will start to coincide together, causing massive packet loss in HFC, DSL, and FTTx access networks. Imagine a cable loop or DSLAM supporting 50 customers, each watching a video delivered in micro-bursts, combined traffic peaks could exceed 2.5Gbps. An unlikely worst case? Maybe, but ever more likely as over-the-top video delivery dynamics continue to shift.

The Fix That Fits

One way operators can effectively address micro-bursts is through high-performance, hardware-based traffic shaping applied in the downstream direction – ideally at each CMTS or DSLAM in bandwidth-limited cable and DSL networks. Hardware-based processing is required because standard shaping offered by most network elements places significant strain on the shared network processor, causing noticeable latency, extensive buffering and packet loss. Dedicated hardware-based shapers, available in the latest generation of Network Interface Devices (unconcerned with complex switching tasks), provide near-zero latency pass-through for real-time flows like VoIP, while efficiently shaping lower-priority traffic. This effectively smoothes out the traffic to squeeze bursts into the limited capacity of the access network. Applying shaping to streaming downloads would have no visible effect to the end user, while assuring QoS for all other applications sharing the network.

You can watch a video of our advanced traffic shaping in action from our lab at www.Accedian.com/shaping.

This entry was posted on Tuesday, April 21st, 2009 at 11:56 am and is filed under Applications, News, Opinion, Solutions. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.