Data networks won't cut it for convergence

Onus on switch, router vendors to keep adding intelligence for real-time apps

Today's data networks won't cut it as foundations for real-time applications like voice and video, experts said this week at the Interop New York conference.

NEW YORK – Today's data networks won't cut it as foundations for real-time applications like voice and video, experts said  this week at the Interop New York 2008 conference.

Users considering deployments of telepresence, collaboration and unified communications (UC) (compare unified communications products) must carefully consider the design of their networks and ensure the switches, routers, bandwidth and WAN links are optimized for carriage of that traffic, along with data. That's why router and switch vendors are baking more intelligence into hardware and software so their devices can recognize and devote appropriate network resources to the unique traffic.

Recent announcements from Foundry Networks, Enterasys and Force10 underscore these initiatives – all addressed support for next-generation environments, such as those harnessing video, unified communications, IPv6 and embedded security that is identity based and policy driven. Cisco, meanwhile, reiterated its intentions to focus squarely on video, virtualization and collaboration as key revenue growth and product development drivers going forward.

And HP ProCurve is hearing the siren song from customers about what the company's switches should be capable of.

"They say, 'I want my network to be UC-ready,' " says Manfred Arndt, distinguished technologist and R&D convergence architect for HP ProCurve.

With good reason. Room-sized telepresence and videoconferencing systems have recently undergone a period of "hypergrowth," according to Wainhouse Research. The current $1.2 billion market grew 39% from 2006 to 2007, according to the firm.

"We're at a tipping point for video where enterprises are seeing it as a critical new tool that they can use," said John Bartlett, principal of consultancy NetForecast, during a conference session on designing networks for telepresence. "Part of it is the network finally being ready to support these applications."

HP and other vendors are already supporting standards such as LLDP and LLDP-MED, and eventually will add support for PoE Plus and Energy Efficient Ethernet for automated discovery, configuration and power management of video and voice systems, and wireless access points. Edge switches use these standards and other proprietary and nonproprietary intelligence to match and enforce policies for user and endpoint network access and resource privileges.

But the onus is on switch and router vendors to keep adding intelligence to their edge devices, where it's as close to the user as possible, and scalable. And that intelligence must include recognition and accommodation of real-time traffic like voice and video, as well as a slew of other considerations that take switches and routers well beyond traditional data packet transport.

Data is bursty in nature, while real-time traffic is not, Bartlett explained. TCP datagrams are also able to retransmit packets dropped due to queuing congestion, while real-time voice and video are not.

Real-time packets that are dropped result in jitter, which degrades the quality of the voice and video transmission.

Bartlett said switches and routers need to implement at least four QoS elements in order to ensure high prioritization for real-time traffic and no packet loss: classification, class of service, bandwidth management with call admission control, and testing and monitoring. QoS also requires separate, high-priority queues in switches and routers for real-time traffic.

Packet classification occurs at the edge of the network with markings that are carried throughout the network indicating high-priority traffic. CoS prioritizes these packets using DiffServ for Layer 3 carriage and IEEE 802.1p and q for Layer 2.

QoS is also required on WAN links because these are usually slower than the LAN access pipes feeding traffic into and receiving it from the WAN. This speed imbalance can disrupt priority queuing, resulting in dropped packet jitter for voice and video, Bartlett explained.

"The place where QoS is most needed is at that boundary," he said.

But bandwidth demand is the most critical component for video, Bartlett said. Users need to pay particular attention to the bandwidth demands of video on the major links of their network by accounting for data's peak bursts; concentrating bandwidth at key locations with conferencing bridges; and maintaining bandwidth demand within the design constraints of the network through call admission control.

"It's not just about bandwidth: Is it the right kind of bandwidth?" says Greg Edwards, distinguished communications architect at Cisco. "Do you have enough bandwidth in the right locations, with QoS?"

If video carriage exceeds the designed bandwidth, routers will drop video packets, Bartlett said. Also average utilization is not an accurate measurement of data behavior because it does not take into account specific peak bursting periods, he said.

"Average utilization is lying to you about what's happening in the network," Bartlett said. "When data wants 100% of the link, we have a conflict there."

Similarly, most data testing and monitoring tools are insufficient for networks optimized for real-time applications because they do not support surveillance of real-time characteristics, he says.

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