Vendors tap Layer 7 switching for VoIP

Layer 7 switching isn't just for Web servers anymore. Two companies are working to integrate the technology into voice-over-IP networks for corporations and service providers.

The ability to route packets at wire speed based on application layer -- or Layer 7 -- information can provide superior quality of service (QoS) for IP voice, as well as load-balancing capabilities for voice-over-IP gateway and IP PBX equipment, some vendors and analysts say.

Specifically, vendors say using Layer 7 switches to identify protocols used in voice-over-IP nets -- such as session initiation protocol (SIP) and H.323 -- can improve the quality of voice-over-IP networks that use standards-based QoS prioritization and packet-tagging techniques, such as type-of-service bit prioritization (which is inherent in IP) and Differentiated Services (Diff-Serv).

H.323 defines everything from specifying call-signaling procedures to describing the services available in desktops, servers, gateways and other devices in IP voice and multimedia applications. SIP sets up calls and voice-routing procedures. SIP is used in LAN telephony phones and servers from vendors such as 3Com, Cisco and Nortel Networks.

At Internet World Fall 2000 in New York this week, Radware will introduce a voice-over-IP software module for its Web Server Director, a Layer 7 switch previously sold as a load balancer for Web server farms.

Instead of load balancing Web servers, the new module is intended to distribute H.323 traffic among multiple voice-over-IP gateway devices or H.323 voice servers in a corporate or service provider network. By looking into Layer 4 through Layer 7 of data packets, the Web Server Director can identify voice traffic using the H.323 protocol and maintain consistent connections between H.323 devices and client phones.

Two versions of the Web Server Director voice-over-IP module are available -- one for companies with support for up to 300 simultaneous calls, and an ISP version with support for up to 100,000 calls. The modules for corporate customers and ISPs cost $14,500 and $48,500, respectively.

Top Layer Networks, which was named one of Network World's "Top 10 Companies to Watch" this year, is also working on software that will let its Layer 7 product, the AppSwitch, provide QoS for carrier and corporate voice-over-IP networks.

The Westborough, Mass., firm is conducting AppSwitch interoperability tests with carrier-class voice-over-IP soft-switch equipment from Nuera Communications. The goal is to provide QoS for voice networks by having the switch inspect packets at Layer 7 where information resides about what voice-over-IP protocol a voice data packet is using, whether it be the H.323 protocol or SIP.

The technology Top Layer is adding to its AppSwitches will include specific SIP "handler" software that will let users set priorities for SIP packets at the AppSwitch to prioritize voice.

"When you have voice traffic coming into a network, it comes in on dynamically allocated [TCP/IP] ports," says Geff Ambrose, technical marketing manager for Top Layer. Ambrose says unless specific ports are defined to have priority for voice traffic, voice-over-IP packets can get lost in the shuffle, resulting in a bad IP phone connection.

Ambrose says the software add-on for the AppSwitch should be available in February of next year.

Voicce over IP and Layer 7 switching are two of the biggest buzzwords in the corporate network industry, due partly to the promising forecasts analysts have made on the two technologies.

Framingham, Mass., research firm IDC predicts the number of voice-over-IP minutes of use by businesses worldwide will jump from 1.16 billion this year to 33.2 billion by 2003.

One analyst says that using Layer 7 switching with IP voice is more than just the marriage of two buzz-laden technologies.

"All the same problems [with making a Web server reliable] seem to apply in the IP telephony area. You need availability and you need scaling," says Peter Christy, an analyst with New York firm Jupiter Communications.

"You have to be Layer 7 because you're dealing with complex, embedded protocols," in IP telephony, such as H.323, he says. "The protocols of voice over IP are involved above the simple connection layer."

However, other vendors of voice-over-IP products believe that using Layer 7 switching in IP telephony is not necessary if standards-based QoS technologies are correctly applied.

"There is no need to use Layer 7 for voice," says Benny Rodrig, senior network architect with Avaya.

Prioritizing voice packets can be done well enough at Layer 2 and 3, he says, with 802.1p, a Layer 2 standard for packet prioritization tagging, and Diff-Serv at Layer 3.

This story, "Vendors tap Layer 7 switching for VoIP" was originally published by Network World.

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