Network Computing is part of the Informa Tech Division of Informa PLC

This site is operated by a business or businesses owned by Informa PLC and all copyright resides with them. Informa PLC's registered office is 5 Howick Place, London SW1P 1WG. Registered in England and Wales. Number 8860726.

Making the Vall on VoIP: Page 2 of 8

Loud and Clear

Lexent learned the hard way about configuring VoIP with encryption. The first voice traffic between headquarters and the Hicksville office experienced a half-second of jitter. The jitter was not only audible on the calls, but it was visible in the diagnostics built into the Cisco 7940 IP phones. The problem began when Lexent was setting up the IPsec tunneling between the VPN in Hicksville and the PIX firewall at headquarters. Lexent's technicians configured the tunneling to terminate the VPN tunnels from the Cisco 4224 router at Hicksville onto the firewall.

"There was no hardware accelerator in our firewall, so anytime IPsec did anything on the firewall or it got busy, it started jitter on the voice packets," says Doug Haluza, director of engineering and new technology for Lexent.

Haluza and his team installed an additional Cisco 3640 router at headquarters and rerouted the IPsec tunneling from the Cisco 4224 router in Hicksville to the new box rather than to the firewall, and the jitter disappeared. Because the hardware accelerators off-load the encryption processing from the software, they eliminate jitter, Haluza says.

That the application was live in the organization made it much easier to detect the VoIP tunneling problem. "We were fortunate we had voice running when we deployed the VPN in Hicksville because we were able to backtrack and work around the problem," he says.