VOIP 911: A low-cost way to expand emergency comm

The nation’s emergency 911 call systems are evolving to accommodate wireless communications and take advantage of the data, text and video capabilities of ubiquitous IP networks.

“I still think voice will be the gold standard” for emergency communications for the foreseeable future, said the technical manager for the Maricopa Region 911, an Arizona consortium of emergency service departments.

But voice traffic also is moving to IP networks, creating new opportunities and challenges, especially for 911 services in which budgets are tight and high availability and reliability are essential. Bandwidth is becoming cheap, but reliability remains expensive.


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“Right now, we are using voice over IP in pockets,” said the technical manager, who did not want to be identified. The consortium would like to move voice entirely to the IP network and eliminate the legacy voice components. “Maintaining both networks is expensive.”

VOIP has matured to the point that it now is the default technology for new telecom installations and can be used without compromising safety for critical systems, as long as redundant connections are available for failover.

“We have that redundancy built in, but it comes at a considerable cost,” the Maricopa manager said. “You’re paying more and more for capacity that is not being used.” Inexpensive retail broadband connections are available that could take the place of higher-cost services such as frame relay, but “when you move off the more expensive offerings you give up some of the service-level agreements.”

Expense vs. reliability

Maricopa Region 911 is solving the expense vs. reliability equation with Adaptive Private Networking from Talari Networks, an intelligent link-aggregation tool that can combine multiple networking paths into a single virtual high-availability WAN.

“Talari allows you to be able to use whatever capacity you have available,” the manager said.

The Maricopa Region is a governmental consortium formed in the mid-1980s to provide 911 services in the Phoenix metro area, including the communities of Scottsdale and Mesa. “We handle a little bit more than Maricopa County,” the manager said. The primary job is to ensure that emergency calls, together with the associated information, are routed to the proper one of 25 Public Service Answering Points in the region.

In 2003, the consortium began moving beyond the traditional analog voice capabilities of its legacy phone carriers, creating a dual hub-and-spoke IP network with two geographically separate call centers acting as hubs and the remaining centers as spokes. Each hub had fiber WAN connections from two service providers. One hub is the head-end for a T3 Frame Relay network connecting to sites via T1 circuits, and the second hub provides up to 20 megabits of backup bandwidth over IPsec VPNs. Failover between the two networks is provided by Cisco routers using the Enhanced Interior Gateway Routing Protocol.

The preferred choice for the 911 network would have been a Synchronous Optical Network (SONET), but most of the call centers are served by legacy copper or coaxial cable connections and money was not available for an upgrade, so that network option was not feasible.

The hub-and-spoke network has performed without problems since 2003, the technical manager said. “We like the network design, with a couple of caveats.” One negative is the cost of idle backup bandwidth and another is the multisecond failover time between links in the event of a problem. “In our business, if we lose two seconds of a phone call, that can be a large liability.”

Failover time cut

To take advantage of the strengths and mitigate the weaknesses of IP networking, the consortium settled on Talari’s Mercury T3000 Adaptive Private Networking appliance for the hubs, with smaller T700s at each call center.

“We believe that by using the Talari products, we can fail off any nonperforming link in less than a second,” the manager said.

The Talari appliances sit inside the firewall, between the WAN router and LAN switch. They constantly test connections between each other, checking for delays, latency and jitter, and they also do packet analysis and tagging to prioritize traffic and select the optimal path. This combination of WAN optimization, link aggregation, load balancing and failover can create a high-availability network out of links that might not provide adequate levels of service on their own. This allows networks to make better use of existing capacity and add capacity more cost-effectively.

“This has freed them from being locked into a particular service provider,” John Dickey, Talari senior vice president of engineering, said of the Maricopa implementation. “They can take advantage of bandwidth that was previously unacceptable.”

Talari likens this solution to the Redundant Array of Inexpensive Disks used for data storage, with Talari producing a redundant array of inexpensive links. This can make consumer broadband offerings, available at monthly rates of $3 to $15 per megabit/sec, practical accompaniments or replacements for more expensive business-class connections, though they might not come with service-level agreements.

Because they are constantly monitoring network performance, the appliances also can retransmit in case of packet loss without requiring applications to request retransmission, and can send traffic over redundant links to ensure it is received. “For voice, it is typical to do that,” Dickey said.

“These are all things that theoretically you could do manually,” the Maricopa technical manager said. But timing would not be accurate or acceptable.

The consortium has begun shifting some legacy 1.5 megabits/sec T1 connections to cable modem links that provide more bandwidth for less cost. This link shifting will allow it to get bigger pipes without increasing the budget and — it is hoped — without sacrificing reliability.

This is not the ultimate solution for the Maricopa Region, the manager said. “We would like to have a SONET or Metro Ethernet fiber-based network. But the reality is we don’t have the money or resources. That’s going to be a years-long evolutionary process.”

In the meantime, Talari is giving the consortium the ability to make better use of affordable bandwidth without sacrificing the reliability needed for emergency services.

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