Failure-proofing NG-911 networks
Maricopa 911’s approach
In Arizona, the Maricopa Region 911 is a consortium of local municipalities in the Phoenix metropolitan area that handles emergency calls through 25 call centers. The dual hub-and-spoke network has two geographically separate network centers. One serves as the head-end for a T3 frame-relay network, while the other provides up to 20 Mb/s of backup bandwidth over IPSec VPNs to each call center. If the frame-relay network fails, routers running Enhanced Gateway Routing Protocol (EIGRP) send failover data to the IPSec VPNs.
While this configuration had performed adequately since it was deployed in 2003, it could take EIGRP up to 8 seconds to transfer data to the backup VPN circuits during a failover. In 2011, Maricopa Region 911 implemented a solution that provides sub-second failover to the VPNs when a frame relay link fails. The solution also monitors link quality and can migrate traffic quickly from poor-quality to high-quality links, while also allowing for the consolidation of data and voice networks (see Figure 1).
According to Maricopa Region 911’s technical manager, one of the most intriguing aspects of the solution is its ability to migrate from suspect links on a sub-second timeframe.
The FCC’s NRIC Council also requires that "PSAPs should and will deploy IP networks within the PSAP, between the PSAP and the sources of calls coming into the system, and between the PSAP and other responders and emergency-service agencies."
But traditional IP-routing technologies alone are not enough—the networks must meet a high standard as detailed in the network recommendation section of the NRIC report. To paraphrase, these networks must be designed to:
- Minimize service interruptions by employing management and continuous monitoring to detect anomalies immediately.
- Ensure no single failure or interruptive incident will create a system outage.
- Negotiate the highest quality of end-to-end service to get the best audio, text and video available.
- Identify 911 calls and treat them on a priority basis.
The solution employed by Maricopa Region 911 accomplishes these goals by aggregating multiple diverse network links and then continuously monitoring the quality and availability of each link. By identifying and directing traffic down the aggregated path so that prioritization is maintained, each class of application receives the quality it needs to perform, and outages are detected and avoided instantly. This solution meets the requirements established by the NRIC, with the added benefit of doing so over private or public networks, thus allowing PSAPs to take advantage of lower costs and available bandwidth.
Alex Ratcliffe is the chief solutions architect at Talari Networks.