In the eye of the storm, better bandwidth through bonding

After an tornado measuring 3 on the Enhanced Fujita Scale tore across 29 miles of northwest Georgia with wind speeds of up to 165 miles an hour on the night of March 2 and 3, the Paulding County Fire Department rolled out its mobile command center with two tactical dispatchers on board to provide 911 service and other emergency communications to a stricken subdivision.

“It did quite a bit of damage,” the department’s Maj. Kevin New said of the tornado. But cell networks in the area were still operating, which was fortunate. “Our command bus relies primarily on cell phone service.”

The vehicle is a converted school bus loaded with equipment to support a multiagency emergency communications team, and it acts as an emergency operations center that can be moved to the site of a disaster or other event.

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Internet service for the mobile command center, which supports 911 computer-aided dispatch service as well as other on board computers, is carried over three cellular channels bonded to provide one multimegabit link.

Paulding County, about 35 miles northwest of Atlanta and part of the Atlanta metro area, is fortunate to be in a well-served area for cellular service, so getting a signal usually is not a problem. But getting adequate bandwidth was, said New, who is a member of the emergency communications team.

When the command vehicle was first put into service more than two years ago, “we were relying on a Sprint card connected to a laptop to provide most of our connectivity,” he said. “It just wasn’t doing it” in situations in which there could be as many as five computers operating in the vehicle at a time.

By tying three cellular channels together through a PortaBella mobile appliance from Mushroom Networks, “it gives us quite a bit of bandwidth,” New said.

Operation of the PortaBella is simple: There are USB ports for up to four cellular data cards, and a single Ethernet port to provide the bonded link. The tricky part is binding the four channels in an intelligent way so that they act as one pipe.

“It’s not an easy task,” said Mushroom CEO Cahit Akin. “They constantly fluctuate, and you have to keep track of the status of each card and schedule each packet.”

This is done using network calculus, a framework for analyzing network performance, which can help take advantage of the full performance of each card without wasting capacity. Available bandwidth still is subject to the fluctuations of wireless performance, but whatever is available is multiplied by the number of cards being used.

“Our algorithms are close to 100 percent effective in allowing you to use what is available,” Akin said. “In practice, the results are surprisingly high performance.”

Although transmission rates vary according to local conditions and carriers, a typical cellular data link can provide about 1 megabit/sec. uplink speed. Using four cards, PortaBella usually can provide uplink speeds of from 3.5 to 5 megabits/sec., Akin said. Downlink speeds are also multiplied. During the handshake portion of most transfer protocols, PortaBella establishes a link with the server through each of the cards; the file request is split into chunks, which are downloaded simultaneously over the multiple links and dynamically managed.

The system not only multiplies available bandwidth but lets the user mix and match carriers to provide a level of redundancy in cases where one carrier’s network is down or its performance is degraded. Paulding County is using two Sprint cards and one Verizon card. PortaBella supports most carriers, and drivers for new cards are provided as free firmware updates.

PortaBella is well adapted to wireless mobile applications like Paulding County’s, but “oddly enough, most of the demand is on the wired side,” in small and medium offices where it can bond multiple wired DSL lines into a single pipe, Akin said. Cloud computing has been a big driver for this because resources that once were local often are no longer available over the local-area network.

“All of a sudden that [wide-area network] connection is very important,” Akin said. “If it is down, all of your business-critical applications are down.” For a small office, bonding four DSL lines might be more affordable than a fractional DS3 circuit.

The appliance also is used for temporary offices and quick set-up situations, such as construction sites or other field work where it might not be feasible to provision a big pipe on short notice or for a limited time.

PortaBella can handle up to 35 megabits/sec. throughput and contains a firewall that can prioritize and block traffic. Bonding channels not only provides greater bandwidth but also allows the channels to be managed to reduce latency for applications that are “chatty” or are otherwise sensitive to latency, such as voice over IP. Even when broadband connectivity is available and affordable, the ability to manage it effectively can make bonding a useful tool.

“There will always be a need to build your own Internet connection with your own levels of service and availability built in,” Akin said.

Paulding County’s fire department, which is combined with the county’s Emergency Management Agency, established the mobile command vehicle to serve as a backup emergency operations center after serious flooding in 2009. It has 911 emergency dispatching capabilities and coordinates communications with first responders within Paulding County and in surrounding counties, so communications was a primary concern for the vehicle. PortaBella was added a year later to boost its Internet bandwidth.

The appliance is connected to a wireless router. “That gives us Wi-Fi on board the bus,” New said. The vehicle’s regular equipment includes two laptops that use the wireless router, and the same link is used by other members of the emergency communications team, which includes the local Amateur Radio Emergency Service organization, whose members can bring their own computers.

“We can also change to a directional router to provide added connectivity for a building,” New said. “I can pull the bus up to a building and point the directional router at it,” and users inside can have access to the vehicle’s cellular link.

Also on board the vehicle is an ACU-1000 multiplexing gateway from Raytheon, which can cross-connect multiple radio networks simultaneously. It can link up VHF, UHF and 800 MHz radio systems and connect them with telephone and satellite systems. The ACU-1000 is connected to the PortaBella so it can be operated remotely by another computer. This enables direct communications not only between different Paulding County departments but between departments of other counties as well.

Emergencies requiring the use of the mobile command vehicle have been rare so far, but the department uses it regularly in training exercises and deploys it for large events such as February’s Firefighters Appreciation Day at Atlanta’s Turner Field, where it served as the command post for visiting firefighters.

“We’re learning as we go how to use the bus,” New said. Other counties in the area use satellite connections for mobile command centers, but “satellite service is very costly,” he said. “This is a much more economical alternative to that.”


About the Author

William Jackson is a Maryland-based freelance writer.


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