Busy Carriers, Busy Signals

Ever see someone pull his wireless phone away from his ear, look at the display and wonder aloud, "Is this thing working?" Not good for an industry that hopes to replace wireline.

Wireless doesn't have an industry standard for acceptable amounts of blocking. Typically, less than 0.1 percent of wireline calls fail to complete; for wireless, it's usually less than 2 percent.

"During the busiest hour of the week, your customers should not experience more than 2 percent blocking," said Phillipe Chartier, Nortel Networks RF-design manager, GSM. "If they experience that, you should do something to correct that."

How much better than 2 percent depends on quality-of-service (QoS) goals. Wireless always has billed itself as a safety asset, and the need to connect quickly and on the first try only will grow with E-911.

Silent retry can mask call-completion failures by automatically redialing the number, but that treats only the symptom and not the underlying problem. Ensuring that calls go through quickly also can help reduce overhead, which can sap capacity. One example is the end-send phenomenon.

"If somebody thinks the call is not going through, then they're going to hang up and try again," said Andy Germano, Qualcomm director of product management. "It can cause network congestion because if everybody starts doing that, it's a spiral effect."

AVERSION TO TRAVERSIONIn both wireless and wireline, the more steps needed to complete a call, the more potential there is for delays or even failure. One way to improve speed and reliability is to eliminate middlemen by building direct trunks between two wireless carriers serving the same geographical area.

"The more wireless subscribers there are, the more direct connections the wireless carriers will have with other networks to complete calls faster," said Randy Snyder, Synacom Technology executive director of marketing.

The same approach could help streamline completion of calls from roamers.

"One of the things the (GSM) Alliance is thinking of doing is building an SS7 backbone network where we connect all our SS7 networks together," said Gowton Achaibar, Powertel vice president of engineering. "That should help."

The potential for failures increases when the call has to traverse local, long-distance and other wireless carriers. Network agreements determine what types of information can be passed between the networks. If there's no tariff to pay for that information, it might be ignored or rejected, and the consequences can range from inaccurate billing to a call that can't be completed.

"You may have an agreement that requires a piece of information that isn't sent," Snyder said. "The terminating network says: 'Wait a minute. I'm supposed to get this piece of information.' There are certain messages and parameters that are sent in the backward direction that act as acknowledgement (and) also say when they're starting to bill for the call. Sometimes, if you don't pass that message properly, there can be issues with billing and whether the call is allowed to be completed or not."

FERRETING OUT GLITCHES & DELAYSAuthentication, prepaid and roamer verification all have evolved from options to staples, but they shouldn't bog down the network to the point that it can't do its main job: completing calls. Some networks verify roamers and set up the call simultaneously, while others wait for verification before doing anything to set up the call.

"All those things do increase call setup, depending on how they're implemented," said Synacom's Snyder. "But it's usually something that's not noticeable to the subscriber. Authentication should happen in hundreds of milliseconds."

Enhanced services also involve database dips, which can slow down or stall call completion. A service control point's response time can slow dramatically when it's forced to process more transactions than it can handle. If the delay is too long, timers in the network can run out, and the call might be abandoned. As a result, equipment provisioning literally can make or break a call.

"Most of the time, (a problem) isn't so much on the signaling side as it is on the provisioning of the equipment," said Pierce Brockman, Inet vice president of software development. "It often manifests itself where you can see the problem occur on the signaling network."

Because capacity affects setup time, carriers such as Cellular One in San Francisco find that monitoring completion rates is an efficient way to catch delays, too.

"Call-completion rates are measured on every cell site in the network on a daily basis," said Ed Evangelista, Cellular One network-engineering manager. "Call-setup times are not specifically monitored. We monitor the network capacity, which ensures that the call-setup times are in-line."

ANALYSIS OR PARALYSISCall-completion rates are probably one of the most monitored statistics in wireless, but numbers alone don't tell the whole story. Between build-outs, acquisitions and battling for market share, there's not always a lot of time left for basic housekeeping. Some other ways to ensure that bigger problems aren't lurking:

* Clean house. Wireless continues to evolve rapidly, so look for unwanted legacies.

"Over time, switch translations seem to build up," said Danny Bazerman, L.A. Cellular vice president of engineering and operations. "Things are left in (and) never taken out. You really need to go through and make sure you analyze what's in there and clean your garage every so often. Sweep out the old stuff that shouldn't be in there. It takes up switch memory and processing time."

* Set standards. There are probably as many ways to engineer a wireless network as there are engineers. Call completion is one area that can suffer when different approaches clash.

"Make sure your engineers across the system are all engineering using the same methodology," Bazerman said. "Every engineer thinks he knows how to engineer a system, and they all have their own spin on it."

L.A. Cellular looked at its processes to determine the best way to do things and then applied those procedures across its 32,000-square-mile network.

"Until we all started to work off the same template, we had problems where the system in Orange County wasn't talking the same in L.A. County," Bazerman said. "Now, we feel we have a cohesive product where (what) you experience in the south part of the network is the same as the north part. And I think our customers will tell you that, as well."

* Anticipate problems. Compile a weekly hit list of problem areas. Members of Sprint's technical-services and network-operations departments even meet with vendors every Friday to review network performance over the previous week. Trending and benchmarking also can help identify problems before they become noticeable to subscribers.

"We do benchmark testing in all of our markets," said Keith Paglusch, Sprint PCS senior vice president of operations. "We drive-test not only ourselves but our competitors to ensure that we're delivering a QoS that's better than our competitors."