Blocked Out

Sep 15, 2001 12:00 PM, By Dan O’Shea, Chief Correspondent

Eliminating blocked calls is a worthy goal, but not a realistic one.

Figures from various industry sources put the average percentage of blocked calls at between 1% and 2% per carrier on a per-market basis. Blocked calls usually are defined technically as calls where users fail to access the network due to network congestion or other capacity shortcomings. However, there are many variations in how blocked calls occur and how users perceive them.

Dave Knutson, vice president of engineering and operations at TeleCorp (www.telecorppcs.com), an AT&T Wireless SunCom affiliate (www.suncompcs.com), said calls can be blocked at three places: the radio level, at the switch or at the network handoff between carriers.

Call blockages can be related directly to network congestion at these points, but technical-equipment problems and other issues also could be the root cause. In any case, the general industry attitude about blocked calls is that they’re going to happen, like it or not. Although carriers obviously try to ensure every call is completed, they usually do not engineer their networks with the goal of zero blocked calls in mind.

“Most carriers have thresholds for the percentage of blocked calls they are willing to live with,” said John Catlin, Agilent (www.agilent.com) eastern regional manager for wireless network services operation. Agilent offers carriers turnkey network planning services — everything from showing them exactly where to put cell sites for optimum reliability to performing ongoing network monitoring and testing.

If an acceptable industry standard exists for blocked calls, it probably is about 2%.

“Two percent is a number that is tolerable and acceptable during peak usage hours,” Knutson said. “At other hours, it would probably be closer to 1%. Reaching 0% is theoretically impossible because it would take too much network capacity that would not always be in use.”

He added, however, that carriers are stringent about maintaining low blocked-call rates when they are launching new markets.

Sometimes blocking is endemic to a network, in that busy intersections or highways are likely to generate blocked calls at certain hours, while there is plenty of network capacity at other times to handle calls without blocking being an issue, said Steve Clark, U.S. Cellular (www.uscc.com) vice president of operations at its customer care center.

Sometimes an abnormally high rate of blocked calls can appear out of nowhere — a car accident that suddenly stalls traffic on an expressway and prompts drivers to use their phones.

Spikes in calling traffic also can surprise network-management staffs if they are not kept up to date on the rate at which a carrier’s field sales crew is closing new accounts, Knutson said.

For the most part, however, carriers can plan for and even predict periods of high network congestion. For instance, Knutson said TeleCorp knows it will need capacity enhancements such as cells on wheels when conventions come to its home city of New Orleans or when the Super Bowl comes to town every few years.

User Acceptance?
Still, even when carriers know what’s coming, users may get a blocked call or two. At this point, are customers even fazed by those blocked calls?

In TeleCorp’s 81 markets, Knutson said users seem to “accept the rare occasion of blocked calls, but if you are the one whose call is blocked, you still aren’t going to be happy.”

“Blocking certainly has not diminished in importance over time,” U.S. Cellular’s Clark added. “Percentage of blocked calls is still one of the key metrics we watch on a daily basis. We don’t see a lot of user complaints about it, but if we are monitoring the network, and we see a trend of blocked calls developing, we look at the data and see what happened.”

Most carriers collect data from their switches on a daily basis that shows them the number of calls attempted, completed, blocked and dropped in progress. They can use these reports to fix capacity or technical problems, as well as plan networks better.

Also, Agilent’s Catlin said the vendor performs drive tests and other services for the carrier customers that can give carriers a good idea of their competitors’ reliability ratings.

As a business practice, carriers rarely use blocked-call percentages as sales and marketing tools. Although these rates might not be effective in selling new accounts, they usually can be used to help retain customers, said TeleCorp’s Knutson.

Tight-Lipped Carriers
Fractional differences in blocked-call rates can acquire some competitive value; because of this, most carriers decline to share information about their blocked-call percentages.

Of the carriers interviewed for this story, those with mostly rural networks were much more forthcoming than large carriers operating in urban environments.

One carrier willing to share its own metrics is Triton PCS, another AT&T Wireless SunCom affiliate (www.tritonpcs.com).

According to a Triton PCS spokesperson, the carrier processed 800 million calls during 2000, with a completion rate of 99.8%. The company recorded blocked-call rates of less than 1% for each quarter last year.

Part of Triton PCS’ strategy for eliminating blocked calls is building its networks with an average of 130 cell sites per 1 million people. The industry average is believed to be closer to 100 sites per million. More cell sites mean more cost to deploy and operate a network, but engineering networks to provide higher quality actually reduces costs and helps retain customers later on, the spokesperson said.

“Zero percent blocked calls may not be a practical goal, but it does not stop us from trying to get there,” she said.