The National Emergency Number Assn. (NENA) asked FCC Wireless Bur...

to 911 networks from both wireline and wireless phones. Wireless networks are particularly subject to this congestion because of the number of eyewitnesses who report critical incidents from a roadside location or other “mobile” spot. “For many years, wire telephone providers and public safety answering points (PSAPs) have engaged in ’sizing’ their respective network segments so as to minimize or contain the effects of ‘mass calling,'” NENA said. “For a number of reasons, this form of ‘congestion control’ has not been adopted in many wireless networks.” NENA asked the FCC for an interpretation of its rules on when a wireless carrier must transmit all wireless 911 calls. NENA asked the FCC to rule that a mobile operator discharges this obligation when passing emergency calls into the trunks that connect a mobile switching center (MSC) to a selective router (SR). To this end, NENA submitted a report from its technical issues director Roger Hixson. The FCC rules at issue, Sec. 20.18(b), require covered operators to transmit all wireless 911 calls without respect to their call validation process to a PSAP or statewide default answering point. Citing Hixson’s report, NENA said call containment through trunk sizing or other methods is closely related to “grade of service” measurements similar to what wireline networks use. The application of a non-discriminatory means of “sizing” calls from customers and non-subscribers wasn’t part of the policy calculus that led to the wording of this section “and therefore not meant to be proscribed by the new rule,” it said. The FCC determined all 911 calls should be passed through regardless of call validation process, NENA said. This was based on a belief that procedures seeking to “verify subscriber status were impeding the delivery of vital communications,” NENA said. It said: “The history of the wireless E911 rules, coupled with the present reality that mass calling about localized emergencies can affect public safety communications across much wider areas, suggests the prudence of the interpretation we request here.” NENA asked the FCC to “reassure wireless carriers” that this language doesn’t rule out reasonable decisions about sizing wireless MSC-to-SR trunks and other kinds of call containment in their networks. NENA said historically, all sources of calls have received equal treatment from origination to completion to give equal probabilities of 911 call delivery. This has been done through so-called P.01 sizing, which means the trunk group sizing is based on that quantity that will let 99 of every 100 calls be completed in the busiest hour over a period of monthly measurement. Hixson’s report said wireline carriers and many wireless carriers do congestion management through MSC-SR trunk group sizing. “Typically, carriers or their agents analyze call volumes over time, and use the engineering process to size, or adjust the size of, the originating trunk group to P.01 service levels,” NENA said. This provides equal access levels across all types of carriers and end offices. NENA said “typical wireless carrier arguments against this technique” have included the extent to which wireline P.01 sizing doesn’t apply to wireless. Mobile operators also have argued they don’t know how many calls are involved so they can’t size trunk groups to P.01 standards, NENA said. NENA said CLECs have addressed the same problem. “The need is to accomplish P.01 by active monitoring of call volumes over time. Make an educated judgment, then adjust,” NENA said.