important for reaching households that do not have conventional landline telephone service. Among the limitations of CMAS are the brevity of the message content and the fact that there is no provision for receipt verification.

  • Localization of CMAS messages by county or equivalent jurisdiction might be too coarse-grained, especially in the case of large counties and highly localized events. Some tighter localization may be possible, but this would be constrained by the size of the regions potentially served by individual cellular towers and their overlapping coverage.12

  • The cellular networks on which CMAS will depend are susceptible to damage in certain types of disasters, and the message length of CMAS is limited. Thus it will be important to educate people to use older technologies such as broadcast radio and television in addition to mobile devices in order to obtain additional information if needed, or as primary sources of information if cellular networks are not available.

  • Further examination of the CMSAAC recommendation13 not to include URLs in CMAS messages is warranted. CMSAAC rightly cautions about the potential for network overload in emergencies. However, if a CMAS message does not point people to an authoritative source of additional information, it is possible that the network will be overloaded as people place calls, browse news Web sites, or search for information to confirm an alert or warning and obtain additional information. In particular, it is worth considering whether a link to a site carefully designed to minimize network traffic might cause less congestion than the information seeking and resulting demands on network capacity that would take place without such a link.


Tests conducted in 2010 by the County of San Diego, State of California, and Sprint, for example, found that localization was more difficult along the coast where the density of cellular towers was highest and there was considerable overlap in the areas that they served. Personal communication with workshop participants Leslie Luke and Stephen Rae, County of San Diego.


CMSAAC, PMG-0035, 2007; and FCC, Public Safety Docket No. 07-287, 2008.

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