tion of how the Internet might be used to disseminate information in a future crisis.
The experiences of September 11 also indicate the value of efficient Internet or Internet-style data communication in a disaster. These alternatives, such as text messaging and e-mail, make more efficient use of limited communications capacity than do other services. By midday on September 11, the cellular-phone networks in Manhattan were severely congested, yet there are reports that people who used their cell phones or wireless-equipped PDAs to send instant messages were able to communicate effectively. E-mail and instant messages were also used as a substitute for telephone calls.
Although better communication over the Internet could simply have been the result of the relative overprovisioning of the Internet-related communication infrastructure, there are several fundamental reasons why, for example, using a PDA to send a short text message such as “I’m OK and am walking home” is far more efficient and more likely to succeed than making a cell-phone call when the network is congested. First, the Internet degrades under load more gracefully than does the voice network. If sufficient capacity is not available, the cell-phone network will not permit new calls to be set up. In contrast, the Internet makes use of mechanisms that continue to accept new messages but reduce transmission rates when the network is congested. Also, by virtue of their flexible design, Internet-style communications lend themselves to human actions that reduce the load—whether by substituting a brief text message for a data-intensive voice call or removing data-intensive graphics from a Web page (as CNN did in the face of high loads). A lesson here is that organizations responsible for disaster planning should encourage awareness of this more efficient way to communicate.