Comments by "Mikko Rantalainen" (@MikkoRantalainen) on "Why Did Facebook Go Down? - Computerphile" video.

  1. A "phone book" was like analog DNS (or LDAP) implemented with ink on paper, but for people and their telephone numbers (and sometimes addresses). The query was done for the name of the person and response was the phone number (or "not found"). It was commonly noticed that names of the people are not unique and sometimes the optionally provided address information was used to disambiquate between different persons. The index of the database did not support reverse lookups (get name when given a phone number). Everybody acquired a new copy of the whole database (called "a phone book") about yearly and if you got a new telephone number, distributing the change to other people took a year when they switched to updated database. In addition, these databases were often distributed locally only and there was no generic method to query telephone number of somebody in another country. A global database using the same implementation would have been too expensive to purchase. The database only included "fully public" access rights for all data and the only alternative was to not include a phone number to database at all. (Note that reverse lookup of phone numbers rarely works even today because all the newer digital databases of phone numbers still work using similar designs to a phone book. In practice, reverse phone number lookup may work nation wide but not globally.)
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