According to CNET.com BlackBerry outage: RIM a victim of its own success? - CNET News
"RIM's service is centralized and it works by routing all BlackBerry e-mails through one of two main NOCs, which are essentially large data centers. One NOC is located in Canada and it primarily services the Western Hemisphere as well as parts of Asia, said analysts familiar with the company. The other data center, located in the U.K., handles e-mail traffic in Europe, Africa and the Middle East.
"The BlackBerry Enterprise Server, which sits on the corporate network, receives e-mails from the company's Exchange or Lotus e-mail server and forwards those e-mails in an encrypted tunnel to one of the NOCs. The NOC then acts as an efficient delivery system that authenticates users and forwards the messages to the appropriate handheld device.
"Because user authentication is handled by RIM away from the corporate network, it protects companies from hackers who may try to obtain information through e-mail servers, which sit inside the company's firewall. RIM's approach also means that corporate IT departments don't have to juggle relationships with multiple mobile operators because RIM handles all of that for them in the NOC."
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