Encyclopedia of Computer Science and Technology

von Neumann, John 497A regular telephone carries the voice as an analog signal over the phone line. For Internet (IP) telephony, however, the user’s voice from themicrophone is converted to a digital signal that is carried by standard Internet packets. At the destination, the packets are reassembled into astream of digital data that is then sent to the sound card to be turned back into voice sounds to be played through the system speaker.over the Internet to the nearest connection point, whereit is placed as a regular phone call. The charges are muchlower than typical long-distance plans. (For example, as of2007 Skype charged a flat rate of $3.00 a month for unlimitedcalls to the United States and Canada and only a fewcents per minute to most developed countries.)Since video can also be sent over the Internet, videoover IP for calling and conferencing is also becoming morecommon. Video does require a higher bandwidth connectionthan does voice.Advantages and DrawbacksVoIP has several advantages over regular phone service.Because it uses the Internet’s flexible packet-switching system,it uses bandwidth more efficiently (indeed, much conventionalphone service is now carried as digital packetsas well). If done through a direct computer-to-computerconnection with free software, VoIP can be essentially freeto the user, since the Internet connection is presumablyalready paid for. (It also follows that VoIP is most advantageousfor long-distance calling.) Finally, VoIP can be usedwith wireless mobile devices, sometimes with lower costthan cell service.At least as currently implemented, VoIP does have somedisadvantages:• Like cordless phones (but unlike traditional phones),VoIP requires that the user be connected to power. Thismay make the system unavailable in an emergency.• Also, in an emergency, a 911 operator has no way toknow where the caller is located geographically. Thiscould be a problem if the caller is unable to providethis information.• While a regular phone is a pretty simple device, VoIPrequires special hardware or a PC, which might fail.• VoIP requires a working Internet connection—inpractice, a high-speed connection (see broadband).Load or instability in the network could cause interruptionsin calls or a lowering of voice quality.• As with other data sent over the Internet, there arepotential security concerns. Encryption can be usedto secure VoIP calls, but this in turn leads to concernsby law enforcement agencies seeking to implementeavesdropping warrants.Despite these disadvantages, VoIP is likely to continueto become more prevalent and reliable due to the advantagesof integrating with the global Internet and a widevariety of devices.Further Reading“History of VoIP.” Available online. URL: http://www.utdallas.edu/~bjackson/history.html. Accessed December 3, 2007.Kelly, Timothy V. VoIP for Dummies. Hoboken, N.J.: Wiley, 2005.Skype. Available online. URL: http://www.skype.com/. AccessedDecember 3, 2007.Valdes, Robert. “How VoIP works.” Available online. URL: http://communication.howstuffworks.com/ip-telephony.htm.Accessed December 3, 2007.Van Meggelen, Jim, Jared Smith, and Leif Madsen. Asterisk: TheFuture of Telephony. Sebastapol, Calif.: O’Reilly, 2005.Venezia, Paul. “Open Source VoIP Makes the Business Connection.”Infoworld, March 19, 2007. Available online. URL:http://www.infoworld.com/article/07/03/19/12FEopenvoip_1.html. Accessed December 3, 2007.Wallingford, Ted. Switching to VoIP. Sebastapol, Calif.: O’Reilly,2005.von Neumann, John(1903–1957)Hungarian–AmericanMathematician, Computer ScientistJohn von Neumann made wide-ranging contributions infields as diverse as pure logic, simulation, game theory, andquantum physics. He also developed many of the key conceptsfor the architecture of the modern digital computerand helped design some of the first successful machines.Von Neumann was born on December 28, 1903, in Budapest,Hungary, to a family with banking interests. As a youthhe showed a prodigious talent for calculation and interest inmathematics, but his father opposed his pursuing a career inpure mathematics. Therefore, when von Neumann enteredthe University of Berlin in 1921 and the Technische Hochschulein 1923, he earned his Ph.D. in chemical engineering.However, in 1926 he went back to Budapest and earned aPh.D. in mathematics with a dissertation on set theory. He