“Plan 55-A”的意思、由来-开放百科全书

Based on the technology of punched paper tape storage, the systems of the design were called reperforators. A reperforator performed functions similar to an email message transfer agent (email server), used much later in the Internet, but it used electro-mechanical technology, which preceded the use of semiconductor circuitry and computers.

A reperforator switching center received messages via serial communication lines from teleprinters, such as the Teletype Model 28 ASR, or from other switching centers on receiving consoles, each consisting of a paper tape punch feeding tape into a paper tape reader via a storage bin. The reader decoded the message header, and sent the header characters to the director. The director, much like a telephone switch, connected the receiving console to a sending console in the same switching center by a cross-office connection. The message was transmitted from the receiving console to the sending console, character by character, punching a second paper tape at the sending console. Cross-office connections, and their readers and punches, were slightly faster than external connections, to limit congestion to the edges of the network.

Each sending console also consisted of a paper tape punch and reader. Output from each sending console was transmitted via outgoing lines to other switching centers or to destination teleprinters.^[3] Each message typically contained one telegram.

Each received message had up to nine routing indicators, or destinations. For two or three destinations, the messages were sent simultaneously on three cross-office connections to outgoing sending consoles. Additional destinations resulted in a copy of the message being sent to the multiple call spillover unit, which removed the routing indicators for destinations already handled and sent the message through the system again.^[3]

Nationwide, Western Union's switching centers were arranged in a hub and spokes architecture involving fifteen locations. The U.S. Air Force used the Plan 55-A system worldwide with ten centers.

An analysis of the queueing delays in Plan 55-A by Leonard Kleinrock^[4] formed part of the theoretical basis for the development of the ARPAnet.

See also

References

1. ^{{cite journal | url=http://www.westernunionalumni.com/mplsrpf.htm | title=The Decline and Fall of the Reperforator | journal=Western Union News | publisher=Western Union | volume=10 | issue=5 |date=May 5, 1977}}
2. ^{{cite journal|last1=Vernam|first1=G.S.|title=Automatic Telegraph Switching System Plan 55-A|journal=Transactions of the American Institute of Electrical Engineers|date=May 1958|pages=239–247|publisher=IEEE|doi=10.1109/TCE.1958.6372793}}
3. ^¹²{{cite book |url=https://www.webcitation.org/5gOoc3dQf |title=Private Wire Services - Plan 55 Switching System - Equipment Description FWS-10 |date=June 1, 1957 |publisher=Western Union }}
4. ^{{cite paper | author=Kleinrock, Leonard | date=December 1962 | publisher=Massachusetts Institute of Technology | location=Cambridge | url=http://dspace.mit.edu/bitstream/handle/1721.1/11562/33840535.pdf | title = Message Delay in Communication Nets with Storage (PhD thesis)}}

External links

year=1956}} A non-technical industrial film showing telegram handling in the 1950s. Plan 55-A switching centers are shown in some detail.