Difference between revisions 104912300 and 104912301 on dewiki

{{Unreferenced|date=October 2008}}
'''Segmented downloading''' (also known as '''multisource downloading''' OR '''swarming download''') can be a more efficient way of [[downloading]] [[Computer file|file]]s from many peers at once.  The one single file is downloaded, in parallel, from several distinct sources or uploaders of the file.  This can help a group of users with [[asymmetric]] connections, such as [[ADSL]] to provide a high total [[Bandwidth (computing)|bandwidth]] to one downloader, and to handle peaks in download demand.

== History ==
Segmented downloads probably have an origin with [[NASA]] and the [[magnetic tape]] based file systems used on [[Deep Space Network]] craft such as those in the [[Voyager Program]].    

NASA missions using some kind of segmented downloading
* [[Mars Rovers]] (for [[ICER]] image files)
* [[New Horizons]] (for [[Jupiter]] flyby data)
* [[Voyager Program]] (historical)

[[Swarmcast]] was the first significant [[peer-to-peer]] (P2P) content delivery system that implemented a kind of segmented downloading technology. The program and protocol was invented and developed in 1999 by Justin Chapweske and sold to [[Opencola]], which released the software under a [[GPL license]].

A lot of the terms used in segmented downloading technology have their origin with [[Swarmcast]], with [[BitTorrent (protocol)|BitTorrent]] being the only other significant contributor to the terms in use.{{FactCitation needed|date=May 2009}}

== Network implications ==
[[Image:Torrentcomp small.gif|frame|In this animation, the coloured bars beneath all of the clients represent individual pieces of the file. After the initial pieces transfer from the seed, the pieces are individually transferred from client to client. The original seeder only needs to send out one copy of the file for all the clients to receive a copy.]]

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* routes to the more obscure parts of the Internet can assert themselves across most of the Internet—this is especially true for dial-up users
* segmented downloading does save some transmission capacity, as the number of lost or redundant megabytes is minimal compared to losing a prolonged [[http]] or [[ftp]] download

Most ISPs have learned to cope with segmented downloading technology, but coping has meant the mandatory deployment of TCP/IP traffic shaping technology.{{
factCitation needed|date=May 2010}}

== Limitations ==
Segmented downloading technology cannot magically solve all downloading problems. There are mathematical constraints on the effectiveness of the technology.

In a group of users that has insufficient upload-bandwidth, with [[Demand (economics)|demand]] higher than [[Supply (economics)|supply]]. Segmented downloading can however very nicely handle traffic peaks, and it can also, to some degree, let uploaders upload "more often" to better utilize their connection.

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== See also ==
* [[Peercasting]]

{{Download managers}}

[[Category:Data transmission]]
[[Category:File sharing]]