Segmented file transfer

Segmented file-transfer (also known as multisource file-transfer or swarming file-transfer) is the coordinated transmission of a computer file sourced from multiple servers to a single destination. It can be applied as well when downloading the same file from the same server in various parts, like some download managers do. A computer program downloads (retrieves) different portions of the file from various sources simultaneously, and assembles the file on the destination computer data storage device.

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. However, from the 1960s to the 1980s there was a lot of experimentation with uploading, downloading (and synchronizing) data over bandwidth restricted telecommunications links by most many mainframe computer users. So the early origins of segmented downloading are not historically clear.

It is understood that some NASA missions use some kind of segmented downloading technique (for either file formats or data streams) :

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 being the only other significant contributor to the terms in use.

Most IP networks are designed for users to download more than they upload, usually with an expected (Download:Upload) ratio of 3:1 or more.

Segmented downloading, when used by only 20% of an ISP's user base, can upset the ISP's network to a point of requiring substantial reprogramming of routers and a rethink of network design.

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