Sneakernet

In a non-network environment, the floppy disk was once the primary means of transferring data between computers. Today, portable flash drives or memory cards would be more practical.

Sneakernet is a tongue-in-cheek term used to describe the transfer of electronic information, especially computer files, by physically carrying removable media such as magnetic tape, floppy disks, compact discs, USB flash drives or external drives from one computer to another.

Sneaker refers to the shoes of the person carrying the media. This is usually in lieu of transferring the information over a computer network. Sneakernets are often used as an academic example to illustrate the trade-off between latency and bandwidth.

Summary and background

Sneakernets are in use throughout the computer world. Sneakernets may be used when computer networks are prohibitively expensive for the owner to maintain, in high-security environments where manual inspection (for re-classification of information) is necessary, where information needs to be shared between networks with different levels of security clearance, when data transfer is impractical due to bandwidth limitations, or when a guest laptop is incompatible with the local network. Because sneakernets take advantage of physical media, different security measures must be taken into account for the transfer of sensitive information.

This form of data transfer is also used for peer-to-peer (or friend-to-friend) file sharing and has grown in popularity in metropolitan areas and college communities, sometimes for the purpose of distributing copyrighted material. The ease of this system has been facilitated by the availability of USB external hard drives, USB flash drives and portable music players such as Apple's iPod.

The United States Postal Service also offers a Media Mail service for computer hard drives and compact discs among other items. This provides a viable mode of transport for long distance sneakernet use. In fact, when mailing a sufficiently large hard drive or a spindle of DVDs, the throughput (amount of data per unit time) may compete favorably with other methods of data transfer.

Theory

Sneakernets can achieve tremendous throughput, but they suffer from high latency (see comparison of latency and throughput).

The throughput of the network is directly proportional to the size of the transmitted file(s). Latency is based on the amount of time it takes to fully process the request for information. Latency would include the time it takes to write the storage media and the time to travel from point A to point B.

For example: Person A requested Person B to send him a DVD (4.7GB) worth of information. Over the Internet the latency for the file request may be milliseconds but at a modest broadband download speed of 50kB/s it may take up to a day to complete the transfer. On the other hand Person B could burn a DVD and deliver it to Person A in an hour. The latency was an hour but the throughput of the transfer is roughly equal to a transfer rate of 1305kB/s.

Similarly, as of 2006 the largest backup tape available is the DLT-S4, with a capacity of 800GB. If a tape of this capacity were sent by overnight mail and were to arrive around 20 hours after it was sent, the effective data rate would be 89 Mb/s. This magnitude of speed would be very difficult to attain without a costly dedicated connection.

Sneakernets may also be used in tandem with computer network data transfer to increase data security. For example, a file or collection of files may be encrypted and sent over the Internet while the encryption key is printed and hand delivered or mailed. This method greatly reduces the possibility of an individual intercepting both the key and encrypted data.

There is also the limitation of read/write speeds on a computer. There are three ways you can increase disk speed. One, you increase the speed of the drive and/or the media. Two, having multiple disks, and getting one in the drive reading while another one is writing. Three, doing the process multiple times simultaneously.

Example (B) You write one disk, start another write cycle, walk, start reading one disk, walk back, take it out and replace it. With transport time being half of write/read time, this would take five elevenths of the time using one disk would. Example (B variant) One person writing, one person transporting, one person reading disks.
Example (C) You buy 4 drives and 2 disks. You use two to write simultaneously, send the two disks over, and use the other two drives to read.

Usage examples

• Google has reportedly used a sneakernet to transport datasets too large for current computer networks, up to 120TB in size.

• The SETI@home project uses a sneakernet to overcome bandwidth limitations: data recorded by the radio telescope in Arecibo, Puerto Rico is stored on magnetic tapes which are then shipped to Berkeley, California for processing. In 2005, Jim Gray reported sending hard drives and even "metal boxes with processors" to transport large amounts of data by postal mail.

• The charity relief organization Information Without Borders is attempting to implement a sneakernet routing protocol for providing cheap Internet access to developing and post-conflict regions using donated PDAs and mobile phones, and also for providing free and open Internet access to repressive regimes that restrict free expression by limiting access.

• Wizzy Digital Courier provides internet access to schools with poor or no network connectivity by implementing UUCP on USB memory sticks. This allows email transport and scoops of web pages that back-fill a web cache.

• When home broadband access was less common, many people downloaded large files over their workplace networks and took them home by sneakernet. Today when home broadband is more common, sometimes technical workers at institutions with congested WAN links do the reverse: downloading data at home in the evening and carrying the files to work on USB flash drives.

• in Amiga demoscene the primary method of exchanging data was using snail mail to exchange floppies between groups. Each group had at least one person designated as a swapper, who would exchange news, data and productions with swappers from other groups this way. Best swappers were known to send and receive over 100 mails a month and using various techniques to illegally avoid the postage fee.

• Online DVD rental services such as Netflix and GameFly are effectively sneakernets, as they deliver data on DVDs and other media via regular mail.

In publication

Never underestimate the bandwidth of a station wagon full of tapes hurtling down the highway.

—Tanenbaum, Andrew S. (1996). Computer Networks. New Jersey: Prentice-Hall. p. 83. ISBN 0-13-349945-6.

The original version of this quotation came much earlier; the very first problem in Tanenbaum's 1981 textbook Computer Networks asks the student to calculate the throughput of a St. Bernard carrying floppy disks (which are said to hold 250 kilobytes of data). The first USENET citation is July 16, 1985, and it was widely considered a chestnut already, possibly dating from the 1970s . Other alleged speakers included Tom Reidel, Warren Jackson, or Bob Sutterfield. The station wagon transporting magnetic tapes is the canonical version, but variants using trucks or Boeing 747s and later storage technologies such as CD-ROMs have frequently appeared.

Similar concepts

• The humorous IP over Avian Carriers (RFC 1149) is an Internet protocol for the transmission of messages via homing pigeon.
• Delay-tolerant networks such as the Haggle project at Cambridge University use portable devices carried by humans to transport data when end-to-end connectivity may not be possible

Opposition

There have been many steps against sneakernets to protect copyrighted information, most notably copy protection placed on audio files as well as physical media to prevent the user from copying and distributing that data.

In 1992 The Software Publisher Association (now known as the SIIA) produced a PSA campaign titled Don't Copy That Floppy.

See also

• Pod slurping
• Darknet
• Jargon File
• Wizzy Digital Courier is a project to distribute data like email to places with no Internet connection, via USB flash drive.

External links

• "Don't Copy That Floppy" in Internet Archive
• Entry for "sneakernet" in The Jargon Wiki
• Entry for "sneakernet" in the Jargon File
• Security risk of sneaker nets and USB devices
• Sneaker Net 2.0