Bandwidth throttling

Bandwidth throttling consists in the intentional limitation of the communication speed (bytes or kilobytes per second) of the ingoing (received) data and/or in the limitation of the speed of outgoing (sent) data in a network node or in a network device.

The data speed and rendering may be limited depending on various parameters and conditions.

Overview

Limiting the speed of data sent by a data originator (a client computer or a server computer) is much more efficient than limiting the speed in an intermediate network device between client and server because while in the first case usually no network packets are lost, in the second case network packets can be lost / discarded whenever ingoing data speed overcomes the bandwidth limit or the capacity of device and data packets cannot be temporarily stored in a buffer queue (because it is full or it does not exist); the usage of such a buffer queue is to absorb the peaks of incoming data for very short time lapse.

In the second case discarded data packets can be resent by transmitter and received again.

When a low level network device discards incoming data packets usually can also notify that fact to data transmitter in order to slow down the transmission speed (see also network congestion).

NOTE: Bandwidth throttling should not be confused with rate limiting which operates on client requests at application server level and/or at network management level (i.e. by inspecting protocol data packets). Rate limiting can also help in keeping peaks of data speed under control.

These bandwidth limitations can be implemented:
* at (a client program or a server program, i.e. ftp server, web server, etc.) which can be run and configured to throttle data sent through network or even to throttle data received from network (by reading data at most at a throttled amount per second);
* at (typically done by an ISP).

The (client/server program) is usually perfectly because it is a choice of the client manager or the server manager (by server administrator) to limit or not to limit the speed of data received from remote program via network or the speed of data sent to target program (server or client).

The (ISP) instead is considered an in the USA under FCC regulations. While ISPs prey on the individuals inability to fight them, fines can range up to $25,000 USD for throttling. In the United States, net neutrality, the principle that Internet service providers (ISPs) treat all data on the Internet the same, and not discriminate, has been an issue of contention between network users and access providers since the 1990s. With net neutrality, ISPs may not intentionally block, slow down, or charge money for specific online content.

Defined as the intentional slowing or speeding of an internet service by an Internet service provider (ISP). It is a reactive measure employed in communication networks to regulate network traffic and minimize bandwidth congestion. Bandwidth throttling can occur at different locations on the network. On a local area network (LAN), a system administrator ("sysadmin") may employ bandwidth throttling to help limit network congestion and server crashes. On a broader level, the Internet service provider may use bandwidth throttling to help reduce a user's usage of bandwidth that is supplied to the local network. Bandwidth throttling is also used as a measurement of data rate on Internet speed test websites.

Throttling can be used to actively limit a user's upload and download rates on programs such as video streaming, BitTorrent protocols and other file sharing applications, as well as even out the usage of the total bandwidth supplied across all users on the network. Bandwidth throttling is also often used in Internet applications, in order to spread a load over a wider network to reduce local network congestion, or over a number of servers to avoid overloading individual ones, and so reduce their risk of the system crashing, and gain additional revenue by giving users an incentive to use more expensive tiered pricing schemes, where bandwidth is not throttled.

Operation

A computer network typically consists of a number of servers, which host data and provide services to clients. The Internet is a good example, in which web servers are used to host websites, providing information to a potentially very large number of client computers. Clients will make requests to servers, which will respond by sending the required data, which may be a song file, a video, and so on, depending on what the client has requested. As there will typically be many clients per server, the data processing demand on a server will generally be considerably greater than on any individual client. And so servers are typically implemented using computers with high data capacity and processing power. The traffic on such a network will vary over time, and there will be periods when client requests will peak or sent responses will be huge, sometimes exceeding the capacity of parts of network and causing congestion, especially in parts of the network that form bottlenecks. This can cause data request failures, or in worst cases, server crashes.

In order to prevent such occurrences, a client / server / system administrator may enable (if available) bandwidth throttling:
* at , to control the speed of ingoing (received) data and/or to control the speed of outgoing (sent) data:
** a client program could be configured to throttle the sending (upload) of a big file to a server program in order to reserve some network bandwidth for other uses (i.e. for sending emails with attached data, browsing web sites, etc.);
** a server program (i.e. web server) could throttle its outgoing data to allow more concurrent active client connections without using too much network bandwidth (i.e. using only 90% of available bandwidth in order to keep a reserve for other activities, etc.);
:: examples: assuming to have a server site with speed access to Internet of 100 MB/s (around 1000 Mbit/s), assuming that most clients have a 1MB/s (around 10Mbit/s) network speed access to Internet and assuming to be able to download huge files (i.e. 1 GB each):
::* with bandwidth throttling, a server using a max. output speed of 100 kB/s (around 1Mbit/s) for each TCP connection, could allow at least (or even 10000 if output is limited to 10kB/s) (active connections means that data content, such as a big file, is being downloaded from server to client);
::* without bandwidth throttling, a server could efficiently serve only (100MB/s / 1MB/s) before saturating network bandwidth; a saturated network (i.e. with a bottleneck through an Internet Access Point) could slow down a lot the attempts to establish other new connections or even to force them to fail because of timeouts, etc.; besides this new active connections could not get easily or fastly their proper share of bandwidth.

* at , to control the speed of data received or sent both at low level (data packets) and/or at high level (i.e. by inspecting application protocol data):
** policies similar or even more sophisticated than those of application software level could be set in low level network devices near Internet access point.

Application

A bandwidth intensive device, such as a server, might limit (throttle) the speed at which it receives or sends data, in order to avoid overloading its processing capacity or to saturate network bandwidth. This can be done both at the local network servers or at the ISP servers. ISPs often employ deep packet inspection (DPI), which is widely available in routers or provided by special DPI equipment. Additionally, today’s networking equipment allows ISPs to collect statistics on flow sizes at line speed, which can be used to mark large flows for traffic shaping. Two ISPs, Cox and Comcast, have stated that they engage in this practice, where they limit users' bandwidth by up to 99%. Today most if not all Internet Service Providers throttle their users' bandwidth, with or without the user ever even realizing it. In the specific case of Comcast, an equipment vendor called Sandvine developed the network management technology that throttled P2P file transfers.

Those that could have their bandwidth throttled are typically someone who is constantly downloading and uploading torrents, or someone who just watches a lot of online videos. If this is done by an ISP, many consider this practice as an unfair method of regulating the bandwidth because consumers