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data communications Data transmission and data reception or, more broadly, data communication or digital communications is the transfer and reception of data in the form of a digital bitstream or a digitized analog signal transmitted over a point-to-point or p ...
, the bandwidth-delay product is the
product Product may refer to: Business * Product (business), an item that serves as a solution to a specific consumer problem. * Product (project management), a deliverable or set of deliverables that contribute to a business solution Mathematics * Produ ...
of a data link's capacity (in
bits per second In telecommunications and computing, bit rate (bitrate or as a variable ''R'') is the number of bits that are conveyed or processed per unit of time. The bit rate is expressed in the unit bit per second (symbol: bit/s), often in conjunction ...
) and its round-trip delay time (in seconds). The result, an amount of data measured in bits (or
byte The byte is a unit of digital information that most commonly consists of eight bits. Historically, the byte was the number of bits used to encode a single character of text in a computer and for this reason it is the smallest addressable uni ...
s), is equivalent to the maximum amount of data on the network circuit at any given time, i.e., data that has been transmitted but not yet acknowledged. The bandwidth-delay product was originally proposed as a rule of thumb for sizing router buffers in conjunction with congestion avoidance algorithm Random Early Detection (RED). A network with a large bandwidth-delay product is commonly known as a long fat network (shortened to LFN). As defined in , a network is considered an LFN if its bandwidth-delay product is significantly larger than 105 bits (12,500 bytes). Ultra-high speed local area networks (LANs) may fall into this category, where protocol tuning is critical for achieving peak throughput, on account of their extremely high bandwidth, even though their delay is not great. While a connection with 1 Gbit/s and a round-trip time below 100 μs is no LFN, a connection with 100 Gbit/s would need to stay below 1 μs RTT to not be considered an LFN. An important example of a system where the bandwidth-delay product is large is that of
geostationary satellite A geostationary orbit, also referred to as a geosynchronous equatorial orbit''Geostationary orbit'' and ''Geosynchronous (equatorial) orbit'' are used somewhat interchangeably in sources. (GEO), is a circular geosynchronous orbit in altitude ...
connections, where end-to-end delivery time is very high and link throughput may also be high. The high end-to-end delivery time makes life difficult for stop-and-wait protocols and applications that assume rapid end-to-end response. A high bandwidth-delay product is an important problem case in the design of protocols such as Transmission Control Protocol (TCP) in respect of TCP tuning, because the protocol can only achieve optimum throughput if a sender sends a sufficiently large quantity of data before being required to stop and wait until a confirming message is received from the receiver, acknowledging successful receipt of that data. If the quantity of data sent is insufficient compared with the bandwidth-delay product, then the link is not being kept busy and the protocol is operating below peak efficiency for the link. Protocols that hope to succeed in this respect need carefully designed self-monitoring, self-tuning algorithms. The TCP window scale option may be used to solve this problem caused by insufficient window size, which is limited to 65,535 bytes without scaling.


Examples

* Moderate speed satellite network: 512 kbit/s, 900 ms round-trip time (RTT) \begin B \times D &= 512 \times 10^ \text \cdot 900 \times 10^ \text \\ &= 460,800 \text = 460.8 \text = 57.6 \text \end * Residential DSL: 2 Mbit/s, 50 ms RTT\begin B \times D &= 2 \times 10^ \text \cdot 50 \times 10^ \text \\ &= 100\times10^3 \text = 100 \text = 12.5 \text \end * Mobile broadband ( HSDPA): 6 Mbit/s, 100 ms RTT\begin B \times D &= 6 \times 10^ \text \cdot 100 \times 10^ \text \\ &= 600\times10^3 \text = 600 \text = 75 \text \end * Residential
ADSL2+ G.992.5 (also referred to as ADSL2+, G.dmt.bis+, and G.adslplus) is an ITU-T standard for asymmetric digital subscriber line (ADSL) broadband Internet access. The standard has a maximum theoretical downstream sync speed of 24 megabits per second ...
: 20 Mbit/s (from DSLAM to residential modem), 50 ms RTT\begin B \times D &= 2 \times 10^ \text \cdot 50 \times 10^ \text \\ &= 10^ \text = 1 \text = 125 \text \end * Residential Cable internet (
DOCSIS Data Over Cable Service Interface Specification (DOCSIS) is an international telecommunications standard that permits the addition of high-bandwidth data transfer to an existing cable television (CATV) system. It is used by many cable televisio ...
): 200 Mbit/s, 20 ms RTT\begin B \times D &= 2 \times 10^ \text \cdot 20 \times 10^ \text \\ &= 4\times10^ \text = 4 \text = 500 \text \end * High-speed terrestrial network: 1 Gbit/s, 1 ms RTT\begin B \times D &= 10^ \text \times 10^ \text \\ &= 10^6 \text = 1 \text = 125 \text \end * Ultra-high speed LAN: 100 Gbit/s, 30 μs RTT\begin B \times D &= 100 \times 10^ \text \cdot 30 \times 10^ \text \\ &= 3\times10^ \text = 3 \text = 375 \text \end * International research & education network: 100 Gbit/s, 200 ms RTT\begin B \times D &= 10^ \text \cdot 0.2 \text \\ &= 2\times10^ \text = 20 \text = 2.5 \text \end


References


See also

* Protocol spoofing * Satellite internet * Internet2 *
Bufferbloat Bufferbloat is a cause of high latency and jitter in packet-switched networks caused by excess buffering of packets. Bufferbloat can also cause packet delay variation (also known as jitter), as well as reduce the overall network throughput. ...
* Many TCP variants have been customized for large bandwidth-delay products ** HSTCP,
FAST TCP FAST TCP (also written FastTCP) is a TCP congestion avoidance algorithm especially targeted at long-distance, high latency links, developed at the Netlab, California Institute of Technology and now being commercialized by FastSoft. FastSoft was a ...
, BIC TCP,
CUBIC TCP CUBIC is a network congestion avoidance algorithm for TCP which can achieve high bandwidth connections over networks more quickly and reliably in the face of high latency than earlier algorithms. It helps optimize long fat networks. In 2006, ...
, H-TCP,
Compound TCP Compound TCP (CTCP) is a Microsoft algorithm that was introduced as part of the Windows Vista and Window Server 2008 TCP stack. It is designed to aggressively adjust the sender's congestion window to optimise TCP for connections with large ba ...
, Agile-SD ** TCP window scale option * For KiB vs KB see: Kibibyte {{DEFAULTSORT:Bandwidth-Delay Product Network performance Computer network analysis