In communication networks, throughput is the amount of digital data per time unit that is delivered over a physical or logical link, or that is passing through a certain network node. For example, it may be the amount of data that is delivered to a certain network terminal or host computer, or between two specific computers. The throughput is usually measured in bit per second (bit/s or bps), occasionally in data packets per second or data packets per timeslot. The term corresponds to digital bandwidth consumption. This article does not cite any references or sources. ... A node is a device that is connected as part of a computer network. ... Look up Terminal in Wiktionary, the free dictionary. ... This article is about computer servers. ... This article is about the unit of information. ... In information technology, a packet is a formatted block of data carried by a computer network. ... Time Division Multiple Access (TDMA) is a technology for shared medium (usually radio) networks. ... This article does not cite any references or sources. ...

The system throughput or aggregate throughput is the sum of the data rates that are delivered to all terminals in a network.

The throughput can be analyzed mathematically by means of queueing theory, where the load in packets per time unit is denoted arrival rate λ, and the throughput in packets per time unit is denoted departure rate μ. Queueing theory (also commonly spelled queuing theory) is the mathematical study of waiting lines (or queues). ...

Maximum throughput and channel utilization

The maximum throughput of a node or communication link is synonymous to its capacity.

The maximum throughput is defined as the asymptotic throughput when the load (the amount of incoming data) is very large. In packet switched systems where the load and the throughput always are equal (where packet loss can not occur), the maximum throughput may be defined as the minimum load in bit/s that causes the delivery time (the latency) to become unstable and increase towards infinity. In computer networking and telecommunications, packet switching is a communications paradigm in which packets (messages or fragments of messages) are individually routed between nodes, with no previously established communication path. ... This page meets Wikipedias criteria for speedy deletion. ...

The maximum throughput is equal to or lower than the net bit rate (the useful bit rate) of a physical link, excluding physical layer protocol overhead such as channel coding. It has been suggested that this article or section be merged with data signaling rate. ... In digital telecommunications, channel coding is a pre-transmission mapping applied to a digital signal or data file, usually designed to make error-correction possible. ...

If the communication is mediated by several links in series with different bit rates, the maximum throughput is lower than or equal to the lowest bit rate.

Throughput ≤ Maximum throughput ≤ Minimum link net bit rate

It is not recommended to measure throughput in percentage, to avoid confusion regarding what the percentage is related to. It is better to use the channel utilization and drop rate in percentage.

The channel utilization in percentage is the achieved throughput related to the net bit rate in bit/s of a digital communication channel (also known as the network access connection speed, the digital bandwidth or the channel capacity). For example, if the throughput is 70 Mbit/s in a 100 Mbit/s Ethernet connection, the channel utilization is 70%. It has been suggested that this article or section be merged with data signaling rate. ... A Communications channel (or channel for short), models the medium through which information is transmitted from a sender (or transmitter) to a receiver. ... This article does not cite any references or sources. ... Channel capacity, is the amount of discrete information that can be reliably transmitted over a channel. ...

In a point-to-point or point-to-multipoint communication link, where only one terminal is transmitting, the maximum throughput is often equivalent to or very near the physical data rate (the channel capacity), since the channel utilization can be almost 100% in such a network, except for a small inter-frame gap. Channel capacity, is the amount of discrete information that can be reliably transmitted over a channel. ...

For example in Ethernet, the interframe gap is 12 bytes, and the maximum frame size 1518 bytes (maximum 1500 byte payload + 8 byte preamble + 14 byte header + 4 Byte trailer ). An additional minimum interframe gap corresponding to 12 byte is inserted after each frame. This corresponds to a maximum channel utilization of 1518/(1518+12)•100% = 99.2%, or a maximum throughput of 99.2 Mbit/s in a 100 Mbit/s Ethernet connection.

In a computer network, the throughput that is achieved from one computer to another may be lower than the maximum throughput, and than the network access channel capacity, for several reasons, for example:

• The traffic load may be lower than the maximum throughput.
• The channel capacity may be shared by other users. If a bottle neck communication link physical data rate R is shared by N users, every user typically achieves a throughput of approximately N/R if fair queuing best-effort communication is assumed.
• Flow control, for example in the TCP protocol, affects the throughput if the Bandwidth-delay product is larger than the TCP window, i.e. the buffer size. In that case the sending computer must wait for acknowledgement of the data packets before it can send more packets.
• Packet loss due to Network congestion. Packets may be dropped in switches and routers when the packet queues are full due to congestion.
• Packet loss due to bit errors.
• TCP congestion avoidance controls the data rate. So called "slow start" occurs in the beginning of a file, and after packet drops caused by router congestion or bit errors in for example wireless links.
• Scheduling algorithms in routers and switches. If fair queuing is not provided, users that send large packet will get higher bandwidth. Some users may be prioritized in a weighted fair queuing (WFQ) algorithm if differentiated or guaranteed quality of service (QoS) is provided.
• Ethernet "backoff" waiting time after collisions.

Fair Queuing (FQ), is a scheduling scheme used in computer networks and statistical multiplexing to allow several data flows to fairly share the link capacity. ... Best effort delivery describes a network service in which the network does not provide any special features that recover lost or corrupted data. ... The flow control mechanism is used for controlling the flow of data in a network under well-defined conditions, while congestion control is used for controlling the flow of data when congestion has actually occurred . ... The Transmission Control Protocol (TCP) is one of the core protocols of the Internet protocol suite, often simply referred to as TCP/IP. Using TCP, applications on networked hosts can create connections to one another, over which they can exchange streams of data using Stream Sockets. ... In data communications, bandwidth × delay product refers to the product of a data links capacity (in bits per second) times its end-to-end delay (in seconds). ... This page meets Wikipedias criteria for speedy deletion. ... In data networking and queueing theory, network congestion occurs when incremental increases in offered load lead either only to small increases in network throughput, or to an actual reduction in network throughput. ... This page meets Wikipedias criteria for speedy deletion. ... The Transmission Control Protocol (TCP) is one of the core protocols of the Internet protocol suite, often simply referred to as TCP/IP. Using TCP, applications on networked hosts can create connections to one another, over which they can exchange streams of data using Stream Sockets. ... Network congestion avoidance is a process used in computer networks to avoid congestion. ... Weighted Fair Queuing (WFQ) is a packet scheduling technique allowing guaranteed bandwidth services. ... In the fields of packet-switched networks and computer networking, the traffic engineering term Quality of Service (QoS) refers to control mechanisms that can provide different priority to different users or data flows, or guarantee a certain level of performance to a data flow in accordance with requests from the... Ethernet is a large, diverse family of frame-based computer networking technologies that operates at many speeds for local area networks (LANs). ...

Goodput and overhead

Main article: Goodput

The maximum throughput is often an unreliable measurement of perceived speed, for example the file transmission speed in bits per seconds. As pointed out above, the achieved throughput is often lower than the maximum throughput. Also, the protocol overhead affects the perceived speed. There are very few or no other articles that link to this one. ...

The throughput is not a well-defined metric when it comes to how to deal with protocol overhead. It is typically measured at a reference point below the network layer and above the physical layer.

The most simple definition is the number of bits per second that are physically delivered. A typical example where this definition is practised is an Ethernet network. In this case the maximum throughput is the gross bitrate or raw bitrate. It has been suggested that this article or section be merged with data signaling rate. ... It has been suggested that this article or section be merged with data signaling rate. ...

However, in schemes that include forward error correction codes (channel coding), the redundant error code is normally excluded from the throughput. An example in modem communication, where the throughput typically is measured in the interface between the PPP protocol and the circuit switched modem connection. In this case the maximum throughput is often called net bitrate or useful bitrate. In telecommunication, forward error correction (FEC) is a system of error control for data transmission, whereby the sender adds redundant data to its messages, which allows the receiver to detect and correct errors (within some bound) without the need to ask the sender for additional data. ... A modem (from modulate and demodulate) is a device that modulates an analog carrier signal to encode digital information, and also demodulates such a carrier signal to decode the transmitted information. ... PPP is an abbreviation for: In real estate: prepayment penalty, a penalty paid when property is sold before an agreed-upon date. ... In telecommunications and computing, bitrate (sometimes written bit rate, data rate or as a variable Rbit) is the number of bits that are conveyed or processed per unit of time. ... It has been suggested that this article or section be merged with data signaling rate. ...

To determine the actual speed of a network or connection, the goodput measurement definition may be used. For example in file transmission, the goodput corresponds to the file size (in bits) divided by the file transmission time. There are very few or no other articles that link to this one. ...

The goodput is the amount of useful information that is delivered per second to the application layer protocol. Dropped packets or packet retransmissions as well as protocol overhead are excluded. Because of that, the goodput is lower than the throughput. Technical factors that affect the difference are presented in the goodput article. There are very few or no other articles that link to this one. ... The application layer is the seventh level of the seven-layer OSI model. ... There are very few or no other articles that link to this one. ...

Maximum throughput over analog channels

The maximum throughput of a point-to-point or point-to-multipoint physical transmission medium, is equal to or near the channel capacity. This is affected by modulation method and physical layer protocol overhead such as error correction coding, bit synchronization and equalizer training sequences. A transmission medium is any material substance, such as fiber-optic cable, twisted-wire pair, coaxial cable, dielectric-slab waveguide, water, or air, that can be used for the propagation of signals, usually in the form of modulated radio, light, or acoustic waves, from one point to another. ... Channel capacity, is the amount of discrete information that can be reliably transmitted over a channel. ... In telecommunications, modulation is the process of varying a periodic waveform, i. ... This article does not cite any references or sources. ... In mathematics, computer science, information theory, the issue of error correction and detection has great practical importance in maintaining data (information) integrety accross noisy channels and less than relyable storage mediums. ...

The maximum throughput may be related to the analog bandwidth of a physical transmission medium, measured in Hertz. The link spectral efficiency in bit/s/Hz is the maximum throughput divided by the analog bandwidth. It is a measure of the efficiency of the digital transmission scheme. This article does not cite any references or sources. ... A transmission medium is any material substance, such as fiber-optic cable, twisted-wire pair, coaxial cable, dielectric-slab waveguide, water, or air, that can be used for the propagation of signals, usually in the form of modulated radio, light, or acoustic waves, from one point to another. ... Spectral efficiency or spectrum efficiency refers to the amount of information that can be transmitted over a given bandwidth in a specific digital communication system. ...

In wireless networks or cellular systems, the system spectral efficiency in bit/s/Hz/area unit, bit/s/Hz/site or bit/s/Hz/cell, is the maximum system throughput (aggregate throughput) divided by the analog bandwidth and some measure of the system coverage area. While the term wireless network may technically be used to refer to any type of network that is wireless, the term is most commonly used to refer to a telecommunications network whose interconnections between nodes is implemented without the use of wires, such as a computer network (which is a... This article or section is not written in the formal tone expected of an encyclopedia article. ... Spectral efficiency or Spectrum efficiency is the amount of information that can be transmitted over a given bandwidth in a specific digital communication system. ...

Throughput and latency

Normally, throughput and latency are opposed goals. To improve latency, you typically want to increase how much the computer checks to see if you are trying to interact. This checking overhead slows you down. However, there is one very common exception to this rule. Network protocols and programs tend to synchronize both ends regularly. If these synchronizations are slow, then throughput can suffer tremendously. A comparison of latency and throughput in telecommunications can address a common misunderstanding that having greater throughput means a faster connection. ... Latency is a time delay between the moment something is initiated, and the moment one of its effects begins. ...

The perceived speed is mostly based on the speed of requests made or responsiveness. As such, responsiveness has far less to do with throughput than latency. To illustrate this, consider a truck full of magnetic tape en route from Moscow to Paris. The time or latency it takes to deliver the data may be several days, but the amount or throughput of data delivered will exceed the throughput of a broadband connection. In contrast, the broadband connection, which has a throughput many times less than that of the truck, has a relatively low latency and can deliver smaller amounts of data much faster. For a user, surfing the Internet for instance, the latter which has a lower latency is perceived as "faster". Broadband in telecommunications is a term which refers to a signaling method which includes or handles a relatively wide range of frequencies which may be divided into channels or frequency bins. ...

Latency is measured from the time a request (e.g. a single packet) leaves the client to the time the response (e.g. an acknowledgment) arrives back at the client from the serving entity. The unit of latency is time. Throughput on the other hand is the amount of data that is transferred over a period of time. For example, if over ten seconds twenty packets are transferred then the throughput would be 20 / 10 = 2 packets per second. Throughput can have many units (for example: "bits/second," "bytes/second," or "packets/second"), but it is always measured in a volume-per-time ratio. Latency is a time delay between the moment something is initiated, and the moment one of its effects begins. ...

See also

• Measuring data throughput
• Goodput
• Link and system spectral efficiency

People are often concerned about measuring the maximum data throughput rate of a communications link. ... There are very few or no other articles that link to this one. ... Spectral efficiency or spectrum efficiency refers to the amount of information that can be transmitted over a given bandwidth in a specific digital communication system. ...

External links

• It's the Latency, Stupid