Editing Network throughput (section)

==Factors affecting throughput==
The throughput of a communication system will be limited by a huge number of factors. Some of these are described below:

===Analog limitations===
The maximum achievable throughput (the channel capacity) is affected by the bandwidth in hertz and [[signal-to-noise ratio]] of the analog physical medium.

Despite the conceptual simplicity of digital information, all electrical signals traveling over wires are analog. The analog limitations of wires or wireless systems inevitably provide an upper bound on the amount of information that can be sent. The dominant equation here is the [[Shannon–Hartley theorem]], and analog limitations of this type can be understood as factors that affect either the analog bandwidth of a signal or as factors that affect the signal-to-noise ratio. The bandwidth of wired systems can be in fact surprisingly{{according to whom?|date=May 2025}} narrow, with the bandwidth of Ethernet wire limited to approximately 1&nbsp;GHz, and PCB traces limited by a similar amount.

Digital systems refer to the 'knee frequency',<ref>Johnson, 1993, 2-5</ref> the amount of time for the digital voltage to rise from 10% of a nominal digital '0' to a nominal digital '1' or vice versa. The knee frequency is related to the required bandwidth of a channel, and can be related to the [[3 db bandwidth]] of a system by the equation:<ref>Johnson, 1993, 9</ref> <math>\ F_{3dB} \approx K/T_r </math>
Where Tr is the 10% to 90% rise time, and K is a constant of proportionality related to the pulse shape, equal to 0.35 for an exponential rise, and 0.338 for a Gaussian rise.

*RC losses: Wires have an inherent resistance, and an inherent [[capacitance]] when measured with respect to ground. This leads to effects called [[parasitic capacitance]], causing all wires and cables to act as RC lowpass filters.
*[[Skin effect]]: As frequency increases, electric charges migrate to the edges of wires or cable. This reduces the effective cross-sectional area available for carrying current, increasing resistance and reducing the signal-to-noise ratio. For [[AWG]] 24 wire (of the type commonly found in [[Cat 5e]] cable), the skin effect frequency becomes dominant over the inherent resistivity of the wire at 100&nbsp;kHz. At 1&nbsp;GHz the resistivity has increased to 0.1 ohm per inch.<ref>Johnson, 1993, 154</ref>
*Termination and ringing: Wires longer than about 1/6 wavelengths must be modeled as [[transmission line]]s with termination taken into account. Unless this is done, reflected signals will travel back and forth across the wire, positively or negatively interfering with the information-carrying signal.<ref>Johnson, 1993, 160-170</ref>
*[[Radio Propagation|Wireless Channel Effects]]: For wireless systems, all of the effects associated with wireless transmission limit the SNR and bandwidth of the received signal, and therefore the maximum bit [[transmission rate]].

===IC hardware considerations===
Computational systems have finite processing power and can drive finite current. Limited current drive capability can limit the effective signal to noise ratio for high [[capacitance]] links.

Large data loads that require processing impose data processing requirements on hardware (such as routers). For example, a gateway router supporting a populated [[class B subnet]], handling 10 × {{nowrap|100 Mbit/s}} Ethernet channels, must examine 16 bits of address to determine the destination port for each packet. This translates into 81913 packets per second (assuming maximum data payload per packet) with a table of 2^16 addresses this requires the router to be able to perform 5.368 billion lookup operations per second. In a worst-case scenario, where the payloads of each Ethernet packet are reduced to 100 bytes, this number of operations per second jumps to 520 billion. This router would require a multi-teraflop processing core to be able to handle such a load.

* [[CSMA/CD]] and [[CSMA/CA]] "backoff" waiting time and frame retransmissions after detected collisions. This may occur in Ethernet bus networks and hub networks, as well as in wireless networks.
* [[flow control (data)|Flow control]], for example in the [[Transmission Control Protocol]] (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.
* TCP [[congestion avoidance]] controls the data rate. A so-called "slow start" occurs in the beginning of a file transfer, and after packet drops caused by router congestion or bit errors in for example wireless links.

===Multi-user considerations===
Ensuring that multiple users can harmoniously share a single communications link requires some kind of equitable sharing of the link. If a bottleneck communication link offering data rate ''R'' is shared by "N" active users (with at least one data packet in queue), every user typically achieves a throughput of approximately ''R/N'', if [[fair queuing]] [[best-effort]] communication is assumed.

* [[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 error]]s.
* Scheduling algorithms in routers and switches. If fair queuing is not provided, users that send large packets 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.
* In some communications systems, such as satellite networks, only a finite number of channels may be available to a given user at a given time. Channels are assigned either through preassignment or through Demand Assigned Multiple Access (DAMA).<ref>Roddy, 2001, 370 - 371</ref> In these cases, throughput is quantized per channel, and unused capacity on partially utilized channels is lost.