Editing Network performance (section)

==Performance measures==
The following measures are often considered important:

* '''Bandwidth''' commonly measured in bits/second is the maximum rate that information can be transferred
* '''Throughput''' is the actual rate that information is transferred
* '''Latency''' the delay between the sender and the receiver decoding it, this is mainly a function of the signals travel time, and processing time at any nodes the information traverses
* '''Jitter''' variation in packet delay at the receiver of the information
* '''Error rate''' the number of corrupted bits expressed as a percentage or fraction of the total sent

===Bandwidth===
{{Main|Bandwidth (computing)}}
The available channel bandwidth and achievable signal-to-noise ratio determine the maximum possible throughput. It is not generally possible to send more data than dictated by the [[Shannon-Hartley Theorem]].

===Throughput===
{{Main|Throughput}}
''Throughput'' is the number of messages successfully delivered per unit time. Throughput is controlled by available bandwidth, as well as the available signal-to-noise ratio and hardware limitations. Throughput for the purpose of this article will be understood to be measured from the arrival of the first bit of data at the receiver, to decouple the concept of throughput from the concept of latency. For discussions of this type, the terms 'throughput' and 'bandwidth' are often used interchangeably.

The ''Time Window'' is the period over which the throughput is measured. The choice of an appropriate time window will often dominate calculations of throughput, and whether latency is taken into account or not will determine whether the latency affects the throughput or not.

===Latency===
{{Main|Latency (engineering)}}
The [[speed of light]] imposes a minimum propagation time on all electromagnetic signals. It is not possible to reduce the latency below

:<math>t=s/c_m</math>

where s is the distance and c<sub>m</sub> is the speed of light in the medium (roughly 200,000&nbsp;km/s for most [[optical fiber|fiber]] or [[electrical cable|electrical]] media, depending on their [[velocity factor]]). This approximately means an additional millisecond [[round-trip delay]] (RTT) per 100&nbsp;km (or 62&nbsp;miles) of distance between hosts.

Other delays also occur in intermediate nodes. In packet switched networks delays can occur due to queueing.

===Jitter===
{{Main|Jitter}}
'''Jitter''' is the undesired deviation from true periodicity of an assumed periodic [[signal]] in [[electronics]] and [[telecommunications]], often in relation to a reference [[clock signal|clock source]]. Jitter may be observed in characteristics such as the [[frequency]] of successive pulses, the signal [[amplitude]], or [[phase (waves)|phase]] of periodic signals. Jitter is a significant, and usually undesired, factor in the design of almost all communications links (e.g., [[USB]], [[PCI-e]], [[SATA]], [[OC-48]]). In [[clock recovery]] applications it is called ''timing jitter''.<ref name=wol91p211>[[#Wol1991|Wolaver, 1991, p.211]]</ref>

===Error rate===
{{Main|Bit error rate}}
In [[digital transmission]], the number of '''bit errors''' is the number of received [[bit]]s of a [[data stream]] over a [[communication channel]] that have been altered due to [[noise (telecommunications)|noise]], [[interference (communication)|interference]], [[distortion]] or [[bit synchronization]] errors.

The '''bit error rate''' or '''bit error ratio''' ('''BER''') is the number of bit errors divided by the total number of transferred bits during a studied time interval. BER is a unitless performance measure, often expressed as a [[percentage]].

The '''bit error probability''' ''p<sub>e</sub>'' is the [[expectation value]] of the BER. The BER can be considered as an approximate estimate of the bit error probability. This estimate is accurate for a long time interval and a high number of bit errors.

===Interplay of factors===

All of the factors above, coupled with user requirements and user perceptions, play a role in determining the perceived 'fastness' or utility, of a network connection. The relationship between throughput, latency, and user experience is most aptly understood in the context of a shared network medium, and as a scheduling problem.