network performance network performance refers to measures of service quality of a network as seen by the customer there are many different ways to measure the performance of a network as each network is different in nature and design performance can also be modeled and simulated instead of measured one example of this is using state transition diagrams to model queuing performance or to use a network simulator performance measures the following measures are often considered important bandwidth commonly measured in bitssecond 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 bandwidth computing the available channel bandwidth and achievable signaltonoise ratio determine the maximum possible throughput it is not generally possible to send more data than dictated by the shannonhartley theorem throughput throughput throughput is the number of messages successfully delivered per unit time throughput is controlled by available bandwidth as well as the available signaltonoise 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 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 latency engineering the speed of light imposes a minimum propagation time on all electromagnetic signals it is not possible to reduce the latency below t s c m displaystyle tscm where s is the distance and cm is the speed of light in the medium this approximately means 1 extra millisecond roundtrip time rtt for 100km62miles of distance between hosts other delays also occur in intermediate nodes in packet switched networks delays can occur due to queueing jitter 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 source jitter may be observed in characteristics such as the frequency of successive pulses the signal amplitude or phase of periodic signals jitter is a significant and usually undesired factor in the design of almost all communications links eg usb pcie sata oc48 in clock recovery applications it is called timing jitter error rate bit error rate in digital transmission the number of bit errors is the number of received bits of a data stream over a communication channel that have been altered due to noise 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 pe 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 algorithms and protocols for some systems latency and throughput are coupled entities in tcpip latency can also directly affect throughput in tcp connections the large bandwidthdelay product of high latency connections combined with relatively small tcp window sizes on many devices effectively causes the throughput of a high latency connection to drop sharply with latency this can be remedied with various techniques such as increasing the tcp congestion window size or more drastic solutions such as packet coalescing tcp acceleration and forward error correction all of which are commonly used for high latency satellite links tcp acceleration converts the tcp packets into a stream that is similar to udp because of this the tcp acceleration software must provide its own mechanisms to ensure the reliability of the link taking the latency and bandwidth of the link into account and both ends of the high latency link must support the method used in the media access control mac layer performance issues such as throughput and endtoend delay are also addressed examples of latency or throughput dominated systems many systems can be characterized as dominated either by throughput limitations or by latency limitations in terms of enduser utility or experience in some cases hard limits such as the speed of light present unique problems to such systems and nothing can be done to correct this other systems allow for significant balancing and optimization for best user experience satellite telephony a telecom satellite in geosynchronous orbit imposes a path length of at least 71000km between transmitter and receiver which means a minimum delay between message request and message receipt or latency of 473 ms this delay can be very noticeable and affects satellite phone service regardless of available throughput capacity deep space communication these long path length considerations are exacerbated when communicating with space probes and other longrange targets beyond earths atmosphere the deep space network implemented by nasa is one such system that must cope with these problems largely latency driven the gao has criticized the current architecture even deeper space communication at interstellar distances the difficulties in designing radio systems that can achieve any throughput at all are massive in these cases maintaining communication is a bigger issue than how long that communication takes offline data transport transportation is concerned almost entirely with throughput which is why physical deliveries of backup tape archives are still largely done by vehicle bitrate measuring network throughput network traffic measurement response time notes rappaport theodore s 2002 wireless communications principles and practice 2 ed upper saddle river nj prentice hall ptr isbn0130422320 roddy dennis 2001 satellite communications 3 ed new york mcgrawhill isbn0071371761 fall kevin a delaytolerant network architecture for challenged internets intel corporation february 2003 doc no irbtr03003 government accountability office gao report 06445 nasas deep space network current management structure is not conducive to effectively matching resources with future requirements april 27 2006 nasas deep space network website its the latency stupid vtemajor fields of computer sciencenote this template roughly follows the 2012 acm computing classification systemhardware printed circuit board peripheral integrated circuit very large scale integration systems on chip socs energy consumption green computing electronic design automation hardware acceleration computer systemsorganization computer architecture embedded system realtime computing dependability networks network architecture network protocol network components network scheduler network performance evaluation network service software organization interpreter middleware virtual machine operating system software quality software notationsand tools programming paradigm programming language compiler 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