Application performance engineering edit
Network bandwidth capacity
The term bandwidth sometimes defines the net bit rate ‘peak bit rate’,’information rate,’ or physical layer ‘useful bit rate’, channel capacity, orthe maximum throughput of a logical or physical communication path in adigital communication system. For example, bandwidth tests measure the maximumthroughput of a computer network. The maximum rate that can be sustained on alink are limited by the Shannon–Hartley channel capacity for thesecommunication systems, which is dependent on the bandwidth in hertz and thenoise on the channel.
Network bandwidth consumption
The consumed bandwidth in bit/s, corresponds to achieved throughput orgoodput, i.e., the average rate of successful data transfer through acommunication path. The consumed bandwidth can be affected by technologiessuch as bandwidth shaping, bandwidth management, bandwidth throttling,bandwidth cap, bandwidth allocation (for example bandwidth allocation protocoland dynamic bandwidth allocation), etc. A bit stream’s bandwidth isproportional to the average consumed signal bandwidth in hertz (the averagespectral bandwidth of the analog signal representing the bit stream) during astudied time interval.Channel bandwidth may be confused with useful data throughput (or goodput).For example, a channel with x bps may not necessarily transmit data at x rate,since protocols, encryption, and other factors can add appreciable overhead.For instance, much internet traffic uses the transmission control protocol(TCP), which requires a three-way handshake for each transaction. Although inmany modern implementations the protocol is efficient, it does add significantoverhead compared to simpler protocols. Also, data packets may be lost, whichfurther reduces the useful data throughput. In general, for any effectivedigital communication, a framing protocol is needed; overhead and effectivethroughput depends on implementation. Useful throughput is less than or equalto the actual channel capacity minus implementation overhead.
The asymptotic bandwidth (formally asymptotic throughput) for a network is themeasure of maximum throughput for a greedy source, for example when themessage size (the number of packets per second from a source) approaches closeto the maximum amount.Asymptotic bandwidths are usually estimated by sending a number of very largemessages through the network, measuring the end-to-end throughput. As otherbandwidths, the asymptotic bandwidth is measured in multiples of bits perseconds. Since bandwidth spikes can skew the measurement, carriers often usethe 95th percentile method. This method continuously measures bandwidth usageand then removes the top 5 percent.
Digital bandwidth may also refer to: multimedia bit rate or average bitrateafter multimedia data compression (source coding), defined as the total amountof data divided by the playback time.Due to the impractically high bandwidth requirements of uncompressed digitalmedia, the required multimedia bandwidth can be significantly reduced withdata compression. The most widely used data compression technique for mediabandwidth reduction is the discrete cosine transform (DCT), which was firstproposed by Nasir Ahmed in the early 1970s. DCT compression significantlyreduces the amount of memory and bandwidth required for digital signals,capable of achieving a data compression ratio of up to 100:1 compared touncompressed media.
Bandwidth in web hosting
In Web hosting service, the term bandwidth is often incorrectly used todescribe the amount of data transferred to or from the website or serverwithin a prescribed period of time, for example bandwidth consumptionaccumulated over a month measured in gigabytes per month. Themore accurate phrase used for this meaning of a maximum amount of datatransfer each month or given period is monthly data transfer.A similar situation can occur for end user ISPs as well, especially wherenetwork capacity is limited (for example in areas with underdeveloped internetconnectivity and on wireless networks).
Internet connection bandwidth
This table shows the maximum bandwidth (the physical layer net bitrate) ofcommon Internet access technologies. For more detailed lists see
Deep space communicationEdit
These long path length considerations are exacerbated when communicating withspace probes and other long-range targets beyond Earth’s atmosphere. The DeepSpace Network implemented by NASA is one such system that must cope with theseproblems. Largely latency driven, the GAO has criticized the currentarchitecture. Several different methods have been proposed to handle theintermittent connectivity and long delays between packets, such as delay-tolerant networking.
Performance engineering within systems engineering encompasses the set ofroles, skills, activities, practices, tools, and deliverables applied at everyphase of the systems development life cycle which ensures that a solution willbe designed, implemented, and operationally supported to meet the performancerequirements defined for the solution.Performance engineering continuously deals with trade-offs between types ofperformance. Occasionally a CPU designer can find a way to make a CPU withbetter overall performance by improving one of the aspects of performance,presented below, without sacrificing the CPU’s performance in other areas. Forexample, building the CPU out of better, faster transistors.However, sometimes pushing one type of performance to an extreme leads to aCPU with worse overall performance, because other important aspects weresacrificed to get one impressive-looking number, for example, the chip’s clockrate (see the megahertz myth).
Application performance engineering
Application Performance Engineering (APE) is a specific methodology withinperformance engineering designed to meet the challenges associated withapplication performance in increasingly distributed mobile, cloud andterrestrial IT environments. It includes the roles, skills, activities,practices, tools and deliverables applied at every phase of the applicationlifecycle that ensure an application will be designed, implemented andoperationally supported to meet non-functional performance requirements.
Performance per watt
System designers building parallel computers, such as Google’s hardware, pickCPUs based on their speed per watt of power, because the cost of powering theCPU outweighs the cost of the CPU itself.
Software performance testing
In software engineering, performance testing is in general testing performedto determine how a system performs in terms of responsiveness and stabilityunder a particular workload. It can also serve to investigate, measure,validate or verify other quality attributes of the system, such asscalability, reliability and resource usage.Performance testing is a subset of performance engineering, an emergingcomputer science practice which strives to build performance into theimplementation, design and architecture of a system.
Performance tuning is the improvement of system performance. This is typicallya computer application, but the same methods can be applied to economicmarkets, bureaucracies or other complex systems. The motivation for suchactivity is called a performance problem, which can be real or anticipated.Most systems will respond to increased load with some degree of decreasingperformance. A system’s ability to accept a higher load is called scalability,and modifying a system to handle a higher load is synonymous to performancetuning.Systematic tuning follows these steps: 1. Assess the problem and establish numeric values that categorize acceptable behavior. 2. Measure the performance of the system before modification. 3. Identify the part of the system that is critical for improving the performance. This is called the bottleneck. 4. Modify that part of the system to remove the bottleneck. 5. Measure the performance of the system after modification. 6. If the modification makes the performance better, adopt it. If the modification makes the performance worse, put it back to the way it was.