|
In telecommunication, jitter is an abrupt and unwanted variation of one or more signal characteristics, such as the interval between successive pulses, the amplitude of successive cycles, or the frequency or phase of successive cycles. Jitter is a significant factor in the design of almost all communications links (e.g. USB, PCI-e, SATA, OC-48). Telecommunication is the transmission of signals over a distance for the purpose of communication. ...
In telecommunication, signalling (or signaling) has the following meanings: The use of signals for controlling communications. ...
Sine waves of various frequencies; the lower waves have higher frequencies than those above. ...
Phase is an overloaded word used for: instantaneous phase: the current position in the cycle of something that changes cyclically phase shift: a constant difference/offset between two instantaneous phases, particularly when one is a standard reference Waves are amplitudes that change cyclically, often modeled as sinusoidal functions of time...
Note: USB may also mean upper sideband in radio. ...
PCI Express (formerly known as 3GIO for 3rd Generation I/O, not to be mistaken with PCI-X) is an implementation of the PCI computer bus that uses existing PCI programming concepts and communications standards, but bases it on a much faster serial communications system. ...
A SATA power connector. ...
OC-48 (Optical Carrier 48) is a fiber optic network line with a SONET rate of 2488. ...
Jitter can apply to a number of signal qualities (e.g. amplitude, phase, pulse width or pulse position), and can be quantified in the same terms as all time-varying signals (e.g. RMS, or peak-to-peak displacement). Also like other time-varying signals, jitter can be expressed in terms of spectral density (frequency content). Generally, very low frequency jitter is not of interest in designing a systems, and the low-frequency cutoff for jitter is typically specified at 1 Hz. In medicine, a persons pulse is the throbbing of their arteries as an effect of the heart beat. ...
In mathematics, the root mean square or rms is a statistical measure of the magnitude of a varying quantity. ...
In theoretical physics, cutoff usually represents a particular energy scale or length scale. ...
A jitter meter is a testing instrument for measuring jitter values and is used in manufacturing DVD and CD-ROM drives. To meet Wikipedias quality standards, this article or section may require cleanup. ...
The CD-ROM (an abbreviation for Compact Disc Read-Only Memory (ROM)) is a non-volatile optical data storage medium using the same physical format as audio compact discs, readable by a computer with a CD-ROM drive. ...
Phase Jitter Metrics
For clock jitter, there are three commonly used metrics: absolute jitter, period jitter, and cycle to cycle jitter. In synchronous digital electronics, such as most computers, a clock signal is a signal used to coordinate the actions of two or more circuits. ...
the clock's frequency was perfectly constant. The absolute jitter metric is important in systems where a large number of clock sources are trying to pass data to one another (eg. SONET). The Synchronous optical network, commonly known as SONET, is a standard for communicating digital information using lasers or light emitting diodes (LEDs) over optical fiber as defined by GR-253-CORE from Telcordia. ...
Period jitter (aka cycle jitter) is the difference between any one clock period and the ideal clock period. Accordingly, it can be thought of as the discrete-time derivative of absolute jitter. Period jitter tends to be important in synchronous circuitry like digital state machines where the error-free operation of the circuitry is limitted by the shortest possible clock period, and the performance of the circuitry is limitted by the average clock period. Hence, synchronous circuitry benefits from minimizing period jitter, so that the shortest clock period approaches the average clock period.
Cycle-to-cycle jitter is the difference in length between any two adjacent clock periods. Accordingly, it can be thought of as the discrete-time derivative of period jitter. It can be important for some types of clock generation circuitry used in microprocessors and RAM interfaces.
All of these jitter metrics are really measures of a single time-dependent quantity, and hence are related by derivatives as described above. Since they have different generation mechanisms, different circuit effects, and different measurement methodology, it is still useful to quantify them separately.
In the telecommunications world, the unit used for the above types of jitter is usually the UI (or Unit Interval) which quantifies the jitter in terms of a fraction of the ideal period of the clock. This unit is useful because it scales with clock frequency and thus allows relatively slow interconnects such as T1 to be compared to higher speed internet backbone links such as OC-192. Absolute units such as picoseconds are more common in microprocessor applications. Units of degrees and radians are also used. Digital signal 1 (DS1, also known as a T1) is a T-carrier signaling scheme devised by Bell Labs. ...
If jitter has a Gaussian distribution (ie. is random), it is usually quantified using the standard deviation of this distribution (aka. RMS). Often, jitter distribution is significantly non-Gaussian. This can occur if the jitter is caused by external sources such as power supply noise. In these cases, peak-to-peak measurements are more useful. Many efforts have been made to meaningfully quantify distributions that are neither Gaussian nor have meaningful peaks (which is the case in all real jitter). All have shortcomings but most tend to be good enough for the purposes of engineering work. Note that typically, the reference point for jitter is defined such that the mean jitter is 0. In mathematics and statistics, the arithmetic mean (or simply the mean) of a list of numbers is the sum of all the members of the list divided by the number of items in the list. ...
In networking, in particular IP networks such as the Internet, jitter can refer to the variation (statistical dispersion) in the delay of the packets (because of routers' internal queues behaviour in certain circumstances, routing changes, etc). A computer network is a system for communication between computers. ...
The Internet Protocol (IP) is a data-oriented protocol used for communicating data across a packet-switched internetwork. ...
A computer network is a system for communication between computers. ...
In descriptive statistics, statistical dispersion (also called statistical variability) is quantifiable variation of measurements of differing members of a population within the scale on which they are measured. ...
A packet is the fundamental unit of information carriage in all modern computer networks that use packet switching. ...
A D-Link Wi-Fi NAT router, popular for home and small office networks A router is a computer networking device that forwards data packets across an internetwork toward their destinations, through a process known as routing. ...
In computer networking the term routing refers to selecting paths in a computer network along which to send data. ...
Jitter prevention
Anti-jitter circuits Anti-jitter circuits (AJCs) are a class of electronic circuits designed to reduce the level of jitter in a regular pulse signal. AJCs operate by re-timing the output pulses so they align more closely to an idealised pulse signal. They are widely used in clock and data recovery circuits in digital communications, as well as for data sampling systems such as the analog-to-digital converter and digital-to-analog converter. Examples of anti-jitter circuits include phase-locked loop and delay-locked loop. Inside digital to analog converters jitter causes unwanted high-frequency distortions. In this case it can be suppressed with high fidelity clock signal usage. An electrical network or electrical circuit is an interconnection of analog electrical elements such as resistors, inductors, capacitors, diodes, switches and transistors. ...
In telecommunication, signalling (or signaling) has the following meanings: The use of signals for controlling communications. ...
Digital communication, as opposed to analogue communication refers to all emerging communications and technologies via a digital platform usually combining text, graphics, sound, and video, utilising computer or mobile technology. ...
An analog-to-digital converter (abbreviated ADC, A/D or A to D) is an electronic circuit that converts continuous signals to discrete digital numbers. ...
In electronics, a digital-to-analog converter (DAC or D-to-A) is a device for converting a digital (usually binary) code to an analog signal (current, voltage or charges). ...
In electronics, a phase-locked loop (PLL) is a closed-loop feedback control system that maintains a generated signal in a fixed phase relationship to a reference signal. ...
In electronics, a Delay-locked Loop (DLL) is a digital circuit similar to a Phase-locked loop (PLL), with the main difference being the absence of an oscillator within the circuit. ...
Jitter buffers Jitter buffers or de-jitter buffers are used to counter jitter introduced by packet networks so that a continuous playout of audio (or video) transmitted over the network can be ensured. The maximum jitter that can be countered by a de-jitter buffer is equal to the buffering delay introduced before starting the play-out of the mediastream.
Some systems use sophisticated delay-optimal de-jitter buffers which are capable of adapting the buffering delay to changing network jitter characteristics. These are known as adaptive de-jitter buffers and the adaptation logic is based on the jitter estimates computed from the arrival characteristics of the media packets. Adaptive de-jittering involves introducing discontinuities in the media play-out which may appear offensive to the listener or viewer. Adaptive de-jittering is usually carried out for audio play-outs which feature a VAD/DTX encoded audio, that allows the lengths of the silence periods to be adjusted, thus minimizing the perceptual impact of the adaptation.
Dejitterizer A dejitterizer is a device that reduces jitter in a digital signal. A dejitterizer usually consists of an elastic buffer in which the signal is temporarily stored and then retransmitted at a rate based on the average rate of the incoming signal. A dejitterizer is usually ineffective in dealing with low-frequency jitter, such as waiting-time jitter. A digital signal is a signal that is both discrete and quantized. ...
In telecommunication, a variable length buffer is a buffer into which data may be entered at one rate and removed at another rate without changing the data sequence. ...
See also In telecommunication, a buffer is a routine or storage medium used in telecommunications to compensate for a difference in rate of flow of data, or time of occurrence of events, when transferring data from one device to another. ...
In telecommunication, a drift is a comparatively long-term change in an attribute or value of a system or equipment operational parameter. ...
In telecommunication, wander are long-term random variations of the significant instants of a digital signal from their ideal positions. ...
References Federal Standard 1037C entitled Telecommunications: Glossary of Telecommunication Terms is a U.S. Federal Standard, issued by the General Services Administration pursuant to the Federal Property and Administrative Services Act of 1949, as amended. ...
MIL-STD-188 is a series of U.S. military standards relating to telecommunications. ...
External links - Fibre Channel MJSQ (Methodology of Jitter Specification & Quality) Information
- Jitter Buffer
- An Introduction to Jitter in Communications Systems
- Jitter Specifications Made Easy A Heuristic Discussion of Fibre Channel and Gigabit Ethernet Methods
- Jitter Test Solutions Be A Jitter Master With Agilent Technologies
|
Feeds |
Contact