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Propagation constant

The propagation constant of a sinusoidal electromagnetic wave is a measure of the change undergone by the amplitude and phase of the wave as it propagates in a given direction. The quantity being measured can be the voltage, the current in a circuit, or a field vector such as electric field strength or flux density. The propagation constant itself measures the dimensionless change in magnitude or phase per unit length. In the context of two-port networks and their cascades, propagation constant measures the change undergone by the source quantity as it propagates from one port to the next.

The propagation constant's value is expressed logarithmically, almost universally to the base e, rather than base 10 that is used in telecommunications in other situations. The quantity measured, such as voltage, is expressed as a sinusoidal phasor. The phase of the sinusoid varies with distance which results in the propagation constant being a complex number, the imaginary part being caused by the phase change.

Alternative names
The term "propagation constant" is somewhat of a misnomer as it usually varies strongly with ω. It is probably the most widely used term but there are a large variety of alternative names used by various authors for this quantity. These include transmission parameter, transmission function, propagation parameter, propagation coefficient and transmission constant. If the plural is used, it suggests that α and β are being referenced separately but collectively as in transmission parameters, propagation parameters, etc. In transmission line theory, α and β are counted among the "secondary coefficients", the term secondary being used to contrast to the primary line coefficients. The primary coefficients are the physical properties of the line, namely R,C,L and G, from which the secondary coefficients may be derived using the telegrapher's equation. In the field of transmission lines, the term transmission coefficient has a different meaning despite the similarity of name: it is the companion of the reflection coefficient.

Definition
The propagation constant, symbol $γ$, for a given system is defined by the ratio of the complex amplitude at the source of the wave to the complex amplitude at some distance $x$, such that,

 * $$ \frac{A_0}{A_x} = e^{\gamma x} $$

Inverting the above equation and isolating $γ$ results in the quotient of the complex amplitude ratio's natural logarithm and the distance $x$ traveled:

 * $$\gamma=\ln\left(\frac{A_0}{A_x}\right)/x$$

Since the propagation constant is a complex quantity we can write:

where
 * $α$, the real part, is called the attenuation constant
 * $β$, the imaginary part, is called the phase constant
 * $$i \equiv j \equiv \sqrt{ -1\ }\ ;$$ more often $j$  is used for electrical circuits.

That $β$ does indeed represent phase can be seen from Euler's formula:

 * $$ e^{i\theta} = \cos{\theta} + i \sin{\theta}\ $$

which is a sinusoid which varies in phase as $θ$ varies but does not vary in amplitude because

 * $$ \left| e^{i\theta} \right| = \sqrt{ \cos^2{\theta} + \sin^2{\theta}\;} = 1 $$

The reason for the use of base $e$ is also now made clear. The imaginary phase constant, $i β$, can be added directly to the attenuation constant, $α$, to form a single complex number that can be handled in one mathematical operation provided they are to the same base. Angles measured in radians require base $e$, so the attenuation is likewise in base $e$.

The propagation constant for conducting lines can be calculated from the primary line coefficients by means of the relationship

 * $$ \gamma= \sqrt{ Z Y\ }$$

where

 * $$ Z = R + i\ \omega L\ ,$$ the series impedance of the line per unit length and,

 * $$ Y = G + i\ \omega C\ ,$$ the shunt admittance of the line per unit length.

Plane wave
The propagation factor of a plane wave traveling in a linear media in the $x$ direction is given by $$ P = e^{-\gamma x} $$ where The sign convention is chosen for consistency with propagation in lossy media. If the attenuation constant is positive, then the wave amplitude decreases as the wave propagates in the $x$ direction.
 * $\gamma = \alpha + i\ \beta = \sqrt{i\ \omega\ \mu\ (\sigma + i\ \omega \varepsilon)\ }\ $
 * $$ x = $$ distance traveled in the $x$ direction
 * $$ \alpha =\ $$ attenuation constant in the units of nepers/meter
 * $$ \beta =\ $$ phase constant in the units of radians/meter
 * $$ \omega=\ $$ frequency in radians/second
 * $$ \sigma =\ $$ conductivity of the media
 * $$\varepsilon = \varepsilon' - i\ \varepsilon'' \ $$ = complex permitivity of the media
 * $$\mu = \mu' - i\ \mu'' \;$$ = complex permeability of the media
 * $$i \equiv \sqrt{-1\ }$$

Wavelength, phase velocity, and skin depth have simple relationships to the components of the propagation constant: $$ \lambda = \frac {2 \pi}{\beta} \qquad v_p = \frac{\omega}{\beta}  \qquad   \delta =  \frac{1}{\alpha} $$

Attenuation constant
In telecommunications, the term attenuation constant, also called attenuation parameter or attenuation coefficient, is the attenuation of an electromagnetic wave propagating through a medium per unit distance from the source. It is the real part of the propagation constant and is measured in nepers per metre. A neper is approximately 8.7 dB. Attenuation constant can be defined by the amplitude ratio

 * $$\left|\frac{A_0}{A_x}\right|=e^{\alpha x}$$

The propagation constant per unit length is defined as the natural logarithm of the ratio of the sending end current or voltage to the receiving end current or voltage, divided by the distance x involved:

 * $$\alpha=\ln\left(\left|\frac{A_0}{A_x}\right|\right)/x$$

Conductive lines
The attenuation constant for conductive lines can be calculated from the primary line coefficients as shown above. For a line meeting the distortionless condition, with a conductance G in the insulator, the attenuation constant is given by

 * $$\alpha=\sqrt{RG}\,\!$$

however, a real line is unlikely to meet this condition without the addition of loading coils and, furthermore, there are some frequency dependent effects operating on the primary "constants" which cause a frequency dependence of the loss. There are two main components to these losses, the metal loss and the dielectric loss.

The loss of most transmission lines are dominated by the metal loss, which causes a frequency dependency due to finite conductivity of metals, and the skin effect inside a conductor. The skin effect causes R along the conductor to be approximately dependent on frequency according to

 * $$R \propto \sqrt{\omega}$$

Losses in the dielectric depend on the loss tangent (tan δ) of the material divided by the wavelength of the signal. Thus they are directly proportional to the frequency.

 * $$\alpha_d={{\pi}\sqrt{\varepsilon_r}\over{\lambda}}{\tan \delta}$$

Optical fibre
The attenuation constant for a particular propagation mode in an optical fiber is the real part of the axial propagation constant.

Phase constant
In electromagnetic theory, the phase constant, also called phase change constant, parameter or coefficient is the imaginary component of the propagation constant for a plane wave. It represents the change in phase per unit length along the path travelled by the wave at any instant and is equal to the real part of the angular wavenumber of the wave. It is represented by the symbol β and is measured in units of radians per unit length.

From the definition of (angular) wavenumber for transverse electromagnetic (TEM) waves in lossless media,
 * $$k = \frac{2\pi}{\lambda} = \beta$$

For a transmission line, the telegrapher's equations tells us that the wavenumber must be proportional to frequency for the transmission of the wave to be undistorted in the time domain. This includes, but is not limited to, the ideal case of a lossless line. The reason for this condition can be seen by considering that a useful signal is composed of many different wavelengths in the frequency domain. For there to be no distortion of the waveform, all these waves must travel at the same velocity so that they arrive at the far end of the line at the same time as a group. Since wave phase velocity is given by

 * $$v_p = \frac{\lambda}{T} = \frac{f}{\tilde{\nu}} = \frac{\omega}{\beta},$$

it is proved that β is required to be proportional to ω. In terms of primary coefficients of the line, this yields from the telegrapher's equation for a distortionless line the condition

 * $$\beta = \omega \sqrt{LC},$$

where L and C are, respectively, the inductance and capacitance per unit length of the line. However, practical lines can only be expected to approximately meet this condition over a limited frequency band.

In particular, the phase constant $$ \beta $$ is not always equivalent to the wavenumber $$k$$. The relation
 * $$ \beta = k $$

applies to the TEM wave, which travels in free space or TEM-devices such as the coaxial cable and two parallel wires transmission lines. Nevertheless, it does not apply to the TE wave (transverse electric wave) and TM wave (transverse magnetic wave). For example, in a hollow waveguide where the TEM wave cannot exist but TE and TM waves can propagate,

 * $$k=\frac{\omega}{c} $$

 * $$\beta=k\sqrt{1-\frac{\omega_c^2}{\omega^2}}$$

Here $$ \omega_{c} $$ is the cutoff frequency. In a rectangular waveguide, the cutoff frequency is

 * $$ \omega_{c} = c \sqrt{\left(\frac{n \pi}{a}\right)^2 + \left(\frac{m \pi}{b}\right) ^2}, $$

where $$m,n \ge 0$$ are the mode numbers for the rectangle's sides of length $$a$$ and $$b$$ respectively. For TE modes, $$ m,n \ge 0$$ (but $$ m = n = 0$$ is not allowed), while for TM modes $$ m,n \ge 1 $$.

The phase velocity equals

 * $$v_p=\frac{\omega}{\beta}=\frac{c}{\sqrt{1-\frac{\omega_\mathrm{c}^2}{\omega^2}}}>c $$

Filters and two-port networks
The term propagation constant or propagation function is applied to filters and other two-port networks used for signal processing. In these cases, however, the attenuation and phase coefficients are expressed in terms of nepers and radians per network section rather than per unit length. Some authors make a distinction between per unit length measures (for which "constant" is used) and per section measures (for which "function" is used).

The propagation constant is a useful concept in filter design which invariably uses a cascaded section topology. In a cascaded topology, the propagation constant, attenuation constant and phase constant of individual sections may be simply added to find the total propagation constant etc.

Cascaded networks

The ratio of output to input voltage for each network is given by

 * $$\frac{V_1}{V_2}=\sqrt{\frac{Z_{I1}}{Z_{I2}}}e^{\gamma_1}$$
 * $$\frac{V_2}{V_3}=\sqrt{\frac{Z_{I2}}{Z_{I3}}}e^{\gamma_2}$$
 * $$\frac{V_3}{V_4}=\sqrt{\frac{Z_{I3}}{Z_{I4}}}e^{\gamma_3}$$

The terms $$\sqrt{\frac{Z_{In}}{Z_{Im}}}$$ are impedance scaling terms and their use is explained in the image impedance article.

The overall voltage ratio is given by

 * $$\frac{V_1}{V_4}=\frac{V_1}{V_2}\cdot\frac{V_2}{V_3}\cdot\frac{V_3}{V_4}=\sqrt{\frac{Z_{I1}}{Z_{I4}}}e^{\gamma_1+\gamma_2+\gamma_3}$$

Thus for n cascaded sections all having matching impedances facing each other, the overall propagation constant is given by

 * $$\gamma_\mathrm{total}=\gamma_1 + \gamma_2 + \gamma_3 + \cdots + \gamma_n$$

title: Propagation constant


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Propagation path obstruction

In telecommunication, a propagation path obstruction is a man-made or natural physical feature that lies near enough to a radio path to cause a measurable effect on path loss, exclusive of reflection effects. An obstruction may lie to the side, above, or below the path. Ridges, bridges, cliffs, buildings, and trees are examples of obstructions. If the clearance from the nearest anticipated path position, over the expected range of Earth radius k-factor, exceeds 0.6 of the first Fresnel zone radius, the feature is not normally considered an obstruction.

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

title: Propagation path obstruction


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Protective distribution system

A protective distribution system (PDS), also called protected distribution system, is a US government term for wireline or fiber-optics telecommunication system that includes terminals and adequate acoustical, electrical, electromagnetic, and physical safeguards to permit its use for the unencrypted transmission of classified information. At one time these systems were called "approved circuits".

A complete protected distribution system includes the subscriber and terminal equipment and the interconnecting lines.

Description
The purpose of a PDS is to deter, detect and/or make difficult physical access to the communication lines carrying national security information. A specification called the National Security Telecommunications and Information Systems Security Instruction (NSTISSI) 7003 was issued in December 1996 by the Committee on National Security Systems. Approval authority, standards, and guidance for the design, installation, and maintenance for PDS are provided by NSTISSI 7003 to U.S. government departments and agencies and their contractors and vendors. This instruction describes the requirements for all PDS installations within the U.S. and for low and medium threat locations outside the U.S. PDS is commonly used to protect SIPRNet and JWICS networks. The document superseded one numbered NASCI 4009 on Protected Distribution Systems, dated December 30, 1981, and part of a document called NACSEM 5203, that covered guidelines for facility design, using the designations "red" and "black".

There are two types of PDS: hardened distribution systems and simple distribution systems.

Hardened distribution
Hardened distribution PDSs provide significant physical protection and can be implemented in three forms: hardened carrier PDSs, alarmed carrier PDSs and continuously viewed carrier PDSs.

Hardened carrier
In a hardened carrier PDS, the data cables are installed in a carrier constructed of electrical metallic tubing (EMT), ferrous conduit or pipe, or rigid sheet steel ducting. All of the connections in a Hardened Carrier System are permanently sealed completely around all surfaces with welds, epoxy or other such sealants. If the hardened carrier is buried under ground, to secure cables running between buildings for example, the carrier containing the cables is encased in concrete.

With a hardened carrier system, detection is accomplished via human inspections that are required to be performed periodically. Therefore, hardened carriers are installed below ceilings or above flooring so they can be visually inspected to ensure that no intrusions have occurred. These periodic visual inspections (PVIs) occur at a frequency dependent upon the level of threat to the environment, the security classification of the data, and the access control to the area.

Alarmed carrier
As an alternative to conducting human visual inspections, an alarmed carrier PDS may be constructed to automate the inspection process through electronic monitoring with an alarm system. In an Alarmed Carrier PDS, the carrier system is “alarmed” with specialized optical fibers deployed within the conduit for the purpose of sensing acoustic vibrations that usually occur when an intrusion is being attempted on the conduit in order to gain access to the cables.

Alarmed carrier PDS offers several advantages over hardened carrier PDS:

 * 1) Provides continuous monitoring 24/7/365
 * 2) Eliminates the requirement for periodic visual inspections
 * 3) Allows the carrier to be hidden above the ceiling or below the floor, since periodic visual inspections are not required
 * 4) Eliminates the need for the welding and epoxying of the connections
 * 5) Eliminates the requirement for concrete encasement outdoors
 * 6) Eliminates the need to lock down manhole covers
 * 7) Enables rapid redeployment for evolving network arrangements

Legacy alarmed carrier systems monitor the carrier containing the cables being protected. More advanced systems monitor the fibers within, or intrinsic to, the cables being protected to turn those cables into sensors, which detect intrusion attempts.

Depending on the government organization, utilizing an alarmed carrier PDS in conjunction with interlocking armored cable may, in some cases, allow for the elimination of the carrier systems altogether. In these instances, the cables being protected can be installed in existing conveyance (wire basket, ladder rack) or suspended cabling (on D-rings, J-Hooks, etc.).

Continuously viewed carrier
A Continuously Viewed Carrier PDS is one that is under continuous observation, 24 hours per day (including when operational). Such circuits may be grouped together, but should be separated from all non-continuously viewed circuits ensuring an open field of view. Standing orders should include the requirement to investigate any attempt to disturb the PDS. Appropriate security personnel should investigate the area of attempted penetration within 15 minutes of discovery. This type of hardened carrier is not used for Top Secret or special category information for non-U.S. UAA. UAA is an Uncontrolled Access Area (UAA). Like definitions include Controlled Access Area (CAA) and Restricted Access Area (RAA). A Secure Room (SR) offers the highest degree of protection.

Therefore, from the least protected (least secure) to the most protected is as follows:

UAA RAA CAA SR

Simple distribution
Simple distribution PDSs are afforded a reduced level of physical security protection as compared to a hardened distribution PDS. They use a simple carrier system and the following means are acceptable under NSTISSI 7003:
 * 1) The data cables should be installed in a carrier
 * 2) The carrier can be constructed of any material (e.g., wood, PVT, EMT, ferrous conduit)
 * 3) The joints and access points should be secured and be controlled by personnel cleared to the highest level of data handled by the PDS
 * 4) The carrier is to be inspected in accordance with the requirements of NSTISSI 7003

title: Protective distribution system


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Protocol-control information

In telecommunication, the term protocol-control information or PCI has the following meanings:

 * 1)  The queries and replies among communications equipment to determine the respective capabilities of each end of the communications link.
 * 2)  For layered systems, information exchanged between entities of a given layer, via the service provided by the next lower layer, to coordinate their joint operation.

title: Protocol-control information


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Protocol data unit

In telecommunications, a protocol data unit (PDU) is a single unit of information transmitted among peer entities of a computer network. It is composed of protocol-specific control information and user data. In the layered architectures of communication protocol stacks, each layer implements protocols tailored to the specific type or mode of data exchange.

For example, the Transmission Control Protocol (TCP) implements a connection-oriented transfer mode, and the PDU of this protocol is called a segment, while the User Datagram Protocol (UDP) uses datagrams as protocol data units for connectionless communication. A layer lower in the Internet protocol suite, at the Internet layer, the PDU is called a packet, irrespective of its payload type.

Packet-switched data networks
In the context of packet switching data networks, a protocol data unit (PDU) is best understood in relation to a service data unit (SDU).

The features or services of the network are implemented in distinct layers. The physical layer sends ones and zeros across a wire or fiber. The data link layer then organizes these ones and zeros into chunks of data and gets them safely to the right place on the wire. The network layer transmits the organized data over multiple connected networks, and the transport layer delivers the data to the right software application at the destination.

Between the layers (and between the application and the top-most layer), the layers pass service data units (SDUs) across interfaces. The higher layer understands the structure of the data in the SDU, but the lower layer at the interface does not; moreover, the lower layer treats the SDU as the payload, undertaking to get it to the same interface at the destination. In order to do this, the protocol (lower) layer will add to the SDU certain data it needs to perform its function; which is called encapsulation. For example, it might add a port number to identify the application, a network address to help with routing, a code to identify the type of data in the packet and error-checking information. All this additional information, plus the original service data unit from the higher layer, constitutes the protocol data unit at this layer.

The SDU and metadata added by the lower layer can be larger than the maximum size of that layer's PDU (known as the maximum transmission unit; MTU). When this is the case, the PDU must be split into multiple payloads of a size suitable for transmission or processing by the lower layer; a process known as IP fragmentation.

The significance of this is that the PDU is the structured information that is passed to a matching protocol layer further along on the data's journey that allows the layer to deliver its intended function or service. The matching layer, or "peer", decodes the data to extract the original service data unit, decide if it is error-free and where to send it next, etc. Unless we have already arrived at the lowest (physical) layer, the PDU is passed to the peer using services of the next lower layer in the protocol "stack". When the PDU passes over the interface from the layer that constructed it to the layer that merely delivers it (and therefore does not understand its internal structure), it becomes a service data unit to that layer. The addition of addressing and control information (encapsulation) to an SDU to form a PDU and the passing of that PDU to the next lower layer as an SDU repeats until the lowest layer is reached and the data passes over some medium as a physical signal.

The above process can be likened to the mail system in which a letter (SDU) is placed in an envelope on which is written an address (addressing and control information) making it a PDU. The sending post office might look only at the postcode and place the letter in a mailbag so that the address on the envelope can no longer be seen, making it now an SDU. The mailbag is labeled with the destination postcode and so becomes a PDU until it is combined with other bags in a crate when it is now an SDU, and the crate is labeled with the region to which all the bags are to be sent, making the crate a PDU. When the crate reaches the destination matching its label, it is opened and the bags (SDUs) removed only to become PDUs when someone reads the code of the destination post office. The letters themselves are SDUs when the bags are opened but become PDUs when the address is read for final delivery. When the addressee finally opens the envelope, the top-level SDU, the letter itself, emerges.

OSI model
Protocol data units of the OSI model are:

 * The Layer 4: transport layer PDU is the segment or the datagram.
 * The Layer 3: network layer PDU is the packet.
 * The Layer 2: data link layer PDU is the frame.
 * The Layer 1: physical layer PDU is the bit or, more generally, symbol.

Given a context pertaining to a specific OSI layer, PDU is sometimes used as a synonym for its representation at that layer.

Internet protocol suite
Protocol data units for the Internet protocol suite are:

 * The transport layer PDU is the TCP segment for TCP, and the datagram for UDP
 * The Internet layer PDU is the packet.
 * The link layer PDU is the frame.

On TCP/IP over Ethernet, the data on the physical layer is carried in Ethernet frames.

Internetwork packet exchange (IPX)

 * For IPX, the IPX packet is the network layer PDU for IPX, and can simultaneously be used in the transport layer as well.
 * The SPX packet on top of IPX, is a transport layer PDU.
 * The link-layer PDU is the frame.

ATM
The data link layer PDU in Asynchronous Transfer Mode (ATM) networks is called a cell.

Media access control protocol data unit
A media access control protocol data unit (MAC PDU or MPDU) is a message that is exchanged between media access control (MAC) entities in a communication system based on the layered OSI model.

In systems where the MPDU may be larger than the MAC service data unit (MSDU), the MPDU may include multiple MSDUs as a result of packet aggregation. In systems where the MPDU is smaller than the MSDU, then one MSDU may generate multiple MPDUs as a result of packet segmentation.

title: Protocol data unit


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Provisioning (technology)

In telecommunication, provisioning involves the process of preparing and equipping a network to allow it to provide new services to its users. In National Security/Emergency Preparedness telecommunications services, "provisioning" equates to "initiation" and includes altering the state of an existing priority service or capability.

The concept of network provisioning or service mediation, mostly used in the telecommunication industry, refers to the provisioning of the customer's services to the network elements, which are various equipment connected in that network communication system. Generally in telephony provisioning this is accomplished with network management database table mappings. It requires the existence of networking equipment and depends on network planning and design.

In a modern signal infrastructure employing information technology (IT) at all levels, there is no possible distinction between telecommunications services and "higher level" infrastructure. Accordingly, provisioning configures any required systems, provides users with access to data and technology resources, and refers to all enterprise-level information-resource management involved.

Organizationally, a CIO typically manages provisioning, necessarily involving human resources and IT departments cooperating to:

 * Give users access to data repositories or grant authorization to systems, network applications and databases based on a unique user identity.
 * Appropriate for their use hardware resources, such as computers, mobile phones and pagers.

As its core, the provisioning process monitors access rights and privileges to ensure the security of an enterprise's resources and user privacy. As a secondary responsibility, it ensures compliance and minimizes the vulnerability of systems to penetration and abuse. As a tertiary responsibility, it tries to reduce the amount of custom configuration using boot image control and other methods that radically reduce the number of different configurations involved.

Discussion of provisioning often appears in the context of virtualization, orchestration, utility computing, cloud computing, and open-configuration concepts and projects. For instance, the OASIS Provisioning Services Technical Committee (PSTC) defines an XML-based framework for exchanging user, resource, and service-provisioning information - SPML (Service Provisioning Markup Language) for "managing the provisioning and allocation of identity information and system resources within and between organizations".

Once provisioning has taken place, the process of SysOpping ensures the maintenance of services to the expected standards. Provisioning thus refers only to the setup or startup part of the service operation, and SysOpping to the ongoing support.

Network provisioning
One type of provisioning. The services which are assigned to the customer in the customer relationship management (CRM) have to be provisioned on the network element which is enabling the service and allows the customer to actually use the service. The relation between a service configured in the CRM and a service on the network elements is not necessarily a one-to-one relationship; for example, services like Microsoft Media Server (mms://) can be enabled by more than one network element.

During the provisioning, the service mediation device translates the service and the corresponding parameters of the service to one or more services/parameters on the network elements involved. The algorithm used to translate a system service into network services is called provisioning logic.

Electronic invoice feeds from your carriers can be automatically downloaded directly into the core of the telecom expense management (TEM) software and it will immediately conduct an audit of each single line item charge all the way down to the User Support and Operations Center (USOC) level. The provisioning software will capture each circuit number provided by all of your carriers and if billing occurs outside of the contracted rate an exception rule will trigger a red flag and notify the pre-established staff member to review the billing error.

Server provisioning
Server provisioning is a set of actions to prepare a server with appropriate systems, data and software, and make it ready for network operation. Typical tasks when provisioning a server are: select a server from a pool of available servers, load the appropriate software (operating system, device drivers, middleware, and applications), appropriately customize and configure the system and the software to create or change a boot image for this server, and then change its parameters, such as IP address, IP Gateway to find associated network and storage resources (sometimes separated as resource provisioning) to audit the system. By auditing the system, you ensure OVAL compliance with limit vulnerability, ensure compliance, or install patches. After these actions, you restart the system and load the new software. This makes the system ready for operation. Typically an internet service provider (ISP) or network operations center will perform these tasks to a well-defined set of parameters, for example, a boot image that the organization has approved and which uses software it has license to. Many instances of such a boot image create a virtual dedicated host.

There are many software products available to automate the provisioning of servers, services and end-user devices. Examples: BMC Bladelogic Server Automation, HP Server Automation, IBM Tivoli Provisioning Manager, Redhat Kickstart, xCAT, HP Insight CMU, etc. Middleware and applications can be installed either when the operating system is installed or afterwards by using an Application Service Automation tool. Further questions are addressed in academia such as when provisioning should be issued and how many servers are needed in multi-tier, or multi-service applications.

In cloud computing, servers may be provisioned via a web user interface or an application programming interface (API). One of the unique things about cloud computing is how rapidly and easily this can be done. Monitoring software can be used to trigger automatic provisioning when existing resources become too heavily stressed.

In short, server provisioning configures servers based on resource requirements. The use of a hardware or software component (e.g. single/dual processor, RAM, HDD, RAID Controller, a number of LAN cards, applications, OS, etc.) depends on the functionality of the server, such as ISP, virtualization, NOS, or voice processing. Server redundancy depends on the availability of servers in the organization. Critical applications have less downtime when using cluster servers, RAID, or a mirroring system.

Service used by most larger-scale centers in part to avoid this. Additional resource provisioning may be done per service.

There are several software on the market for server provisioning such as Cobbler or HP Intelligent Provisioning.

User provisioning
User provisioning refers to the creation, maintenance and deactivation of user objects and user attributes, as they exist in one or more systems, directories or applications, in response to automated or interactive business processes. User provisioning software may include one or more of the following processes: change propagation, self-service workflow, consolidated user administration, delegated user administration, and federated change control. User objects may represent employees, contractors, vendors, partners, customers or other recipients of a service. Services may include electronic mail, inclusion in a published user directory, access to a database, access to a network or mainframe, etc. User provisioning is a type of identity management software, particularly useful within organizations, where users may be represented by multiple objects on multiple systems and multiple instances.

Self-service provisioning for cloud computing services
On-demand self-service is described by the National Institute of Standards and Technology (NIST) as an essential characteristic of cloud computing. The self-service nature of cloud computing lets end users obtain and remove cloud services―including applications, the infrastructure supporting the applications, and configuration― themselves without requiring the assistance of an IT staff member. The automatic self-servicing may target different application goals and constraints (e.g. deadlines and cost), as well as handling different application architectures (e.g., bags-of-tasks and workflows). Cloud users can obtain cloud services through a cloud service catalog or a self-service portal. Because business users can obtain and configure cloud services themselves, this means IT staff can be more productive and gives them more time to manage cloud infrastructures.

One downside of cloud service provisioning is that it is not instantaneous. A cloud virtual machine (VM) can be acquired at any time by the user, but it may take up to several minutes for the acquired VM to be ready to use. The VM startup time is dependent on factors, such as image size, VM type, data center location, and number of VMs. Cloud providers have different VM startup performance.

Mobile subscriber provisioning
Mobile subscriber provisioning refers to the setting up of new services, such as GPRS, MMS and Instant Messaging for an existing subscriber of a mobile phone network, and any gateways to standard Internet chat or mail services. The network operator typically sends these settings to the subscriber's handset using SMS text services or HTML, and less commonly WAP, depending on what the mobile operating systems can accept.

A general example of provisioning is with data services. A mobile user who is using his or her device for voice calling may wish to switch to data services in order to read emails or browse the Internet. The mobile device's services are "provisioned" and thus the user is able to stay connected through push emails and other features of smartphone services.

Device management systems can benefit end-users by incorporating plug-and-play data services, supporting whatever device the end-user is using.. Such a platform can automatically detect devices in the network, sending them settings for immediate and continued usability. The process is fully automated, keeping the history of used devices and sending settings only to subscriber devices which were not previously set. One method of managing mobile updates is to filter IMEI/IMSI pairs. Some operators report activity of 50 over-the-air settings update files per second.

Mobile content provisioning
This refers to delivering mobile content, such as mobile internet to a mobile phone, agnostic of the features of said device. These may include operating system type and versions, Java version, browser version, screen form factors, audio capabilities, language settings and many other characteristics. As of April 2006, an estimated 5,000 permutations were relevant. Mobile content provisioning facilitates a common user experience, though delivered on widely different handsets.

Mobile device provisioning
Provisioning devices involves delivering configuration data and policy settings to the mobile devices from a central point – Mobile device management system tools.

Internet access provisioning
When getting a customer online, the client system must be configured. Depending on the connection technology (e.g., DSL, Cable, Fibre), the client system configuration may include:
 * Modem configuration
 * Network authentication
 * Installing drivers
 * Setting up Wireless LAN
 * Securing operating system (primarily for Windows)
 * Configuring browser provider-specifics
 * E-mail provisioning (create mailboxes and aliases)
 * E-mail configuration in client systems
 * Installing additional support software or add-on packages

There are four approaches to provisioning internet access:

 * Hand out manuals: Manuals are a great help for experienced users, but inexperienced users will need to call the support hotline several times until all internet services are accessible. Every unintended change in the configuration, by user mistake or due to a software error, results in additional calls.
 * On-site setup by a technician: Sending a technician on-site is the most reliable approach from the provider's point of view, as the person ensures that the internet access is working, before leaving the customer's premises. This advantage comes at high costs – either for the provider or the customer, depending on the business model. Furthermore, it is inconvenient for customers, as they have to wait until they get an installation appointment and because they need to take a day off from work. For repairing an internet connection on-site or phone support will be needed again.
 * Server-side remote setup: Server-side modem configuration uses a protocol called TR-069. It is widely established and reliable. At the current stage it can only be used for modem configuration. Protocol extensions are discussed, but not yet practically implemented, particularly because most client devices and applications do not support them yet. All other steps of the provisioning process are left to the user, typically causing many rather long calls to the support hotline.
 * Installation CD: Also called a "client-side self-service installation" CD, it can cover the entire process from modem configuration to setting up client applications, including home networking devices. The software typically acts autonomously, i.e., it doesn't need an online connection and an expensive backend infrastructure. During such an installation process the software usually also install diagnosis and self-repair applications that support customers in case of problems, avoiding costly hotline calls. Such client-side applications also open completely new possibilities for marketing, cross- and upselling. Such solutions come from highly specialised companies or directly from the provider's development department.

title: Provisioning (technology)


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Pseudorandom noise

In cryptography, pseudorandom noise (PRN ) is a signal similar to noise which satisfies one or more of the standard tests for statistical randomness. Although it seems to lack any definite pattern, pseudorandom noise consists of a deterministic sequence of pulses that will repeat itself after its period.

In cryptographic devices, the pseudorandom noise pattern is determined by a key and the repetition period can be very long, even millions of digits.

Pseudorandom noise is used in some electronic musical instruments, either by itself or as an input to subtractive synthesis, and in many white noise machines.

In spread-spectrum systems, the receiver correlates a locally generated signal with the received signal. Such spread-spectrum systems require a set of one or more "codes" or "sequences" such that
 * Like random noise, the local sequence has a very low correlation with any other sequence in the set, or with the same sequence at a significantly different time offset, or with narrow band interference, or with thermal noise.
 * Unlike random noise, it must be easy to generate exactly the same sequence at both the transmitter and the receiver, so the receiver's locally generated sequence has a very high correlation with the transmitted sequence.

In a direct-sequence spread spectrum system, each bit in the pseudorandom binary sequence is known as a chip and the inverse of its period as chip rate; compare bit rate and symbol rate.

In a frequency-hopping spread spectrum sequence, each value in the pseudorandom sequence is known as a channel number and the inverse of its period as the hop rate. FCC Part 15 mandates at least 50 different channels and at least a 2.5 Hz hop rate for narrow band frequency-hopping systems.

GPS satellites broadcast data at a rate of 50 data bits per second – each satellite modulates its data with one PN bit stream at 1.023 million chips per second and the same data with another PN bit stream at 10.23 million chips per second. GPS receivers correlate the received PN bit stream with a local reference to measure distance. GPS is a receive-only system that uses relative timing measurements from several satellites (and the known positions of the satellites) to determine receiver position.

Other range-finding applications involve two-way transmissions. A local station generates a pseudorandom bit sequence and transmits it to the remote location (using any modulation technique). Some object at the remote location echoes this PN signal back to the location station – either passively, as in some kinds of radar and sonar systems, or using an active transponder at the remote location, as in the Apollo Unified S-band system. By correlating a (delayed version of) the transmitted signal with the received signal, a precise round trip time to the remote location can be determined and thus the distance.

PN code
A pseudo-noise code (PN code) or pseudo-random-noise code (PRN code) is one that has a spectrum similar to a random sequence of bits but is deterministically generated. The most commonly used sequences in direct-sequence spread spectrum systems are maximal length sequences, Gold codes, Kasami codes, and Barker codes.

title: Pseudorandom noise


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Psophometer

In telecommunications, a psophometer is an instrument that measures the perceptible noise of a telephone circuit.

The core of the meter is based on a true RMS voltmeter, which measures the level of the noise signal. This was used for the first psophometers, in the 1930s. As the human-perceived level of noise is more important for telephony than their raw voltage, a modern psophometer incorporates a weighting network to represent this perception. The characteristics of the weighting network depend on the type of circuit under investigation, such as whether the circuit is used to normal speech standards (300 Hz – 3.3 kHz), or for high-fidelity broadcast-quality sound (50 Hz – 15 kHz).

Etymology
The name was coined in the 1930s, on a basis from ψόφος, itself derived from ψό. It is unrelated to σοφός.

The '-meter' suffix μέτρον was already widely used in English, but also derives originally from Greek.

title: Psophometer


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Psophometric voltage

Psophometric voltage is a circuit noise voltage measured with a psophometer that includes a CCIF-1951 weighting network.

"Psophometric voltage" should not be confused with "psophometric emf," i.e., the emf in a generator or line with 600 Ω internal resistance. For practical purposes, the psophometric emf is twice the corresponding psophometric voltage.

Psophometric voltage readings, V, in millivolts, are commonly converted to dBm(psoph) by dBm(psoph) = 20 log10V – 57.78.

title: Psophometric voltage


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Public land mobile network

In telecommunication, a public land mobile network (PLMN) is a combination of wireless communication services offered by a specific operator in a specific country. A PLMN typically consists of several cellular technologies like GSM/2G, UMTS/3G, LTE/4G, NR/5G, offered by a single operator within a given country, often referred to as a cellular network.

PLMN code
A PLMN is identified by a globally unique PLMN code, which consists of a MCC (Mobile Country Code) and MNC (Mobile Network Code). Hence, it is a five- to six-digit number identifying a country, and a mobile network operator in that country, usually represented in the form 001-01 or 001–001.

A PLMN is part of a:
 * Location Area Identity (LAI) (PLMN and Location Area Code)
 * Cell Global Identity (CGI) (LAI and Cell Identifier)
 * IMSI (see PLMN code and IMSI)

Leading zeros in PLMN codes
Note that an MNC can be of two-digit form and three-digit form with leading zeros. It is administered by the respective national numbering plan administrator. From PLMN assignments, it is apparent that such dualities of two-digit and three-digit MNCs with the same number value are avoided (see the list of mobile country codes and mobile network codes). An example for an actual three-digit/two-digit MNC with leading zeros is in Bermuda MCC, 350-007 and 350-00, 350-01.

PLMN code and IMSI
The IMSI, which identifies a SIM or USIM for one subscriber, typically starts with the PLMN code. For example, an IMSI belonging to the PLMN 262-33 would look like 262330000000001. Mobile phones use this to detect roaming, so that a mobile phone subscribed on a network with a PLMN code that mismatches the start of the USIM's IMSI will typically display an "R" on the icon that indicates connection strength.

PLMN services
A PLMN typically offers the following services to a mobile subscriber:

 * Emergency calls to local Fire/Ambulance/Police stations.
 * Voice calls to/from any other PLMN ("cellular network") or PSTN ("landline"/VoIP).
 * Short message service (SMS) services to/from any other PLMN or SIP service (the original form of texting on a mobile phone, now often replaced by Messaging apps).
 * Multimedia Messaging Service (MMS) services to/from any other PLMN or SIP service.
 * Unstructured Supplementary Service Data (USSD) for operator specific interactions (e.g. dialing "*#100#" to indicate the current balance).
 * Internet data connectivity for arbitrary services, e.g. via GPRS in GSM, IuPS in UMTS, or LTE.

The availability, quality and bandwidth of these services strongly depends on the particular technology used to implement a PLMN.

title: Public land mobile network


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Pulse

In medicine, a pulse represents the tactile arterial palpation of the cardiac cycle (heartbeat) by fingertips. The pulse may be palpated in any place that allows an artery to be compressed near the surface of the body, such as at the neck (carotid artery), wrist (radial artery or ulnar artery), at the groin (femoral artery), behind the knee (popliteal artery), near the ankle joint (posterior tibial artery), and on foot (dorsalis pedis artery). The radial pulse is commonly measured using three fingers. This has a reason: the finger closest to the heart is used to occlude the pulse pressure, the middle finger is used get a crude estimate of the blood pressure, and the finger most distal to the heart (usually the ring finger) is used to nullify the effect of the ulnar pulse as the two arteries are connected via the palmar arches (superficial and deep). The study of the pulse is known as sphygmology.

Physiology
Claudius Galen was perhaps the first physiologist to describe the pulse. The pulse is an expedient tactile method of determination of systolic blood pressure to a trained observer. Diastolic blood pressure is non-palpable and unobservable by tactile methods, occurring between heartbeats.

Pressure waves generated by the heart in systole move the arterial walls. Forward movement of blood occurs when the boundaries are pliable and compliant. These properties form enough to create a palpable pressure wave.

Pulse velocity, pulse deficits and much more physiologic data are readily and simplistically visualized by the use of one or more arterial catheters connected to a transducer and oscilloscope. This invasive technique has been commonly used in intensive care since the 1970s.

The pulse may be further indirectly observed under light absorbances of varying wavelengths with assigned and inexpensively reproduced mathematical ratios. Applied capture of variances of light signal from the blood component hemoglobin under oxygenated vs. deoxygenated conditions allows the technology of pulse oximetry.

Rate
The rate of the pulse can be observed and measured on the outside of an artery by tactile or visual means. It is recorded as arterial beats per minute or BPM. Although the pulse and heart beat are related, they are not the same. For example, there is a delay between the onset of the heart beat and the onset of the pulse, known as the pulse transit time, which varies by site. Similarly measurements of heart rate variability and pulse rate variability differ.

In healthy people, the pulse rate is close to the heart rate, as measured by ECG. Measuring the pulse rate is therefore a convenient way to estimate the heart rate. Pulse deficit is a condition in which a person has a difference between their pulse rate and heart rate. It can be observed by simultaneous palpation at the radial artery and auscultation using a stethoscope at the PMI, near the heart apex, for example. Typically, in people with pulse deficit, heart beats do not result in pulsations at the periphery, meaning the pulse rate is lower than the heart rate. Pulse deficit has been found to be significant in the context of premature ventricular contraction and atrial fibrillation.

Rhythm
A normal pulse is regular in rhythm and force. An irregular pulse may be due to sinus arrhythmia, ectopic beats, atrial fibrillation, paroxysmal atrial tachycardia, atrial flutter, partial heart block etc. Intermittent dropping out of beats at pulse is called "intermittent pulse". Examples of regular intermittent (regularly irregular) pulse include pulsus bigeminus, second-degree atrioventricular block. An example of irregular intermittent (irregularly irregular) pulse is atrial fibrillation.

Volume
The degree of expansion displayed by artery during diastolic and systolic state is called volume. It is also known as amplitude, expansion or size of pulse.

Hypokinetic pulse
A weak pulse signifies narrow pulse pressure. It may be due to low cardiac output (as seen in shock, congestive cardiac failure), hypovolemia, valvular heart disease (such as aortic outflow tract obstruction, mitral stenosis, aortic arch syndrome) etc.

Hyperkinetic pulse
A bounding pulse signifies high pulse pressure. It may be due to low peripheral resistance (as seen in fever, anemia, thyrotoxicosis,, A-V fistula, Paget's disease, beriberi, liver cirrhosis), increased cardiac output, increased stroke volume (as seen in anxiety, exercise, complete heart block, aortic regurgitation), decreased distensibility of arterial system (as seen in atherosclerosis, hypertension and coarctation of aorta).

The strength of the pulse can also be reported:
 * 0 = Absent
 * 1 = Barely palpable
 * 2 = Easily palpable
 * 3 = Full
 * 4 = Aneurysmal or bounding pulse

Force
Also known as compressibility of pulse. It is a rough measure of systolic blood pressure.

Tension
It corresponds to diastolic blood pressure. A low tension pulse (pulsus mollis), the vessel is soft or impalpable between beats. In high tension pulse (pulsus durus), vessels feel rigid even between pulse beats.

Form
A form or contour of a pulse is palpatory estimation of arteriogram. A quickly rising and quickly falling pulse (pulsus celer) is seen in aortic regurgitation. A slow rising and slowly falling pulse (pulsus tardus) is seen in aortic stenosis.

Equality
Comparing pulses and different places gives valuable clinical information.

A discrepant or unequal pulse between left and right radial artery is observed in anomalous or aberrant course of artery, coarctation of aorta, aortitis, dissecting aneurysm, peripheral embolism etc. An unequal pulse between upper and lower extremities is seen in coarctation to aorta, aortitis, block at bifurcation of aorta, dissection of aorta, iatrogenic trauma and arteriosclerotic obstruction.

Condition of arterial wall
A normal artery is not palpable after flattening by digital pressure. A thick radial artery which is palpable 7.5–10 cm up the forearm is suggestive of arteriosclerosis.

Radio-femoral delay
In coarctation of aorta, femoral pulse may be significantly delayed as compared to radial pulse (unless there is coexisting aortic regurgitation). The delay can also be observed in supravalvar aortic stenosis.

Patterns
Several pulse patterns can be of clinical significance. These include:
 * Anacrotic pulse: notch on the upstroke of the carotid pulse. Two distinct waves (slow initial upstroke and delayed peak, which is close to S2). Present in AS.
 * Dicrotic pulse: is characterized by two beats per cardiac cycle, one systolic and the other diastolic. Physiologically, the dicrotic wave is the result of reflected waves from the lower extremities and aorta. Conditions associated with low cardiac output and high systemic vascular resistance can produce a dicrotic pulse.
 * Pulse deficit: difference in the heart rate by direct cardiac ausculation and by palpation of the peripheral arterial pulse rate when in atrial fibrillation (AF).
 * Pulsus alternans: an ominous medical sign that indicates progressive systolic heart failure. To trained fingertips, the examiner notes a pattern of a strong pulse followed by a weak pulse over and over again. This pulse signals a flagging effort of the heart to sustain itself in systole. It also can be detected in HCM with obstruction.
 * Pulsus bigeminus: indicates a pair of hoofbeats within each heartbeat. Concurrent auscultation of the heart may reveal a gallop rhythm of the native heartbeat.
 * Pulsus bisferiens: is characterized by two beats per cardiac cycle, both systolic, unlike the dicrotic pulse. It is an unusual physical finding typically seen in patients with aortic valve diseases if the aortic valve does not normally open and close. Trained fingertips will observe two pulses to each heartbeat instead of one.
 * Pulsus tardus et parvus, also pulsus parvus et tardus, slow-rising pulse and anacrotic pulse, is weak (parvus), and late (tardus) relative to its expected characteristics. It is caused by a stiffened aortic valve that makes it progressively harder to open, thus requiring increased generation of blood pressure in the left ventricle. It is seen in aortic valve stenosis.
 * Pulsus paradoxus: a condition in which some heartbeats cannot be detected at the radial artery during the inspiration phase of respiration. It is caused by an exaggerated decrease in blood pressure during this phase, and is diagnostic of a variety of cardiac and respiratory conditions of varying urgency, such as cardiac tamponade.
 * Tachycardia: an elevated resting heart rate. In general an electrocardiogram (ECG) is required to identify the type of tachycardia.
 * Pulsatile This description of the pulse implies the intrinsic physiology of systole and diastole. Scientifically, systole and diastole are forces that expand and contract the pulmonary and systemic circulations.
 * A collapsing pulse is a sign of hyperdynamic circulation, which can be seen in AR or PDA.

Common palpable sites
Sites can be divided into peripheral pulses and central pulses. Central pulses include the carotid, femoral, and brachial pulses.

Upper limb

 * Axillary pulse: located inferiorly of the lateral wall of the axilla
 * Brachial pulse: located on the inside of the upper arm near the elbow, frequently used in place of carotid pulse in infants (brachial artery)
 * Radial pulse: located on the lateral of the wrist (radial artery).  It can also be found in the anatomical snuff box.
 * Ulnar pulse: located on the medial of the wrist (ulnar artery).

Lower limb

 * Femoral pulse: located in the inner thigh, at the mid-inguinal point, halfway between the pubic symphysis and anterior superior iliac spine (femoral artery).
 * Popliteal pulse: Above the knee in the popliteal fossa, found by holding the bent knee. The patient bends the knee at approximately 124°, and the health care provider holds it in both hands to find the popliteal artery in the pit behind the knee (popliteal artery).
 * Dorsalis pedis pulse: located on top of the foot, immediately lateral to the extensor of hallucis longus (dorsalis pedis artery).
 * Tibialis posterior pulse: located on the medial side of the ankle, 2 cm inferior and 2 cm posterior to the medial malleolus (posterior tibial artery). It is easily palpable over Pimenta's Point.

Head and neck

 * Carotid pulse: located in the neck (carotid artery). The carotid artery should be palpated gently and while the patient is sitting or lying down. Stimulating its baroreceptors with low palpitation can provoke severe bradycardia or even stop the heart in some sensitive persons. Also, a person's two carotid arteries should not be palpated at the same time. Doing so may limit the flow of blood to the head, possibly leading to fainting or brain ischemia. It can be felt between the anterior border of the sternocleidomastoid muscle, above the hyoid bone and lateral to the thyroid cartilage.
 * Facial pulse: located on the mandible (lower jawbone) on a line with the corners of the mouth (facial artery).
 * Temporal pulse: located on the temple directly in front of the ear (superficial temporal artery).

Although the pulse can be felt in multiple places in the head, people should not normally hear their heartbeats within the head. This is called pulsatile tinnitus, and it can indicate several medical disorders.

Torso

 * Apical pulse: located in the 5th left intercostal space, 1.25 cm lateral to the mid-clavicular line. In contrast with other pulse sites, the apical pulse site is unilateral, and measured not under an artery, but below the heart itself (more specifically, the apex of the heart). See also apex beat.

History
Pulse rate was first measured by ancient Greek physicians and scientists. The first person to measure the heart beat was Herophilus of Alexandria, Egypt (c. 335–280 BC) who designed a water clock to time the pulse. Rumi has mentioned in a poem that "The wise physician measured the patient's pulse and became aware of his condition." It shows the practice was common during Rumi's era and geography. The first person to accurately measure the pulse rate was Santorio Santorii who invented the pulsilogium, a form of pendulum which was later studied by Galileo Galilei. A century later another physician, de Lacroix, used the pulsilogium to test cardiac function.

title: Pulse


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Pulse-address multiple access

In telecommunications, pulse-address multiple access (PAMA) is a channel access method that enables the ability of a communication satellite to receive signals from several Earth terminals simultaneously and to amplify, translate, and relay the signals back to Earth, based on the addressing of each station by an assignment of a unique combination of time and frequency slots.

This ability may be restricted by allowing only some of the terminals access to the satellite at any given time.

title: Pulse-address multiple access


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Pulse duration

In signal processing and telecommunication, pulse duration is the interval between the time, during the first transition, that the amplitude of the pulse reaches a specified fraction (level) of its final amplitude, and the time the pulse amplitude drops, on the last transition, to the same level.

The interval between the 50% points of the final amplitude is usually used to determine or define pulse duration, and this is understood to be the case unless otherwise specified. Other fractions of the final amplitude, e.g., 90% or 1/e, may also be used, as may the root mean square (rms) value of the pulse amplitude.

In radar, the pulse duration is the time the radar's transmitter is energized during each cycle.

title: Pulse duration


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Pulse link repeater

In telecommunications, a pulse link repeater (PLR) is a device that interfaces concatenated E and M signaling paths.

A PLR converts a ground, received from the E lead of one signal path, to −48 VDC, which is applied to the M lead of the concatenated signal path.

In many commercial carrier systems, the channel bank cards or modules have a "PLR" option that permits the direct concatenation of E&M signaling paths, without the need for separate PLR equipment.

title: Pulse link repeater


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Pulsing

Pulsing may refer to:

 * Pulsing (bodywork)
 * Pulse (signal processing)

title: Pulsing


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Pumping

Pumping may refer to:

 * The operation of a pump, for moving a liquid from one location to another
 * The use of a breast pump for extraction of milk
 * Pumping (audio), a creative misuse of dynamic range compression
 * Pumping (computer systems), the number of times data is transmitted per clock cycle
 * Pumping (oil well), injecting chemicals into a wellbore
 * Pumping (noise reduction), an unwanted artifact of some noise reduction systems
 * Pumping lemma, in the theory of formal languages
 * Gastric lavage, cleaning the contents of the stomach
 * Optical pumping, in which light is used to raise electrons from a lower energy level to a higher one
 * Pump (skateboarding), accelerating without pushing off of the ground
 * "Pumping" (My Heart), a 1976 song by Patti Smith Group

title: Pumping


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Push-to-type operation

Push-to-type operation: In telegraph or data transmission systems, that method of communication in which the operator at a station must keep a switch operated in order to send messages.

Push-to-type operation is used in radio systems where the same frequency is employed for transmission and reception.

Push-to-type operation is a derivative form of transmission and may be used in simplex, half-duplex, or duplex operation. Synonym press-to-type operation.

This is similar to Push-to-talk operation for radio phone communications.

title: Push-to-type operation


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Quadrature

Quadrature may refer to:

In signal processing:
 * Quadrature phase, oscillations that are said to be in quadrature if they are separated in phase by 90° ($\pi$/2, or 𝜆/4)
 * Quadrature component of a composite signal
 * Quadrature filter, the analytic signal of a real-valued filter
 * Quadrature amplitude modulation (QAM), a modulation method of using both an (in-phase) carrier wave and a 'quadrature' carrier wave that is 90° out of phase with the main, or in-phase, carrier
 * Quadrature phase-shift keying (QPSK), a phase-shift keying of using four quadrate points on the constellation diagram, equispaced around a circle

In mathematics:
 * Quadrature (geometry), drawing a square with the same area as a given plane figure (squaring) or computing that area
 * Quadrature of the circle
 * Numerical integration is often called "numerical quadrature" or simply "quadrature"
 * Gaussian quadrature, a special case of numerical integration
 * Quadrature (differential equations), expressing a differential equation solution in terms of integrals.
 * Formerly, a synonym for "integral"
 * Integral
 * Antiderivative
 * Addition in quadrature, combining the magnitude of uncorrelated signals by taking the square root of the sum of their squares

In physics:
 * Optical phase space quadratures, operators which represent the real and imaginary parts of the complex amplitude

In astronomy:
 * Quadrature (astronomy), the position of a body (moon or planet) such that its elongation is 90° or 270°; i.e., the body-earth-sun angle is 90°

In Hedge-funds:
 * Quadrature (hedge-fund), the quant hedge-fund created in 2010, in London, England.

Quadrature may also refer to:
 * Quadrature encoder, a device that detects mechanical position changes and direction of movement
 * Illusionistic ceiling painting, sometimes called quadrature after the Italian term, quadratura
 * La Quadrature du Net (Squaring of the Net in French), a French advocacy group that promotes digital rights and freedoms of citizens
 * "Quadrature", a song by Squarepusher from the album Just a Souvenir

title: Quadrature


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Quality control

Quality control (QC) is a process by which entities review the quality of all factors involved in production. ISO 9000 defines quality control as "a part of quality management focused on fulfilling quality requirements".

This approach places emphasis on three aspects (enshrined in standards such as ISO 9001):

 * 1) Elements such as quack, job management, defined and well managed processes,  performance and integrity criteria, and identification of records
 * 2) Competence, such as knowledge, skills, experience, and qualifications
 * 3) Soft elements, such as personnel, integrity, confidence, organizational culture, motivation, team spirit, and quality relationships.

Inspection is a major component of quality control, where physical product is examined visually (or the end results of a service are analyzed). Product inspectors will be provided with lists and descriptions of unacceptable product defects such as cracks or surface blemishes for example.

History and introduction
Early stone tools such as anvils had no holes and were not designed as interchangeable parts. Mass production established processes for the creation of parts and system with identical dimensions and design, but these processes are not uniform and hence some customers were unsatisfied with the result. Quality control separates the act of testing products to uncover defects from the decision to allow or deny product release, which may be determined by fiscal constraints. For contract work, particularly work awarded by government agencies, quality control issues are among the top reasons for not renewing a contract.

The simplest form of quality control was a sketch of the desired item. If the sketch did not match the item, it was rejected, in a simple Go/no go procedure. However, manufacturers soon found it was difficult and costly to make parts be exactly like their depiction; hence around 1840 tolerance limits were introduced, wherein a design would function if its parts were measured to be within the limits. Quality was thus precisely defined using devices such as plug gauges and ring gauges. However, this did not address the problem of defective items; recycling or disposing of the waste adds to the cost of production, as does trying to reduce the defect rate. Various methods have been proposed to prioritize quality control issues and determine whether to leave them unaddressed or use quality assurance techniques to improve and stabilize production.

Notable approaches
There is a tendency for individual consultants and organizations to name their own unique approaches to quality control—a few of these have ended up in widespread use:

In project management
In project management, quality control requires the project manager and/or the project team to inspect the accomplished work to ensure its alignment with the project scope. In practice, projects typically have a dedicated quality control team which focuses on this area.

title: Quality control


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Quasi-analog signal

In telecommunication, a quasi-analog signal is a digital signal that has been converted to a form suitable for transmission over a specified analog channel.

The specification of the analog channel should include frequency range, bandwidth, signal-to-noise ratio, and envelope delay distortion. When quasi-analog form of signaling is used to convey message traffic over dial-up telephone systems, it is often referred to as voice-data. A modem may be used for the conversion process.

title: Quasi-analog signal


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Queuing delay

In telecommunication and computer engineering, the queuing delay or queueing delay is the time a job waits in a queue until it can be executed. It is a key component of network delay. In a switched network, queuing delay is the time between the completion of signaling by the call originator and the arrival of a ringing signal at the call receiver. Queuing delay may be caused by delays at the originating switch, intermediate switches, or the call receiver servicing switch. In a data network, queuing delay is the sum of the delays between the request for service and the establishment of a circuit to the called data terminal equipment (DTE). In a packet-switched network, queuing delay is the sum of the delays encountered by a packet between the time of insertion into the network and the time of delivery to the address.

Router processing
This term is most often used in reference to routers. When packets arrive at a router, they have to be processed and transmitted. A router can only process one packet at a time. If packets arrive faster than the router can process them (such as in a burst transmission) the router puts them into the queue (also called the buffer) until it can get around to transmitting them. Delay can also vary from packet to packet so averages and statistics are usually generated when measuring and evaluating queuing delay.

As a queue begins to fill up due to traffic arriving faster than it can be processed, the amount of delay a packet experiences going through the queue increases. The speed at which the contents of a queue can be processed is a function of the transmission rate of the facility. This leads to the classic delay curve. The average delay any given packet is likely to experience is given by the formula 1/(μ-λ) where μ is the number of packets per second the facility can sustain and λ is the average rate at which packets are arriving to be serviced. This formula can be used when no packets are dropped from the queue.

The maximum queuing delay is proportional to buffer size. The longer the line of packets waiting to be transmitted, the longer the average waiting time is. The router queue of packets waiting to be sent also introduces a potential cause of packet loss. Since the router has a finite amount of buffer memory to hold the queue, a router which receives packets at too high a rate may experience a full queue. In this case, the router has no other option than to simply discard excess packets.

When the transmission protocol uses the dropped-packets symptom of filled buffers to regulate its transmit rate, as the Internet's TCP does, bandwidth is fairly shared at near theoretical capacity with minimal network congestion delays. Absent this feedback mechanism the delays become both unpredictable and rise sharply, a symptom also seen as freeways approach capacity; metered onramps are the most effective solution there, just as TCP's self-regulation is the most effective solution when the traffic is packets instead of cars). This result is both hard to model mathematically and quite counterintuitive to people who lack experience with mathematics or real networks. Failing to drop packets, choosing instead to buffer an ever-increasing number of them, produces bufferbloat.

Notation
In Kendall's notation, the M/M/1/K queuing model, where K is the size of the buffer, may be used to analyze the queuing delay in a specific system. Kendall's notation should be used to calculate the queuing delay when packets are dropped from the queue. The M/M/1/K queuing model is the most basic and important queuing model for network analysis.

title: Queuing delay


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Radiation angle

In fiber optics, the radiation angle is half the vertex angle of the cone of light emitted at the exit face of an optical fiber.

The cone boundary is usually defined (a) by the angle at which the far-field irradiance has decreased to a specified fraction of its maximum value or (b) as the cone within which there is a specified fraction of the total radiated power at any point in the far field.

title: Radiation angle


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Radiation mode

For an optical fiber or waveguide, a radiation mode or unbound mode is a mode which is not confined by the fiber core. Such a mode has fields that are transversely oscillatory everywhere external to the waveguide, and exists even at the limit of zero wavelength.

Specifically, a radiation mode is one for which
 * $$\beta = \sqrt{n^2(a) k^2 -(l/a)^2}$$

where β is the imaginary part of the axial propagation constant, integer l is the azimuthal index of the mode, n(r) is the refractive index at radius r, a is the core radius, and k is the free-space wave number, k = 2π/λ, where λ is the wavelength. Radiation modes correspond to refracted rays in the terminology of geometric optics.

title: Radiation mode


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Radiation pattern

In the field of antenna design the term radiation pattern (or antenna pattern or far-field pattern) refers to the directional (angular) dependence of the strength of the radio waves from the antenna or other source.

Particularly in the fields of fiber optics, lasers, and integrated optics, the term radiation pattern may also be used as a synonym for the near-field pattern or Fresnel pattern. This refers to the positional dependence of the electromagnetic field in the near field, or Fresnel region of the source. The near-field pattern is most commonly defined over a plane placed in front of the source, or over a cylindrical or spherical surface enclosing it.

The far-field pattern of an antenna may be determined experimentally at an antenna range, or alternatively, the near-field pattern may be found using a near-field scanner, and the radiation pattern deduced from it by computation. The far-field radiation pattern can also be calculated from the antenna shape by computer programs such as NEC. Other software, like HFSS can also compute the near field.

The far field radiation pattern may be represented graphically as a plot of one of a number of related variables, like the field strength at a constant (large) radius (an amplitude pattern or field pattern), the power per unit solid angle (power pattern) and the directive gain. Very often, only the relative amplitude is plotted, normalized either to the amplitude on the antenna boresight, or to the total radiated power. The plotted quantity may be shown on a linear scale, or in dB. The plot is typically represented as a three-dimensional graph (as at right), or as separate graphs in the vertical plane and horizontal plane. This is often known as a polar diagram.

Reciprocity
It is a fundamental property of antennas that the receiving pattern (sensitivity as a function of direction) of an antenna when used for receiving is identical to the far-field radiation pattern of the antenna when used for transmitting. This is a consequence of the reciprocity theorem of electromagnetics and is proved below. Therefore, in discussions of radiation patterns the antenna can be viewed as either transmitting or receiving, whichever is more convenient. This applies only to the passive antenna elements; active antennas that include amplifiers or other components are no longer reciprocal devices.

Typical patterns

Since electromagnetic radiation is dipole radiation, it is not possible to build an antenna that radiates coherently equally in all directions, although such a hypothetical isotropic antenna is used as a reference to calculate antenna gain.

The simplest antennas, monopole and dipole antennas, consist of one or two straight metal rods along a common axis. These axially symmetric antennas have radiation patterns with a similar symmetry, called omnidirectional patterns; they radiate equal power in all directions perpendicular to the antenna, with the power varying only with the angle to the axis, dropping off to zero on the antenna's axis. This illustrates the general principle that if the shape of an antenna is symmetrical, its radiation pattern will have the same symmetry.

In most antennas, the radiation from the different parts of the antenna interferes at some angles; the radiation pattern of the antenna can be considered an interference pattern. This results in minimum or zero radiation at certain angles where the radio waves from the different parts arrive out of phase, and local maxima of radiation at other angles where the radio waves arrive in phase. Therefore, the radiation plot of most antennas shows a pattern of maxima called "lobes" at various angles, separated by "nulls" at which the radiation goes to zero. The larger the antenna is compared to a wavelength, the more lobes there will be.

In a directional antenna in which the objective is to emit the radio waves in one particular direction, the antenna is designed to radiate most of its power in the lobe directed in the desired direction. Therefore, in the radiation plot this lobe appears larger than the others; it is called the "main lobe". The axis of maximum radiation, passing through the center of the main lobe, is called the "beam axis" or boresight axis". In some antennas, such as split-beam antennas, there may exist more than one major lobe. The other lobes beside the main lobe, representing unwanted radiation in other directions, are called minor lobes. The minor lobes oriented at an angle to the main lobe are called "side lobes". The minor lobe in the opposite direction (180°) from the main lobe is called the "back lobe".

Minor lobes usually represent radiation in undesired directions, so in directional antennas a design goal is usually to reduce the minor lobes. Side lobes are normally the largest of the minor lobes. The level of minor lobes is usually expressed as a ratio of the power density in the lobe in question to that of the major lobe. This ratio is often termed the side lobe ratio or side lobe level. Side lobe levels of −20 dB or greater are usually not desirable in many applications. Attainment of a side lobe level smaller than −30 dB usually requires very careful design and construction. In most radar systems, for example, low side lobe ratios are very important to minimize false target indications through the side lobes.

Proof of reciprocity
For a complete proof, see the reciprocity (electromagnetism) article. Here, we present a common simple proof limited to the approximation of two antennas separated by a large distance compared to the size of the antenna, in a homogeneous medium. The first antenna is the test antenna whose patterns are to be investigated; this antenna is free to point in any direction. The second antenna is a reference antenna, which points rigidly at the first antenna.

Each antenna is alternately connected to a transmitter having a particular source impedance, and a receiver having the same input impedance (the impedance may differ between the two antennas).

It is assumed that the two antennas are sufficiently far apart that the properties of the transmitting antenna are not affected by the load placed upon it by the receiving antenna. Consequently, the amount of power transferred from the transmitter to the receiver can be expressed as the product of two independent factors; one depending on the directional properties of the transmitting antenna, and the other depending on the directional properties of the receiving antenna.

For the transmitting antenna, by the definition of gain, $$G$$, the radiation power density at a distance $$r$$ from the antenna (i.e. the power passing through unit area) is

 * $$\mathrm{W}(\theta,\Phi) = \frac{\mathrm{G}(\theta,\Phi)}{4 \pi r^{2}} P_{t}$$.

Here, the angles $$\theta$$ and $$\Phi$$ indicate a dependence on direction from the antenna, and $$P_{t}$$ stands for the power the transmitter would deliver into a matched load. The gain $$G$$ may be broken down into three factors; the antenna gain (the directional redistribution of the power), the radiation efficiency (accounting for ohmic losses in the antenna), and lastly the loss due to mismatch between the antenna and transmitter. Strictly, to include the mismatch, it should be called the realized gain, but this is not common usage.

For the receiving antenna, the power delivered to the receiver is

 * $$P_{r} = \mathrm{A}(\theta,\Phi) W\,$$.

Here $$W$$ is the power density of the incident radiation, and $$A$$ is the antenna aperture or effective area of the antenna (the area the antenna would need to occupy in order to intercept the observed captured power). The directional arguments are now relative to the receiving antenna, and again $$A$$ is taken to include ohmic and mismatch losses.

Putting these expressions together, the power transferred from transmitter to receiver is

 * $$P_{r} = A \frac{G}{4 \pi r^{2}} P_{t}$$,

where $$G$$ and $$A$$ are directionally dependent properties of the transmitting and receiving antennas respectively. For transmission from the reference antenna (2), to the test antenna (1), that is

 * $$P_{1r} = \mathrm{A_{1}}(\theta,\Phi) \frac{G_{2}}{4 \pi r^{2}} P_{2t}$$,

and for transmission in the opposite direction

 * $$P_{2r} = A_{2} \frac{\mathrm{G_{1}}(\theta,\Phi)}{4 \pi r^{2}} P_{1t}$$.

Here, the gain $$G_{2}$$ and effective area $$A_{2}$$ of antenna 2 are fixed, because the orientation of this antenna is fixed with respect to the first.

Now for a given disposition of the antennas, the reciprocity theorem requires that the power transfer is equally effective in each direction, i.e.

 * $$\frac{P_{1r}}{P_{2t}} = \frac{P_{2r}}{P_{1t}}$$,

whence

 * $$\frac{\mathrm{A_{1}}(\theta,\Phi)}{\mathrm{G_{1}}(\theta,\Phi)} = \frac{A_{2}}{G_{2}}$$.

But the right hand side of this equation is fixed (because the orientation of antenna 2 is fixed), and so

 * $$\frac{\mathrm{A_{1}}(\theta,\Phi)}{\mathrm{G_{1}}(\theta,\Phi)} = \mathrm{constant}$$,

i.e. the directional dependence of the (receiving) effective aperture and the (transmitting) gain are identical (QED). Furthermore, the constant of proportionality is the same irrespective of the nature of the antenna, and so must be the same for all antennas. Analysis of a particular antenna (such as a Hertzian dipole), shows that this constant is $$\frac{\lambda^{2}}{4\pi}$$, where $$\lambda$$ is the free-space wavelength. Hence, for any antenna the gain and the effective aperture are related by

 * $$\mathrm{A}(\theta,\Phi) = \frac{\lambda^{2} \mathrm{G}(\theta,\Phi)}{4 \pi}$$.

Even for a receiving antenna, it is more usual to state the gain than to specify the effective aperture. The power delivered to the receiver is therefore more usually written as

 * $$P_{r} = \frac{\lambda^{2} G_{r} G_{t}}{(4 \pi r)^{2}} P_{t}$$

(see link budget). The effective aperture is however of interest for comparison with the actual physical size of the antenna.

Practical consequences

 * When determining the pattern of a receiving antenna by computer simulation, it is not necessary to perform a calculation for every possible angle of incidence. Instead, the radiation pattern of the antenna is determined by a single simulation, and the receiving pattern inferred by reciprocity.
 * When determining the pattern of an antenna by measurement, the antenna may be either receiving or transmitting, whichever is more convenient.
 * For a practical antenna, the side lobe level should be minimum, it is necessary to have the maximum directivity.

title: Radiation pattern


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Radio fix

In telecommunication and position fixing, the term radio fix has the following meanings:

 * The locating of a radio transmitter by bearings taken from two or more direction finding stations, the site of the transmitter being at the point of intersection.
 * The location of a ship or aircraft by determining the direction of radio signals coming to the ship or aircraft from two or more sending stations, the locations of which are known.

Compare triangulation.

Obtaining a radio fix

A single transmitter can be used to give a line of position (LOP) of the craft. The (true) bearing to the station from the craft, TB or QUJ, is composed of the true heading, TH, plus the relative bearing, RB, of the station. The bearing from the station (QTE) is found by adding 180° to the QUJ figure.

The line of position is then the line of bearing QUJ (i.e. from the station to the receiver) passing through the station.

 * $$\mbox{LOP}=\mbox{TH}+\mbox{RB}+180$$

For the diagram on the right, we have:

 * $$\mbox{LOP}=120+40+180$$
 * $$\mbox{LOP}=340$$

A radio fix on two stations can be found in exactly the same way. The intersection of the two position lines gives the position of the receiver. For the diagram on the right, the LOPs are found as before:

 * $$\mbox{LOP1}=120+320+180$$
 * $$\mbox{LOP1}=260$$

 * $$\mbox{LOP2}=120+40+180$$
 * $$\mbox{LOP2}=340$$

Remembering that the LOPs pass through their respective stations, it is now simple to find the location of the craft.

Remember too, that bearings and direction are given/recorded with respect to True North and to Magnetic North. Values used by mobile stations usually need to be converted from Magnetic to True. (Fixed stations are expected to use True).

title: Radio fix


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Radiometry

Radiometry is a set of techniques for measuring electromagnetic radiation, including visible light. Radiometric techniques in optics characterize the distribution of the radiation's power in space, as opposed to photometric techniques, which characterize the light's interaction with the human eye. The fundamental difference between radiometry and photometry is that radiometry gives the entire optical radiation spectrum, while photometry is limited to the visible spectrum. Radiometry is distinct from quantum techniques such as photon counting.

The use of radiometers to determine the temperature of objects and gasses by measuring radiation flux is called pyrometry. Handheld pyrometer devices are often marketed as infrared thermometers.

Radiometry is important in astronomy, especially radio astronomy, and plays a significant role in Earth remote sensing. The measurement techniques categorized as radiometry in optics are called photometry in some astronomical applications, contrary to the optics usage of the term.

Spectroradiometry is the measurement of absolute radiometric quantities in narrow bands of wavelength.

Integral and spectral radiometric quantities
Integral quantities (like radiant flux) describe the total effect of radiation of all wavelengths or frequencies, while spectral quantities (like spectral power) describe the effect of radiation of a single wavelength $λ$ or frequency $ν$. To each integral quantity there are corresponding spectral quantities, defined as the quotient of the integrated quantity by the range of frequency or wavelength considered. For example, the radiant flux Φe corresponds to the spectral power Φe,$λ$ and Φe,$ν$.

Getting an integral quantity's spectral counterpart requires a limit transition. This comes from the idea that the precisely requested wavelength photon existence probability is zero. Let us show the relation between them using the radiant flux as an example:

Integral flux, whose unit is W: $$\Phi_\mathrm{e}.$$ Spectral flux by wavelength, whose unit is : $$\Phi_{\mathrm{e},\lambda} = {d\Phi_\mathrm{e} \over d\lambda},$$ where $$d\Phi_\mathrm{e}$$ is the radiant flux of the radiation in a small wavelength interval $$[\lambda - {d\lambda \over 2}, \lambda + {d\lambda \over 2}]$$. The area under a plot with wavelength horizontal axis equals to the total radiant flux.

Spectral flux by frequency, whose unit is : $$\Phi_{\mathrm{e},\nu} = {d\Phi_\mathrm{e} \over d\nu},$$ where $$d\Phi_\mathrm{e}$$ is the radiant flux of the radiation in a small frequency interval $$[\nu - {d\nu \over 2}, \nu + {d\nu \over 2}]$$. The area under a plot with frequency horizontal axis equals to the total radiant flux.

The spectral quantities by wavelength $λ$ and frequency $ν$ are related to each other, since the product of the two variables is the speed of light ($$\lambda \cdot \nu = c$$):
 * $$\Phi_{\mathrm{e},\lambda} = {c \over \lambda^2} \Phi_{\mathrm{e},\nu},$$ or $$\Phi_{\mathrm{e},\nu} = {c \over \nu^2} \Phi_{\mathrm{e},\lambda},$$ or $$\lambda \Phi_{\mathrm{e},\lambda} = \nu \Phi_{\mathrm{e},\nu}.$$

The integral quantity can be obtained by the spectral quantity's integration:

$$\Phi_\mathrm{e} = \int_0^\infty \Phi_{\mathrm{e},\lambda}\, d\lambda = \int_0^\infty \Phi_{\mathrm{e},\nu}\, d\nu = \int_0^\infty \lambda \Phi_{\mathrm{e},\lambda}\, d \ln \lambda = \int_0^\infty \nu \Phi_{\mathrm{e},\nu}\, d \ln \nu.$$

title: Radiometry


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Randomizer

Randomizer may refer to:
 * Scrambler, a telecommunications device
 * Video game randomizers
 * Random number generator

title: Randomizer


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Random number

A random number is generated by a random (stochastic) process such as throwing Dice. Individual numbers can't be predicted, but the likely result of generating a large quantity of numbers can be predicted by statistics.

Algorithms and implementations
Random numbers are frequently used in algorithms such as Knuth's 1964-developed algorithm for shuffling lists. (popularly known as the Knuth shuffle or the Fisher–Yates shuffle, based on work they did in 1938).

In 1999, a new feature was added to the Pentium III: a hardware-based random number generator. It has been described as "several oscillators combine their outputs and that odd waveform is sampled asynchronously." These numbers, however, were only 32 bit, at a time when export controls were on 56 bits and higher, so they were not state of the art.

Common understanding
In common understanding, "1 2 3 4 5" is not as random as "3 5 2 1 4" and certainly not as random as "47 88 1 32 41" but "we can't say authoritavely that the first sequence is not random ... it could have been generated by chance."

When a police officer claims to have done a "random .. door-to-door" search, there is a certain expectation that members of a jury will have.

Real world consequences
Flaws in randomness have real-world consequences.

A 99.8% randomness was shown by researchers to negatively affect an estimated 27,000 customers of a large service and that the problem was not limited to just that situation.

title: Random number


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Receive-after-transmit time delay

In telecommunication, receive-after-transmit time delay is the time interval between (a) the instant of keying off the local transmitter to stop transmitting and (b) the instant the local receiver output has increased to 90% of its steady-state value in response to an RF (radio-frequency) signal from another transmitter.

The RF signal from the distant transmitter must exist at the local receiver input prior to, or at the time of, keying off the local transmitter.

Receive-after-transmit time delay applies only to half-duplex operation.

title: Receive-after-transmit time delay


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Received noise power

In telecommunications, received noise power is a measure of noise in a receiver. For example, the received noise power might be:
 * 1) The calculated or measured noise power, within the bandwidth being used, at the receive end of a circuit, channel, link, or system.
 * 2) The absolute power of the noise measured or calculated at a receive point. The related bandwidth and the noise weighting must also be specified.
 * 3) The value of noise power, from all sources, measured at the line terminals of a telephone set's receiver.' Either flat weighting or some other specific amplitude-frequency characteristic or noise weighting characteristic must be associated with the measurement.

title: Received noise power


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Attack-time delay

In telecommunications, attack-time delay is the time needed for a receiver or transmitter to respond to an incoming signal.

For a receiver, the attack-time delay is defined as the time interval from the instant a step radio-frequency (RF) signal, at a level equal to the receiver's threshold of sensitivity, is applied to the receiver input, to the instant when the receiver's output amplitude reaches 90% of its steady-state value. If a squelch circuit is operating, the receiver attack-time delay includes the time for the receiver to break squelch.

For a transmitter, the attack-time delay is defined as the interval from the instant the transmitter is keyed-on to the instant the transmitted RF signal amplitude has increased to a specified level, usually 90% of its key-on steady-state value. The transmitter attack-time delay excludes the time required for automatic antenna tuning.

title: Attack-time delay


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Recorder warning tone

A recorder warning tone is a tone transmitted over a telephone line to indicate to the called party that the calling party is recording the conversation.

In the United States, the recorder warning tone is a half-second burst of 1400 Hz applied every 15 seconds. The recorder warning tone is required by law to be generated as an integral part of any recording device used for the purpose of recording telephone calls and is required to be not under the control of the calling party. The tone is recorded together with the conversation.

title: Recorder warning tone


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Recovery procedure

In telecommunication, a recovery procedure is a process that attempts to bring a system back to a normal operating state. Examples:
 * 1) The actions necessary to restore an automated information system's data files and computational capability after a system failure.
 * 2) In data communications, a process whereby a data station attempts to resolve conflicting or erroneous conditions arising during the data transfer.

title: Recovery procedure


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Reference circuit

A reference circuit is a hypothetical electric circuit of specified equivalent length and configuration, and having a defined transmission characteristic or characteristics, used primarily as a reference for measuring the performance of other, i.e., real, circuits or as a guide for planning and engineering of circuits and networks.

Normally, several types of reference circuits are defined, with different configurations, because communications are required over a wide range of distances. Another type of reference circuit shows how to configure integrated circuits into function blocks, which Analog Devices provides for electrical design engineers. Analog Devices' Circuits from the Lab reference circuits are fully tested and come with the schematics, evaluation boards, and device drivers necessary for system integration. A group of related reference circuits is also called a reference system.

title: Reference circuit


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Reference clock

A reference clock may refer to the following:

 * A master clock used as a timekeeping standard to regulate or compare the accuracy of other clocks
 * In electronics and computing, the clock signal used to synchronise and schedule operations

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title: Reference clock