Initialize an application from an options object ora set of JSON and JavaScript files.
NOTE: This module is primarily intended for use with LoopBack 2.0.It does work with LoopBack 1.x applications, butnone of the LoopBack 1.x examples or generated code (scaffolding) use it.
USB 3.0 Loopback plugs are one of the fastest methods to diagnose, troubleshoot and load test your PC's USB functions. Active loopback plugs are the quickest, most effective way to verify that a PC's USB ports are working correctly. The Red, Green and Yellow LED's on the front of this USB adapter plug provide a quick visua. Applies to: Scarlett 3rd Gen Units compatible with Focusrite Control 3.0 (4i4, 8i6, 18i8, 18i20) On supported Scarlett 3rd gens we have included Loopback. Focusrite Control's Loopback feature lets you record other audio sources from within your computer (e.g., the audio output from a web browser). The address 127.0.0.1 is the standard address for IPv4 loopback traffic; the rest are not supported by all operating systems. However, they can be used to set up multiple server applications on the host, all listening on the same port number. The IPv6 standard assigns only a single address for loopback:::1.
This function takes an optional argument that is either a stringor an object.
If the argument is a string, then it sets the application root directorybased on the string value. Then it:
Creates DataSources from the
datasources.jsonfile in the applicationroot directory.Configures Models from the
model-config.jsonfile in the applicationroot directory.Configures the LoopBack Application object from the
config.jsonfilein the application root directory. These properties can be accessedusingapp.get('propname').
If the argument is an object, then it looks for models, dataSources,'config', modelsRootDir, dsRootDir, appConfigRootDir and appRootDirproperties of the object.
If the object has no appRootDir property then it sets the current workingdirectory as the application root directory.
The execution environment, {env}, is established from, in order,
options.envprocess.env.NODE_ENV,- the literal
development.
Then it:
Creates DataSources from the
options.dataSourcesobject, if provided;otherwise, it searches for the filesdatasources.json,datasources.local.jsordatasources.local.json(only one),datasources.{env}.jsordatasources.{env}.json(only one)
in the directory designated by 'options.dsRootDir', if present, or theapplication root directory. It merges the data source definitions fromthe files found.
Creates Models from the
options.modelsobject, if provided;otherwise, it searches for the filesmodel-config.json,model-config.local.jsormodel-config.local.json(only one),model-config.{env}.jsormodel-config.{env}.json(only one)
in the directory designated by 'options.modelsRootDir', if present, orthe application root directory. It merges the model definitions from thefiles found.
Silkypix mac. Configures the Application object from the
options.configobject,if provided;otherwise, it searches for the filesconfig.json,config.local.jsorconfig.local.json(only one),config.{env}.jsorconfig.{env}.json(only one)
in the directory designated by 'options.appConfigRootDir', if present, orthe application root directory. It merges the properties from the filesfound.
In both cases, the function loads JavaScript files in the/boot subdirectory of the application root directory with require().
Alien skin blow up 3 1 3 259. NOTE: The version 2.0 of loopback-boot changed the way how models are created. The model-config.json file contains only configuration options like dataSource and extra relations. To define a model, create a per-model JSON file in models/ directory.
NOTE: Mixing bootLoopBackApp(app, bootConfig) and app.model(name, modelConfig) in multiple files may result in models being undefined due to race conditions. To avoid this when using bootLoopBackApp() make sure all models are passed as part of the models definition.
Throws an error if the config object is not valid or if boot fails.
Loopback (also written loop-back) is the routing of electronic signals, digital data streams, or flows of items back to their source without intentional processing or modification. It is primarily a means of testing the communications infrastructure.
There are many example applications. It may be a communication channel with only one communication endpoint. Any message transmitted by such a channel is immediately and only received by that same channel. In telecommunications, loopback devices perform transmission tests of access lines from the serving switching center, which usually does not require the assistance of personnel at the served terminal. Loop around is a method of testing between stations that are not necessarily adjacent, wherein two lines are used, with the test being done at one station and the two lines are interconnected at the distant station. A patch cable may also function as loopback, when applied manually or automatically, remotely or locally, facilitating a loop-back test.
Where a system (such as a modem) involves round-trip analog-to-digital processing, a distinction is made between analog loopback, where the analog signal is looped back directly, and digital loopback, where the signal is processed in the digital domain before being re-converted to an analog signal and returned to the source.
Telecommunications[edit]
In telecommunications, loopback, or a loop, is a hardware or software method which feeds a received signal or data back to the sender. It is used as an aid in debugging physical connection problems. As a test, many data communication devices can be configured to send specific patterns (such as all ones) on an interface and can detect the reception of this signal on the same port. This is called a loopback test and can be performed within a modem or transceiver by connecting its output to its own input. A circuit between two points in different locations may be tested by applying a test signal on the circuit in one location, and having the network device at the other location send a signal back through the circuit. If this device receives its own signal back, this proves that the circuit is functioning.
A hardware loop is a simple device that physically connects the receiver channel to the transmitter channel. In the case of a network termination connector such as X.21, this is typically done by simply connecting the pins together in the connector. Media such as optical fiber or coaxial cable, which have separate transmit and receive connectors, can simply be looped together with a single strand of the appropriate medium.
A modem can be configured to loop incoming signals from either the remote modem or the local terminal. This is referred to as loopback or software loop.
Serial interfaces[edit]
A serial communications transceiver can use loopback for testing its functionality. For example, a device's transmit pin connected to its receive pin will result in the device receiving exactly what it transmits. Moving this looping connection to the remote end of a cable adds the cable to this test. Moving it to the far end of a modem link extends the test further. This is a common troubleshooting technique and is often combined with a specialized test device that sends specific patterns and counts any errors that come back (see Bit Error Rate Test). Some devices include built-in loopback capability.
A simple serial interface loopback test, called paperclip test, is sometimes used to identify serial ports of a computer and verify operation. It utilizes a terminal emulator application to send characters, with flow control set to off, to the serial port and receive the same back. For this purpose, a paperclip is used to short pin 2 to pin 3 (the receive and transmit pins) on a standard RS-232 interface using D-subminiature DE-9 or DB-25 connectors.
Virtual loopback interface[edit]
Implementations of the Internet protocol suite include a virtual network interface through which network applications can communicate when executing on the same machine. It is implemented entirely within the operating system's networking software and passes no packets to any network interface controller. Any traffic that a computer program sends to a loopback IP address is simply and immediately passed back up the network software stack as if it had been received from another device. Unix-like systems usually name this loopback interface lo or lo0.
Various Internet Engineering Task Force (IETF) standards reserve the IPv4 address block 127.0.0.0/8, in CIDR notation and the IPv6 address ::1/128 for this purpose. The most common IPv4 address used is 127.0.0.1. Commonly these loopback addresses are mapped to the hostnames, localhost or loopback.
MPLS[edit]
One notable exception to the use of the 127.0.0.0/8 network addresses is their use in Multiprotocol Label Switching (MPLS) traceroute error detection, in which their property of not being routable provides a convenient means to avoid delivery of faulty packets to end users.
Loopback 2 1 3 0 M
Martian packets[edit]
Any IP datagram with a source or destination address set to a loopback address must not appear outside of a computing system, or be routed by any routing device. Packets received on an interface with a loopback destination address must be dropped. Such packets are sometimes referred to as Martian packets.[1] As with other bogus packets, they may be malicious and any problems they might cause can be avoided by applying bogon filtering.
Management interface[edit]
Some computer network equipment use the term 'loopback' for a virtual interface used for management purposes. Unlike a proper loopback interface, this type of loopback device is not used to talk with itself.
Such an interface is assigned an address that can be accessed from management equipment over a network but is not assigned to any of the physical interfaces on the device. Such a loopback device is also used for management datagrams, such as alarms, originating from the equipment. The property that makes this virtual interface special is that applications that use it will send or receive traffic using the address assigned to the virtual interface as opposed to the address on the physical interface through which the traffic passes.
Loopback interfaces of this sort are often used in the operation of routing protocols, because they have the useful property that, unlike real physical interfaces, they will not go down when a physical port fails.
Other applications[edit]
Loopback /32
The audio systems Open Sound System (OSS), Advanced Linux Sound Architecture (ALSA) and PulseAudio have loopback modules for recording the audio output of applications for testing purposes. Unlike physical loopbacks, this does not involve double analog/digital conversion and no disruption is caused by hardware malfunctions.
See also[edit]
References[edit]
This article incorporates public domain material from the General Services Administration document: 'Federal Standard 1037C'. (in support of MIL-STD-188)
External links[edit]
Loopback 2 1 3 0 9
