What Is a Demultiplexer?

Multiplexer (Multiplexer) is a comprehensive system, usually contains a certain number of data inputs, n address inputs (select a data input in binary form). The multiplexer has a separate output that is the same as the selected data input value. Reuse technology may follow one of the following principles, such as: TDM, FDM, CDM, or WDM. Multiplexing technology is also applied to software operations, such as transmitting multi-threaded information streams to devices or programs at the same time.

Chinese name: multiplexer

Foreign name: Multiplexer

Time division multiplexer

multiplexer

Time division multiplexing refers to a technology that transmits multiple digitized data, voice, and video signals on the same communication medium at the same time through cross-bit pulses in different channels or time slots. The channel bandwidth basically used in telecommunications is DS0, and its channel width is 64 kbps. The telephone network (PSTN) is based on TDM technology and is often referred to as a TDM access network. Telephone switching supports TDM through several formats: DS0, T1 / E1 TDM, and BRI TDM. E1 TDM supports a 2.048 Mbps communication link, which is divided into 32 time slots, each interval being 64 kbps. T1 TDM supports a 1.544 Mbps communication link, which is divided into 24 time slots, each spaced at 64 kbps, of which 8 kbps channels are used for synchronous operation and maintenance processes. E1 and T1 TDM were originally used for digital voice transmission in telephone companies, and are no different from other types of data that later appeared. E1 and T1 TDM are also used for WAN links. BRI TDM is provided through the switch's basic rate interface (BRI, which supports basic rate ISDN and can be used as a data channel for one or more static PPP links). The basic rate interface has two 64 kbps time slots. TDMA is also applied to cell networks for mobile wireless communications.

A time division multiplexer is a device that utilizes TDM technology and is mainly used to combine multiple low-rate data streams into a single high-rate data stream. Data from multiple different sources is broken down into parts (bits or groups of bits), and these parts are transmitted in a prescribed order. Each input data stream then becomes a "time segment" in the output data stream. The transmission sequence must be maintained so that the input data stream can be reassembled at the destination. It is particularly worth noting that the same device can perform the opposite process through the same TDM technology principle, that is, the high-rate data stream is decomposed into multiple low-rate data streams, which is called demultiplexing technology. Therefore, it is common to have both a time division multiplexer and a demultiplexer in the same box.

Wavelength Division Multiplexer

WDM technology principle

In analog carrier communication systems, frequency division multiplexing is usually used to increase the transmission capacity of the system, making full use of the bandwidth resources of the cable, that is, transmitting the signals of several channels at the same time in the same cable. The receiving end is based on the different carrier frequencies. The signal of each channel can be filtered out with a band-pass filter. Similarly, in the optical fiber communication system, the frequency division multiplexing method of light can also be used to increase the transmission capacity of the system. At the receiving end, a demultiplexer (equivalent to an optical band-pass filter) is used to separate the optical carriers of each signal. Because the signal frequency difference is relatively large in the frequency domain of light, the wavelength is generally used to define the frequency difference. This multiplexing method is called wavelength division multiplexing [2]. WDM technology is to make full use of the huge bandwidth resources brought by the low loss area of single-mode fiber. According to the frequency (or wavelength) of each channel's light wave, the low loss window of the fiber can be divided into several channels, and the light wave is used as the carrier of the signal. At the transmitting end, a wavelength division multiplexer (multiplexer) is used to combine signal optical carriers of different specified wavelengths and send them to a single optical fiber for transmission. At the receiving end, a wavelength division multiplexer (wave splitter) separates these optical carriers carrying different signals at different wavelengths in a multiplexing manner. Because the optical carrier signals of different wavelengths can be regarded as independent of each other (when fiber nonlinearity is not considered), multiple optical signals can be multiplexed and transmitted in one optical fiber. Two-way transmission can be achieved by arranging signals in two directions for transmission at different wavelengths. Depending on the wavelength division multiplexer, the number of wavelengths that can be multiplexed is different, ranging from 2 to tens. The general commercialization is 8-wavelength and 16-wavelength systems, which depends on the interval of allowed optical carrier wavelengths. Size, Figure 1 shows the system composition.

WDM WDM is essentially a frequency division multiplexing FDM technology on the optical frequency, and each wavelength path is realized by frequency domain division. Each wavelength path occupies the bandwidth of a section of optical fiber, which is different from the previous coaxial cable FDM technology: (1) the transmission medium is different, the WDM system is the frequency division on the optical signal, and the coaxial system is the frequency division on the electrical signal. (2) On each path, the coaxial cable system transmits an analog signal 4KHz voice signal, and the WDM system on each wavelength path is a digital signal SDH2.5Gb / s or higher digital system.

Main features of WDM technology

WDM technology has many advantages. It can use the bandwidth resources of the optical fiber to increase the transmission capacity of a single fiber by several times to several tens of times compared to single-wavelength transmission. Multi-wavelength multiplexed transmission in single-mode fiber can save a lot of fiber during large-capacity long-distance transmission. The installed cables have fewer cores and can be used for capacity expansion without major changes to the original system by using wavelength division multiplexing. Because the signal wavelengths transmitted in the same fiber are independent of each other, they can transmit signals with completely different characteristics. Complete the integration and separation of various telecommunication service signals, including digital and analog signals, as well as the integration and separation of PDH signals and SDH signals; WDM channels are transparent to the data format, which is independent of the signal rate and electrical modulation method.

Multiplexer Terminal Multiplexer

Terminal Multiplexer Introduction

Tellabs 6320 edge node is suitable for access and area layer of SDH transmission network. Can realize a complete and compact multi-service add / drop multiplexer (ADM) with STM-1, STM-4 line interface, or terminal multiplexer (TM). Supports a full range of PDH tributary interfaces and STM-1 optical and electrical interfaces. Provides synchronous and asynchronous service delivery, as well as an integrated ATM STM-1 user network interface with ATM layer cross-connect capability.

Terminal multiplexer

Terminal Multiplexer Product Details

Highly integrated, single-board ADM / TM

Scalable modular structure

Provide FE interface

Easy integration of ATM-based services

Support for synchronous status information (SSM)

Partial load interface

Advanced network and network element management

Multiple types of mechanical chassis

ATM STM-1 UNI optical port with integrated ATM cross-connect function

Supports broadcast functions with drop and resume

Data multiplexer

The data multiplexer is a 64Kbps five-channel synchronous multiplexer using time division multiplexing (TDM) technology. It multiplexes multiple 9600-38.4Kbps data onto a 64Kbps data channel, thereby saving communication line costs and equipment costs . Each sub-channel has a 96-bit flexible memory to support the tail circuit, so that the sub-channel can be tailed to a communication line to extend to the remote. Each sub-channel can be added with a synchronous / asynchronous conversion module, so that the sub-channel can be connected to any asynchronous communication device.

Multiplexer time division multiplexing

In order to improve channel utilization, multiple signals are transmitted along the same channel without interfering with each other. This is called multiplexing. The more commonly used are frequency division multiplexing and time division multiplexing. Frequency division multiplexing is used for analog communications, such as carrier communications, and time division multiplexing is used for digital communications, such as PCM communications.

Time division multiplexing? Time-division multiplexing communication is the communication of each signal occupying different time slots on the same channel. It can be known from the foregoing sampling theory that an important role of sampling is to change a continuous signal in time into a discrete signal in time. The limited time it takes on a channel provides conditions for multiple signals to be transmitted along the same channel. Specifically, it is to divide the time into some uniform time gaps, and allocate the transmission time of each signal to different time gaps to achieve the purpose of being separated from each other without interference. Each signal is limited to a frequency band below 3400Hz by a low-pass filter, and then added to a fast electronic rotary switch (called splitter). The switch continuously and repeatedly rotates at a uniform speed. The time for each rotation is equal to a sampling period T. Each signal is sampled once every cycle T time. It can be seen that the originating distributor not only plays the role of sampling, but also plays the role of multiplexing and combining. The combined sampling signal is sent to a PCM encoder for quantization and coding, and then the digital signal code is sent to the channel. At the receiving end, these channel codes sent from the transmitting end are decoded in sequence, and the restored PAM signal is turned on by each of the signals in turn by the rotary switch K2 of the receiving end, which is then low-pass smoothed and reconstructed into a voice signal. It can be seen that the receiving end distributor plays a role of time division multiplexing, so the receiving end distributor is also called a branch gate.

It should be noted that: to ensure normal communication, the rotary switches at the receiving and sending ends must be at the same frequency and in phase. The same frequency means that the rotation speed must be exactly the same. The same phase means that when the sending end rotary switch is connected to the first signal, the receiving end rotary switch K2 must also be connected to the first channel, otherwise the receiving end will not receive the signal of this channel. It is required that the receiving and sending parties must maintain strict synchronization.

Frequency Division Multiplexer

The use of single-sideband modulation frequency-division multiplexing in multi-carrier phones is mainly to save the transmission frequency band to the greatest extent. Each telephone signal is limited to 300-3400Hz, and its bandwidth is the same as the modulated signal after single-sideband modulation. In order to leave a guard band between the modulated signals of adjacent channels, so that the filter has an achievable transition band, usually 4kHz is used as the standard frequency band for each voice signal. In order to facilitate the grouping and grouping of large-capacity carrier phones during transmission, a set of standard levels has now been formed.

The base group consists of 12 voice signals, and the frequency spectrum of the modulated signal after frequency division multiplexing. It should be pointed out that the basic frequency band of the various group signals is not the frequency band transmitted in the actual channel, and it is often necessary to perform a spectrum shift before entering the channel. In addition, from the above-mentioned frequency spectrum, it can be known that the generation, modulation, demodulation, and filtering of various carrier frequencies are the main components in carrier telephone equipment.

Optical Multiplexer

The optical multiplexer is literally a composite device of light path signals and circuit signals. A common optical cat is an optical fiber transceiver. (An optical cat is different from an optical fiber transceiver. Optical fiber transceivers only have signal conversion and no protocol conversion. (Including protocol conversion) is a device that converts electrical signals into optical signals. A multiplexer is a device that combines multiple electrical signals onto the optical path. This device should be a general term for a system. In practice, such equipment is not used. Many, the other is a combination of multiple optical paths, but this composite modulation will use different wavelengths of light to transmit multiple signals, and then demodulate after arriving. This kind of equipment is only used in the national backbone optical fiber network. Expansion using the inherent optical cable resources is very expensive.

Multiplexer other

Multiplexers (MUX) and demultiplexers (DEMUX) always appear in pairs.

MUX = multiplexer DEMUX = demultiplexer

To put it simply, a multiplexer is to combine a large number of signals together in a certain way to facilitate transmission. The demultiplexer is to separate the composite signals according to the multiplexer composite mode for subsequent analysis. Therefore, the multiplexer is a collective name, and it is not limited to the photoelectric multiplexer.

The technology used by fashionable CDMA mobile phones is CDMA code division multiple access technology, which is also a technology of signal recombination. In comparison, the information flow is larger and more complex, and it is more difficult to crack.