Statistical multiplexing is a type of communication link sharing, very similar to dynamic bandwidth allocation (DBA). In statistical multiplexing, a communication channel is divided into an arbitrary number of variable bitrate digital channels or data streams. The link sharing is adapted to the instantaneous traffic demands of the data streams that are transferred over each channel. This is an alternative to creating a fixed sharing of a link, such as in general time division multiplexing (TDM) and frequency division multiplexing (FDM). When performed correctly, statistical multiplexing can provide a link utilization improvement, called the ''statistical multiplexing gain''.
Statistical multiplexing is facilitated through packet mode or packet-oriented communication, which among others is utilized in packet switched computer networks. Each stream is divided into packets that normally are delivered asynchronously in a first-come first-served fashion. In alternative fashion, the packets may be delivered according to some scheduling discipline for fair queuing or differentiated and/or guaranteed quality of service.
Statistical multiplexing of an analog channel, for example a wireless channel, is also facilitated through the following schemes:
* Random frequency-hopping orthogonal frequency division multiple access (RFH-OFDMA)
* Code-division multiple access (CDMA), where different amount of spreading codes or spreading factors can be assigned to different users.
Statistical multiplexing normally implies "on-demand" service rather than one that preallocates resources for each data stream. Statistical multiplexing schemes do not control user data transmissions.
Comparison with static TDM
Time domain statistical multiplexing (packet mode communication) is similar to
time-division multiplexing
Time-division multiplexing (TDM) is a method of transmitting and receiving independent signals over a common signal path by means of synchronized switches at each end of the transmission line so that each signal appears on the line only a fracti ...
(TDM), except that, rather than assigning a data stream to the same recurrent time slot in every
TDM, each data stream is assigned time slots (of fixed length) or
data frames (of variable lengths) that often appear to be scheduled in a randomized order, and experience varying delay (while the delay is fixed in TDM).
Statistical multiplexing allows the bandwidth to be divided arbitrarily among a variable number of channels (while the number of channels and the channel data rate are fixed in TDM).
Statistical multiplexing ensures that slots will not be wasted (whereas TDM can waste slots). The transmission capacity of the link will be shared by only those users who have packets.
Static TDM and other circuit switching is carried out at the
physical layer
In the seven-layer OSI model of computer networking, the physical layer or layer 1 is the first and lowest layer; The layer most closely associated with the physical connection between devices. This layer may be implemented by a PHY chip.
The ...
in the
OSI model and
TCP/IP model, while statistical multiplexing is carried out at the
data link layer and above.
Channel identification
In statistical multiplexing, each packet or frame contains a channel/data stream identification number, or (in the case of
datagram communication) complete destination address information.
Usage
Examples of statistical multiplexing are:
* The
MPEG transport stream
MPEG transport stream (MPEG-TS, MTS) or simply transport stream (TS) is a standard digital container format for transmission and storage of audio, video, and Program and System Information Protocol (PSIP) data. It is used in broadcast systems ...
for
digital TV transmission. Statistical multiplexing is used to allow several video, audio and data streams of different data rates to be transmitted over a bandwidth-limited channel (see
Statistical multiplexer
Statistical multiplexing is a type of communication link sharing, very similar to dynamic bandwidth allocation (DBA). In statistical multiplexing, a communication channel is divided into an arbitrary number of variable bitrate digital channels or ...
). The packets have constant lengths. The channel number is denoted Program ID (PID).
* The
UDP and
TCP
TCP may refer to:
Science and technology
* Transformer coupled plasma
* Tool Center Point, see Robot end effector
Computing
* Transmission Control Protocol, a fundamental Internet standard
* Telephony control protocol, a Bluetooth communication s ...
protocols, where data streams from several application processes are multiplexed together. The packets may have varying lengths. The
port numbers constitute channel identification numbers (and also address information).
* The
X.25 and
Frame Relay packet-switching protocols, where the packets have varying lengths, and the channel number is denoted virtual connection identifier (VCI). The international collection of
X.25 providers, using the
X.25 protocol suite was colloquially known as "the Packet switched network" in the 1980s and into the beginning of the 1990s.
* The
Asynchronous Transfer Mode packet-switched protocol, where the packets have fixed length. The channel identification number consists of a
virtual connection identifier (VCI) and a
Virtual Path Identifier (VPI).
Statistical multiplexer
In digital audio and video broadcasting, for example, a statistical multiplexer is a content aggregating device that allows broadcasters to provide the greatest number of audio or video services for a given bandwidth by sharing a pool of fixed bandwidth among multiple services or streams of varying bitrates. The multiplexer allocates to each service the bandwidth required for its real-time needs so that services with complex scenes receive more bandwidth than services with less complex ones. This bandwidth sharing technique produces the best video quality at the lowest possible aggregate bandwidth.
Examples of statistical multiplexers include the
Imagine Communications (RGB Networks) BNPXr product line,
Harmonic Inc.
Harmonic Inc. is an American technology company that develops and markets video routing, server, and storage products for companies that produce, process, and distribute video content for television and the Internet.
History
Harmonic was init ...
ProStream, Electra and VOS product families or the
Motorola (
Terayon) DM6400 and TMIR
See also
*
Data fragmentation
*
Dynamic bandwidth allocation
*
Dynamic TDMA
*
Packet
*
Packet switching
External links
Example of Statistical Multiplexing(Chart from a real DVB-T multiplex)
{{DEFAULTSORT:Statistical Multiplexing
Multiplexing
Packets (information technology)
Network scheduling algorithms
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