packet switching

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packet switching

[′pak·ət ‚swich·iŋ]
(communications)

Packet switching

A software-controlled means of directing digitally encoded information in a communication network from a source to a destination, in which information messages may be divided into smaller entities called packets. Switching and transmission are the two basic functions that effect communication on demand from one point to another in a communication network, an interconnection of nodes by transmission facilities. Each node functions as a switch in addition to having potentially other nodal functions such as storage or processing.

Switched (or demand) communication can be classified under two main categories: circuit-switched communication and store-and-forward communication. Store-and-forward communication, in turn, has two principal categories: message-switched communication (message switching) and packet-switched communication (packet switching).

In circuit switching, an end-to-end path of a fixed bandwidth (or speed) is set up for the entire duration of a communication or call. The bandwidth in circuit switching may remain unused if no information is being transmitted during a call. In store-and-forward switching, the message, either as a whole or in parts, transits through the nodes of the network one node at a time. The entire message, or a part of it, is stored at each node and then forwarded to the next.

In message switching, the switched message retains its integrity as a whole message at each node during its passage through the network. For very long messages, this requires large buffers (or storage capacity) at each node. Also, the constraint of receiving the very last bit of the entire message before forwarding its first bit to the next node may result in unacceptable delays. Packet switching breaks a large message into fixed-size, small packets and then switches these packets through the network as if they were individual messages. This approach reduces the need for large nodal buffers and “pipelines” the resources of the network so that a number of nodes can be active at the same time in switching a long message, reducing significantly the transit delay. One important characteristic of packet switching is that network resources are consumed only when data are actually sent.

All public packet networks require that terminals and computers connecting to the network use a standard access protocol. Interconnection of one public packet network to others is carried out by using another standardized protocol.

Packet-switched networks using satellite or terrestrial radio as the transmission medium are known as packet satellite or packet radio networks, respectively. Such networks are especially suited for covering large areas for mobile stations, or for applications that benefit from the availability of information at several locations simultaneously.

Asynchronous transfer mode (ATM) is a type of packet switching that uses short, fixed-size packets (called cells) to transfer information. The ATM cell is 53 bytes long, containing a 5-byte header for the address of the destination, followed by a fixed 48-byte information field. The rather short packet size of ATM, compared to conventional packet switching, represents a compromise between the needs of data communication and those of voice and video communication, where small delays and low jitter are critical for most applications.

Data communication (or computer communication) has been the primary application for packet networks. Computer communication traffic characteristics are fundamentally different from those of voice traffic. Data traffic is usually bursty, lasting from several milliseconds to several minutes or hours. The holding time for data traffic is also widely different from one application to another. These characteristics of data communication make packet switching an ideal choice for most applications. The principal motivation for ATM is to devise a unified transport mechanism for voice, still image, video, and data communication. See Data communications

packet switching

(communications)
A communications paradigm in which packets (messages or fragments of messages) are individually routed between nodes, with no previously established communication path. Packets are routed to their destination through the most expedient route (as determined by some routing algorithm). Not all packets travelling between the same two hosts, even those from a single message, will necessarily follow the same route.

The destination computer reassembles the packets into their appropriate sequence. Packet switching is used to optimise the use of the bandwidth available in a network and to minimise the latency. X.25 is an international standard packet switching network.

Also called connectionless. Opposite of circuit switched or connection-oriented. See also virtual circuit, wormhole routing.

packet switching

A digital network technology that breaks up a message into smaller chunks (packets) for transmission. Unlike circuit switching in traditional telephone networks, which requires the establishment of a dedicated point-to-point connection, each packet in a packet-switched network contains a destination address. Thus, all packets in a single message do not have to travel the same path. As traffic conditions change, they can be dynamically routed via different paths in the network, and they can even arrive out of order. The destination computer reassembles the packets into their proper sequence.

Data, Voice and Video
Packet switching always excelled at handling messages of different lengths, as well as different priorities, providing the attributes for quality of service (QoS) were included in the design of the network. However, packet switching was originally created for data. Today, using the global standard IP protocol (see TCP/IP), packet networks have become the norm for voice and video as well (see IP on Everything).

The First Packet Switches
The first international standard for wide area packet switching networks was X.25, which was defined at a time when circuits were analog and very susceptible to noise. Subsequent packet technologies, such as frame relay, were designed for almost-error-free digital lines.

ATM uses a cell-switching technology that provides the bandwidth-sharing efficiency of packet switching with the guaranteed bandwidth of circuit switching. See X.25, frame relay and ATM. Contrast with circuit switching.


From FDM to TDM to IP
IP-based packet switching has become the transport for nearly everything, including voice and video. For voice conversations especially, analog and digital-based circuit switching waste as much as 75% of the bandwidth due to pauses in speech and one person listening while the other talks.
References in periodicals archive ?
Contact centers with packet switched technology could generate cost savings of 7% from additional utilization.
With this approach, wireless service providers can continue to support their existing customer base, provide new revenue streams and services with application awareness such as Voice over IP (VoIP), real-time video connectivity, and online gaming, while converging on an IP/MPLS packet switched network.
The Packet Switched Streaming Activity Group was formed by the IMTC in order to perform interoperability tests for Packet-Switched Streaming according to 3GPP Technical Specifications 26.
Moreover, the group has published an `Implementation Guide' containing clarifications and interpretations to the Packet Switched Streaming specifications, in order to encourage the development of interoperable solutions.
The factors behind this expansion are twofold: Firstly, the mobile media industry anticipates that Packet Switched Streaming will emerge as a significant technology of the future, enabling exciting new applications in mobile multimedia communications.
The products, known as the Intel(R) NetStructure(TM) ZT 5504 System Master Processor Board with an Intel(R) Pentium III processor and the Intel(R) NetStructure(TM) ZT 5090 4U General Purpose Packet Switched Platform, include chassis, backplanes, hot-swap power supplies and fail-over capabilities.
Moreover, developers may take advantage of packet switched technology as this Kontron platform supports dual redundant Ethernet switches (2 fabric slots + 14 nodes).
today announced that it has expanded its innovative OMC product line into packet switched networks (OMC-PS).
The comprehensive WatchMark OMC-PS monitors fault alerts, service disruptions, unauthorized entry and usage levels from an easy-to-use, integrated desktop that helps service providers run their packet switched network with greater efficiency and profitability.
Data Services Over A Combination Of Packet Switched Networks
5 generation services, and to add packet switched capabilities to its circuit switched communication network.
This is because GPRS is a data packet switched based technology, as opposed to current circuit switched based networks used for voice traffic.