Information about Packet Switching
Packet switching is a communications paradigm in which packets (discrete blocks of data) are routed between nodes over data links shared with other traffic. In each network node, packets are queued or buffered, resulting in variable delay. This contrasts with the other principal paradigm, circuit switching, which sets up limited number of constant bit rate and constant delay connections between the nodes for their exclusive use for the duration of the communication.
Packet mode or packet oriented communication may be utilized with or without a packet switch or router. Examples of the latter case are point-to-point data links, digital video and audio broadcasting or a shared physical medium, such as a bus network, ring network, or hub network.
Packet mode communication is a statistical multiplexing technique, also known as a dynamic bandwidth allocation method, where a physical communication channel is divided into an arbitrary number of logical variable bit-rate channels or data streams. Each stream is divided into packets that normally are forwarded by a network node asynchronously in a first-come first-serve fashion. Alternatively, the packets may be forwarded according to some scheduling discipline for fair queuing or differentiated and/or guaranteed Quality of service. In case of a shared physical media, the packets may be delivered according to some packet-mode multiple access scheme.
Networks using packet switching can use datagrams or connectionless messages and/or virtual circuit switching (also known as connection oriented). Some connectionless protocols include Ethernet, UDP, IP. Some connection oriented protocols include TCP, Multiprotocol Label Switching (MPLS), Asynchronous Transfer Mode (ATM), X.25 and Frame relay.
It's also entirely possible to have to weigh the various metrics against each other. For example, reducing the hop count could increase the latency to an unacceptable limit and some kind of balance would need to be found. For multi-parameter optimization, some form of optimization may be needed.
Once a route is determined for a packet, it is entirely possible that the route may change for the next packet, thus leading to a case where packets from the same source headed to the same destination could be routed differently.
Packet switching influenced the development of the Actor model of concurrent computation in which messages sent to the same address may be delivered in an order different from the order in which they were sent.
The most well-known use of packet switching is the Internet and local area networks. The Internet uses the Internet protocol suite over a variety of data link layer protocols. For example, Ethernet and Frame relay are very common. Newer mobile phone technologies (e.g., GPRS, I-mode) also use packet switching.
X.25 is a notable use of packet switching in that, despite being based on packet switching methods, it provided virtual circuits to the user. These virtual circuits carry variable-length packets In 1978, X.25 was used to provide the first international and commercial packet switching network, the International Packet Switched Service (IPSS). Asynchronous Transfer Mode (ATM) also is a virtual circuit technology, which uses fixed-length cell relay connection oriented packet switching.
Datagram packet switching is also called connectionless networking because no connections are established. Technologies such as Multiprotocol Label Switching (MPLS) and the Resource Reservation Protocol (RSVP) create virtual circuits on top of datagram networks. Virtual circuits are especially useful in building robust failover mechanisms and allocating bandwidth for delay-sensitive applications.
MPLS and its predecessors, as well as ATM, have been called "fast packet" technologies. MPLS, indeed, has been called "ATM without cells" [1]. Modern routers, however, do not require these technologies to be able to forward variable-length packets at multigigabit speeds.
Baran developed the concept of packet switching during his research at the RAND Corporation for the US Air Force into survivable communications networks, first published as RAND Paper P-2626 in 1962 [1], and then including and expanding somewhat within a series of eleven papers titled On Distributed Communications in 1964 [2]. Baran's P-2626 paper described a general architecture for a large-scale, distributed, survivable communications network. The paper focuses on three key ideas: first, use of a decentralized network with multiple paths between any two points; and second, dividing complete user messages into what he called message blocks (later called packets); then third, delivery of these messages by store and forward switching.
Baran's study made its way to Robert Taylor and J.C.R. Licklider at the Information Processing Technology Office, both wide-area network evangelists, and it helped influence Lawrence Roberts to adopt the technology when Taylor put him in charge of development of the ARPANET.
Baran's packet switching work was similar to the research performed independently by Donald Davies at the National Physical Laboratory, UK. In 1965, Davies developed the concept of packet switched networks and proposed development of a UK wide network. He gave a talk on the proposal in 1966, after which a person from the Ministry of Defense told him about Baran's work. Davies met Lawrence Roberts at the 1967 ACM Symposium on Operating System Principles, bringing the two groups together.
Interestingly, Davies had chosen some of the same parameters for his original network design as Baran, such as a packet size of 1024 bits. Roberts and the ARPANET team took the name "packet switching" itself from Davies's work.
| Multiplex techniques |
| Circuit mode — for constant bandwidth |
| TDM | FDM | WDM | Polarization multiplexing | Spatial multiplexing (MIMO) |
| Statistical multiplexing — for variable bandwidth |
| Packet mode | Dynamic TDM | FHSS | DSSS | OFDMA |
| Related topics |
| Channel access methods | Media Access Control
|
Packet mode communication is a statistical multiplexing technique, also known as a dynamic bandwidth allocation method, where a physical communication channel is divided into an arbitrary number of logical variable bit-rate channels or data streams. Each stream is divided into packets that normally are forwarded by a network node asynchronously in a first-come first-serve fashion. Alternatively, the packets may be forwarded according to some scheduling discipline for fair queuing or differentiated and/or guaranteed Quality of service. In case of a shared physical media, the packets may be delivered according to some packet-mode multiple access scheme.
Networks using packet switching can use datagrams or connectionless messages and/or virtual circuit switching (also known as connection oriented). Some connectionless protocols include Ethernet, UDP, IP. Some connection oriented protocols include TCP, Multiprotocol Label Switching (MPLS), Asynchronous Transfer Mode (ATM), X.25 and Frame relay.
Connectionless packet switching and routing
Packets are routed to their destination as determined by a routing algorithm. The routing algorithm can create paths based on various metrics and desirable qualities of the routing path. For example, low latency may be of paramount concern and everything else is secondary, or a minimum hop count.It's also entirely possible to have to weigh the various metrics against each other. For example, reducing the hop count could increase the latency to an unacceptable limit and some kind of balance would need to be found. For multi-parameter optimization, some form of optimization may be needed.
Once a route is determined for a packet, it is entirely possible that the route may change for the next packet, thus leading to a case where packets from the same source headed to the same destination could be routed differently.
Packet switching influenced the development of the Actor model of concurrent computation in which messages sent to the same address may be delivered in an order different from the order in which they were sent.
Packet switching in networks
The most well-known use of packet switching is the Internet and local area networks. The Internet uses the Internet protocol suite over a variety of data link layer protocols. For example, Ethernet and Frame relay are very common. Newer mobile phone technologies (e.g., GPRS, I-mode) also use packet switching.
X.25 is a notable use of packet switching in that, despite being based on packet switching methods, it provided virtual circuits to the user. These virtual circuits carry variable-length packets In 1978, X.25 was used to provide the first international and commercial packet switching network, the International Packet Switched Service (IPSS). Asynchronous Transfer Mode (ATM) also is a virtual circuit technology, which uses fixed-length cell relay connection oriented packet switching.
Datagram packet switching is also called connectionless networking because no connections are established. Technologies such as Multiprotocol Label Switching (MPLS) and the Resource Reservation Protocol (RSVP) create virtual circuits on top of datagram networks. Virtual circuits are especially useful in building robust failover mechanisms and allocating bandwidth for delay-sensitive applications.
MPLS and its predecessors, as well as ATM, have been called "fast packet" technologies. MPLS, indeed, has been called "ATM without cells" [1]. Modern routers, however, do not require these technologies to be able to forward variable-length packets at multigigabit speeds.
History of packet switching
The concept of packet switching was first explored by Paul Baran in the early 1960's, and then independently a few years later by Donald Davies (Abbate, 2000). Leonard Kleinrock conducted early research and published a book in the related field of digital message switching (without the packets) in 1961, and also later played a leading role in building and management of the world's first packet switched network, the ARPANET.Baran developed the concept of packet switching during his research at the RAND Corporation for the US Air Force into survivable communications networks, first published as RAND Paper P-2626 in 1962 [1], and then including and expanding somewhat within a series of eleven papers titled On Distributed Communications in 1964 [2]. Baran's P-2626 paper described a general architecture for a large-scale, distributed, survivable communications network. The paper focuses on three key ideas: first, use of a decentralized network with multiple paths between any two points; and second, dividing complete user messages into what he called message blocks (later called packets); then third, delivery of these messages by store and forward switching.
Baran's study made its way to Robert Taylor and J.C.R. Licklider at the Information Processing Technology Office, both wide-area network evangelists, and it helped influence Lawrence Roberts to adopt the technology when Taylor put him in charge of development of the ARPANET.
Baran's packet switching work was similar to the research performed independently by Donald Davies at the National Physical Laboratory, UK. In 1965, Davies developed the concept of packet switched networks and proposed development of a UK wide network. He gave a talk on the proposal in 1966, after which a person from the Ministry of Defense told him about Baran's work. Davies met Lawrence Roberts at the 1967 ACM Symposium on Operating System Principles, bringing the two groups together.
Interestingly, Davies had chosen some of the same parameters for his original network design as Baran, such as a packet size of 1024 bits. Roberts and the ARPANET team took the name "packet switching" itself from Davies's work.
See also
- Store and forward delay
- Circuit switching
- Message switching
- Public switched data network
- Packet switched network
- Optical burst switching
- Statistical multiplexing
- ALOHAnet
References
- Leonard Kleinrock, Information Flow in Large Communication Nets, (MIT, Cambridge, May 31, 1961) Proposal for a Ph.D. Thesis
- Leonard Kleinrock. Information Flow in Large Communication Nets (RLE Quarterly Progress Report, July 1961)
- Leonard Kleinrock. Communication Nets: Stochastic Message Flow and Delay (Mcgraw-Hill, New York, 1964)
- Paul Baran et al., On Distributed Communications, Volumes I-XI (RAND Corporation Research Documents, August, 1964)
- Paul Baran, On Distributed Communications: I Introduction to Distributed Communications Network (RAND Memorandum RM-3420-PR. August 1964)
- Paul Baran, On Distributed Communications Networks, (IEEE Transactions on Communications Systems, March 1964)
- D. W. Davies, K. A. Bartlett, R. A. Scantlebury, and P. T. Wilkinson, A digital communications network for computers giving rapid response at remote terminals (ACM Symposium on Operating Systems Principles. October 1967)
- R. A. Scantlebury, P. T. Wilkinson, and K. A. Bartlett, The design of a message switching Centre for a digital communication network (IFIP 1968)
- Larry Roberts and Tom Merrill, Toward a Cooperative Network of Time-Shared Computers (Fall AFIPS Conference. October 1966)
- Lawrence Roberts, The Evolution of Packet Switching (Proceedings of the IEEE, November, 1978)
Further reading
- Katie Hafner, Where Wizards Stay Up Late (Simon and Schuster, 1996) pp 52-67
- Janet Abbate, Inventing the Internet (MIT Press, 2000) ISBN 0-262-51115-0
External links
- Packet Switching History and Design, site reviewed by Baran, Roberts, and Kleinrock
- Paul Baran and the Origins of the Internet
- A Brief History of the Internet
Since the late 1960s, the word paradigm (IPA: /ˈpærədaɪm/) has referred to a thought pattern in any scientific discipline or other epistemological context.
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Routing (or routeing) is the process of selecting paths in a network along which to send data or physical traffic. Routing is performed for many kinds of networks, including the telephone network, the Internet, and transport networks.
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A node is a device that is connected as part of a computer network. For example, a node may be a computer, personal digital assistant, cell phone, router, switch, or hub.
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In telecommunications, a circuit switching network is one that establishes a dedicated circuit (or channel) between nodes and terminals before the users may communicate. Each circuit that is dedicated cannot be used by other callers until the circuit is released and a new
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In electronics, telecommunications and computer networks, multiplexing (short muxing) is a term used to refer to a process where multiple analog message signals or digital data streams are combined into one signal. The aim is to share an expensive resource.
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In telecommunications, a circuit switching network is one that establishes a dedicated circuit (or channel) between nodes and terminals before the users may communicate. Each circuit that is dedicated cannot be used by other callers until the circuit is released and a new
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Time-Division Multiplexing (TDM) is a type of digital or (rarely) analog multiplexing in which two or more signals or bit streams are transferred apparently simultaneously as sub-channels in one communication channel, but physically are taking turns on the channel.
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In fibre-optic communications, wavelength-division multiplexing (WDM) is a technology which multiplexes multiple optical carrier signals on a single optical fibre by using different wavelengths (colours) of laser light to carry different signals.
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Statistical multiplexing is a type of communication link sharing. In statistical multiplexing, a communication channel is divided into an arbitrary number of variable bit-rate digital channels or data streams.
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Packet switching is a communications paradigm in which packets (discrete blocks of data) are routed between nodes over data links shared with other traffic. In each network node, packets are queued or buffered, resulting in variable delay.
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Frequency-hopping spread spectrum (FHSS) is a method of transmitting radio signals by rapidly switching a carrier among many frequency channels, using a pseudorandom sequence known to both transmitter and receiver.
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In telecommunications, direct-sequence spread spectrum (DSSS) is a modulation technique. As with other spread spectrum technologies, the transmitted signal takes up more bandwidth than the information signal that is being modulated.
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Orthogonal Frequency Division Multiple Access (OFDMA) is a multi-user version of the popular OFDM digital modulation scheme. Multiple access is achieved in OFDMA by assigning subsets of subcarriers to individual users as shown in the figure below.
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In telecommunications and computer networks, a channel access method or multiple access method allows several terminals connected to the same physical medium to transmit over it and to share its capacity.
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Media Access Control (MAC) data communication protocol sub-layer, also known as the Medium Access Control, is a part of the data link layer specified in the seven-layer OSI model (layer 2).
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Statistical multiplexing is a type of communication link sharing. In statistical multiplexing, a communication channel is divided into an arbitrary number of variable bit-rate digital channels or data streams.
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First come, first served (sometimes first-come, first-served or simply FCFS) is a service policy whereby the requests of customers or clients are attended to in the order that they arrived, without other biases or preferences.
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Fair queuing (FQ), is a scheduling scheme used in computer networks and statistical multiplexing to allow several data flows to fairly share the link capacity. The advantage over conventional first in first out (FIFO) queuing, is that an ill-behaved flow (consisting of large data
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Quality of Service, abbreviated QoS, refers to resource reservation control mechanisms. Quality of Service can provide different priority to different users or data flows, or guarantee a certain level of performance to a data flow in accordance with requests from the
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In telecommunications and computer networks, a channel access method or multiple access method allows several terminals connected to the same physical medium to transmit over it and to share its capacity.
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In a packet-switched network, connectionless mode transmission is a transmission in which each packet is prepended with a header containing a destination address sufficient to permit the independent delivery of the packet without the aid of additional instructions.
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In telecommunications and computer networks, a virtual circuit (VC), synonymous to virtual connection and virtual channel, is a connection oriented communication service that is delivered by means of packet mode communication.
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In telecommunications, connection-oriented describes a means of transmitting data in which the devices at the end points use a preliminary protocol to establish an end-to-end connection before any data is sent, and in which data is sent over the same path during the communication.
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Ethernet is a family of frame-based computer networking technologies for local area networks (LANs). The name comes from the physical concept of the ether. It defines a number of wiring and signaling standards for the physical layer, through means of network access at the Media
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UDP can refer to:
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- User Datagram Protocol, an Internet protocol
- Usenet Death Penalty
- Ulster Democratic Party
- Uridine diphosphate
- Universidad Diego Portales
- União Democrática Popular, a left-wing political party in Portugal
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Internet protocol may refer to:
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- The Internet Protocol, a data-oriented protocol used for communicating data across a packet-switched internetwork
- The Internet protocol suite, a set of communications protocols that implement the protocol stack on which the Internet runs
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TCP may stand for:
Computing
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Computing
- Transmission Control Protocol, a transportation protocol that is one of the core protocols of the Internet protocol suite
- Trusted Computing Platform Alliance's Trusted Computing Platform
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In computer networking and telecommunications, Multi Protocol Label Switching (MPLS) is a data-carrying mechanism that belongs to the family of packet-switched networks.
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Asynchronous Transfer Mode (ATM) is a cell relay, packet switching network and data link layer protocol which encodes data traffic into small (53 bytes; 48 bytes of data and 5 bytes of header information) fixed-sized cells.
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X.25 is an ITU-T standard protocol suite for connection to packet switched wide area networks using leased lines, the phone or ISDN system as the networking hardware. It was developed before the OSI Reference Model or the equivalent Network Access Layer of the DoD protocol model,
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