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.
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 discuss edit
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.
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 Main article: Packet switched network
Packet switching is used to optimize the use of the channel capacity available
in a network, to minimize the transmission latency (i.e. the time it takes for
data to pass across the network), and to increase robustness of communication.
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.
Attributes and Credits
The information and facts supplied on this subject
derive from http://en.wikipedia.org/wiki/Main_Page
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.
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 discuss edit
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.
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 Main article: Packet switched network
Packet switching is used to optimize the use of the channel capacity available
in a network, to minimize the transmission latency (i.e. the time it takes for
data to pass across the network), and to increase robustness of communication.
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.
Attributes and Credits
The information and facts supplied on this subject
derive from http://en.wikipedia.org/wiki/Main_Page
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