Packet Switching vs. Circuit Switching

DIFFERENCE BETWEEN PACKET SWITCHING AND CIRCUIT SWITCHING IS AS FOLLOW:

Switched networks today get data across the network through packet switching, the concept of circuit switching should be no
mystery to the average tech, let alone the tech wannabe.

There are at least two good reasons to learn the difference.

First of all, there is plenty of legacy hardware out there to support.

Second, and perhaps more or at least very important, it could well turn up on the test. If one question stands between you
and passing, don’t make this the one you miss.

In principle, circuit switching and packet switching both are used in high-capacity networks. In circuit-switched networks, network resources are static, set in “copper” if you will, from the sender to receiver before the start of the transfer, thus creating a “circuit”. The resources remain dedicated to the circuit during the entire transfer and the entire message follows the same path. In packet-switched networks, the message is broken into packets, each of which can take a different route to the destination where the packets are recompiled into the original message.

All the above can be handled by a router or a switch but much of IT today is going toward flat switched networks. So when we’re talking about circuit switching or packet switching, we are more and more talking about doing it on a switch.

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 somewhatwithin 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.

Packet Switching in NETWORKS

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.

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 a 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.

SWITCHING

The term switching was originally used to describe packet-switch technologies, such as Link Access Procedure, Balanced (LAPB), Frame Relay, Switched Multimegabit Data Service (SMDS), and X.25. Today, switching refers to a technology that is similar to a bridge in many ways.

The term bridging refers to a technology in which a device (known as a bridge) connects two or more LAN segments. A bridge transmits datagrams from one segment to their destinations on other segments. When a bridge is powered and begins to operate, it examines the Media Access Control (MAC) address of the datagrams that flow through it to build a table of known destinations. If the bridge knows that the destination of a datagram is on the same segment as the source of the datagram, it drops the datagram because there is no need to transmit it. If the bridge knows that the destination is on another segment, it transmits the datagram on that segment only. If the bridge does not know the destination segment, the bridge transmits the datagram on all segments except the source segment (a technique known as flooding). The primary benefit of bridging is that it limits traffic to certain network segments.

Like bridges, switches connect LAN segments, use a table of MAC addresses to determine the segment on which a datagram needs to be transmitted, and reduce traffic. Switches operate at much higher speeds than bridges, and can support new functionality, such as virtual LANs.