Packet Switching-Networking

January 9, 2016 by afaqahmad

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Last modified January 9, 2016

Packet switching is a digital network communication method which groups all transmitted data in sufficiently large blocks, called packets, which via a medium that can be shared by more than one simultaneous communications are transferred sessions. Packet Switched network increases efficiency, robustness, and makes technological convergence of many applications on the same network.

Packets are composed of a header and payload. The information in the header is used by the network hardware to direct the packet to the place of destination where the charge is extracted and used by software.

From the late 1950s, the American computer scientist Paul Baran developed the concept of Distributed Adaptive Message Block Transfer with the aim of a fault-tolerant, efficient routing method for telecommunication posts as part of a research program at the RAND Corporation, funded by the US Department of Defense.

This concept contrast and contradicted the established theretofore principles of pre-allocation of network bandwidth, especially strengthened by the development of telecommunications in the Bell System. The new concept found little resonance among network administrators to independently work by Donald Davies at the National Physical Laboratory (United Kingdom) (NPL) in the late 1960s Davies is credited with coining the modern name of packet switching and inspiring numerous packet switching networks in Europe in the next ten years, including the integration of the concept in the early ARPANET in the United States.

Concept:-

A simple definition of packet switching is:

The routing and transferring data by means of addressed packets so that a channel is occupied during the transmission of the packet, and only after termination of the communication channel is made available for the transmission of other traffic

Packet switching characteristics delivery of variable bit rate data streams, realized as sequences of packets, then acomputer network transmission allocates resources as necessary using statistical multiplexing and dynamic bandwidth allocation techniques. By traversing network nodes, such as switches and routers, packets are buffered and queued, resulting in variable latency and throughput depending on the torque capacity and traffic load on the network.

Packet switching contrasts with other principal paradigm, circuit switching network, a method in which previously dedicated network allocates bandwidth specifically for each communications session, each of a constant bit rate and latency between nodes. In case of billable services, such as mobile communication is circuit switched characterized by a charge per unit of connection time, even when no data is being transferred, and packet switching are characterized by a charge information transmitted per unit, such as characters, packets or messages.

Packet-mode communication can be performed with or without intermediate forwarding nodes (packet switches and routers). Packages are normally routed through intermediate network nodes asynchronously using first-in, first-out buffering, but can be transmitted according to some planning discipline for fair queuing, traffic shaping, or differentiated and guaranteed quality of service, such as weighted fair queuing or leaky bucket. In a shared physical medium (e.g. radio or 10Base5), the packets can be delivered in accordance with a multiple access scheme.

History:-

In the late 1950s, the US Air Force has a wide area network for the Semi-Automatic Ground Environment (SAGE) radar defense system. They wanted a system that could survive a nuclear attack, to allow for a reaction, thus reducing the attractiveness of the first strike advantage by enemies.

Leonard Kleinrock conducted early research queuing theory that have proven important in packet switching, and a book turn in the related field of digital message (with the package) was published in 1961; He later played a leading role in the construction and management of the world’s first packet-switched network, the ARPANET.

The concept of switching small blocks of data was first analyzed independently by Paul Baran at the RAND Corporation in the United States and Donald Davies at the National Physical Laboratory (NPL) in the UK in the early to mid-1960.

Baran developed the concept of distributed adaptive message block switching during his research at the RAND Corporation for the US Air Force in survivable communications for the first time presented to the Air Force in the summer of 1961 when briefing B-265, later published as RAND report P -2 626 in 1962, and finally in the report of RM 3420 in 1964.Report P-2626 described a general architecture for a large-scale, distributed, survivable communications network. The work focuses on three key ideas: the use of a decentralizednetwork with multiple paths between two points, dividing the user messages into message blocks, later called packets, and store the delivery of these messages and forward switching.

Baran’s work was announced that Robert Taylor and JCR Licklider’s Information Processing Technology Office, which called for wide area networks and influenced Lawrence Roberts adopt the technology in the development of the ARPANET.

Beginning in 1965, Donald Davies at the National Physical Laboratory, UK, independently developed the same message routing method developed by Baran. He called the packet switching, a more accessible than Baran’s name, and proposed a nationwide network in the UK.He gave a lecture on the proposal in 1966, after which a person from the Ministry of Defence (MoD) told him about Baran Building works. A member of Davies’ team (Roger Scantlebury) met Lawrence Roberts at the 1967 ACM Symposium on Operating System Principles and suggested for use in the ARPANET.

Davies had some of the same parameters as well as his original network design Baran selected, for example a packet size of 1024 bits. In 1966, Davies proposed a network to be constructed in the laboratory to serve the needs of NPL and demonstrate the feasibility of packet switching. The NPL Data Communications Network in service in 1970.

The first computer network and packet switching network used for sharing the computing resource was the Octopus Network at the Lawrence Livermore National Laboratory, which started connecting four Control Data 6600 computer to multiple shared storage devices (including an IBM 2321 Data Cell in 1968 and an IBM Photo Store in 1970) and up to several hundred Teletype Model 33 ASR terminals for timeshares to begin in 1968.

In 1973, Vint Cerf and Bob Kahn wrote the specifications for Transmission Control Protocol (TCP), an internetworking protocol for sharing resources using packet-switching between the nodes.

Connectionless and connection-oriented modes:-

Packet switching connectionless are classified into packet-switched, also known as datagram switching and connection-oriented packet switching, also known as a virtual circuit switching.

Examples of connectionless protocols, Ethernet, Internet Protocol (IP) and the User Datagram Protocol (UDP). Connection-oriented protocols include X.25, Frame Relay, Multi Protocol Label Switching (MPLS), and the Transmission Control Protocol (TCP).

In connectionless mode, each package contains complete address. The packets are individually led, which sometimes leads to different paths and out-of-order delivery. Each package is marked with a destination address, source address and port numbers. It can also be labeled with the sequence number of the packet. This avoids the need for a specific path to package its way to its destination, but means that much more information is needed in the packet header, which therefore increases, and this information must be searched in energy-hungry content -addressable memory. Each packet is sent and can go through different routes; if necessary, the system do so much work for each packet as a connection-oriented system should do link building, but with less information on the application requirements. At the destination, the original message / data is then in the correct order based on the package number. Thus, a virtual connection, also known as a virtual circuit orbyte stream is to the end user by a transport layer protocol, but intermediate network nodes gives only a connectionless network layer service.

Connection-oriented transmission requires an installation stage in which each such node before a packet is transferred to the parameters of the communication. The packages include a connection identification number instead of address information, and to be negotiated between the end points so that they are delivered in order with error checking. Details on until each node in the connection set-up phase, when the route to the destination is detected and an entry is added to the switching table, each network node through which the connection passes. The signaling protocols used to specify the application to its demands and discover clutch parameters. Acceptable values ​​for the service parameters can be negotiated. Routing a packet is to search for the node of the connection ID in the table. The packet header can be small, since it must only this code and all information, such as length, time stamp or sequence number, which is different for different packets contain.

Packet switching networks:-

Packet switching is used for the optimization of minimizing the use of the channel capacity in digital telecommunications networks such as computer networks, the transmission latency (the time that pass data on the network), and to increase robustness of the communication.

The most famous use of packet switching the Internet and most local networks. The Internet is performed by the Internet Protocol Suite with different link Layer Technologies. For example, Ethernet and Frame Relay are common. Newer mobile phone technologies (GPRS, i-mode) also use packet switching.

X.25 is a remarkable use of packet switching, that in spite of packet switching methods based on virtual circuits provided to the user. These virtual circuits carry variable-length packets. In 1978, X.25 provided the first international and commercial packet switching network, the International Packet Switched Service (IPSS). Asynchronous Transfer Mode (ATM) is also a virtual circuit technology, which uses a fixed length cell relay connection-oriented packet switching.

Datagram packet switching is also called connectionless networks because there are no connections are established. Technologies such as Multiprotocol Label Switching (MPLS) and there source reservation protocol (RSVP) to create virtual circuits on top of datagram networks. Virtual circuits are especially useful in the construction of robust failover mechanisms and allocating bandwidth for the delay-sensitive applications.

X25 vs. Frame Relay:-
Both X25 and Frame Relay offer connection-oriented operations. X.25 but does it on the network layer of the OSI model. Frame Relay does at level two, the data link layer. Another important difference between X.25 and Frame Relay X.25 that requires a handshake between the communicating parties for each user packets are sent. Frame Relay define no such handshakes. X.25 not define operations in the packet-switched network. It works only on the user-network interface (UNI). Thus, the provider is free to want to use the network a procedure. X.25 does give limited re-transmission procedures at the UNI, and the link layer protocol (LAPB) offers conventional HDLC-type link management procedures. Frame Relay is a modified version of the ISDN protocol layer two, and LAPD LAPB. As such, the integrity activity only relates to a connection between nodes, no end-to-end. Each transfer must be done by higher layer protocols. The UNI X.25 protocol is part of the X.25 protocol suite, consisting of the lower three layers of the OSI model. Much was used UNI for packet networks in the 1980s and early 1990s, a standardized interface to and from packet networks. Some implementations used in the X.25 network as well, but the connection oriented features in this setup cumbersome and inefficient. Frame Relay operates mainly in two layers of the OSI model. However, the address field can be (the Data Link Connection ID or DLCI) are used in the OSI network layer, with a minimum set of procedures. So gets rid of many X.25 layer 3 charges, but has DLCI as ID passed a node-to-node communication protocol layer two. The simplicity of Frame Relay makes it faster and more efficient than X.25. Since Frame Relay is a data link layer protocol, such as X.25 does not define the internal network routing operations. X.25 packet IDs are — the virtual circuit and virtual channel numbers should be correlated to network addresses. The same applies to the Frame Relay DLCI. How this is done is up to the provider. Frame Relay, on the grounds of having no network layer is connection-oriented procedures on layer two, using the HDLC / LAPD / LAPB Set Asynchronous Balanced Mode (SABM). X.25 connections are normally set for each communication session, but it has a feature that allows a limited amount of traffic on the UNI passed without connection oriented handshake. For a while, Frame Relay was used to connect LANs over wide area networks to each other. However, X.25 and Frame Relay as well is displaced by the Internet Protocol (IP) at the network layer and the Asynchronous Transfer Mode (ATM), and whether the versions of the Multi-Protocol Label Switching (MPLS) at layer two. A typical configuration is to run over IP ATM or a version of MPLS. <Uyless Black, X.25 and related protocols, IEEE Computer Society, 1991> <Uyless Black, Frame Relay networks, McGraw-Hill, 1998> <Uyless Black, and MPLS Label Switching Networks, Prentice Hall, 2001> <Uyless Black, ATM, Volume I, Prentice Hall, 1995>

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