Switching methods

Switching:

A network is a set of connected devices. Whenever we have multiple devices, we have the problem of how to connect them to make one to one communication possible. One solution is to make a point to point connection between each pair of devices (a mesh topology) of between a central device and every other device (star topology). These methods, however, are impractical and wasteful when applied to very large networks. A better solution is switching.

A switched network consists of a series of interlinked nodes, called switches. Switches are devices capable of creating temporary connections between two or more devices linked to the switch. In switched network, some of these nodes are connected to the end systems (computers ortelephones).

There are basically three types of switching methods are made available. Out of three methods, circuit switching and packet switching are commonly used but the message switching has been opposed out in the genera communication procedure but is still used in the networking application.

1) Circuit Switching

2) Packet Switching

3) Message Switching

Circuit Switching

Circuit Switching is generally used in the public networks. It comes into existence for handling voice traffic in addition to digital data. However digital data handling by the use of circuit switching methods are proved to be inefficient.

The end to end communication was established during the duration of call.· In circuit switching the routing decision is made when the path is set up across the given network. After the link has been sets in between the sender and the receiver then the information is forwarded continuously over the provided link.· In Circuit Switching a dedicated link/path is established across the sender and the receiver which is maintained for the entire duration of conversation.

Packet Switching

In Packet Switching, messages are broken up into packets and each of which includes a header with source, destination and intermediate node address information. Individual Packets in packet switching technique take different routes to reach their respective destination. Independent routing of packets is done in this case for following reasons:

1. Bandwidth is reduces by the splitting of data onto different routes for a busy circuit.

2. For a certain link in the network, the link goes down during transmission the remaining packet can be sent through another route.

Packet Switching Network

· The major advantage of Packet switching is that they are used for performing data rate conversion.

· When traversing the network switches, routers or the other network nodes then the packets are buffered in the queue, resulting in variable delay and throughput depending on the network’s capacity and the traffic load on network.

· Packet switching contrasts with another principal networking paradigm, circuit switching, a method which sets up a limited number of dedicated connections of constant bit rate and constant delay between nodes for exclusive use during the communication session.

· In cases where traffic fees are charged, for example in cellular

communication, packet switching is characterized by a fee per unit of

Information transmitted.

Message Switching

In case of Message Switching it is not necessary to establish a dedicated path in between any two communication devices. Here each message is treated as an independent unit and includes its own destination source address by its own. Each complete message is then transmitted from one device to another through internetwork.

Message Switching Data Network

· Each intermediate device receive the message and store it until the nest device is ready to receive it and then this message is forwarded to the next device. For this reason a message switching network is sometimes called as Store and Forward Switching.

· Message switches can be programmed with the information about the most efficient route as well as information regarding to the near switches that can be used for forwarding the present message to their required destination.

· The storing and Forwarding introduces the concept of delay. For this reasons this switching is not recommended for real time applications like voice and video arrival at the destination host is not the final objective of data communications on the Internet. 

overview of tcp/ip

Overview of TCP/IP:

The TCP/IP protocol suit was developed prior to the OSI model. The TCP/IP protocol suit was defined as having four layers: host-to-network, internet, transport and application. TCP/IP is a hierarchical protocol made up of interactive modules, each of which provides a specific functionality.

The term hierarchical means that each upper level protocol is supported by one or more lower level protocols. At transport layer TCP/IP defines three protocols: (TCP) Transmission Control Protocol, UDP (User Datagram Protocol), and (SCTP) Stream Control Transmission Protocol. At physical and data link layers, TCP/IP does not define any specific protocol. It supports all the standard and proprietary protocols. At the network layer, TCP/IP supports the Internetworking Protocols. IP, in turn uses four supporting protocols: ARP(Address Resolution  Protocol), RARP(Reverse Address Resolution Protocol), ICMP (Internet Control Message Protocol), and IGMP(Internet Group Message Protocol). Addressing: Four level of addresses are used in an internet employing TCP/IP protocols:

1. Physical address: It is also called link address, is the address of a node as defined by its LAN WAN. It is included in the frame used by the data link layer. It is the lowest level address. The size and format of these addresses vary depending on the network. For example Ethernet uses a 5 byte(48bit) physical address that is imprinted on the network interface card.

2. Logical Address: these address are necessary for universal communications that are independent of underlying physical networks. Physical addresses are not adequate in an internetwork environment where different networks can have different address formats. A universal addressing system is needed in which each host can be identified uniquely, regardless of the underlying physical network. The logical address in the Internet is currently a 32 bit address that can uniquely define a host connected to the Internet. No two publicly addressed and visible hosts on the Internet can have the same IP address.

3. The IP address and the physical address are necessary for a quantity of data to travel from a source to the destination host. However, arrival at the destination host is not the final objective of data communications on the Internet. Today computers are devices that can run multiple processes at the same time. The end objective of Internet communication is a process communicating with another process. For these processes to receive data simultaneously, we need a method to label the different processes. In other words they need addresses. In the TCP/IP architecture, the label assigned to a process is called a port address. A port address in TCP/IP is 16 bits in length.

4. Specific Address: Some applications have user friendly addresses that are designed for that specific address. Examples include the email address (vineetkathuria2000@yahoo.com) and the URL www.netsetgo.co.in the addresses however get changed to the corresponding port and logical addresses by the sending computer.

New Syllabus of BCA session 2017-2020