Electronic Switching Switching System A switch responds to an external force to mechanically change an electric signal. Switch are used to turn electric circuits ON and OFF and to switch electric circuits.. A Switching system can be understood as a collection of switching elements arranged a controlled in such a way as to set up a common path between any two distant points. T introduction of switching systems reduced the complexity of wiring and made the telepho hassle-free. Relays are normally used in the control panels, manufacturing and building automation control the power along with switching the smaller current values in a control circuit. ays are used where it is necessary to control a circuit by an independent low-power low signal, or where eral circuits must be controlled by one signal. The switching systems in the early stages were operated manually. The connections were made by the operators at the telephone exchanges in order establish a connection. To minimize the disadvantages of manual operation, automat switching systems were introduced The Automatic switching systems are classified as the following − Electromechanical Switching Systems − Here, mechanical switches are electrical operated. Electronic Switching Systems − Here, the usage of electronic components such diodes, transistors and ICs are used for the switching purposes. Electromechanical Switching Systems The Electromechanical switching systems are a combination of mechanical and electric switching types. The electrical circuits and the mechanical relays are deployed in them. Th Electromechanical switching systems are further classified into the following. Step-by-step - The Step-by-step switching system is also called the Strowger switchin system after its inventor A B Strowger. The control functions in a Strowger system ar performed by circuits associated with the switching elements in the system. Crossbar - The Crossbar switching systems have hard-wired control subsystems whic use relays and latches. These subsystems have limited capability and it is virtuall impossible to modify them to provide additional functionalities. Electronic Switching Systems he Electronic Switching systems are operated with the help of a processor or a computer which control th witching timings. he instructions are programmed and stored on a processor or computer that control the operations. his method of storing the programs on a processor or computer is called the Stored Program Contro PC) technology. New facilities can be added to a SPC system by changing the control program. he switching scheme used by the electronic switching systems may be either Space Division Switching o me Division Switching. pace Division Switching- a dedicated path is established between the calling and the called subscribers fo e entire duration of the call me division switching - Sampled values of speech signals are transferred at fixed Intervals. The tim vision switching may be analog or digital. In analog switching, the sampled voltage levels are transmitte they are. However, in binary switching, they are binary coded and transmitted. the coded values are transferred during the same time interval from input to output, the technique lled Space Switching. the values are stored and transferred to the output at a time interval, the technique is called Tim witching. A time division digital switch may also be designed by using a combination of space and tim witching techniques. Telecommunication Network A Telecommunication network is a group of systems that establishes a dista call. The switching systems are part of a telecommunication network. The switching stations provide connection between different subscribers. Su switching systems can be grouped to form a telecommunication network. The switching systems are connected using lines called the Trunks. The lin hat run to the Subscriber premises are called the Subscriber Lines. The following figure shows a telecommunication network. From the early to the later stages of the 20th 20 Century (1900-80), when a person needed ke a distant call, the call was first routed to the operator at the nearest switching center and then mber and location of the called subscriber was noted down. Here, the job of the operator was blish a call to the remote switching center and then recall the calling subscriber to establish nection. This system of making calls was called the Trunk call system. For example, a person at Hyderabad can book a trunk call to Mumbai and wait for the opera call back when the operator establishes connection through the trunk lines and the switch ems. Basics of a Switching System lets and Outlets The set of input circuits of an exchange are called Inlets and the set of outp circuits are called the Outlets. The primary function of a switching system is establish an electrical path between a given inlet-outlet pair. Usually, N indicates the inlets and the outlets are indicated by M. So, a switchi network has N inlets and M outlets. witching Matrix The hardware used to establish connection between inlets and outlets is call he Switching Matrix or the Switching Network. This switching network is t group of connections formed in the process of connecting inlets and outlets. Hen t is different from the telecommunication network mentioned above. Types of Connections There are four types of connections that can be established in telecommunication network. The connections are as follows − Local call connection between two subscribers in the system. Outgoing call connection between a subscriber and an outgoing trunk. Incoming call connection between an incoming trunk and a local subscriber. Transit call connection between an incoming trunk and an outgoing trunk. Folded Network When the number of inlets is equal to the number of outlets for a switchin etwork, such a network is called the Symmetric Network, which means N=M. etwork where the outlets are connected to the inlets, is called the Folded Networ n a Folded Network, the N number of inlets which come as outlets are again folde ack to the inlets. Nevertheless, the switching network provides connections to th nlets and outlets as per the requirement. requirement The following figure will help yo nderstand how the Switching Network works. works As one connection can be given to one line per time, only N/2 connections are established for N inlets o lded network. Such a network can be called as Non-blocking blocking network. In a non-blocking network, as long as lled subscriber is free, a calling subscriber will be able to establish a connection to the called subscriber. In the above figure, only 4 subscribers were considered - where line 1 is busy with line 2 and line 3 is b th line 4. While the call is in progress, there used to be no chance for making another call and hence, only a sin nnection was made. Hence for N inlets, only N/2 lines are connected. At times, it might happen that the inlet and outlet connections are continuously used to make Transit c rough trunk lines only, but not among the local subscribers. subscribers The inlet and outlet connections if used in an Int change transmission such that the exchange does not support connection between local subscribers, then i lled the Transit Exchange. A switching network of such kind is called the Non-folded network. s is shown in the following figure − Blocking Network If there are no switching paths free in the network, the call requested will be denied, where the subscrib said to be blocked and the network is called the Blocking Network. In a blocking network, the number multaneous switching paths is less than the maximum number of simultaneous conversations that can take plac he probability that a user may get blocked is called the Blocking Probability. A good design should ensure lo ocking probability. affic The product of the calling rate and the average holding time is defined as the Traffic Intensity. T ntinuous sixty-minute period during which the traffic intensity is high is the Busy Hour. When the traffic excee e limit to which the switching system is designed, a subscriber experiences blocking. lang The traffic in a telecommunication network is measured by an internationally accepted unit of traf tensity known as Erlang (E). A switching resource is said to carry one Erlang of traffic if it is continuous cupied through a given period of observation. Message switching techniques • Switched communication networks are those in which data transferred from source to destination is routed between various intermediate nodes. • Switching is the technique by which nodes control or switch data to transmit it between specific points on a network. • There are 3 common switching techniques: 1.Circuit Switching 2.Packet Switching 3.Message Switching Message Switching Message switching was a technique developed as an alternative to circuit switching before packet switching was introduced. In message switching, end-users users communicate by sending and receiving messages that included the entire data to be shared. Messages are the smallest individual unit. Also, the sender and receiver are not directly connected. There are a number of intermediate nodes that transfer data and ensure that the message reaches its destination. Message switched data networks are hence called hop-by-hop systems. They provide 2 distinct and important characteristics: Store and forward – The intermediate nodes have the responsibilit of transferring the entire message to the next node. Hence, each node must have storage capacity. A message will only be delivered the next hop and the link connecting it are both available, otherwise it’ll be stored indefinitely. A store-and-forward store switch forwards a message only if sufficient resources are available and the next hop i accepting data. This is called the store-and-forward property. Message delivery – This implies wrapping the entire information in a single message and transferring it from the source to the destination node. Each message must have a header that contain the message routing information, including the source and destination. • Message switching network consists of transmission links (channels), store-and-forward forward switch nodes, and end stations as shown in the following picture: Characteristics of message switching – Message switching is advantageous as it enables efficient usage of network resources. Also, because of the store-and and-forward capability of intermediary nodes, traffic can be efficiently regulated and controlled. Message delivery as one unit, rather than in pieces, is another benefit. However, message switching has certain disadvantages as well. Since messages are stored indefinitely at each intermediate node, switches require a large storage capacity. Also, these are pretty slow. This is because at each node, first there is a wait till the entire message is received, then it must be stored and transmitted after processing the next node and links to i depending on availability and channel traffic. Hence, message switching cannot be used for real-time or interactive applications like a video conference. Advantages of Message Switching – • Message switching has the following advantages: 1.As message switching is able to store the message for which communication channel is not available, it helps in reducing the traffic congestion in the network. 2.In message switching, the data channels are shared by the network devices. 3.It makes traffic management efficient by assigning priorities to the messages. 4.Because the messages are delivered via a store and forward method, it is possible to include priority in them. 5.It allows for infinite message lengths.. 6.Unlike circuit switching, it does not necessitate the actual connection of source and destination devices. Disadvantages of Message Switching – • Message switching has the following disadvantages: 1.Message switching cannot be used for real-time applications as storing messages causes delay. 2.In message switching, the message has to be stored for which every intermediate device in the network requires a large storing capacity. 3.Because the system is so intricate, people are frequently unaware of whether or not messages are correctly conveyed. This could cause problems in social relationships. 4.The type of message switching does not create a dedicated path between the devices. It is not dependable communication because there is no direct relationship between sender and receiver. Applications – • The store-and-forward method was implemented in telegraph message switching centres. Today, although many major networks and systems are packet-switched packet or circuit-switched networks, their delivery processes can be based on message switching. For example, in most electronic mail systems the delivery process is based on message switching, while the network is in fact either circuit-switched switched or packet-switched. What is circuit switching? • Circuit switching is a type of network configuration in which a physical path is obtained and dedicated to a single connection between two endpoints in the network for the duration of a dedicated connection. Ordinary voice phone service uses circuit switching. This reserved circuit is used for the duration of a call. As long as the call lasts, the circuit cannot be used for anything else. • In circuit switching, the bandwidth and data transmission rate are fixed. Circuit switching is connection-oriented, meaning a physical connection between hosts is required for it to work. What is circuit switching used for? Examples of where circuit switching is used include the following: Continuous connections. Circuit switching is used for connections that must be continuous for long periods of time, such as long-distance communication. Traditional telephone systems -- i.e., landlines -- are an example of a technology that uses circuit switching. Dial-up network connections. When computers connect to the internet via a dial-up service, it uses the public switched network. With dial-up, Internet Protocol (IP) data packets are carried over a circuitswitched telephone network. Optical circuit switching. Data center networks also use circuit switching. Optical circuit switching is used to scale traditional data centers and meet growing bandwidth requirements. What are the switching? phases of circuit • These are the three main phases of circuit switching: 1.Connection establishment. Also called call setup, this phase establishes a dedicated circuit between two communicating endpoints.. The parties send a message back and forth acknowledging the established connection. There are usually intermediate links or switches between the two parties. 2.Data transfer. Data -- usually voice -- is transmitted from the source to the destination. The connection remains intact for the length of the interaction. 3.Connection relinquishment. This is also called the teardown phase.. At the end of the interaction, one of the two endpoints sends a message initiating a disconnection. The communication path, including the intermediate links, is terminated. • How do packet-switched and circuit-switched networks differ? • The main difference between packet-switched packet vs. circuit-switched networks is that circuit-switched networks are connection-oriented and packet-switched networks are connectionless. Voice over IP is a telephony protocol that uses packet switching. • In packet switching, information is broken into data packets that are sent through the network independently of one another. There is no fixed, dedicated channel as there is in circuit switching. Instead, packets are sent over a network that other hosts share. Transmission also is not continuous. continuous Some packet-switched networks, such as X.25, have switched virtual circuits. Virtual circuit switching establishes a dedicated connection using packet-switching switching technology. A virtual circuitswitched connection is a dedicated, logical connection that enables multiple virtual circuit connections to share a physical path. Packet switching does not reserve all the bandwidth for a connection in advance. Because of that, it is more energy-efficient One drawback to packet switching is that transmission quality can be poor because there can be lost or dropped packets. • What are the advantages of circuit-switched circuit networks? • The advantages of circuit-switched switched networks include the following: • Dedicated channel. Circuit-switched switched networks reserve a dedicated communications channel circuit that only the two endpoints can access. • Reliable. A dedicated circuit between two hosts for the duration of that connection decreases the potential for data loss or other reliability problems. • Security. Circuit-switched switched networks are more secure than packetpacket switched networks due to having only two communicating parties on a dedicated circuit. • Quality. Once a connection is established, this type of network generally has a consistent connection quality without delays in data flow. • What are the disadvantages of circuit-switching? circuit • The drawbacks of using a circuit-switched switched network include the following: • Limited use. Circuit-switched switched networks can only be used for voice communication and aren't available for other types of connections. • Inefficient. When a circuit is continuously reserved even when it's not in use, network bandwidth is wasted. • Inflexible. A dedicated channel can only be used for circuit-switched circuit network traffic and nothing else. And, if there aren't enough dedicated channels, calls can fail. • Higher cost. A dedicated channel costs more per use. • Latency. Extra time is required to establish a connection before data is sent. • The takeaway • Circuit switching is the foundation of traditional telecommunication systems and landlines. Packet switching is the basis of the modern internet. Each has advantages and disadvantages. And, sometimes, they overlap - for example, when a packet switching network emulates circuit-switching switching technology and establishes a connectionconnection oriented method of data transfer. • Today, the internet and most phone services rely on packet switching. But most legacy networks were designed for circuitcircuit switched traffic. New optical routing architecture could help close this gap. • The takeaway • Circuit switching is the foundation of traditional telecommunication systems and landlines. Packet switching is the basis of the modern internet. Each has advantages and disadvantages. And, sometimes, they overlap - for example, when a packet switching network emulates circuit-switching switching technology and establishes a connectionconnection oriented method of data transfer. • Today, the internet and most phone services rely on packet switching. But most legacy networks were designed for circuitcircuit switched traffic. New optical routing architecture could help close this gap. • A packet switched network is one of the most commonly used computer networks. It is widely implemented on local networks and the Internet. • A PSN generally works on the Transmission Control Protocol/Internet Protocol (TCP/IP) protocol suite or the Open Systems Interconnection (OSI) layer. For data to be transmitted over a network, it is first distributed into small packets, which depend on the data's protocol and overall size. Each packet contains various details, such as a source IP address, destination IP address and unique data and packet identifiers. • The segregation of data into small packets enables efficient data transportation and better utilization of the network medium/channel. More than one user, application and/or node may take turns sending and receiving data without permanently retaining the underlying medium/channel, as in a circuit switched network. • What is the difference between VoIP and landline phones? • The main difference between VoIP phones and landline phones is that a landline phone is hardwired into a physical location using copper wires. A VoIP phone, on the other hand, makes and receives calls over the internet and is not bound to a specific location. location • Traditional telephones use analog lines to carry voice signals. If you want to make calls, you have to have extra wiring installed. How does VoIP work? • Voice over IP converts your voice to a digital file, compresses it, and sends it over the internet. The VoIP service provider (much like your internet service provider) sets up the call. call Many people choose VoIP over traditional landlines because there is less startup cost involved and they can make calls using the internet, which saves them money on longdistance charges. • Voice over IP uses Internet Protocol, an essential building block of the internet. IP telephony is a massive innovation from the century-old telecommunications system. For phone calls, the conversation is exchanged using small data packets. The internet can send these data packets around the world in less than a second. For internet telephony, these packets travel between your phone and a VoIP provider. provider A VoIP phone system facilitates calls between other phones or over to another telephone company. It also provides other useful functions like voicemail, call forwarding, call recording, and more. In four steps, here’s how VoIP works. works .Your phone connects to your switch or router in your Local Area Network (LAN). .When you dial a telephone number, your IP phone tells your VoIP service provider to call the other party. party .Your VoIP service establishes the call and exchanges data packets from your IP phone. .Your VoIP phone converts these digital signals back into the sound you can hear. • Voice over Internet Protocol bypasses the telephone company entirely. Wherever you have a broadband internet connection, you can use VoIP. It’s a significant upgrade from an analog phone system. • You used to need expensive, proprietary equipment to use VoIP — but that was over 20 years ago! Today, VoIP is built upon open standards such as Session Initiation Protocol (SIP). SIP provides complete interoperability between different desk phones, conference phones, and VoIP apps. • Cloud-based PBXs are responsible for features like voicemail, conferencing, and call routing. When you think about it, they act as their own full-service phone companies that you control. • All you need is a broadband internet connection (cable, DSL, or fiber) and you can reap all the benefits of VoIP.
