We all are aware about the Importance of Data Communication and how the invention of the telephone, computer, and the Internet have transformed the way we communicate. The fundamental purpose of data communications is to exchange information between user’s computers, terminals and applications programs. For a better communication having a well-established network has become an important part, as the need for Computer networks help users on the network to share the resources and in communication which could be a File sharing or even a Hardware sharing.
Thus, Data communications (DC) is the process of using computing and communication technologies to transfer data from one place to another, and vice versa. It enables the movement of electronic or digital data between two or more nodes, regardless of geographical location, technological medium or data contents. This transfer of data takes place over the computer network over which the data travels smoothly. For the delivery of data or information with the ease of accuracy various types of Switching Techniques are employed in the Data Communication and Networking.
Brief History of Switching
Over the past decade data communications has been revolutionized. In 1968 virtually all interactive data communication networks were circuit switched, the same as the telephone network. Circuit switching networks pre -allocate transmission bandwidth for an entire call or session. However, since interactive data traffic occurs in short bursts 90 percent or more of this bandwidth Is wasted. Thus, as digital electronics became inexpensive enough, it became dramatically more cost-effective to completely redesign communications networks. introducing the concept of packet switching where the transmission bandwidth is dynamically allocated, permitting many users to share the same transmission line previously required for one user. Packet switching has been so successful, not only in improving the economics of data communications but in enhancing reliability and functional flexibility as well, that in 1978 virtually all mew data networks being built throughout the world are based on packet switching.
Before the advent of computers, dynamic-allocation systems were necessarily limited to nonreal time communications, since many manual sorting and routing decisions were required along the path of each message. However, the rapid advances in computer technology have not only removed this limitation but have even made feasible dynamic- allocation communications systems that are superior to pre-allocation systems in connect time, reliability, economy and flexibility.
The growing use of smartphone, tablets, wearable, and other mobile device has accelerated the development of mobile network to a great extent. Nowadays networking is common amongst everyone as mobile communication network has reached nearly every corner of the world, internet being the most popular network has also increased the importance of network in day to day life of a person. Hence proper functioning of these networks is crucial activity to the end user and a standard (QoS) must be maintained.
Whenever communicating parties or users wants to communicate with each other, both the party uses network as a medium, the network in turn is responsible for transmission of right data to the right party. For the efficient transmission of the right data to the right user, network uses various techniques to carry out this whole operation, one of which is “Switching Technique”.
Types of Switching
Switching play a greater role in the network paradigm. There are various types of switching and these are hardware based as well as their latency is different. Switching technology is provided by local exchange and long distance carrier.
- LAN Switch or Active Hub
Also known as the local area network or Ethernet switch, this device is used to connect points on a company’s internal LAN. It blocks the overlap of data packets that run through a network by allocating the bandwidth economically. When we say bandwidth, it refers to the amount of data that can be carried from one point to the other under a given period of time. With a LAN switch, it reduces the network traffic by delivering the data only to its intended recipient. The important bandwidth would first be delivered before the subsequent ones.
- Unmanaged Network Switches
Mostly used in home networks and small companies or businesses, this device allows other devices on the network to connect with each other; it could be from one computer to the other, or a computer connected to a printing device. As what the name suggests, this type of device does not need to be watched constantly and it is the easiest and simplest installation, because of its small cable connections.
- Managed Switches
Unlike the unmanaged network switch, this device is customizable; because of this feature, you can enhance the functionality of a certain network. This device has two types – Smart switches and Enterprise switches.
Smart switches have limited features, but provide a web interface and accept configurations of basic settings. They are perfect for fast and constant LANs which support gigabit data transfer and allocations.
Enterprise switches have a wide range of management features and the capability to fix, copy, and transform and display network configurations. They are usually found in large companies which contain large numbers of connections, nodes, switches, and ports. Having more features than the smart switches, Enterprise switches are usually more expensive.
You may be more familiar with this device than any other switches that were described. A router is an electronic device that sends data along networks. It is usually connected to LANs or WANs, and is capable of connecting more than two networks.
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 general communication procedure but is still used in the networking application.
1) Circuit Switching
2) Packet Switching
3) Message Switching
Circuit Switching is generally used in the public networks. It come 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 network for Circuit Switching is shown in figure.
Here the network connection allows the electrical current and the associated voice with it to flow in between the two respective users. 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.
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:
Bandwidth is reduced by the splitting of data onto different routes for a busy circuit.
For a certain link in the network, the link goes down during transmission the remaining packet can be sent through another route.
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.
In case of Message Switching it is not necessary to established 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.
Each intermediate device receives the message and store it until the next 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 reason, this switching is not recommended for real time applications like voice and video
Development of Switching Technology
- Manual systems – in the infancy of telephony, exchanges were built up with manually operated switching equipment (the first one in 1878 in New Haven, USA)
- Electromechanical systems – manual exchanges were replaced by automated electromechanical switching systems – a patent for automated telephone exchange in 1889 (Almon B. Strowger) – step-by-step selector controlled directly by dial of a telephone set – developed later in the direction of register-controlled system in which number information is first received and analyzed in a register – the register is used to select alternative switching paths (e.g. 500 line selector in 1923 and crossbar system in 1937) – more efficient routing of traffic through transmission network – increased traffic capacity at lower cost
- Computer-controlled systems – FDM was developed round 1910, but implemented in 1950’s (ca. 1000 channels transferred in a coaxial cable) – PCM based digital multiplexing introduce in 1970’s – transmission quality improved – costs reduced further when digital group switches were combined with digital transmission systems – computer control became necessary – the first computer controlled exchange put into service in 1960 (in USA) – strong growth of data traffic resulted in development of separate data networks and switches – advent of packet switching (sorting, routing and buffering) – N-ISDN network combined telephone exchange and packet data switches – ATM based cell switching formed basis for B-ISDN – next step is to use optical switching with electronic switch control – all optical switching can be seen in the horizon.
Definition of Switching
Switching defines when and how the packets are forwarded to the network, so that it may reach its actual destination. Circuit switching and Packet switching are the two popular switching techniques
Switches are devices capable of creating temporary connections between two or more devices linked to it. Some of these Switches are connected to the end systems (computers or telephones) and others are used only for Routing.
In the next three subsections, we present the three switching techniques used in networks in detail: circuit switching, datagram packet switching and virtual circuit packet switching.
Fig : The two different bitstreams flow on two separate circuits.
Circuit switching is the transmission technology that has been used since the first communication networks in the nineteenth century. In circuit switching, a caller must first establish a connection to a callee before any communication is possible. During the connection establishment, resources are allocated between the caller and the callee. Generally, resources are frequency intervals in a Frequency Division Multiplexing (FDM) scheme or more recently time slots in a Time Division Multiplexing (TDM) scheme. The set of resources allocated for a connection is called a circuit, as depicted in Figure. A path is a sequence of links located between nodes called switches. The path taken by data between its source and destination is determined by the circuit on which it is flowing, and does not change during the lifetime of the connection. The circuit is terminated when the connection is closed.
In circuit switching, resources remain allocated during the full length of a communication, after a circuit is established and until the circuit is terminated and the allocated resources are freed. Resources remain allocated even if no data is flowing on a circuit, hereby wasting link capacity when a circuit does not carry as much traffic as the allocation permits. This is a major issue since frequencies (in FDM) or time slots (in TDM) are available in finite quantity on each link, and establishing a circuit consumes one of these frequencies or slots on each link of the circuit. As a result, establishing circuits for communications that carry less traffic than allocation permits can lead to resource exhaustion and network saturation, preventing further connections from being established. If no circuit can be established between a sender and a receiver because of a lack of resources, the connection is blocked.
establishing a connection. In a communication network, circuit-switched or not, nodes need to lookup in a forwarding table to determine on which link to send incoming data, and to actually send data from the input link to the output link. Performing a lookup in a forwarding table and sending the data on an incoming link is called forwarding. Building the forwarding tables is called routing. In circuit switching, routing must be performed for each communication, at circuit establishment time. During circuit establishment, the set of switches and links on the path between the sender and the receiver is determined and messages are exchanged on all the links between the two end hosts of the communication in order to make the resource allocation and build the routing tables. In circuit switching, forwarding tables are hardwired or implemented using fast hardware, making data forwarding at each switch almost instantaneous. Therefore, circuit switching is well suited for long-lasting connections where the initial circuit establishment time cost is balanced by the low forwarding time cost.
The circuit identifier (a range of frequencies in FDM or a time slot position in a TDM frame) is changed by each switch at forwarding time so that switches do not need to have a complete knowledge of all circuits established in the network but rather only local knowledge of available identifiers at a link. Using local identifiers instead of global identifiers for circuits also enables networks to handle a larger number of circuits.
Traffic engineering (TE) consists in optimizing resource utilization in a network by choosing appropriate paths followed by flows of data, according to static or dynamic constraints . A main goal of traffic engineering is to balance the load in the network, i.e., to avoid congestion on links on a network while other links are under-utilized. To achieve such goals, traffic engineering methods can vary from offline capacity planning algorithms to automatic, dynamic changes. Since circuit switching allocates a fixed path for each flow, circuits can be established according to traffic engineering algorithms.
On the other hand, circuit switching networks are not reactive when a network topology change occurs. For instance, on a link failure, all circuits on a failed link are cut and communication is interrupted. Special mechanisms that handle such topological changes have been be devised. Traffic engineering can alleviate the consequences of a link failure by pre-planning failure recovery. A backup circuit can be established at the same time or after the primary circuit used for a communication is set up, and traffic can be rerouted from the failed circuit to the backup circuit if a link of the primary circuit fails. Circuit switching networks are intrinsically sensitive to link failures and rerouting must be performed by additional traffic engineering mechanisms.
Datagram packet switching
Conceived in the 1960’s, packet switching is a more recent technology than circuit switching which addresses a disadvantage of circuit switching: the need to allocate resources for a circuit, thus incurring link capacity wastes when no data flows on a circuit. Packet switching introduces the idea of cutting data on a flow into packets which are transmitted over a network without any resource being allocated. If no data is available at the sender at some point during a communication, then no packet is transmitted over the network and no resources are wasted. Packet switching is the generic name for a set of two
different techniques: datagram packet switching and virtual circuit packet switching. Here, we give an overview of datagram packet switching.
Fig : Packets from a given flow are independent and a router can forward two packets from the same flow on two different links.
Different from circuit switching, datagram packet switching does not require to establish circuits prior to transmission of data and terminate circuits after the transmission of data. The switches, called routers, have to make a lookup in the forwarding table, called routing table, for each incoming packet. A routing table contains a mapping between the possible final destinations of packets and the outgoing link on their path to the destination. Routing tables can be very large because they are indexed by possible destinations, making lookups and routing decisions computationally expensive, and the full forwarding process relatively slow compared to circuit switching. In datagram packet switching networks, each packet must carry the address of the destination host and use the destination address to make a forwarding decision. Consequently, routers do not need to modify the destination addresses of packets when forwarding packets.
Since each packet is processed individually by a router, all packets sent by a host to another host are not guaranteed to use the same physical links. If the routing algorithm decides to change the routing tables of the network between the instants two packets are sent, then these packets will take different paths and can even arrive out of order. In Figure for instance, packets use two different paths to go from User 1 to User 5. Second, on a network topology change such as a link failure, the routing protocol will automatically recompute routing tables so as to take the new topology into account and avoid the failed link. As opposed to circuit switching, no additional traffic engineering algorithm is required to reroute traffic.
Since routers make routing decisions locally for each packet, independently of the flow to which a packet belongs. Therefore, traffic engineering techniques, which heavily rely on controlling the route of traffic, are more difficult to implement with datagram packet switching than with circuit switching.
Virtual circuit packet switching
Fig : All packets from the same flow use the same virtual circuit.
Virtual circuit packet switching (VC-switching) is a packet switching technique which merges datagram packet switching and circuit switching to extract both of their advantages. VC-switching is a variation of datagram packet switching where packets flow on so-called logical circuits for which no physical resources like frequencies or time slots are allocated (see Figure). Each packet carries a circuit identifier which is local to a link and updated by each switch on the path of the packet from its source to its destination. A virtual circuit is defined by the sequence of the mappings between a link taken by packets and the circuit identifier packets carry on this link. This sequence is set up at connection establishment time and identifiers are reclaimed during the circuit termination.
We have seen the trade-off between connection establishment and forwarding time costs that exists in circuit switching and datagram packet switching. In VC-switching, routing is performed at circuit establishment time to keep packet forwarding fast. Other advantages of VC-switching include the traffic engineering capability of circuit switching, and the resources usage efficiency of datagram packet switching. Nevertheless, a main issue of VC-Switched networks is the behaviour on a topology change. As opposed to Datagram Packet Switched networks which automatically recomputed routing tables on a topology change like a link failure, in VC-switching all virtual circuits that pass through a failed link are interrupted. Hence, rerouting in VC-switching relies on traffic engineering techniques.
In practice, major implementations of VC-switching are X.25 , Asynchronous Transfer Mode (ATM ) and Multiprotocol Label Switching (MPLS ). The Internet, today’s most used computer network, is entirely built around the Internet Protocol (IP), which is responsible for routing packets from one host to another. Because of the central role of IP in the Internet, we now discuss how ATM and MPLS interact with IP.
- Switches allow reduction in overall network cost by reducing number and/or cost of transmission links required to enable a given user population to communicate.
- Limited number of physical connections implies need for sharing of transport resources, which means – better utilization of transport capacity and use of switching.
- Switching systems are central components in communications networks.
Switching and routing are core functions of any network, but they have grown beyond the traditional role of connecting network segments. Solution providers can see that switches and routers are getting more intelligent; even low-end and mid-range products now include features that were once found only in enterprise data centers. But what capabilities are really important for your client and their network? Here are five major considerations for your next network infrastructure project:
- Consider rich security features available on the device. Network security is no longer an afterthought addressed with separate appliances or software. “In this day of regulatory compliance and the legal impact of information leakage, it’s important for an organization to know what’s traveling through the pipes,” said Steven Reeves, director of solutions marketing for Nexus Information Systems, a Cisco channel partner headquartered in Valencia, Calif. Solution providers can select switches and routers with user login/authentication features, integrated firewalls, intrusion detection/prevention (IDS/IPS), and a variety of other port level checks and filtering features.
- Consider virtualization features emerging on the device. Network virtualization combines different LANs into a single network. It can also create multiple virtual LANs from a single physical network infrastructure. Successful network virtualization requires intelligent switches and routers that can execute virtualization software and provide superior interoperability between other virtualized devices.
- Consider management capabilities including centralized and remote features. Management should be a key point of evaluation for any switch or router. The device should support conventional command line interfaces (CLI) along with a graphical user interfaces (GUI) available across a secure Web connection (such as SSL). The management interface should be sensible, intuitive, and easy to navigate. “When it comes to routers and switches, 95% of what we need to do involves only 5% of the features on the device,” said Karl W. Palachuk, CEO of KPEnterprises Business Consulting Inc., a small business IT consulting firm located in Sacramento, Calif. “The configuration, troubleshooting, and documentation of those key features should be as useful as possible.” Also look for management interoperability between switches. For example, a solution provider may select a new switch that uses the same OS as an existing switch, allowing both devices to use the same known commands — easing the learning curve for the new device.
- Look for centralized management that emphasizes management features, especially when it comes to upgrades. “It can be very labor intensive to backup the configuration, apply updates, backup the configuration again, and test systems,” Palachuk said. “The more automated this process from a central location, the better.” Also look for centralized management of other devices through the switch or router. The device should support network monitoring and provide a single view of network health. The device should also enforce global network policies and push upgrades to other devices on the network.
- Other advanced switch management features include 802.1X network access control (NAC), VLAN awareness and configuration, link aggregation (a.k.a. port trunking), port spanning, and SNMP monitoring of device and link health.
- Consider features that optimize traffic performance. Most clients employ video, voice or other rich media traffic in their enterprise. The core network devices should implement Quality of Service (QoS) features to prioritize desired traffic types or the ports channeling that traffic. Prioritization also prevents packet discard and delay which can disrupt rich media types. Bandwidth rate limiting (also dubbed “bandwidth throttling”) and I/O queues allow devices to further control traffic and prevent network link saturation caused by busy applications or overused network segments.
- Consider powerful logging and reporting features. Finally, solution providers should consider switches and routers that include versatile and detailed logging, reporting and diagnostic capabilities. Logging and reporting should be clear and easy to understand, and the device should push the logs to an external server for storage and further analysis. Network professionals like Michael S. Wherry, technical architect for the Global Hyatt Corporation in Chicago Il, suggest selecting devices that generate standardized NetFlow data which can be assessed in detail using tools like NetFlow Analyzer from ManageEngine. Reporting and logging should also provide clear and useful information about any virtual LANs configured on the device.
- While basic reporting is often built into the firmware of low-to mid-range switches and routers, enterprise-class devices may offer management and monitoring tools as an application module such as 3Com’s Network Monitoring Module for the Switch 8800.
Inshort: Cisco delivers a complete line of networking products that provide a strategic platform for basic data connectivity as well as security, voice, and wireless services.