Switching

 

Switching

In computer networking, Switching is the process of transferring data packets from one device to another in a network, or from one network to another, using specific devices called switches. A computer user experiences switching all the time for example, accessing the Internet from your computer device, whenever a user requests a webpage to open, the request is processed through switching of data packets only.

 

Switching takes place at the Data Link layer of the OSI Model. This means that after the generation of data packets in the Physical Layer, switching is the immediate next process in data communication. In this article, we shall discuss different processes involved in switching, what kind of hardware is used in switching, etc.

 

Network Switching:

A switch is a dedicated piece of computer hardware that facilitates the process of switching i.e., incoming data packets and transferring them to their destination. A switch works at the Data Link layer of the OSI Model. A switch primarily handles the incoming data packets from a source computer or network and decides the appropriate port through which the data packets will reach their target computer or network.

 

A switch decides the port through which a data packet shall pass with the help of its destination MAC(Media Access Control) Address. A switch does this effectively by maintaining a switching table, (also known as forwarding table).

A network switch is more efficient than a network Hub or repeater because it maintains a switching table, which simplifies its task and reduces congestion on a network, which effectively improves the performance of the network.

Types of Switching

There are three types of switching methods:

·      Message Switching

·      Circuit Switching

·      Packet Switching

§  Datagram Packet Switching

§  Virtual Circuit Packet 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 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 responsibility of transferring the entire message to the next node. Hence, each node must have storage capacity. A message will only be delivered if the next hop and the link connecting it are both available, otherwise, it’ll be stored indefinitely. A store-and-forward switch forwards a message only if sufficient resources are available and the next hop is 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 contains the message routing information, including the source and destination.

Message switching network consists of transmission links (channels), store-and-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-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 it 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 –

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.

In message switching, the data channels are shared by the network devices.

It makes traffic management efficient by assigning priorities to the messages.

Because the messages are delivered via a store and forward method, it is possible to include priority in them.

It allows for infinite message lengths.

Unlike circuit switching, it does not necessitate the actual connection of source and destination devices.

Disadvantages of Message Switching :

Message switching cannot be used for real-time applications as storing messages causes delay.

In message switching, the message has to be stored for which every intermediate device in the network requires a large storing capacity.

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.

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 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 or packet-switched.

 

 

 

 

 

 

 

 

Circuit Switching

In circuit switching network resources (bandwidth) are divided into pieces and bit delay is constant during a connection. The dedicated path/circuit established between sender and receiver provides a guaranteed data rate. Data can be transmitted without any delays once the circuit is established. 

Telephone system network is one of the example of Circuit switching. TDM (Time Division Multiplexing) and FDM (Frequency Division Multiplexing) are two methods of multiplexing multiple signals into a single carrier. 

 

·       Frequency Division Multiplexing : Divides into multiple bands 
Frequency Division Multiplexing or FDM is used when multiple data signals are combined for simultaneous transmission via a shared communication medium.It is a technique by which the total bandwidth is divided into a series of non-overlapping frequency sub-bands,where each sub-band carry different signal. Practical use in radio spectrum & optical fibre to share multiple independent signals.
 

·       Time Division Multiplexing : Divides into frames 
Time-division multiplexing (TDM) is a method of transmitting and receiving independent signals over a common signal path by means of synchronized switches at each end of the transmission line. TDM is used for long-distance communication links and bears heavy data traffic loads from end user. 
Time division multiplexing (TDM) is also known as a digital circuit switched.

 

Diagram:

 

Drawbacks:

Inefficient use of resources: Circuit switching requires the establishment of a dedicated communication path between two nodes, which means that the resources along that path, such as bandwidth and switch ports, are reserved for the duration of the communication. This can result in inefficient use of resources, as the resources may remain unused during periods of low or no communication.

Limited scalability: Circuit switching is not well-suited for large-scale networks with many nodes, as it requires a dedicated communication path between each pair of nodes. This can result in a high degree of complexity and difficulty in managing the network.

Vulnerability to failures: Circuit switching relies on a dedicated communication path, which can make the network vulnerable to failures, such as cable cuts or switch failures. In the event of a failure, the communication path must be re-established, which can result in delays or loss of data.

Delay and latency: Circuit switching requires the establishment of a dedicated communication path, which can result in delay and latency in establishing the path and transmitting data. This can impact the real-time performance of applications, such as voice and video.

High cost: Circuit switching requires the reservation of resources, which can result in a high cost, particularly in large-scale networks. This can make circuit switching less practical for some applications.

Lack of flexibility: Circuit switching is not flexible as it only allows one type of communication at a time, such as voice or data. This can limit the ability of users to perform multiple tasks simultaneously.

Limited mobility: Circuit switching is not well-suited for mobile devices or nodes that move frequently, as it requires the establishment of a dedicated communication path. This can result in communication disruptions or dropped calls.

Limited capacity: Circuit switching can have limited capacity as it requires the establishment of a dedicated communication path between two nodes. This can limit the number of simultaneous communications that can occur.

High setup time: Circuit switching requires a significant setup time to establish the dedicated communication path between two nodes. This can result in delays in initiating communication.

No prioritization: Circuit switching does not provide any mechanism for prioritizing certain types of traffic over others. This can result in delays or poor performance for time-critical applications, such as voice or video.

 

 

 

 

 

Advantages of Circuit Switching: 
It has the following advantages: 
 

1.   The main advantage of circuit switching is that a committed transmission channel is established between the computers which give a guaranteed data rate.

2.   In-circuit switching, there is no delay in data flow because of the dedicated transmission path.

3.   Reliability: Circuit switching provides a high level of reliability since the dedicated communication path is reserved for the entire duration of the communication. This ensures that the data will be transmitted without any loss or corruption.

4.   Quality of service: Circuit switching provides a guaranteed quality of service, which means that the network can prioritize certain types of traffic, such as voice and video, over other types of traffic, such as email and web browsing.

5.   Security: Circuit switching provides a higher level of security compared to packet switching since the dedicated communication path is only accessible to the two communicating parties. This can help prevent unauthorized access and data breaches.

6.   Ease of management: Circuit switching is relatively easy to manage since the communication path is pre-established and dedicated to a specific communication. This can help simplify network management and reduce the risk of errors.

7.   Compatibility: Circuit switching is compatible with a wide range of devices and protocols, which means that it can be used with different types of networks and applications. This makes it a versatile technology for various industries and use cases.

Disadvantages of Circuit Switching: 
It has the following disadvantages : 
 

1.   It takes a long time to establish a connection.

2.   More bandwidth is required in setting up dedicated channels.

3.   It cannot be used to transmit any other data even if the channel is free as the connection is dedicated to circuit switching.

4.   Limited Flexibility: Circuit switching is not flexible as it requires a dedicated circuit between the communicating devices. The circuit cannot be used Waste of Resources for any other purpose until the communication is complete, which limits the flexibility of the network.

5.   Waste of Resources: Circuit switching reserves the bandwidth and network resources for the duration of the communication, even if there is no data being transmitted. This results in the wastage of resources and inefficient use of the network.

6.   Expensive: Circuit switching is an expensive technology as it requires dedicated communication paths, which can be costly to set up and maintain. This makes it less feasible for small-scale networks and applications.

7.   Susceptible to Failure: Circuit switching is susceptible to failure as it relies on a dedicated communication path. If the path fails, the entire communication is disrupted. This makes it less reliable than other networking technologies, such as packet switching.

8.   Not suitable for bursty traffic: Circuit switching is not suitable for bursty traffic, where data is transmitted intermittently at irregular intervals. This is because a dedicated circuit needs to be established for each communication, which can result in delays and inefficient use of resources.

Packet Switching

 

Packet Switching in computer networks is a method of transferring data to a network in the form of packets. In order to transfer the file fast and efficiently manner over the network and minimize the transmission latency, the data is broken into small pieces of variable length, called Packet. At the destination, all these small parts (packets) have to be reassembled, belonging to the same file. A packet is composed of a payload and various control information. No pre-setup or reservation of resources is needed.

Packet Switching uses the Store and Forward technique while switching the packets; while forwarding the packet each hop first stores that packet then forwards. This technique is very beneficial because packets may get discarded at any hop for some reason. More than one path is possible between a pair of sources and destinations. Each packet contains the Source and destination address using which they independently travel through the network. In other words, packets belonging to the same file may or may not travel through the same path. If there is congestion at some path, packets are allowed to choose different paths possible over an existing network.

Diagram of Packet Switching

In packet switching the data is divided into small packets which allow faster movement of data. Each packet contains two parts that is Header and Payload, the header on each packet conation information. Below is the diagram of how packet switching works.

Types of Delays in Packet Switching

Transmission Delay: Time required by the spentstation to transmit data to the link.

Propagation Delay: Time of data propagation through the link.

Queueing Delay: Time spent by the packet at the destination’s queue.

Processing Delay: Processing time for data at the destination.

Advantages of Packet Switching over Circuit Switching:

§  More efficient in terms of bandwidth, since the concept of reserving a circuit is not there.

§  Minimal transmission latency.

§  More reliable as a destination can detect the missing packet.

§  More fault tolerant because packets may follow a different path in case any link is down, Unlike Circuit Switching.

§  Cost-effective and comparatively cheaper to implement.

§  Disadvantage of Packet Switching over Circuit Switching

§  Packet Switching doesn’t give packets in order, whereas Circuit Switching provides ordered delivery of packets because all the packets follow the same path.

§  Since the packets are unordered, we need to provide sequence numbers for each packet.

§  Complexity is more at each node because of the facility to follow multiple paths.

§  Transmission delay is more because of rerouting.

§  Packet Switching is beneficial only for small messages, but for bursty data (large messages) Circuit Switching is better.

Types of Packet Switching

1. Connection-oriented Packet Switching (Virtual Circuit)

Before starting the transmission, it establishes a logical path or virtual connection using a signaling protocol, between sender and receiver and all packets belongs to this flow will follow this predefined route. Virtual Circuit ID is provided by switches/routers to uniquely identify this virtual connection. Data is divided into small units and all these small units are appended with help of sequence numbers. Packets arrive in order at the destination. Overall, three phases take place here- The setup, data transfer and tear-down phases.

All address information is only transferred during the setup phase. Once the route to a destination is discovered, entry is added to the switching table of each intermediate node. During data transfer, packet header (local header) may contain information such as length, timestamp, sequence number, etc.

 

Connection-oriented switching is very useful in switched WAN. Some popular protocols which use the Virtual Circuit Switching approach are X.25, Frame-Relay, ATM, and MPLS(Multi-Protocol Label Switching).

 

2.Connectionless Packet Switching (Datagram)

Unlike Connection-oriented packet switching, In Connectionless Packet Switching each packet contains all necessary addressing information such as source address, destination address, port numbers, etc. Packets belonging to one flow may take different routes because routing decisions are made dynamically, so the packets that arrived at the destination might be out of order. It has no connection setup and teardown phase, like Virtual Circuits.

Packet delivery is not guaranteed in connectionless packet switching, so reliable delivery must be provided by end systems using additional protocols.

 

 

 

 

 

 

 

 

 

 

Difference Between Circuit , Message and Packet Switching

 

Basics	Circuit Switching	Message Switching	Packet Switching
Connection Creation	Connection is created between the source and destination by establishing a dedicated path between source and destination.	Links are created independently one by one between the nodes on the way.	Links are created independently one by one between the nodes on the way.
Queuing	No queue is formed.	Queue is formed.	Queue is formed.
Message and Packets	There is one big entire data stream called a message.	There is one big entire data stream called a message.	The big message is divided into a small number of packets.
Routing	One single dedicated path exists between the source and destination.	Messages follow the independent route to reach a destination.	Packets follow the independent path to hold the destination.
Addressing and sequencing	Messages need not be addressed as there is one dedicated path.	Messages are addressed as independent routes are established.	Packets are addressed, and sequencing is done as all the packets follow the independent route.
Propagation Delay	No	Yes	Yes
Transmission Capacity	Low	Maximum	Maximum
Sequence Order	Message arrives in Sequence.	Message arrives in Sequence.	Packets do not appear in sequence at the destination.
Use Bandwidth	Wastage	Bandwidth is used to its maximum extent.	Bandwidth is used to its maximum extent.

 

 

 

 

 

 

 

 

 

 

Reference Website:

1.      What is Switching? - GeeksforGeeks.

2.      Differentiate between Circuit Switching, Message Switching, and Packet Switching (tutorialspoint.com)

Submitted By:

1.Sudharshan P(21USC024).

2.Kathiravan R(21USC010).

REVIEWED BY:

          C R SAKTHIVEL ,MCA.,M.Phil., Ph.D