Network Core | Packet Switching | Circuit Switching | Message Switching

Introduction

A core network is a collection of network hardware, devices, and software that provides the fundamental services for organizations. The network core is also referred as the mesh of routers that interconnect the internet’s end systems. Network is also known as backbone network. The connection of different network segment together and process to transmit data packets across the network. It is implemented through the use of switching techniques.

Basic methods of switching are: Packet Switching, Circuit Switching, Message Switching.

Packet Switching

Packet switching is the transfer of small pieces of data across various networks. These data chunks or “packets” allow for faster, more efficient data transfer. There are two types of packet-switching techniques: Connectionless Packet Switching and Connection oriented packet switching.

Connection less packet switching

In this type of packet switching includes multiple packets, each packet pass through individually route. It means each packet has complete routing information—but it also means different paths of transmission and out-of-order delivery are possible, depending on the fluctuating loads on the network’s nodes (adapters, switches and routers) at the moment. This kind of packet switching is sometimes called datagram switching.

Figure: Connection less Packet Switching

Each packet in connectionless packet switching includes the following information in its header section: Source address, Destination address, Total number of packets, Sequence number (Seq#) for reassembly. Once the packets reach their destination via various routes, the receiving devices rearrange them to form the original message using the sequence number.

 

Connection oriented packet switching

This method is also called virtual circuit packet switching. In this method, a dedicated path must be established between a source and a destination before data transmission process. For example, Telephone System.

Figure: Three phases of Connection-oriented packet switching

A route, which consists of a logical connection is first established between two users. The process is completed in three main phases: Establishment, Data Transfer, Connection Release.

Establishment: During this phase, the two users not only agree to setup a connection but also decide upon the QoS. After establishment packets transfer bidirectional.

Data Transfer: During this performs flow control and error control. The error control service ensures correct sequencing of packets. Flow control service control faster sender and slower receiver.

Connection Release: When the station wishes to close down the virtual circuit, one station can terminate the connection with a clear request packet.

Figure: Connection oriented packet switching

Advantages:

Resource utilization more efficiently.

Small amount of time required to establish or terminate circuit.

It is more flexible.

Small size packet reduces transmission delay.

Disadvantages:

Complex protocol for packet switching.

Algorithms are more complicated.

Switching processor must be powerful.

Packets may lose during switching.

 

Circuit Switching

The telephone system as it historically developed was designed for voice and analog signals. For voice signals, a relatively large amount of distortion is acceptable, since the human error can understand voice even with distortion. For digital signals, these distortions may cause the receiver to misinterpret that signal, it produces errors. The interoffice lines are called trunks. Any phone line can connect one user to another through the phone system, the user has a line assigned randomly. This is called the dial-up or switched network.

Figure: Circuit Switching

Telephone networks are connection oriented because they require the setting up of connection before the actual transfer of information can take place. An end-to-end path setup beginning of a session, dedicated to the application, and then released at the end of session. This is called circuit switching.

Advantages:

Fixed bandwidth and guaranteed capacity.

Low variance end to end delay.

Disadvantages:

Connection setup and termination generate extra traffic.

User pay for circuit, even when not sending data.

Other user cannot use circuit even if it is free.

 

Message Switching

Message switching is used to describe the telegraph network. No need to establish dedicated path. When the sender has a block of data to be sent, it is stored in router and forward to next hop. Each block is received in its entirely, inspected for errors, and then transmitted. A network using this technique is called store and forward network. 

Figure: Message Switching

With message switching, there is no limit of block size, it means that router must have large buffer size. Message switching does not involve a call setup. It can achieve a high utilization of the transmission line.

Advantages:

Efficient traffic management.

Reduce network traffic congestion.

Efficient use of traffic channel.

Disadvantages:

Store and forward technique increase delay in data transmission.

Each node requires large capacity for storing.

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