Digital Communication


Digital Communication

Master/Slave: definition of the master/slave principle


The master/slave principle is an information technology architectural concept that governs the management of access to shared resources. The master controls and decides when the slaves use the resources. This principle finds application, for example, in the generation of piconets via Bluetooth.

What is the Master/Slave principle?

The master/slave principle describes a resource control and distribution concept in the field of information technology. It helps when multiple devices, processes, or applications rely on the same resources. This is the case, for example, when transferring data via the data bus. The Master/Slave principle regulates requests so that communication takes place without interference or signal changes by other participants and all processes can be carried out correctly.

Since the term “master/slave” has a negative connotation due to the reference to slavery, more and more alternative terms are used. The alternatives to master/slave are “primary and secondary” (Primary and Secondary) or “primary and replica” (Primary and Replica).

Use cases of the Master/Slave principle

The master/slave principle is used in the following use cases, for example:

  • Regulation and coordination of bus systems for the exchange of information: the master coordinates and controls the slaves and ensures that the data bus receives and processes information correctly.
  • Organization of resources within a computer network: the master releases the resources available within a network according to a specific logic, and ensures that all participants perform their tasks.
  • Creating a piconet of terminals via Bluetooth: the Master/Slave principle is used to create piconets. This is about [Personal Area Network] (or Personal Area Network), a particular type of network where terminals connect via Bluetooth.
  • Access control to a host system: a host station provides resources within a computer network. The master regulates the access of the participants.

How does the master/slave principle work?

The master always makes the decision according to the master/slave principle: all communications are deployed only from master to slave. Communication from the slave to the master is not provided. Resources are therefore always controlled unidirectionally.

The master grants the slave the rights it needs. These are, for example, access or communication rights. I’slave acts only at the request of the masterwhile the master acts freely and uninvited.

What are the characteristics of the Master/Slave principle?

The fundamental aspect of the master/slave principle: the master has control and must be understood as a controlling authority. All built-in slaves are always passive and wait for authorization from the master to use the required resources. The master has a wider range of functions due to its control function. He is also able to control a large number of slaves. The master addresses the slaves via a physical address or line. For some systems, it is possible to define the master when initializing a system of peer stations.

What are the advantages and disadvantages of the master/slave principle?

The Master/Slave principle is a common concept for controlling and regulating shared resources. One of the main advantages is that the master controls all access relationships. It occupies a central position in system planning and thus greatly simplifies them. Such a principle prevents the unauthorized exchange of information. The unidirectional direction of communication is on the other hand a disadvantage. Slaves cannot communicate directly with the master. The queries sent by the master to the slaves through polling (a poll that determines the state of hardware or software) are inefficient.

What are the alternatives to the Master/Slave principle?

The Master/Slave concept is not the only architectural model for controlling resources. THE [modèle client-serveur] is a known alternative. In this model, servers provide services that clients use as needed. This corresponds to the most widely used architectural model on the Internet. Sending e-mails using the SMTP, IMAP or POP protocols, sending http requests to a Web server as well as transferring data to a server by File Transfer Protocol, abbreviated FTP, are examples made in using the client/server model.

Another relevant architecture model in this context is the peer-to-peer model. A peer program constitutes the server and the client both in this model. Contrary to the Master-Slave principle, the peers are on an equal footing and perform both server and client tasks. Peer-to-peer architecture is mainly used for file sharing or grid computing services.

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