Multiple Access Protocol

Multiple Access Control (MAC) is a mechanism used in the Data Link Layer of the OSI model to control access to a shared communication medium by multiple devices. In a network where multiple devices share a common communication channel, the MAC protocol regulates how the devices access the channel to avoid collisions and ensure efficient use of the channel.

There are three types of MAC protocols, including:

• Random Access Protocol – Random Access Protocol is a type of Media Access Control (MAC) protocol used in the Data Link Layer of computer networks. In a random access protocol, each device on the network has an equal opportunity to access the communication medium, regardless of its priority or status. Devices transmit data onto the medium as soon as they have data to send, without waiting for permission from a central controller.

Some examples of random access protocols include:

1. Carrier Sense Multiple Access (CSMA): In CSMA, a device listens to the communication medium before transmitting data, and waits for a random amount of time if the medium is busy.
2. Carrier Sense Multiple Access with Collision Detection (CSMA/CD): In CSMA/CD, devices also listen for collisions and stop transmitting if a collision is detected, waiting for a random amount of time before retrying.
3. Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA): In CSMA/CA, devices use a virtual carrier sensing mechanism to avoid collisions by sending a small control packet before sending data, to reserve the medium for a specific amount of time.
4.  Aloha: In Aloha, the communication medium is divided into time slots, and each device can only transmit data at the beginning of a time slot.

Random access protocols are widely used in Ethernet networks, wireless networks, and satellite communication systems, among others.

Controlled Access Protocol – Controlled Access Protocol is a type of Media Access Control (MAC) protocol used in the Data Link Layer of computer networks. In a controlled access protocol, devices on the network access the communication medium in a controlled manner, either by taking turns or by following a pre-determined schedule.

Examples of controlled access protocols include:

1. Polling: In polling, a central controller polls each device on the network in turn, allowing it to transmit data when its turn comes up. Polling can be either centralized, where the controller polls each device in a predetermined order, or distributed, where devices poll each other in a peer-to-peer fashion.
2. Token Passing: In token passing, a token is passed between devices on the network, allowing each device to transmit data when it has the token. Token passing can be either centralized, where a central controller issues the token, or distributed, where the devices themselves pass the token between them.
3. Reservation: In reservation, devices reserve the communication medium in advance, ensuring that they have exclusive access to the medium for a specified time period. This protocol can be used in networks with high bandwidth requirements or where data must be transmitted in real time.

Controlled access protocols are used in a variety of applications, such as in wireless networks, satellite communication systems, and some forms of Ethernet networks.

• Channelization – Channelization protocols are used to divide a single communication channel into multiple sub-channels or time slots, allowing multiple devices to transmit data simultaneously without interfering with each other.

There are three main types of channelization protocols:

1. Frequency Division Multiple Access (FDMA): In FDMA, the frequency spectrum is divided into multiple non-overlapping frequency bands, with each band assigned to a different user or device. Each user or device is allocated a dedicated frequency band to transmit and receive data. FDMA is commonly used in analog communication systems such as FM radio and television broadcasting.
2. Time Division Multiple Access (TDMA): In TDMA, the communication channel is divided into time slots, with each user or device assigned a specific time slot to transmit data. Users take turns transmitting data during their allocated time slot. TDMA is commonly used in digital communication systems such as GSM cellular networks and satellite communication systems.
3. Code Division Multiple Access (CDMA): In CDMA, each user is assigned a unique code that is used to spread their signal across the entire frequency spectrum. This allows multiple users to transmit data simultaneously using the same frequency band, with each user’s data being separated by their unique code.

Conclusion:

Channelization protocols are essential in communication systems that require multiple users or devices to share a single communication channel. They allow multiple users to transmit data simultaneously, increasing the efficiency of the communication system while minimizing interference between users.