Multiple Access Protocols in Computer Networks
Channel allocation in computer networks refers to the process of assigning available communication channels to multiple users or devices that share a network. The main goal is to efficiently utilize the limited bandwidth while minimizing interference between users.
Static Channel Allocation
In this scheme, a fixed portion of the frequency channel is permanently assigned to each user. For N competing users, the bandwidth is divided into N equal-sized sub-channels using frequency division multiplexing (FDM), and each portion is assigned to one user.
Dynamic Channel Allocation
In dynamic channel allocation, frequency bands are not permanently assigned to users. Instead, channels are allotted to users dynamically as needed, from a central pool. The allocation considers various parameters to minimize transmission interference.
Types of Multiple Access Protocols:
- Carrier Sense Multiple Access (CSMA):
- CSMA/CD (Collision Detection): Used in Ethernet networks, devices listen before transmitting to avoid collisions. If a collision is detected, a backoff algorithm is used.
- CSMA/CA (Collision Avoidance): Common in wireless networks, devices sense the channel before transmitting to reduce collisions.
- Time Division Multiple Access (TDMA): Divides time into slots, assigning each slot to a specific device for data transmission. Common in cellular networks.
- Frequency Division Multiple Access (FDMA): Allocates different frequency bands to devices for simultaneous transmission without interference. Used in radio communication and satellite systems.
- Code Division Multiple Access (CDMA): Assigns a unique code to each device, enabling multiple devices to transmit simultaneously on the same frequency. Widely used in wireless communication systems like 3G and 4G networks.
- Space Division Multiple Access (SDMA): Utilizes spatial separation techniques to allow multiple devices to transmit simultaneously without interference, often through methods like beamforming in wireless communication systems.
Applications of Multiple Access Protocols:
- Ethernet Networks: Historically used CSMA/CD for shared communication mediums.
- Wireless Networks: Commonly use CSMA/CA to avoid collisions and enable shared channel access.
- Cellular Networks: Employ TDMA and CDMA for efficient time allocation and simultaneous communication.
- Satellite Communication: Utilizes FDMA to allocate different frequencies to communication channels for simultaneous operation.
Multiple access protocols face challenges like collision management, efficiency optimization, scalability, security concerns, and the need to evolve with advancing technologies like 5G networks and Machine-to-Machine (M2M) communication.