Fixed Assignment Schemes refer to MAC protocols that allocate communication resources, such as time slots or frequency channels, to specific devices in advance.
In other words, each device is assigned a fixed resource for communication, and it must use that resource exclusively for all its transmissions.
Some of the most common types of fixed assignment schemes:
1. TDMA (Time Division Multiple Access): In TDMA, the communication channel is divided into fixed time slots, and each device is assigned a specific time slot for its transmissions. This ensures that each device gets a fair share of the channel and reduces the likelihood of collisions.
2. FDMA (Frequency Division Multiple Access): In FDMA, the communication channel is divided into fixed frequency channels, and each device is assigned a specific frequency channel for its transmissions. This ensures that each device gets a dedicated frequency band and reduces the likelihood of interference.
3. CDMA (Code Division Multiple Access): In CDMA, each device is assigned a unique code that is used to differentiate its transmissions from those of other devices. This allows multiple devices to transmit data simultaneously on the same frequency channel, while still maintaining their privacy.
Fixed assignment schemes advantages:
Fixed assignment schemes, such as TDMA, FDMA, and CDMA, have several advantages over dynamic allocation schemes, such as CSMA/CA.
1. Guaranteed Bandwidth: In fixed assignment schemes, each device is allocated a fixed resource for communication, such as a time slot or frequency channel. This ensures that each device gets a guaranteed amount of bandwidth for its transmissions, and there is no contention for resources.
2. Reduced Collisions: Since each device is assigned a fixed resource for communication, there is a reduced likelihood of collisions between devices trying to transmit data at the same time. This improves network performance and reduces the likelihood of data loss.
3. Fairness: Fixed assignment schemes ensure that each device gets a fair share of the communication channel, and there is no bias towards any particular device or application. This improves network performance and reduces the likelihood of congestion.
4. Security: Fixed assignment schemes can provide improved security over dynamic allocation schemes, as each device is assigned a unique resource that is used exclusively for its transmissions. This can help prevent unauthorized access and eavesdropping.
5. Predictable Performance: Fixed assignment schemes provide predictable performance, as the bandwidth and resources allocated to each device are known in advance. This makes it easier to plan and optimize network performance.
Fixed assignment schemes disadvantages:
While fixed assignment schemes, such as TDMA, FDMA, and CDMA, offer several advantages over dynamic allocation schemes, they also have some disadvantages that should be considered.
1. Reduced Flexibility: Fixed assignment schemes are less flexible than dynamic allocation schemes, as the resources allocated to each device are fixed in advance. This can make it difficult to add or remove devices from the network, or to allocate resources dynamically based on changing network conditions.
2. Scalability: Fixed assignment schemes may not scale well to large networks, as allocating fixed resources to a large number of devices can become impractical. This can limit the number of devices that can be supported by the network.
3. Inefficient Use of Resources: Fixed assignment schemes may not make efficient use of network resources, as some devices may not use their allocated resources fully. This can lead to wasted bandwidth and reduced network performance.
4. Channel Allocation: In FDMA and TDMA, channel allocation can be a complex task. Allocating frequency bands and time slots to devices requires careful planning to ensure that there is no interference or collisions.
5. Vulnerability: Fixed assignment schemes can be vulnerable to certain types of attacks, such as jamming or interference. Since each device is assigned a fixed resource, an attacker can disrupt communication by jamming the assigned resource.