CAC (Call Admission Control)

Call Admission Control (CAC) is a mechanism used in communication networks to manage and regulate call traffic. CAC is particularly important in real-time applications, such as voice and video communications, where maintaining quality of service (QoS) is crucial. CAC controls the acceptance of new calls and the allocation of resources, such as bandwidth, to ensure that the network can maintain its QoS requirements.

In this article, we will explain CAC in detail, including its definition, types, importance, and implementation in various communication networks.

Definition of CAC

CAC is a network control mechanism that regulates the admission of new calls into the network. It determines whether there is enough available resources, such as bandwidth, to accommodate the new call, and if so, assigns the necessary resources to it. CAC is particularly important in networks that provide real-time services, such as voice and video communications, where maintaining QoS is essential.

The purpose of CAC is to prevent overloading of the network, which can lead to congestion and a degradation in QoS. CAC ensures that the network can meet its QoS requirements by managing the admission of new calls in a way that balances the available resources and demand.

Types of CAC

There are three main types of CAC: static, dynamic, and hybrid. Each type of CAC uses a different approach to regulate call admission and resource allocation.

Static CAC

Static CAC is a simple, fixed method that determines the maximum number of calls that can be accepted into the network based on a predefined threshold. The threshold is usually set by the network administrator, and it is based on the network's capacity and the desired QoS level. Static CAC allocates a fixed amount of resources for each call and rejects any call requests that exceed the threshold. This type of CAC is relatively easy to implement and requires minimal computational resources.

The disadvantage of static CAC is that it does not take into account the dynamic nature of network traffic. The predefined threshold may be too low, leading to a high rate of call rejections, or too high, leading to congestion and a degradation in QoS.

Dynamic CAC

Dynamic CAC is a more sophisticated approach that uses real-time traffic monitoring to adjust the admission threshold and resource allocation. Dynamic CAC continuously monitors the network traffic and adjusts the admission threshold based on the current demand and available resources. This allows for a more flexible allocation of resources and better utilization of the network capacity.

Dynamic CAC can use various algorithms to adjust the admission threshold, such as threshold-based, prediction-based, and feedback-based algorithms. Threshold-based algorithms adjust the admission threshold based on predefined thresholds, while prediction-based algorithms use statistical analysis to predict the future demand and adjust the threshold accordingly. Feedback-based algorithms use feedback from the network to adjust the threshold and resource allocation.

Dynamic CAC is more complex to implement than static CAC, and it requires more computational resources. However, it provides better QoS and utilization of network resources.

Hybrid CAC

Hybrid CAC is a combination of static and dynamic CAC. It uses a static threshold as a starting point and adjusts it dynamically based on the real-time network traffic. Hybrid CAC provides the flexibility of dynamic CAC while maintaining the simplicity and stability of static CAC.

Importance of CAC

CAC is important in communication networks that provide real-time services, such as voice and video communications. In these networks, maintaining QoS is essential, and overloading the network can lead to a degradation in QoS and a poor user experience.

CAC ensures that the network can meet its QoS requirements by managing the admission of new calls in a way that balances the available resources and demand. CAC regulates the admission of new calls based on the network's capacity and the desired QoS level, preventing congestion and ensuring that each call has the necessary resources to maintain a high-quality connection.

Without CAC, the network can become overloaded, leading to dropped calls, poor audio and video quality, and delayed transmissions. This can be particularly problematic in emergency situations, where reliable communication is crucial for public safety and security.

CAC also helps to optimize the utilization of network resources. By managing the admission of new calls, CAC ensures that resources are used efficiently and effectively, reducing the likelihood of network congestion and maximizing the capacity of the network.

Implementation of CAC

CAC can be implemented in various communication networks, including circuit-switched networks, packet-switched networks, and wireless networks.

Circuit-switched Networks

In circuit-switched networks, CAC is implemented at the call setup stage. When a user initiates a call, the network checks whether there is enough available resources, such as bandwidth, to accommodate the new call. If there are enough resources, the network sets up the call and allocates the necessary resources. If there are not enough resources, the network rejects the call setup request.

Static CAC is commonly used in circuit-switched networks. The maximum number of calls that can be accepted into the network is determined by the network capacity and the desired QoS level. If the network reaches its capacity, any additional call requests are rejected.

Packet-switched Networks

In packet-switched networks, CAC is implemented at the packet level. When a user initiates a call, the network checks whether there is enough available bandwidth to accommodate the new call. If there is enough bandwidth, the network assigns a virtual circuit to the call, which guarantees a certain level of QoS.

Dynamic CAC is commonly used in packet-switched networks. The admission threshold and resource allocation are adjusted in real-time based on the network traffic and demand.

Wireless Networks

In wireless networks, CAC is implemented at the radio access network (RAN) level. When a user initiates a call, the RAN checks whether there is enough available resources, such as radio spectrum and network capacity, to accommodate the new call. If there are enough resources, the RAN sets up the call and allocates the necessary resources. If there are not enough resources, the RAN rejects the call setup request.

Dynamic CAC is commonly used in wireless networks. The admission threshold and resource allocation are adjusted in real-time based on the network traffic and demand.

Conclusion

CAC is an important mechanism for managing and regulating call traffic in communication networks. CAC ensures that the network can maintain its QoS requirements by managing the admission of new calls and allocating the necessary resources to each call. CAC can be implemented in various communication networks, including circuit-switched networks, packet-switched networks, and wireless networks. Different types of CAC, such as static, dynamic, and hybrid, are used to regulate call admission and resource allocation. Overall, CAC is essential for maintaining a reliable and high-quality communication network.