AAR (AA request)

AAR (also known as AA request) stands for Admission, Authorization, and Resource Reservation. It is a mechanism used in communication networks to ensure that there are sufficient resources available for a particular communication session. This process is essential in the provision of Quality of Service (QoS) for real-time communication applications, such as voice and video.

AAR is typically used in IP-based networks, such as Voice over IP (VoIP) and multimedia conferencing systems. The basic idea behind AAR is to reserve the necessary network resources before the start of a communication session. This is done by sending a request to the network to ensure that the necessary resources, such as bandwidth and processing power, are available.

The AAR process consists of three main phases: Admission, Authorization, and Resource Reservation.

1. Admission The admission phase involves checking if there are sufficient resources available in the network to accommodate a new communication session. The goal of this phase is to ensure that the network is not overloaded, which can result in poor QoS. In the admission phase, the requestor sends a message to the network asking for resources to be reserved for a communication session. The network then checks its resources and determines if it can accommodate the request. If there are enough resources available, the request is accepted, and the process moves on to the authorization phase. If there are not enough resources available, the request is rejected, and the communication session cannot proceed.
2. Authorization The authorization phase involves checking if the requestor is authorized to use the requested resources. This phase is necessary to ensure that the network is not used by unauthorized users. In the authorization phase, the requestor's credentials are checked to determine if they are authorized to use the requested resources. If the credentials are valid, the request is accepted, and the process moves on to the resource reservation phase. If the credentials are not valid, the request is rejected, and the communication session cannot proceed.
3. Resource Reservation The resource reservation phase involves reserving the requested resources for the communication session. In this phase, the network reserves the necessary resources for the requested communication session. Once the resources are reserved, the communication session can proceed with the assurance that there are sufficient resources to provide the required QoS.

The AAR process is essential in ensuring that real-time communication sessions, such as voice and video, have sufficient resources to provide high-quality performance. Without AAR, these communication sessions could suffer from delays, packet loss, and other issues that would degrade the quality of the session.

In addition to the basic AAR process, there are several variations and extensions that can be used to further enhance the QoS of communication sessions. These include:

1. Dynamic Resource Allocation (DRA) DRA is a process where network resources are dynamically allocated to communication sessions based on their needs. This allows for a more efficient use of network resources and can help to optimize QoS.
2. Preemption Preemption is a process where resources allocated to one communication session can be preempted in favor of a higher-priority session. This ensures that high-priority sessions always have sufficient resources, even if it means interrupting lower-priority sessions.
3. Call Admission Control (CAC) CAC is a process where the admission phase of AAR is extended to include a more detailed analysis of the network's current and predicted load. This allows the network to make more informed decisions about whether to accept or reject a communication session request.
4. Bandwidth Broker (BB) BB is a process where a central server is used to allocate network resources to different communication sessions. This allows for a more centralized and coordinated approach to resource allocation and can help to optimize QoS.

Overall, AAR is an essential mechanism for ensuring that real-time communication sessions have the necessary resources to provide high-quality performance and avoid issues such as delays, packet loss, and other QoS-related problems. By reserving network resources in advance, AAR helps to avoid congestion, which can occur when there are more communication sessions than the network can handle. Congestion can result in delays and lost packets, which can degrade the QoS of real-time communication sessions.

In addition to its benefits for real-time communication sessions, AAR is also useful for other types of applications, such as file transfers and data backups. In these cases, AAR can be used to ensure that the necessary bandwidth and storage resources are available to complete the transfer or backup in a timely and efficient manner.

One of the challenges of implementing AAR is the need for coordination between the different network elements involved in the process. These elements include the end systems (such as the VoIP phone or multimedia endpoint), the network equipment (such as routers and switches), and the network management systems (such as call control servers and bandwidth brokers). To ensure that AAR operates smoothly, these different elements must be properly configured and integrated with each other.

Another challenge of implementing AAR is the need for standardized protocols and interfaces. There are a number of different AAR-related protocols and interfaces that have been developed by various organizations and standardization bodies. These include protocols such as RSVP (Resource Reservation Protocol) and H.323, as well as interfaces such as the Telecommunications Information Networking Architecture (TINA) and the Common Open Policy Service (COPS) protocol.

To ensure that AAR operates correctly, it is important to choose the right protocol and interface for the specific application and network environment. Factors to consider when choosing a protocol or interface include the level of QoS required, the complexity of the network environment, and the availability of vendor support and interoperability.

In summary, AAR is a mechanism used in communication networks to ensure that there are sufficient resources available for real-time communication sessions. The AAR process consists of three main phases: Admission, Authorization, and Resource Reservation. AAR is essential for providing high-quality performance for real-time communication applications such as voice and video. To ensure that AAR operates correctly, it is important to coordinate the different network elements involved in the process and choose the right protocol and interface for the specific application and network environment.