ARP (allocation and retention priority)

Last updated on Feb 27, 2023

Allocation and Retention Priority (ARP) is a mechanism used in Long-Term Evolution (LTE) cellular networks to manage resources for different Quality of Service (QoS) requirements of different network services. ARP enables network operators to prioritize and allocate network resources to different users and services based on their importance, which is determined by the service's QoS requirements.

In this article, we will discuss ARP in detail, including its purpose, how it works, and its benefits.

Purpose of ARP:

ARP is used to manage resources in the LTE network for different services. The main purpose of ARP is to ensure that the QoS requirements of different services are met. This is important because different network services have different QoS requirements, which can range from low to high priority. For example, a video streaming service may require high bandwidth and low latency to deliver a smooth streaming experience, while a simple text messaging service may require low bandwidth and can tolerate higher latency.

ARP is used to allocate resources to different services based on their QoS requirements. The higher the QoS requirements, the higher the ARP priority, and the more resources are allocated to the service. This ensures that critical services, such as emergency services, are given the highest priority, while less critical services, such as email, are given a lower priority.

How ARP works:

ARP is implemented in the Radio Access Network (RAN) of the LTE network. When a user initiates a data transfer, the User Equipment (UE) sends a request to the network to establish a connection. This request includes the QoS requirements of the service. The network then uses ARP to allocate resources to the connection based on the service's ARP priority.

The ARP priority is assigned to the connection based on the QoS requirements of the service. The QoS requirements are defined in terms of the following parameters:

QCI (QoS Class Identifier): This is a value that defines the QoS requirements of the service. The QCI ranges from 1 to 9, where a higher value indicates higher QoS requirements.
Priority Level: This is a value that defines the relative importance of the service. The priority level ranges from 1 to 16, where a higher value indicates higher priority.
Preemption Capability: This is a flag that indicates whether the service can be preempted by a higher-priority service. If the Preemption Capability flag is set to True, the service can be preempted by a higher-priority service.

The network uses these parameters to assign an ARP priority to the connection. The ARP priority ranges from 1 to 15, where a higher value indicates higher priority.

Once the ARP priority is assigned, the network uses it to allocate resources to the connection. The higher the ARP priority, the more resources are allocated to the connection. The resources include the following:

Bandwidth: The network allocates a certain amount of bandwidth to the connection based on its ARP priority.
Latency: The network ensures that the latency of the connection meets the QoS requirements of the service. The latency is the time it takes for the data to travel from the UE to the network and back.
Packet Loss: The network ensures that the packet loss rate of the connection meets the QoS requirements of the service. Packet loss occurs when data packets are lost during transmission.
Jitter: The network ensures that the jitter of the connection meets the QoS requirements of the service. Jitter is the variation in latency over time.

Benefits of ARP:

ARP provides several benefits to network operators and users. Some of the key benefits are:

Improved QoS: ARP ensures that the QoS requirements of different services are met. This improves the overall user experience and satisfaction.
Efficient Resource Allocation: ARP enables network operators to efficiently allocate resources to different services based on their QoS requirements. This helps to optimize the use of network resources and improve network efficiency.
Prioritization of Critical Services: ARP enables network operators to prioritize critical services, such as emergency services, over less critical services, such as email. This ensures that critical services are given the highest priority and receive the necessary resources to function properly.
Support for Diverse Services: ARP supports a wide range of services with different QoS requirements. This enables network operators to offer diverse services to their users while maintaining QoS standards.
Fairness: ARP ensures that all services are allocated resources based on their QoS requirements and priority levels. This ensures that all users receive fair treatment and equal opportunities to use the network.

ARP in Action:

To illustrate how ARP works in practice, let's consider an example where a user is streaming a video while also downloading a file on their LTE-enabled device. The video streaming service requires high bandwidth and low latency, while the file download service requires high bandwidth but can tolerate higher latency.

When the user initiates the data transfer, the UE sends a request to the network that includes the QoS requirements of both services. The network then assigns ARP priorities to the two connections based on their QoS requirements.

Assuming that the video streaming service has a QCI value of 6 and a priority level of 8, while the file download service has a QCI value of 8 and a priority level of 6, the network would assign ARP priorities of 11 and 9, respectively.

The network would then allocate resources to the two connections based on their ARP priorities. The video streaming service would receive more bandwidth and lower latency than the file download service, as it has a higher ARP priority.

If a higher-priority service, such as an emergency call, were to initiate a data transfer while the video streaming and file download services were active, the network would preempt the lower-priority services and allocate resources to the emergency call based on its higher ARP priority.

Conclusion:

Allocation and Retention Priority (ARP) is a key mechanism used in LTE networks to manage resources for different Quality of Service (QoS) requirements of different network services. ARP enables network operators to allocate resources to different services based on their importance, which is determined by the service's QoS requirements.

ARP provides several benefits, including improved QoS, efficient resource allocation, prioritization of critical services, support for diverse services, and fairness. ARP ensures that all services are allocated resources based on their QoS requirements and priority levels, ensuring fair treatment and equal opportunities for all users.

In summary, ARP is a critical component of LTE networks that helps to ensure that users receive the best possible network experience while maintaining QoS standards and network efficiency.