What is ARP in LTE?
In LTE, ARP stands for Allocation and Retention Priority. It’s a key part of the Quality of Service (QoS) framework used to determine how important a particular data flow is when the network is congested. If you and I are working on LTE design or optimization, understanding ARP becomes essential because it impacts how resources are assigned and managed — especially during times when the radio network is under pressure.
Unlike QCI (QoS Class Identifier), which deals with packet delay and loss sensitivity, ARP is about deciding who gets served first when radio resources are limited. So, think of ARP as the “admission control” gatekeeper.
Key Components of ARP
There are three main parts to ARP:
- Priority Level: A numeric value from 1 (highest) to 15 (lowest). A lower number means higher priority. For example, emergency calls would have a priority of 1 or 2.
- Pre-emption Capability: Indicates whether the bearer can preempt another existing bearer with a lower priority if needed.
- Pre-emption Vulnerability: Specifies whether a bearer can be preempted by a higher-priority bearer during congestion.
How ARP Works in Real Scenarios
Imagine you’re managing a cell site where many users are connected. Suddenly, a new request comes in for a high-priority VoLTE emergency call. Now the scheduler checks ARP values to decide if it should preempt some of the existing lower-priority data bearers to make room for this new request. If those bearers are marked as vulnerable, they might be dropped to free up resources.
As we discussed earlier in topics like QCI classes and bearer management, ARP doesn’t affect ongoing data flow quality but only matters during bearer establishment. This makes ARP critical during network congestion, initial connection setup, and handovers involving new bearer setup.
ARP Use Case Table
| Service Type | ARP Priority | Pre-emption Capability | Pre-emption Vulnerability |
|---|---|---|---|
| Emergency VoLTE | 1 | Yes | No |
| Video Streaming | 8 | No | Yes |
| Background Downloads | 13 | No | Yes |
As you explore deeper into LTE QoS handling, you’ll see ARP working alongside other parameters like QCI, GBR (Guaranteed Bit Rate), and MBR (Maximum Bit Rate). This combined setup makes LTE very flexible in delivering differentiated services to different user types — from casual web browsing to mission-critical communication.
And just like we covered earlier in the article about QCI, both ARP and QCI are assigned during bearer setup by the MME and communicated to the eNodeB to enforce the correct behavior on the radio side.