NAS - ARP
ARP is Allocation and Retention Priority. Understanding ARP requires to chase multiple Specs for its functionality.
As per 3GPP TS 36.413 version 12.3.0 Release 12
ARP contains 3 Mandatory IE's:
1. Priority Level
2. Pre-Emption Capability
3. Pre-Emption Vulnerability
Priority Level - Range: 0 to 15
0 - Logical Error
1 - Highest Priority
14 - Lowest Priority
15 - No Priority
Pre-Emption Capability
It has 2 Enumerated Value:
1. shall not trigger pre-emption, - Cannot preempt other bearers during resource crunch
2. may trigger preemption - Can Trigget preemtion of other bearers during resource crunch
Pre-Emption Vulnerability
It has 2 Enumerated Value:
1. not preemptable - This bearer cannot be pre-emptable by other bearers
2. preemptable - This bearer can be release during resource crunch by other bearers.
As per spec 23.401 Rel 11, 4.7.3 Bearer level QoS parameters
1. The primary purpose of ARP is to decide whether a bearer establishment / modification request can be accepted or needs to be rejected due to resource limitations (typically available radio capacity for GBR bearers).
2. The priority level information of the ARP is used for this decision to ensure that the request of the bearer with the higher priority level is preferred. In addition, the ARP can be used (e.g. by the eNodeB) to decide which bearer(s) to drop during exceptional resource limitations (e.g. at handover).
3. The pre-emption capability information of the ARP defines whether a bearer with a lower ARP priority level should be dropped to free up the required resources. The preemption vulnerability information of the ARP defines whether a bearer is applicable for such dropping by a pre-emption capable bearer with a higher ARP priority value.
4. Once successfully established, a bearer's ARP shall not have any impact on the bearer level packet forwarding treatment (e.g. scheduling and rate control). Such packet forwarding treatment should be solely determined by the other EPS bearer QoS parameters: QCI, GBR and MBR, and by the AMBR parameters.
NOTE 1: The ARP is not included within the EPS QoS Profile sent to the UE. So UE will not know about ARP configurations eventhough its one of a Bearer Qos Parameter.
NOTE 2: The ARP should be understood as "Priority of Allocation and Retention"; not as "Allocation, Retention, and Priority".
NOTE 3: Video telephony is one use case where it may be beneficial to use EPS bearers with different ARP values for the same UE. In this use case an operator could map voice to one bearer with a higher ARP, and video to another bearer with a lower ARP. In a congestion situation (e.g. cell edge) the eNodeB can then drop the "video bearer" without affecting the "voice bearer". This would improve service continuity. ETSI 3GPP TS 23.401 version 11.3.0 Release 11 65 ETSI TS 123 401 V11.3.0 (2012-11)
NOTE 4: The ARP may also be used to free up capacity in exceptional situations, e.g. a disaster situation. In such a case the eNodeB may drop bearers with a lower ARP priority level to free up capacity if the pre-emption vulnerability information allows this.
ARP is Allocation and Retention Priority. Understanding ARP requires to chase multiple Specs for its functionality.
As per 3GPP TS 36.413 version 12.3.0 Release 12
ARP contains 3 Mandatory IE's:
1. Priority Level
2. Pre-Emption Capability
3. Pre-Emption Vulnerability
Priority Level - Range: 0 to 15
0 - Logical Error
1 - Highest Priority
14 - Lowest Priority
15 - No Priority
Pre-Emption Capability
It has 2 Enumerated Value:
1. shall not trigger pre-emption, - Cannot preempt other bearers during resource crunch
2. may trigger preemption - Can Trigget preemtion of other bearers during resource crunch
Pre-Emption Vulnerability
It has 2 Enumerated Value:
1. not preemptable - This bearer cannot be pre-emptable by other bearers
2. preemptable - This bearer can be release during resource crunch by other bearers.
As per spec 23.401 Rel 11, 4.7.3 Bearer level QoS parameters
1. The primary purpose of ARP is to decide whether a bearer establishment / modification request can be accepted or needs to be rejected due to resource limitations (typically available radio capacity for GBR bearers).
2. The priority level information of the ARP is used for this decision to ensure that the request of the bearer with the higher priority level is preferred. In addition, the ARP can be used (e.g. by the eNodeB) to decide which bearer(s) to drop during exceptional resource limitations (e.g. at handover).
3. The pre-emption capability information of the ARP defines whether a bearer with a lower ARP priority level should be dropped to free up the required resources. The preemption vulnerability information of the ARP defines whether a bearer is applicable for such dropping by a pre-emption capable bearer with a higher ARP priority value.
4. Once successfully established, a bearer's ARP shall not have any impact on the bearer level packet forwarding treatment (e.g. scheduling and rate control). Such packet forwarding treatment should be solely determined by the other EPS bearer QoS parameters: QCI, GBR and MBR, and by the AMBR parameters.
NOTE 1: The ARP is not included within the EPS QoS Profile sent to the UE. So UE will not know about ARP configurations eventhough its one of a Bearer Qos Parameter.
NOTE 2: The ARP should be understood as "Priority of Allocation and Retention"; not as "Allocation, Retention, and Priority".
NOTE 3: Video telephony is one use case where it may be beneficial to use EPS bearers with different ARP values for the same UE. In this use case an operator could map voice to one bearer with a higher ARP, and video to another bearer with a lower ARP. In a congestion situation (e.g. cell edge) the eNodeB can then drop the "video bearer" without affecting the "voice bearer". This would improve service continuity. ETSI 3GPP TS 23.401 version 11.3.0 Release 11 65 ETSI TS 123 401 V11.3.0 (2012-11)
NOTE 4: The ARP may also be used to free up capacity in exceptional situations, e.g. a disaster situation. In such a case the eNodeB may drop bearers with a lower ARP priority level to free up capacity if the pre-emption vulnerability information allows this.
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