RAN and UE driven L4S marking and processing for congestion management in an O-RAN based network architecture
A system and method for reducing bottleneck queues in the O-RAN architecture through classification of a PDCP queue at a CU-UP server with a CU Congestion Indicator, and classification of a RLC queue at a DU server with a DU Congestion Indicator. The CU Congestion Indicator determines a category for the PDCP queue for a DRB, x and the DU Congestion Indicator determines a category for the RLC queue for a DRB, y. The DU server transmitting the CE indication to UE when the CU Congestion Indicator or the DU Congestion Indicator classifies the DRB x or DRB y as CE, which in turn, communicates a congestion occurrence to an application source. The application source modifies a data rate for data traffic that is sent to the UE based on the CE indication.
1 . A system for reducing bottleneck queues in the Open Radio Access Network (O-RAN) comprising:
a Centralized Unit-User Plane (CU-UP) server;
a Distributed Unit (DU) server coupled to said CU-UP server;
a User Equipment (UE) coupled to said DU server;
an application source coupled to said UE;
software executing on said CU-UP server comprising a CU Congestion Indicator that measures data congestion in a Packet Data Convergence Protocol (PDCP) queue of said CU-UP server, the CU Congestion Indicator analyzing and classifying a Data Radio Bearer (DRB) x in the PDCP queue;
software executing on said DU server comprising a DU Congestion Indicator that measures data congestion in a Radio Link Control (RLC) queue of the said DU server, the DU Congestion Indicator analyzing and classifying a DRB y in the RLC queue;
wherein if the CU Congestion Indicator or the DU Congestion Indicator classifies the DRB x or DRB y respectively as Congestion Experienced (CE), said DU server transmits a CE indication to said UE;
said UE uses the CE indication to communicate a congestion occurrence message to said application source using: Low Latency, Low Loss, and Scalable throughput Medium Access Control (L4S MAC) Control Element (MAC CE) or Explicit Congestion Notification (ECN) bits in a Transmission Control Protocol (TCP) header from a PDCP header; and
wherein said application source modifies a data rate for data traffic that is sent to said UE based on the CE indication.
2 . The system according to claim 1 , wherein the CU Congestion Indicator comprises an L4S module at said CU-UP server.
3 . The system according to claim 1 , wherein the ECN bits in the TCP header comprise two reserved bits from a PDCP header and are used to communicate the CE indication from said CU-UP server to said DU server for each DRB.
4 . The system according to claim 3 , wherein the first bit is used to indicate whether the DRB is carrying L4S traffic, and the second bit is used to indicate the CE indication.
5 . The system according to claim 4 , wherein the second bit is updated as a packet moves from said CU-UP server to said DU server.
6 . The system according to claim 4 , wherein the UE continues to send the CE indication to said application source until:
said DU server indicates to the UE that a select DRB is no longer experiencing congestion; or
said DU server sends a message to the UE indicating that said DU server has adapted a data transmission rate in response to information received from the UE.
7 . The system according to claim 1 , wherein
the PDCP queue for DRB x at said CU-UP server is categorized as high, medium or low, and
the RLC queue for DRB y at said DU server is categorized as high, medium or low.
8 . The system according to claim 7 , wherein once a category for the RLC or the PDCP queues has been derived at said DU server, the category is transmitted to the CU-CP server by adding objects in a F1-C interface protocol.
9 . The system according to claim 8 , wherein the CE indication is sent to said UE via a UE-specific Radio Resource Control (RRC) message.
10 . The system according to claim 9 , further comprising a field that is added in the UE-specific RRC message to indicate the occurrence of congestion.
11 . The system according to claim 1 , wherein the CU Congestion Indicator further monitors and classifies an air-interface and a Mid-haul link, which indications are transmitted to the UE.
12 . The system according to claim 1 , wherein the CE indication comprises L4S MAC Control Element (MAC CE).
13 . A method for reducing bottleneck queues in the Open Radio Access Network (O-RAN) having a Centralized Unit-User Plane (CU-UP) server, a Distributed Unit (DU) server coupled to the CU-UP server, a User Equipment (UE) coupled to the DU server and an application source coupled to the UE, the method comprising the steps of:
measuring data congestion in a Packet Data Convergence Protocol (PDCP) queue of the CU-UP server with a CU Congestion Indicator;
the CU Congestion Indicator analyzing and classifying a Data Radio Bearer (DRB) x in the PDCP queue;
measuring data congestion in a Radio Link Control (RLC) queue of the DU server with a DU Congestion Indicator;
wherein the DU Congestion Indicator analyzes and classifies a Data Radio Bearer (DRB) y in the RLC queue;
wherein when the CU Congestion Indicator or the DU Congestion Indicator classifies the DRB x or DRB y respectively as Congestion Experienced (CE), the DU server transmits the CE indication to the UE;
wherein the UE communicates a congestion occurrence message to the application source based on the received CE indication, the UE transmitting the congestion occurrence message using: L4S MAC Control Element (MAC CE) or Explicit Congestion Notification (ECN) bits in a Transmission Control Protocol (TCP) header from a PDCP header; and
wherein the application source modifies a data rate for data traffic that is sent to the UE based on the CE indication.
14 . The method according to claim 13 , wherein the CU Congestion Indicator is an L4S module.
15 . The method according to claim 13 , wherein the ECN bits in the TCP header are two reserved bits from a PDCP header and are used to communicate the CE indication from the CU-UP server to the DU server for each DRB.
16 . The method according to claim 15 , wherein the first bit is used to indicate whether the DRB is carrying L4S traffic, and the second bit is used to indicate the CE indication.
17 . The method according to claim 13 , wherein
the PDCP queue for DRB x at the CU-UP server is categorized as high, medium or low, and
the RLC queue for DRB y at the DU server is categorized as high, medium or low.