LTE PDCP Protocol Rel8 Sung Duck Chun duckychunlge

LTE PDCP Protocol (Rel-8) Sung. Duck Chun (duckychun@lge. com) Click to to edit Master subtitle style July 30, 2009 Copyright Notification . No part may be reproduced except as authorized by written permission. The copyright and the foregoing restriction extend to reproduction in all media. ⓒ 2009. LG 3 GPP RAN 2 team. All rights reserved. LG Electronics RAN 2 Team

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PDCP – Vertical View RLC • HTTP, FTP, etc - IP • Header compression and Security • Framing and ARQ MAC • Multiplexing and Scheduling PHY • Physical layer processing App PDCP Copyright All Rights Reserved 3 / 27 LG Electronics RAN 2 Team

PDCP Role PDCP SDU Header Compression • Increase radio efficiency Security Management PDCP • Ciphering • Integrity protection Selective Forwarding • Lossless and efficient HO support PDCP PDU Copyright All Rights Reserved 4 / 27 LG Electronics RAN 2 Team

PDCP model PDCP-SAP SDU numbering Re-ordering Header Compression Header Decompression Integrity Protection Integrity Verification Ciphering Deciphering C-SAP Add PDCP header Remove PDCP header Radio Bearer RLC UM/TM-SAP Copyright All Rights Reserved RLC UM/TM-SAP RLC AM-SAP 5 / 27 RLC Sub-layer LG Electronics RAN 2 Team

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Header Compression (1) SRC Address: x. x Dest. Address: y. y Header checksum IP Header User datagram • Many packets have identical information • Transmitting same information is the root of inefficiency IP Packet 1 Identical Information Protocols SRC Address: x. x Dest. Address: y. y Header checksum IP Header Copyright Header Compression All Rights Reserved User datagram • Framework: RFC 4995 • Profiles: RFC 4815/3095/etc Implementation • Not specified in 36. 323 • A black box approach IP Packet 2 7 / 27 LG Electronics RAN 2 Team

Header Compression (2) IP Packet 1 Context setup SRC: x. x Dest: y. y Payload IR Packet Header checksum • Used to establish/refresh Context • Include full header information • Different Contexts use separate CIDs SRC: x. x Header checksum IP Packet 2 IR packet Context Dest: y. y Compression Payload compressed Packet + De-Compression SRC: x. x Dest: y. y Payload Header checksum Compressed Packet • After Context establishment, only changed information is transmitted Standalone packet Feedback Header Compressor Copyright All Rights Reserved Header Decompressor 8 / 27 • Feedback LG Electronics RAN 2 Team

Header Compression (3) Two Types of PDUs D/C=D PDCP SN PDCP PDU Header • Header (de)compression entity generates two types of packets Data PDCP PDU Payload Compressed Packet D/C=C PDU Type = feedback PDCP PDU Header Data (ROHC feedback packet) PDCP PDU Payload • Related to PDCP SDU • Have a SN • May include feedback Standalone packet • Not related to PDCP SDU • No PDCP SN • Not ciphered Copyright All Rights Reserved 9 / 27 LG Electronics RAN 2 Team

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Security – Ciphering (1) Orig. Data Key. Stream 1 Generator 1 1 1 0 1 0 0 Unsuccessful decoding Copyright 0 Purpose • Prevent unauthorized user from seeing the content of communication Ciphered data + (xor) 1 0 0 + (xor) 0 Decipher engine 1 1 Cipher engine Incorrect keystream 1 0 All Rights Reserved 0 1 0 0 Decipher engine + (xor) 1 0 0 • Apply Keystream to the original data De-ciphering • Apply Keystream to the received data 0 Successful decoding 11 / 27 LG Electronics RAN 2 Team

Security – Ciphering (2) Key. Stream Generator Key count bearer Direction Length • Transmitter and receiver should generate identical key stream Input • Unique generation against replay-attack • Key (Ck) • Count: • instance of generation • HFN + SN • Bearer: ID of bearer • Direction: UL/DL • Length Key. Stream Generator Key stream Copyright All Rights Reserved 12 / 27 LG Electronics RAN 2 Team

Security – Integrity Protect (1) Key count bearer Direction Auth Code Generator Orig. MSG Key count bearer Transmitter MAC-I MACI Air Interface All Rights Reserved • Calculates unique value based on the message • Attaches the value to the end of message Receiver Direction Auth Code Generator Copyright Rx MAC-I • Used to detect whether a text is tampered during delivery. + Mac-I Orig. MSG Rx MSG Integrity Protection x. Mac-I Compare 13 / 27 • Calculate unique value based on the received message • Compare the calculated value to the received value LG Electronics RAN 2 Team

Security – Integrity Protect (2) PDCP SN Data MAC-I PDCP PDU Header PDCP PDU Payload Security Info PDCP SN PDCP PDU Header Copyright All Rights Reserved Integrity Protection • Applied only to SRB 2 formats Data • MAC-I field is used for PDCP PDUs over SRBs • MAC-I field is not used for PDCP PDUs over DRBs PDCP PDU Payload 14 / 27 LG Electronics RAN 2 Team

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Data Handling at handover (DL) UMTS Cumulative Forwarding Source RNC PDCP 1 2 3 4 2 3 5 4 Target RNC PDCP 5 2 2 3 4 3 1 1 3 Wasteful retransmission 5 UE PDCP LTE Selective Forwarding Source e. NB PDCP 1 2 5 3 4 2 5 Target e. NB PDCP 4 2 2 3 1 1 3 4 Reordering 5 Cumulative Forwarding • During HO, Source RNC forwards to Target RNC all SDUs from the first SDU not acknowledged by UE, and UE discards received SDUs from the first missing SDU • After HO, UE receives SDUs from Target RNC from the first missing SDU Selective Forwarding • During HO, Source e. NB forwards to Target e. NB only SDUs not acknowledged by UE • After HO, UE receives not yet received SDUs from Target e. NB, and performs reordering UE PDCP Copyright All Rights Reserved 16 / 27 LG Electronics RAN 2 Team

Impact of Incomplete information (1) PDU 1 PDU 2 PDU 3 PDU 1 PDU 3 NACK 2 ACK 1, 3 PDU 4 PDU 5 Handover PDU 3 PDU 5 Transmitting PDCP Copyright All Rights Reserved Transmitting RLC Receiving RLC 17 / 27 Receiving PDCP LG Electronics RAN 2 Team

Impact of Incomplete information (2) 1 2 3 4 Incomplete information 5 Selective Forwarding Source e. NB PDCP 1 2 3 4 Target e. NB PDCP 2 5 1 2 3 4 5 3 1 1 3 5 UE PDCP Wasteful retransmission Copyright All Rights Reserved 18 / 27 • The source e. NB’s understanding of successful transmission is not always correct or up-to-date. • Loss of Status Report or delay in transmission of status report causes incomplete information Effect • Unnecessarily, more Data are forwarded from Se. NB to Te. NB • Unnecessarily, more Data are transmitted from Te. NB to UE LG Electronics RAN 2 Team

Status Reporting (DL) 1 2 3 4 Status Reporting 5 Selective Forwarding Source e. NB PDCP 1 2 3 4 Target e. NB PDCP 2 5 1 2 3 4 1 3 4 NACK 2, 4 ACK 1, 3, 5 Copyright 1 All Rights Reserved 3 5 • To fill the gap of the incomplete information, when a UE accesses to Te. NB, the UE transmit PDCP status Report • PDCP Status Report indicates the missing PDCP PDUs and successfully received PDCP PDUs Effect • Unnecessary transmission is prevented 5 UE PDCP 19 / 27 LG Electronics RAN 2 Team

Re-ordering required at HO PDU 1 PDU 3 PDU 5 PDU 2 PDU 1 Reordering PDU 2 PDU 4 PDU 3 PDU 4 PDU 5 Se. NB Copyright All Rights Reserved Te. NB UE PDCP 20 / 27 LG Electronics RAN 2 Team

Reception: Always Re-order (1) Duplicate RX_HFN-1 RX_HFN Always Re-ordering 0 RX_HFN-1 • Outside of HO, in-order delivery is always guaranteed. Thus, strictly speaking, Re-ordering is not needed outside of HO. • However, due to possible security de-synchronization, reordering is always performed. RX_HFN 0 RX_HFN+1 0 Normal Progress RX_HFN+1 0 RX_HFN-1 RX_HFN 0 Recovery at HO RX_HFN-1 RX_HFN 0 Copyright All Rights Reserved Assumption • e. NB always transmit SDUs in ascending sequence. • I. e. , if UE receives PDCP Count=N, it means that UE PDCP will not be received Count<N. • The only exception is the time period of PDCP/RLC Reestablishment • RX_HFN is related to next RX SN • Next RX > Last Submit Received SN 21 / 27 Last Submit Next RX LG Electronics RAN 2 Team

Reception: Always Re-order (2) Duplicate RX_HFN-1 RX_HFN Received SN • SN of just received PDU 0 Last Submit RX_HFN-1 RX_HFN • SN of the last PDU delivered to upper layer 0 RX_HFN Next RX RX_HFN+1 0 • Next SN of Highest RXed SN Normal Progress RX_HFN Received SN < Last Submit RX_HFN+1 0 RX_HFN-1 • This is duplicate. • Discard after header decompression. RX_HFN Actions 0 Recovery at HO RX_HFN-1 RX_HFN 0 RX_HFN-1 RX_HFN Received SN 0 Copyright All Rights Reserved • For the not-discarded PDU, decompress and decipher • For the PDU received normally, deliver all the PDUs with SN < received SN • For the PDUs received due to reestablishment, just store the PDUs. 22 / 27 Last Submit Next RX LG Electronics RAN 2 Team

Data Handling at handover (UL) UMTS No Forwarding Source RNC PDCP 1 3 Target RNC PDCP 5 1 2 3 4 5 UE PDCP LTE 3 3 Target e. NB PDCP 5 5 3 Reordering 1 2 3 4 5 UE PDCP Copyright All Rights Reserved • During HO, Source RNC does not forward any SDUs to Target RNC • After HO, UE transmits to Target RNC from the first SDU not acknowledged by Source RNC Selective Retransmission Selective Forwarding Source e. NB PDCP 1 Wasteful retransmission Cumulative Retransmission 23 / 27 • During HO, Source e. NB forwards to Target e. NB all 5 SDUs from the first missing SDU • After HO, UE transmits to Target RNC only the SDUs not acknowledged by Source RNC, and Target RNC performs reordering LG Electronics RAN 2 Team

Status Reporting (UL) 3 5 Selective Forwarding Source e. NB PDCP 1 3 Target e. NB PDCP 2 NACK 2, 4 ACK 1, 3, 5 5 3 3 1 4 1 2 3 4 All Rights Reserved • To fill the gap of the incomplete information, when a UE accesses to Te. NB, the Te. NB transmit PDCP status Report • PDCP Status Report indicates the missing/received PDCP PDUs Effect • Unnecessary transmission is prevented 5 UE PDCP Copyright 5 Status Reporting 24 / 27 LG Electronics RAN 2 Team

PDCP Status Report D/C=C FMS PDU Type = status report Bitmap FMS • First missing SN PDCP PDU Header PDCP PDU Payload Bitmap Example NOT RECEIVED … … PDU 1 PDU 2 PDU 3 RECEIVED PDU 4 PDU 5 PDU 6 D/C=C 0 PDU Type = status report 0 0 0 1 0 0 FMS=1 Bitmap PDCP PDU Header Copyright All Rights Reserved PDCP PDU Payload 25 / 27 0 • The first bit indicates reception status of SN = FMS+1. • The Nth bit indicates reception status of SN=FMS+N. • ‘ 1’ means retransmission is not needed • ‘ 0’ means retransmission needed. • The size of ‘bitmap’ field is multiple of 8 bit. LG Electronics RAN 2 Team

Delay control RRC MSG IP Packet Discard Timer PDCP Start SDU Buffer start sto p X Process expir y RRC MSG IP Packet Stop Expiry RLC SUCCESSFUL DELIVERY Copyright All Rights Reserved • Related to buffer/delay management • Defines maximum wait time DISCARD INFORMATION 26 / 27 • When a PDCP SDU is received from upper layer, discard timer for the SDU is started. • When a discard timer expires, either the PDCP SDU is discarded or indication is sent to lower layer. LG Electronics RAN 2 Team

Thank You!! Authorized by LG Electronics 3 GPP RAN 2 Team Copyright All Rights Reserved 27 / 27 LG Electronics RAN 2 Team