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1、LTE 空中接口L2(层2)协议介绍,主要内容,MAC层,RLC层,PDCP层,LTE架构和协议概述,LTE整体架构,LTE用户面协议栈,LTE控制面协议栈,Uu S1接口协议栈,L2协议,L2协议总览,RB承载,逻辑信道,传输信道,物理信道,MAC层,RLC层,PDCP层,LTE 架构和协议概述,PDCP所处位置,The Packet Data Convergence Protocol(PDCP)layer,This layer processes Radio Resource Control(RRC)messages in the control plane and Internet Pr
2、otocol(IP)packets in the user plane.Depending on the radio bearer,the main functions of the PDCP layer are header compression,security(integrity protection and ciphering),and support for reordering and retransmission during handover.There is one PDCP entity per radio bearer.,PDCP function,Header com
3、pression and decompression for user plane data.Security functions:ciphering and deciphering for user plane and control plane data;integrity protection and verification for control plane data.,PDCP function(cont.),Handover support functions:in-sequence delivery and reordering of PDUs for the layer ab
4、ove at handover;lossless handover for user plane data mapped on RLC Acknowledged Mode,User Plane PDCP,Control Plane PDCP,PDCP PDU Formats,PDCP PDUs for user plane data comprise a D/C field in order to distinguish Data and Control PDUs,PDCP PDU,PDCP Data PDU for control plane data and for user plane
5、data.-Control plane data:RRC message-User plane data:VoIP、wapPDCP Control PDU only has two types-ROHC feedback-PDCP Status Report,MAC层,RLC层,PDCP层,LTE 架构和协议概述,RLC层所处位置,The Radio Link Control(RLC)layer,The main functions of the RLC layer are segmentation and reassembly of upper layer packets in order
6、to adapt them to the size which can actually be transmitted over the radio interface.For radio bearers which need error-free transmission,the RLC layer also performs retransmission to recover from packet losses.Additionally,the RLC layer performs reordering to compensate for out-of-order reception d
7、ue to Hybrid Automatic Repeat reQuest(HARQ)operation in the layer below.There is one RLC entity per radio bearer.,Segmentation/Concatenation,Re-segmentation,Re-segmentation就是重分段，LTE中它只在AM实体的发送侧执行。RLC AM 实体支持ARQ重传，当重传的RLC PDU无法适配到由MAC层指示的总的RLCPDU大小时，RLC层就会根据此情况对重传的RLC PDU执行分段操作，让生成的RLC PDU分段能适配进去,RLC
8、的丢包功能,当收到高层丢弃指示命令丢弃特定的RLC SDU时，UM或AM RLC实体的发送端应该丢弃指示的RLC SDU(只有在该SDU还没有被映射到RLC 数据PDU中),RLC Entities,Transparent Mode(TM)RLC EntityUnacknowledged Mode(UM)RLC EntityAcknowledged Mode(AM)RLC Entity,TM mode,As the name indicates,the TM RLC entity is transparent to the PDUs that pass through it no functi
9、ons are performed and no RLC overhead is addedOnly RRC messages which do not need RLC configuration can utilize the TM RLC,such as broadcast system information messages,paging messages,and RRC messages which are sent when no Signalling Radio Bearers(SRBs)other than SRB0 are available。(BCCH PCCH CCCH
10、)TM RLC is not used for userplane data transmission in LTE,UM mode,UM RLC provides a unidirectional data transfer service like TM RLCUM RLC is mainly utilized by delay-sensitive and error-tolerant real-time applications,especially VoIP and other delay-sensitive streaming services,UM function,Segment
11、ation and concatenation of RLC SDUs;Reordering of RLC PDUs;Duplicate detection of RLC PDUs;Reassembly of RLC SDUs.,UM RLC entity,AM mode,AM RLC provides a bidirectional data transfer serviceThe most important feature of AM RLC is retransmission.An Automatic Repeat reQuest(ARQ)operation is performed
12、to support error-free transmissionAM RLC is mainly utilized by error-sensitive and delay-tolerant non-real-time applications.such as web browsing and file downloading.In the control plane,RRC messages typically utilize the AM RLC in order to take advantage of RLC acknowledgements and retransmissions
13、 to ensure reliability,AM function,Retransmission of RLC Data PDUs;Re-segmentation of retransmitted RLC Data PDUs;Polling;Status reporting;Status prohibit.,AM RLC entity,RLC AM的ARQ功能,RLC AM实体的发送侧发送RLC数据PDUs到对端RLC AM实体，对端接收侧接收到RLC数据PDUs，并在以下两种情况下发送状态报告给发送侧-收到发送侧发来的Polling-检测到RLC数据PDU接收失败发送侧会进行重传在以下两种
14、情况-收到接收侧发来的状态报告指示有数据包未接收成功-本发送侧底层发来的HARQ发送失败指示,RLC PDU Formats,RLC数据PDUTMD PDU，UMD PDU，AMD PDU，第一次发送的RLC SDU的一部分生成 的PDU，或则在重传的时候不需要分段的PDUAMD PDU segment，重传的PDU需要分段，从而产 生的RLC 控制PDU Status Report,Transparent Mode Data PDU Format,The Transparent Mode Data(TMD)PDU consists only of a data field and does
15、not have any RLC headers.Since no segmentation or concatenation is performed,an RLC SDU is directly mapped to a TMD PDU.,Unacknowledged Mode Data PDU Format,Framing Info(FI).This 2-bit field indicates whether the first and the last data field elements are complete SDUs or partial SDUsLength Indicato
16、r(LI).This 11-bit field indicates the length of the corresponding datafield element present in the UMD PDU,Acknowledged Mode Data PDU Format,Data/Control(D/C).This 1-bit field indicates whether the RLC PDU is an RLC Data PDU or an RLC Control PDU.It is present in all types of PDU used in AM RLC.Rese
17、gmentation Flag(RF).This 1-bit field indicates whether the RLC PDU is an AMD PDU or an AMD PDU segment.Polling(P).This 1-bit field is used to request a status report from the peer receivingside.,AMD PDU Segment Format,Last Segment Flag(LSF).This 1-bit field indicates whether or not this AMD PDU segm
18、ent is the last segment of an AMD PDU.Segmentation Offset(SO).This 15-bit field indicates the starting position of the AMD PDU segment within the original AMD PDU.,STATUS PDU Format,Control PDU Type(CPT).This 3-bit field indicates the type of the RLC Control PDUACK_SN.This 10-bit field indicates the
19、 SN of the first AMD PDU which is neither received nor listed in this STATUS PDUNACK_SN List.This field contains a list of SNs of the AMD PDUs that have not been completely received,optionally including indicators of which bytes of the AMD PDU are missing in the case of resegmentation.,MAC,RLC,PDCP,
20、LTE 架构和协议概述,MAC层所处位置,Medium Access Control(MAC),The MAC layer performs multiplexing and demultiplexing between logical channels and transport channels,MAC Overall Architecture,Channel Maping,Logic Channel ID,Values of LCID for UL-SCH,Values of LCID for DL-SCH,MAC Function,SchedulingScheduling Information Transfer(BSR)Random Access ProcedureUplink Timing AlignmentDiscontinuous Reception(DRX)Multiplexing and Logical Channel Prioritization,MAC PDU Formats,总结(Downlink),总结(Uplink),Questions？,Thank you！,
