[信息与通信]LTE空口L2协议.ppt

LTE 空中接口空中接口L2(层层2)协议介绍协议介绍主要内容MACMAC层层RLCRLC层层PDCPPDCP层层LTELTE架构和协议概述架构和协议概述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MACMAC层层RLCRLC层层PDCPPDCP层层LTE LTE 架构和协议概述架构和协议概述PDCP所处位置The Packet Data Convergence Protocol (PDCP) layernThis layer processes Radio Resource Control (RRC) messages in the control plane and Internet Protocol(IP) packets in the user plane. nDepending 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. nThere is one PDCP entity per radio bearer.PDCP functionnHeader compression and decompression for user plane data.nSecurity functions:– ciphering and deciphering for user plane and control plane data;– integrity protection and verification for control plane data.PDCP function (cont.)nHandover support functions:– in-sequence delivery and reordering of PDUs for the layer above at handover;– lossless handover for user plane data mapped on RLC Acknowledged Mode User Plane PDCPControl Plane PDCPPDCP PDU FormatsnPDCP PDUs for user plane data comprise a ‘D/C’ field in order to distinguish Data and Control PDUsPDCP PDUnPDCP Data PDU for control plane data and for user plane data.--Control plane data: RRC message--User plane data: VoIP、wapnPDCP Control PDU only has two types--ROHC feedback--PDCP Status ReportMACMAC层层RLCRLC层层PDCPPDCP层层LTE LTE 架构和协议概述架构和协议概述RLC层所处位置The Radio Link Control (RLC) layernThe main functions of the RLC layer are segmentation and reassembly of upper layer packets in order to adapt them to the size which can actually be transmitted over the radio interface. nFor 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 due to Hybrid Automatic Repeat reQuest (HARQ) operation in the layer below. nThere is one RLC entity per radio bearer.Segmentation / ConcatenationRe-segmentationnRe-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的丢包功能n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 EntitiesnTransparent Mode (TM) RLC EntitynUnacknowledged Mode (UM) RLC EntitynAcknowledged Mode (AM) RLC EntityTM modenAs the name indicates, the TM RLC entity is transparent to the PDUs that pass through it –no functions are performed and no RLC overhead is addednOnly 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)nTM RLC is not used for userplane data transmission in LTEUM modenUM RLC provides a unidirectional data transfer service like TM RLCnUM RLC is mainly utilized by delay-sensitive and error-tolerant real-time applications, especially VoIP and other delay-sensitive streaming servicesUM functionnSegmentation and concatenation of RLC SDUs;nReordering of RLC PDUs;nDuplicate detection of RLC PDUs;nReassembly of RLC SDUs.UM RLC entityAM modenAM RLC provides a bidirectional data transfer servicenThe most important feature of AM RLC is ‘retransmission’. An Automatic Repeat reQuest (ARQ) operation is performed to support error-free transmissionnAM RLC is mainly utilized by error-sensitive and delay-tolerant non-real-time applications. such as web browsing and file downloading.nIn the control plane, RRC messages typically utilize the AM RLC in order to take advantage of RLC acknowledgements and retransmissions to ensure reliabilityAM functionnRetransmission of RLC Data PDUs;nRe-segmentation of retransmitted RLC Data PDUs;nPolling ;nStatus reporting;nStatus prohibit.AM RLC entityRLC AM的ARQ功能nRLC 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n发送侧会进行重传在以下两种情况--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 FormatsnRLC数据PDUØကTMD PDU，ØကUMD PDU，ØကAMD 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PDUØကAMD PDU segment，重传的PDU需要分段，从而产 生的nRLC 控制PDUØ Status ReportTransparent Mode Data PDU FormatnThe Transparent Mode Data (TMD) PDU consists only of a data field and does 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 FormatnFraming Info (FI). This 2-bit field indicates whether the first and the last data field elements are complete SDUs or partial SDUsnLength Indicator (LI). This 11-bit field indicates the length of the corresponding datafield element present in the UMD PDUAcknowledged Mode Data PDU FormatnData/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.nResegmentation Flag (RF). This 1-bit field indicates whether the RLC PDU is an AMD PDU or an AMD PDU segment.nPolling (P). This 1-bit field is used to request a status report from the peer receivingside.AMD PDU Segment FormatnLast Segment Flag (LSF). This 1-bit field indicates whether or not this AMD PDU segment is the last segment of an AMD PDU.nSegmentation Offset (SO). This 15-bit field indicates the starting position of the AMD PDU segment within the original AMD PDU.STATUS PDU FormatnControl PDU Type (CPT). This 3-bit field indicates the type of the RLC Control PDUnACK_SN. This 10-bit field indicates the SN of the first AMD PDU which is neither received nor listed in this STATUS PDUnNACK_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.MACMACRLCRLCPDCPPDCPLTE LTE 架构和协议概述架构和协议概述MAC层所处位置Medium Access Control (MAC)nThe MAC layer performs multiplexing and demultiplexing between logical channels and transport channelsMAC Overall ArchitectureChannel MapingLogic Channel IDValues of LCID for UL-SCHIndexLCID values00000CCCH00001-01010Identity of the logical channel01011-11001Reserved11010Power Headroom Report11011C-RNTI11100Truncated BSR11101Short BSR11110Long BSR11111PaddingValues of LCID for DL-SCHIndexLCID values00000CCCH00001-01010Identity of the logical channel01011-11011Reserved11100UE Contention Resolution Identity11101Timing Advance Command11110DRX Command11111PaddingMAC FunctionnSchedulingnScheduling Information Transfer(BSR)nRandom Access ProcedurenUplink Timing AlignmentnDiscontinuous Reception (DRX)nMultiplexing and Logical Channel PrioritizationMAC PDU Formats总结(Downlink)总结(Uplink)Questions？Thank you！。