SRB( Signaling Radio Bearer)就是無線信令承載;SRBs(Signalling Radio Bearers)是傳輸RRC和NAS消息的無線承載;根據(jù)3GPP TS38.331,5G (NR)的SRB有四種:
1.SRB的類型
SRB#0 RRC消息承載于CCCH信道
SRB#1 RRC和NAS消息,用在SRB2(含NAS消息)建立之前,承載于DCCH信道;
SRB#2 NAS消息,承載于DCCH信道;空口加密完成后由網(wǎng)絡(luò)側(cè)配置,SRB2較SRB1優(yōu)先級(jí)低,;
SRB#3 UE雙連接(EN-DC)中RRC消息,承載于DCCH信道;
SRB的功能在5G(NR)和LTE網(wǎng)絡(luò)中相同。5G(NR)網(wǎng)絡(luò)中只是增加了SRB3,它用在雙連接(EN-DC)中,通過5G(NR)無線網(wǎng)絡(luò)傳遞UE與SgNB之間SRB3消息;
2.SRB配置表
Information Element
SRB#1
SRB#2
SRB#3
PDCP-Config
t-Reordering
Infinite
RLC-Config CHOICE
AM
ul-RLC-Config
sn-FieldLength
size12
t-PollRetransmit
ms45
pollPDU
Infinity
pollByte
maxRetxThreshold
t8
dl-RLC-Config
t-Reassembly
ms35
t-StatusProhibit
ms0
logicalChannelIdentity
1
2
3
LogicalChannelConfig
priority
prioritisedBitRate
logicalChannelGroup
0
3.SRBs中NAS和 RRC消息映射
Message(消息)
Direction(方向)
Logical Channel (邏輯信道)
RLC Mode(模式)
SRB Mapping(映射)
MasterInformationBlock
UE <– NW
BCCH
TM
N/A
SIB1
SystemInformation
RRCSetupRequest
UE –> NW
CCCH
SRB0
RRCSetup
RRCResumeRequest1
CCCH1
RRCSystemInfoRequest
RRCReject
RRCResumeRequest
RRCReestablishmentRequest
RRCSetupComplete
DCCH
SRB1
RRCRelease
RRCReconfiguration
SRB1,SRB3
RRCReconfigurationComplete
MeasurementReport
MobilityFromNRCommand
Paging
PCCH
RRCReestablishment
RRCReestablishmentComplete
RRCResume
RRCResumeComplete
SecurityModeCommand
SecurityModeComplete
SecurityModeFailure
UEAssistanceInformation
UECapabilityEnquiry
UECapabilityInformation
ULInformationTransfer
SRB1,SRB2
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