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释放流程及异常释放原
因分析
2016-05
张恒
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概述
主要内容说明
本次主要讨论的内容：
LTE业务释放类型及相应信令流程的详解；相关的counter触发定义，以及异常问题分析；
通过对这些内容的梳理和讨论，能够了解LTE释放的理论知识，并且在日常KPI和Log分
析方面，提供帮助。
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释放流程及异常释放原因分析
主要内容
<Change information classification in footer>
- 业务承载类型及业务建立过程
- 业务释放类型及相应流程、原因
• E-RAB release
• UE context release
• RRC connection release
- 异常释放的触发情景详解
• UE initiated drop
• eNB initiated drop
- 异常释放related Counter Triggers
- Network/Field KPI及Drops分析
- Summary
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业务承载类型
LTE业务承载类型
LTE的业务承载类型分为默认承载、专用承载两种：
默认承载：UE开机时获得承载，一定是MME发起的业务，优先级特别低，Non GBR；
专用承载：一定是由PGW触发建立的； 一个UE可以有不同的专用承载；
GTP variant: EPS bearer termination in PGW SRB与默认、专用承载关系
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业务承载类型
无线承载分类
SRB
– Signalling Radio Bearers（SRBs）的定义是，仅用于传输RRC和NAS消息的RB（Radio
Bearer）；
DRB
– Data Radio Bearer，用于传输业务数据的无线承载；与S1-U承载共同组成E-RAB.分为
UM、AM两种；
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业务承载类型
UE context及E-RAB
E-RAB
– UE至SGW之间的承载，E-RAB是指用户平面的承载，由S1-U承载和DRB（Data Radio
Bearer，数据无线承载）串联而成，进入LTE系统的业务数据主要通过E-RAB进行传输。
因此对于LTE，业务管理主要是在E-RAB层次上进行的。
– 一个UE可以有多个E-RAB，目前最多支持8个EPS承载（５个AM DRB，3个UM DRB）.
– 在应用上，E-RAB常出现于性能指标的统计中，例如：E-RAB建立成功率。E-RAB建立
成功指eNodeB成功为UE分配了通信通道的无线资源和用户面的无线承载，所以这个指标
反映了eNodeB或小区接纳业务的能力，可以用来考虑系统负荷情况。
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业务承载类型
UE context及E-RAB
UE context
– Including E-RAB context, security context, roaming restriction, UE S1 signalling
connection ID(s), etc. in the eNB.在源eNB的UE上下文中还包含了与漫游和接入限制有关
的信息；
– Initial UE context只能由MME发起，一个UE只有一个UE context；
– 一个eNB UE context是eNB内和一个处于激活状态的UE相关联的一个信息块。这块信息
是为了维持E-UTRAN提供给这个激活态UE的服务所必须的信息；
– eNB UE context是在UE迁移到激活状态之后开始建立的；或者，eNB UE context是在切
换目标eNB完成切换资源分配（切换准备阶段）之后开始建立的。
RRC connection
层三信令连接，UE保持非IDLE的必须连接，一个UE只有一个RRC connection，一旦
连接释放，UE所有业务释放，并进入RRC_IDLE态；
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LTE完整业务流程
默认承载建立信令流程（Attach）
Steps:
1. Random Access
2. Initial NAS msg
3. NAS security
4. S1 init setup
5. RRC sec + UE cap
6. SRB2/DRB setup
7. NAS reply
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LTE完整业务流程
RA及RRC连接建立流程
SRB0：
RRC connection request、
RRC connection setup（消
息中包含SRB1建立的相关信
息）；
SRB1：
RRC connection setup
complete；
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LTE完整业务流程
专用承载建立流程
Dedicated Bearer
Establishment：
E-RAB建立
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释放流程及异常释放原因分析
主要内容
<Change information classification in footer>
- 业务承载类型及业务建立过程
- 业务释放类型及相应流程、原因
• E-RAB release
• UE context release
• RRC connection release
- Abnormal release的触发情景详解
• UE initiated drop
• eNB initiated drop
- 异常释放related Counter Triggers
- Network/Field KPI及Drops分析
- Summary
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业务释放类型
release
根据业务承载类型，业务释放过程也分为三类：
E-RAB release
The purpose of the E-RAB Release procedure is to enable the release of already
established E-RABs for a given UE；
E-RAB释放后，UE仍然可以处于ECM-CONNECTED状态；
UE context release
If the eNB wants to remove all remaining E-RABs, ., for user inactivity, the UE Context
Release Request procedure shall be used instead.
当UE回到ECM-IDLE状态时，MME向eNodeB发UE CONTEXT RELEASE消息。收到这条
消息后，eNodeB删除eNB UE context。MME继续保留MME UE context.
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业务释放类型
release
根据业务承载类型，业务释放过程也分为两类：
RRC connection release
The purpose of this procedure is to release the RRC connection, which includes the
release of the established radio bearers as well as all radio resources；
RRC连接释放后，UE进入RRC_IDLE状态。
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E-RAB release
释放类型：E-RAB release
根据3GPP定义(3GPP TS )，E-RAB release过程分为两大类：
ENodeB Initiated
MME Initiated
E-RAB管理的相关信息都embed在context管理信令中。
MME Initiated ENodeB Initiated
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释放流程信令详解
E-RAB release ：MME Initiated
E-RAB release command消息内容：
shall contain the information required by the eNB to release at least one E-RAB in the E-
RAB To Be Released List IE. If a NAS-PDU IE is contained in the message, the eNB shall
pass it to the UE.
- E-RAB To Be Released List IE. the UE Aggregate Maximum Bit Rate IE.
E-RAB release response消息内容：
- A list of E-RABs which are released successfully shall be included in the E-RAB Release
List IE.
- A list of E-RABs which failed to be released, if any, shall be included in the E-RAB Failed
to Release List IE.
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释放流程信令详解
E-RAB release ：MME Initiated
eNB收到E-RAB RELEASE COMMAND后，eNB将会释放被请求的ERABs. 对于每一个要
释放的E-RAB，eNB会释放其相应的DRB和空口资源。
The eNB shall pass the value contained in the E-RAB ID IE received for the E-RAB to the
radio interface protocol for each Data Radio Bearer to be released. The eNB shall release
allocated resources on S1 for the E-RABs requested to be released.
Network triggered (from Delete Bearer)
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释放流程信令详解
E-RAB release ：eNB Initiated
E-RAB RELEASE INDICATION消息内容：
The E-RAB RELEASE INDICATION message shall contain at least one E-RAB released
at the eNB, in the E-RAB Released List IE.
Upon reception of the E-RAB RELEASE INDICATION message the MME shall normally
initiate the appropriate release procedure on the core network side for the E-RABs
identified in the E-RAB RELEASE INDICATION message.
Interaction with UE Context Release Request procedure:
If the eNB wants to remove all remaining E-RABs, ., for user inactivity, the UE Context
Release Request procedure shall be used instead.
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释放流程及异常释放原因分析
主要内容
<Change information classification in footer>
- 业务承载类型及业务建立过程
- 业务释放类型及相应流程、原因
• E-RAB release
• UE context release
• RRC connection release
- Abnormal release的触发情景详解
• UE initiated drop
• eNB initiated drop
- 异常释放related Counter Triggers
- Network/Field KPI及Drops分析
- Summary
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UE context release
释放类型：UE context release
根据3GPP定义(3GPP TS )，UE context过程同样分为两大类：
ENodeB Initiated
MME Initiated
This procedure is used to release the logical S1-AP signalling connection (over S1-MME)
and all S1 bearers (in S1-U) for a UE. The procedure will move the UE from ECM-
CONNECTED to ECM-IDLE in both the UE and MME, and all UE related context
information is deleted in the eNode B.
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UE context release
释放的触发条件—UE Context Release Request
该信令，使基站可以根据E-UTRAN的需要，向MME请求UE-associated S1链接的释放；
ENodeB发起的Context release情况：
Normal release：“User Inactivity”，‘CS Fallback triggered’，‘UE Not Available for PS
Service’，‘Inter-RAT Redirection’，‘Time Critical Handover’，‘Handover Cancelled’，
“Detach”
Abnormal release：“Radio Connection With UE Lost”, “CSG Subscription Expiry”,
“Redirection towards 1xRTT”，Unspecified Failure，O&M Intervention，Repeated RRC
signalling Integrity Check Failure，etc.
ENodeB Initiated
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UE context release
释放的触发条件—UE Context Release Command
MME Initiated
该信令，使MME在多种情形下，可以控制UE-associated 链接的释放；
MME发起的Context release情况：
Normal release：
, completion of a transaction between the UE and the EPC, or completion of successful
handover, or completion of handover cancellation, or release of the old UE-associated logical S1-
connection when two UE-associated logical S1-connections toward the same UE is detected after
the UE has initiated the establishment of a new UE-associated logical S1-connection, or the UE is
no longer allowed to access the CSG cell
(., the UE becomes a non-member of the currently used CSG cell).
Abnormal release： “Load Balancing TAU Required”，‘authentication failure’, ‘detach’,
‘not allowed CSG’ celetc.
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UE context release
正常释放原因信令实例
eNB initiated
MME initiated
MME initiated
eNB initiated
eNB initiated
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UE context release
异常释放原因信令实例
MME initiated
eNB initiated
MME initiated
MME initiated
MME initiated
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释放流程信令详解
UE context release：ENodeB Initiated
The UE CONTEXT RELEASE REQUEST message shall indicate the appropriate cause
value, ., “User Inactivity”,“Radio Connection With UE Lost”, “CSG Subscription Expiry”,
“CS Fallback triggered”, “Redirection towards1xRTT”, “Inter-RAT Redirection”, “UE Not
Available for PS Service”, for the requested UE-associated logical S1-connection release.
Interactions with UE Context Release procedure:
The UE Context Release procedure should be initiated upon reception of a UE CONTEXT
RELEASE REQUEST message.
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释放流程信令详解
UE context release：ENodeB Initiated
Transition due to inavtivity.
UE consumes less battery power in idle mode; Less active Ues which network has to
handle; Fast going to inactivity has drawback of longer connection setup time(more
transitions idle to connected).
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释放流程信令详解
UE context release：ENodeB Initiated
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释放流程信令详解
UE context release：MME Initiated
The UE CONTEXT RELEASE COMMAND message shall contain the UE S1AP ID pair IE
if available, otherwise the message shall contain the MME UE S1AP ID IE.
The MME provides the cause IE set to “Load Balancing TAU Required” in the UE
CONTEXT RELEASE COMMAND message sent to the eNB for all load balancing and
offload cases in the MME.
MME UE S1AP is released when the S1 connection is released (next time a new
value is assigned) eNB UE S1AP is released
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释放流程信令详解
UE context release：MME Initiated
Upon reception of the UE CONTEXT RELEASE COMMAND message, the eNB shall
release all related signalling and user data transport resources and reply with the UE
CONTEXT RELEASE COMPLETE message. In case of eNB
supporting L-GW function for LIPA operation, the eNB shall also release the node internal
tunnel resources.
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释放流程信令详解
UE context release：MME Initiated
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释放流程信令详解
UE context release：MME Initiated
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释放流程及异常释放原因分析
主要内容
<Change information classification in footer>
- 业务承载类型及业务建立过程
- 业务释放类型及相应流程、原因
• E-RAB release
• UE context release
• RRC connection release
- Abnormal release的触发情景详解
• UE initiated drop
• eNB initiated drop
- 异常释放related Counter Triggers
- Network/Field KPI及Drops分析
- Summary
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RRC connection release
释放类型
根据3GPP定义(3GPP TS )，E-UTRAN initiates the RRC connection release
procedure to a UE in RRC_CONNECTED：
RRC connection release
The purpose of this procedure is to release the RRC connection, which includes the
release of the established radio bearers as well as all radio resources.
RRC connection release requested by upper layers
The purpose of this procedure is to release the RRC connection. Access to the current
PCell may be barred as a result of this procedure.
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RRC connection release
释放原因
The release of the RRC connection is initiated by E-UTRAN. The procedure may be used
to re-direct the UE to another frequency or RAT. In exceptional cases the UE may abort
the RRC connection, to RRC_IDLE without notifying E-UTRAN.
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释放流程及异常释放原因分析
主要内容
<Change information classification in footer>
- 业务承载类型及业务建立过程
- 业务释放类型及相应流程、原因
• E-RAB release
• UE context release
• RRC connection release
- Abnormal release的触发情景详解
• UE initiated drop
• eNB initiated drop
- 异常释放related Counter Triggers
- Network/Field KPI及Drops分析
- Summary
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Call drop
Who Initiates Drops, UE, MME or eNB?
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• UE can ”initiate a drop” by starting RRC Connection Re-establishment
• Note: besides RLF also other causes can trigger RRC Conn Re-
Establishment
• eNB can initiate abnormal S1 + RRC release due to
• Radio network layer problem (TA timer, RLF, PDCCH Order failure)
• Transport network layer problem (GTP-U error, Treloc expiry, Path
Switch problem)
• Other abnormal cause
• MME can initiate abnormal S1 + RRC release due to
• Radio network layer problem
• Other abnormal cause
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UE initiated drop
RLF
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- When UE is in RRC_CONNECTED and RRC security is active, it can
trigger RRC Connection Re-establishment
1. upon T310 expiry
2. upon reaching the maximum number of UL RLC retransmissions
3. upon handover failure (T304 expiry)
4. upon non-HO related random access problem
- If successful, RRC Conn Re-Establishment
• reconfigures SRB1 to resume data transfer of RRC msgs
• re-activates RRC security without changing algorithms
• NOTE: DRB should be re-configured after SRB1
- NOTE: if UE is in RRC_CONNECTED while RRC security is not active, UE goes to RRC_IDLE,
performs cell reselection and TAU
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UE initiated drop
RLF due to T310 Expiry at UE
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UE initiated drop
RLF due to Maximum UL RLC Re-Tx Reached
<Change information classification in footer>
from RRC Connection Reconfiguration:
drb-ToAddModList
drb-ToAddModList value 1
drb-Identity : 1
rlc-Config
am
ul-AM-RLC
t-PollRetransmit : ms40
pollPDU : p32
pollByte : kB25
maxRetxThreshold: t8
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39 © Nokia Solutions and Networks 2015
UE initiated drop
RLF due to HO Failure
<Change information classification in footer>
from RRC Connection Reconfiguration:
mobilityControlInfo
targetPhysCellId : 33
t304 : ms1000
newUE-Identity
Bin : 14 EB (= 5355)
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40 © Nokia Solutions and Networks 2015
UE initiated drop
RLF Due to Non-HO Random Access Failure
<Change information classification in footer>
- “Non-HO random access” means
• PDCCH order -triggered RA
• Random Access Scheduling Request
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41 © Nokia Solutions and Networks 2015
释放流程及异常释放原因分析
主要内容
<Change information classification in footer>
- 业务承载类型及业务建立过程
- 业务释放类型及相应流程、原因
• E-RAB release
• UE context release
• RRC connection release
- Abnormal release的触发情景详解
• UE initiated drop
• eNB initiated drop
- 异常释放related Counter Triggers
- Network/Field KPI及Drops分析
- Summary
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42 © Nokia Solutions and Networks 2015
eNB initiated drop
RLF
<Change information classification in footer>
• eNB can drop the call due to following triggers
• eNB-detected radio link problems
- PUSCH RLF
- CQI RLF
- Ack/Nack RLF
- PDCCH Order failure
- SRS RLF
• TA timer expiry
• Maximum RLC retransmissions exceeded
• GTP-U failure
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eNB initiated drop
Radio Link Problem Detection at eNB
<Change information classification in footer>
- eNB radio link problem detection mechanisms are NSN-internally specified
- Multiple methods (called “link monitors”) are defined to detect a radio link problem in
the eNB.
- When one link monitor detects a problem, it is really a radio link problem even if
other link monitors have not yet indicated anything.
- Each link monitor has its internal criteria to decide when radio link problem is
flagged and de-flagged (radio link recovers).
- If the RLP persists longer than T_RLF, RRC+S1 release is triggered
• T_RLF = t310 + t311 (eNB-internal timer)
- Link monitors:
1. Uplink PUSCH DTX detection for scheduled uplink data
2. CQI DTX detection for periodic CQI reports in PUCCH and PUSCH
3. Uplink Ack/Nack DTX detection for transmitted downlink data
4. PDCCH Order RLF
5. SRS DTX detection (TD-LTE)
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44 © Nokia Solutions and Networks 2015
eNB initiated drop
1. PUSCH RLF: RlsCause_PuschRlf_ON
<Change information classification in footer>
- When UE is scheduled for PUSCH transmission, eNB expects to receive UL
transmission on the scheduled PRBs
- If signal from UE cannot be detected at all, PUSCH DTX is declared
• NOTE: The case where UL TBS is received but it fails CRC check is not DTX (it’s a NACK)
- DTX PUSCH indication is provided by the UL physical layer.
- The result is received by LTE MAC in reliableULtransmissionFlag parameter.
- Both counter-based and timer-based RLF detection is supported
- Timer-based PUSCH RLF detection:
• If “DTX“ is received on the PUSCH for a configurable period of time (rlpDetMaxTimeUl), PUSCH RLF is set
on
- Counter-based PUSCH RLF detection:
• If “DTX“ is received on the PUSCH for a consecutive number of times (rlpDetMaxNoUl), PUSCH RLF is set
on
- The recovery of the radio link is indicated when for a configurable number of
contiguous UL resource assignments data is detected on PUSCH (ACK or NACK
received).
• Defined by parameter rlpDetEndNoUl.
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45 © Nokia Solutions and Networks 2015
eNB initiated drop
1. PUSCH RLF: RlsCause_PuschRlf, Counter-based RLF Detection Example
<Change information classification in footer>
T_RLF = T310 + T311
<p name="rlpDetMaxNUl">3</p>
<p name="rlpDetEndNUl">2</p>
vendor-file parameters in this example:
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46 © Nokia Solutions and Networks 2015
eNB initiated drop
2. Periodic CQI RLF: RlsCause_CqiRlf_ON
<Change information classification in footer>
- The eNB supports CQI DTX detection for periodic CQI reports on PUCCH and
PUSCH.
- If MAC layer receives nCqiDtx consecutive reports from UL PHY, the MAC declares
CqiRLF_ON
- If the MAC has set CqiRLF_ON for a specific UE and nCqiRec consecutive CQI
reports are again detected successfully for that UE, the MAC sets CqiRLF_OFF
- The parameters nCqiDtx and nCqiRec are in the vendor-specific parameter file
- For both PUSCH and PUCCH the periodic CQI is encoded using a Reed Muller
block code and comes along without any CRC. Hence, the UL PHY indicates a DTX
detection for periodic CQI reports on PUCCH or PUSCH whenever a report is
configured but no reliable transmission from the UE could be detected. So the
output of the detector shall be either the detected CQI report or a DTX indication.
- NOTE: CQI_RLF detection does not apply to aperiodic CQI report on PUSCH
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47 © Nokia Solutions and Networks 2015
eNB initiated drop
2. Periodic CQI RLF: RlsCause_CqiRlf, Example
<Change information classification in footer>
<p name="nCqiDtx">6</p>
<p name="nCqiRec">1</p>
vendor-file parameters in this example:
T_RLF = T310 + T311
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48 © Nokia Solutions and Networks 2015
eNB initiated drop
3. Ack/Nack RLF: RlsCause_AckNackRlf_ON
<Change information classification in footer>
- After DL scheduled data, eNB expects HARQ ACK or NACK on PUCCH or PUSCH
at known UL TTI
- Timer-based ACK/NACK RLF detection:
• If ACK/NACK “DTX“ is received for a configurable period of time (rlpDetMaxTimeDl), ACK/NACK RLF is set
on
- Counter-based ACK/NACK RLF detection:
• If ACK/NACK “DTX“ is received for a consecutive number of times (rlpDetMaxNoDl), ACK/NACK RLF is set
on
- The recovery of the RLF is indicated when for a configurable number of contiguous
ACK/NACK opportunities ACK or NACK is detected on PUSCH or PUCCH (no
DTX).
• Defined by parameter rlpDetEndNoDl.
- .
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49 © Nokia Solutions and Networks 2015
eNB initiated drop
4. PDCCH Order RLF
<Change information classification in footer>
- If there DL data in eNB buffer and UE is out-of-sync, UE must be brought back to in-
sync (time aligned) with a RA procedure before DL data can be sent
• Signaling of dedicated RA preamble via PDCCH (so-called PDCCH order) is done using
DCI format 1A
• In case that PDCCH order fails for a UE (., no transmission of assigned dedicated
preamble detected by eNodeB, or no msg3 transmission) the PDCCH order shall be
repeated noRepPdcchOrder times (R&D configurable parameter, range 0-3, default 1),
again using the selected preamble and considering DRX status of the UE accordingly.
• Final failure of the PDCCH order process shall be indicated as radio link problem to
higher layers with cause “PDCCH order failure”
• If inactivity timer for the UE has expired then there is no T_RLF timer involved S1
and RRC released immediately
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50 © Nokia Solutions and Networks 2015
eNB initiated drop
5. SRS RLF
<Change information classification in footer>
- The eNB supports SRS DTX detection for radio link problem detection
- If MAC layer receives nSrsDtx consecutive reports from UL PHY, the MAC declares
SRS RLF
- If the MAC has set SRS RLF for a specific UE and nSrsRec consecutive SRS
transmissions are succesfully detected the UE, the MAC sets SRS RLF OFF
• Hence the SRS RLF has similar mechanism as CQI DTX RLF
- The parameters nSrsDtx and nSrsRec are operator-configurable
- P7 default values from RL15 SCF:
<p name="nSrsDtx">8</p>
<p name="nSrsRec">1</p>
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51 © Nokia Solutions and Networks 2015
eNB initiated drop
When is Drop (= RRC + S1 release) Triggered by eNB?
<Change information classification in footer>
- 3GPP does not specify eNB radio link failures, but NSN eNB mimics the
behaviour of the UE RLF specified in 3GPP.
- When a radio link problem is detected, an eNB-internal timer (T_RLF) is
started. The timer T_RLF is stopped when in case of radio link failure
recovery.
- For a given UE, T_RLF is started when any of the PUSCH RLF, CQI RLF,
SRS RLF or AckNack RLF is set to ON state
- For a given UE, T_RLF is stopped only if all RLFs are OFF
- When the timer T_RLF expires, the UE is released from the eNB using
eNB initiated S1 release + RRC connection release –> call drop
- T_RLF = T310 + T311
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52 © Nokia Solutions and Networks 2015
eNB initiated drop
RLF Triggering by eNB, Signalling
<Change information classification in footer>
Only L2 Ack needed for successful RRC Conn Release. If L2 Ack not received after
timer tL2AckRrcRel expires (def=800ms), RRC is released anyway.
NOTE: No RLC Ack needed for RRC Connection Release. No reTx for RRC Connection Release
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53 © Nokia Solutions and Networks 2015
eNB initiated drop
In-Sync and Out-Of-Sync States: Overview
<Change information classification in footer>
RRC connected substates: UL in-sync and UL out-of-sync
Uplink RA SR or
downlink PDCCH
order to bring UE
back in-sync
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54 © Nokia Solutions and Networks 2015
eNB initiated drop
TA Timer Expiry at UE
<Change information classification in footer>
- As UE detects Out-of-Sync status using a Timing Alignment Timer, the timer shall
be started or restarted whenever an initial TA or a TA update command is received
(see [], section ). If the timer expires, the UE detects out-of-sync
status.
- 3GPP TS : When timeAlignmentTimer expires at UE, UE MAC layer shall:
- flush all HARQ buffers;
- notify RRC layer to release PUCCH/SRS;
- clear any configured downlink assignments and uplink grants
- 3GPP TS : Upon receiving a PUCCH/ SRS release request from MAC layer,
the UE RRC shall:
• release periodic CQI reporting config, ie it stops CQI reporting on
PUCCH
• release Scheduling Request Config
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55 © Nokia Solutions and Networks 2015
eNB initiated drop
In-Sync, Out-Of-Sync Handling in RL30
<Change information classification in footer>
•Parameter LNCEL/applyOutOfSyncState defines how eNB handles TA
expiry
• extendedDrxOnly: only UEs being configured with extended settings for the long
DRX cycle are not dropped if TA timer expires (default)
• allDrx: all UEs being configured for DRX provided that applied DRX profile allows
are not dropped if TA timer expires
• allUEs: all UEs independently of DRX configuration provided that bearer
combination allows are kept RRC Connected even if TA timer expires.
- If DRX is not used at all, then setting ‘allUEs’ should be used to prevent
eNB drops due to TA timer expiry
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56 © Nokia Solutions and Networks 2015
eNB initiated drop
In-Sync Normal Case
<Change information classification in footer>
•Procedure describes how an UE gets back into UL synchronization
from a state in which the time alignment has been lost
- eNB detects that the time alignment of the UE is UL out-of-sync
(. expiration of time alignment timer)
- UE also detects out-of-sync (same trigger) and releases
resources on PUCCH for CQI reporting and scheduling request
- If eNB detects DL data (either data traffic or RRC signalling)
• eNB sends a PDCCH order for RA procedure to UE (DCI 1A with specific
codepoint; preferably non-contention based RA depending on preamble
availability)
• UE starts a random access procedure
• eNB recognizes when random access of the UE was successful and UE UL time
alignment is back “in-sync”
- If UE detects UL data (either data traffic or RRC signalling):
• UE starts a random access procedure (contention-based)
• eNB recognizes when random access of the UE was successful and UE UL time
alignment is back “in-sync”
- eNB triggers the RRC procedure RRC Connection
Reconfiguration to configure (again) the PUCCH resources for
CQI reporting and scheduling request
• Same resource used for simplification but could be optimized optionally
- Note: the RRC message
RRCConnectionReconfigurationComplete is already sent using
the configured PUCCH resources for scheduling request.
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57 © Nokia Solutions and Networks 2015
eNB initiated drop
In-Sync Failure Case
<Change information classification in footer>
•Procedure describes how eNB detects that an UE has been
lost – triggered by downlink traffic
- eNB detects that the time alignment of the UE is “out-of-
sync” (. expiration of time alignment timer)
- UE detects also that the time alignment is out-of-sync
and releases its PUCCH resources for CQI reporting
and scheduling request and/or UE detects a radio link
failure and moves to RRC_IDLE
- If eNB detects DL data (either data traffic or RRC
signalling)
• eNB sends a PDCCH order DCI 1A to UE (may include
several re-tries)
• UE will not recognize this PDCCH order because it has
gone to RRC_IDLE
• eNB recognizes that the random access of the UE was
not successful (UE does not send any random access
preamble) and that the “in-sync” handling has failed
- This event is handled as a new trigger for the radio link
failure procedure
• eNB starts a supervision timer T-RLF and triggers UE
Context Release after timer expiration
• Note: by using the supervision timer, UE is able to return
to cell via the RRC Connection Reestablishment
procedure
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58 © Nokia Solutions and Networks 2015
eNB initiated drop
User Inactivity Detection During Out-Of-Sync
<Change information classification in footer>
•Procedure describes how eNB handles an UE whose time alignment is out
-of-sync and whose inactivity timer has expired
- eNB detects that the time alignment of the UE is “out-of-sync” (.
expiration of time alignment timer)
- The inactivity timer for the UE expires. In the meantime, UE may still
be RRC_CONNECTED or may have gone to RRC_IDLE silently
- eNB checks the reachability of the UE by sending the PDCCH order
(DCI 1A)
- If UE performs a random access
• eNB recognizes that this is a normal “user inactivity” case
• eNB sends the RRC message RRCConnectionReconfiguration to configure
PUCCH/SRS resources
• eNB sends the message UE CONTEXT RELEASE REQUEST to MME with
cause “User Inactivity”
• If MME starts the UE Context Release procedure
- eNB sends the RRC message RRCConnectionRelease to UE and releases the UE context.
• If MME does not start the UE Context Release procedure
- eNB keeps the current configuration.
- Note: this may happen if new DL data arrive - either data traffic or S1AP signalling
- If eNB does not recognize any random access by the UE
• eNB recognizes that this is a RLF trigger.
• eNB starts immediately the UE Context Release procedure for RLF
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59 © Nokia Solutions and Networks 2015
eNB initiated drop
RRC + S1 Release after TA Timer Expiry at eNB When Out-Of-Sync Handling
Not Used for UE
<Change information classification in footer>
NOTE: TA out-of-sync
causes immediate release
(no T_RLF involved)
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eNB initiated drop
TA Timer Expiry at eNB, User-Configurable Parameters
<Change information classification in footer>
Outdated: Always check the current values (defaults and the actual used)
of the eNB sw version in use.
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eNB initiated drop
TA Timer Expiry at eNB, Vendor Parameters
<Change information classification in footer>
Outdated: Always check the current values (defaults and the actual used)
of the eNB sw version in use.
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eNB initiated drop
RLC Layer STATUS Polling Mechanism
<Change information classification in footer>
- RLC layer retransmissions only in RLC acknowledged mode
- RLC AM transmitter requests a STATUS PDU from RLC receiver (sets poll bit on in
RLC header)
• After the number of bytes transmitted since previous poll exceeds the
value of amRlcPBTab3ulPollByte (uplink, ue cat3) or
amRlcPBTab3dlPollByte (downlink, ue cat3), or
• After pollPdu RLC PDUs have been transmitted since previous poll
• in the last data PDU in the RLC transmit buffer
- The RLC AM receiver responds to polling request by transmitting a STATUS PDU
which acknowledges successfully received PDUs and also selectively nacks
unsuccessfully received PDUs.
• RLC receiver also sends STATUS PDU if tReord timer expires.
• RLC receiver will not send STATUS PDU more often than interval
defined by parameter tProhib.
• NOTE: default PDDB settings tProhib=50ms and tReord=50ms.
- If RLC transmitter receives no STATUS PDU within tPollretr, a new poll request
along with unacknowledged data will be sent to RLC receiver
- RLC AM window size is fixed to 512 RLC PDUs (segments of an RLC PDU are
counted as one PDU).
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eNB initiated drop
RLC Layer ARQ Mechanism
<Change information classification in footer>
- RLC transmitter will retransmit all data that is nacked in the STATUS PDU
- Maximum number of UL and DL RLC retransmissions is defined by vendor parameter
drbAmMxRtxTh (default=16)
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64 © Nokia Solutions and Networks 2015
eNB initiated drop
Release due to Maximum Number of Downlink RLC Retransmissions (eNB-
triggered)
<Change information classification in footer>
- Vendor parameter drbAmMxRtxTh (default=16)
- SRB1 or SRB2: after max RLC retransmissions
has been reached
- eNB releases the UE immediately (S1 + RRC release).
- DRB: after max RLC retransmissions has been
reached
- eNB starts a timer T_RLC (T311+200ms) to wait for an
UE triggered RRC Connection Reestablishment. If the
timer expires: eNB releases the UE.
- Otherwise: UE has triggered a RRC Connection
Reestablishment procedure and eNB performs the RRC
Connection Reestablishment procedure (as for a RLF).
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65 © Nokia Solutions and Networks 2015
eNB initiated drop
Release due to Maximum Number of RLC Retransmissions (eNB-triggered)
<Change information classification in footer>
Time applied
for DRBs only.
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eNB initiated drop
Release due to GTP-U Error Indication from S-GW (eNB-triggered)
<Change information classification in footer>
- Handling of Event "GTP-U Error Indication"
- eNB may receive a “GTP-U Error Indication” on an active (single) S1 bearer (S-GW
has rejected the reception of uplink data packets). In that case eNB shall send the
S1AP message UE CONTEXT RELEASE REQUEST with cause “TNL Cause
Transport Resource Unavailable” to MME
- Example: This failure cause happens S-GW relocation attempt is not successful in
X2 handover. In RL40/50, there is no support for S-GW relocation (. no support
of new uplink transport layer address and uplink GTP-TEID in PATH SWITCH
REQUEST ACKNOWLEDGE message).
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67 © Nokia Solutions and Networks 2015
释放流程及异常释放原因分析
主要内容
<Change information classification in footer>
- 业务承载类型及业务建立过程
- 业务释放类型及相应流程、原因
• E-RAB release
• UE context release
• RRC connection release
- Abnormal release的触发情景详解
• UE initiated drop
• eNB initiated drop
- 异常释放related Counter Triggers
- Network/Field KPI及Drops分析
- Summary
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68 © Nokia Solutions and Networks 2015
释放相关counter解析
RRC重建相关counter
<Change information classification in footer>
eNB initiated： MME initiated：
M8008C4 RRC_CON_RE_ESTAB_ATT
M8008C6 RRC_CON_RE_ESTAB_ATT_HO_FAIL
M8008C8 RRC_CON_RE_ESTAB_ATT_OTHER
M8008C5 RRC_CON_RE_ESTAB_SUCC
M8008C7 RRC_CON_RE_ESTAB_SUCC_HO_FAIL
M8008C9 RRC_CON_RE_ESTAB_SUCC_OTHER
RRC Conn Re-Est can only succeed in a cell that has:
• short MAC-I of the source cell
• PCI of the source cell
• C-RNTI in the source cell
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69 © Nokia Solutions and Networks 2015
释放相关counter解析
RRC重建相关counter
<Change information classification in footer>
eNB initiated： MME initiated：
M8008C0 REJ_RRC_CONN_RE_ESTAB
- Re-establishment fails if target cell has not been prepared , eNB responds with
reject UE performs cell reselection + TAU
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释放相关counter解析
正常释放相关counter
<Change information classification in footer>
eNB initiated： MME initiated：
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71 © Nokia Solutions and Networks 2015
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正常释放相关counter
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分类
counter
ID
counter name counter定义 counter计数
eNB
initiate
d
M8006C10 ENB_EPS_BEARER_REL_REQ_NORM The number of released E-RABs initiated by the eNB due to user inactivity.
Updated: This counter is updated when the S1AP: UE CONTEXT RELEASE REQUEST message (eNB -> MME; 3GPP TS
) is transmitted with release cause "User inactivity".
This counter is also updated with the number of released E-RABs.
M8006C15 ENB_EPSBEAR_REL_REQ_RNL_REDIR The number of released E-RABs initiated by the eNB due to Redirect.
Updated: This counter is updated when the S1AP: UE CONTEXT RELEASE REQUEST message (eNB -> MME; 3GPP TS
) is transmitted in case that one of the following release causes is used:
- Release due to E-UTRAN Generated Reason
- Inter-RAT redirection
- Redirection towards 1xRTT
- CS Fallback Triggered
This counter is also updated with the number of released E-RABs.
M8013C13 ENB_INIT_TO_IDLE_NORM_REL
The number of eNB-initiated transitions from the ECM-CONNECTED to ECM-IDLE
state due to "User Inactivity" or "Redirect". The UE-associated logical S1-
connection is released.
Updated: The transmission of an S1AP: UE Context Release Request from the eNB to MME with
the following release causes:
- RNL User Inactivity
- RNL E-UTRAN Generated Reason in case of Redirect to LTE
- RNL Inter-RAT Redirection.
M8007C3 RB_REL_REQ_NORM_REL
The number of released Data Radio Bearers due to "normal release" per cell.
It comprises also the released Data Radio Bearers originally setup due to an
incoming Handover.
Updated: Transmission of S1AP E-RAB RELEASE INDICATION or S1AP UE CONTEXT RELEASE
REQUEST message from eNB to MME due to user inactivity
or
reception of S1AP UE CONTEXT RELEASE COMMAND or S1AP E-RAB RELEASE COMMAND
with release cause "normal" and not received as a response to a Release message previously
sent to the MME
or
reception of X2AP UE CONTEXT RELEASE message due to outgoing X2-Handover (also intra
eNB HO is included).
If the release procedure is executed for more than one Data Radio Bearer (DRB), the counter is
pegged for each released DRB.
3GPP (S1AP E-RAB RELEASE INDICATION,
S1AP UE CONTEXT RELEASE REQUEST,
S1AP E-RAB RELEASE COMMAND,
S1AP UE CONTEXT RELEASE COMMAND)
3GPP TS36423 (X2AP UE CONTEXT RELEASE)
MME
initiate
d
M8006C6 EPC_EPS_BEARER_REL_REQ_NORM
The number of released Data Radio Bearers due to "normal release per call". Each
bearer of the "E-RAB To Be Released List" IE has to be counted. In case of a UE
context release
command, all established EPS Bearers are counted.
Updated: Reception of an S1AP:E-RAB RELEASE COMMAND or an S1AP:UE CONTEXT RELEASE
COMMAND message sent by MME to the eNB. The counter is not incremented in case
that the S1AP:UE CONTEXT RELEASE COMMAND is received as a response to a previously
sent S1AP:UE CONTEXT RELEASE REQUEST.
M8006C7 EPC_EPS_BEARER_REL_REQ_DETACH
The number of EPC-initiated EPS Bearer Release requests due to the Detach procedure
by the UE or MME (NAS cause). Each bearer of the "E-RAB To Be Released List" IE has
to be counted. In case of a UE context release command, all established EPS Bearers
are counted.
Reception of an S1AP:E-RAB RELEASE COMMAND or an S1AP:UE CONTEXT RELEASE
COMMAND message sent by MME to the eNB. The counter is not incremented in case
that the S1AP:UE CONTEXT RELEASE COMMAND is received as a response to a previously
sent S1AP:UE CONTEXT RELEASE REQUEST.
M8013C9 EPC_INIT_TO_IDLE_UE_NORM_REL
The number of EPC-initiated transitions to the ECM-IDLE state due to a Normal
release
by the UE .
Updated: The reception of an S1AP:UE Context Release Command message sent by the MME
to eNB.
M8013C10 EPC_INIT_TO_IDLE_DETACH
The number of EPC-initiated transitions to the ECM-IDLE state due to the Detach
procedure by the UE or the MME .
Updated: The reception of an S1AP:UE Context Release Command message sent by the MME
to eNB.
M8007C4 RB_REL_REQ_DETACH_PROC The number of Radio Bearer Release requests due to Detach procedure
Updated: Transmission of an RRC CONNECTION RELEASE message due to reception of
S1AP:UE CONTEXT RELEASE COMMAND.
R 18
G 65
B 145
R 0
G 201
B 255
R 104
G 113
B 122
R 216
G 217
B 218
R 168
G 187
B 192
Core and background colors:
72 © Nokia Solutions and Networks 2015
释放相关counter解析
异常释放相关counter
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eNB initiated：
eNodeB initiated EPS bearer release (abnormal)
M8006C12 ENB_EPS_BEARER_REL_REQ_RNL
M8006C14 ENB_EPS_BEARER_REL_REQ_TNL
M8006C13 ENB_EPS_BEARER_REL_REQ_OTH
M8006C134 ENB_EPS_BEAR_REL_REQ_R_QCI1
M8006C143 ENB_EPS_BEAR_REL_REQ_O_QCI1
M8006C152 ENB_EPS_BEAR_REL_REQ_T_QCI1
eNodeB initiated UE Context Release (abnormal)
M8013C15 ENB_INIT_TO_IDLE_RNL
M8013C16 ENB_INIT_TO_IDLE_OTHER
Radio bearer release (abnormal)
M8007C5 RB_REL_REQ_RNL
M8007C6 RB_REL_REQ_OTHER
R 18
G 65
B 145
R 0
G 201
B 255
R 104
G 113
B 122
R 216
G 217
B 218
R 168
G 187
B 192
Core and background colors:
73 © Nokia Solutions and Networks 2015
释放相关counter解析
异常释放相关counter
<Change information classification in footer>
MME initiated：
MME initiated EPS bearer release (abnormal)
M8006C8 EPC_EPS_BEARER_REL_REQ_RNL
M8006C9 EPC_EPS_BEARER_REL_REQ_OTH
MME initiated UE Context Release (abnormal)
M8013C11 EPC_INIT_TO_IDLE_RNL
M8013C12 EPC_INIT_TO_IDLE_OTHER
Cause value mapping should
be checked from MME
R 18
G 65
B 145
R 0
G 201
B 255
R 104
G 113
B 122
R 216
G 217
B 218
R 168
G 187
B 192
Core and background colors:
74 © Nokia Solutions and Networks 2015
释放相关counter解析
异常释放相关counter
<Change information classification in footer>
eNB initiated： MME initiated：
R 18
G 65
B 145
R 0
G 201
B 255
R 104
G 113
B 122
R 216
G 217
B 218
R 168
G 187
B 192
Core and background colors:
75 © Nokia Solutions and Networks 2015
释放相关counter解析
异常释放相关counter
<Change information classification in footer>
counter ID counter name counter定义 counter计数
eNB initiated
M8006C12 ENB_EPS_BEARER_REL_REQ_RNL
The number of E-RABs requested to be released in case a Radio Link
Failure is detected
by eNB.
Updated: The transmission of an S1AP: UE CONTEXT RELEASE REQUEST message from the
eNB to the MME in case this message is sent due to a detected Radio Link Failure (RNL cause
"Radio Connection with UE lost"). All released E-RABs are counted.
M8006C13 ENB_EPS_BEARER_REL_REQ_OTH
The number of eNB-initiated EPS Bearer Release requests due to Other
causes . In case of a UE context release request, all the established
EPS Bearers are counted.
Updated: The transmission of an S1AP:E-RAB RELEASE INDICATION or an S1AP: UE Context
Release Request from the eNB to MME. The counter is updated if the release request detected
does not match any other failure counter
M8006C14 ENB_EPS_BEARER_REL_REQ_TNL
The number of eNB-initiated EPS Bearer Release requests due to
Transport Layer Cause
Updated: The transmission of an S1AP:E-RAB RELEASE INDICATION or an S1AP: UE Context
Release Request from the eNB to the MME.
M8013C15 ENB_INIT_TO_IDLE_RNL
The number of eNB initiated transitions from the ECM-CONNECTED to ECM-
IDLE
state when the Radio Connection to the UE is lost. The UE-associated
logical S1-connection is
released.
Updated: The transmission of an S1AP: UE Context Release Request from the eNB to the MME
with release cause "RNL Radio Connection with UE Lost".
M8013C16 ENB_INIT_TO_IDLE_OTHER
The number of eNB-initiated transitions from the ECM-CONNECTED to ECM-
IDLE
state due to Other causes than "User Inactivity", "Redirect" or "Radio
Connection Lost".
Updated: The transmission of an S1AP: UE Context Release Request from the eNB to MME.
The counter is updated if the use case does not match "User Inactivity", "Redirect" and "Lost Radio
Connection".
MME initiated
M8006C8 EPC_EPS_BEARER_REL_REQ_RNL
The number of EPC-initiated EPS Bearer Release requests due to the
Radio Network Layer cause. Each bearer of the "E-RAB to be Released
List" IE is counted. In case of a UE
context release command, all established EPS Bearers are counted.
Updated: Reception of an S1AP:E-RAB RELEASE COMMAND or an S1AP:UE CONTEXT RELEASE
COMMAND message sent by MME to the eNB. The counter is not incremented in case
that the S1AP:UE CONTEXT RELEASE COMMAND is received as a response to a previously
sent S1AP:UE CONTEXT RELEASE REQUEST.
M8006C9 EPC_EPS_BEARER_REL_REQ_OTH
The number of released Data-Radio Bearers due to Other Reasons. Each
bearer of
the "E-RAB To Be Released List" IE has to be counted. In case of a UE
context release command,
all established EPS Bearer are counted.
Updated: Reception of an S1AP:E-RAB RELEASE COMMAND or an S1AP:UE CONTEXT RELEASE
COMMAND message sent by MME to the eNB. The counter is not incremented in case
that the S1AP:UE CONTEXT RELEASE COMMAND is received as a response to a previously
sent S1AP:UE CONTEXT RELEASE REQUEST.
The counter is updated if the release cause does not match any other failure counter.
M8013C12 EPC_INIT_TO_IDLE_OTHER
The number of EPC-initiated transitions to the ECM-IDLE state due to
Other causes.
Updated: The reception of an S1AP:UE Context Release Command message sent by the MME
to eNB. The counter is updated if the failure detected does not match any other failure counter
M8013C13 ENB_INIT_TO_IDLE_NORM_REL
The number of eNB-initiated transitions from the ECM-CONNECTED to ECM-
IDLE state due to "User Inactivity" or "Redirect". The UE-associated
logical S1-connection is released.
Updated: The transmission of an S1AP: UE Context Release Request from the eNB to MME with
the following release causes:
- RNL User Inactivity
- RNL E-UTRAN Generated Reason in case of Redirect to LTE
- RNL Inter-RAT Redirection.
M8007C5 RB_REL_REQ_RNL
The number of released Data Radio Bearers due to "lost radio
connection" between UE and eNB.
It comprises also the release of Data Radio Bearers originally setup
due to an incoming Handover.
Updated: Transmission of S1AP UE CONTEXT RELEASE REQUEST message from eNB to
MME due to lost radio connection.
If the release procedure is executed for more than one Data Radio Bearer (DRB) the counter is
pegged for each released DRB.
3GPP ( S1AP UE CONTEXT RELEASE REQUEST)
M8007C6 RB_REL_REQ_OTHER
The number of released Data Radio Bearers due to "other reasons".
It comprises also the release of Data Radio Bearers originally setup
due to an incoming Handover.
Updated: Transmission of S1AP E-RAB RELEASE INDICATION or S1AP UE CONTEXT RELEASE
REQUEST message from eNB to MME due to for example Transport Network failure or
any reason different to "user inactivity" or "lost radio connection".
If the release procedure is executed for more than one Data Radio Bearer (DRB) the counter is
pegged for each released DRB.
3GPP (S1AP E-RAB RELEASE INDICATION, S1AP UE CONTEXT RELEASE REQUEST)
R 18
G 65
B 145
R 0
G 201
B 255
R 104
G 113
B 122
R 216
G 217
B 218
R 168
G 187
B 192
Core and background colors:
76 © Nokia Solutions and Networks 2015
释放流程及异常释放原因分析
主要内容
<Change information classification in footer>
- 业务承载类型及业务建立过程
- 业务释放类型及相应流程、原因
• E-RAB release
• UE context release
• RRC connection release
- Abnormal release的触发情景详解
• UE initiated drop
• eNB initiated drop
- 异常释放related Counter Triggers
- Network/Field KPI及Drops分析
- Summary
R 18
G 65
B 145
R 0
G 201
B 255
R 104
G 113
B 122
R 216
G 217
B 218
R 168
G 187
B 192
Core and background colors:
77 © Nokia Solutions and Networks 2015
释放相关counter解析
KPI掉线率定义
<Change information classification in footer>
E-RAB掉线率
=（sum(M8006C8+M8006C9+M8006C12+M8006C14+M8006C13)）/sum(M8006C10+M8
006C15+M8006C6+M8006C7+M8006C174+M8006C175+M8006C8+M8006C9+M8006C1
2+M8006C14+M8006C13)
UE-context掉线率= sum (M8006C12+M8006C14+M8006C13) / sum
(M8006C10+M8006C15+M8006C174+M8006C175+M8006C12+M8006C14+M8006C13)
省网优考核指标公式：E-RAB掉话率= 所有QCI类型E-RAB异常释放次数/ 所有QCI类型E-
RAB建立成功次数(包括切换入的E-RAB的数目） *100%
R 18
G 65
B 145
R 0
G 201
B 255
R 104
G 113
B 122
R 216
G 217
B 218
R 168
G 187
B 192
Core and background colors:
78 © Nokia Solutions and Networks 2015
释放相关counter解析
KPI掉线率定义
<Change information classification in footer>
• LTE_5004a Radio Bearer Drop Ratio
•Formula: (Logical)
RB DR=(abnormal RB releases / total RB releases)*100%
•
Formula: (NE names)
100*sum([Number of released Data Radio Bearers due to Lost Radio Connection]+ [Number of
released Data Radio Bearers due to Other Reasons]) / sum([Number of released Data Radio Bearers
due to Normal Release]+ [ Number of released Data Radio Bearers due to Detach]+ [Number of
released Data Radio Bearers due to Lost Radio Connection]+ [Radio Bearer Release requests
including redirect information due to Radio Network Layer
causes (RLF)]+ [Number of released Data Radio Bearers due to Other Reasons])
•100*sum([M8007C5])+([M8007C6]) /
sum([M8007C3]+([M8007C4]+[M8007C5]+[M8007C13]+[M8007C6])
•NOTE: Also handovers included in DRB drop ratio
R 18
G 65
B 145
R 0
G 201
B 255
R 104
G 113
B 122
R 216
G 217
B 218
R 168
G 187
B 192
Core and background colors:
79 © Nokia Solutions and Networks 2015
释放相关counter解析
路测掉线率定义
<Change information classification in footer>
数据业务掉线率=数据业务掉线次数/成功完成连接建立次数×100%
数据业务掉线次数：UE在没有收到RRC Release的情况下回到Idle，但要排除UE发起
Detach而回到空闲态的情况
成功完成连接建立次数：ERB建立成功次数
It is the ratio between abnormally released bearers and the overall number of established
EPS bearers. An abnormal release is defined as any EPS bearer termination that was not
triggered by the mobile user (from UE side).
Dropping the bearer becomes visible to the end-user if an application service is actively
using it. If the application automatically re-establishes the bearer, it remains unnoticed by
the user.
R 18
G 65
B 145
R 0
G 201
B 255
R 104
G 113
B 122
R 216
G 217
B 218
R 168
G 187
B 192
Core and background colors:
80 © Nokia Solutions and Networks 2015
释放流程及异常释放原因分析
主要内容
<Change information classification in footer>
- 业务承载类型及业务建立过程
- 业务释放类型及相应流程、原因
• E-RAB release
• UE context release
• RRC connection release
- Abnormal release的触发情景详解
• UE initiated drop
• eNB initiated drop
- 异常释放related Counter Triggers
- Network/Field KPI及Drops分析
- Summary
R 18
G 65
B 145
R 0
G 201
B 255
R 104
G 113
B 122
R 216
G 217
B 218
R 168
G 187
B 192
Core and background colors:
81 © Nokia Solutions and Networks 2015
Summary
<Change information classification in footer>
通过对释放类型的总结，对现场掉线率机制进行相应的优化。
感谢您的支持
