Post on 18-Apr-2015
Dr. Stefan BrückQualcomm Corporate R&D Center Germany
3G/4G Mobile Communications Systems
Chapter IV: Radio Interface and Application Protocols
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Protocols
Slide 2
Radio Interface and Application Protocols
� Logical, Transport and Physical Channels
� Channel Mapping in UMTS and LTE
� Layer 3 Control Plane Protocol� Radio Resource Control (RRC)
� Layer 2 Protocols� Radio Link Control (RLC)
� Medium Access Control (MAC)
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� Medium Access Control (MAC)
� MAC Architecture in HSPA and LTE� PDU Formats for MAC-hs, MAC-ehs, LTE MAC (DL-SCH)
� Stop and Wait Hybrid Automatic Repeat Request Protocol
� Example of an Application Protocol: X2 Application Protocol
Slide 3
UMTS and LTE Channels
� Downlink – transmitted by UTRAN, received by UE
� Uplink – transmitted by UE, received by UTRAN
� Common – carriers information to/from multiple UEs
� Dedicated – carries information to/from a single UE using dedicated resources
� Shared – carries information to/from a single UE using shared resources
� Logical – defined by what type of information is transferred, e.g., signaling or
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� Logical – defined by what type of information is transferred, e.g., signaling or user data
� Transport – defined by how data is transferred over the air interface, e.g., multiplexing of logical channels
� Physical – defined by physical mapping and attributes used to transfer data over the air interface, e.g. spreading rate
Slide 4
Channel Mapping – UMTS Release 99 Channels
5 Slide 5
Channel Mapping – UMTS Dedicated Channels
� These channels carry user and signaling data between UTRAN and an individual UE
� DCCH carries RRC and NAS signaling
� The number of DTCH assigned is determined by the application, e.g. for voice three DTCHs are assigned to one UE
� DCCHs and DTCHs are mapped to a
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� DCCHs and DTCHs are mapped to a single DCH or may be assigned an individual DCH
� In R99 deployments all DCHs are mapped to a single DPDCH
� The DPCCH carries information generated at PHY such as pilot, power control bits. There is always exactly one DPCCH
Slide 6
Typical UMTS R99 Service Combinations
Service Combination Uplink Service Combination Downl ink
3.4kbps signalling + PS I&B 64kbps + AMR Voice 12.2kbps
3.4kbps signalling + PS I&B 64kbps + AMR Voice 12.2kbps
3.4kbps signalling + PS I&B 128kbps 3.4kbps signalling + PS I&B 384kbps
3.4kbps signalling + PS I&B 8kbps + PS Strm64kbps+ AMR Voice 12.2kbps
3.4kbps signalling + PS I&B 8kbps + PS Strm16kbps+ AMR Voice12.2kbps
3.4kbps signalling + AMR Voice 12.2kbps 3.4kbps signalling + AMR Voice 12.2kbps
7 Slide 7
3.4kbps signalling + AMR Voice 12.2kbps 3.4kbps signalling + AMR Voice 12.2kbps
3.4kbps signalling + CS 64kbps 3.4kbps signalling + CS 64kbps
I&B ≡ Interactive & BackgroundStrm ≡ Streaming
HSDPA and HSUPA Channel Mapping
8 Slide 8
Typical UMTS HSPA Service Combinations
Service Combination Uplink Service Combination Downl ink
3.4kbps signalling + PS I&B 64kbps 3.4kbps signalling + PS I&B HSDSCH
3.4kbps signalling + PS I&B 64kbps + CS 64kbps
3.4kbps signalling + PS I&B HSDSCH + CS 64kbps
3.4kbps signalling + PS I&B 384kbps 3.4kbps signalling + PS I&B HSDSCH
3.4kbps signalling + PS I&B 8kbps + AMR Voice 12.2kbps
3.4kbps signalling + PS I&B HSDSCH + AMR Voice 12.2kbps
9 Slide 9
Voice 12.2kbps Voice 12.2kbps
3.4kbps signalling + PS Strm 32kbps +PS I&B 8kbps+ AMR Voice 12.2kbps
3.4kbps signalling + PS Strm HSDSCH 32kbps + PS I&B HSDSCH + AMR Voice 12.2kbps
3.4kbps signalling + PS I&B EDCH 3.4kbps signalling + PS I&B HSDSCH
EDCH signalling + PS I&B EDCH 3.4kbps signalling + PS I&B HSDSCH
Channel Mapping – LTE Downlink
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� Most DL data is carried on the DL-SCH and its corresponding PDSCH
� In contrast to UMTS, there are no dedicated transpo rt channels in LTE
Slide 10
Channel Mapping – LTE Uplink
� Most UL data is carried on the UL-SCH and its corresponding PDSCH
� In contrast to R99 UMTS, there are no dedicated transport channels in LTE
11 Slide 11
Layer 2 Overview
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� The Layer 2 consists of the following sublayers� Packet Data Convergence Protocol (PDCP) – performs header compression and
decompression of IP streams
� Broadcast/Multicast (BMC) – supports cell broadcast functions
� Radio Link Control (RLC) – performs segmentation, reassembly, concatenation and provides various data transfer mode
� Medium Access Control – maps logical channels onto transport channels, performs traffic volume reporting, scheduling
Slide 12
Layer 2 Overview – SDUs and PDUs
� Protocol Data Unit� Unit of data exchanged between
peer layers in a network
� May contain information, addressing, and data
� Service Data Unit� Set of data sent by a user of the
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� Set of data sent by a user of the services of a given layer
� Transmitted to the peer service semantically unchanged
Slide 13
Layer 2 Overview – Data Flow Example (UMTS)
14 Slide 14
UMTS Protocol Stack – Control Plane
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Radio Resource Control (RRC)• Access stratum control• System information processing• Paging and notification• RRC connection management• NAS layer message routing• Ciphering and integrity protection control• Radio Bearer management• RRC mobility• Measurement control and reporting
Slide 15
UMTS Protocol Stack – User Plane
Physical Layer (PHY)• Error detection on transport channels• Forward error correction encoding/decoding• Interleaving/deinterleaving of transport channels• Multiplexing/demultiplexing of transport channels• Rate matching• Modulation/demodulation • Spreading/despreading• Measurements (e.g., FER, transmit power)
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Radio Link Control (RLC)• Segmentation, reassembly, concatenation, padding• Retransmission control, flow control• Duplicate detection, in-sequence delivery• Error correction• Ciphering – acknowledged and unacknowledged mode
Medium Access Control (MAC)• Mapping and multiplexing of logical to transport channels• Priority handling of data flows• UE identification on common channels • Traffic volume measurements• Random Access Channel procedure• Scheduling• Ciphering – transparent mode
Slide 16
RLC Overview – Functions (TS 25.322, TS 36.322)
� Radio Link Control Functions� Transfer of user data and signaling
� Segmentation and reassembly
� Concatenation
� Padding
� Error correction
� In-sequence delivery of upper layers PDUs
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� In-sequence delivery of upper layers PDUs
� Duplicate detection
� Flow control
� Sequence number check
� Protocol error detection and recovery
� Ciphering (UM and AM only)
� SDU discard
Slide 17
RLC Overview – Architecture
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� The primary function of the RLC is to transfer user data and signaling
� Data flow to and from upper layers are carried by Radio Bearers and may carry either signaling data (Signaling Radio Bearer) or user data (Radio Access Bearer)
� Each Radio Bearer is mapped to a RLC entity, which operates in of the three data transfer modes: transparent mode (TM), unacknowledged mode UM, or acknowledge mode (AM)
Slide 18
RLC Overview – Data Transfer Modes
� Transparent Mode (TM)� Unreliable service
� Separate receive and transmit entities
� Supports a set of fixed SDU sizes configured by RRC
� Unacknowledged Mode (UM)� Unreliable service
� Separate receive and transmit entities
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� Separate receive and transmit entities
� Supports arbitrary SDU sizes
� Acknowledged Mode (AM)� Reliable service
� Bidirectional entity
� Supports arbitrary SDU sizes
Slide 19
RLC Overview – Data Transfer Modes (cntd.)
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� Radio Bearers using RLC TM: BCCH, PCCH, CS Voice DTCH
� Radio Bearers using RLC UM: one DCCH, PS DTCH used for error tolerant and delay sensitive applications
� Radio Bearers using RLC AM: one DCCH, PS DTCH used for error sensitive and delay tolerant applications
Slide 20
RLC Transparent Mode
� In TM Mode, PDUs are transferred with little interaction by RLC� No header is added
� Segmentation and reassembly� If the SDU size is too large to fit into a
single PDU, it may segmented at Tx and reassembled at Rx side
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and reassembled at Rx side
� Ciphering for logical channels is performed by the MAC
Slide 21
RLC Unacknowledged Mode
� A small header containing information about segmentation, concatenation and sequence number is added
� Segmentation and reassembly
� Sequence number check� Used during reassembly to detect
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� Used during reassembly to detect corrupted SDUs
Slide 22
RLC Acknowledged Mode
� AM Mode provides reliable service based on ACKs and NACKs
� Segmentation and reassembly
� Error correction� PDUs received in error are
retransmitted
� In-sequence delivery
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� In-sequence delivery� PDUs are delivered to upper layers
in the same order as they were submitted to the transmitted RLC
� Flow control� Configurable transmit and receive
window sizes
� Ciphering of logical channels is performed by RLC
Slide 23
U-Plane Protocol Stack (System Simulator)
24 Slide 24
Example: Parameters for DL 384 kbps / PS RAB
RLC SDU Size
25 Slide 25
Table taken from 3GPP TS 34.108, v5.3.0
MAC Overview – Functions (TS 25.321, TS 36.321)
� Medium Access Control (MAC) Functions� Logical and transport channel mapping
� Identification of UEs on common transport channels
� Prioritizing logical channels
� Multiplexing/de-multiplexing of logical channels
� Transport format combination selection
� (Scheduling)
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� (Scheduling)
� Ciphering (for RLC TM only)
� (Segmentation)
� (Reordering)
� (HARQ)
Slide 26
UTRAN MAC Overview – Architecture I/III
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� The MAC in R99 consists of three parts� MAC-c/sh: controls access to the common transport channels
� MAC-b: controls access to the broadcast channel
� MAC-d: controls access to the dedicated channels
Slide 27
UTRAN MAC Overview – Architecture II/III
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� The MAC in R5 was extended to support HSDPA� MAC-hs: This part of the MAC resides in the Node B to allow fast Hybrid ARQ. It is
also responsible for scheduling of the HS-DSCH
Slide 28
UTRAN MAC Overview – Architecture III/III
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� The MAC in R6 was extended to support HSUPA� MAC-e: provides fast retransmissions by HARQ
� MAC-es: provides reordering functionalities
� On the UTRAN the MAC is split between the Node B (MAC-e) and the RNC (MAC-es)
Slide 29
MAC Entity and HARQ Entity in 3GPP
� Common definitions in LTE and HSDPA� There is one MAC entity per cell� There is one HARQ entity per supported UE
� The HARQ entity handles the hybrid ARQ functionality for one user� A number of parallel HARQ processes are used to support the HARQ entity� The HARQ processes are of stop and wait type
� The HARQ process can be re-used if the associated ACK/NACK is received again
� Definitions in HSDPA
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� Definitions in HSDPA � There is one HARQ process per TTI for single stream transmission � There two HARQ processes per TTI for dual stream transmission
� This definition applies for MAC-ehs only
� Definitions in LTE� A HARQ process is associated with one or two MAC PDUs
Slide 30
� The queues store MAC-d PDUs which are also called MAC-hs SDUs
� In the MAC-hs only entire MAC-d PDUs from one priority queue can be mapped into one MAC-hs PDU
� Multiplexing and segmentation of MAC-d PDUs is not offered in the
MAC-hs
MAC – Control
Priority Queuedistribution
MAC-d flows
Priority Queuedistribution
PriorityQueue
PriorityQueue
PriorityQueue
PriorityQueue
Scheduling/Priority handling
MAC-hs Entity in the UTRAN (Rel5, Rel6)
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MAC-d PDUs is not offered in the MAC-hs
� The MAC-hs header indicates the queue ID, the TSN and the MAC-d PDU sizes. The smallest size 21 bits
HS-DSCH
TFRC selection
Associated DownlinkSignalling
Associated UplinkSignalling
HARQ entity
Slide 31
� The queues store MAC-d PDUs which are also called MAC-ehs SDUs
� A reordering SDU is a complete or a segment of a MAC-ehs SDU
� A reordering PDU consists of several reordering SDUs of the same priority queue
� Finally, a MAC-ehs PDU consists of one or several reordering PDUs from
MAC-ehs
MAC – Control
MAC-d flows
Priority Queue
Scheduling/Priority handling
Priority Queue
LCH-ID MUX
Segment Segment
LCH-ID MUX
MAC-ehs Entity in the UTRAN (Rel7)
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Finally, a MAC-ehs PDU consists of one or several reordering PDUs from up to three priority queues
� The MAC-ehs offers multiplexing and segmentation
� The MAC-ehs header indicates the logical channel ID, the TSN, segmentation and SDU sizes. The smallest size is 24 bits
HS-DSCH
TFRC selection
Associated Downlink Signalling
Associated Uplink Signalling
Segmentation
HARQ entity
Segmentation
Slide 32
MAC-hs and MAC-ehs Entities in the UE
� The disassembly unit removes the MAC-hs/MAC-ehs header and potential padding bits� Padding is introduced since a finite set of
MAC-hs/MAC-ehs PDUs is allowed
� New ‘octed-aligned’ PDU sizes have been introduced together with MAC-ehs, i.e. the PDU sizes are multiples of one byte
� The reordering queue distribution routes
MAC-hs
MAC – Control
Associated Uplink Signalling
To MAC-d
Associated Downlink Signalling
HS-DSCH
HARQ
Reordering Reordering
Re-ordering queue distribution
Disassembly Disassembly
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� The reordering queue distribution routes the received MAC-hs PDUs or the reordering PDUs to the correct reordering queues � based on the queue ID or received logical
channel identifier
� The reordering entity reorders received MAC-hs PDUs/reordering PDUs according to the received TSN
� The reassembly entity reassembles segmented MAC-ehs SDUs
M AC-ehs
M AC – Contro l
Associated Uplink Signalling
To M AC-d
Associated Downlink Signa lling
HS-DSC H
HARQ
Reordering Reordering
Re-o rdering queue distributio n
LCH-ID D em ux LCH-ID D em ux
Reassembly
Disassembly
Reassembly
Associated Uplink SignallingAssociated Downlink Signalling
Slide 33
� In Rel. 5 – 6 the RLC PDU sizes was either fixed to 336 bits or 656 bits
� The RLC protocol applies a window based ARQ mechanism with a window size W of up to 4095 PDUs� The RLC protocol can send at most 4095 PDUs before a status report is
received from the UE.
� Some UEs only support a window size of 2047 PDUs
� In the RLC protocol the maximal throughput T is limited to
[bits] Size PDU W ⋅
Why MAC-ehs Segmentation in HSDPA
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� The RLC round trip time is typically in the order of 80ms – 120ms in real world
� The timer status prohibit should be set to similar values as the RLC RTT
� Therefore it is very difficult to achieve 14.4 Mbps in HSDPA with realistic parameter settings and window sizes of 2047 PDUs
� The flexible RLC PDU size (up to 1500 bytes) introduced in Rel. 7 together with MAC-ehs segmentation overcomes this bottleneck
Prohibit StatusTimer RTT RLC TT
[bits] Size PDU WT
+⋅≤
Slide 34
Differences of MAC-hs/ehs and LTE MAC
� MAC-hs does not support segmentation
� MAC-ehs segmentation needed in HSDPA � The RLC protocol resides in the RNC
� The RLC does not have fast information about required MAC-ehs SDU sizes in the Node B
� In LTE both RLC and MAC reside in the Node B � The MAC can inform the RLC about required MAC SDU sizes per TTI.
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� Segmentation is done in the RLC
� Additionally, no re-ordering is supported in the LTE MAC� Reordering to higher layers is done in the RLC
Slide 35
MAC PDU Formats
Queue ID TSN SID1 N1 F1 SID2 N2 F2 SIDk Nk Fk
MAC-hs header MAC-hs SDU Padding (opt) MAC-hs SDU
Mac-hs payload
VF
SI1 LCH-ID1 TSN1 L1 TSNk Lk LCH-IDk SIk F1 Fk
MAC-hs PDU
MAC-ehs PDU
36 Slide 36
MAC-ehs header Reordering PDU Padding (opt) Reordering PDU
Mac-ehs payload
MAC-ehs PDU
LTE MAC PDU(DL-SCH)
DL transmissionat NodeB
DL receptionat UE
DL processingat UE
HARQprocess #1
HARQprocess #2
HARQprocess #3
HARQprocess #4
HARQprocess #5
HARQprocess #6
2 ms
HARQprocess #1
HARQprocess #2
HARQprocess #3
HARQprocess #4
HARQ process #1
HARQ process #2
HARQprocess #1
ACK/NACK
feedb
ack t
o Node
B
...
HARQprocess #2
......
...
Stop and Wait HARQ Protocol in HSDPA and LTE
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� A HARQ process is in charge of the transmission (and possible subsequent re-transmission) of one MAC PDUs
� Once the MAC PDU is sent the HARQ process waits for the ACK/NACK from the UE to decide whether to schedule a re-transmission or a new MAC-hs PDU transmission.
� The round trip time delay is typically 6 TTI = 12 ms in HSDPA
� In LTE the round trip time is 8 TTI = 8 ms
Slide 37
Horizontal Layers – Vertical Planes
� The protocol structure consists of two main layers, Radio Network Layer and Transport Network Layer� Vertically, the protocols are separated in control and user plane
� All (E)-UTRAN related issues are visible only in the Radio Network Layer � The Transport Network Layer applies standard transport technology that is
selected for (E)-UTRAN without any (E)-UTRAN specific requirements
� Application protocols (AP) are control plane protocols in the Radio Network Layer of entities
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Layer of entities� They control the signaling to other entities
� Examples of Applications Protocols in UTRAN� NBAP: Node B – RNC
� RANAP: RNC – SGSN/MSC
� RNSAP: RNC – RNC
� Examples for Applications Protocols in E-UTRAN� X2AP: eNB – eNB
� S1AP: eNB – MME
Slide 38
LTE X2 Protocol Structure (TS 36.423)
X2-AP
Transport Network Layer
User Transport Network
Plane
Control Plane User Plane
Transport
User
Network
Plane
Radio Network Layer
GTP-U
UDP
User Plane PDUs
SCTP
Signaling Transport
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UDP
IP
Data link layer
Physical layer
SCTP
IP
Data link layer
Physical layer
� Clear separation between radio network and transport network layers
� The radio network layers defines interaction between eNBs
� The transport network layer provides services for user plane and signaling transport
Data Transport
Slide 39
X2 Application Protocol (X2AP)
� The X2AP is responsible for providing signaling between eNBs
� X2AP functions are executed by so called Elementary Procedures� Rel. 8 defines eleven EPs related to different X2AP functions
� In Rel. 9 four additional EPs have been defined
� Class 1: EPs with response (success or failure)
� Class 2: EPs without response
� In LTE Rel. 8/9 limited load management functionality is supported� Its functionality is extended in Rel. 10
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� Its functionality is extended in Rel. 10
Function Elementary Procedure(s) Mobility Management a) Handover Preparation
b) SN Status Transfer c) UE Context Release d) Handover Cancel
Load Management a) Load Indication b) Resource Status Reporting Initiation c) Resource Status Reporting
Reporting of General Error Situations Error Indication Resetting the X2 Reset Setting up the X2 X2 Setup eNB Configuration Update eNB Configuration Update Mobility Parameters Management Mobility Settings Change Mobility Robustness Optimisation a) Radio L ink Failure Indication
b) Handover Report Energy Saving Cell Activation
Release 8
Release 9
Slide 40
X2 AP Load Management
� The X2AP load management function is used by the eNBs to indicate resource status, overload and traffic load to each other
� The load management function consists of the EPs � Load Indication (class 2)
� Purpose: Transfer load and interference coordination information between eNBs
� An eNB initiates the procedure by sending LOAD INFORMATION message to another eNB
eNB1
LOAD INFORMATION
eNB2
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INFORMATION message to another eNB
� Resource Status Reporting Initiation (class 1)� Purpose: Request the reporting of load measurements to
another eNB
� The procedure is initiated with a RESOURCE STATUS REQUEST message sent from eNB1 to eNB2 and eNB2 answers with RESOURCE STAUS RESPONSE message
� Resource Status Reporting (class 2)� Purpose: Report the result of measurements admitted by
eNB2 following a successful Resource Status Reporting Initiation procedure
� The eNB2 reports the results of the measurements in RESOURCE STATUS UPDATE message
Slide 41
eNB1 eNB2
RESOURCE STATUS UPDATE
eNB1 eNB2
RESOURCE STATUS REQUEST
RESOURCE STATUS RESPONSE
Information Elements of LOAD INFORMATION
� UL Interference Overload Indication IE: � Indicates the interference level experienced by the indicated cell on all resource
blocks, per PRB.
� Values: High Interference, Medium Interference, Low Interference
� UL High Interference Indication IE: � Indicates, per PRB, the occurrence of high interference sensitivity, as seen from
the sending eNB.
� The receiving eNB should try to avoid scheduling cell edge UEs in its cells for the concerned PRBs
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concerned PRBs
� Values: High Interference Sensitivity, Low Interference Sensitivity
� Relative Narrowband Tx Power (RNTP) IE:� Indicates, per PRB, whether downlink transmission power is lower than the value
indicated by the RNTP Threshold IE
� Values: Tx power exceeding RNTP threshold, Tx power not exceeding RNTP threshold
� Detailed definition of interference, interference sensitivity are implementation specific
Slide 42
RESOURCE STATUS REQUEST Message
� The reporting can be periodic or event based
� In case of periodic reporting request, the RESOURCE STATUS UPDATE message is used � Periodicity is either 1s, 2s, 5s, 10s
� Supported measurements� Radio Resource Status IE indicates the usage of the PRBs in Downlink and Uplink
� DL GBR PRB usage, UL GBR PRB usage, DL non-GBR PRB usage, UL non-GBR PRB usage, DL Total PRB usage, UL Total PRB usage
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usage, DL Total PRB usage, UL Total PRB usage
� The report is an integer value ranging from 0 to 100
� S1 TNL Load Indicator IE indicates the status of the S1 Transport Network Load experienced by the cell� Low Load, Medium Load, High Load, Overload
� Hardware Load Indicator IE indicates the status of the Hardware Load experienced by the cell� Low Load, Medium Load, High Load, Overload
� Composite Available Capacity Group IE indicates the overall available resource level in the cell in Downlink and Uplink.
� Detailed definition of measurements are implementation specific
Slide 43