3gpp Lte Pdcp
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EventHelix.com • telecommunication design • systems engineering • real-time and embedded systems
3GPP LTE Packet Data Convergence Protocol (PDCP) Sub Layer © 2009 EventHelix.com Inc. All Rights Reserved.
LTE PDCP Sub Layer Functions Header compression and decompression with ROHC
•
Ciphering and deciphering of user and control plane data
• • •
•
PDCP
•
Transfer of data and PDCP sequence number maintenance
Integrity protection and verification of control plane data
• • •
EventHelix.com • telecommunication design • systems engineering • real-time and embedded systems
Header compression and decompression of IP data flows using the ROHC protocol; Transfer of data (user plane or control plane); Maintenance of PDCP SNs; In-sequence delivery of upper layer PDUs at re-establishment of lower layers; Duplicate elimination of lower layer SDUs at re-establishment of lower layers for radio bearers mapped on RLC AM; Ciphering and deciphering of user plane data and control plane data; Integrity protection and integrity verification of control plane data Timer based discard Duplicate discarding
© 2009 EventHelix.com Inc.
2
PDCP in the LTE Protocol Stack
MME
eNodeB
NAS
EventHelix.com • telecommunication design • systems engineering • real-time and embedded systems
UE NAS
RRC
RRC
PDCP
PDCP
RLC
RLC
MAC
MAC
PHY
PHY
© 2009 EventHelix.com Inc.
3
EventHelix.com
LTE PDCP – Layer View UE/E-UTRAN PDCP entiy
• telecommunication design • systems engineering • real-time and embedded systems
Radio Bearers
PDCP-SAP
PDCP-SAP
C-SAP
PDCP sublayer
PDCP entity
PDCP entity
PDCP - PDU RLC - SDU
RLC AM-SAP
RLC UM-SAP
© 2009 EventHelix.com Inc.
RLC sublayer
4
EventHelix.com • telecommunication design • systems engineering • real-time and embedded systems
PDCP Layer Functions UE/E-UTRAN
E-UTRAN/UE Transmitting PDCP entity
Receiving PDCP entity
Sequence numbering
In order delivery and duplicate detection (u-plane only)
Header Compression (u-plane only)
Header Decompression (uplane only) Packets associated to a PDCP SDU Integrity Verification (c-plane only)
Ciphering
Deciphering
Add PDCP header
Packets not associated to a PDCP SDU
Integrity Protection (c-plane only)
Packets not associated to a PDCP SDU
Packets associated to a PDCP SDU
Remove PDCP Header
Radio Interface (Uu) © 2009 EventHelix.com Inc.
5
EventHelix.com • telecommunication design • systems engineering • real-time and embedded systems
3GPP LTE Packet Data Convergence Protocol (PDCP) Sub Layer
ROBUST HEADER COMPRESSION
© 2009 EventHelix.com Inc.
6
EventHelix.com
RoHC Modes
• telecommunication design • systems engineering • real-time and embedded systems
Unidirectional Mode (U-Mode) • Packets are only sent in one direction: from compressor to decompressor. • This mode therefore makes ROHC usable over links where a return path from decompressor to compressor is unavailable or undesirable. Bidirectional Optimistic Mode (O-Mode)
• Similar to the Unidirectional mode, except that a feedback channel is used to send error recovery requests and (optionally) acknowledgments of significant context updates from the decompressor to compressor. • The O-mode aims to maximize compression efficiency and sparse usage of the feedback channel. Bidirectional Reliable Mode (R-Mode) • More intensive usage of the feedback channel and a stricter logic at both the compressor and the decompressor that prevents loss of context synchronization between compressor and decompressor.
© 2009 EventHelix.com Inc.
7
EventHelix.com
RoHC Compressor States Initialization and Refresh State
• Compressor has just been created or reset • Full packet headers are sent
First Order State • Detected and stored static fields (such as IP address and port number) • Sending dynamic field differences • Compressing all static fields and most dynamic fields
© 2009 EventHelix.com Inc.
• telecommunication design • systems engineering • real-time and embedded systems
Second Order State • Suppressing all dynamic fields such as RTP sequence numbers, and send only a logical sequence number and partial checksum • Other end regenerates the headers and verifies the headers. • Compressing all static and dynamic fields 8
RoHC Compressor States in Unidirectional Mode (U-Mode)
EventHelix.com • telecommunication design • systems engineering • real-time and embedded systems
Optimistic
Optimistic
Init and Refresh
Optimistic
First Order Timeout
Second Order
Timeout/Update Timeout
© 2009 EventHelix.com Inc.
9
RoHC Compressor States in Bidirectional Optimistic Mode (O-Mode)
EventHelix.com • telecommunication design • systems engineering • real-time and embedded systems
Optimistic/Ack
Optimistic /Ack Init and Refresh
Optimistic /Ack First Order
Static Nack
Second Order
Nack/Update
Static Nack
© 2009 EventHelix.com Inc.
10
EventHelix.com
RoHC Compressor States in Bidirectional Reliable Mode (R-Mode)
• telecommunication design • systems engineering • real-time and embedded systems
Ack
Ack
Init and Refresh
Ack
First Order Static Nack
Second Order
Nack/Update
Static Nack
© 2009 EventHelix.com Inc.
11
EventHelix.com
RoHC Decompressor States
• telecommunication design • systems engineering • real-time and embedded systems
Success Success
No Context
Static Context
Multiple Compression Failures
Full Context
Multiple Compression Failures
© 2009 EventHelix.com Inc.
12
EventHelix.com • telecommunication design • systems engineering • real-time and embedded systems
3GPP LTE Radio Link Control (RLC) Sub Layer
PDCP PDU FORMATS
© 2009 EventHelix.com Inc.
13
EventHelix.com • telecommunication design • systems engineering • real-time and embedded systems
Control Plane PDCP PDUs
PDU for Interspersed ROHC Feedback (RLC AM and UM Mapped DRBs)
PDU for SRB
R
R
R
PDCP SN Data
Oct 1 Oct 2
D/C
PDU Type
R
R
R
Interspersed ROHC feedback packet
... MAC-I
R
Oct 1 Oct 2
...
Oct N-3
MAC-I (cont.)
PDU for PDCP Status Report Oct N-2 (RLC AM Mapped DRBs)
MAC-I (cont.)
Oct N-1
MAC-I (cont.)
Oct N
D/C
SRB: Signaling Radio Bearer DRB: Data Radio Bearer
PDU Type
FMS
Oct 1
FMS (cont.)
Oct 2
Bitmap1 (optional)
Oct 3
... BitmapN (optional)
© 2009 EventHelix.com Inc.
Oct 2+N
14
EventHelix.com • telecommunication design • systems engineering • real-time and embedded systems
User Plane PDCP PDUs Data PDU with Long PDCP SN (12 bit) (RLC AM and UM Mapped DRBs)
Data PDU with Short SN (7 bit) (RLC UM Mapped DRBs)
D/C
D/C
R
R
R
PDCP SN
Oct 1
PDCP SN
Oct 1
Data
Oct 2
...
PDCP SN (cont.)
Oct 2
Data
Oct 3
...
© 2009 EventHelix.com Inc.
15
EventHelix.com
PDCP PDU Fields 1
• telecommunication design • systems engineering • real-time and embedded systems
PDCP SN (Serial Number) • 5 bit for SRBs • 7 or 12 bit for DRBs Data
• Uncompressed PDCP SDU (user or control plane data) • Compressed PDU SDU (user plane data only) MAC-I • Contains message authentication code • Contains 0 in control plane messages COUNT • 32 bit number made from Hyper Frame Number (HFN) and PDCP SN • HFN bits = 32 – PDCP SN bits R (1 bit) • Reserved. Should be set to 0.
© 2009 EventHelix.com Inc.
16
EventHelix.com
PDCP PDU Fields 2
• telecommunication design • systems engineering • real-time and embedded systems
D/C (1 bit) • 0 = Control PDU; 1 = Data PDU PDU Type (3 bit)
• 0 = PDCP Status; 1 = Interspersed ROHC Feedback Packet; Rest Reserved FMS (12 bit)
• PDCP SN of the first missing PDCP SDU Bitmap
• The MSB of the first octet of the type "Bitmap" indicates whether or not the PDCP SDU with the SN (FMS + 1) modulo 4096 has been received and, optionally decompressed correctly. • The LSB of the first octet of the type "Bitmap" indicates whether or not the PDCP SDU with the SN (FMS + 8) modulo 4096 has been received and, optionally decompressed correctly. Interspersed ROHC Feedback Packet
• Contains ROHC Feedback packet
© 2009 EventHelix.com Inc.
17
EventHelix.com
PDCP Variables
• telecommunication design • systems engineering • real-time and embedded systems
Next_PDCP_TX_SN •The variable Next_PDCP_TX_SN indicates the PDCP SN of the next PDCP SDU for a given PDCP entity. •At establishment of the PDCP entity, the UE shall set Next_PDCP_TX_SN to 0. TX_HFN •The variable TX_HFN indicates the HFN value for the generation of the COUNT value used for PDCP PDUs for a given PDCP entity. •At establishment of the PDCP entity, the UE shall set TX_HFN to 0. •The receiving side of each PDCP entity shall maintain the following state variables: Next_PDCP_RX_SN •The variable Next_PDCP_RX_SN indicates the next expected PDCP SN by the receiver for a given PDCP entity. •At establishment of the PDCP entity, the UE shall set Next_PDCP_RX_SN to 0. RX_HFN
•The variable RX_HFN indicates the HFN value for the generation of the COUNT value used for the received PDCP PDUs for a given PDCP entity. •At establishment of the PDCP entity, the UE shall set RX_HFN to 0. Last_Submitted_PDCP_RX_SN •For PDCP entities for DRBs mapped on RLC AM the variable Last_Submitted_PDCP_RX_SN indicates the SN of the last PDCP SDU delivered to the upper layers. •At establishment of the PDCP entity, the UE shall set Last_Submitted_PDCP_RX_SN to 4095.
© 2009 EventHelix.com Inc.
18
EventHelix.com
Explore More
• telecommunication design • systems engineering • real-time and embedded systems
Specification
Title
3GPP TS 36.323
Evolved Universal Terrestrial Radio Access (E-UTRA); Packet Data Convergence Protocol (PDCP) specification
3GPP TS 36.300
Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Radio Access Network (E-UTRAN); Overall description; Stage 2
3GPP TS 36.321 3GPP TS 36.322 3GPP TS 36.211
Evolved Universal Terrestrial Radio Access (E-UTRA); Medium Access Control (MAC) protocol specification Evolved Universal Terrestrial Radio Access (E-UTRA) Radio Link Control (RLC) protocol specification Evolved Universal Terrestrial Radio Access (E-UTRA); Physical channels and modulation
© 2009 EventHelix.com Inc.
19
EventHelix.com
Thank You
• telecommunication design • systems engineering • real-time and embedded systems
Thank you for visiting EventHelix.com. The following links provide more information about telecom design tools and techniques: Links
Description
EventStudio System Designer 4.0
Sequence diagram based systems engineering tool.
VisualEther Protocol Analyzer 1.0
Wireshark based visual protocol analysis and system design reverse engineering tool.
Telecom Call Flows
GSM, SIP, H.323, ISUP, LTE and IMS call flows.
TCP/IP Sequence Diagrams
TCP/IP explained with sequence diagrams.
Real-time and Embedded System Articles
Real-time and embedded systems, call flows and object oriented design articles.
© 2009 EventHelix.com Inc.
20
3GPP LTE Packet Data Convergence Protocol (PDCP) Sub Layer © 2009 EventHelix.com Inc. All Rights Reserved.
LTE PDCP Sub Layer Functions Header compression and decompression with ROHC
•
Ciphering and deciphering of user and control plane data
• • •
•
PDCP
•
Transfer of data and PDCP sequence number maintenance
Integrity protection and verification of control plane data
• • •
EventHelix.com • telecommunication design • systems engineering • real-time and embedded systems
Header compression and decompression of IP data flows using the ROHC protocol; Transfer of data (user plane or control plane); Maintenance of PDCP SNs; In-sequence delivery of upper layer PDUs at re-establishment of lower layers; Duplicate elimination of lower layer SDUs at re-establishment of lower layers for radio bearers mapped on RLC AM; Ciphering and deciphering of user plane data and control plane data; Integrity protection and integrity verification of control plane data Timer based discard Duplicate discarding
© 2009 EventHelix.com Inc.
2
PDCP in the LTE Protocol Stack
MME
eNodeB
NAS
EventHelix.com • telecommunication design • systems engineering • real-time and embedded systems
UE NAS
RRC
RRC
PDCP
PDCP
RLC
RLC
MAC
MAC
PHY
PHY
© 2009 EventHelix.com Inc.
3
EventHelix.com
LTE PDCP – Layer View UE/E-UTRAN PDCP entiy
• telecommunication design • systems engineering • real-time and embedded systems
Radio Bearers
PDCP-SAP
PDCP-SAP
C-SAP
PDCP sublayer
PDCP entity
PDCP entity
PDCP - PDU RLC - SDU
RLC AM-SAP
RLC UM-SAP
© 2009 EventHelix.com Inc.
RLC sublayer
4
EventHelix.com • telecommunication design • systems engineering • real-time and embedded systems
PDCP Layer Functions UE/E-UTRAN
E-UTRAN/UE Transmitting PDCP entity
Receiving PDCP entity
Sequence numbering
In order delivery and duplicate detection (u-plane only)
Header Compression (u-plane only)
Header Decompression (uplane only) Packets associated to a PDCP SDU Integrity Verification (c-plane only)
Ciphering
Deciphering
Add PDCP header
Packets not associated to a PDCP SDU
Integrity Protection (c-plane only)
Packets not associated to a PDCP SDU
Packets associated to a PDCP SDU
Remove PDCP Header
Radio Interface (Uu) © 2009 EventHelix.com Inc.
5
EventHelix.com • telecommunication design • systems engineering • real-time and embedded systems
3GPP LTE Packet Data Convergence Protocol (PDCP) Sub Layer
ROBUST HEADER COMPRESSION
© 2009 EventHelix.com Inc.
6
EventHelix.com
RoHC Modes
• telecommunication design • systems engineering • real-time and embedded systems
Unidirectional Mode (U-Mode) • Packets are only sent in one direction: from compressor to decompressor. • This mode therefore makes ROHC usable over links where a return path from decompressor to compressor is unavailable or undesirable. Bidirectional Optimistic Mode (O-Mode)
• Similar to the Unidirectional mode, except that a feedback channel is used to send error recovery requests and (optionally) acknowledgments of significant context updates from the decompressor to compressor. • The O-mode aims to maximize compression efficiency and sparse usage of the feedback channel. Bidirectional Reliable Mode (R-Mode) • More intensive usage of the feedback channel and a stricter logic at both the compressor and the decompressor that prevents loss of context synchronization between compressor and decompressor.
© 2009 EventHelix.com Inc.
7
EventHelix.com
RoHC Compressor States Initialization and Refresh State
• Compressor has just been created or reset • Full packet headers are sent
First Order State • Detected and stored static fields (such as IP address and port number) • Sending dynamic field differences • Compressing all static fields and most dynamic fields
© 2009 EventHelix.com Inc.
• telecommunication design • systems engineering • real-time and embedded systems
Second Order State • Suppressing all dynamic fields such as RTP sequence numbers, and send only a logical sequence number and partial checksum • Other end regenerates the headers and verifies the headers. • Compressing all static and dynamic fields 8
RoHC Compressor States in Unidirectional Mode (U-Mode)
EventHelix.com • telecommunication design • systems engineering • real-time and embedded systems
Optimistic
Optimistic
Init and Refresh
Optimistic
First Order Timeout
Second Order
Timeout/Update Timeout
© 2009 EventHelix.com Inc.
9
RoHC Compressor States in Bidirectional Optimistic Mode (O-Mode)
EventHelix.com • telecommunication design • systems engineering • real-time and embedded systems
Optimistic/Ack
Optimistic /Ack Init and Refresh
Optimistic /Ack First Order
Static Nack
Second Order
Nack/Update
Static Nack
© 2009 EventHelix.com Inc.
10
EventHelix.com
RoHC Compressor States in Bidirectional Reliable Mode (R-Mode)
• telecommunication design • systems engineering • real-time and embedded systems
Ack
Ack
Init and Refresh
Ack
First Order Static Nack
Second Order
Nack/Update
Static Nack
© 2009 EventHelix.com Inc.
11
EventHelix.com
RoHC Decompressor States
• telecommunication design • systems engineering • real-time and embedded systems
Success Success
No Context
Static Context
Multiple Compression Failures
Full Context
Multiple Compression Failures
© 2009 EventHelix.com Inc.
12
EventHelix.com • telecommunication design • systems engineering • real-time and embedded systems
3GPP LTE Radio Link Control (RLC) Sub Layer
PDCP PDU FORMATS
© 2009 EventHelix.com Inc.
13
EventHelix.com • telecommunication design • systems engineering • real-time and embedded systems
Control Plane PDCP PDUs
PDU for Interspersed ROHC Feedback (RLC AM and UM Mapped DRBs)
PDU for SRB
R
R
R
PDCP SN Data
Oct 1 Oct 2
D/C
PDU Type
R
R
R
Interspersed ROHC feedback packet
... MAC-I
R
Oct 1 Oct 2
...
Oct N-3
MAC-I (cont.)
PDU for PDCP Status Report Oct N-2 (RLC AM Mapped DRBs)
MAC-I (cont.)
Oct N-1
MAC-I (cont.)
Oct N
D/C
SRB: Signaling Radio Bearer DRB: Data Radio Bearer
PDU Type
FMS
Oct 1
FMS (cont.)
Oct 2
Bitmap1 (optional)
Oct 3
... BitmapN (optional)
© 2009 EventHelix.com Inc.
Oct 2+N
14
EventHelix.com • telecommunication design • systems engineering • real-time and embedded systems
User Plane PDCP PDUs Data PDU with Long PDCP SN (12 bit) (RLC AM and UM Mapped DRBs)
Data PDU with Short SN (7 bit) (RLC UM Mapped DRBs)
D/C
D/C
R
R
R
PDCP SN
Oct 1
PDCP SN
Oct 1
Data
Oct 2
...
PDCP SN (cont.)
Oct 2
Data
Oct 3
...
© 2009 EventHelix.com Inc.
15
EventHelix.com
PDCP PDU Fields 1
• telecommunication design • systems engineering • real-time and embedded systems
PDCP SN (Serial Number) • 5 bit for SRBs • 7 or 12 bit for DRBs Data
• Uncompressed PDCP SDU (user or control plane data) • Compressed PDU SDU (user plane data only) MAC-I • Contains message authentication code • Contains 0 in control plane messages COUNT • 32 bit number made from Hyper Frame Number (HFN) and PDCP SN • HFN bits = 32 – PDCP SN bits R (1 bit) • Reserved. Should be set to 0.
© 2009 EventHelix.com Inc.
16
EventHelix.com
PDCP PDU Fields 2
• telecommunication design • systems engineering • real-time and embedded systems
D/C (1 bit) • 0 = Control PDU; 1 = Data PDU PDU Type (3 bit)
• 0 = PDCP Status; 1 = Interspersed ROHC Feedback Packet; Rest Reserved FMS (12 bit)
• PDCP SN of the first missing PDCP SDU Bitmap
• The MSB of the first octet of the type "Bitmap" indicates whether or not the PDCP SDU with the SN (FMS + 1) modulo 4096 has been received and, optionally decompressed correctly. • The LSB of the first octet of the type "Bitmap" indicates whether or not the PDCP SDU with the SN (FMS + 8) modulo 4096 has been received and, optionally decompressed correctly. Interspersed ROHC Feedback Packet
• Contains ROHC Feedback packet
© 2009 EventHelix.com Inc.
17
EventHelix.com
PDCP Variables
• telecommunication design • systems engineering • real-time and embedded systems
Next_PDCP_TX_SN •The variable Next_PDCP_TX_SN indicates the PDCP SN of the next PDCP SDU for a given PDCP entity. •At establishment of the PDCP entity, the UE shall set Next_PDCP_TX_SN to 0. TX_HFN •The variable TX_HFN indicates the HFN value for the generation of the COUNT value used for PDCP PDUs for a given PDCP entity. •At establishment of the PDCP entity, the UE shall set TX_HFN to 0. •The receiving side of each PDCP entity shall maintain the following state variables: Next_PDCP_RX_SN •The variable Next_PDCP_RX_SN indicates the next expected PDCP SN by the receiver for a given PDCP entity. •At establishment of the PDCP entity, the UE shall set Next_PDCP_RX_SN to 0. RX_HFN
•The variable RX_HFN indicates the HFN value for the generation of the COUNT value used for the received PDCP PDUs for a given PDCP entity. •At establishment of the PDCP entity, the UE shall set RX_HFN to 0. Last_Submitted_PDCP_RX_SN •For PDCP entities for DRBs mapped on RLC AM the variable Last_Submitted_PDCP_RX_SN indicates the SN of the last PDCP SDU delivered to the upper layers. •At establishment of the PDCP entity, the UE shall set Last_Submitted_PDCP_RX_SN to 4095.
© 2009 EventHelix.com Inc.
18
EventHelix.com
Explore More
• telecommunication design • systems engineering • real-time and embedded systems
Specification
Title
3GPP TS 36.323
Evolved Universal Terrestrial Radio Access (E-UTRA); Packet Data Convergence Protocol (PDCP) specification
3GPP TS 36.300
Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Radio Access Network (E-UTRAN); Overall description; Stage 2
3GPP TS 36.321 3GPP TS 36.322 3GPP TS 36.211
Evolved Universal Terrestrial Radio Access (E-UTRA); Medium Access Control (MAC) protocol specification Evolved Universal Terrestrial Radio Access (E-UTRA) Radio Link Control (RLC) protocol specification Evolved Universal Terrestrial Radio Access (E-UTRA); Physical channels and modulation
© 2009 EventHelix.com Inc.
19
EventHelix.com
Thank You
• telecommunication design • systems engineering • real-time and embedded systems
Thank you for visiting EventHelix.com. The following links provide more information about telecom design tools and techniques: Links
Description
EventStudio System Designer 4.0
Sequence diagram based systems engineering tool.
VisualEther Protocol Analyzer 1.0
Wireshark based visual protocol analysis and system design reverse engineering tool.
Telecom Call Flows
GSM, SIP, H.323, ISUP, LTE and IMS call flows.
TCP/IP Sequence Diagrams
TCP/IP explained with sequence diagrams.
Real-time and Embedded System Articles
Real-time and embedded systems, call flows and object oriented design articles.
© 2009 EventHelix.com Inc.
20
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