PDCP Layer in LTE
The Packet Data Convergence Protocol (PDCP) is an important component of the LTE protocol stack. As a sublayer within the LTE architecture, PDCP plays a critical role in enabling efficient and secure data transmission. Situated between the Radio Resource Control (RRC) layer and the Radio Link Control (RLC) layer, PDCP handles tasks such as header compression, ciphering, and integrity protection.
3gpp Specification number for PDCP Layer is 36.323.
In the context of LTE, which is designed to support high-speed data communication, PDCP's functions are essential for optimizing the network's performance and maintaining the security of user data.
Overview of PDCP Architecture
The PDCP layer's architecture can be divided into two primary components: the PDCP structure and the PDCP entities. These components work together to manage the flow of data and signaling messages within the LTE network.
PDCP Structure
The PDCP structure consists of several PDCP entities, each associated with a specific Radio Bearer (RB). These entities are responsible for managing the data flow for their respective bearers. The PDCP layer is designed to be flexible, allowing it to handle different types of bearers, including split bearers and LTE-WLAN Aggregation (LWA) bearers.
For each RB, there is a corresponding PDCP entity, which interacts with one or more RLC entities depending on the direction of data flow (uplink or downlink) and the mode of operation (acknowledged or unacknowledged mode). The PDCP entities are configured by the RRC layer, ensuring that they operate in accordance with the overall network configuration.
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PDCP Entity:
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Service Access Points (SAPs):
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Radio Bearers:
PDCP-PDU and RLC-SDU:
Consolidated procedure:
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PDCP Entities and Functions
The PDCP layer's entities and functions are designed to manage the various tasks involved in data transmission within the LTE network. These functions are essential for ensuring that data is transmitted efficiently, securely, and in the correct order.
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Control Plane PDCP Entities
Control plane PDCP entities are responsible for handling signaling messages, which are critical for maintaining the connection between the UE and the eNB. These entities provide functions such as integrity protection and ciphering, ensuring that signaling messages are transmitted securely.
The integrity protection function ensures that signaling messages have not been tampered with during transmission, while the ciphering function protects the confidentiality of these messages. Together, these functions ensure the secure and reliable transmission of control plane data within the LTE network.
User Plane PDCP Entities
User plane PDCP entities manage the transmission of user data, performing tasks such as header compression, ciphering, and sequence number management. These entities are crucial for optimizing the use of network resources and ensuring the efficient transmission of data.
The header compression function reduces the overhead associated with transmitting IP packets over the LTE air interface, while the ciphering function protects the confidentiality of user data. Sequence number management ensures that data packets are transmitted in the correct order, preventing issues such as data duplication or loss.
Functions of PDCP
The PDCP layer performs several key functions that are essential for the efficient operation of the LTE network. These functions include header compression and decompression, ciphering and deciphering, integrity protection and verification, sequence number handling, in-sequence delivery and reordering, duplicate elimination, timer-based discard, and routing and reordering for split and LWA bearers.
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PDCP Procedures
The PDCP layer is crucial in managing data transmission within the LTE network, ensuring data is processed, transmitted, and received securely and efficiently.
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PDCP Parameters
discardTimer:
?? Started on the transmitter side upon reception of an SDU from the upper layer.
?? Duration is configured by upper layers.
t-Reordering:
?? Used on the receiver side to detect loss of PDCP PDUs when the reordering function is active.
?? Only one t-Reordering timer runs per PDCP entity at a time.
?? Duration is configured by upper layers.
t-StatusReportType1:
?? Used on the receiver side for LWA bearers to trigger status report transmission.
?? Duration is configured by upper layers (statusPDU-Periodicity-Type1).
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t-StatusReportType2:
?? Also used on the receiver side for LWA bearers to trigger status report transmission.
?? Duration is configured by upper layers (statusPDU-Periodicity-Type2 and statusPDU-Periodicity-Offset).
?? The first run of the timer after (re)configuration considers both periodicity and offset.
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