LTE: What is the functionality of PDCP layer ?

Question

In 3GPP 36.323 specification mentioned that the size of PDCP SDU is 8188 Octets. From where this number comes ?

Answer 1

LTE PDCP Functions:

• 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

Answer 2

PDCP stands for "Packet data convergence protocol". PDCP layer provides some services to its upper layers (like RRC and S1-U Application). Its main functionality has been listed below:
1. IP header compression and decompression.
2. Duplicate packet detection while re-establishment handling.
3. In-sequence delivery of packets.
4. Encryption and Integrity protection and verification of control plane data.
5. Encryption of user plane data etc.

Answer 3

PDCP layer performs the following functions:

1. Header compression and decompression plane of the user data;
2. Security features:
   encryption and deciphering the user plane and control plane data;
   the protection of the integrity and operation of the plane data;
3. Provide support functions:
   order to delivery and reorder PDU to the layer above a waiver;
   lossless transmission of user plane data associated with the RLC admitted mode.
4. To cancel the user data plane due to timeout.

PDCP layer manages data streams in a plane, and in the plane (or Protocol), only for holders of a radio channel for control (DCCH) or channel dedicated to motion (DTCH). PDCP layer architecture varies the user plane and control plane, as shown figures.