Method for transmitting an explicit signal of layer-2 state variables for d2d communication system and device therefor

Abstract

The present invention relates to a wireless communication system. More specifically, the present invention relates to a method and a device for transmitting an explicit signal of layer-2 state variables for D2D communication system, the method comprising: generating a configuration message including initial values of RLC (Radio Link Control) state variables used for an receiving RLC entity of a peer UE; and transmitting the configuration message to the peer UE; and transmitting, by a transmitting RLC entity, RLC PDUs to the receiving RLC entity of the peer UE by considering the initial values; wherein the configuration message is transmitted before transmission of the RLC PDUs using the initial values.

1 - 19 . (canceled) 
     
     
         20 . A method for a User Equipment (UE) operating in a wireless communication system, the method comprising:
 receiving a configuration message including initial values of an PDCP (Packet Data Convergence Protocol) state variables from a peer UE;   setting, by a receiving PDCP entity, PDCP state variables to the initial values included in the received configuration message; and   processing PDCP PDUs (Protocol Data Units) received after reception of the configuration message using the PDCP state variables.   
     
     
         21 . The method according to  claim 20 , wherein the configuration message is received per radio bearer for D2D (Device to Device). 
     
     
         22 . The method according to  claim 20 , wherein the configuration message includes at least one of an initial value of Next_PDCP_RX_SN or an initial value of RX_HFN.
 wherein the Next_PDCP_RX_SN indicates a next expected PDCP SN by a receiver for a given PDCP entity, and   wherein the RX_HFN indicates a HFN value for the generation of the COUNT value used for the received PDCP PDUs for a given PDCP entity.   
     
     
         23 . The method according to  claim 20 , wherein the configuration message is received in different forms of Layer-2 signaling. 
     
     
         24 . The method according to  claim 20 , further comprising:
 requesting of the peer UE to transmit the configuration message, when problem with a received packet is detected.   
     
     
         25 . A method for a User Equipment (UE) operating in a wireless communication system, the method comprising:
 generating COUNT for ciphering a first packet; and   transmitting MSB (Most Significant Bit) parts of the COUNT to a peer UE via a direct interface between the UE and the peer UE.   
     
     
         26 . The method according to  claim 25 , wherein the COUNT is transmitted using a PDCP (Packet Data Convergence Protocol) PDU (Protocol Data Unit). 
     
     
         27 . A method for a User Equipment (UE) operating in a wireless communication system, the method comprising:
 receiving MSB (Most Significant Bit) parts of COUNT from a peer UE via a direct interface between the UE and the peer UE;   receiving a PDCP (Packet Data Convergence Protocol) PDU (Protocol Data Unit) from the peer UE via the direct interface between the UE and the peer UE;   generating COUNT using the MSB parts of the COUNT and a PDCP SN (Sequence Number) of the received PDCP PDU; and   deciphering the PDCP PDU using the COUNT.   
     
     
         28 . The method according to  claim 27 , wherein PDCP SN is occupied in LSB parts of the COUNT. 
     
     
         29 . (canceled)