LTE: Attach Call flow

Source: https://www.eventhelix.com/lte/attach/lte-attach.pdf

UL-SCH: UE -> eNodeB RRC Connection Request 

• The UE has received the Random Access Response based on the RA-RNTI. 
• The Random Access Response assigns a C-RNTI and resources for transmission of the RRC Connection Request 
• The message identifies the UE with the CRNTI 
• The message contains the UE-Identity 
• IMSI is sent in the message if this is the first attach to the network 
• If the terminal had attached previously, the S-TMSI is included in the message
• STMSI = MMEC + M-TMSI 
• ue-Identity (Initial UE-Identity): This IE is included to facilitate contention resolution by lower layers. It can be either S-TMSI (40-bits) or a bit string of randomValue (40-bits). If the upper layers provide S-TMSI, then S-TMSI is used as the ue-Identity; else a random value in the range of 0 … 2⁴⁰-1 is drawn and used as the ue-Identity. Upper layers provide the S-TMSI if the UE is registered in the TA of the current cell


• establishmentCause:The main cause values and the corresponding NAS procedure whichtriggers the RRC connection establishment are presented below:
• emergency: This corresponds to NAS Procedure “MO-CS fallback Emergency call”
• mt-Access: Corresponding NAS procedures are “Service Request” (paging response for PS domain) or “Extended Service Request”(MT-CS fallback)
• mo-Signalling: Corresponding NAS procedures are Attach, Detach, and TAU
• mo-Data: Corresponding NAS Procedures are “Service Request” and “Extended Service Request”
• Note that th eNodeB may optionally send a contention resolution message on receipt of this message

DL-SCH: UE <- eNodeB     RRC Connection Setup

 

• The message identifies the signaling radio bearer (SRB) 
• RLC Uplink Configuration 
• Timer for status report polling
• Number of retransmissions of buffer status report 
• Control plane retransmission limit
• RLC Downlink Configuration 
• The maximum time to wait for packet reordering 
• UL-SCH configuration
• Maximum number of Hybrid ARQ transmissions 
• Periodic and regular buffer status report (BSR) timer 
• Power Headroom Report (PHR) Configuration
• Periodicity of the PHR • 
• Downlink Path Loss more than the specified value also triggers PHR (provided the Prohibit PHR timer has expired)  
• Uplink Power Control Parameters
•  P0-UE-PUSCH and P0-UE-PCCH values are used to determine the nominal power of the uplink transmissions 
• “pSRS Offset” determines the uplink Sounding Reference Signal power 
• Delta MCS (choose between Ks = 0 and Ks = 1.25) 
• Filter Coefficient value for RSRP (Reference Signal Received Power) measurement used to calculate path loss •
• Reference: 36.213 clause 5.1.1.1 

Source https://www.netmanias.com/en/?m=view&id=techdocs&no=10440