Why attach request is embedded in RRC connection setup complete message ?

Question

During attach procedure, UE sends "Attach Request" along with "RRC Connection Setup Complete", eNodeB sends "Attach Accept" along with "RRC Connection Reconfiguration then why UE does not send "Attach Complete" along with "RRC Connection Reconfiguration Complete" message ? What could be the reason for defining the messages so ?

Answer 1

1.LTE is a flat architecture and for signalling we are using MME and for data we are using eNodeb path.
2.in UMTS the RNC can handling both signalling and data for UE's because it is a hierarchical network.
3.in order to reduce the complexity,latency and better throughput the flat architecture has been deployed,so now come to the main point
" in RRC connection request msg we need to provide the basic identity (S-TMSI or random number) and establishment cause(MO-Signaling/Data.emergency etc) then only eNodeb can possible to give all lower layer configurations info(PDSCH,PUCCH,PUSCH,UL-Power,CQI,Schduling req),SRB,DRB info,
SPS Config info to the UE
4.Then only UE can does all proper configurations and then communicate with Core network nodes,other wise it is not possible for UE to do."
5.that's why Attach request is embedded in RRC connection setup complete.