What will be the MSG3 if RACH triggered to get an UL grant alone?

Question

If no SR is configured at UE side, then IF UE triggeres RACH then what will be the MSG3 content? How ENB knows UE is triggering an RACH for UL grant?

Answer 1

In this case msg-3 would be MAC-CRNTI with/without data
And, msg-4 would be pdcch scrambled with CRNTI (as contention resolution)

Answer 2

Hi,

eNB gets to know from Establishment Cause , which means that why UE need to connect to network.

Comments

This is normal data transmission and already in connected mode. Why UE sends establishment cause in connected mode?

---

Hi, let me understand  your problem
"If UE is in connected mode, how eNB knows that UE has initiated RACH for UL Grant ?

---

Yeah my problem is same. UE is in connected mode but SR is not configured. (SR configuration is not mandatory in connected mode).
If UE has uplink data then UE does RACH in connected mode to get an Grant. But what UE sends in MSG3 is my question?

Answer 3

If UE is in connected mode why it will go for RACH ? if it has to ask for grant it will ask in PUCCH resources right ?

Comments

I have multiple question here :
1. UE is in Connected mode, does that mean RRC connected or EPC connected ?
2. If it is in RRC connected mode, then UE will have SR(PUCCH), it can ask for grant.
3. If UE is in EPC connected mode, it means that UE is in RRC Idle state and it can ask for grant.

May be better expert can comment here.