Hello Experts.
In 5G NR there is something called Configured Grants that gives the UE possibility to transmit in the UL with no need to ask for resources for transmission using SR.
Question: assuming the UE doesn’t need all the configured grant resources (for example little is left in its buffer) can it stop request to end the configuration process?
If yes, how does it do it?
Hi @new_moon.
My understanding is, UE is configured with periodic BSR reporting in general to let network know about the available buffer at UE.
After sending all data in buffer, corresponding bsr will be sent and network can stop configured grants with RRC reconfiguration/PDCCH signalling.
If network doesn’t stop giving configured grants even after sending updated BSR, it’s just bad network implementation.
Contrary to this, if there is a VoNR call in place, network can assign the periodic resources using configured grants for UL RTP pkts on IMS bearer as long as the call is active.
Thanks for your info.
If there is still data at UE buffer means that UE doesnt need grant?
If yes, why?
Appreciate if you can explain the point why we need to know the UE buffer status.
Thanks!
But might be UE buffer still has some data and UE request SR.
So UE buffer status isn’t the key for stop/non stop dynamic grants.
No?
It’s just the general understanding. How can network know what amount of UL grants to be given to a UE? It is through BSR (apart from other parameters like PHR, SRS etc).
UE sends SR when it doesn’t have grants and have accumulated some data in any LCG. Suppose, a VoNR call is going on and configured grants are scheduled for IMS bearer. Now, UE started accumulating data for an LCG on internet PDN(where only dynamic scheduling is configured as per network config) and doesn’t have grants for internet data, then UE sends SR on the PUCCH resource linked to that LCG.
In general, configured grants and SPS is applicable to VoNR/VoLTE calls as it is not feasible to schedule resources periodically for such small data (RTP). Those features were introduced with the intent to save PDCCH resources. This way, more number of Volte calls can be accommodated in the cell.
Yes, you are right but meant there might be another factor included to decide when to stop/nonstop dynamic grants.
You know there might be some data left on UE buffer like scenarios of where we send uplink signal (SRS lets say) in pusch or in PUCCH.
It depends if you have on UE buffer data. If so then mostly PUSCH used and else then we send it on PUCCH.
What you’re saying make sense and I understand.
But I see we are missing something here for deciding when to stop/nonstop dynamic grants… 
SRS is not linked to PuCCH/PUSCH. It has seperate scheduling.
Lets take scenario.
Assume UE requests SR, okay?
Then started to be scheduled. Let’s say there was a little data remained on UE buffer.
Then by somehow UE decided to detach from network (let’s assume it).
Now UE detached and has a little data in his buffer.
So under your assumption that UE would still get dynamic grants even if he decided to not be scheduled (assumption).
Now got my point? Guess there is another factor to be considered…
I gave an example above.
That SRs was an example for the concept that UE data buffer may represents some other factors and not specifically mean UE is under scheduling or not.
When UE is detached, stack is reset. so, all buffers will be flushed. Now, application needs to requeue the data to LCG once it has the connection back.
But please read section 7.4.4.3 in 5G in NR Bullets book. Most of your doubts will be clarified…
Hi @pradeep. Thank you very much. At high level can you please explain to me how data arrives from the application layer to phy layer? What phases does it go thru?
For LTE/NSA: APP–>PDCP–>RLC—>MAC–>PHY
For SA: APP–>SDAP–>PDCP–>RLC—>MAC–>PHY
Thanks @pradeep, I’ve re read it again.
Status of buffer. If it’s empty it means UE would request SR else (if there is any data left on UE buffer) then UE wouldn’t request any SR.
I’m still in doubt about dynamic grants. Is it like gNB sends the UE periodically grants within fixed period? Like every 2ms for example?
Appreciate if you could clarify that point of using dynamic grants and how it works.
Thanks @ran_core_consultant, I’ve read this too (from your link).
But there not mentioned any dynamic grants aspects…
Hi @pradeep. Thank you very much. Where does RRC stand at this point in this chain? Appreciate your help
RRC layer comes into picture only for signalling messages. For user data coming from application, RRC is not involved in the chain.
RRC pkts would route to PDCP. Please check https://blogs.keysight.com/blogs/inds.entry.html/2020/07/23/5g_nr_protocol_struc-UHiS.html to understand the flow and mapping between various channels.