Hi Experts.
A general question:
We say UDP is a connectionless protocol, which means it does not provide any guarantees regarding the delivery of data packets.
As a result, there is no concept of retransmission in the UDP layer itself.
But I believe the above statement is an application layer point of view.
And in cellular technology like LTE/NR, RLC and MAC layers will still perform retransmissions whether the packet is TCP or UDP.
Any other opinions from anyone for above?
Depends on what kind of transmission you have even in UDP.
For RLC layer, there are three modes of transmission:
If you read you will understand more on this. I think (can’t remember exactly) UDP that UDP is unacknowledged mode when it comes to RLC retransmission.
As for MAC layer, retransmission at MAC layer is a different concept than retransmission in UDP / TCP.
MAC retransmission (i.e. HARQ retransmission) i meant to cover signal loss / corruption. It happens even if you have TCP or UDP transmission.
Exactly!
AM / UL / TM modes of RLC layer are per DRB.
If 5QI-9 DRB of NR is set to AM (which will always be AM in any NW), then packet is TCP or UDP, RLC retransmission will be be there if required.
Voice is UM mode, but still have retransmission on PDSCH.
It has HARQ/MAC retransmissions. Not RLC retransmissions.
That is true!
I think it is more about QCI being followed. If the QCI is GBR then retransmission will be done… otherwise best effort should be used without retransmissions.
TCP & UDP are application layer protocols and have nothing to do with telecom data transmission.
Indeed @moeedkh is correct. RAN scheduler on the MAC/RLC layer does not know (or care) about the type of packet being transmitted. It can be UDP/ TCP or AlienP… The RAN layers will work based on their transmission mode (which is usually governed by the QCI in use).
A RAN packet on the RLC/MAC does not equal a packet on TCP/UDP layer. A TCP packet may be chopped into smaller RAN blocks while being transmitted on the air interface, or even multiple TCP packets may be transmitted together on the air interface etc…
TCP:
Phy: HARQ (control by Mac)
Rlc: AM (if respective 5qi configure with AM only, here we can configure um also)
Application layer: TCP retransmission (TCP & UDP are application layer protocols)
Phy: HARQ (control by Mac)
Rlc: UM (if respective 5qi configure with UM only, here we can configure AM also)
Application layer: TCP retransmission (TCP & UDP are application layer protocols)
UDP:
Phy: HARQ (control by Mac)
Rlc: AM (if respective 5qi configure with AM only, here we can configure um also)
Phy: HARQ (control by Mac)
Rlc: UM (if respective 5qi configure with UM only, here we can configure AM also)
You use UDP/TCP or any private protocol (consignment), that’s application level.
HARQ is there to ensure reliable delivery of packets over air interface (ship).
May it be RLC-AM, UM or TM.
For example, there are harq retransmissions for VOIP over QCI-1(GBR).
RLC retransmission is in AM mode only, is a sort of ‘1+1’ configuration, a dual mechanism to recover packets when max HARQ retransmissions are attempted to no gain. It won’t occur for rest of RLC modes.
The highest layer at eNB is PDCP.
Above TCP / UDP, eNB can not know which kind of services, right?
Interesting complementary (extra and related) reading:
TCP vs. UDP — What’s the Difference and Which Protocol is Faster?
If you’re getting into computer networking, or if you’ve dug through the network settings of some applications, you’ve likely seen these terms: TCP and UDP.
TCP, which stands for Transmission Control Protocol, and UDP, or User Datagram Protocol, are part of the internet protocol suite. TCP and UDP are different methods to send information across the internet.
But even knowing what they stand for, it’s hard to know which protocol you should use, or why you would use one over the other.
In this article, we’ll go over computer networking basics, the differences between TCP and UDP, when each is used, and more.
Computer Networking Basics
Before diving into how TCP and UDP work, it’s helpful to know the basics about how the internet works.
Generally speaking, the internet is a network of connecting devices. Each device, whether it’s your smartphone or a server, communicate through the internet protocol suite.
The internet protocol suite is a collection of different protocols, or methods, for devices to communicate with each other. Both TCP and UDP are major protocols within the internet protocol suite:
Each device that’s connected to the internet has a unique IP address. And whenever two devices communicate over the internet, they’re likely using either TCP or UDP to do so.
Here’s a brief comparison between the two: Check out this below 
image for difference between TCP and UDP.
I hope this content helped you understand some of the nuances between TCP and UDP. **And if someone asks which is faster, tell 'em what you read here: "UDP is faster.**
Credits:
