Amd link failure11/26/2023 ![]() ![]() My recommendation for you is to draw this kind of illustrations for as many diverse case as possible and get clear understandings for each case in your own words before you come across any issues. In many case you would see lack ofĭetailed information in both UE log nor in network log. Once you see the problems it would not be easy to troubleshoot. But this may hold trun only before you see some problem. I often see people underestimate the importance of RLC operation and they think RLC is working in a very simple logic. The illustration and comments would need to be changes if the test condition gets different.įor now, I am illustrating only one specific cases but you can draw varying illustrations depending on situation. The illustrations shown here are examples for a specific case (typical max throughput condition). This data flow can be illustrated as below. I would suggest you to understand how user data follow through these layers. If you try to associate this diagram and the RLC description you will have more practical understanding of RLC and will help you greatly for protocol stack implementation and troubleshooting. Mapping would be a kind of 'Textbook' mapping.Īs we go through this section, you will see the detailed behavior of each RLC mode. Unlike the channel mapping, the association between each message and RLC type is not so tight meaning that network can allocate RLC types a little bit different from what is shown below, but I would say the following Most of signaling message is using RLC and each of the message is a specific types of RLC mode, TM/UM/AM. Why ? This is also what you have to figure out later.Īnother picture that I want you to keep in mind is shown below. But in AM, both Uplink and Downlink path are merged into a single entity. There are separate entity (thread or task) for Uplink and Downlink RLC for TM and UM. What else you can read from the diagram above ? It may not be a perfect analogy but this terminology change made me much more comfortable when I am reading the specs. I just take the term 'entity' as a kind of 'thread' or 'task' in software terminology. it was the term 'entity' which sounded too abstract to me. There are another small issues that scared me. What is the lower layer in this case ? It is simple. you see another layer labelled 'lower layer'. Then, in which case the upper layer should be RRC Layer and in which case it should be PDCP or TE port ? These are what you have to figure out as you go along this document.Īnd then. What do you read from the diagram above ? First you will see the layers labeled 'upper layer' and 'lower layer' ? What does these layer specifically mean ? 'Upper layer' in this case would mean 'RRC layer' or 'PDCP Layer' or in some case (especially in the simulation or testing environment' it can be a TE port ( a kind of data Input/Output port). The first diagram you will see in LTE RLC specification(TS 36.322) is as follows: but this part will be updated forever as I get more and more insight on this layer.Īs in the section for other layer, let's start by "Reading (Verbalizing)" the pictures from the specification. It will be explained as you go along with this section. I will not explain on these topics right now. Ii) Segmentation (Splitting) and Concatenation (Combining) mechanism I) Understanding three types of RLC Mode : TM, UM, AM Variables, constants and timers for RLCĪs far as I experienced, there are three main topics we have to master on this layer to make our knowledge practical enough to the development or troubleshooting.Example 3 : in LTE - RLC Bidirectional (From LTE Attach to YouTube).Example 2 : in LTE - RLC Transmission from Network (LTE Registration).Example 1 : in LTE - RLC Transmission from Network (IP Throughput).Case 5 : RLF(Radio Link Failure) due to Max Retransmission Failure.Case 4 : Retransmission due to RLC NACK.Case 3 : Retransmission due to t-PollRetransmit timeout.Case 2 : Poll bit and RLC ACK operates by sequence number.Summary of RLC AM Data Flow - Reception.Summary of RLC AM Data Flow - Transmission.Summary of RLC UM Data Flow - Reception.Summary of RLC UM Data Flow - Transmission. ![]() First, understand the details RLC PDU/SDU structure and go through a lot of examples. Another difficulties is that I don't find any books or other training material explaining very detail on this area, whereas you would find a lot of books and materials digging veryįollowings are topics that will be described in this page. At the beginning it seems to be simple, but as I getting deeper and deeper into this layer I get more and more confused. Personally to me, RLC layer is one of the trickest area to understand in very detail.
0 Comments
Leave a Reply.AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |