LTE RLC PDU Structure
In this tutorial the basic of LTE RLC PDU structure is discussed. The detail encoding of RLC PDUs will be discussed in the upcoming tutorials.
In LTE RLC PDUs can be categorized as:
Data PDU
Control PDU
- Status PDU
RLC Data PDU
Note: RLC SDUs are bit strings which are bye aligned (Multiple of 8 bits)
TM Data PDU (TMD PDU)
TMD PDU consists only of Data field and does not consist of any RLC header.
UM Data PDU (UMD PDU)
UMD PDU consists of UMD PDU header and the data part.
UMD PDU Header
UMD PDU Header consists of:
Fixed Part
- Framing Info (FI)
- Extension bit (E)
- Sequence Number (SN)
Extension Part
- Extension bit (E)
- Length Indicator (LI)
NOTE: RRC can configure UM RLC to use 5 bit or 10 bit SN
- When 5 bit SN is used the length of the fixed part of the UMD header is 1 byte.
- When 10 bit SN is used the length of the fixed part of the UMD header is 2 bytes with 3 bits of R1 fields.
There are different types of encoding schemes of UMD PDUs can be possible.
NOTE: The different encoding schemes will be described with examples in upcoming tutorials.
UMD PDU with 5 bit SN
UMD PDU with 10 bit SN (No LI)
UMD PDU with 5 bit SN (Odd number of LIs)
UMD PDU with 5 bit SN (Even number of LIs)
UMD PDU with 10 bit SN (Odd number of LIs)
UMD PDU with 10 bit SN (Even number of LIs)
AM Data PDU (AMD PDU)
AMD PDU is byte aligned. The AMD PDU header part consists of a fixed part and an extension part.
AMD PDU Header
Fixed Part
- Data/Control bit (D/C)
- Re-segmentation Flag (RF)
- Polling bit (P)
- Framing Info (FI)
- Extension bit (E)
- Sequence Number (SN)
Extension Part
- Extension bit (E)
- Length Indicator (LI)
AMD PDU (No LI)
AMD PDU (Odd number of LIs)
AMD PDU (Even number of LIs)
AMD PDU Segment
AMD PDU segment header consists of a fixed part and an extension part.
Fixed part
- Data/Control (D/C)
- Re-segmentation Flag (RF)
- Polling bit (P)
- Framing Info (FI)
- Extension bit (E)
- Sequence Number (SN)
- Last segment Flag (LSF)
- Segment Offset (SO)
Extension part
- Extension (E)
- Length Indicator (LI)
AMD PDU segment (No LI)
AMD PDU segment (Odd number of LIs)
AMD PDU segment (Even number of LIs)
RLC Control PDU
Status PDU
STATUS PDU consists of a STATUS PDU payload and a RLC control PDU header.
NOTE: All the RLC PDU structure will be described with examples in separate tutorials.
Reference
- LTE Radio Link Control (RLC) protocol specification (Release 8):
http://www.3gpp.org/ftp/Specs/latest/Rel-8/36_series/36322-880.zip
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Hi Prashant,
Nice basic article on RLC PDU. Can you please send me the tutorial link where I can understand by an example RLC PDU.Many thanks.
Cheers,
Vinita
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Hi,
I Will try to add some examples for RLC PDUs.
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Hi Prashant….the article is really nice. Thanks.
I have one qury for RLC though. For doing arithmtic comparison, it is mentiond in spec to do absolute comparison. Does it mean taking Abs and then take modulus. Will this sort out roll over problem also?
like [VR(R) – VR(R)] modulo 1024 ….dos it mean Abs(VR(R) – VR(R)) modulo 1024
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Hi prasanth,
I’m masters student doing my project in the area of LTE. Our project is about implementing RLC layer in omnet++. Idea is since there is no module for simulating LTE in omnet++, we thought of implementing basic mac and complete RLC layer. We are looking at “3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA); Radio Link Control (RLC) protocol specification(Release 9)” . We are creating a dummy mac which will just requst RLC to send the data. Can u please tell us what is the maximum size of RLC pdu that mac can handle. In theory we learnt that eNodeb and UE have same RLC functionality. Is there any difference ?? Please help us out.
Regards,
Nagarrajan
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Great post and vivid examples to clarify things that perhaps are hard to understand directly from the specs. I would greatly appreciate some more examples and post on AM mode of RLC too. Looking forward to some more learning from this blog. Thanks.
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@adnanayad I will add some LTE RLC AM tutorial soon.
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Hi. Sorry for the late reply. I will check this and answer soon.
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@prashant.panigrahi hi sorry for late reply…hello In theory we learnt that eNodeb and UE have same RLC functionality. Is there any difference ?? Please help us out.
regards
nagu
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hello In (LTE) theory we learnt that eNodeb and UE have same RLC functionality. Is there any difference ?? Please help us out.
regards
nagu
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@nagu99 The RLC protocol is totally symmetric and peer entities have exactly same functionalities. No difference between RLC in UE and eNodeB.
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@adnanayad hello thanks for reply….I’m currently modelling this in OMNet++…in OMNeT++ there is no LTE module…so i took an existing framework which had Appln layer, network layer, mac and phy… it is implementing csma in mac layer…i have just put my RLC module in it …just implemented only TM mode….and i’m trying to configure the phy layer parameters with lte phy parameters…is it right or how to proceed??? and i read in spec that if segmentation and concatenation is configured in upper layer then only do segmentation in this layer….so how should i proceed…this is my masters project…is it ok…
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Can you please let me know why we need
AMD PDU segment (Odd number of LIs) table , what is purpose of this table . what case we use this table .