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Even segmentation is already done on RLC SDUs ,why resegmentation of rlc pdus are required in LTE .

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why resegmentation is required in LTE

posted Jan 27, 2015 by Aaditri Thakur

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1 Answer

+1 vote

Lets first understand the ARQ a bit, data transmission utilizes various forms of Automatic Repeat reQuest (ARQ), where data which has not been received or correctly decoded is automatically requested. This guarantees delivery of the full packet of data, for instance to make sure that the whole web page is displayed. When data is known not to have been received, there normally follows several further attempts to send/receive the data in the same format.

Usually this will be sufficient to ensure the data gets through, however if the data is still not received and decoded correctly even after several repeat attempts, it could be that more protection needs to be added to the basic data or for it to be formatted in a different manner. LTE utilizes a process known as re-segmentation, which essentially allows blocks of previously formatted data to be segmented further. The data can then be sent in smaller packets with added protection, hopefully giving the data a better chance of being received and decoded correctly.

I hope this clarifies a bit, by the way re-segmentation is used only for AM mode.

answer Jan 27, 2015 by Salil Agrawal
Hi salil agarwal,

No, This is wrong. because re segmentation is done because In RLC re tx time If RLC dows n't have enough grant to send RLC PDU means he will do re segmentation.
Like for e.g RLC has send 1500 bytes of data to UE, If it gets NACK then again RLC will ask MAC to send Retx of RLC PDU but if MAC has only 1000 bytes grant then RLC has to do re segmentation  and can only send 1000bytes of data, Not to add any protection , Because no protection mechanism done at RLC in LTE.

Happy Learning :)
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As RLC layer Seq. numbering is used to keep a track of packets to ARQ and PDCP, then SN should be given to RLC PDU, otherwise how it will happen in case of Segmentation and Re-segmentation?

+1 vote

Why do we need segmentation or concatenation for the RLC re-transmission?

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