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To download the Data in LTE what all channels & layer 2 messages involved after UE is in connected state?

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To download the Data in LTE what all channels & layer 2 messages involved after UE is in connected state?
posted Jan 23, 2018 by Mohit Mohan

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2 Answers

+2 votes

Once the UE gets connected to LTE network, it can download the data from LTE network. I would like to write down few points as following:
1. Soon after UE attach procedure, when a user browse something in his handset browser, DNS query is generated. DNS server IP is communicated to UE as part of attach procedure.
2. After DNS query resolution, It makes TCP connection with external website server (in case of web browsing).
3. Application running at UE side, it generates application signalling or data. As I mentioned in the above step where UE initiates TCP signalling.
3. Application data is packed into IP packet and reach to PDCP layer of UE side. PDCP layer job is compression/de-compression and apply security on that.
4. RLC layer at UE takes the SDU from PDCP and it adds its own header and forward to MAC layer. Based on the size of packet, MAC asks for radio resource grant from eNodeB MAC layer.Once the UE side MAC layer gets the enough radio resource grant, it sends packet towards eNodeB MAC using radio channel PUSCH because it is uplink packet (going towards eNodeB)
5. EnodeB MAC receives the packet and forward to upper layer i.e RLC after doing its processing.
6. RLC layer at eNodeB does its processing (removing its header) and sends the remaining packet to PDCP layer.
7. PDCP layer at eNodeB performs the security validation, header de-compression. After this steps, PDCP layer is ready with the same IP placket that was generated at UE side.
8. PDCP layer encapsulates this UE IP packet within the GTP header and sends to SGW and SGW modifies GTP header to send the packet to PGW.
9. PGW removes the GTP header and send the packets to external server.

I explained about data flow in uplink direction. Similarly downlink data flows in reverse direction.

answer Jan 24, 2018 by Harshita
Thanks for the answer Harshita. could you please share how downlink data transfer will start  & what all channels involved in protocol layers?
If UE is in connected state ,then DL data will reach PGW -> SGW -> ENB. In ENB PDCP will forward to RLC then to MAC.MAC will send DCI in PDCCH,then PDSCH data will be forwarded, UE sends ACK/NACK in PUCCH/PUSCH
0 votes

Hello Harshita ,Can you explain what message later PGW->web server and down link flow
Thanks in advance

answer Jan 24, 2018 by Yeshwanth
PGW->web server there will be a routers and GW's , these will communicate via IP protocol.
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