Telecom Tutorials by Samir Amberkar

LTE - end-to-end data flow eNB [Under LTE]
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Below diagram describe protocols involved in end-to-end data flow, starting at UE application till PGW:

Application TCP/UDP/IP Adaptor PDCP RLC MAC PHY		Relay PDCP GTP-U RLC UDP/IP MAC L2 PHY L1		Relay GTP-U UDP/IP L2 L1		Relay   IP   GTP-U UDP/IP L2 L2 L1 L1		IP   L2 L1
UE	DRBs (RRC DRB identity, MAC LCID)	eNB	S1 bearers (E-RAB ID, GTP TEID)	SGW	S5/S8 bearers (EPS bearer ID, GTP TEID)	PGW	PDN transport (PDN address)	PDN

Below diagram shows how data flows at eNB:

eNB Access stack

PDCP 3GPP TS 36.323, TCP/UDP/IP header compression/decompression, sequence numbering, ciphering/deciphering PDCP header  SDU    .  .  .  Relay Implementation specific (mainly buffering, scheduling) IP header  Data    .  .  .

GTP Tunnels

eNB EPC stack

GTP-U 3GPP TS 29.281, sequence numbering, tunneling GTP-U header  IP datagram    .  .  .  Socket UDP IETF rfc768 UDP header  Data    .  .  .  IP v4 IETF rfc791, v6 IETF rfc2460, fragmentation & reassembly, addressing IP header  Data (fragments)    .  .  .  L2 transport channels L2 (L2 specific)    .  .  .  L1 (L1 specific)    .  .  .

Between UE and eNB, data flow are managed with Data Radio Bearers. eNB maps these DRBs to E-RAB ID and GTP tunnels between eNB and SGW. SGW further maps it to EPS Bearer ID and GTP tunnels between itself and PGW. PGW extracts the IP data coming from UE and routes it to PDN.

References: SAE and the Evolved Packet Core: Driving the Mobile Broadband Revolution by Olsson, Sultana, Rommer, Frid, and Mulligan.

Copyright © Samir Amberkar 2010-11

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