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another knowledge site

LTE - dedicated bearer setup

LTE - dedicated bearer setup [Under LTE]
» E-UTRA and E-UTRAN overall description - 36.300, Rel 8 «
» E-UTRAN access - 23.401, Rel 8 «
» EMM and ESM - 24.301, Rel 8 «
» GTPv2-C - 29.274, Rel 8 «
» S1AP - 36.413, Rel 8 «
» NAS overall - 24.007/8, Rel 8 «
» RRC - 36.331, Rel 8 «

As mentioned in last article, dedicated bearer is meant for specific QoS and always associated with default bearer (which provide initial/basic PDN connectivity). Dedicated bearer setup is always initiated by EPC. EPC triggers dedicated bearer setup due to incoming packet connection (call) or due to ESM request sent by UE.

Below is a end-to-end signaling diagram for dedicated bearer setup.

 UE   

 eNB   

 MME   

 SGW   

 PGW   

Default EPS bearer is assumed to be present.
UE require bearer with specific QoS (mostly different than that provided by default bearer). UE in RRC-Connected, EMM-Registered, ECM-Connected state.
EPS bearer 23.401:4.7.2
Bearers/QoS 36.300:13

RRC - UL Information Transfer
[ESM - Bearer Resource Allocation Request (Specific QoS, default EPS bearer ID)]
ESM 24.301:6.5.3.2
EPS QoS 23.401:4.7.3
default EPS bearer ID coding 24.007:11.2.3.1.5
The default bearer ID comes in Activate Default EPS Bearer Context Request ESM message sent along with Attach Accept EMM message during attach procedure.
S1AP - UL Nas Transport
[ESM pdu]
S1AP 36.413:8.6.2.3
GTP-C - Bearer Resource Command
(Flow QoS, default EPS bearer ID)
GTP-C 29.274:7.2.5
GTP-C - Bearer Resource Command
GTP-C 29.274:7.2.5
This would result into invocation of dedicated bearer activation procedure. PGW uses QoS policy (local or coming from PCRF) to come out with negotiated QoS.
Overall 23.401:5.4.1
GTP-C - Create Bearer Request
(Bearer Context - Bearer level QoS{QCI, ARP, GBR, MBR}, TFT, S5/S8 GTP TEID, PCO)
GTP-C 29.274:7.2.3
TFT 24.008:10.5.6.12
GTP-C - Create Bearer Request
(Bearer Context - Bearer level QoS{QCI, ARP, GBR, MBR}, TFT, S1 GTP TEID, PCO)
GTP-C 29.274:7.2.3
TEID is GTP Tunnel ID over S1-U interface (corresponding to S5/S8 TEID). This would be same as that setup during default bearer setup.
EPS bearer over GTP 36.300:4.7.2.2
S1AP - E-RAB Setup Request
(new EPS bearer ID, EPS bearer QoS)
[ESM pdu - Activate Dedicated EPS Bearer Context Request (Negotiated QoS no ARP, TFT, PCO]
S1AP 36.413:8.2.1
ESM 24.301:6.4.2.2
eNB App/RRM (Admission control & Scheduling) plays an important part here. RRM comes out with Radio QoS out of given EPS QoS based on current radio load situation and invokes RRC Reconfig procedure.
RRM functions 36.300:16.1

RRC Connection Reconfiguration
[EPS bearer ID, DRB ID, Radio configs - RLC/PDCP/MAC/PHY, ESM pdu]
RRC 36.331:5.3.5

RRC Connection Reconfiguration Complete
RRC 36.331:5.3.5

S1AP- E-RAB Setup Response
S1AP 36.413:8.2.1.2

RRC - UL Information Transfer
[ESM - Activate Dedicated EPS Bearer Context Accept]
ESM 24.301:6.4.2.3
S1AP - UL Nas Transport
[ESM pdu]
GTP-C - Create Bearer Response
GTP-C 29.274:7.2.4
GTP-C - Create Bearer Response
GTP-C 29.274:7.2.4

References: 3G Evolution: HSPA and LTE by Dahlman, Parkvall, Sköld, and Beming, LTE - From Theory to Practice, Edited by Sesia, Toufik, and Baker, and SAE and the Evolved Packet Core: Driving the Mobile Broadband Revolution by Olsson, Sultana, Rommer, Frid, and Mulligan.

Copyright © Samir Amberkar 2010-11§

LTE - end-to-end UE initial attach « LTE Index » LTE - end-to-end data flow UE