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LTE - Signaling stacks UE

LTE - Signaling stacks UE[Under LTE]
» E-UTRA and E-UTRAN overall description - 36.300, Rel 8 «
» E-UTRAN access - 23.401, Rel 8 «

In following articles, we would look at end-to-end protocols involved in control and user paths. We will start with signaling stacks at UE. Below digram show the signaling stacks at various nodes.

AT interface
Adaptor
ESM
EMM
RRC
PDCP
RLC
MAC
PHY
RRM/Relay
RRC S1AP
PDCP SCTP
RLC IP
MAC L2
PHY L1
MME AL
ESM GTP-C
EMM
S1AP
SCTP UDP
IP IP
L2 L2
L1 L1
SGW AL
GTP-C
UDP
IP
L2
L1
Towards PGW
UE SRBs
(RRC SRB0/1/2,
MAC LCID 0/1/2)
eNB S1
(S1AP ID)
MME GTP-C
(IMSI,
EPS bearer ID)
SGW

LTE does not support circuit switched connections; it supports only packet switched connections or "bearers". Bearer capabilities are expressed in terms of QoS. Bearer management (setup/modify/release) functions are handled by ESM layer (located in UE and MME). We will cover more details on end-to-end data path/bearers, QoS etc. in later articles.

Below diagram shows the signaling entities at UE, one possible view of their internals, and their important functions.

AT Interface
AT Command interpreter


.. 27.007, Few related commands
+COPS PLMN selection
+CGATT PS attach
+CGDCONT Define PDN connection
+CGDSCONT Define bearer resource
+CGACT Deactivate/Activate bearer resource

Adaptor
ESM EMM Access stratum Data plane management


.. Implementation specific, usually functionality wise modules (e.g. EMM-Adaptor module to talk to NAS EMM module for EMM specific commands & indications), framework for data plane management, adopter may also be in charge of talking to MMI, additional drivers like bluetooth, COM port, USB etc.
ESM
Bearer context1 .. Bearer context2 . . . Bearer context11


.. 24.301, EPS bearer context management
EMM

EMM state machine



.. 24.301, mobility management like attach/detach, tracking area update, authentication, providing NAS signaling connection, NAS ciphering and integrity protection
RRC
RRC state machine
SRB0 SRB1 SRB2


.. 36.331, signaling connection management/configuration, data radio bearer configuration, measurement reporting, configuring AS ciphering and integrity protection, handling broadcast system info, paging, handover
PDCP
Control
SRB1 SRB2 DRB1 . . DRB11*



RRC
To
RLC

.. 36.323, integrity protection, ciphering
RLC
Control
SRB0 SRB1 SRB2 DRB1 . . DRB11*


.. 36.322, buffering, segmentation, concatenation, reassembly, ARQ
MAC
Logical channels
CCCH DCCH DTCH PCCH BCCH
Transport channels
RACH PCH BCH SCH


.. 36.321, channel mapping, multiplexing, channel prioritisation, HARQ
PHY
Transport channels
RACH PCH BCH SCH
Physical channels
PRACH PBCH PSCH PCCH
Phy procedures


.. 36.201 modulation, coding, power control, cell search, measurements, CRC insertion and other phy specific procedures
* as per RRC TS 36.331, sec 6.4, maxDRB is 11; but as per MAC TS 36.321, section 6.2.1, 11 LCIDs are possible, three of which goes for SRB 0-2, leaving maximum 8 for DRBs !

In next article, we will look at eNB from same angle.

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 - UL PHY Structure example (15 RB, 3 MHz) « LTE Index » LTE - Signaling stacks eNB