How does UE identify paging message and wakes up for receiving DL data?

UE receive paging Frame from UE PDCCH  channel then
UE decodes Paging from the PDSCH Resource Block within which the PAGING message is sent
If UE doesn't find it's own UE identity then it returns to monitor the Paging Occasion.
UE Identity ( S-TMSI and for abnormal IMSI)

Mobility Management in LTE

Mobility Management as name implies it is related to management of user mobility or roaming. User is free to walk in all geographical location. Hence it is responsibility of network to manage user mobility to provide seamless calling(manage handover). Once user gets attach to the network(UE Attach Procedure), network should capable to  support all kind of roaming and user mobility like user moving away from network or moving towards other service provider network or in the worst crossing some enemy line.

LTE support for user mobility

• TAU(Tracking Area Update) - In This procedure user has to update its location which is mappeded with one ID call TAI(Tracking Area Identity). Network maintains list of all TAI in TAL(Tracking Area List) and use this list when user in Idle mode and some downling packets or downling call arrives for user. 
• User roaming  

LTE supports different types of Handover to provide user uninterrupted service. Some of Handover Techniques discussed below

Inter RAT(Radio Access technology) handover, in this user moves into other Technology's network(LTE to 3G/2G).

Intra RAT handover, in this user move into same RAT but in different geographical location.

Inter PLMN handover,  User moves to different service provider area, as a result PLMN also gets changed . Now user is having different sets of MCC(Mobile Country Code) and MNC(Mobile Network Code).

National and International Roaming,  In National Roaming user moves to different service provider(operator) PLMN or same operator PLMN but in National Roaming defined area. When user moves into same service provider area but in National roaming areas means now user moved from H-PLMN(Home-PLMN) to V-PLMN(Visited PLMN). In Nation Roaming user can use either of PLMN(HPLMN and VPLMN), this is the point where User moved into roaming area(V-PLMN) but LTE/PGW still in H-PLMN.

  International Roaming, where user switches to different PLMN from its HPLMN but out side the country region.

LTE Protocol Architecture

LTE protocol Architecture is organized on the basis of User Plane(data plane) and Control Plane.

User Plane Protocol Architecture 

 User plane is design to support high throughput. Here in above diagram we can see UE's PDCP layer downward all layers are mapped with eNodeB layers. They are involve in packet transmission and their security over radio link. What each layer does we will see in layers in LTE  description section. From eNodeB onward SGW and PGW from core network, involved in data transmission.

Between UE and eNodeB we have open air LTE-Uu interface.
Between eNodeB and SGW and SGW to PGW, GTP-U (GPRS Tunnelling Protocol- User) is used and UDP(Transport Layer)  is used as underlying protocol.

Control Plane Protocol Architecture 

Control Plane in LTE is introduced to manage Mobility and Session of users. These protocol are resposible for transmission of all kind of signal which is used in user's roaming, user service use(session establishment), session termination, user's authentication and user's tracking. 

The upper most layer of UE LTE Stack is NAS layer. NAS is only communicate with MME NAS via eNodeB so eNodeB passes NAS information to MME without seeing into them as transparent buffer.

From RRC layers downward all layers are mapped with eNodeB layers. These layers are responsible for establishing, modification and releasing of radio interface between UE and eNodeB and maintaining the security over open air interface.


Interface between UE and eNodeB is LTE-Uu.
Between eNodeB and MME we have S1-MME interface which work on S1-AP application layer protocol.

References :

• 3GPP 23.401 TS
• LTE--the UMTS long term evolution Book by Stefania Sesia

EPC ( Evolved Packet Core)

EPC is stands for Evolved Packet Core, it is core network of LTE, where all mobility and session related monitoring happens.

Major components of Core newtowrks are
MME, SGW, PGW, HSS, PCRF

Core network is responsible for UE attachment, Authentication, mobility, Service bearer establishment and charging.


References : 
http://www.3gpp.org/technologies/keywords-acronyms/100-the-evolved-packet-core

LTE Architecture

Above diagram represents non-roaming architecture of  LTE network. Entire architecture devided into two part Radio network part called E-UTRAN(Evolved - Universal Terrestrial radio Access Network) and Core network part called EPC(Evolved Packet Core). Both combinedly  called EPS ( Evolved Packet System).

LTE architecture is very simple in terms of accessing the packet, it is already separated Control Plane and User Plane.

Components of LTE networks are

UE(User Equipment) - End user mobile device.

E-UTRAN or eNodeB(evolved NodeB) - Radio Antenna tower or base station.

MME (Mobility Management Entity) - Main node of LTE core network.

SGW (Serving Gateway) - Pivot of LTE network and user roaming.

PGW(PDN Gateway) - Packet Data Network Gateway, connector to IP world.

HSS(Home Subscription Server)- Centralized data base of User information.

PCRF(Policy and Charging Rule Function) - QoS rule for services and their charging. 

SGSN(Serving GPRS Support Node); Main component of GPRS network.

Reference :

3GPP 23.401 TS.

What is LTE?

LTE stands for Long Term Evolution, commonly known as 4G. Mainly it is deployed for High speed data for mobile phone users with minimal latency less than 5ms. Standard specification is given by 3GPP(3rd Generation Partnership Project) from release 8 onwards, later releases standardize for LTE Advanced. LTE supports wide range of carrier bandwidth from 1.4MHz to 20MHz used by IMT(International Mobile Telecommunication) system, and supports both mode of duplex TDD(Time Division Duplex) and FDD(Frequency Division Duplex). LTE network completely based on Packet Switching system, not much rely on circuit switching connection oriented protocols, So this makes it very cost effective and easy to deploy with other existing networks. Even LTE architecture is very simple and comprehensive and designed to support a maximum downlink speed of 300Mbps and maximum uplink speed of 70-75Mbps and promised to enhance up to 1Gbps.

Based on its internal architecture and QoS supported, It provides dedicated services like Real time voice/video streaming, real time gaming, high speed data transfer, Emergency calling system, IMS based calling, High speed browsing and addition features like MBMS.