Chapter 3 LTE Network

Outline 3.1 LTE Network Architecture 3.2 Protocol Stack 3.1.1 Overall Architecture 3.1.2 Basic functions of all entities 3.1.3 LTE interfaces 3.2 Protocol Stack 3.2.1 User plane protocol stack 3.2.2 Control plane protocol stack 3.3 Traffic flow on LTE/EPC 3.4 LTE identifiers 3.4.1 UE and ME Identifier 3.4.2 NE and Location Identifier 3.4.3 EPS Session/Bearer Identifier

Introduction The LTE network called EPS (Evolved Packet System) is an end-to-end (E2E) all IP network EPS = LTE + EPC LTE: Technology related to a radio access network (E-UTRAN) EPC: Technology related to a core network

3.1.1 Overall Architecture

3.1.2 Basic functions of all entities LTE Entities

3.1.2 Basic functions of all entities EPC Entities

3.1.2 Basic functions of all entities

3.1.3 LTE Interfaces

3.1.3 LTE Interfaces

3.2 Protocol Stacks 3.2.1 User plane protocol stack 3.2.2 Control plane protocol stack

3.2.1 User plane protocol stack

3.2.1 User plane protocol stack LTE-Uu Interface PDCP protocol: Support transport of IP packets over the radio link. It performs header compression, Access Stratum (AS) security, packet-reordering/retransmission during handover RLC protocol: segmentation/concatenation of PDCP PDUs during the construction of RLC PDU. MAC protocol: MAC layer is connected to the RLC layer through logical channels, and to the PHY layer through transport channels. supports multiplexing and de-multiplexing between logical channels and transport channels. Higher layers use different logical channels for different QoS metrics. S1-U/S5/X2 interface GTP-U: GTP-U protocol is used to forward user IP packets over S1-U, S5 and X2 interfaces.

3.2.2 Control plane protocol stack

3.2.2 Control plane protocol stack

3.2.2 Control plane protocol stack LTE-Uu Interface NAS: mobility management and bearer management functions RRC: Supports the transfer of the NAS signaling. Broadcasting of system information. Setup, reconfiguration, reestablishment and release of the RRC connection Setup, modification and release of the radio bearer X2 interface X2AP: supports UE mobility and SON functions within the E-UTRAN User data forwarding Transfer of SN status and UE context release

3.2.2 Control plane protocol stack S1-MME interface S1AP: support functions: S1 interface management, E-RAB management NAS signaling transport, UE context management delivers the initial UE context to the eNB to setup E-RAB S11/S5/S10 interfaces GTP-C: supports exchange of control information for creation, modification and termination for GTP tunnels S6a interface Diameter: supports delivery of PCC rules from the PCRF to the PCEF (P-GW)

3.2.2 Control plane protocol stack Gx interface Diameter: supports delivery of PCC rules from the PCRF to the PCEF (P-GW) Gy interface Diameter: supports exchange of real-time credit control information between the P-GW and OCS. Gz interface GTP’: supports CDR transfer from the P-GW to the OFCS.

3.3 Traffic flow on the LTE network IP packets are forwarded through the GTP tunnel over S1-U and S5 interfaces. These GTP tunnels are established per EPS bearer when a user is attached to the LTE network More than one EPS bearer is established on each of the S1-U and S5 interfaces  in order to identify these bearers, a Tunnel Endpoint Identifier (TEID) is assigned to the end points (UL and DL) of each GTP tunnel When identifying a GTP tunnel, a TEID, IP address and UDP port number are used The receiving end side of the GTP tunnel locally assigns the TEID value the transmitting side has to use The TEID values are exchanged between tunnel endpoints using control plane protocols

3.3 Traffic flow on the LTE network

3.3 Traffic flow on the LTE network Traffic flow in uplink direction: from UE to the Internet A UE transfers user IP packets to an eNB over LTE-Uu interface The eNB encapsulates the user IP packets with the S1 GTP tunnel header and forwards to the S-GW After receiving the outer IP packets, the S-GW strips off the S1 GTP tunnel header, encapsulates the user IP packets (the inner IP packets) with the S5 GTP tunnel header and forwards to the P-GW After receiving the outer IP packets, the P-GW gets the user IP packets by stripping off the S5 GTP tunnel header and transfers them to the Internet through IP routing

3.3 Traffic flow on the LTE network Traffic flow in downlink direction: from the Internet to UE A P-GW receives IP packets destined for a UE over the Internet The P-GW encapsulates the user IP packets with the S5 GTP tunnel header and forwards to the S-GW After receiving the outer IP packets, the S-GW strips off the S5 GTP tunnel header, encapsulates the user IP packets (the inner IP packets) with the S1 GTP tunnel header and forwards to the eNB After receiving the outer IP packets, the eNB gets the user IP packets by stripping off the S1 GTP tunnel header and transfers them to the UE through the Data Radio Bearer (DRB) over the radio link

3.4 LTE Identifiers 3.4.1 UE and ME Identifier 3.4.1.1 Classification of LTE IDs 3.4.1.2 User Equipment IDs 3.4.1.3 Mobile Equipment IDs 3.4.2 NE and Location Identifier 3.4.2.1 Classification 3.4.2.2 Network Equipment IDs 3.4.2.3 Location IDs 3.4.3 EPS Session/Bearer Identifier 3.4.3.1 EPS Session and Bearer Overview 3.4.3.2 EPS Session/Bearer Identifier

3.4.1.1 Classification of LTE IDs Feature of these LTE IDs: Creation time Created when equipment installation Created by operator before or during service operation Created on-demand as a user accesses the network or uses services Type Temporary Permanent Range Each LTE ID is uniquely identified across the world, operator networks, entities or channels

3.4.1.1 Classification of LTE IDs

3.4.1.1 Classification of LTE IDs

3.4.1.1 Classification of LTE IDs

3.4.1.2 User Equipment IDs PLMN ID (Public Land Mobile Network) indicating the network that a user has subscribed to

3.4.1.2 User Equipment IDs IMSI (International Mobile Subscriber Identity) Permanent ID allocated to a mobile subscriber Identifying a mobile subscriber globally

3.4.1.2 User Equipment IDs GUTI (Globally Unique Temporary Identifier) Security problems if IMSI is frequently exposed over the radio link Allocated to a UE by an MME when the UE attaches to the Network, and used instead of the IMSI to identify the UE GUTI allocation

3.4.1.2 User Equipment IDs GUTI Format MME Identifier = MME group ID + MME code GUMMEI : Globally Unique MME Identifier M-TMSI : MME Temporary Mobile Subscriber Identity Allocated by MME

3.4.1.2 User Equipment IDs IP Address allocated by an LTE network to a UE in order for the UE to connect to a PDN (i.e. an IP network) Each UE has a different IP address per PDN IP address allocation Static: an operator allocates a permanent IP address to a UE at the time of subscription Dynamic: a P-GW has an IP pool and dynamically assigns an available IP address from the pool every time a UE performs initial attach to an LTE network

3.4.1.2 User Equipment IDs

3.4.1.2 User Equipment IDs

3.4.1.2 User Equipment IDs C-RNTI (Cell Radio Network Temporary Identifier) Allocated to a UE by an eNB through a random access procedure in a cell controlled by the eNB and is effective only within the [serving] cell C-RNTI allocation

3.4.1.2 User Equipment IDs Paired UE S1AP IDs : needed to distinguish UEs over the S1-MME interface S1AP layer handles the control messages between an eNB and an MME over an S1-MME interface The eNB uses the same S1 link for all the S1AP control messages In order to tell which S1AP message is for which UE, an eNB allocates an ID (eNB UE S1AP ID) to each UE when it sends the first S1AP message for a UE to an MME Similarly, MME UE S1AP ID is allocated by MME for each UE

3.4.1.2 User Equipment IDs UE S1AP ID allocation and S1AP layer

3.4.1.2 User Equipment IDs Paired UE X2AP IDs X2AP layer handles the control messages (X2AP messages) between two neighbor eNBs over an X2 interface UE X2AP ID allocation and X2AP layer

3.4.1.3 Mobile Equipment IDs A UE consists of an ME and a UMTS Subscriber identity Module (USIM) ME can further be divided into Terminal Equipment (TE) and a Mobile Terminal (MT)

3.4.1.3 Mobile Equipment IDs IMEI and IMEISV IDs permanently owned by an ME An IMEI is given when an ME is being manufactured, and contains information about the manufacturer, model, and serial number of the ME IMEI is composed of a Type Allocation Code (TAC), a Serial Number (SNR) and a Check Digit (CD) IMEI/SV is composed of a TAC, an SNR and a Software Version Number (SVN) A TAC is made up of a Reporting Body Identifier (RBID) that indicates a reporting body An ME Type ID that represents the manufacturer’s name and the model identifier Serial numbers are assigned by the manufacturer

3.4.1.3 Mobile Equipment IDs

3.4.2 NE and Location Identifier 3.4.2.1 Classification 3.4.2.2 Network Equipment IDs 3.4.2.3 Location IDs

3.4.2 NE and Location Identifier 3.4.2.1 Classification 3.4.2.2 Network Equipment IDs 3.4.2.3 Location IDs

3.4.2.1 Classification

3.4.2.1 Classification

3.4.2.2 Network Equipment IDs GUMMEI, MMEI, MMEGI and MMEC IDs to Identify MME MMEI (MME Identifier) is used when identifying an MME in the network of an operator GUMMEI (Globally Unique MME Identifier), combination of a PLMN ID and an MMEI, is used when identifying an MME outside of the network of the operator MMEGI that represents an MME group MMEC that represents a particular MME in the MME group

3.4.2.2 Network Equipment IDs IDs to identify MME and format

3.4.2.2 Network Equipment IDs eNB ID and Global eNB ID IDs to identify eNB An eNB ID is used for identifying an eNB within an operator’s network only Global eNB ID, combination of a PLMN ID and an eNB ID, is used for identifying one outside the network

3.4.2.2 Network Equipment IDs P-GW ID : ID to identify P-GW P-GW ID allocation Fixed allocation: network operator provisions a P-GW ID as a subscribed profile in the HSS Dynamic allocation: MME selects a P-GW according to the P-GW selection policy set by the operator Either IP address or FQDN (Fully Qualified Domain name) forms

3.4.2.3 Location IDs TAC and TAI : TAC (Tracking Area Code) and TAI (Tracking Area Identifier) IDs to identify the location of a UE The TAC is used to identify a TA in the network of an operator, whereas the TAI, combination of a PLMN ID and a TAC, is used to uniquely identify a TA globally

3.4.2.3 Location IDs The MME allocates a TAI list to the UE at its initial attach, and keeps track of its location. The UE informs the MME of its new location and requests for TA update whenever it leaves its registered TA If the current TA renewal period is expired, the UE has to inform the MME of its current TA, even while staying in TAs listed in the list If the UE is in active state, the MME knows in which cell the UE is  forward data If the UE is in idle state  the MME perform Paging procedure to find the UE UE knows the TA change by listening to the broadcast information from the cell

3.4.3 EPS Session/Bearer Identifier 3.4.3.1 EPS Session and Bearer Overview 3.4.3.2 EPS Session/Bearer Identifier

3.4.3.1 EPS Session and Bearer Overview

3.4.3.1 EPS Session and Bearer Overview represented by an IP address of the UE and a PDN ID (Access Point Name (APN)) has more than one EPS bearer to deliver user traffic and applies the service quality (QoS) policy always has a default bearer EPS Bearer A UE can have multiple EPS bearers concurrently Different EPS bearers are identified by their EPS bearer ID, which is allocated by an MME EPS Bearer = Data Radio Bearer + S1 Bearer + S5 Bearer

3.4.3.1 EPS Session and Bearer Overview Types of EPS Bearers Each PDN must have one default EPS bearer, but may have none to many dedicated EPS bearers Multiple dedicated bearers can be created if required by the user or the network When there is no user traffic, these dedicated EPS bearers can be removed, whereas the default one is never removed

3.4.3.2 EPS Session/Bearer Identifier PDN ID (APN) (Packet Data Network ID or Access point name) APN = Network ID + Operator ID

3.4.3.2 EPS Session/Bearer Identifier EPS Bearer IDs A UE can have up to 11 EPS bearers and their ID values Bearer IDs allocators

3.4.3.2 EPS Session/Bearer Identifier EPS Bearer IDs

3.4.3.2 EPS Session/Bearer Identifier E-RAB ID : assigned by an eNB, generally with the same value as the EPS bearer ID during the setup procedure of the EPS bearer, the MME requests the eNB for e-RAB setup, the eNB creates DRB with the UE and S1 bearer with the S-GW DRB ID assigned by an eNB upon establishment of the EPS bearer, and is mapped with EPS bearer IDs on 1:1 basis the eNB creates DRB for communication with the UE by assigning a DRB ID and selecting logical channel configuration parameters based on the required QoS TEID While EPS bearers are being set up, for S5 bearer, the S-GW allocates DL S5 TEID and the P-GW allocates UL S5 TEID. For S1 bearer, the S-GW assigns UL S1 TEID and the eNB assigns DL S1 TEID

3.4.3.2 EPS Session/Bearer Identifier Summary

References Technical documents from www.netmanias.com “LTE Network Architecture: Basic” “LTE Identification I: UE and ME Identifier” “LTE Identification II: NE and Location Identifiers” “ LTE Identification III: EPS Session/Bearer Identifier ”