Introducere in LTE UTCN
Oct 28, 2014
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Long Term Evolution
Retele de generatia a 4-a “all IP” Retele LTE (Long Term Evolution)• 3GPP Release 8• Viteze de transfer mari; costuri reduse; OFDM/MIMO• Suport pentru mai multe retele de acces radio (RAN) eterogene – inclusiv
non 3GPP (WiMax)• Mobilitate intre retele de acces radio diferite• Arhitectura simplificata
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3GPP releases
• Next step for GSM/WCDMA/HSPA and cdma2000
LTE (long Term Evolution)
year
UMTS Rel 99/4UMTS Rel 99/4 UMTS Rel 5UMTS Rel 5 UMTS Rel 6UMTS Rel 6 UMTS Rel 7UMTS Rel 7
2007200520032000 2008
IMSHSDPA
MBMSWLAN IWHSUPA
IMS EvolutionLTE Studies
Specification:
2009
• 3GPP started working on System Architecture Evolution (SAE) in the end of 2004
• Feasibility of technical options was studied in 2005-2006
• Actual standardisation started after the feasibility study in the beginning of 2007
• Nowadays, the system is called Evolved Packet System (EPS) instead of SAE
– The PS core part is called Evolved Packet Core (EPC)
• LTE have been developed by the same standardization organization – 3GPP. The target has been simple multimode implementation and backwards compatibility.
UMTS Rel 8UMTS Rel 8
LTE & EPC
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Targets in EPS standardisation
•LTE as true mobile broadband access– High bitrates (173/58 Mbps)
•Delay optimizations– Fast access to services
– Minimized latency and round-trip delay
•Optimization for IP traffic– Network architecture to match with high bitrate radio
– Voice over IP
•Harmonized architecture for 3GPP accesses and interworking with non-3GPP accesses
– Optimized interworking with 3GPP and CDMA accesses
– Use of common subscriber and service control solutions
•Low cost per bit
•Keep-it-simple
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Reduced Network Complexity
• Flat, scalable IP based architecture
Flat Architecture: 2 nodes architectureIP based Interfaces
Access Core Control
Evolved Node B GateWay
IMS HLR/HSS
Flat, IP based architecture
Internet
MME
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Comparison of Throughput and Latency
HSPA R6
Max. peak data rate
Mb
ps
Evolved HSPA (Rel. 7/8, 2x2 MIMO)
LTE 2x20 MHz (2x2 MIMO)
LTE 2x20 MHz (4x4 MIMO)
Downlink
Uplink
350
300
250
200
150
100
50
0HSPAevo
(Rel8)
LTE
* Server near RAN
Latency (Rountrip delay)*
DSL (~20-50 ms, depending on operator)
0 20 40 60 80 100 120 140 160 180 200
GSM/EDGE
HSPARel6
min max
ms
Enhanced consumer experience:- drives subscriber uptake
- allow for new applications
- provide additional revenue streams
• Peak data rates of 173 Mbps/58 Mbps
• Low latency 10-20 ms
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Comparison of UMTS and EPSEvolved Packet Core
eUTRAN
UMTS Core Network
UTRAN
NBNB
NBNB
MSCMSC
Iu-CS
Iur
NBNB
RNCRNC
Iu-PS
eNB evolved NodeB
MME Mobility Management Entity
SGW Serving Gateway
PGW PDN Gateway
MSC Mobile Switching CenterNB NodeBRNC Radio Network ControllerSGSN Serving GPRS Support NodeGGSN Gateway GPRS Support Node
IubeNBeNB
S1-U
X2
S1-MME
eNBeNB
eNBeNB
MMEMMESGSNSGSN
GGSNGGSN
SGWSGW
PGWPGW
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OperatorServices
Internet
CorporateServices
Overall Evolved Packet System architecture
Evolved Packet Core
PCRF
ePDG
Gb
Iu S4
S1-MME
S1-U
S11
S2c
S2a
S2b
Gx
Rx+
SGi
HSS
S6b
S5
User planeControl plane
S3
S6a
SGSN
BSC
RNC
S10
AAA
RAN
NodeB
eNodeB
PGW
S12
Gxc
SGW
MMELTE
3G
2G
Non 3GPP
Untrusted Non-3GPP IP Access
Trusted Non-3GPP IP Access
Gr/S6d
S16
SWx
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LTE Network Nodes and Interfaces
From IP point of view the LTE network can be split in three parts:
•Access Network and Transport Network
•Evolved Packet Core
•Applications
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LTE Network Nodes and Interfaces
Evolved Node B•It is the only network element defined as part of EUTRAN.
•It replaces the old Node B / RNC combination from 3G.
•It terminates the complete radio interface including physical layer.
•It provides all radio management functions
•An eNB can handle several cells
•To enable efficient inter-cell radio management for cells not attached to the same eNB,
• there is a inter-eNB interface X2 specified.
Mobility Management Entity•It is a pure signaling entity inside the EPC; P-GW & S-GW selection
•SAE uses tracking areas to track the position of idle UEs. The basic principle is identical to location or routing areas from 2G/3G.
•MME handles attaches and detaches to the SAE system, as well as tracking area updates
•NAS signaling & security - The Non-Access Stratum (NAS) signaling terminates at the MME and it is also responsible for generation and allocation of temporary identities to UEs
•Interface towards the HSS which stores the subscription relevant information and the currently assigned MME in its permanent data base.
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LTE Network Nodes and Interfaces
Serving Gateway
•Manages the user data path (SAE bearers) within EPC
•It connects via the S1-U interface towards eNB and receives uplink packet data from here and transmits downlink packet data on it.
•The serving gateway has packet data anchoring function within EPC.
• It relays the packet data within EPC via the S5/S8 interface to or from the PDN gateway.
•A serving gateway is controlled by one or more MMEs via S11 interface.
Packet Data Network Gateway•The PDN gateway provides the connection between EPC and a number of external data networks.
•PDN Gateway is comparable to GGSN in 2G/3G networks.
•Mobility anchor for mobility between 3GPP access systems and non-3GPP access systems.
•Policy Enforcement (PCEF)
•Per User based Packet Filtering (i.e. deep packet inspection)
•Charging & Lawful Interception support
•IP Address Allocation for UE
•Packet screening (firewall functionality)
PCRF
PGWSGW
MMEPDN
SAE GW
AAAHSS
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LTE Network Nodes and Interfaces
Policy and Charging Rule Function
•The PCRF major functionality is the Quality of Service (QoS) coordination
Home Subcriber Server
•Permanent and central subscriber database
•Stores mobility and service data for every subscriber
•Contains the Authentication Center (AuC) functionality.PCRF
PGWSGW
MMEPDN
SAE GW
AAAHSS
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LTE Network Nodes and Interfaces
LTE Interfaces• S1-MME: used for signaling between the Evolved Node B (eNB) and the MME
• S1-U: defines user plane between eNB and serving gateways
• S10: used by MMEs to support MME changes
• X2: used to support intra-MME handover with no packet loss
• S11: used by the MME to control path switching and bearer establishment in the serving gateway and PDN gateway
• S6a: used by the MME to retrieve subscriber data from home subscriber server (HSS)
• S5: a signaling interface for establishing bearers between the serving gateway and the PDN gateway or between serving gateways, for serving gateway change
• Gx: used by the PCRF to convey policy enforcement to the P-GW, and also used to retrieve traffic flow data.
• SGi: the interface into the IP PDN. This is where the IP visibility into the UE IP address(es) is exposed.
• S8: analogous to the S5 except that it is used in roaming scenarios.
• Rx: used by application functions, such as the IMS P-CSCF, to convey policy data to the PCRF.
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Evolution towards a flat architecture
Iu over IP
Separation of CP and UP:Direct Tunnel Implementation
NodeB becomes intelligent,
with RNC functionality
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3G vs LTE access network
• A hub-and-spoke topology enables communica-tion from base station to controller and controller to base station.
• In an LTE RAN, the base station itself consists of controller functionality and can communicate with another base station directly via any-to-any topology.
LTE network design goals implies coexistence, interoperability, roaming, and handover between LTE and existing 2G/3G networks and services. The expected goal of service providers is to backhaul 2G/3G/LTE mobile traffic through a converged IP/MPLS core network for cost efficiency.
Solutions used in the backhaul IP transport network layer (TNL) for 2G, 3G, and LTE should be similar to use and unify operational tasks such as provisioning, monitoring, and OAM procedures.
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eNB functional planes
The interfaces of eNB are referred as functional planes, all are based on IP:
•User plane (U): this functional plane is used to transfer user data between eNB and S-GW. For each UE a GTP-U tunnel is build between eNB and S-GW.
•Control Plane (C): SCTP is the protocol used to carry control plane protocols, S1-AP between eNB and MME and X2-AP between adjacent eNBs.
•Management Plane (M): the O&M traffic to administer the Flexi BTS
•Synchronization Plane (S): PTP protocol is used to provide synchronization from grandmaster to base station
• The eNB can be configured with separate IP addresses for User, Control, Management and Synchronization Plane applications.
• All applications can share the same IP address, the eNB features a single IP address.
In real world the preferred deployment is to separate management plane form other planes using L2 VLAN traffic separation.
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IPsec Transport
eNodeB has incorporated IPSec functionality
→ each eNodeB site instantiates one Security Gateway function
IPSec Architecture can be implemented in two variants:
• IPSec with „X2 Star“ Architecture: no direct IPSec tunnels between eNBs;
X2 traffic routed through (central) Security Gateway (SEG)
• IPSec with „X2 Mesh“ Architecture: direct IPSec tunnels between eNBs (X2 latency optimization);
X2 traffic switched or routed in mobile backhaul network
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LTE synchronization
2G/3G methods to synchronize the base stations
• clock reference provision by BSC/RNC over T1/E1 connections
• external source such as GPS
LTE synchronization
•Timing-over-Packet is a solution based on IEEE 1588v2 Precision Time Protocol (PTP)
•Synchronization over Packet Network via Ethernet Interface, eliminates the need for TDM link or GPS
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LTE Access Network – Last mile
Two transport medium are used in LTE
• Fiber Access
• Microwave technology
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Protocol Stacks
PDCP
RLC
MAC
UE eNB MME
NAS NAS
RRC
SCTP
IP
L2
L1
S1AP
UDP
IP
L2
L1
GTP-Cv2
S-GW
Uu S1-MME S11
RLC
PHY
RRC
PHY
MAC
PDCP SCTP
L2
L1
S1AP
UDP
IP
L2
L1
GTP-Cv2PMIP
IP
PDCP
UE eNB S-GW
UDP
IP
L2
L1
UDP
IP
L2
L1
PDN-GW
Uu S1-U S5/S8
PHYPHY
PDCP
UDP
L2
L1
UDP
IP
L2
L1
IP
GTP-U
MAC
RLC
GTP-U GTP-U/GRE GTP-U/GRE
RLC
MACUse
r P
lan
e
Co
ntr
ol P
lan
e
P-GW
UDP
IP
L2
L1
GTP-Cv2PMIP
S5/S8
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MME Pooling – S1 Flex
• LTE brings the incorporation of a flexible architecture
• The S1 Flex concept or MME Pooling provides network redundancy and traffic load sharing
• With S1 Flex the eNB is allowed to connect to a maximum of sixteen MMEs
• The operator can increase the overall network availability
• In practice geographical redundancy is desired, connecting each eNB to two MMEs, in different locations.
• The equivalent feature in 3G is Iu Multipoint of SGSN Pooling.
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Multiple Operator Core Network
The MOCN enables the service providers to have separate core networks (MME, SGW, PDN GW) while the E-UTRAN (eNBs) is jointly shared by them.
This is enabled by the S1-flex mechanism by enabling each eNB to be connected to multiple core networks entities.
Options to design the transport between eNB and core networks when MOCN is in use
• Shared Access & Aggregation Network, Separate IP Core Networks
• VLAN Based Traffic Differentiation for Network Separation
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S6a interface
In 3G networks the Gr interface between SGSN and HLR is used to fetch the subscriber profile.
•Gr is based on E1 lines and SS7 protocols
•SIGTRAN (SS7 over IP) implementation brings IP on this interface.
In LTE the MME is using S6a interface, pure IP interface, with SCTP as transport protocol and Diameter as application protocol.
•HSS is implemented using a frontend/backend architecture.
•The design of S6a interface is recommended to be done in such a way that MME maintains Diameter connections to several HSS-FE in parallel (pre-configured Primary and Secondary SCTP paths).
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Optimizing Diameter Network architecture using Diameter Relay Agents
• A fully meshed Diameter network is regarded as quite complex in administration and configuration
• To optimize the network architecture Diameter Relay Agents are introduced
• Diameter Relay Agent is used to forward protocol messages to appropriate Diameter Server.
• DRA plays similar role as STP in SS7 networks
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Diameter Proxies
In roaming case the visited MME has to contact the home HSS in order to fetch the profile of the subscriber.
S6a is pure IP interface with Diameter protocol at application layer
Diameter Based Protocol defines the function of Proxying:
•The operator will use edge proxies to connect to GRX provider
•Edge Proxy Agent is the only point of contact into and out of an operator network at Diameter application layer
•Multiple edge-proxies are recommended for resilience and scalability.
•A Diameter Proxy Agent has similar function as Diameter Relay Agent but it can modify the content of the message in order to address routing of diameter messages between different domains.
•Diameter Proxy Agent can modify messages to enable policy enforcement, resource usage control, admission and provisioning, functions that cannot be done by Diameter Relay Agent.
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Gateway deployments; S5/S8 interface
The main change between 3G gateway (GGSN) and LTE gateway is that LTE gateway functionality is spilt in two elements: S-GW and P-GW.
The interface between S-GW and PGW is called S5 and has two variants: GTP and PMIP.
•S5-PMIP interface CP is based on Proxy Mobile IPv6 and UP is based on GRE
•S5-GTP interface CP is based on GTPv2 and UP is based on GTPv1
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Roaming in LTE
• Roaming for home routed traffic is the similar scenario used at the moment in 3G data networks
• Subscriber traffic is routed from Visited PLMN to Home PLMN via the GRX provider
• The S8 interface is the reference point between visited S-GW and home P-GW
• S8-GTP is a natural choice for roaming as many operators are using GTP for roaming in 2G/3G
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Interworking with other networks
Connection to other PDN networks is managed trough different types of interfaces (S2a/b/c) that also imply different logic for IP address preservation in case of handover.
Most frequent PMIP roles (depending on roaming scenario, roles can be changed):
•S-GW takes the role of a Mobile Access Gateway (MAG), if PMIP-based S5 or S8 is used
•PGW represents the Local Mobility Anchor (LMA) if PMIP-based S5 or S8, or if S2a or S2b is used
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Proxy Mobile IPv6•Managementul mobilitatii localizat
•Terminalul mobil nu e implicat in semnalizarea MIPv6 -> router de acces mobil (MoAR)
•PMIPv6 - (NetLMM – Network Localised Mobility Management)
HA-LMA (Local Mobility Anchor)
AR-MAG (Mobile Access Gateway)
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----------- | HSS/AAA | ----------- | S6 |------------------------------- | ----------- | | | MME | | ------ ----------- S1 | ----------- S5 ----------- | SGi | UE |--+--| eNodeB |--+-|--| UPE |--+--|LTE Anchor|-|--+-- ------ ----------- | | (MAG) | | (LMA) | | | ---------- ------------ | | <----------------> | | routing management by NETLMM | -------------------------------- Evolved Packet Core
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Mobility ManagementMobility Management
– MME – IDLE Mobility and Handovers
– S-GW – LTE and 3GPP user plane mobility
– P-GW – Mobility for non 3GPP interworking
• Mobility Management states– EMM-DEREGISTERED - The UE is not reachable by a MME
– EMM-REGISTERED - The UE location is known and UE has at least one PDN connection
– ECM-IDLE - No NAS signaling connection between UE and network
– ECM-CONNECTED – Signaling connection between the UE and the MME
• Mobility Management Procedures– IDLE mobility – TAU inside of LTE
– Handover – X2 and S1 handover for different scenarios
– Intersystem Mobility – For Idle mobility TAU/RAU
and for handover Relocation/PS handover
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LTE Tracking Area
Tracking area 1Tracking area 2
Tracking area update
MME
Tracking area (TA) is similar to Location/routing area in 2G/3G
Tracking Area Identity = MCC (Mobile Country Code), MNC (Mobile Network Code) and TAC (Tracking Area Code)
When UE is in Idle, MME knows UE location with Tracking Area accuracy
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Handover:• X2 handover (X2 interface between eNodeBs)
– UE Moves from eNodeB to eNodeB using X2
– MME is not changed S-GW can be changed
– eNodeBs makes preparation – MME update GW for downlink
• S1 handover
– The S1-based handover procedure is used when the X2-based handover cannot be used.
– No X2 interface or MME change
– MME handle handover signalling and update S-GW
• Inter RAT handover
– Relocation used in UTRAN
– PS handover used in GERAN
Mobility Management Procedures
MKu
Ue
Source
eNodeB
Target
eNodeB SAE GWMME
Forwarding of Data
Path Switch Request
UP Update Request
UP Update Response
Release Recourse
X2 HO as an example Procedure
Path Switch Ack
Downlink Data
Uplink Data
Downlink Data
End Marker
HO Preparation
HO execution
HO Completion
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Terminology in LTE and in 3G Connection and Mobility Management
3G LTE
PDP context EPS bearer
Location area Not relevant (no CS core)
Routing area Tracking area
Radio access bearer Radio bearer + S1 bearer
GPRS attached EMM registered
Handovers (DCH) when RRC connected
Handovers when RRC connected
RNC hides mobility from core network
Core network sees every handover
Connection management
Mobility management
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Voice solutions
Voice solutions over EPS:
•IMS based VoIP
•Single Radio Voice Call Continuity (SRVCC)
•Circuit Switched Fallback (CSFB)
•NVS VoIP over EPS
IMS provides:•service info via Rx interface•SIP session control for VoIP•Voice application server (CS compatible)•QoS and policy control (Gx, Rx interface)•VoIP emergency call•Gm over Gi (SIP) for voice data transfer
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IMS based VoIP
• IMS Voice machinery is used for PS Voice
• Gx is used for dynamic policy control
• EPS offers dedicated GBR bearer for Voice
MME
S1-MME
S1-U
S11
SGi
User planeControl plane
GatewayPDNServing
LTE
OperatorServices
Internet
CorporateServices
IMS
Gx+
PCRF Rx+
RAN EPC
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Reţele auto-organizante SON
Standardizate 3GPP, NGMN şi studiate în proiectul EU FP7 SOCRATES
Auto-configurare : integrarea automată în reţea a noilor staţii de bază LTE cu ajutorul procedurilor de auto-conectare şi auto-configurareAuto-optimizare : reglarea parametrilor reţelei pentru funcţionare optimă cu ajutorul măsurătorilor Auto-vindecare : detecţie automată, localizarea şi eliminarea erorilorAuto-planificare : recalcularea dinamică a planului de reţea
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Reţele auto-organizante SON
• Procedura de autoconfigurare• Relaţii de vecinătate automate –
procedura ANR• Economisirea energiei• Optimizarea acoperirii si a capacitatii• Adaptarea schemelor multi-antenă (SIMO,
MIMO)• Optimizarea robustă a mobilităţii (Mobility
Robust Optimization)• Optimizarea distribuţiei sarcinilor la
mobilitate
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New concepts for telecom networks
Virtualization
Automatic management of resources
Examples of virtualization of telecom elements:Nokia Siemens Networks – “Open Core System” concept
• “Virtualization achieves extreme flexibility and efficiency in open core networks” • “Open Core software application runs on legacy equipment, on the latest state-of-the-art Commercial off-the-shelf ATCA platforms and on other generic multi-purpose hardware.”
Alcatel Lucent – CloudBand concept• “Using CloudBand, service providers can ‘virtualize’ many of the critical elements of their
networks by converting them into software which is run in the cloud and accessed on demand”
Ericsson – Network-enabled Cloud concept• “The Network-Enabled Cloud builds on computing power in today's telecom assets to both
embed enhanced functionality and to expose network capabilities for new service creation”
Virtual Operator Concept; RAN, Backbone and even Core going towards virtualization
Complex networks are self-managed and self-organized
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References
http://www.3gpp.org/specs/numbering.htm
http://www.3gpp.org/ftp/Specs/html-info/23401.htm
http://www.3gpp.org/ftp/Specs/html-info/23402.htm
http://www.3gpp.org/ftp/Specs/html-info/23060.htm
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