evolved epc for lte by cisco
DESCRIPTION
Evolved EPC for LTE by CiscoTRANSCRIPT
BRKSPG-2022
Evolved Packet Core for LTE Networks
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Mobile Network Evolution - From 2G to 3G
LTE/EPC introduction
LTE/EPC Interfaces and Basic Procedures
- LTE/EPC Architecture and Interfaces
- Basic call flows (attach, intra-LTE mobility)
- Bearers, PDN connections and QoS
- Security
Delivering voice with LTE/EPC
Agenda Evolved Packet Core
From 2G to 3G R8
Improving the mobile data services
© 2012 Cisco and/or its affiliates. All rights reserved. Cisco Public BRKSPG-2022 5
Voice oriented architecture
Re-define fixed wireline services (e.g. SS and IN)
SMS is a signalling transport rather than a data service
Network transport based on TDM
There was wireless ISDN (aka GSM)
Base Station
Controller
(BSC)
Mobile Switching Center +
Visitor Location Register
(MSC/VLR)
Base Transceiver
System (BTS) Mobile
Station
Home Location
Register (HLR) Service Control
Point (SCP) In the beginning….
© 2012 Cisco and/or its affiliates. All rights reserved. Cisco Public BRKSPG-2022 6
… data was circuit switched
One burst every TDMA frame was sufficient to transport a speech frame with source rate of 13 kbit/s
GSM Phase 2 (circa 1996) added Circuit Switched Data support offering 9.6 kbit/s service
High Speed CSD consisted in aggregating multiple timeslot for a single user but resource intensive
BSC MSC
Modem Interworking Function (IWF)
Modified V.110
3.1 kHz audio
or
V110 64k UDI
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BSC MSC/VLR Gateway MSC
BTS
.. and eventually packet data with General Packet Radio System was bolted on
GSM
Radio
GSM
Radio 64 kbps 64 kbps L1bis
MAC
IP
RLC
LLC
SNDCP
Relay MAC
RLC
Nw Services
BSSGP
Relay
L1bis
Nw Services
BSSGP
LLC
SNDCP
L1
L2
IP
UDP
GTP
Relay
L1
L2
IP
UDP
GTP
IP
Packet Control
Unit (PCU) Serving GPRS
Support Node
(SGSN)
Gateway GPRS
Support Node
(GGSN)
IP
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BSC SGSN GGSN
GRX
Visited PLMN Home PLMN
BTS
Home Based GGSN Roaming
GPRS Roaming Exchange (GRX)
GRX Services (as per GSMA IR.34)
DNS routing (for APN translation)
IP transport including routing & QoS
Security
In future release, GRX is enhanced to become IPX (IP exchange) and supports application proxy capabilities (e.g. for SIP), charging, etc.
© 2012 Cisco and/or its affiliates. All rights reserved. Cisco Public BRKSPG-2022 10
3GPP UMTS System
First step towards an all IP network
New radio designed to accommodate greater packet throughput (up to 2Mbits/s initially… In reality, can support up to 384 kbit/s)
Core network remains largely unchanged from 2.5G
Migration to ATM for Radio Access Transport
More control into the RNC
3G RNC
3G MSC
3G SGSN GGSN
IP
ATM/AAL2
ATM/AAL5
Node B
PSTN
© 2012 Cisco and/or its affiliates. All rights reserved. Cisco Public BRKSPG-2022 11
3G Packet Architecture
Radio Network
Controller (RNC) 3G SGSN GGSN
Iu-ps Gn/Gp
WCDMA
Radio
WCDMA
Radio ATM
MAC
IP
RLC
PDCP
Frame
Protocol
AAL2
ATM
AAL2
MAC
RLC
PDCP
ATM
AAL5
IP
UDP
GTP-U
IP
UDP
GTP-U
IP
UDP
GTP-U
ATM
AAL5
L1
L2
IP
UDP
GTP-U
L1
L2
IP
NodeB
© 2012 Cisco and/or its affiliates. All rights reserved. Cisco Public BRKSPG-2022 12
Still Voice over CS bearer on the radio access, data bearer not suitable (latency, overhead)
Option to transport Voice over IP in the Core (see TS 23.205)
Introduction of SS7oIP transport
3GPP R4 Voice Services
Iu-cs
IP
MGW MGW
MSC-s MSC-s
HLR
ATM
Iu-UP
L1/2
IP AAL2
UDP
RTP
L1/2
IP
M3UA
TCAP
INA
P
MA
P
SCTP
SCCP BIC
C o
r S
IP-T
H.2
48
Nb-UP
© 2012 Cisco and/or its affiliates. All rights reserved. Cisco Public BRKSPG-2022 13
L1
RLC
PDCP
MAC
UDP
GTP-U
IP
3GPP R5 to R7: Addressing the Bottlenecks
Serving RNC 3G SGSN GGSN
Gn Iu-ps
IP
UDP
GTP-U
L1
L2
IP
IP
UDP
GTP-U
L1
L2
IP
UDP
GTP-U
L1
AAL5/ATM AAL5/ATM
L1
Frame
Protocol
AAL2/ATM
RLC
PDCP
WCDMA
IP
MAC
L1
Frame
Protocol
AAL2/ATM
WCDMA
Drift RNC
L1
FP
L1
FP
AAL2 AAL2
Node B
HSDPA Removes Drift RNC and
adds intelligence to the Node B
Direct Tunnel allows
SGSN to remove itself
from data plane
HSPA+: Distribute RNC
Data plane to Node B
MAC-HS MAC-HS L2
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3G architrecture summary
Highlighting the growing importance of IP transport
3G MSC-S
3G SGSN GGSN
Core IP
IP RAN
w/ ATM PW
or Native IP
Node B
PSTN
3G RNC
3G MGW
HLR/HSS
SGW
Introducing LTE
The 3GPP All-IP architecture
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What is the LTE/SAE?
Evolved Packet System (EPS) is the technology direction for 3GPP based networks
Long Term Evolution (LTE) is the next generation 3GPP radio access network
- Evolved UMTS Terrestrial Radio Access Network (E-UTRAN)
System Architecture Evolution (SAE) is the 3GPP next generation standard for mobile networks providing:
- Increased Bandwidth
- End-to-End IP
- Simplified Architecture
- Support for multiple radio access technologies
Evolved Packet Core (EPC) is the next generation 3GPP packet core
Consists of (3) main components (MME, SGW, and PGW)
© 2012 Cisco and/or its affiliates. All rights reserved. Cisco Public BRKSPG-2022 17
The LTE Revolution
Radio Side (Evolved UTRAN - EUTRAN)
- Improvements in spectral efficiency, user throughput, latency
- Simplification of the radio network
- Efficient support of packet based services: Multicast, VoIP, etc.
Network Side (Evolved Packet Core - EPC)
- Improvement in latency, capacity, throughput, idle to active transitions
- Simplification of the core network
- Optimization for IP traffic and services
- Simplified support and handover to non-3GPP access technologies
© 2012 Cisco and/or its affiliates. All rights reserved. Cisco Public BRKSPG-2022 18
LTE/EPC Key Attributes
Higher Bandwidth (>100 kbps per user on average) and improved latency
- Transmission and transition delays <10 & 100ms resp. in unloaded conditions
Service independent and data-only architecture
- Strict data QoS mechanism with no voice dedicated bearer identifictaion
Always-on model
- All registered users have a default bearer established used for signalling
IP addressing
- IPv6 by default with dual stack sessions (IPv4v6)
Support of alternative access technologies
- 3GPP and non-3GPP architecture, including possible wireline access
Local breakout
- Part of the traffic may be routed directly in the visited network
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3GPP Mobile Network Evolution
EPS = Evolved Packet System
GERAN
UTRAN
E-UTRAN
(LTE)
Non-3GPP
Access
Evolved
Packet Core
(EPC)
CS Network
LTE (Long Term Evolution) is the 3GPP WI that defined the E-UTRAN
SAE (System Architecture Evolution) is the 3GPP WI that defined the EPC
IP Services
/ Internet
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Evolved Packet System Architecture
GGSN RNC SGSN
NodeB
RNC
PGW
MME
eNodeB
SGW
PDN/
Internet
PDN/
Internet
From hierarchical architecture to flat IP topology
Open to centralized or distributed deployments
RNC functions distributed between the eNB and the EPC
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Destination
Network
LTE/EPC Key Components
Next
Generation
Cell Site
Mobility
Control
Node
PDN
interconnect
Mobility
Anchor
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UMTS, LTE/SAE Architecture:
Comparison
SGSN MME + Serving GW
- In the LTE architecture the SGSN functionality is split into MME & Serving GW
MME = Control Plane of SGSN
Serving GW = Data Plane of SGSN
GGSN PDN GW
- The PDN GW has similar function as the GGSN
IP Anchor
Policy Enforcement
Accounting/Charging
Deep Packet Inspection
© 2012 Cisco and/or its affiliates. All rights reserved. Cisco Public BRKSPG-2022 23
UMTS, LTE/SAE Architecture:
Comparison
eNB
MME S-GW
P-GW
eNB
RNC
nodeB
SGSN
GGSN
nodeB
SGSN
GGSN
AAA HSS PCRF
UMTS UMTS
(Direct Tunnel) LTE-SAE
HSS/HLR
IuPs
Gn/Gp
Gi
Gi
Gx
Gr
S6a S6b
Gx
GTP-U
IuPs
S1-MME
S5/S8
S1-U
Gxc
SGi
Iub
S11
Gr
Gx
Iub
Gn/Gp
RNC
nodeB nodeB
Iub Iub
S10 Gn/Gp Gn/Gp
OCS CGF
Ro Ga
LI
ADMF/DF
X1,x2,x3
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Key 3G <-> LTE terminology differences
3G
Primary PDP Context
Secondary PDP Context
Routing Area
P-TIMSI (Packet-
Temporary IMSI)
Attach
RAB Assignment
Request (Primary)
RAB Assignment
Request (Secondary)
LTE
Default Bearer
Dedicated Bearer
Tracking Area
GUTI (Globally Unique Temp ID)
includes GUMMEI)
Attach + Default Bearer Act
Initial Content Setup Request
Bearer Setup Request
© 2012 Cisco and/or its affiliates. All rights reserved. Cisco Public BRKSPG-2022 25
EPC Protocol Stacks – Signalling Plane
UE
MME
S-GW
Evolved UTRAN (E-UTRAN) Evolved Packet Core (EPC)
HSS
PCRF
PDN-GW
MAC
RLC
PDCP
OFDMA
NAS
MAC
RLC
PDCP
OFDMA
L2
IP
L1
SCTP
S1-AP RRC RRC
L2
IP
L1
SCTP
S1-AP
NAS
S1-MME
36.413
S1-MME
eNodeB
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EPC Protocol Stacks – Data Plane
UE
MME
S-GW
Evolved UTRAN (E-UTRAN) Evolved Packet Core (EPC)
HSS
PCRF
PDN-GW
IP
L1
L2
IP (user)
IP
UDP
GTP-U
L1
L2 MAC
RLC
PDCP
OFDMA
IP (user)
MAC
RLC
PDCP
OFDMA
IP
UDP
GTP-U
L1
L2
IP
UDP
GTP-U
L1
L2
PMIP
S1-U S5/S8
S1-U
36.414 GRE GRE UDP
PMIP GTP-U S5/S8
29.274
(GTP)
-
29.275
(PMIPv6)
eNodeB
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EPC Protocol Stacks – X2 interface
UE
MME
S-GW
Evolved UTRAN (E-UTRAN) Evolved Packet Core (EPC)
HSS
PCRF
PDN-GW
X2
L2
IP
L1
SCTP
X2-AP
L2
IP
L1
SCTP
X2-AP
X2-C
L2
IP
L1
UDP
GTP-U
L2
IP
L1
UDP
GTP-U
X2-U
36.423 36.424
eNodeB
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EPC Roaming
Home Gateway Model
UE vS-GW
HSS PCRF
hPDN-GW
S8
MME
Visited Network
Home Network
S6a
Gx
eNodeB
Operator’s
IP Services
(e.g. video, IMS)
Rx
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EPC Roaming
Visited Gateway Model aka Local Breakout
UE eNodeB vS-GW
HSS hPCRF
vPDN-GW
MME
Visited Network
Home Network
vPCRF
S9 S6a
Gx
Operator’s
IP Services
(e.g. video, IMS)
Rx
LTE/EPC Interfaces and Basic Procedures
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PCRF HSS
Gx
eNodeB combines some RNC functionality with LTE radio
MME (Mobility Management Entity) controls network selection, attach and mobility
- HSS for subscriber authentication
SGW (Serving GateWay) provides local mobility anchor, inter PLMN roaming, accounting
PGW (Packet Data Network GateWay) provides IP anchor, QoS and charging enforcement PCRF for PCC and QoS rules, service authorization
In case of PMIP access, the SGW interacts with PCRF and PGW with AAA
S5/S8 SGi S1-U
S1-MME
S11
S6a
LTE-Uu
PDN
DNS
UE selects PLMN and eNodeB and sets
up radio resources
eNB selects MME and sets up
connection if none established
previously
MME retrieves subscription information
and/or authenticates UE with HSS
DNS used to resolve APN and aid in
selecting PGW/SGW
MME sends Create Session Request to
SGW to set up default bearer
SGW forwards Create Session Request
to PGW to set up default bearer (GTP
S5 case)
PGW may retrieve PCC and QoS rules
for default bearer from PCRF
PGW assigns IP address(es) and binds
bearer to the PCC/QoS/billing rules
All elements (SGW, MME, eNB) are
updated and now traffic can flow
LTE Initial Attach
SGW PGW
eNB UE
MME
TS 23.401 Ch. 5.3.2.1 (for GTP S5)
or TS 23.402 Ch. 5.2 (for PMIP S5)
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EPS Bearers
An EPS bearer uniquely identifies traffic flows that receive a common QoS treatment between a UE and a PDN GW (GTP) or SGW (PMIP)
Default bearer is assigned during attach and provides always‐on IP connectivity
- Internet‐like default connectivity for QoS‐agnostic needs (browser, email, etc.)
Dedicated bearer is assigned only when needed to provide guaranteed bit rate QoS control
- Assigned only for those QoS sensitive applications that can be recognized
PGW SGW UE S5
eNB
Default Bearer: network initiated during the Attach
PDN/
Internet
Dedicated Bearer: network initiated when needed
S1 SGi
1 PDN Connection
Example for S5 GTP
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Multiple PDNs Connectivity
Each PDN connection has one default bearer - possibly one or more dedicated bearers
All bearers of the same PDN Connection use the same IP address(es) - IPv4, IPv6, or IPv4v6 (dual-stack)
Multiple PDN connections may be served by one or more PGW nodes - The UE can be attached to a single SGW at any point in time
Corporate
Network
Internet
IMS
PGW
SGW UE eNB
PGW
APN “corp.com”
PDN Type IPv4
APN “internet”
PDN Type IPv4v6
APN “IMS”
PDN Type IPv6
Default Bearer
Dedicated Bearer
© 2012 Cisco and/or its affiliates. All rights reserved. Cisco Public BRKSPG-2022 36
Dedicated Bearer Activation
The PGW may activate a dedicated bearer, possibly after indications from UE or PCRF
The UE can only ask for the amount of resources, the network decides whether an existing bearer is modified or a new one is established.
3. Create Bearer Request
MME Serving GW PDN GW PCRF
4. Bearer Setup Request/ Session Management Request
5. RRC Connection Reconfiguration
2. Create Bearer Request
6. RRC Connection Reconfiguration Complete
7. Bearer Setup Response
10. Create Bearer Response
eNodeB UE
(A)
(B)
1. IP-CAN Session Modification
12. IP-CAN Session Modification
11. Create Bearer Response
8. Direct Transfer 9. Session Management Response
© 2012 Cisco and/or its affiliates. All rights reserved. Cisco Public BRKSPG-2022 37
Setting up additional PDN connection
The UE initate the request indicating the APN for the PDN connection
Multiple APNs/PDNs must be managed by the UE and the applications
PDN Connectivity Request (APN,…)
UE MME S/PGW
Create Session Request
Create Session REsponse Bearer Setup Req. (def bearer)
eNB
RRC Bearer Setup Resp
PDN Connectivity Accept
PDN Connectivity Complete Modify Bearer
© 2012 Cisco and/or its affiliates. All rights reserved. Cisco Public BRKSPG-2022 38
Quality of Service in the EPS
• QoS parameters per EPS‐bearer
- QoS Class Identifier (QCI)
Scalar value used for scheduling/RRM decisions
- Allocation and Retention Priority (ARP)
Used to accept/modify/drop bearers in case of resource limitation
- Guaranteed Bit Rate (GBR) and Maximum Bit Rate (MBR) only for dedicated bearers
• QoS paramers per group of EPS‐bearers
- Aggregate Maximum Bit Rate (AMBR)
Only for non‐GBR bearers, APN-AMBR and UE-AMBR
• Static mapping to/from 3GPP QoS partially standardized
- QCI ranges Traffic Classes
TS 23.401 Annex E
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EPS Security
E- UTRAN
MME
eNB
UE
HSS S6a
(Auth Vectors)
EPS AKA via S6a
Challenge and keys exchange
Mutual Authentication
NAS Integrity/Ciphering RRC Integrity and ciphering
U-Plane Ciphering
USIM required for LTE
Different set of keys used for ciphering, derived from the same original K stored in the USIM/HSS
© 2012 Cisco and/or its affiliates. All rights reserved. Cisco Public BRKSPG-2022 40
LTE Mobility Management
EPS Mobility Management (EMM) defines the relation between UE and MME resulting from mobility
EPS Connectivity Management (ECM) is related to the signaling connection between UE and MME
RRC state is related to the connection established between UE and E‐UTRAN
ECM-IDLE
EMM-DEREGISTERED
UE position unknown
No Context allocated
Signaling connection
establishment
Signaling connection
release
Attach
Detach
EMM-REGISTERED
ECM-CONNECTED
RRC_IDLE RRC_CONNECTED
ECM-IDLE
RRC_IDLE
UE position known at eNB level
Network controlled HO
Power
On
IP address(es)
allocated to the UE
UE position known at TA level
Cell reselection, paging
© 2012 Cisco and/or its affiliates. All rights reserved. Cisco Public BRKSPG-2022 41
EPS Connectivity
UE and E‐UTRAN enter RRC‐CONNECTED state when the signaling connection is established between UE and E‐UTRAN
UE and MME enter ECM‐CONNECTED state when the signaling connection is established between UE and MME
Discontinuous Reception/Transmission (DRX/DTX) on the radio can influence the time the UE is in Connected/Idle mode
- E.g. maintain the UE in Connected mode with DRX cycle as long as the paging interval to save battery when the user is not transferring data
MME eNB UE RRC Connection S1 Connection
ECM Connection
TS 36.331 TS 36.413
© 2012 Cisco and/or its affiliates. All rights reserved. Cisco Public BRKSPG-2022 42
TAI list 1
Short TA List: more TAU, less Paging
Long TA list: less TAU, more Paging
Tracking Area Update vs. Paging
MME
Enter Idle
Mode
Paging
Paging
Paging
Paging Paging
Paging
Incoming data
Enter
Connected
Mode
TAI list 2
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TAU Procedure
The TAU may require a relocation of the MME (as in the picture) and/or also of the SGW
The new MME identifies the old MME from the MME Id included in the GUTI (Global Unique Temp. Id) sent in the Request
eNB eNB
Old MME
TAI not in
TAI list
Context Resp
Context
Request.
No UE context
availablle
TAU Request
HSS
NewMME
TAI list 2 TAI list 1 TAU Accept
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X2 Based Handover
Data forwarding over X2 interface only during the handover
Fully eNB controlled, the EPC network is notified at the end
Better performance than S1 based handover, but requires additional connectivity in the RAN
eNB eNB
MME SGW
Measurement
Reports
HO Request
HO Request Ack.
HO Command Data forwarding
HO
Confirm
Path Switch Req.
Update Bearer
© 2012 Cisco and/or its affiliates. All rights reserved. Cisco Public BRKSPG-2022 45
MME Pooling
Load Balancing: the MME sends a weight factor (RMC) to be used by the eNB for MME selection
Load re-balancing: procedures for node offload (O&M operation)
MME relocation required for load re-balancing or for mobility across different MME pool areas
UE
eNB eNB eNB eNB eNB
E-UTRAN MME Pool: area served by
one or more MME within
which a UE may be served
without need to change the
serving MME.
MME-1
RMC=1
MME-3
RMC=3
MME-2
RMC=2
RMC = Relative MME Capacity
© 2012 Cisco and/or its affiliates. All rights reserved. Cisco Public BRKSPG-2022 46
EPC Node Selection
Process of Discovering/Choosing PGW, SGW, MME: - Initial Attach (PGW and SGW)
- Additional PDN Connection (PGW)
- Relocation/Handover (SGW, MME)
The MME shall select: - a PGW that provides the connectivity for a given APN
- a SGW to serve UE’s location
- a new MME to serve the target location (in case of relocation)
Dynamic discovery via DNS NAPTR - APN-FQDN for PGW
internet.apn.epc.mnc123.mcc456.3gppnetwork.org
- TAI-FQDN for SGW and MME
tac-lb12.tac-hb34.tac.epc.mnc123.mcc456.3gppnetwork.org
Selection based on multiple criteria - Co-location, static DNS indications
TS 23.003,
TS 29.003
TS 23.401
© 2012 Cisco and/or its affiliates. All rights reserved. Cisco Public BRKSPG-2022 47
PMIP tunnel (no QoS)
Policy Control
GTP S5 Gx for enforcement in the PGW - PCEF (Policy and Charging Enforcement) in the PGW
PMIP S5 Gxc for enforcement in the SGW - No QoS information in PMIP
PGW
PCRF
TS 29.212
SGW UE
AF
S5
Gxc
Gx
Rx Event &
Access
Info
QoS
rules
Rules
Event &
Access
Info
Notifications
session
request
eNB
EPS bearer with PMIP S5
EPS bearer with GTP S5 On-path PCC
Off-path PCC
TS 29.214
Voice over LTE Strategies
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Voice & SMS Services Providing Legacy Services in an LTE Network
The EPS architecture (3GPP Rel 8) is the first 3GPP all-IP architecture
Voice and SMS are still the cash cows for mobile operators
• Migration is critical
• User experience must be preserved
CSFB is the interim solution recommended by NGMN
IMS is the target solution for Telephony and Multimedia Services
OneVoice IMS profile ‘simplifies’ implementation for VoLTE
NGMN and OneVoice initiatives reduce risk of industry fragmentation
SMS typically required before voice due to EU regulatory requirements for data roaming services
© 2012 Cisco and/or its affiliates. All rights reserved. Cisco Public BRKSPG-2022 50
Circuit Switched Fallback (23.272) Delivery of SMS to EPC Attached Subscriber
S1-MME
SGs
S11
S6a
IuCS / A
S1-U
During EPC attach, CSFB UE’s are also attached over SGs to MSC
MME maintains mapping of TA to LA to determine appropriate MSC to establish SGs association with
SMS can be delivered/sent without FallBack to legacy radio (SGs interface includes SMS payload capability)
CSFB UE E-UTRAN Serving/ PDN GW
MME
UTRAN / GERAN
MSC
HSS
Incoming SMS 1
SMS is delivered via SGs interface 2
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Circuit Switched Fallback (23.272) Delivery of Terminating Voice Session to EPC Attached Subscriber
S1-MME
SGs
S11
S6a
IuCS / A
S1-U
SGs interface is used to inform UE of incoming call
SGs Paging triggers UE to retune to 2G or 3G legacy network
Page Response sent via the legacy radio network
Call terminates to UE ‘normally’
CSFB UE E-UTRAN Serving/ PDN GW
MME
CSFB UE UTRAN / GERAN
MSC
HSS
Incoming Call – delivered to VMSC which has SGs association for this subscriber
1
UE is paged via the SGs interface 2
UE retunes to 2G/3G RAT on receipt of page
3
UE Responds to paging – incoming call terminated via standard 2G/3G procedures
4
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Voice over IMS Mobile Origination
ISC
Mw
S1-MME
Sv
S11
Mg
SGi
(Gm from UE)
S6a
IuCS / A
IuPS / Gb
S3
S1-U
Cx
IMS (HPLMN)
To enable mid-call mobility, S-CSCF anchors call at SCC AS
TAS provides end-user services (e.g. IR.92)
MGCF provides breakout to PSTN or other CS networks
P-CSCF
SR-VCC UE E-UTRAN Serving/
PDN GW
MME
UTRAN /
GERAN
MSC Server
(SR-VCC)
SGSN
(SR-VCC)
I/S-CSCF
HSS
TAS SCC AS IP-SM-GW
MGCF
Subscriber has already registered
into IMS following EPC attach
UE Originates
Call
1
2
© 2012 Cisco and/or its affiliates. All rights reserved. Cisco Public BRKSPG-2022 53
Voice over IMS UE roams during active call – SR-VCC mobility
ISC
Mw
S1-MME
Sv
S11
Mg
SGi
(Gm from UE)
S6a
IuCS / A
IuPS / Gb
S3
S1-U
Cx
IMS (HPLMN)
SCC AS performs leg management – hides mobility events from other IMS application servers
SR-VCC only works in one direction – LTE -> 2G/3G
Requires upgrades on legacy MSC infrastructure
P-CSCF
SR-VCC UE E-UTRAN Serving/
PDN GW
MME
SR-VCC UE UTRAN /
GERAN
MSC Server
(SR-VCC)
SGSN
(SR-VCC)
I/S-CSCF
HSS
TAS SCC AS IP-SM-GW
MGCF
UE retunes to 2G/3G
RAT during active call
1
New call leg
established
2
SCC AS performs
bearer management
and tears down original
leg
3
© 2012 Cisco and/or its affiliates. All rights reserved. Cisco Public BRKSPG-2022 54
CSFB – Deployment Challenges
Some of the major challenges/difficulties facing CSFB rollout are:
Legacy network dependencies
Continued legacy network spend/investment
Fallback latency / post-dial delay
Ongoing operational complexity (TA/LA mapping)
© 2012 Cisco and/or its affiliates. All rights reserved. Cisco Public BRKSPG-2022 55
CSFB – MSC/VLR Selection As defined in 23.272
TA1 TA2 TA3
LA1 LA2
MSC/VLR1
MSC/VLR2
TA1 TA2 TA3
LA1 LA2
MME
MSC/VLR1
MSC/VLR2
TA LA MSC/VLR
TA1 LA1 MSC/VLR1
TA2 LA1 MSC/VLR1
TA3 LA2 MSC/VLR2 MME
TA LA MSC/VLR
TA1 LA1 MSC/VLR1
TA2 LA1 MSC/VLR1
TA3 LA2 MSC/VLR2
Mapping Error Area
© 2012 Cisco and/or its affiliates. All rights reserved. Cisco Public BRKSPG-2022 56
Roaming Retry TS 23.272/23.018
The Roaming Retry (complex) procedure is applied for mobile terminated calls where the MSC, to which the UE sends the LAU, is different from the MSC that sent the paging message to the UE.
MME
GMSC
VMSC
VMSC
1. IAM 4. IAM
5. SGs Page
6. Page
7. Location Update
HLR
2. SRI
3. PRN
8. UL
MME
GMSC
VMSC
VMSC
10. RCH (Resume Call Handling)
13. Call Establishment
HLR
11. SRI
9. Cancel Location
12. PRN
12. IAM
Scenario Leading to Roaming Retry Requirement
Roaming Retry Invocation
© 2012 Cisco and/or its affiliates. All rights reserved. Cisco Public BRKSPG-2022 57
TA to LA Mapping Implementation Challenges
Most network operates deploying LTE already have both 2G and 3G networks
Mapping process has to take into account
When UE falling back, is it likely to go to 2G or 3G overlapping cells?
Where cell boundaries between 4G and 2G (or 3G) do not perfectly align, which is provisioned?
As cells ‘breathe’, boundaries become less predictable
4G networks will be growing rapidly in near-term – requires constant ‘tweaking’ of provisioning tables
4G TA’s
3G LA’s
2G LA’s
?
One major tier-1 EMEA operator has already concluded that it is not difficult to maintain accurate TA to LA mappings... ...it is, in their view, impossible
Therefore, Roaming Retry invocation will be more common than expected even though considerable effort may be expended maintaining tables
© 2012 Cisco and/or its affiliates. All rights reserved. Cisco Public BRKSPG-2022 58
Dependencies for CSFB As Specified by TS 23.272
UE
UE must support CSFB procedures as defined with TS 23.272
MME
Must support SGs interface
Must support MSC/VLR selection procedures
MSC
Must support SGs interface (legacy MSC’s will require addition of IP interface cards)
Should support Roaming Retry procedure to minimise call drops
HLR
Should support Roaming Retry procedure to minimise call drops
© 2012 Cisco and/or its affiliates. All rights reserved. Cisco Public BRKSPG-2022 59
Cisco CSFB Product Strategy
Cisco has developed a CSFB product strategy that addresses:
Inefficient operational deployment model – operators not forced to upgrade legacy MSC and HLR platforms
Investment legacy Capex spend – no investment required on legacy MSC or HLRs
Complicated MME provisioning procedure – requires only static TA-LA mappings
The Cisco solution places no dependencies on existing network elements (CS or EPC)
Supports both SMS (originate/terminate) and Voice (CSFB)
Roaming Retry procedural support not required
© 2012 Cisco and/or its affiliates. All rights reserved. Cisco Public BRKSPG-2022 60
CSFB IWF – Architectural Fit
CSFB IWF
MSC/VLR
MMESGs
E-UTRANS1-MME
GERAN/
UTRAN
A/Iu
UE
LTE-Uu
Um
HSS
S6a
HLR
MAP
MAP
SMSC
MAP
CSFB IWF supports only SGs and MAP interfaces
Appears as a ‘thin’ MSC/VLR – is allocated a pseudo LA
Does not touch the bearer traffic within legacy network
© 2012 Cisco and/or its affiliates. All rights reserved. Cisco Public BRKSPG-2022 61
EPC Attach / Location Update Procedure
1. UE Registers in LTE
2. Serving MME registers with HSS
3. Serving MME informs registered VLR
(CSFB IWF)
4. CSFB IWF registers as serving MSC with
HLR
HLR
MME
3G Core
4G Core HSS
MSC
RNC
3G Access
4G Access
CSFB IWF
4
3
2
1
MAP
SGs
4G UE
E-UTRAN
3G/4G Device
© 2012 Cisco and/or its affiliates. All rights reserved. Cisco Public BRKSPG-2022 62
Mobile Originated SMS
1. UE initiates SMS
2. MME sends SMS to serving MSC (CSFB
IWF)
3. CSFB IWF sends SMS to SMSC › CSFB IWF performs SMS MO service logic › CSFB IWF performs SMS MO billing › CSFB IWF performs LI if required
HLR
MME
3G Core
4G Core HSS
MSC
BSC/RNC
3G Access
4G Access
CSFB IWF
3
2
MAP
SGs
SMSC
4G UE
E-UTRAN
3G/4G Device
1
© 2012 Cisco and/or its affiliates. All rights reserved. Cisco Public BRKSPG-2022 63
Mobile Termination SMS
1. Incoming SMS to SMSC
2. SMSC queries HLR to determine routing
3. SMSC sends SMS to serving MSC (CSFB
IWF)
4. CSFB IWF sends SMS to MME › CSFB IWF performs SMS MT service logic › CSFB IWF performs SMS MT billing › CSFB IWF performs LI if required
5. MME sends SMS to UE
HLR
MME
3G Core
4G Core HSS
MSC
RNC
3G Access
4G Access
CSFB IWF
3
2
MAP
SGs
SMSC
4
1
4G UE
E-UTRAN
3G/4G Device
5
© 2012 Cisco and/or its affiliates. All rights reserved. Cisco Public BRKSPG-2022 64
Mobile Origination
1. UE leaves LTE and re-tunes to
GSM/UMTS
2. UE Location Updates on GSM/UMTS
3. HLR sends Cancel Subscriber to CSFB IWF
› CSFB IWF Removes subscriber from VLR
4. UE initiates call
HLR
MME
3G Core
4G Core HSS
MSC
RNC
3G Access
4G Access
CSFB IWF
4
2
1
3G Device
MAP
SGs
3
4G UE
E-UTRAN
3G/4G Device
Note: MO Procedure utilised for Call Originations,
USSD and also for SS modifications
© 2012 Cisco and/or its affiliates. All rights reserved. Cisco Public BRKSPG-2022 65
Mobile Terminated Call Signalling times and delays example
MME
GMSC
IWF
VMSC
1. IAM
5. Page
HLR
2. MAP SRI
10. MAP PRN
Note: only key messages are shown for simplicity (e.g. not all acknowledgments are shown)
4. SGs Page T0+7ms
6. LU
7. MAP UL
8. MAP CL T0+2222ms
9. SRI T0+2767ms
12. SRI ACK T0+2869
13. MAP PRN Resp T0+2880ms
11. MAP PRN Resp
14. MAP SRI Ack
15. IAM
16. Page
3. MAP PRN T0
Inserts MSRN from VMSC into original PRN
Response This delay may vary depending on RAN
conditions
500 ms additional delay to avoid race conditions
© 2012 Cisco and/or its affiliates. All rights reserved. Cisco Public BRKSPG-2022 66
Benefits of CSFB IWF
Solution enables deployment of SMS over SGs and CSFB through a centralised gateway
Does not require SGs software licensing (or IP hardware upgrades) on any network MSCs
Operators no longer locked in to a existing vendors (current MSC suppliers) for CSFB solution
Reduced operational rollout costs and complexity
Common platform for other Cisco CSP services – ensures investment protection moving forward into IMS
Requires no specific TA to LA mapping changes on MME (i.e. MME is provisioned as if it is connecting to standard SGs interface)
Does not require or utilize Roaming Retry
Signalling only solution, no bearer impact
© 2012 Cisco and/or its affiliates. All rights reserved. Cisco Public BRKSPG-2022 67
VoLTE (IMS) – Deployment Challenges
Some of the major challenges/difficulties facing VoLTE rollout are:
Service parity/consistency
Network complexity
Back office (re)integration
Legacy network dependencies (SR-VCC)
Call routing and optimisation
© 2012 Cisco and/or its affiliates. All rights reserved. Cisco Public BRKSPG-2022 68
Single Radio Voice Call Continuity
SR-VCC
Voice call anchored in IMS over PS (e.g. LTE) access
UE moves to area of CS access only
UE is capable of transmitting/receiving on only one of those access networks at a given time.
Mobility handled at two levels
Radio
S1, Sv and MAP-E signaling
Application
SIP / SDP
Requires Service Centralization and Continuity Application Server (SCC AS)
From SCC AS perspective, seen as a PS to CS access transfer
© 2012 Cisco and/or its affiliates. All rights reserved. Cisco Public BRKSPG-2022 69
Additional Resources
- www.3gpp.org
- http://www.thespectool.com/v2/index.php
Relevant 3GPP Specifications:
• TS 36.300 E-UTRA and E-UTRAN Overall description; Stage 2
• TS 36.331 E-UTRA; Radio Resource Control (RRC); Protocol specification
TS 23.401 GPRS enhancements for E-UTRAN access (EPC)
TS 23.402 Architecture enhancements for non-3GPP access
• TS 24-301: Non-Access-Stratum (NAS) protocol for EPS; Stage 3
• TS 29.272: EPS; MME and SGSN related interfaces based on Diameter protocol
• TS 33.401 3GPP SAE; Security architecture
Recommended Reading
Please visit the Cisco Store for suitable reading.
© 2012 Cisco and/or its affiliates. All rights reserved. Cisco Public BRKSPG-2022 71
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