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Efficient Mobile Backhaul
with Carrier Ethernet
Lubo Tancevski

Agenda

LTE Requirements
Impact on Transport Networks:
- OAM and Protection
- QoS
- Services
- Synchronization
- Security
MPLS-TP for LTE backhaul
Conclusions

2 | FutureNet 2010| May 2010

LTE Transformation - Key Technology Shifts
2G/3G
CS Core

MSC
PS Core
GGSN
BTS Backhaul RNC Internet
(Ethernet/TDM/ATM)
SGSN

1 2 3 4 5 6
Radio Mobility Backhaul transition RNC Bearer mobility MCS voice and SGSN CS and PS
Intelligence placed in To IP/Ethernet collapse into packet mobility Collapse into a Pure data services
the eNB the SGW collapse into Unified IP incl. VoIP
Distributed and flat RNC control the SGW backbone
Substantial increase New revenue
IP Architecture collapse into SGSN control
in traffic volume generating services
the MME collapse into
the MME

LTE MME
Multi-Media
Services
Service
Backhaul aware and
mobile aware PCRF
(IP/Ethernet)
IP network P-GW
S-GW

Cost optimization


Transport Requirements for LTE

Node B BSC / IP
RNC
ATM
Core TDM
BTS
Access ePC
node Backhaul transport (MPLS-TP)
(IP/MPLS)
Aggregation S- GW MME
Node B node
eNB

P- GW PCRF
LTE will be introduced as a hotspot in existing 2G and 3G networks
 variety of clients (TDM, ATM, IP/Ethernet)
 Much higher traffic volumes from new data services (video, gaming, SMS)
Transport network technology needed that:
 Is multiservice
 Has low cost per bit for wholesale transport of data services
 Enables seamless transition from existing SONET/SDH to packet transport
and features transport-grade operation in terms of protection and OAM
 Interoperation with the IP/MPLS packet core
MPLS-TP fulfills the above criteria

How is LTE affecting the Network requirements?
Large amount of data traffic accentuates the need for efficient operation and favors L2
transport

 Very fast protection switching and powerful OAM to minimize disruptions and
downtime and facilitate troubleshooting and recovery; L2 transport for lowest-cost
operation
Distributed architecture and new functionalities increase the level of complexity

 Increased security concerns; requirements for L2VPNs; comprehensive OAM to assist
with network operation

VoIP puts strong emphasis on controlled delay/jitter and resilience
 requires OAM with performance monitoring of delay and jitter; strong QoS; fast
protection switching with TE capability

Support for new end user services brings additional requirements

 Requires multicast/broadcast support; heightens security/privacy sensitivities for
banking, location-based services; QoS requirements for video traffic; OAM with
performance measurement for video traffic; interoperation with ePC for e2e support


S1-U interface
S11 interface
S1-MME interface

Interconnection between Transport and ePC S5 interface
X2 interface

bearer

MS-PW [Static/T-LDP] PCRF

MPLS-TP IP/MPLS MME
(L2VPN) (L3VPN)

Transport S-GW ePC P-GW

LSP [Static/GMPLS-RSVP-TE] LSP [Static] LSP [RSVP-TE/LDP]
Flattening of the architectures drives similar requirements across the network
 VPN support in both Transport and ePC
 Bearer concept spans radio, S1 and S5 interface and needs to be
provisioned in both Transport and ePC with similar parameters
 Coordination required between S1 and S5 for support of services;
coordinated support for handover
MS-PW for e2e interoperation incl. monitoring and redundancy; Coordinated
tunnel set up
LTE requires stronger coordination between Transport and ePC than 2G/3G
MPLS-TP facilitates coordinated set-up and interoperation

OAM Requirements
Client monitoring (Y.1731)
MS-PW monitoring
LSP monitoring
PCRF
Tandem monitoring

MME
MPLS-TP IP/MPLS
S-GW ePC P-GW
Transport

 Very fast fault detection to detect failures and assist in sub-50ms protection
 Fault localization and notification to assist with troubleshooting complex
network
 Alarm issuance and suppression to simplify management and operation
 Multi-level operation to isolate and monitor section of the network to assist
with troubleshooting
 Delay and loss measurement (on demand and continuous), to assists with SLA
verification and detect causes of performance degradation
MPLS-TP features comprehensive set of OAM tools meeting above requirements


Protection, Client protection and Dual Homing

eNB Access node Access node Aggregation node
Aggregation node S-GW
eNB to access node Transport Network Transport node to S-GW
 Typically several  Mesh and rings  Redundancy in case of
S-GW failure as well as
cables or, less  Failure detection dual-homed links
frequently, several through OAM (MPLS-  Failure Detection
fibers TP) through 802.1ag
 Failure detection CFM/Y.1731; also
 Sub-50ms protection Physical LOS
through 802.3ah EFM switching (linear and
 Detection through
/802.1ag/Y.1731; also ring) MPLS-TP OAM possible
physical LOS  1+1, 1:1, 1:N, bi-  VRRP and MC-LAG
 Protection through directional operation  L2VPN and MAC re-
link aggregation  Local and e2e learning
protection


QOS: the bearer concept
GBR bearer
Non-GBR bearer
EndPoints
transport ePC

UE Radio
S1 S-GW
S5 P-GW
bearer bearer bearer

A bearer provides same packet treatment to the flows from UE to P-GW
(includes radio, S1, and S5 interface)
Guaranteed Bit Rate bearer is characterized by Guaranteed Bit Rate (GBR) and
Maximum Bit Rate (MBR) and guarantees no packet loss due to congestion
Non-Guaranteed Bit Rate bearer offers no guarantees and is the default
Flows mapped to bearers based on demands
 Each flow characterized by QoS Class Identifier QCI and Allocation and Retention
Priority ARP (for establishment and handover)


QOS Mapping
NOTE: The mapping is configurable by operators.

Application layer QoS (QCI) eNodeB P-GW
Signalling, RT/NRT traffic, OM data

mapping Transport (S1) + S5
signal/PTRAU
UDP/TCP UDP/TCP
IP QoS
DSCP marking, DiffServ IP IP
L2/3
Data link layer L2
mapping Physical layer
Physical layer Physical layer
Data link layer QoS
-PPP priority: MC-PPP
-Ethernet QoS: IEEE802.1p/q

In Transport (S1 interface) L2 operation per class of service following MEF 22
(less than 9 CoS)
 Bearers mapped on class of service depending on their requirements
 QoS determined by p-bits, that could be further mapped into MPLS-TP EXP bits
H-QoS needed on the P-GW

Requirements for Multi-Point Operation
New services introduce requirements for the S1 interfaces
 Multicasting support for video: -> E-LAN or E-TEE

 VoIP and data/web: -> E-LINE
 Handover through X2 interfaces with direct communications between eNBs
 E-LAN (preferred) or E-LINE

Architectural requirements for multipoint connections -> L2VPN required
 S1-Flex
 S-GWs pools and MME pools; load balancing
 MME and control signaling
- idle mode tracking and paging; connect set-up
MPLS-TP efficiently supports LTE services
 Support for MEF requirements and specifications

 Full flexibility of operation with L2VPNs


S1-U interface
S11 interface
S1-MME interface

Services for LTE S5 interface
X2 interface

E-LAN for X2
E-TREE for S1

MME

EPC

Transport S-GW PCRF
P-GW

X2 interface defined for handover S1 interfaces carry traffic to/from the
between eNBs S-GW
 Low bandwidth, low delay requirements  UL point to point
 Up to 16 X2 interfaces, (depending on  DL could be point to point or could be
the density of the coverage) point-to-multipoint (video, gaming)
Could be realized by E-LAN or E-LINE Could be realized by E-LAN, E-TREE or
E-LINE

Tracking Area, S-GW Service Area and MME Pool Area
MME Pool Area

S-GW service area
S-GW
MME Pool
S-GW service area
S-GW

MME Pool Area

S-GW service area
PCRF

Tracking area MME Pool
P-GW

Tracking area

S-GW Pool

Tracking Area, S-GW Serving Area and MME Pool Area are important architectural
elements in LTE
 L2VPNs can be set-up per each or combination of them

S1-U interface
S11 interface
S1-MME interface
S1-Flex S5 interface
X2 interface

MME Pool
S-GW 1
L2VPN100

PCRF
S-GW 2 P-GW

S-GW 3

Each eNB needs to have a connectivity to several S-GWs and MMEs:
 UE connect procedure
 Change of MME during handoff/roaming or load balancing
For the connect procedure MME selects an S-GW out of many available S-GWs
 selection based on location, or based on low probability for changing S-GW
MME can initiate load balancing
 initiate load balancing by S1 bearer release with TAU load balancing.
 Establishment of a new S1 bearer to a new S-GW
 MME can initiate an S1 overload and specify new S-GW
L2VPNs facilitate operation

Synchronization requirements: what is important?

Frequency Synchronization
 Always required
 All BS types: Macro, Micro, Pico, Femto
 3GPP values: Wide Area BS 0.05 ppm, Medium Range BS 0.1 ppm, Local Area BS 0.1 ppm

 Single value so far for LTE: Max 50 ppb (ref. 3GPP 36.104 section 6.5.1)

Time Synchronization (same frame start-time among BS) required if
 TDD mode, whatever the BS type (macro, femto etc.)
 FDD mode, in case one of the following features are used (NA for femto)
 eMBMS/COMP/network MIMO
 HO eHRPD / LTE
1588 and Synchronous Ethernet Requirement on every transport node


Synchronization distribution
 IEEE1588v2  GPS
 1588 Master server could be co-  Receiver inside the eNB.
located with the MME or transport  interface RS422
networks will provide time
 Frequency & Phase
synchronization to eNB via specific
1pps + ToD connector  Synchronous Ethernet
 Transport network has its own  Requires Layer 1 clock tree through
master and server all Ethernet devices between clock
master and eNB’s.
 Recommended clock delivery over
IP networks  Synchronous Ethernet supporting
intermediate nodes
 External Timing Port
 High stability internal clock: optional
Synchronous
Ethernet Sync Ethernet
clock master

GPS Ethernet MME PCRF

S-GW P-GW
1588v2 1588v2
client IEEE1588v2 Precision Time server
Protocol

IPSec tunnel
Tunnel endpoints
Security LSP
Security of heightened concern in LTE because of location-based services and
because of the distribution of the role of RNC
Especially concern in the case of mobile backhaul providers
Several technologies could be used depending on the required level of security:
 Radius/EAP
 IPSec for S1 and (less likely) for X2
 Tunnels and 802.1X for X2 or as an alternative to IPSec for S1

Un-trusted Trusted

Transport ePC
MME

Security S-GW
eNB GW PCRF
P-GW


MPLS-TP
MPLS-TP will enable efficient packet transport by transport profiling of IP/MPLS

 Basic MPLS constructs (PW, LSP, tunnel…) assuring seamless interconnection with
IP/MPLS

 Comprehensive multi-level OAM in the data plane only with fast failure
detection, fault localization, alarms and suppression, performance monitoring
and tandem connection monitoring

 Separation of the control and data plane and operation through control plane,
and through NMS without any control plane support
 Fast protection switching in the data plane with support from OAM

 IP-less and IP-based mode of operation in the data plane

Joint work by ITU-T and IETF ensuring convergence of transport and routing specs

 ITU-T TMPLS G.81xx specs available; further TMPLS standardization stopped and
ITU-T will align existing G.81xx specs to the MPLS-TP RFCs when completed

MPLS-TP can provide very efficient backhaul for LTE

Conclusions
LTE brings profound changes:
 Transition to all-packet services including VoIP
 Much increased data rates up to 300Mb/s
 Flat IP and distributed architecture
The transport infrastructure needs to support LTE as well as existing 2G and 3G
LTE has major impact in the following areas:
 Support for Services
 Synchronization
 QoS
 OAM and Resilience
 Security
 Interoperation with packet core
MPLS-TP is shown to be good candidate for LTE transport

www.alcatel-lucent.com
www.alcatel-lucent.com


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