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Efficient Mobile Backhaul

with Carrier Ethernet

Lubo Tancevski

2 | FutureNet 2010| May 2010

Agenda

LTE Requirements

Impact on Transport Networks:

- OAM and Protection - QoS- Services- Synchronization- Security

MPLS-TP for LTE backhaul

Conclusions


LTE Transformation - Key Technology Shifts

2G/3G

RNCGGSN

LTE

Radio Mobility

Intelligence placed in

the eNB

Pure data services

incl. VoIP

1 2 4

BTS Internet

Multi-Media

Services

SGSN

Cost optimization

MSC

Backhaul

(Ethernet/TDM/ATM)

S-GW

RNC Bearer mobility

collapse into

the SGW

3Backhaul transition

To IP/Ethernet

Backhaul

(IP/Ethernet)

MCS voice and SGSN

packet mobility

collapse into

the SGW RNC control

collapse into

the MME

SGSN control

collapse into

the MME

CS Core

PS Core

5

CS and PS

Collapse into a

Unified IP

backbone

Service

aware and

mobile aware

IP network

6

MME

Substantial increase

in traffic volume

Distributed and flat

IP Architecture

P-GW

PCRF

New revenue

generating services


Transport Requirements for LTE

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

BSC / RNC

BTS

Node B

Node BeNB

ePC

(IP/MPLS)

Core

Backhaul transport (MPLS-TP)

IP

ATM

TDM

P- GW

MMES- GW

Accessnode

Aggregationnode

PCRF


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


MPLS-TP(L2VPN)

Interconnection between Transport and ePC

IP/MPLS(L3VPN)

LSP [Static/GMPLS-RSVP-TE] LSP [RSVP-TE/LDP]LSP [Static]

MS-PW [Static/T-LDP]

MME

ePC

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

Transport S-GW

S1-U interface

S11 interface

S1-MME interface

S5 interface

X2 interface

S1-U interface

S11 interface

S1-MME interface

S5 interface

X2 interface

P-GW

bearer

PCRF


OAM Requirements

MME

ePCTransport S-GW P-GW

MS-PW monitoring

Client monitoring (Y.1731)

LSP monitoring

Tandem monitoring

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

IP/MPLSMPLS-TP

PCRF


Protection, Client protection and Dual Homing

eNB to access node

Typically several

cables or, less

frequently, several

fibers

Failure detection

through 802.3ah EFM

/802.1ag/Y.1731; also

physical LOS

Protection through

link aggregation

Transport Network

Mesh and rings

Failure detection through OAM (MPLS-TP)

Sub-50ms protection switching (linear and ring)

1+1, 1:1, 1:N, bi-directional operation

Local and e2e protection

S-GW

Transport node to S-GW

Redundancy in case of S-GW failure as well as dual-homed links

Failure Detection through 802.1ag CFM/Y.1731; also Physical LOS

Detection through MPLS-TP OAM possible

VRRP and MC-LAG

L2VPN and MAC re-learning

eNB Access node Aggregation node

Access node Aggregation node


QOS: the bearer concept

UE S-GW

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)

GBR bearer

Non-GBR bearer

P-GWS1 bearer

S5bearer

Radio bearer

EndPoints

transport ePC


QOS Mapping

signal/PTRAU

UDP/TCP

IP

Data link layer

Physical layer

Application layer QoS (QCI)Signalling, RT/NRT traffic, OM data

IP QoSDSCP marking, DiffServ

mapping

Data link layer QoS-PPP priority: MC-PPP

-Ethernet QoS: IEEE802.1p/q

eNodeB

IP

L2

Physical layer

P-GW

NOTE: The mapping is configurable by operators.

mapping

UDP/TCP

Transport (S1) + S5

L2/3

Physical layer

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


Services for LTE

EPC

S-GW

E-LAN for X2

Transport

MME

S1-U interface

S11 interface

S1-MME interface

S5 interface

X2 interface

S1-U interface

S11 interface

S1-MME interface

S5 interface

X2 interface

X2 interface defined for handover between eNBs

Low bandwidth, low delay requirements

Up to 16 X2 interfaces, (depending on the density of the coverage)

Could be realized by E-LAN or E-LINE

P-GW

E-TREE for S1

S1 interfaces carry traffic to/from the S-GW

UL point to point

DL could be point to point or could be point-to-multipoint (video, gaming)

Could be realized by E-LAN, E-TREE or E-LINE

PCRF


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

MME Pool

S-GW

MME Pool

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

MME Pool Area

MME Pool Area

S-GW service area

S-GW service area

S-GW

S-GW service area

Tracking area

Tracking area

P-GW

PCRF


S1-Flex

S1-U interface

S11 interface

S1-MME interface

S5 interface

X2 interface

S1-U interface

S11 interface

S1-MME interface

S5 interface

X2 interface

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

MME Pool

S-GW 2

L2VPN100

P-GW

S-GW 3

S-GW 1

PCRF


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

1588 Master server could be co-located with the MME or transport networks will provide time synchronization to eNB via specific 1pps + ToD connector

Transport network has its own master and server

Recommended clock delivery over IP networks

External Timing Port

GPS

Receiver inside the eNB.

interface RS422

Frequency & Phase

Synchronous Ethernet

Requires Layer 1 clock tree through all Ethernet devices between clock master and eNB’s.

Synchronous Ethernet supporting intermediate nodes

High stability internal clock: optional

EthernetGPS

1588v2 server

Synchronous

Ethernet

1588v2 client

IEEE1588v2 Precision Time

Protocol

Sync Ethernet clock master

S-GW P-GW

MME PCRF


P-GW

Security

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

eNB

S-GWSecurity

GW

MMETransport ePC

Trusted Un-trusted

IPSec tunnel

Tunnel endpoints

LSP

PCRF


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


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