Frequently Asked Questions

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Carrier Ethernet for Mobile Backhaul

MEF Mobile Backhaul Working Group

January 2009

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MEF 22 Mobile Backhaul Implementation Agreement

Frequently Asked Questions

Appendix: Mobile Backhaul Synchronization over Public Switched Networks

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MEF Mobile Backhaul Implementation Agreement

• What is it?– Provides generic specification for Ethernet backhaul

architectures for mobile networks (2G, 3G, 4G)– Explains how to apply existing MEF specifications– User-Network Interface requirements– Service Requirements

• Service Definitions• Clock synchronization for

application support

FAQs

Carrier Ethernet Network

UNI

RAN BS

RAN NC

UNI

RAN BS

UNI

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MEF Mobile Backhaul Q&A (Continued)

• What is the role of Mobile Backhaul Implementation Agreement (MBH IA) document? – The role of the document is to provide guidelines for implementing

Mobile Backhaul network that is based on Metro Ethernet.– The document includes requirement and recommendations for the

equipment, architecture & operation of Mobile Backhaul network.

• What is the meaning of the term Implementation Agreement? Is it a specification? – Mobile Backhaul Implementation Agreement is a specification– It provides a set of requirements and guidelines detailing the use of

existing MEF standards and other industry standards in a way that best fit Mobile Backhaul requirements.

– The Implementation Agreement aims to describe best practices as a blueprint for a successful implementation of mobile backhaul services.

FAQs

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• What is in the Scope of the Implementation Agreement? – Utilize existing MEF technical specifications with required

extensions to interface and service attributes. – Provide requirements for UNI-C and UNI-N beyond those in

MEF 13 & MEF 20.– Define requirements for the implementation of Ethernet

Services.– Provide requirements for the usages of Link OAM and Service

OAM Fault Management.– Use a single Metro Ethernet Network with external interfaces

being only UNIs.– Provide high-level requirements for Class of Service.– Define synchronization requirements where possible for

transparent packet based synchronization methods.– Specify functional requirements applicable to legacy mobile

technology using the Generic Inter-Working Function (GIWF) interfaces.

FAQs

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• What new business opportunities does the Mobile Backhaul Implementation Agreement (MBH IA) enable?– It allows mobile backhaul service providers to participate in two

rapidly growing markets (Mobile Backhaul applications and Carrier Ethernet)

– It does present opportunities for fixed network operators to provide wholesaling services to mobile operators and reuse of existing plant

• Other than Existing large scale service providers, who else can benefit from the MBH IA?– Any service provider or operator with available capacity in their

packet based networks is a candidate to provide mobile backhaul services over Carrier Ethernet. These operators are more likely to be in a position to integrate wire line and mobile backhaul services in an integrated system

FAQs

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• What is the status of the Implementation Agreement– is it official by now? – MEF 22 Mobile Backhaul Implementation Agreement Phase 1 was

approved as an official MEF Specification in January 2009.

• Is there a 2nd phase planned for the MBH IA document?– Yes, the 1st phase includes:

• EVCs spanning a single MEN (Metro Ethernet Network).• Packet based synchronization method that is transparent to the

MEN• GSM, WCDMA, CDMA, CDMA2000, and WiMAX 802.16e.

– Later phases will include: • EVCs spanning arbitrary number of MENs.• Other synchronization methods.• Other mobile standards, such as LTE (Long Term Evolution).• Synchronous Ethernet • And other topics

FAQs

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• Why does the MBH IA not cover the both Phase 1 and Phase 2 content in the MBH IA document? – MEF assigns high priority to bring value on time.– Not all standards were finalized when MEF agreed on the scope of the

document. Therefore the approach of 1st phase & 2nd phase was preferred.

• What is the scope of the “Mobile Backhaul” network?– The Mobile Backhaul is defined as the network between the:

• Radio Network Controllers (RNCs), and• Radio Access Networks Base Station (RAN BS).

– Mobile Backhaul Implementation Agreement provides guidelines to architecture, equipment & operation to that part of the network

FAQs

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• What Network Elements are addressed by the Mobile Network document ? – In short RAN CE as depicted at the following chart:

FAQs

– The RAN CE is a generic term that identifies a mobile network node or site, such as a RAN network Controller or RAN Base Station .

– A RAN NC may be a single network controller or a site composed of several network elements including: OSS, WCDMA Radio Network Controller or Synchronization Server.

– A RAN BS may also be a single base station or a collection of several base stations.

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• On what other MEF documents is the Mobile Backhaul Implementation Agreement based? – The services and requirements that appear at the Mobile Backhaul

Implementation Agreement doc are based on:• The services defined in MEF 6.1 Ethernet Service Definition – Phase 2 • The attributes defined in MEF 10.1 Ethernet Service Attributes – Phase 2• MEF 13 & MEF 20 (UNI Types 1 & 2)• Other documents currently under development by the MEF Technical

Committee (Ethernet Classes of Service, Service-OAM and External Network-to-Network Interface technical specifications)

– It is highly recommended to be familiar with the requirements in the above two documents before reading the Mobile Backhaul Implementation Agreement document. These are available on the MEF Public web site Information Center

FAQs

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• Does the agreement take into account the migration phase from legacy to Carrier Ethernet backhaul (1)?– The Mobile Backhaul Implementation Agreement covers various steps

in the migration phase– It describes two use cases of Mobile Backhaul networks that are

composed of a legacy network and a Carrier Ethernet network in parallel.

– The first of these two “Use cases” employs a “Generic Inter-working Function” to interface between the legacy base station / network controller and the Carrier Ethernet network:

FAQs


Legacy Network

Non-Ethernet I/F

UNI Non-Ethernet I/F

UNIGIWFRAN BS RAN NCGIWF

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• Does the agreement take into account the migration phase from legacy to Carrier Ethernet backhaul (2)?– The second legacy use case describes a hybrid offload model.

The network controller and base stations maintain legacy network (TDM, ATM, or HDLC/PPP) connections for voice traffic and native Carrier Ethernet interfaces for data traffic:

FAQs


Legacy Network

UNI UNIRAN BS RAN NC

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• What is Mobile backhaul GIWF (Generic Interworking Function)? – Mobile Backhaul Generic Interworking Function (GIWF) provides

adaptation and interconnection between any legacy mobile equipments (TDM/ATM/HDLC based) in the base station and network controller and the Metro Ethernet network at the UNI.

– It enables the joint backhaul of any combination of 2G, 2.5G, 3G (legacy based) and Evolved-3G & 4G (Ethernet based) voice and data traffic over a single Carrier Ethernet RAN (Radio Access Network).

– The adaptation of the legacy mobile traffic to the Carrier Ethernet service can be based on TDM circuit emulation standards as well as ATM/HDLC pseudo-wire standards.

FAQs

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• How does the GIWF handles existing GSM based networks?– GSM uses a number of T1 (1.5 Mbit/s) or E1 (2 Mbit/s) circuits to connect

the base station with the network controller.– The GIWF terminates a circuit emulation service (CES) per such E1/T1

circuit at the cell site or service edge and at the network controller site– A variety of circuit emulation services can be used in the implementation

agreement (MEF8 (CESoE), TDMoMPLS (MFA8), SAToP (RFC4553), CESoPSN (RFC5086))

FAQsCES IWF: Circuit Emulation Interworking Function


ATM Pseudo-wire

Ethernet UNI

Ethernet UNI

Ethernet

E-Line Service

Ethernet ATM/TDMATM/TDM CES IWF

CES IWF

ATM / TDM BS demarcation

ATM / TDM Network Interface

Service Provider NetworkCarrier Ethernet

Network

RAN BSRAN NC

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• How does the GIWF handles existing UMTS / WCDMA based networks?– These Technologies uses ATM over a number of bundled T1 (1.5 Mbit/s) or E1 (2

Mbit/s) circuits to connect the base station with the network controller.– The GIWF terminates an ATM pseudo-wire or a TDM circuit emulation tunnel at

the cell site or service edge and at the network controller site– A variety of ATM pseudo-wire and/or TDM circuit emulation standards can be

used in the implementation agreement

FAQs


ATM Pseudo-wire

Ethernet UNI

Ethernet UNI

Ethernet

E-Line Service

Ethernet ATM/TDMATM/TDM CES IWF

CES IWF

ATM / TDM BS demarcation

ATM / TDM Network Interface

Service Provider NetworkCarrier Ethernet

Network

RAN BSRAN NC

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• How does the MEF implementation agreement align with ATM pseudo-wire and TDM circuit emulation solutions?– The MEF has defined MEF 8 for TDM over Ethernet circuit

emulation; the specification is maintained by the MEF– The MPLS backhauling of Ethernet, TDM and ATM circuits is

being defined by the IP/MPLS Forum. The MEF liaises with the IP/MPLS Forum to ensure the specifications are aligned.

FAQs

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MEF Mobile Backhaul Q&A (Continued)• What is the relationship between the MEF’s MBH IA and the

IP/MPLS forum’s Specification?– The MEF MBH IA describes a superset of potential implementations

that fulfill the service layer requirements (UNIs, EVCs) of mobile radio systems (RAN CE devices) with Ethernet interfaces.

– The MBH work of the IP/MPLS Forum provides a specific network implementation reference based on MPLS that fulfils the performance and connectivity requirements of mobile radio systems.

FAQs

Base Station

MPLS NetworkMPLS Network

E-Line Service

Ethernet

Ethernet UNI Ethernet UNI

Network Controller

Ethernet


MPLS Service Termination

MPLS Service Termination

Pseudo-wire Service

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• What is the approach to provide synchronization to the radio access network?– There are 3 principal types of synchronization that are of importance:

• Frequency synchronization • Phase synchronization • Time synchronization

– Following approaches are possible:• outside of the Ethernet transport network (e.g. via GPS) • Packet Based Synch using dedicated packet flow (e.g.IEEE 1588

V2, NTP) or using the clock carried by circuit emulated data (following methods are possible : Differential Clock Recovery, Adaptive Clock Recovery)

• Synchronous Ethernet – The MBH IA approach is to focus on packet based timing methods. – The synchronization requirements are derived from the ITU-T

Recommendation G.8261

(See appendix of this FAQ document for more information about clock synchronization)

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• Where can I find more information regarding MBH synchronization requirements?– For more information on MBH synchronization please refer to

the appendix of this slide deck.

• What are the main QoS requirements, that the MBH IA specifies? – The MBH IA specifies QoS requests to enable Service Class

differentiation. The “must” request is to support at least two Class of Service. But the recommended request is to support four Class of Service.

FAQs

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• What approach does the MEF recommend in terms of the Use Cases in the implementation agreement?– The MEF anticipates case-by-case decisions based on local

considerations such as the desire to separate and contain legacy voice traffic over existing networks, the desire or ability to maintain two networks vs. cash and ROI of immediately moving to an all Carrier Ethernet Backhaul Network

• How did the MEF validate the requirements in the MBH IA?– Independent research commissioned by the MEF

• Evaluate network planning assumptions and integrate the derived needs from the MEF Implementation Agreement (IA)

• 41 operators/worldwide coverage (APAC 20%, EMEA 49%, NA 27% and LA 5%)

– On going discussions with industry analysts FAQs

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• What are the highlights of the MEF commissioned survey for MBH – validating assumptions for the IA?

FAQs

MEF 10.1 (76%) IETF/ITU

2 or 3 levels (44%) All services created equally

5 9s and up (49%) 4 9s and below

<1ms, 1-3ms, 3-5ms (78%) 5-10ms

Require (78%) Likely

Likely (51%) Not so likely

3 or 4 (75%) 5 or 8

- Ethernet performance attributes Standards?

- Single or multiple Availability Requirements?

- Availability Requirements?

- Latency budget for synchronization?

- Will you require Ethernet Service OAM (IEEE 802.1ag, ITU-T Y.1731)?

- How likely to transport legacy traffic over Ethernet using an interworking function?

- How Many CoS?

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• What MEF services are requested for MBH? – Typically there are 1-2 RNC sites and between hundreds to

thousands of RAN BS sites– Bandwidth requirements for a base station site will vary and

may range from a few Mbps to over a Gbps– Services need to be:

• Scalable• Flexible• Cost effective

– Generally, the requirement is to follow one of the following MEF services: • Ethernet Private Line Service• Ethernet Virtual Private Line Service• Ethernet Private LAN Service• Ethernet Virtual Private LAN service• Ethernet Private Tree Service• Ethernet Virtual Private Tree Service

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• Does the MEF support the integration of mobile backhaul services and business services over the same infrastructure?– Definitely. Most service providers strive to integrate multiple

services in their backbones, which improves coverage and cost efficiency.

• How is the MEF certification program aligned with the Mobile backhaul initiative?– MEF 9, 14 and 18 as well as upcoming UNI Type 2 certifications

already handle several aspects of Carrier Ethernet service certification individually. The end-to-end mobile backhaul service cannot easily be subject to standardized certification, as operators have diverging requirements based on their migration plans, legacy migration plans and mobile network types (2G, 3G, WiMAX) FAQs

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• The Specifications and presentations refer to MENs (Metro Ethernet Networks) not Carrier Ethernet Networks. Why is that? – The technical work of the MEF as described in the

specifications, together with the work of associated standards bodies, collectively enable the functionality and attributes of Carrier Ethernet

– The completed specifications continue to refer to MENs (Metro Ethernet Networks) but this is now a generic term covering the enabled service network in the increasing variety of access, metro and long haul networks

– Some Specifications refer to CENs (Carrier Ethernet Networks) this term may be used interchangeably with MENs

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• What are the issues that make this time sensitive?– Two elements.

• The very rapid increase of bandwidth hungry applications (driven by iPhone/Blackberry in some markets and mobile broadband connected homes in other markets) that would require unacceptably high cost of expansion of legacy networks (if they could meet the demand at all). This accelerates the need for Carrier Ethernet.

• The financial strain on the economy anticipated to continue for the next 12 to 18 months makes continued investment in expensive legacy solutions unacceptable. It may render the ability of a Service Provider to maintain separate legacy voice and next generation data networks for mobile backhaul moot. This means that more care will be needed when moving rapidly to an all Carrier Ethernet network

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• What exactly will be the cost savings of Carrier Ethernet for Mobile backhaul?– Although this is not within the scope of either the MBH IA or the

MEF, the following data from Infonetics gives some strong implications:

• PDH (T1/E1 etc.) costs climb directly with bandwidth

• Ethernet wire-line costs grow gently with large bandwidth increases (Eth, DSL, PON, cable)

• New IP/Ethernet wire-line options to satisfy the #1 investment driver: operational cost savings

FAQs

Copyright © Infonetics Research 2009

Source: Infonetics Research, Mobile Backhaul Equipment, Installed Base, and Services October 2008

Backh

au

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erv

ice C

harg

es p

er

Con

necti

on

Stay on PDH

Or, move to Ethernet

PDH and ATM over PDH vs New Wireline: Mobile First Mile Backhaul Service Charges per Connection

$37,044

$6,887

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Appendix:Timing & Synchronization over Packet Based Network

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• What are the relevant ITU Standards for Clock Requirements concerning Circuit Emulate services?– The synchronization requirements are derived from the ITU-T

Recommendation G.8261, which studies timing and synchronization over packet based networks and examines the requirements for different mobile technologies.

– Subsequent versions of this ITU specify clocks conforming to G.823 (for signals related to the E1-hierarchy) or G.824 (for T1-hierarchy signals)

– These standards define the permissible output jitter and wander for two levels

• Clock (Jitter and wander) requirements for the traffic interface are defined in ITU-T G.823, Section 5 for E1 and in ITU-T G.824, Section 5, for T1

• Clock (Jitter and wander) requirements for the synchronization interface are defined in ITU-T G.823, Section 6.2.4 for E1 and in ITU-T G.824, section 6.2.2 for T1

FAQs

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• What are the principle types of synchronization?– There are 3 principal types of synchronization that are of

importance:• Frequency synchronization

– Relate to the alignment of clocks in frequency, a process that is also referred to as syntonization

• Phase synchronization– Imply that the two clocks are aligned in phase, a

process that also referred to as relative-time synchronization

• Time synchronization– Also referred to as time-of-day synchronization or wall-

clock synchronization where the clocks in question are traceable to a common, universal, time-base such as UTC

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• What are the important synchronization types and requirements in cellular networks (1)?– GSM Base Station (frequency synchronization)

• Timing requirement applicable to the GSM radio interface can be found in the ETSI technical specification TS 145.010

• The radio interface requirement for a GSM base station is frequency accuracy of ±50 ppb and ±100 ppb (pico BS)

– The need for this requirement stems primarily from the need to support handover of mobiles between base stations

– UMTS FDD Base Station (frequency synchronization)• The timing requirement applicable to the WCDMA FDD radio

interface can be found in the ETSI technical specification TS 125.104

• The radio interface requirement for UMTS FDD base stations is a frequency accuracy of ± 50ppb (wide area), ±100 ppb (local area) and ±250 ppb (Home BS); for the FDD mode there are no phase alignment requirements

FAQs

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• What are the important synchronization types and requirements in cellular networks (2)?– UMTS TDD Base Station (frequency and phase synchronization)

• The timing requirement applicable to the WCDMA TDD radio interface can be found in the ETSI technical specification TS 125.105

• The radio interface requirement for UMTS TDD base stations is a frequency accuracy of ±50 ppb; for the TDD mode there is the additional requirement for the phase alignment of neighboring base stations to within 2.5 µs.

– 3GPP2 CDMA2000 Base Station (frequency and time synchronization)• The relevant CDMA2000 standards are the 3GPP2 C.S0010-B and 3GPP2

C S0002-B• According to the CDMA2000 specifications the average frequency

difference between the actual CDMA transmit carrier frequency and specified CDMA transmit frequency assignment shall be less than ±50 ppb

• the time error should be less than 3μs: due to that it is a common practice to equip CDMA base stations with GPS receivers

FAQs

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• How is network synchronization achieved for emulated circuits over a packet-based infrastructure (1)?– There are 3 major methods:1. Network Synchronous Method.

• This is supported via a local GPS or via a master –slave synchronization network using the physical layer to distribute the synchronization

2. Differential clocking mode• A PRC-traceable reference is required at both ends of the packet

network. However often a this may not be available for service providers at every possible site, such as a remote cell site

• The system will use the PRC-traceable clock source as well as observe the time stamps received from the circuit emulation service (CESoE / SAToP / CESoPSN) packets received from the packet network and calculate the differential to recover an accurate clock

• This recovered clock reference is then used to transmit the TDM frames

FAQs

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• How is network synchronization achieved for emulated circuits over a packet-based infrastructure (2)?

3. Adaptive Clock Recovery• In some deployments, there is no PRC-traceable reference

nor GPS source available at the remote site• The CPE at the cell site has to completely rely on the

incoming packet stream from the Ethernet network to calculate the clocking reference

• The clock accuracy, thus derived, should be of suitable high quality, sufficient to recover a timing signal compliant to the 3GPP mobile standards (e.g. accuracy of 16 ppb or higher)

• The central office will be using a primary clock source reference, and the receiving site will derive the clock based on the incoming circuit emulation service packets

FAQs

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MEF Mobile Backhaul Q&A (Continued)• What are the requirements from Clock Recovery over PSN based

MBH?

– Any clock recovery over packet mechanism should be designed to meet the clock synchronization requirements for the service that is carried (e.g. E1) and to support requirements of the wireless technology (e.g. GSM and UMTS RANs as specified in ETSI EN 300 912 and TS 125 402 "Synchronization in UTRAN stage 2”)

– Jitter and wander measured at the output of the GIWF TDM-bound interface should meet the traffic interface requirements specified in ITU-T recommendations (G.823/G.824/G.825)

– The wander budget allocated to the MEN and the GIWF as measured at the output of the GIWF TDM-bound interface should meet the traffic interface requirements of ITU-T G.8261, Deployment Case 2

– Frequency accuracy in holdover should conform to a standard Clock as applicable

– A robust clock recovery mechanism should also maintain its outstanding performance even under the most demanding network conditions, such as high Packet Delay Variation (jitter) and packet loss ratio

FAQs

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• How are clock recovery solutions related to 1588v2 and NTP?– IEEE 1588v2 and NTP (Network Time Protocol) define how to

transport time information over the network• The algorithms to reconstruct and recover the clock are

vendor specific• This is an "implementation" issue rather protocol

– 1588v2 implementation actually calls for a standardized implementation of the information carried while maintaining the high clock accuracy currently achieved through clock recovery implementations

• The clock recovery implementations should interoperable and complement 1588v2 standard.

– The clock recovery implementations should comply with G.823, G.824, G.8261, G.8264, G.8265 and G.8266 as applicable

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End of Appendix

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