Technical Specification
MEF 3
Circuit Emulation Service Definitions, Framework and Requirements in Metro Ethernet Networks
April 13, 2004
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Circuit Emulation Service Definitions, Framework and
Requirements in Metro Ethernet Networks
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Circuit Emulation Service Definitions, Framework and
Requirements in Metro Ethernet Networks
Table of Contents
1. ABSTRACT .................................................................................................................................................. 8
2. TERMINOLOGY ......................................................................................................................................... 8
3. SCOPE ........................................................................................................................................................ 10
4. COMPLIANCE LEVELS .......................................................................................................................... 10
5. MEF DOCUMENT ROADMAP ................................................................................................................ 10
6. CIRCUIT EMULATION SERVICE DEFINITION .................................................................................. 11
6.1 TDM LINE SERVICE (T-LINE)................................................................................................................. 11
6.1.1 Operational Modes of a T-Line Service .......................................................................................... 12
6.1.1.1 Unstructured Emulation mode .................................................................................................... 12
6.1.1.2 Structured Emulation mode ........................................................................................................ 13
6.1.1.3 Multiplexing mode..................................................................................................................... 13
6.1.2 Bandwidth Provisioning for a T-Line Service ................................................................................. 14
6.1.2.1 Bandwidth allocation at 100 kbit/s granularity ............................................................................ 14
6.1.2.2 TDM multiplexing ..................................................................................................................... 14
6.1.2.3 Ethernet multiplexing................................................................................................................. 15
6.2 TDM ACCESS LINE SERVICE (TALS) ..................................................................................................... 15
6.2.1 Operational Modes of a TALS Service ............................................................................................ 16
6.3 CUSTOMER OPERATED CES ................................................................................................................... 17
6.4 MIXED-MODE CES OPERATION ............................................................................................................. 18
7. CIRCUIT EMULATION SERVICE FRAMEWORK .............................................................................. 19
7.1 GENERAL PRINCIPLES ............................................................................................................................ 19
7.1.1 Use of External Standards ............................................................................................................. 19
7.2 SERVICE INTERFACE TYPES .................................................................................................................... 19
7.2.1 Examples of TDM Service Interfaces .............................................................................................. 20
7.2.2 TDM Service Processor (TSP) ....................................................................................................... 20
7.2.3 Circuit Emulation Inter-working Function (CES IWF) .................................................................... 21
7.2.3.1 PDH Circuit Emulation Service .................................................................................................. 22
7.2.3.2 SONET/SDH Circuit Emulation Service .................................................................................... 22
7.2.4 Emulated Circuit De/Multiplexing Function (ECDX) ...................................................................... 23
7.2.5 Ethernet Flow Termination Function (EFT) ................................................................................... 23
7.2.6 Direction terminology .................................................................................................................... 23
7.3 SYNCHRONIZATION ................................................................................................................................ 23
7.3.1 CES Interworking Function- Synchronization Description .............................................................. 25
7.3.2 Synchronous IWF and Associated Tributaries ................................................................................ 27
7.3.2.1 Synchronous IWF and Tributaries .............................................................................................. 27
7.3.2.2 Synchronous IWF and Asynchronous Tributaries ....................................................................... 27
7.3.3 Asynchronous IWF and Associated Tributaries .............................................................................. 27
7.3.3.1 Asynchronous IWF, Asynchronous Tributaries ........................................................................... 28
7.3.3.2 Asynchronous IWF, Synchronous Tributaries ............................................................................. 28
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Circuit Emulation Service Definitions, Framework and
Requirements in Metro Ethernet Networks
7.3.4 Synchronization Administration ..................................................................................................... 28
7.3.4.1 Single Service-Provider Owned Network ................................................................................... 29
7.3.4.2 Multi Service-Provider Owned Network ..................................................................................... 31
7.3.4.3 Private (customer owned) Network ............................................................................................ 34
7.4 PERFORMANCE MONITORING AND ALARMS ............................................................................................ 35 7.4.1 Facility Data Link.......................................................................................................................... 35
7.4.2 Alarms ........................................................................................................................................... 35
7.4.2.1 Unstructured Service .................................................................................................................. 35
7.4.2.2 Structured Service ...................................................................................................................... 36
7.4.2.3 Buffer Underflow and Overflow ................................................................................................. 36
7.4.2.4 Alarms in CCS Signaling ........................................................................................................... 36
7.4.3 End-to-End Delay .......................................................................................................................... 36
7.5 SERVICE IMPAIRMENT ............................................................................................................................ 36
7.5.1 Errors within the MEN causing TDM service impairment ............................................................... 37
7.5.1.1 Frame Loss ................................................................................................................................ 37
7.5.1.2 Frame Delay and Frame Jitter..................................................................................................... 37
7.5.1.3 Bit Errors ................................................................................................................................... 37
7.5.1.4 Frame Error Ratio and IWF behaviour........................................................................................ 37
7.5.2 Relationship to TDM service impairment metrics ........................................................................... 38
7.5.3 Errored Seconds Requirement for PDH Circuits ............................................................................ 38
7.5.4 Severely Errored Seconds Requirement for PDH Circuits ............................................................... 39 7.5.5 Service Impairments for SONET/SDH Circuits ............................................................................... 41
7.5.5.1 Performance Objectives for the SONET/SDH network ............................................................... 41
7.5.5.2 MEN Performance Objectives .................................................................................................... 42
7.5.5.3 Summary & Discussion.............................................................................................................. 45
7.5.6 Availability Requirements .............................................................................................................. 45
7.6 TDM SIGNALING ................................................................................................................................... 46
7.7 LOOPBACKS ........................................................................................................................................... 46
7.7.1 Provider Controlled Loopbacks ..................................................................................................... 46
7.7.2 Customer Controlled Loopbacks .................................................................................................... 47
7.8 PROTECTION .......................................................................................................................................... 48
7.8.1 Scenario 1 – dual unprotected services........................................................................................... 48 7.8.2 Scenario 2 – dual protected services .............................................................................................. 48 7.8.3 Scenario 3 – Single protected service ............................................................................................. 49 7.8.4 Scenario 4 – Single to dual interface service .................................................................................. 49 7.9 SERVICE QUALITY ................................................................................................................................. 50
7.10 EFFICIENCY ........................................................................................................................................... 50
7.11 NON-REQUIREMENTS ............................................................................................................................. 50
8. CIRCUIT EMULATION SERVICE REQUIREMENTS .......................................................................... 51 8.1 STRUCTURED DS1/E1 NX64 KBIT/S SERVICE .......................................................................................... 51 8.1.1 TDM Framing ............................................................................................................................... 51
8.1.2 Timeslot Assignment ...................................................................................................................... 51
8.1.3 Multiplexing Support ..................................................................................................................... 51
8.1.4 Clocking ........................................................................................................................................ 52
8.1.5 Jitter and Wander .......................................................................................................................... 52
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Circuit Emulation Service Definitions, Framework and
Requirements in Metro Ethernet Networks
8.1.6 Facility Data Link.......................................................................................................................... 52
8.1.7 Bit Oriented Messages ................................................................................................................... 52
8.1.8 Alarms ........................................................................................................................................... 52
8.1.9 Signaling Bits ................................................................................................................................ 53
8.1.10 Lost and Out of Sequence Frames .................................................................................................. 53
8.1.11 Buffer Overflow/Underflow ............................................................................................................ 53
8.2 DS1/E1 UNSTRUCTURED SERVICE ......................................................................................................... 53 8.2.1 Framing ........................................................................................................................................ 54
8.2.2 Clocking ........................................................................................................................................ 54
8.2.3 Jitter and Wander .......................................................................................................................... 54
8.2.4 Facility Data Link.......................................................................................................................... 54
8.2.5 Alarms ........................................................................................................................................... 54
8.2.6 Lost and Out of Sequence Frames .................................................................................................. 55
8.2.7 Buffer Overflow/Underflow ............................................................................................................ 55
8.3 UNSTRUCTURED DS3/E3 SERVICE .......................................................................................................... 55 8.3.1 Framing ........................................................................................................................................ 55
8.3.2 Clocking ........................................................................................................................................ 56
8.3.3 Jitter and Wander .......................................................................................................................... 56
8.3.4 Alarms ........................................................................................................................................... 56
8.3.5 Lost and Out of Sequence Frames .................................................................................................. 56
8.3.6 Buffer Overflow/Underflow ............................................................................................................ 57
8.4 SONET/SDH INTERFACES ..................................................................................................................... 57 8.4.1 Framing and Overhead Processing ................................................................................................ 57
8.4.2 Clocking ........................................................................................................................................ 58
8.4.3 Pointer Adjustments ....................................................................................................................... 59
8.4.4 Jitter and Wander .......................................................................................................................... 60
8.4.5 Alarms ........................................................................................................................................... 60
8.4.6 Buffer Overflow/Underflow ............................................................................................................ 60
8.5 GENERAL REQUIREMENTS ...................................................................................................................... 61 8.5.1 Loopbacks ..................................................................................................................................... 61
8.5.2 Frame Loss and Reordering ........................................................................................................... 61
8.5.3 Efficiency ...................................................................................................................................... 61
9. MEN REQUIREMENTS ............................................................................................................................ 62
9.1 FRAME DELAY ....................................................................................................................................... 62
9.2 ETHERNET FRAME JITTER....................................................................................................................... 62 9.3 ETHERNET FRAME LOSS ......................................................................................................................... 63 9.4 NETWORK AVAILABILITY....................................................................................................................... 63 9.5 BANDWIDTH PROVISIONING ................................................................................................................... 63 10. REFERENCES ........................................................................................................................................... 64
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Circuit Emulation Service Definitions, Framework and
Requirements in Metro Ethernet Networks
List of Figures
Figure 1: TDM Line Service over Metro Ethernet Networks .................................................................................. 11 Figure 2: Possible TDM Virtual Private Line Configurations ................................................................................. 12 Figure 3: Example Multi-point to Point T-Line Multiplexed service ...................................................................... 14 Figure 4: Multiplexing across a single Ethernet Virtual Connection ....................................................................... 15 Figure 5: Handoff of a multiplexed trunk to an external network ........................................................................... 16
Figure 6: Possible TDM Handoff Configurations .................................................................................................. 17 Figure 7: Customer Operated CES over a Metropolitan Ethernet Service (e.g. E-Line) .......................................... 17
Figure 8: Mixed-Mode Service ............................................................................................................................. 18 Figure 9: Functional Elements and Interface Types ............................................................................................... 19
Figure 10: Functional Elements of SONET/SDH emulation service ....................................................................... 22
Figure 11: Interworking function direction ............................................................................................................ 23 Figure 12: Timing distribution architecture showing clock domains....................................................................... 24 Figure 13: CES IWF Synchronization Reference Model ........................................................................................ 26 Figure 14: Synchronization Administration for a Single Service-Provider Network ............................................... 30
Figure 15: Synchronization Administration for a Multi Service-Provider Network ................................................. 31
Figure 16: Synchronization Administration for a Private Network ......................................................................... 34 Figure 17: Allowed Frame Error Ratio to meet ES objectives ................................................................................ 39 Figure 18: Relationship between Packing and FER for 0.01% SES ........................................................................ 40
-3Figure 19: Relationship between Packing and FER for 0.01% SES based on 10 BER on end to end TDM data
stream ........................................................................................................................................................... 41 Figure 20: Provider Controlled Loopback Points ................................................................................................... 47 Figure 21: Customer Controlled Loopback Points ................................................................................................. 47 Figure 22: Dual unprotected services .................................................................................................................... 48 Figure 23: Dual protected services ........................................................................................................................ 49 Figure 24: Single protected service ....................................................................................................................... 49 Figure 25: Single to dual interface connection ....................................................................................................... 49
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Circuit Emulation Service Definitions, Framework and
Requirements in Metro Ethernet Networks
List of Tables
Table 1: TDM Service Interfaces .......................................................................................................................... 20 Table 2: CES TDM Interface Definition................................................................................................................ 22 Table 3: Timing Distribution Definitions .............................................................................................................. 24 Table 4: CE Synchronization modes and Expected Timing performance ................................................................ 25
Table 5: CES IWF Synchronization Definitions .................................................................................................... 26
Table 6: Timing Options per Synchronization Domain .......................................................................................... 28 Table 7: CES Services and supporting Synchronization Administration Models ..................................................... 29
Table 8: Timing Options Single-Service Provider Owned Network ....................................................................... 30 Table 9: Timing Options Multi-Service Provider Owned Network ......................................................................... 32
Table 10: Timing Options for a Private Network ................................................................................................... 34 Table 11: Example conversion from ES to FER for Ethernet Virtual Circuit .......................................................... 38
Table 12: Sparse FER objectives for MEN [G.826] ............................................................................................... 43 Table 13: Background FER and BER objectives for MEN [G.826] ........................................................................ 43 Table 14: Maximal FER accounted by SESR [G.826] ........................................................................................... 44 Table 15: MEN FER Requirements for SDH/SONET CES .................................................................................... 45
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Circuit Emulation Service Definitions, Framework and
Requirements in Metro Ethernet Networks
1. Abstract
The emulation of TDM circuits over a Metro Ethernet Network (known as Circuit Emulation Services, or CES) is a useful technique to allow MEN service providers to offer TDM services to customers. This document outlines the types of the TDM services that can be offered over a MEN, and the requirements of such services. It covers both PDH services (e.g. Nx64 kbit/s, T1, E1, T3, E3) and SONET/SDH services (STS-1, STS-3, STS-3c, STS-12, STS-12c and European equivalents).
The document contains three sections:
- a set of service definitions for Circuit Emulation Services (CES) in the Metro Ethernet Forum context, - a framework section explaining issues with the implementation of such services - a set of requirements needed for providing such services in Metro Ethernet Networks (MEN). Separate implementation agreements for PDH and SONET/SDH services will be produced which cover the implementation of these services in an inter-operable manner. This document is intended as a reference against which any Implementation Agreement can be compared to ensure that all the service requirements have been met. 2. Terminology
Term Definition
AIS Alarm Indication Signal
ANSI American National Standards Institute
APS Automatic Protection Switching
BER Bit Error Ratio
BBER Background Block Error Ratio
BLSR Bi-directional Line Switched Ring
CAS Channel Associated Signaling
CCS Common Channel Signaling
CE Customer Equipment
CES Circuit Emulation Services
CR Clock Recovery.
CRC Cyclic Redundancy Check
CUET Customer Unit Edge Terminal
DSTM Derived System Timing Mode.
The IWF system clock is derived from the incoming Ethernet frames.
DTM Derived Timing Mode.
The recovered service clock is derived from the incoming Ethernet frames.
E-Line Ethernet Line Service
ECDX Emulated Circuit De/Multiplexing Function
ECID Emulated Circuit Identifier
EFT Ethernet Flow Termination
ES Errored Second
ESR Errored Second Ratio
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Circuit Emulation Service Definitions, Framework and
Requirements in Metro Ethernet Networks
Term Definition
ESF Extended Super Frame
EVC Ethernet Virtual Circuit FDL Facility Data Link
FER Frame Error Ratio
HOVC Higher Order Virtual Container IA Implementation Agreement IETF Internet Engineering Task Force ITU-T International Telecommunication Union – Telecommunication standardization sector
IWF Inter-Working Function LOH Line OverHead
LOPS Loss Of Packet Synchronization LOS Loss Of Signal
LOVC Lower Order Virtual Container LTE Line Termination Equipment MIB Management Information Base MEN Metro Ethernet Networks NE Network Equipment
NNI Network to Network Interface PDH Plesiochronous Digital Hierarchy.
PDH refers to the DS1/DS2/DS3 and E1/E3/E4 family of signals
PE Provider Edge
PLL Phase Locked Loop
PRS Primary Reference Source PSTN Public Switched Telephone Network PWE3 Pseudo-Wire Emulation Edge to Edge (an IETF working group)
RDI Remote Defect Indication SDH Synchronous Digital Hierarchy SES Severely Errored Second SESR Severely Errored Second Ratio SF Super Frame
SLA Service Level Agreement SLS Service Level Specification SONET Synchronous Optical Network SSM Synchronization Status Message TALS TDM Access Line Service TDM Time Division Multiplexing
(examples of TDM services include Nx64 kbit/s, T1, T3, E1, E3, OC-3, STM-1, OC-12, STM-4)
T-Line TDM Line Service
TSP TDM Service Processing
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Circuit Emulation Service Definitions, Framework and
Requirements in Metro Ethernet Networks
Term Definition
UNI User Network Interface
VC Virtual Container
VT Virtual Tributary
Mapper A device or logic that implements a mapping function
Mapping The process of associating each bit transmitted by the service into the SDH/SONET payload
structure that carries the service. For example, mapping a DS1 service into SONET VT-1.5 /
SDH VC-11 associate each bit of the DS1 with a location in the VT-1.5/VC-11
Multiplex Transmit one or more channels over a single channel
Pointer A part of the SDH/SONET overhead that locates a floating payload structure. Frequency
differences between SDH/SONET network elements or between the payload and the
SDH/SONET equipment can be accommodated by adjusting the pointer value.
3. Scope
The scope of this document is to address the particular requirements of transport over MEN for edge-to-edge-emulation of circuits carrying time division multiplexed (TDM) digital signals. It makes references to requirements and specifications produced by other standards organizations (notably the ITU, ANSI, IETF PWE3 and ATM Forum), and adapts these to address the specific needs of MEN. It is not in the scope of this document to duplicate any work of other related standardization bodies.
The document covers the definition of such services, a framework in which the service provision can be understood, and also the requirements for the defined services. The actual implementation of these services in an inter-operable manner will be the subject of separate Implementation Agreements, and hence is outside the scope of this document.
4. Compliance Levels
The key words “MUST”, “MUST NOT”, “REQUIRED”, “SHALL”, “SHALL NOT”, “SHOULD”, “SHOULD
NOT”, “RECOMMENDED”, “MAY”, and “OPTIONAL” in this document are to be interpreted as described in
[RFC 2119]. All key words must be use upper case, bold text.
5. MEF Document Roadmap
MEF draft specifications and the document roadmap are available in the members area on the Metro Ethernet Forum website at http://www.metroethernetforum.net/.
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