Contents

Introduction .................................................................................................... 1

An NTU (Network Termination Unit) for Every Need ......................................... 1

The Importance of OAM................................................................................... 3

The Need to Support E1/T1 and E3/T3 Circuits................................................. 4

Pseudo-Wire/Circuit Emulation......................................................................... 5

Multiservice Ethernet Network Termination Units ............................................. 6

Ethernet and TDM Service Delivery to Out-of-Footprint Geographies................ 7

RAD Data Communications Solutions ............................................................... 8

Summary......................................................................................................... 9

White Paper: Ethernet OAM

Introduction

As the benefits of Ethernet networking in the metro and wide-area have become clear,

service providers are lining up to meet the rapidly growing demand for Ethernet services. As

with any mainstream telecommunications service, providers need a reliable way to deliver,

control and maintain their offerings. Customers are selecting providers who can offer

Service Level Agreements (SLAs) tied to a variety of service packages. This paper will

explore the benefits multiservice network termination units offer in economical Ethernet

service delivery, while supporting revenue-generating legacy TDM services.

An NTU (Network Termination Unit) for Every Need

A clear demarcation point between the service provider and customer network is a

prerequisite for reliable service delivery and SLA management. As shown in the following

diagram, the “demarc” serves as the formal dividing line for defining network ownership

and responsibility. Service providers frequently prefer to own the termination equipment at

the customer premises to ensure reliable service delivery at the formal hand-off to the

customer.

Customer Premises

CPENTU

ServiceProviderNetwork

Demarcation Point

CustomerNetwork

ProviderNetwork

Customer Premises

CPENTU



Demarcation Point

CustomerNetwork

ProviderNetwork

Figure 1 – Demarcation Point

Network Termination Units can vary from very simple to sophisticated devices. If the service

provider is delivering simple, “best effort” Ethernet service, a simple media converter that

translates between the last mile fiber feed and the customer’s internal network may be

sufficient. However, should the provider wish to have more control over the service, an

intelligent Ethernet NTU (E-NTU) is necessary. Finally, if the customer also needs support

for legacy TDM services over the Ethernet connection, a multiservice NTU is required.

© 2006 RAD Data Communications Ltd. 1


The following diagram provides an overview of these NTU capabilities.

The network interface side of the NTU provides the physical termination of the service

provider’s fiber loop. Fiber is typically used due to the distance that has to be covered

between the customer and the closest POP, as well as the high data rates customers

demand. It must have the flexibility to accommodate a variety of data rates, fiber modes

and wavelengths to ensure scalable and economical service reach from short distances to

dozens of miles. In addition, the network interface needs to support a variety of remote

OAM functions for ensuring maximum up-time and eliminating costly “truck rolls” to

diagnose and correct problems. These functions include remote diagnostic and loopback

tests, fault propagation, inband and out-of-band management and remote software

download and configuration.

The user interface side of the Ethernet NTU enables service providers to offer critical

capabilities such as flexible bandwidth granularity, CoS and VLANs, in effect allowing them

to offer SLA guarantees to their customers. Certain applications, such as VoIP and circuit

emulation, require prioritization to ensure dependable delivery of real-time traffic,

especially in the presence of excess traffic from lower priority sources. The prioritization

and associated rate limitation are typically controlled on a per-service and aggregate basis.

VLAN tagging and stacking is needed in order to separate traffic sources from different

customers, minimize the number of VLANs in the provider’s network, provide VLAN

2 © 2006 RAD Data Communications Ltd.


tunneling, and to control the Tunnel P-bit (class of service) and ensure that service provider

traffic doesn’t interfere with user traffic.

Figure 2 below shows how NTUs fit within service provider networks.

End - to - end service control, SLA monitoring and diagnostics

tomer Premise

Multiservice NTU

Customer Premises

Multiservice NTU

ServiceProvider

Eth

T1

Eth

T1

Customer Premises

Multiservice NTU

Customer Premises

Multiservice NTU

ServiceProviderService Provider

Eth

T1/E1

Eth

T1/E1

Figure 2 – End-To-End Service Control, SLA Monitoring And Diagnostics

The Importance of OAM

In addition to providing a clear demarcation and service/SLA management capabilities, a

suite of fault monitoring, diagnostic and control capabilities are required to manage the

Ethernet services. These include fault indication and isolation, link monitoring, remote

diagnostic and loopback tests, connectivity verification, performance monitoring, fault

propagation, inband and out-of-band management and remote software download and

configuration. These capabilities have been part of traditional carrier class technologies like

TDM and ATM for years and successful carrier class Ethernet service delivery and

management depend upon an equivalent set of capabilities.

Consider the loopback diagnostic tool, a critical function for both TDM and Ethernet

networks. Service providers need the ability to test their circuit all the way to the customer

premises for new service provisioning or when troubleshooting the network. A basic feature

in TDM networks is the ability to activate a remote CPE CSU loop command from the central

office. This places the CSU on the customer premises into a test loop state towards the

network. For Ethernet networks, the service provider will need to conduct a similar loopback

test with the Ethernet NTU looping back packets it receives from the network per port and

per VLAN.



Substantial progress from recent standards activity promises widespread availability and

interoperability of Ethernet OAM tools. For instance, the IEEE 802.1ag and ITU Y.1731

standards are close to finalization and RAD as well as some other manufacturers have

already incorporated pre-standard implementations into their Ethernet demarcation

devices.

The Need to Support E1/T1 and E3/T3 Circuits

If end user applications only required Ethernet services, a Metro Ethernet connection along

with an intelligent Ethernet NTU device might be adequate to satisfy their needs. However,

the installed base of TDM equipment and services is very large and continues to grow.

Adding TDM support to the E-NTU broadens the customer base by addressing the need for

multiservice support to justify the purchase of Ethernet services. In fact, the Metro Ethernet

Forum (MEF) has defined TDM support as one of the five basic attributes that define

carrier-class Ethernet.

In the past years we have seen a decline in residential telephone landlines due to the

consumer shift to cellular phones. Paradoxically this trend has actually created an increase

in the demand for TDM services for backhauling cellular traffic from between cellular base

stations and MSC/BSC aggregation points. The cellular operators’ increased demand for

E1/T1 and E3/T3 services is attracting new service providers, namely cable multiservice

operators (MSOs), which have advanced Ethernet networks and extensive fiber

infrastructure. Circuit emulation enables the cellular operators to backhaul E1/T1 traffic (2G)

over Ethernet networks while laying the foundation for 3G with high speed Ethernet. By

providing multiservice delivery, the cable MSOs can now offer the cellular operators a choice

of facilities to effectively compete with the incumbent LECs.

E1/T1 circuits are also extensively used in enterprise voice networks. Traditional PBXs use

E1/T1/PRI circuits as the primary connections to service providers as well as for inter-facility

voice trunking. Although many organizations are moving to replace these systems with IP

PBXs, this transition will take years or decades. In fact, a large percentage of organizations

have no current plans to move to VoIP – they are perfectly happy with their existing

functional and reliable phone systems.



Pseudo-Wire/Circuit Emulation

Once organizations begin using high bandwidth, low cost Ethernet connections for LAN

traffic, they will naturally want to converge most, if not all, of their other types of

telecommunications services onto it. But as just discussed, these other “non-Ethernet”

services are typically TDM circuits that are not compatible with packet transport. However,

this is not the case where a pseudo-wire or circuit emulation technology is used.

Consider for example, TDMoIP®, a circuit emulation/pseudo-wire technology pioneered by

RAD Data Communications and ratified as an implementation agreement by the MFA forum

(MPLS - Frame Relay ATM) and in recommendations by the ITU-T and IETF PWE3 groups. As

its name implies, TDMoIP is a technology for transporting TDM circuits such as E1/T1 or

E3/T3 across IP or MPLS networks, and recently was expanded to use Ethernet networks in

accordance with the MEF 8 Implementation Agreement. TDMoIP is similar to ATM AAL1 in

that both technologies are used to emulate circuits over packet switched networks.

However, unlike ATM, Ethernet networks provide no inherent timing mechanism.

Additionally, packet delay variation (aka jitter), packet delay and packet loss create a hostile

environment for transmission of synchronous TDM traffic.

TDMoIP features a variety of techniques for overcoming these challenges. In general, the

synchronous TDM frame is first segmented and then headers are applied to each segment.

The headers provide MAC, IP or MPLS addressing together with VLAN and class of service

information. The packets are forwarded across the Ethernet connection. At the other end,

the original bit stream is reconstructed by removing the headers, concatenating the

segments and regenerating the timing. See Figure 3 below for a detailed depiction of

TDMoIP.

• The synchronous bit stream is segmented

• Headers are added to each segment to form the Packet

• Packets are forwarded to destination over the PSN network

• At destination, the original bit stream is transparently reconstructed

T1/E1Frame

T1/E1FrameEthernet Frames Ethernet Frames

ETH / IP / MPLS

Network

T1/E1Frame

T1/E1FrameEthernet Frames Ethernet Frames

ETH / IP / MPLS

Network

Figure 3 - TDMoIP



Among the challenges with pseudo-wire circuit emulation technology, regenerating accurate

clock timing and ensuring low latency are among the most difficult. A number of

applications – chief among them cellular backhaul – depend on extremely low latency and

regenerated clock accuracy measured in parts-per-billion in order to ensure successful

operation.

The rate limitation and priority functions of an NTU are critical for circuit emulation and

VoIP. Circuit emulation requires an “always-on” bandwidth pipe, typically 2/1.5 Mbps per

E1/T1. Since commercial Ethernet services over fiber start as low as 5 Mbps, circuit

emulation must take priority over all other services and the Ethernet NTU must ensure this

happens.

Multiservice Ethernet Network Termination Units

With Ethernet and TDM being price competitive services, integration of both capabilities

into one multiservice NTU contributes to a lower service provisioning cost in several ways. A

single multiservice NTU reduces inventory levels, provides for simpler management, reduces

the possible points of failure at the customer premises, and ultimately costs less than two

discrete NTUs.

Customer requirements range from the need to support a few E1/T1 circuits to dozens of

E1/T1 or E3/T3 lines. Service providers also require aggregation devices located in their COs

or POPs that efficiently interwork with the integrated Ethernet and TDMoIP bit streams

coming from multiple customer locations. In addition to handling the switched Ethernet

traffic, these devices need to “reassemble” the TDMoIP streams back into E1/T1, E3/T3 or

into channelized E3/T3, OC-3 or STM-1 formats and pass them off to existing TDM

infrastructures.

Service providers require that the capital cost of multiservice NTU be as low as possible.

Equally important is the need for minimized OAM costs associated with their access

networks.



Ethernet and TDM Service Delivery to Out-of-Footprint Geographies

An example of where multiservice Ethernet NTUs are needed is in the delivery and

management of Ethernet along with E1/T1 circuits for out-of-footprint customers. Since

Ethernet connections must frequently be leased from a wholesale carrier (regional metro

Ethernet service provider), the Primary carrier (IXC or CLEC service provider) needs to add a

layer of intelligence to support end-to-end NTU functionality. Since the primary service

provider will likely have customers located in a variety of territories, it is important to

provide a consistent method of delivering service and supporting OAM functions. A

multiservice Ethernet NTU provides these critical capabilities as shown below in Figure 4.

WholesaleCarrier

CPE

NTU

In-Footprint location

GE

NMS

Customer Premises10GE

NTU

-End-to-end Service control, SLA monitoring and diagnostics

Out-of-footprint monitoring segmentMonitoring segment

Customer data

n*T1/E1

n*T1/E1

PrimaryCarrier

Out-of Footprint location

Co-lo

NTU

WholesaleCarrier

CPE

NTU

In-Footprint location

GE

NMS

Customer Premises10GE

NTU

-End-to-end Service control, SLA monitoring and diagnostics

Out-of-footprint monitoring segmentMonitoring segment

Customer data

n*T1/E1

n*T1/E1

PrimaryCarrier

Out-of Footprint location

Co-lo

NTU

Figure 4 – Multiservice Ethernet NTU



RAD Data Communications Solutions

Table 1 – RAD Ethernet and TDM Services Over Packet Access Solutions

ETX-102 ETX-202 IPmux-11/14 IPmux-16 Gmux-2000

TDM ports None None 1/2/4 X T1/ E1

4/8/12/16 x E1/T1

2 x E3/T3 or 2 x CT3

196 x E1/T1

2 x OC-3/STM-1 w/ APS link redundancy

ETH Network port

1 or 2 x 100BaseFX

Fiber SFP based

Redundant uplink

1 or 2 x GbE UTP

Fiber SFP based

Redundant uplink

1 or 2 x UTP/100FX

1 or 2 x UTP/100FX

Redundant uplink

2 x GbE, SFP based

Redundant uplink

User LAN ports

1-4 X 10/100BaseT

1-4 x 10/100/1000Base/ GbE Fiber

2 x

10/100BaseT/100Fx

6 x

10/100BaseT/ 100FX

N/A

QoS/Rate Limitation

Rate control

Traffic classification and prioritization

VLAN tagging and stacking

Rate control



Rate control



Rate control



VLAN tagging

Management

Terminal

Telnet

Web browser

RADview Lite

SNMP

Remote s/w download and configuration

Terminal

Telnet

Web browser

RADview Lite

SNMP


Terminal

Telnet

Web browser

RADview/Service Center

SNMP


Terminal

Telnet


SNMP


Terminal

Telnet


SNMP




Summary

With Ethernet services becoming the metropolitan – and ultimately wide area – access

technology of choice, coupled with the large installed base of TDM devices, a next

generation multiservice Ethernet NTU is clearly needed. This next generation multiservice

Ethernet NTU must perform the traditional demarcation and OAM functions, as well as

provide support for TDM and analog circuits via pseudo-wire/circuit emulation techniques.

This critical pseudo-wire capability must meet strict performance requirements for a variety

of applications such as cellular backhaul.


Multiservice EthernetNetwork Termination Units

Corporate Headquarters

RAD Data Communications Ltd.

24 Raoul Wallenberg Street

Tel Aviv 69719, Israel

Tel: 972-3-6458181

Fax: 972-3-6498250


www.rad.com

Corporate Headquarters U.S. Headquarters

RAD Data Communications Inc.

900 Corporate Drive

Mahwah, NJ 07430 USA

Tel: (201) 529-1100,

Toll Free: 1-800-444-7234

Fax: (201) 529-5777


www.radusa.com

U.S. Headquarters

The RAD name and logo are registered trademarks of RAD Data Communications Ltd.TDMoIP is a registered trademark of RAD Data Communications Ltd.© 2006 RAD Data Communications. All rights reserved. Subject to change without notice.Catalog no. 802355 Version 3/2006

www.rad.com

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Multiservice Ethernet Network Termination Units

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