Application Notes EDD-Ethernet Demarcation Device IERU Communications Ltd EDD Page 1 of 8
2000 EDD 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. EDD-Ethernet Demarcation Device (the NTU): 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 EDD 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. 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 or EDD) is necessary. Finally, if the customer also needs support for legacy TDM services over the Ethernet connection, a multi-service EDD is required. IERU Communications Ltd EDD Page 2 of 8
The following diagram provides an overview of these EDD capabilities: Media Converters: Single user port Media conversion Management (simple) Basic fault diagnostics Ethernet NTU: End-to-end OAM/CFM Uplink redundancy Traffic classification and prioritization Extensive statistics and threshold notifications Per-service rate control VLAN tagging / stacking Extensive diagnostics EDD: TDM private and leased-lines services E1 diagnostics, including loopback Carrier-class clock recovery and regeneration SLA and CoS The network interface side of the EDD 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/CFM 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, in-band 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 tunneling, and to control the Tunnel P-bit (class of service) and ensure that service provider traffic doesn t interfere with user traffic. IERU Communications Ltd EDD Page 3 of 8
Figure 2 below shows how EDDs fit within service provider networks. DMView NMS Customer Premises EDD MPLS/Metro Network Customer Premises EDD PBX E1 E1 PBX End-to-end service control, SLA, monitoring, and diagnostics The Importance of OAM/CFM 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, in-band and out-of-band management and remote software download and configuration. These capabilities have been part of traditional carrier class technologies like TDM, SDH 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 guarantees widespread availability and interoperability of Ethernet OAM and CFM tools. IERU Metro Ethernet devices fully comply with the latest standards, for instance, the IEEE 802.1ag (CFM), IEEE 802.1ah (OAM/EFM) and ITU-T Y.1731. Those standards plus the certification of interoperability and compliance to MEF-Metro Ethernet Forum recommendations guarantee the original carrier orientation of IERU products. IERU Communications Ltd EDD Page 4 of 8
The Need to Support TDM 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 and E3 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 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 circuits are also extensively used in enterprise voice networks. Traditional PBXs use E1/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, a circuit emulation/pseudo-wire technology ratified as an implementation agreement by the MFA forum (MPLS - Frame Relay ATM) and in recommendations by the ITU-T and IETF PWE3 groups. Those are the RFCs 5086 (CESoPSN) and 4553 (SAToP). As its name implies, circuit emulation/pseudo-wire 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 IERU Communications Ltd EDD Page 5 of 8
accordance with the MEF 8 Implementation Agreement. Pseudo-wire 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. Pseudo-wire 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 TDM over IP encapsulation. 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 EDD 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 multi-service EDD must ensure this happens. Multiservice EDD With Ethernet and TDM being price competitive services, integration of both capabilities into one multi-service EDD contributes to a lower service provisioning cost in several ways. A single multi-service EDD 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 circuits to dozens of E1 or E3 lines. Service providers also require aggregation devices located in their Cos or POPs that efficiently interwork with the integrated Ethernet and Pseudo-wire bit streams coming from multiple customer locations. In addition to handling the switched Ethernet traffic, these devices need to reassemble the Pseudo-wire streams back into E1, E3 or into channelized E3, or STM-1 formats and passes them off to existing TDM/SDH infrastructures. IERU Communications Ltd EDD Page 6 of 8
Service providers require that the capital cost of multi-service EDD be as low as possible. Equally important is the need for minimized OAM costs associated with their access networks. Ethernet and TDM Service Delivery through 3 rd party operators An example of where multi-service Ethernet NTUs are needed is in the delivery and management of Ethernet along with E1/T1 circuits for outof-footprint customers. Since Ethernet connections must frequently be leased from a wholesale/primary 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. DMView NMS Customer Premises Customer Premises EDD Main/Primary Operator 3 rd Party Operator EDD PBX E1 E1 PBX Segment monitoring Monitoring through 3 rd party infrastructure End-to-end service control, SLA, monitoring, and diagnostics IERU Solutions 2104 si 2104 sii 2104 WRI 2106-2GX 2106-4GX 2106-4GX- 8E1 L2 Wire-speed Switch L3 NO YES NO NO NO NO Router QoS 4 queues MAC 4K 8K address PEW3 1 x E1 4 x E1 8 x E1 Ports 4 electrical 2 optical (100 or 1000Mbps) 4 electrical 2 optical (100 or 1000Mbps) 2 electrical 2 optical (1000Mbps) 6 electrical 2 optical (1000Mbps) 4 electrical 4 optical (100 or 1000Mbps) 4 electrical 4 optical (100 or 1000Mbps) Cabinet Plastic Metallic Plastic Wallmounted Other VLAN, Q-in-Q, RSTP/MSTP, EAPS, Jumbo Frames, RADIUS, TACACS, OAM/CFM, CESoPSN, SAToP, QoS, L2 tunneling, traffic monitoring, etc. IERU Communications Ltd EDD Page 7 of 8
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 multi-service EDD is clearly needed. This next generation multi-service EDD must perform the traditional demarcation and OAM/CFM 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. IERU Metro Ethernet products are MEF certified. MEF 9 and MEF 14 recommendations. The IERU name and logo are registered trademarks of IERU Communications Ltd. All other IERU product names are trademarks of IERU Communications Ltd. All other trademarks are the property of their respective holders. 2010 IERU Communications Ltd. All rights reserved. IERU Communications Ltd No. 2 Ha'Haroshet St. 44640 - Kfar Saba, Israel Tel: +972 (9) 7662599 Fax: +972 (9) 7651093 E-mail : contact@ieru.net www.ieru.net IERU Communications Ltd EDD Page 8 of 8