Carrier Ethernet Defined

Transcription

1 Carrier Ethernet Defined A comparison of the key WAN transport methods now available for delivering high-value Ethernet services Describing each method s capabilities and how they support the end-user network This white paper addresses: Benefits of three primary Carrier Ethernet services A comparison of Ethernet features important to enterprises Appropriate applications for each Carrier Ethernet service

2 Contents Carrier Ethernet Evolves as a Wide Area Network Service...3 Ethernet-over-Fiber-MPLS Enhances Carrier Ethernet Services...6 Ethernet-over-SDH Expands Across Networks...7 Ultra-High Bandwidth of Ethernet-over-WDM Attracts Data Center Use...8 Choose Service Based On Application Requirements...8 Carrier Ethernet Service Capabilities Encourage Widespread Use...9 Glossary

3 Carrier Ethernet Evolves as a Wide Area Network Service Initially developed by carriers to deliver Ethernet to enterprise customers at bandwidth levels previously unavailable (10 Mbps, 100 Mbps and 1Gbps), Carrier Ethernet services are becoming prevalent across leading European metropolitan centers. Some services are available across national boundaries. Carrier Ethernet services offer enterprises an alternative WAN transport service to augment and replace existing leased line and data services. Carrier Ethernet has been developed from Ethernet for local area networks with modifications to enable its use in the wide area. These modifications include: Enhanced equipment redundancy in hardware and software to make them carrier class. Traffic engineering techniques, such as Multiprotocol Label Switching (MPLS) to scale network services with consistently high resiliency and Quality of Service (QoS). MPLS provides a target of 50 ms restoration for network services. Implementation of Virtual Private LAN Services (VPLS) to provide multipoint Ethernet for a single company across geographic locations. VPLS overcomes the inherent limitations of Ethernet VLANs by adopting MPLS for multipoint applications, using a defined encapsulation scheme for Ethernet traffic. Enhancement of SDH technology, to transport efficiently Ethernet traffic across optical networks, through the Generic Framing Procedure (GFP) and Link Capacity Adjustment Scheme (LCAS). These enhancements give the carrier a data service that enables service level agreements (SLAs) for business customers. These SLAs establish metrics for guaranteed data delivery over a specified timeframe, with defined refunds or credits when these metrics are not met. The very top level guarantees little or no time lag for data packets, which is suitable for MPEG 2 video traffic. The lowest level provides only best efforts delivery of traffic, with no guarantees. Because the highest quality Carrier Ethernet is now capable of providing compressed MPEG 2 video quality transport that eliminates freeze frames, several carriers are deploying Carrier Ethernet for aggregation and backhaul of video, voice and Internet services over DSL, commonly referred to as the Triple Play. 3

4 There are three types of Carrier Ethernet: Ethernet-over-SDH (EoS) Ethernet-over-Fiber (EoF) Ethernet-over-WDM (EoW) Since each is supported by a separate network infrastructure using different optical transport technology, they differ in terms of resiliency, bandwidth-level offered and available footprint. Incumbent national carriers and leading alternative carriers are the primary providers of Ethernet Wide Area Network (WAN) transport services. Ethernet-over-Fiber was the first deployed by alternative carriers to attract enterprises away from the leased line, Frame Relay and ATM services of incumbent national carriers. EoF services have continued to improve through traffic engineering techniques, specifically MPLS. Since national carriers widely deployed SDH for ultra-reliable E1, E3, STM-1, STM-4 and STM-16 transport, Ethernet-over-SDH has become one of the preferred technologies for these carriers. Ethernet-over-WDM has been proven inside core networks and in ultra-high bandwidth applications that require n x 100 Mbps, 1 Gbps or 10 Gbps throughput, such as realtime disk mirroring between dispersed data centers. While point-tomultipoint services are becoming available in all these cases, most services today are still point-to-point. Enterprises are generally uninterested in underlying network technology. But they do care about application-sensitive service attributes like bandwidth, quality of service, restoration and resiliency, latency and future enhancement of existing network assets to support Carrier Ethernet. EoS, EoF and EoW differ considerably in these service attributes, as shown in Table 1 on the next page. 4

5 Service Attribute Bandwidth Speeds Quality of Service Restoration/ Resiliency EoF 10 to 100 Mbps and 1 Gbps Equal CIR and PIR Others: PIR larger than CIR Rapid Spanning Tree Protocol (RSTP) typically over 100 ms in a moderate-sized network. The actual restoration time is dependent on the number of nodes. EoF-MPLS networks have a target restoration time of 50 ms. EoS (Leased Line, Switched) 2, 4, 6, 8, 10, 50, 100 Mbps and 1 Gbps Guaranteed (EoS LL*) Through CIR and PIR for Sw EoS** with PIR > CIR 10 to 50 ms or less for EoS LL For Switched EoS, there are three options: (1) SDH protection at 50 ms, (2) Rapid Spanning Tree Protocol at > 50 ms and (3) Link Capacity Adjustment Scheme (LCAS) at 50 ms EoW Latency Medium, rises w/traffic Low Low Connectivity between Enterprise to Carrier POP Generally a single link, unless the customer requests redundant connections Redundant connection through SDH access ring Point-to-Point Yes Yes Yes 1 Gbps, 10 Gbps, 200 Mbps ESCON, 1.25 Gbps FICON, 1 and 2 Gbps Fiber Channel Guaranteed Optical protection to 50 ms Single or redundant link from the enterprise to POP Multipoint-to- Multipoint Strengths Limits Common Use Application Carriers Yes Price Multipoint support Non-ring based Can t transport TDM, voice and Ethernet simultaneously Lack of service > 1 Gbps Replacement for or to augment Frame Relay (FR) or ATM for Internet access and site-to-site links Colt Telecom France Telecom Telefonica No (EoS LL) Yes (Sw EoS) Ring resiliency and transport for voice and data across multiple sites Low latency Lack of bandwidth greater than 1 Gbps EoS LL replacement for leased line (LL) Sw EoS replacement for or to augment ATM and FR and some leased line for Internet access, site- to-site and storage transport Service aggregation for LL, voice (packet or TDM), Ethernet in one interface Colt Telecom Deutsche Telekom France Telecom Telefonica No Ultra-high bandwidth (1 Gbps and greater) Low-latency Generally for bandwidth options of 100 Mbps and greater only Storage transport between corporate site to in-house or thirdparty data center Colt Telecom BT ** EoS LL = Ethernet-over-SDH Leased Line ** SwEoS = Switched Ethernet-over-SDH Table 1. Comparison of Carrier Ethernet Services 5

6 Ethernet-over-Fiber-MPLS Enhances Carrier Ethernet Services Carriers initially deployed EoF services to connect enterprise LANs across metro regions over fiber, and several carriers have active EoF services today. Enterprise customers generally use the service as a replacement or addition to a lower-speed ATM or Frame Relay data service for Internet access or site-to-site connections. EoF service is usually available as point-to-point or multipoint-to-multipoint at the following bandwidth levels: 10 to 100 Mbps and 1 Gbps. The foundation of an EoF network is either a point-to-point Ethernet connection through carrier-grade Ethernet switches or a mesh network of Ethernet switches. Enterprises connect to the Ethernet core network at the central office through a fiber interface powered by an optical device that drops an Ethernet connection to the user, and an enterprise connection may have two diverse routes from the enterprise site to the central office or POP. Enterprises need to be cautious, because some EoF network services offer best efforts only. Where service providers do not provide SLAs, packet transport performance is limited by subscription levels. When these networks are oversubscribed, latency and jitter across paths increase. As a result, enterprises can see a marked decrease in network performance, which affects applications that use the EoF link. Newer EoF networks are addressing latency and restoration time issues found in earlier networks. Carriers now use MPLS traffic engineering capability inside the core of an EoF network to offer point-to-point services, along with multipoint-to-multipoint services enabled by VPLS, a new standard that uses MPLS and the Martini encapsulation scheme. VPLS gives carriers a way to deliver virtual private network services, commonly referred to as E-LANs by the Metro Ethernet Forum. Local area specifications for Ethernet do not scale in the wide area because the number of VLAN tags is limited by specification. VPLS overcomes this problem and provides additional resiliency. Some carriers have adopted VPLS in their networks, while others plan to deploy the technology to offer robust VPN, multipoint services. These point-to-point and multipoint-to-multipoint services can provide reduced latency and decreased restoration time of less than 50 ms, equal to the restoration time of EoS or EoW. These EoF-MPLS networks are being adopted by enterprises because they offer SLAs that are similar to those available through ATM and Frame Relay. The key advantages of EoF-MPLS are competitive pricing and availability. The key disadvantage of EoF-MPLS is its higher latency caused by buffering of traffic as it traverses multiple Ethernet switches. In addition to MPLS, another solution is to use Ethernet-over-SDH at the core to take advantage of SDH s proven reliability. This has the important added advantage of facilitating handoffs to the installed base of legacy infrastructure found in carrier networks today. EoF with MPLS or SDH at its core will become more attractive to business users who may move away from their existing lower-speed Frame Relay and ATM services. 6

7 Ethernet-over-SDH Expands Across Networks Ethernet-over-SDH emerged as carriers and system vendors developed specifications to extend the functionality of SDH networks to support Ethernet traffic at bandwidth levels that are friendly to enterprise applications. To ensure consistent deployment across SDH networks, rapid adoption, and eventual ubiquity, Ethernet-over-SDH is anchored by a set of standards developed by leading SDH vendors. There are two types of EoS services: EoS Leased line (EoS LL) uses a dedicated SDH channel per customer. Essentially, EoS LL is a Leased Line service with a native Ethernet interface. Switched EoS (Sw EoS) shares an SDH connection among several enterprises. To ensure service quality, each enterprise is assigned a VLAN tag and specific QoS through a committed information rate (CIR) for guaranteed bandwidth and a peak information rate (PIR) for traffic bursts. Effectively, Sw EoS offers a bandwidth-guaranteed Ethernet service that takes advantage of the low latency and minimal jitter of SDH at a lower price than EoS LL. EoS Leased Line and Switched EoS are the premier Ethernet WAN transport services and offer the following advantages: Very low latency, since buffering is administered only on the ingress and egress switches and not across intermediate switches Very high resiliency and restoration. EoS LL as a TDM service takes advantage of SDH s 50 ms restoration, while Sw EoS can use SDH or LCAS for 50 ms restoration and Rapid Spanning Tree Protocol which restores from 50 ms to seconds Low jitter Guaranteed quality for EoS LL, since it is a TDM service, and high QoS for Sw EoS since it offers CIR and PIR on VLAN-designated traffic Resilient transport across multiple sites for TDM, voice (packet and TDM) and data services with ring technology EoS LL is well suited to augment or replace an existing leased line service like E1, E3 or STM-1, while Sw EoS is better suited to augment or replace Frame Relay or ATM connections. Together, EoS LL and Sw EoS can support all business Ethernet WAN transport needs. National carriers are significant providers of EoS services with services available in leading metropolitan centers in Europe. Carriers deploy EoS using new multiservice provisioning platforms (MSPPs) or existing SDH equipment, coupled with EoS line cards or external devices that map native Ethernet traffic to SDH frames. Service providers have also adapted service management systems to support Ethernet. They currently offer point-to-point services through EoS LL and may offer multipoint-tomultipoint service through Sw EoS. 7

8 Ultra-High Bandwidth of Ethernet-over-WDM Attracts Data Center Use Ethernet-over-WDM emerged as carriers wanted to offer ultra-high bandwidth services (GigE level) to connect customers data centers and meet the needs of other specialized, bandwidth-hungry applications, such as video transport. In addition, EoW also supports storage network transport and large file transfers between corporate sites or data centers. EoW is deployed using either Dense Wavelength Division Multiplexer (DWDM) or Coarse Wavelength Division Multiplexer (CWDM) technology. Generally, carriers use less-expensive CWDM to connect the customer site to the service provider POP and DWDM between POPs to transport site-to-site traffic. However, some carriers may use DWDM across the entire network from customer site to POP. EoW offers high potential resiliency through optical protection at 50 ms or less and very low latency. Protected and unprotected links are available. Service providers offer Ethernet-over-WDM services at 1 Gbps and 10 Gbps. In addition to Ethernet, many wavelength services offer support for multiple protocols, such as ESCON, FICON and Fibre Channel. EoW s primary strength is augmenting leased line data connections to support storage and ultra-high speed data transport. Choose Service Based On Application Requirements According to a recent survey by International Orange Strategies, a leading telecommunications analyst firm, file transfer, Internet access, LAN-to- LAN and communications are the dominant applications for many medium to large enterprises with at least 3 E1s of bandwidth, while VoIP and storage transport applications also feature prominently. In order to support these services through Carrier Ethernet, enterprises need to weigh their bandwidth requirements and the latency and resiliency characteristics of the various Ethernet services. EoS and EoW have low latency because they require minimal packet buffering across nodes. With EoF-MPLS, latency is greater and degrades per node and does not compare to the levels offered by EoS or EoW. Graph 1 compares relative latency among EoF-MPLS, EoS and EoW Latency End-to-End Normalized Latency * Normalized latency with EoS = 1 per node. The lower the number the better the latency EoW EoS EoF- MPLS Graph 1. Normalized End-to-End Latency* 8

9 Common enterprise applications like traditional LAN-to-LAN transport, , Internet access and latency-dependent applications such as VoIP, storage networking, imaging and video can be transported through MPLSengineered EoF services, EoS or EoW. Network resiliency and restoration time can be different across EoS, EoF- MPLS and EoW. EoS Leased line offers failover within 50 ms. Switched EoS can provide failover to 50 ms depending on the restoration scheme, and EoW provides failover as quickly as EoS. EoF-MPLS networks has restoration goals of within 50 ms. According to a leading market research firm*, medium and large enterprises give high priority to reliability, redundant connections, service level agreements and low latency. Table 2 summarizes how each Carrier Ethernet service measures up to these concerns. * International Orange Strategies Service Attribute EoS LL Sw EoS EoF EoW Reliability and restoration Redundant Connections High with 50 ms restoration time Medium to high with 50 ms restoration time available through SDH or LCAS or greater if RSTP is used Medium to high, with target of 50 ms Available Available Available, but not-standard High with 50 ms restoration time Available SLAs Guaranteed CIR, PIR, with PIR > CIR CIR, PIR, with PIR Guaranteed = CIR generally Latency Low Low Medium Low Table 2. Comparison of Ethernet Features Important To Enterprises Carrier Ethernet Service Capabilities Encourage Widespread Use Enterprise customers have a number of options for Ethernet services across the WAN. Many enterprise applications such as , Web access, VoIP and file transfer can be adequately served by EoF-MPLS and services from such networks will attract more ATM and Frame Relay users for common enterprise application demands. Multipoint applications such as VPNs can be served through EoF-MPLS networks by using VPLS as the enabling technology EoS LL and Sw EoS are premier Ethernet services offering high resiliency and low latency at a variety of bandwidth levels. This makes them appropriate for most, if not all, enterprise business applications, including , file transfer, VoIP, storage transport, imaging and Internet access. As a ring-based service, EoS is highly suitable for connections with multiple sites and for transport of TDM voice and data services. 9

10 EoW offers ultra-high bandwidth with low latencies and high resiliency, making it ideal for very large file transfer and storage transport. In addition to data center connectivity, enterprises can use EoW between other bandwidth-hungry links. These Carrier Ethernet options allow medium and large enterprises to select the most appropriate way to meet their existing business requirements. They can choose among services from their incumbent national service provider or existing WAN vendor, enjoy more bandwidth and benefit from the operational savings that are available through Carrier Ethernet. The author wishes to recognize Bell Laboratories for their contribution to this paper. 10

11 Glossary Committed Information Rate (CIR) The throughput rate provided a service provider guarantees for a network service. Ethernet-over-SDH Leased Line (EoS LL) A service that allows enterprises to connect multiple locations using Ethernet as an end-to-end protocol over a SDH ring. EoS LL uses a dedicated SDH channel to transport the Ethernet traffic end-to-end. EoS LL corresponds to the Metro Ethernet Forum s E-Line service. Generic Framing Procedure (GFP) GFP provides a bandwidth efficient way to map multiple protocols (eg., Etherent) onto packets for transport over an optical network such as SDH. Link Capacity Adjustment Scheme (LCAS) A signaling protocol used in relation to the hitless increase and decrease of SDH bandwidth. Multiprotocol Label Switching (MPLS) MPLS is a set of standards that bridges the gap between connectionless IP networks, where routing decisions are made at every hop, and connection-oriented networks that deliver point-to-point services such as ATM and Frame Relay. MPLS uses pre-determined data connections, known as Label Switched Paths (LSPs), to transport traffic through core networks. Like ATM virtual circuits, these MPLS LSPs have defined properties such as bandwidth availability, bandwidth utilization and a QoS level. MPLS standards define Fast Reroute recovery mechanisms to survive link or nodal failures with the goal of a 50 ms restoration. Packet Buffering Memory deployed in networking equipment to manage the flow of packets in and out of line cards, and thus in and out of networking nodes. They are used in conjunction with packet classification and processing functions performed by the switch or router. Packet buffers add some latency in the transmission of packets through a networking node, however. Peak Information Rate (PIR) Defines an upper limit to the throughput rate a service provider allows for a network service. Traffic can burst beyond the CIR up to the PIR in cases where the PIR > CIR. Rapid Spanning Tree Protocol (RSTP) A standard to detect loops and activate redundant paths to enable an Ethernet network to reconverge and transmit traffic in event of a failure. Rapid Spanning Tree Protocol improves upon Spanning Tree Protocol by speeding up reconvergence time. It specifies all links as point-to-point rather than LAN connections and eliminates the long timeouts before reconvergence. Switched Ethernet-over-SDH (Sw EoS) A service that allows enterprises to share an SDH connection among multiple locations using Ethernet as an end-to-end protocol. Sw EoS enables a multipoint service that can be compared to the Metro Ethernet Forum s E-LAN service. Synchronous Digital Hierarchy (SDH) The standard for transmission on optical fiber used by telecommunication operators for more than 10 years. Time Division Multiplexing (TDM) A traditional multiplexing solution where each signal is assigned to a time slot, classically used to carry PCM voice, n x 64 Kbps leased lines or ISDN. Wavelength Division Multiplexing (WDM) A solution to multiplex optical signals on the same fiber using a set of different wavelengths. 11

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