Deploying Multiservice Applications Using RPR Over the Existing SONET Infrastructure

Deploying Multiservice Applications Using RPR Over the Existing SONET Infrastructure

Introduction The migration of Ethernet technology from the LAN to metro networks, driven by increasing demand in VoIP, data and video traffic, makes metro Ethernet service one of the most promising networking opportunities. However, due to lack of resiliency in native Ethernet features and current economic conditions, service providers are looking at deploying Ethernet services over their existing, proven and reliable SONET infrastructure with the new, emerging, data friendly, next-generation SONET technologies such as GFP, VCAT and RPR. This paper discusses why these emerging technologies over SONET are attractive to provide metro Ethernet services, how these technologies can be used to deploy Ethernet and what services can be offered. Metro Ethernet Service On The Rise Service providers have increased their CAPEX spending on network transport equipment with Ethernet interfaces to meet growing customer demand for IP and Ethernet services to carry voice, data and video traffic via the metro network. The metro Ethernet equipment market will have a more than 50% CAGR from 2003 to 2008 according to recently published reports. Ethernet was initially developed as a LAN technology. The biggest challenge in deploying Ethernet service in the MAN or WAN is how to offer carrier-class features with a more reliable and manageable solution than Ethernet running in the LAN environment. Many standards bodies, including the IEEE, ITU, IETF and MEF, are working to define new capabilities to make Ethernet services as reliable as traditional TDM services. For example, issues are being addressed to provide faster protected switching with better performance monitoring, troubleshooting, and improved OAM features. Ethernet, which offers higher bandwidth at a lower price per bit, is a simpler protocol and has been deployed for years in the LAN. Ethernet provides a cost-effective, common interface to deliver different services. Service providers plan to offer more IP and Ethernet related services, including Internet access, Wi-Fi, IP VPN, IP telephony, VoD and remote storage. Most of the Ethernet services offered today are either private line service-based (point-to-point) or transparent LAN service-based with best-effort class of service only. With the advancement of Ethernet standards and new emerging services, service providers will begin to roll out classes of servicedifferentiated offerings supported with SLAs. Also, service providers are moving toward traffic aggregation and switched Ethernet transport to optimize network bandwidth and resources rather than simply providing point-to-point Ethernet transport. A carrier-class Ethernet access technology that can carry multiservice traffic with Layer 2 switching capabilities, SLAs, QoS guarantees and traffic prioritization is highly desirable. For your convenience, a list of acronyms can be found at the end of this document. 1

One of the most promising access technologies is RPR. RPR is designed to provide carrier-class features to transport customer traffic via a shared media ring with multiple service classes. Proprietary versions of RPR have previously been available, but the recent IEEE 802.17 RPR ratification has created an industry standard. This standardization will help to improve interoperability and drive down equipment cost. Standardization of RPR also encourages more service providers, equipment vendors and chip manufacturers to enter the RPR market. What is RPR? RPR consists of two counter-rotating rings called inner and outer ringlets. Packet traffic travels in one direction in one ringlet and in the opposite direction in another ringlet. Unicast packets are stripped from the ring by the destination RPR station. Multicast and broadcast packets are stripped from the ring by the source station, copied into target receiver stations and continue downstream. The stations on the ring can automatically negotiate for bandwidth among themselves via a fairness algorithm. Each station has a topology map of the ring and can send data on the optimal ringlet towards its destination. Both ringlets can be used to carry working traffic. The protection algorithm avoids failed spans to protect against fiber station failure. RPR is a MAC layer protocol and can be carried over different physical media. Key features include: Class of Service One of the key features in the RPR specification provides class of service to support multiservice traffic with different delay and jitter characteristics. Three classes of service are defined for RPR MAC: high, medium and low. The high-priority class supports strictly bounded delay and jitter applications such as VoIP and real-time video applications with non-preemptive bandwidth guarantees. The medium-priority class supports applications that are less sensitive to delay and jitter such as non-real-time video and VPN services. User-provisioned CIR and EIR guarantees are supported for different service requirements. The low-priority class of service supports best-effort applications that do not need bandwidth guarantees such as consumer Internet access. With three unique classes of service, service providers can offer differentiated Ethernet services with different price points to satisfy different customer requirements. Spatial Reuse Removing the packet from the ring by the destination station provides spatial reuse of the ring bandwidth since the path between the source and destination RPR stations only belongs to part of the total ring length. 2

Fairness Algorithm The fairness algorithm is important for resource allocation, ensuring the fairness-eligible traffic has fair access to the ring bandwidth. The fairness-eligible traffic is low-priority or excess traffic in the mediumpriority class and the fairness algorithm regulates this traffic. The goal is to inject as much traffic into the ring for best utilization, without violating the SLA. Protection RPR has a dual ringlet. Two paths always exist between any two nodes in the ring so if a span in one ringlet fails, traffic can be automatically switched into another path within 50 ms. Why use RPR and what are the challenges? RPR is a distributed switch, peer-to-peer architecture. The most significant economic impact RPR offers is in driving down the CAPEX savings by maximizing the bandwidth utilization in the network. RPR provides a high-capacity gain by sharing the entire ring bandwidth with all the RPR stations that belong to the ring. Therefore, RPR simplifies the network architecture and reduces the network equipment used. The major challenge for RPR is that the technology is still new so interoperability and management support can be an issue. Most of the incumbent service providers OSSs are circuit-based for point-to-point circuits so enhancements are needed to support a shared multi-point solution such as RPR. Why RPR over SONET? RPR was originally designed as a possible alternative to SONET. Special attention was given in the standard to ensure that RPR provided a SONET-like sub-50 ms resiliency. RPR uses packet-switching technology while SONET uses TDM technology to add and drop traffic from nodes in ring topologies. But SONET is still the dominant transport infrastructure and has a large installed base. Replacing embedded SONET networks with any new architecture is not feasible under current economic conditions. The slow down of the North American telecommunication industry and the cost pressures faced by carriers are contributing to the viability of SONET for today's transport network. So instead of replacing SONET with RPR, service providers plan to deploy RPR over SONET and equipment vendors are working to integrate RPR functionality into their MSPPs. MSPPs provide an optimized, cost-saving solution to consolidate video, data and voice services on the existing SONET-based network infrastructure. Running RPR over SONET gives service providers efficiency in supporting Ethernet while continuing to run TDM services (DS1, DS3, OC-N) over the remaining SONET capacity. RPR and other SONET architectures such as UPSR can co-exist on the same ring. For example, in Figure 1, the OC-48 SONET ring is running a STS-24 RPR ring for data service with the other half of ring bandwidth used for traditional TDM services. So, part of the ring bandwidth can be used to run TDM service with UPSR or BLSR protection and the other ring bandwidth can be used to run data or video traffic using an RPR layer of protection. 3

MSPP, RPR Station Ethernet, DS3, DS1, DS3, DS1, RPR over SONET Ring DS3, DS1, OC-48 MSPP/ADM MSPP/ADM STS-24 RPR Ring STS-24 for TDM Ethernet, DS3, DS1, MSPP, RPR Stations Ethernet, DS3, DS1, Figure 1: RPR Shared Path Over Existing SONET Transport of data or digital video over SONET has traditionally been problematic due to the inefficient manner that data or video is mapped into standard SONET/SDH time slots (e.g. STS-1, STS-3c, STS-12c, etc.) because none of the current data or video interface standards was designed for WAN transport. VCAT with point-to-point EoS solutions has reduced this inefficiency somewhat. But, the inherent bursty nature of Ethernet traffic still results in some inefficiency on point-to-point links. Running RPR over SONET provides a statistical multiplexing layer, allowing sharing of SONET paths for bursty data traffic among multiple nodes on a ring to increase bandwidth efficiency. 4

What is VCAT? VCAT is an inverse multiplexing technique that enables an arbitrary number of either low-order (VT1.5) or high-order (STS-1/STS-3c) SONET channels to be bundled into one VCG. The VCG members can be transported across the SONET network in different paths and recombined at the drop side of the connection. Several key benefits of VCAT include: Finer granularity of SONET bandwidth mapping for transporting various video and data interfaces (STS-1-nv, STS-3c-nv) Diverse routing so individual transport paths can be routed independently through the network to lift the constraint of the contiguous concatenation of the traditional SONET payload Virtual concatenation transparency to intermediate nodes so only the transport nodes in the add/drop point are required to upgrade to support VCAT Thus, the VCAT standard helps to optimize time slot mapping to maximize available bandwidth. VCAT allows selection and combination of smaller elements of the SONET/SDH bandwidth (VT1.5-nv, STS-1-nv, STS-3c-nv) for better use of the SONET bandwidth. RPR over SONET provides a flexible partition of the ring bandwidth for running legacy TDM, data traffic using RPR and even other emerging protocols such as DVB-ASI, Fibre Channel, FICON and ESCON using GFP framing directly over SONET. STS - TDM TDM Voice/Data/Video Ethernet RPR VCAT SONET GFP DVB-ASI SAN STS-DVB, SAN STS-RPR Figure 2: MSPP Protocol Stack and Bandwidth Allocation 5

Some service providers may want to deliver VoIP service instead of traditional TDM-based voice service. VoIP traffic can run over RPR rings since the high-priority voice traffic enters into the ring and gets precedence over low-priority data traffic. This process helps to reduce the jitter and delay of the voice traffic when it flows via the RPR network. Another key benefit of RPR, which is similar to VCAT, is that RPR blades are only added to SONET NEs where RPR ingress/egress is needed. The remaining SONET nodes are transparent to the RPR traffic. This process keeps service providers investment low in terms of equipment and operational upgrade expenses, while helping to leverage SONET to generate added revenue from new services. RPR over SONET: Applications RPR is a carrier-class Ethernet access technology that can carry multiservice traffic with Layer 2 switching capabilities, SLAs, QoS guarantees and traffic prioritization. RPR is desirable for a wide range of voice, data, and video applications in the access network such as Ethernet private LAN services, metro Ethernet transport and video distribution. RPR can support a number of applications, including: Transparent LAN Service TLS or Ethernet Private LAN service is an application to interconnect enterprise or business users with multiple sites over a private or public network. Private Ring A dedicated ring is a distinct private ring that has all its bandwidth dedicated to one customer. Some large enterprises and organizations in the healthcare, financial, education and manufacturing industries prefer to have their own dedicated ring to interconnect their sites. Deploying RPR over SONET provides a data-aware SONET ring to the customer s many locations with better bandwidth management capabilities to leverage multi-point bursty Ethernet traffic. Service providers are also considering providing RPR dedicated ring service for a managed TLS metro ring service to enterprises. This service provides a better bandwidthefficient solution than the current dedicated SONET ring offering using, DS1 or DS3 TDM circuits for interconnections between locations. 6

100 Mbps GigE RPR over SONET 10 Mbps 100 Mbps GigE Figure 3: Ethernet Dedicated Private Ring for a Single Customer Shared Ring A shared RPR ring provides any-point-to-any-point connectivity between an enterprise s various sites, but may be shared by many customers as in a VPN. A shared RPR ring can also allow companies in multi-tenant office buildings to share capacity on metro networks. Customer B Customer B Customer A RPR over SONET Customer B Customer A Customer A Figure 4: Ethernet Shared Access Ring for Customers A and B 7

Internet Access Statistically multiplexed point-to-point access service networks aggregate different customer access links into a GigE interface before entering a carrier s service network. 10/100 Mbps A B C D A, B, C, D, E,F GigE RPR over SONET 10/100 Mbps A E GigE B E F Figure 5: Internet Access using RPR 8

Video Distribution The ring-based architecture of RPR is ideal for broadcast video and multicast applications where a single copy of the video stream is moving around the network and the video stream is selectively dropped at each location per customer demand. Drop and Repeat RPR Node Pass-Through RPR Node RPR Node Return Path Drop RPR Node Single Head End Channels are dropped and repeated at each node and passed onto next node on the SONET ring. Distribute Video to Different Hubs Figure 6: Video Distribution using RPR Conclusion The development of next-generation SONET technologies, such as GFP, VCAT and RPR, gives service providers a new opportunity to build a converged network without replacing their metro SONET networks. The RPR solution is integrated into the MSPP platform as an interface card and provides multiple service classes from best-effort to voice-grade services with sub-50ms restoration. The solution can be used to roll out Ethernet Private LAN services in metro and access networks. The challenges that remain include solving the interoperability issue and determining the best way to manage services within the existing OSS framework. References [1] IEEE 802.17, Resilient Packet Ring [2] ITU-T G7041, Generic Framing Procedure [3] ITU-T G707, Network node interface for the synchronous digital hierarchy [4] ANSI T1.105-1991, Digital Hierarchy Optical Interface Rates and Formats Specifications 9

Acronym BLSR CAGR CAPEX CIR EIR EoS GFP GigE IEEE IETF IP ITU LAN MAC MAN MEF MSPP NE OSS QoS RPR SDH SLA SONET TDM TLS UPSR VCAT VCG VoD VoIP VPN WAN Descriptor Bi-directional Line Switched Ring Compound Annual Growth Rate Capital Expense Committed Information Rate Excess Information Rate Ethernet over SONET Generic Framing Procedure Gigabit Ethernet Institute of Electrical and Electronic Engineers Internet Engineering Task Force Internet Protocol International Telecommunications Union Local Area Network Medium Access Control Metro Area Network Metro Ethernet Forum MultiService Provisioning Platform Network Element Operational Support System Quality of Service Resilient Packet Ring Synchronous Digital Hierachy Service Level Agreement Synchonous Optical Network Time Division Multiplexing Transparent LAN Service Unidirectional Path Switched Ring Virtual Concatenation Virtual Concatenation Group Video on Demand Voice over IP Virtual Private Network Wide Area Network 10