Enabling High Availability for Voice Services in Cable Networks

Transcription

1 White Paper Enabling High Availability for Voice Services in Cable Networks When customers place a telephone call, they expect it to go through on the first attempt and they expect it to continue without disruption. This user expectation requires a very high level of availability, which has traditionally been measured as network availability. Certainly, network availability is a primary concern of cable operators. But as cable operators deploy IP-based voice telephony services, they want to achieve availability levels comparable to the public switched telephone network (PSTN). To deliver a PSTN-equivalent user experience, it is essential to measure both network availability and availability of the voice service. All advanced cable services place stringent requirements on the network for availability, latency, jitter, and other parameters that contribute to a user s experience (Figure 1). This paper focuses on the availability aspect of these requirements. Figure 1 Among the Advanced Cable Services, PSTN-Equivalent Voice Has the Most Stringent Requirements for the Factors that Affect a User s Experience PSTN-Grade; Has Stringent; Effort; Loss; Best-Effort; PSTN-Equivalent; PSTN-Equivalent; On-Demand; High-Definition Example: PSTN Grade Voice has Stringent Network Requirements Other Applications / Services Have similar Network Requirements Availability effort PSTN Equivalent VoIP 99.94% Commercial Services On Demand Video Jitter <40ms <0.25% Packet Loss loss Digital Video <150ms High Definition TV Online Games Latency Best Effort effort Data PSTN Equivalent Voice The concept of service availability is also important for services such as commercial high-speed data, broadcast video, and video on demand (Figure 2). With its leading, comprehensive set of products and technologies for IP-based data networks, voice over IP (VoIP), and video, Cisco Systems offers cable operators the solutions that enable high availability today for advanced cable services. However, because PSTN-equivalent voice communications have among the most stringent requirements, this paper focuses on service availability for IP-based voice telephony services on a cable network. All contents are Copyright All rights reserved. Important Notices and Privacy Statement. Page 1 of 5

2 Figure 2 The Different Advanced Cable Services have Different Requirements for Service Availability Availability Requirement Commercial High-Speed Data PSTN Equivalent Voice Second/Teen Line Voice Video on Demand Broadcast Video Residential High-Speed Data () High-Speed Data Voice Video Services How Many Nines? Measuring True Network and Service Availability Five nines is the classic measurement of PSTN availability, meaning the network is up percent of the time. However, in the document VoIP Availability and Reliability Model for the PacketCable Architecture (Document: PKT-TR-VoIPAR-V ), PacketCable notes that the popular myth of five nines ( percent) for end-to-end PSTN reliability is incorrect. To calculate a truly equivalent value for PSTN availability, the document breaks down the subsections of the PSTN and draws a direct analogy to an equivalent, IP-based network. Based on this analysis, PacketCable determined that the end-to-end availability of a VoIP network should be greater than percent. In addition to uptime, other service-availability metrics are important because they directly affect the user experience. For voice, these metrics are the number of existing calls that are dropped and the number of ineffective attempts for new calls. As defined in the PacketCable document, the end-to-end network should have service-availability metrics of no more than 125 calls dropped per million and 500 ineffective attempts per million. These values are exactly the same as the PSTN requirements for network and service availability as set forth in the Bellcore GR series specifications. When evaluating network and service availability, cable operators need to consider the end-to-end network and the Cisco portion, not just individual network elements. Figure 3 presents a reference architecture for an end-to-end cable network; the Cisco portion of the network is shown in the highlighted box. The Cisco portion of the network excludes the cable modem and hybrid fiber-coaxial (HFC) plant at one end and the local exchange and access networks at the point where the cable network connects to the PSTN. To meet the PacketCable guidelines, Cisco recommends that its portion of the network have uptime of greater than percent, with fewer than 65 calls dropped per million and fewer than 275 ineffective attempts per million. Based on these values, a cable operator can be confident of achieving PSTN-equivalent availability when deploying IP-based voice telephony services today. All contents are Copyright All rights reserved. Important Notices and Privacy Statement. Page 2 of 5

3 Figure 3 Availability Metrics in the Cisco Portion are Key Contributors to End-to-End Network Availability] A Leading Perspective for Assuring High Availability Unlike vendors that offer products only for selected services or areas in a cable operator s network, Cisco Systems offers voice solutions that cover that network from an HFC plant to a PSTN gateway. With this systemwide perspective, Cisco can deliver an integrated approach to service availability identifying optimal features and implementing them on the most appropriate platforms. Cisco continues to develop high-availability features that will help reduce outage time for a voice call if the network fails. These features include fundamental capabilities such as support for software and hardware redundancy; routing-optimization technologies for fast convergence; and fiber transport technologies with features for rapid failure recovery such as Dynamic Packet Transport (DPT). Cisco offers additional, innovative features for high availability, including Cisco Nonstop Forwarding (NSF), Cisco Stateful Switchover (SSO), and in-service software upgrades. Planned for delivery in phases throughout , these features will be implemented as appropriate in Cisco routers, switches, PSTN gateways, and cable modem termination systems (CMTSs). As shown in Figure 4, all of these Cisco features will further reduce a cable operator s defects-per-million (DPM) value for calls dropped and ineffective attempts. All contents are Copyright All rights reserved. Important Notices and Privacy Statement. Page 3 of 5

4 Figure 4 Cisco Plans to Release Additional High Availability Features by Year End 2004, Incrementally Reducing the Values for the Two Key Voice Service Metrics. Fast Convergence for Layer 3 Routing Within the IP network, the Layer 3 routing architecture and its ability to recover (converge) quickly from a failure is an important aspect of high availability. If a component or link failure causes a Layer 3 topology change, the routing architecture should enable fast convergence to prevent dropped calls, meaning a convergence time of less than three seconds (the calls-dropped threshold). Fast convergence also helps reduce mean time to repair (MTTR) a measurement of how quickly a router recovers from a failure which has a direct impact on service availability metrics. Cisco s leading technologies for IP routing enable Layer 3 convergence in less than three seconds (and in certain cases even faster). This reduced router convergence time is possible because of Cisco s enhancements to shortest-path-first (SPF) calculation algorithms, exponential timers, and subsecond hellos. The Impact of Operational Practices on High Availability Day-to-day operational activities and procedures can have a significant, ongoing impact on network and service availability. Cisco has helped some of the largest service providers in the world to improve their operational practices and associated impact on service availability. For example, in a Cisco consulting engagement for a major U.S. service provider, a joint team focused on several aspects of network operations, including: Regression testing of changes in network elements to minimize unplanned outages Processes and procedures for planned outages to deploy hardware and software upgrades Network management practices that can proactively address availability issues Architecture and planning to consider network and service availability A systemwide troubleshooting methodology and escalation process for fast response to outages As a result of this engagement, Cisco helped the service provider reduce DPM for data services from more than 2000 to fewer than 100 a 95 percent improvement. All contents are Copyright All rights reserved. Important Notices and Privacy Statement. Page 4 of 5

5 Cisco Leadership for High Availability in Cable Networks With its focus on service and network availability, Cisco Systems leads the industry in delivering cable network solutions that support the stringent requirements of voice telephony. This focus is implemented through high-availability technologies and advanced Layer 3 routing in Cisco networking products and Cisco IOS Software, as well as guidance for cable operators on network design and operational procedures. An end-to-end Cisco network can help cable operators meet PacketCable specifications for network and service availability today and deliver the positive user experience that can make voice telephony services a market success. For More Information To learn more about Cisco products and services for cable operators, visit: Corporate Headquarters 170 West Tasman Drive San Jose, CA USA Tel: NETS (6387) Fax: European Headquarters Cisco Systems International BV Haarlerbergpark Haarlerbergweg CH Amsterdam The Netherlands www-europe.cisco.com Tel: Fax: Americas Headquarters 170 West Tasman Drive San Jose, CA USA Tel: Fax: Asia Pacific Headquarters Capital Tower 168 Robinson Road #22-01 to #29-01 Singapore Tel: Fax: Cisco Systems has more than 200 offices in the following countries and regions. Addresses, phone numbers, and fax numbers are listed on the Cisco Web site at /go/offices Argentina Australia Austria Belgium Brazil Bulgaria Canada Chile China PRC Colombia Costa Rica Croatia Czech Republic Denmark Dubai, UAE Finland France Germany Greece Hong Kong SAR Hungary India Indonesia Ireland Israel Italy Japan Korea Luxembourg Malaysia Mexico The Netherlands New Zealand Norway Peru Philippines Poland Portugal Puerto Rico Romania Russia Saudi Arabia Scotland Singapore Slovakia Slovenia South Africa Spain Sweden Switzerland Taiwan Thailand Turkey Ukraine United Kingdom United States Venezuela Vietnam Zimbabwe All contents are Copyright All rights reserved. CCIP, CCSP, the Cisco Arrow logo, the Cisco Powered Network mark, Cisco Unity, Follow Me Browsing, FormShare, and StackWise are trademarks of ; Changing the Way We Work, Live, Play, and Learn, and iquick Study are service marks of ; and Aironet, ASIST, BPX, Catalyst, CCDA, CCDP, CCIE, CCNA, CCNP, Cisco, the Cisco Certified Internetwork Expert logo, Cisco IOS, the Cisco IOS logo, Cisco Press, Cisco Systems, Cisco Systems Capital, the Cisco Systems logo, Empowering the Internet Generation, Enterprise/Solver, EtherChannel, EtherSwitch, Fast Step, GigaStack, Internet Quotient, IOS, IP/TV, iq Expertise, the iq logo, iq Net Readiness Scorecard, LightStream, MGX, MICA, the Networkers logo, Networking Academy, Network Registrar, Packet, PIX, Post-Routing, Pre-Routing, RateMUX, Registrar, ScriptShare, SlideCast, SMARTnet, StrataView Plus, Stratm, SwitchProbe, TeleRouter, The Fastest Way to Increase Your Internet Quotient, TransPath, and VCO are registered trademarks of and/or its affiliates in the U.S. and certain other countries. All other trademarks mentioned in this document or Web site are the property of their respective owners. The use of the word partner does not imply a partnership relationship between Cisco and any other company. (0304R) RDA /03