Pipeline Publishing, Volume 3, Issue 11
This Month's Issue:
The Long Arm of Telecommunications Law
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Carrier Grade: The Myth and the Reality of Five Nines
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Maintainability, Manageability, Scalability, Accountability, and Durability are directly contained in the concept – sort of the faces of one six-sided dice. Too these, Securability and Survivability are recent critically expected features. Just because a single KPI, the notorious five-nines, is the flagship indicator, does not exclude the specifications for these other factors. This is very evident in the Bellcore documents which, in addition to all these, link in Safety. With software and servers, Reliability, Availability, Serviceability, Usability, and Install-ability combine in the acronym RASUI.

Getting Realistic: Big Customer Requirements

The US Government has issued a comprehensive RFP [Networx Universal RFP; TQC-JTB-05-0001; 05/06/2005] for bidders wishing to supply the next generation network for the US Government. Considerable thought has gone into setting acceptable quality levels for networks – taking into account the differing use needs and technical facilities of each network technology. This is perhaps the most complete, openly viewable and usable description of realistic network service goals. Many dozens of tables describe the acceptable availability and other quality measures for each network technology. Further they go a step further and provide for both normal and mission critical network needs. “For certain services, when required by agency customers, two service levels are specified. Routine service levels apply for most Government applications. Critical service levels are defined for Agency applications requiring higher levels of availability, performance, or restoral <sic>criteria.” Voice networks are generally given normal availability goals of 99.5% and critical service goals of 99.95%. Data network technologies are usually about one magnitude more stringent – 99.95% for normal use and 99.995% for critical service uses. Networx provides a modern and realistic reliability guideline for networks. It is the new baseline benchmark, below which a network is unacceptable, and above which is the narrow window of competitive differentiation.

Nevertheless, SLA’s are subject to extreme competitive pressures, which have backed their availability promises right up against the wall. “Verizon Business’s Network Availability Commitment is to have its IP Network available 100% of the time … Verizon Business will credit Customer’s account if Verizon Business fails to meet this Network Availability Commitment during any given calendar month.” [‘Verizon business SLA for DSl.pdf’] Since 100% availability is very difficult to achieve, SLAs become a kind of amortization game. You give an SLA with the up front knowledge that you will inevitably give back


some revenue to your customers. Access links from the customer premise into the network have always been the achilies heal when engineering for redundancy. Even with low failure rate, a MTTR of about 3 hours on access links forces availabilities that are likely far from 100%. Instead, the revenue loss from SLA penalty payments is offset by increased prices or customer satisfaction with the SLA. In the early days SLAs actually made money. One prominent carrier offered the only SLA and charged a premium because their ‘network was so good it could support an SLA.’ While truthfully, their network was no better than most other carriers, they earned 10x more in extra income from the higher prices charged than they had to payout for SLA violation rebates.

But today is perhaps different: claims of network performance can be validated more easily by customers. “Because of its built-in redundancy, Internap can offer aggressive performance guarantees, including 100% availability, 0.3% packet loss and 45 milliseconds of latency. “We offer 100% availability border to border, from where a customer intersects our network to where the customer's traffic leaves our network," Flynn says.” [Case Study submitted by Carolyn Duffy Marsan of Network World to TMF]

Getting better and better

Several organizations are devoted to helping make networks and network components better. For example, there is the Technical Committee on Communications Quality & Reliability (CQR). It focuses on and advocates worldwide communications and reliability on behalf of, and within, the Communications Society (formerly known as the Quality Assurance Management Committee (QAMC) ). And while the customer driven goals may be less than five-nines, this level of performance is realistic and achievable across complex networks when best design practices are utilized. The fine-nines, never a requirement myth for equipment, is now moving from myth to reality for networks too.

And software, once considered hopelessly incapable of quality, now sets itself some of the highest reliability goals. CGL (Linux) OSDL standard allows system registration to 'carrier grade' standards. “Carrier Grade Linux' is a set of specifications which detail standards of availability, scalability, manageability, and service response characteristics which must be met in order for Linux to be considered "carrier-grade" (i.e. ready for use within the telecommunications industry). Improvements are expected. . “Carrier-grade is a term for public network telecommunications products that require up to 5 or 6 nines (or 99.999 to 99.9999 percent) reliability…. The term "5 nines" is

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