Ready, set, crash!

"Roughly 33 million customers over the past three years, or 30,000 customers a day, have lost access to the public network for an average of five hours as a result of facilities outages."

This statement in a 1996 report, published by the Network Reliability Steering Committee of the Alliance for Telecommunications Industry Solutions, exemplifies a growing problem throughout the United States.

Because our unprecedented dependence upon telecom, the impact of extended, unplanned public network outages is becoming more devastating. Yet outages are occurring more frequently.

Generally, network outages can be categorized into two primary classifications-natural disasters and environmental causes and human intervention (Table 1).

An FCC report of major outages-defined as affecting more than 30,000 individual customers for at least 30 minutes-indicates that carriers in the United States experienced a total of 175 incidents between July 1, 1996 and June 30, 1997. These outages typically occur on the most robust networks boasting the best technology.

Unfortunately, statistics on "minor" network outages that affect only a few customers are not tracked. For example, a 24-hour outage caused by the backhoe of a careless construction crew cutting service to a number of large business customers would not be reported. These types of outages occur with a greater frequency than the tracked "major" outages.

A breakdown of the failure categories for the 175 major incidents shows that 82% were a combination of facilities failures, local switch and tandem switch failures. In a statement concerning these, the NRSC said that facility outage frequencies have continued to increase since July 1992, the first year measurement began. Facility outage frequencies are significantly higher than any other category. Similarly, local switch outage frequencies are significantly higher than any other category apart from facility.

As an individual category, facilities failure occurrences clearly represent more than double any other individual outage classification. In fact, a significant overall increase continues in the number of facilities outages since the 1993 baseline year when FCC reporting began (Table 2).

Commenting in its 1997 annual report, the NRSC said that facility outages continue to be the major contributor to outage frequency, are more severe and potentially affect more customers than outages in most other categories and have longer duration than outages in other categories. A quarterly report measuring outages from October through December 1997 shows facility failures represented 66% of all network outages for the quarter. The 27 facility outages represent the highest number ever reported in a quarter.

Current strategies Although companies take reasonable steps to protect their businesses from telecom disasters, solutions have been limited by available routing options, technology and financial feasibility. For example, the advent of competing carriers in the long-distance industry helps by enabling a multivendor networking model as a business continuance planning tool. If one provider experiences an outage, customers can route some if not all service via alternate carriers.

But the Achilles' heel to disaster avoidance remains in the local exchange network. Corporate networks, whatever their size, remain vulnerable to local loop outages because incumbent telcos deliver the majority of network traffic to and from each long-distance carrier's respective point of presence. This has limited the options to protect applications relying on local network facilities.

In a local loop scenario, planners may back up leased lines and request circuit diversity. This is not good insurance if the backup line is part of the same cable or terminates in the same central office as the primary line. And although some additional diversity can be provided by using competitive local exchange carriers' switching and access alternatives through their own or leased fiber network, these companies have penetrated a relatively small percentage of the commercial buildings nationally.

Further, despite their alternative resources, most CLECs remain vulnerable to many of the same types of outages as the incumbent telcos because their networks are terrestrially based and share-both inside and outside a building-common sections of the very networks they were designed to protect. This limits their usefulness as a diverse alternative.

Last, it has been shown that even self-healing services cannot be 100% relied upon. Indeed, the only feasible way to get absolute assurance of service continuity is to obtain services from two COs, preferably from two different carriers. The degree of physical diversity between the carriers' networks dictates the level of protection a customer can expect to achieve.

The next evolution in network continuance As history demonstrates, telecom decision-makers have gravitated to solutions that best meet their individual network diversity requirements. Clearly, the limiting factors to complete diversity and redundancy have been available technology within reasonable financial parameters. Because these solutions have often been unavailable or prohibited by price, many customers are forced to accept the risks of downtime without a viable alternative.

Fortunately, technology does not stand still. An alternative to conventional protection is now available to carriers and end users: digital broadband wireless.

This solution can be engineered to deliver 99.999% availability, which translates to slightly more than five minutes of downtime a year despite adverse atmospheric conditions such as rain, snow or fog. The technology has been used for many years as an integral part of networks throughout the world and now is being deployed in the United States by local and long-distance carriers.

When connected to a CO switching platform, digital broadband wireless is a viable alternative to fiber for applications requiring capacities of DS-0 (64 kb/s) to OC-3 (155.5 Mb/s). Service providers can furnish local exchange and long-distance services, along with broadband data capabilities.

Figure 1 illustrates this point. In this scenario, a 12-inch antenna is installed on top of the customer's building to serve as the connection point back to the wireless CLEC's network. The antenna is connected via coaxial cable to an indoor unit in the customer's building. The indoor unit is mounted in a standard 19-inch relay rack along with power supplies and a digital cross-connect frame panel. The circuits are distributed to their ultimate destinations within the building.

Furthermore, because the service takes to the air, it delivers on several essentials for disaster avoidance. These include diverse network routing, dual entrance facilities (roof vs. basement), independence in transport medium (wireless vs. terrestrial) and CO diversity.

As a result, users' applications are better protected from the types of outages prone to terrestrially based networks. Customers are able to use the wireless connection and alternate switching platform to balance their network traffic load by splitting their communication requirements between their terrestrial and wireless providers. In the event of a terrestrial outage, the customer can redirect traffic to available capacity on the wireless connection to maintain connectivity to the public network.

Natural disasters-earthquakes, hurricanes or tornadoes-can wreak havoc with even the most reliable networks. A key determinant to deciding which network equipment and services to include within a business continuance plan is how a specific technology solution will hold up under severe circumstances.

A good case study is the Jan. 17, 1995, earthquake in Kobe, Japan, which registered 7.2 on the Richter scale. During that event, a major global provider of data and information services reported that only one of its end user customers did not experience a service outage during the earthquake. This customer, located on an island in the bay area near Kobe, was served by wireless line-of-sight technology.

If a particular environmental disaster knocks out all telecom services, fast restoration is essential to ensure continuance of business operations. In the case of digital wireless networks, service providers can re-establish service quickly by re-aligning antennas. Troubleshooting, fault location and splicing issues that often delay optical restoration do not apply to the wireless technology.

The exponential growth of network-based business applications forces telecom managers to place unprecedented reliance on public networks. Coincident with this increased reliance, network outages are rising at alarming rates. Heretofore, cost-efficient solutions to true network diversity have been available to only a select group of customers.

Digital broadband wireless technology, teamed with an alternative CO switching platform, can be an answer to an autonomous physical network route and independent switching platform. By routing portions of their network applications over this transport, customers have a higher assurance of achieving the levels of diversity and overall network reliability they require.