PDF of this tutorialWe have come to expect that our phones will work under even the most adverse of conditions, providing lifeline service in times of power outage, earthquakes, and other natural disasters. We have come to expect to be able to succeed in making a call each and every time we pick up the phone. We have come to take for granted the high voice quality in our phone conversations. Any alternative to the existing PSTN that does not meet these standards will be sorely challenged to prove its worthiness; after all, as the old saying goes, “If it ain’t broke, don’t fix it.”
So what does it mean to be carrier-grade? And exactly what does it take to get there for a next-generation telecom software provider? There are several components involved in achieving carrier-grade status: reliability, scalability, and primary-line capability.
- Reliability—The PSTN has set a high standard for quality and reliability, and these standards must be met or exceeded for next-generation products to be accepted into the central office (CO). Some key issues involved include the following:
- Network equipment building standards (NEBS) compliance
- Active calls should be preserved in case of failure.
- No single point of failure
- 99.999 percent availability
- Software, not just hardware, reliability and fault tolerance
- Scalability—The next-generation solution must have the ability to be extensible and handle more service instances, new features, and more users in an easy, affordable manner. The main architectural issue in scalability is whether to build a distributed versus centralized solution. In reality, it is difficult to meet both reliability and scalability requirements in a centralized solution. While fault tolerance is achievable in a centralized solution, it does not scale well. Moreover, the service provider can add new services and features in a non–service-affecting manner with a distributed solution, whereas the centralized solution does not afford them this luxury.
- Primary-line capability—The next-generation platform must empower service providers to offer primary-line service to their customers. This enables service providers to reap the economic benefits of owning the entire communications interface with their customers, not just the secondary line. There are two requirements in order to be primary-line capable:
- Lifeline service—Also known as enhanced 911 or E911 in the United States, lifeline service is a regulatory requirement. This means that all emergency lifeline calls must be supported with the ability to pinpoint the physical location of the incoming call. For the PSTN, with its dedicated circuits, this is not a difficult task, but in IP telephony it becomes a much greater challenge. Packets must be stripped off according to their priority (so the platform must have some call-shedding intelligence that allows emergency calls to “bubble up”) and then mapped to a physical address. But, of course, IP addresses do not necessarily correspond to physical addresses.
- Lawful intercept—Also known as the Communications Assistance for Law Enforcement Act (CALEA) in the United States, lawful intercept is another regulatory requirement that must be met in order to provide primary-line service. Because the U.S. specifications have not even been set definitely yet, this will be a difficult one to implement immediately. The fundamental problem needs to be addressed both in the software and hardware of the next-generation platform. The software must contain the intelligence to identify and control legally intercepted calls, and the hardware must be able to physically peel off the packets marked for intercept and send them to the appropriate address.
