PDF of this tutorialTo isolate a reported Internet problem effectively, more information and data must be analyzed by the test system than in the past, when the only service offered by carriers was POTS. LECs must look out to the customer premises, look at the link between the CO and the RAS, and look in to the data network (see Figure 5).
Figure 5. Internet Network Architecture
"Looking Out" Ensures That the Loop and Customer Premise Equipment (CPE) Can Carry the Service Being Marketed
As the voice and data networks have converged with the rapid introduction of the Internet, loop diagnostic capability must continue to measure physical aspects of the local loop (opens, contact faults, length, etc.). Meanwhile, the Internet has created new requirements such as speed measurements and interaction with additional network elements like analog modems, ISDN terminations, splitters, xDSL modems, ISDN line cards, and digital subscriber line-access multiplexers (DSLAMs). Looking-out capability ensures network integrity between the CO and CPE.
New capability in the measurement unit that has traditionally been in the CO or the digital loop carrier (DLC) is required. These new loop diagnostic units will need measurement systems that are software-based and utilize digital signal processing (DSP). DSP provides the processing power to deliver more diverse measurements and faster test results. DSP enables reductions in hardware size and cost. Another important characteristic is that it provides interfacing solutions to current and next-generation switching systems. Because these systems also use DSP, test and measurement functionality and switching could potentially be fully integrated in common hardware.
"Looking At" Ensures the Integrity of the Path from CO to RAS
The DSP technology in the loop diagnostic unit can be leveraged to also test the segment of the end-to-end network between the CO and the RAS at the POP. Emulating a subscriber modem, a call is placed to the RAS. As this call is connected, the DSP technology is used to confirm connect speeds and measure parametrics, such as attenuation and noise levels. This "looking at" functionality confirms expected connection and speed performance to the RAS or allows fault isolation of speed impairments, such as attenuating voice-line cards commonly in the path of an Internet connection today.
"Looking In" Provides End-to-End Data-Communication Protocols
Testing the Internet requires the acquisition of information beyond the status of the physical network through the use of an Internet diagnostic unit. The layered protocols used in Internet transactions are subject to errors, blockage, and latency, as introduced by network element and configuration problems. To diagnose and isolate these problems, the test system must have the ability to generate arbitrary bit patterns, representing specific protocols at their various layers. This, in turn, allows the emulation of end users—either a PC or Web site—as well as isolating specific transactions, tracing paths, and verifying packet destinations.
Monitoring specific Internet transactions at the data level presents segmented information about the status of the network. Emulating the transaction provides the ability to replicate problems encountered by end users while tracing the transaction. This information is passed to the analysis subsystem, where it is integrated with other gathered measurements, to deliver fault isolation for problem resolution (see Figure 6).
Figure 6. Internet Test System Architecture
Using Expert Systems for Analysis and Presentation
The expertise required to establish an efficient sequence of diagnostic and repair steps, execute them, and isolate and repair faults successfully is formidable. Expert systems technology not only allows for the capture of this complex information but also ensures that it is used consistently by large organizations. Expert systems technology consists of multiple, linked, reasoning paradigms. These reasoners mimic human problem-solving techniques, each optimized for various performance conditions. Examples of reasoning paradigms include rules-based reasoners (RBR), case-based reasoners (CBR), neural nets, decision trees, and genetic algorithms.
System Interconnection and Interfacing with ORBs
Recent software technologies, such as common object request broker architecture (CORBA), allow a variety of software applications to be interconnected through a common software backplane. Interface definition language (IDL) provides a standard notation for software interfaces. Such standard interfaces allow for interconnection of these new capabilities to existing systems. A further benefit is the ability for multiple suppliers to extend the capability of the system through interconnected solutions.
