The case for DOCSIS 3.1 system validation

Quality assurance testing provides an insurance against the damages from malfunctioning systems. In insurance it’s all about cost vs. risk, where risk is the probability of the issue times its impact.

Over the years, Excentis has spotted dozens of hardware, software, configuration and integration issues with severe real-life impact on both CAPEX (unneeded or wrong investments), OPEX (flood of customer calls and field operations) and revenue (customer churn and brand damage). The reported issues have blocked mass production of flawed equipment or halted planned roll-out of malfunctioning new software.

Deployment of malfunctioning equipment causes

  • Customer complaints and eventually churn and bad publicity
  • Increased OPEX due to service calls and truck rolls
  • Increased workload across the operation: service desk agents, NOC staff, field technicians, engineers and management
  • High recall costs (in case of hardware issues)
  • Consultancy & debug costs; resolving field issues is both urgent and complex

For complex systems like access networks, a 100% ironclad insurance is not feasible – let alone cost-effective given the immense amount of cases and scenarios. So while the case for QA testing should be clear, the case for individual test cases must be made. With 20 years of DOCSIS experience Excentis focusses on those tests that uncover issues with the highest probability and/or the biggest impact.

System testing to rule out interoperability issues

Because certain key features of the DOCSIS technology hugely depend on the interaction between the CM and the CMTS, it is highly advised to test these features on the full system, rather than separately on the modem and the CMTS. While DOCSIS is a standardized specification, and cable modems are mostly certified, interoperability issues can still exist. By verifying specific functionality on the full system, such interoperability problems are ruled out.

An example test case: profile switching

What does it do?

In the profile switching test we introduce noise in the setup, both in the upstream and downstream, to verify that the CMTS and modem intelligently deal with this. DOCSIS 3.1 OFDM(A) channels can support multiple profiles, and based on the signal quality of these channels, the CMTS should assign the highest usable profile. With changing environments, the CMTS and modem must be able to dynamically change the profile usage, to get the highest possible capacity from your network.

Why do we propose this test?

If this functionality is not used properly and in an intelligent way, you can either have service interruptions or loss of capacity. The golden spot is where the CMTS correctly decides - based on modem input - to demote and promote the profiles at the right time, and the modem follows these changes fluently. The specification leaves a lot of freedom to use dynamic profile switching, which makes it very important to properly verify the system behavior in this context.

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