Reliable, Robust, and Resilient in Modern Communications

Reliable, robust, and resilient are terms regularly encountered in the descriptions of modern communications systems.

These terms each carry distinct definitions and attributes that need to be understood when considering a solution.

Ofttimes, the meaning of these words get lost – or misused - in the positioning statements encountered in industry websites and articles.  This erodes clarity, making it more difficult for a user to evaluate and differentiate potential solutions for their critical applications.

This is particularly true in the usage of the term resilient, which has recently become something of a buzz word in the defense and critical communications industries.

This Insight aims to better define these terms in the context of modern communications systems.

Reliable

A reliable solution has a high probability of functioning correctly and consistently over time when the operating environment is within its design parameters.

From a technical and operational standpoint, reliable communications equipment typically possesses these attributes:

·      High Availability:  The equipment or system is considered available and usable for a high percentage of time.  This is commonly represented in an availability metric, such as 99.999% availability, or “five nines.”

·      Low Failure Rates:  System components exhibit low probabilities of failure.  These incidents are commonly measured in Mean Time Between Failures (MTBF).  Industry standards tend to range from 200,000 to 500,000 hours.  Top-tier communications equipment often possesses an MTBF of between 500,000 to 1,000,000+ hours.

·      Performance Stability:  For reliable systems, consistent performance under normal conditions is quantitatively defined in product specifications, Key metrics often include Bit Error Rate (BER), throughput, latency, and jitter.

·      Environmental and Mechanical Stability:  Reliable hardware exhibits durability and consistency across physical factors including temperature, moisture, vibration, and shock.  This performance typically detailed in the product specification and its compliance with standards, such as MIL-STD.

·      Maintainability and Serviceability:  Although clear metrics to assess maintainability and serviceability are not generally available, these are critical factors in avoiding downtime.  Educated users look for items including modular construction, internal diagnostics, alerting, and clear documentation in assessing reliability.

Reliability is an essential element of all modern communications systems, whether deployed in a data center or in a harsh terrain.  It is the foundation of a modern infrastructure, preventing operational and financial losses.

Robust

A robust solution has a high probability of working acceptably when facing anticipated stressors that are outside standard operating environments, often through designed-in margins, redundancy, and protection mechanisms.

Robust systems are designed against a known set of threats and conditions.  In communication systems, these include anomalies such as predictable hardware failures, load spikes, rain fade, and RF interference.

·      Redundancy and Fault Tolerance:  Robust systems incorporate redundancy in terms of hardware, signal paths, and power with automated failovers.   This allows the system to improve its reliability as measured in higher availability and lower system failure rates.

·      Harsh Environment Tolerance:  Robust systems are often ruggedized to operate in harsh environments where wide temperature ranges, chemical exposure, shock, vibration, dust, moisture, and sand pose risk to reliable operation.  These systems are often validated in MIL-STD, IEC, and IP67-IP69K ratings.

·      Forward Error Correction (FEC):  This digital transmission method enables the sender to add structured redundant bits of data that the receiver detects to automatically correct errors without requesting a resend of the data.  This allows the system to overcome degraded network conditions, improving availability and performance stability.

·      Automated Power Control:  Wireless and RF systems – such a Ku-band satellite communications – are susceptible to atmospheric disturbances, such as rain fade.  Automated Power Control systems monitor and adjust power levels in real-time to optimize the signal path and help maintain high availability.

·      Link Adaptation:  A dynamic process where wireless systems adjust transmission parameters – like coding, power, and modulation – to match changing radio conditions.  This performance is measured Signal-to Interference-plus-noise ratios (SINR) and Channel Quality Indicators (CQI).

Depending on the service and operational environments, there are many additional design considerations to ensure robust performance.  These include interference mitigation, electromagnetic and electrical immunity, over-provisioning, and controlled behavior under misuse/attack.

Resilient

A resilient solution has the ability not only to withstand but also to adapt and recover from failures, attacks, or disasters, including unforeseen conditions, by reconfiguring, rerouting, or degrading gracefully while restoring service.

Resilience is a system-level property that relies heavily on the attributes of the equipment and subsystems that it is comprised from.

·      Continuity of Critical Functions:  This is a Quality of Service (QoS) attribute where the equipment, together with the surrounding network, keeps high-priority services (such as command data and emergency channels) running even when non-critical services are degraded or shut down.

·      Multi-path and Diversity:  Routing across multiple network paths (such as satellite + terrestrial + radio) with the ability to reroute or bond across alternate paths when conditions on one degrade.  This can also apply to power systems that can intelligently balance loads and leverage backup systems.

·      Automatic Detection, Failover, and Self-healing:  Build in monitoring, alarms, and control logic that detect faults and trigger automated recovery actions.  These actions include rerouting, interface switchover, and configurations changes with minimal need for human intervention.

·      Cyber Resilience:  The ability to anticipate, withstand, recover from, and adapt to breaches in security. Cyber resilience extends beyond threat prevention to focus on preserving system integrity and successful outcomes.  This often includes rerouting of critical traffic to decentralized servers and attack analysis for rapid recovery.

·      Graceful Degradation:  Instead of an on/off approach, resilient systems possess the ability to scale down capacity, QoS, and other features (such as video resolution) while preserving basic connectivity and critical traffic.

Resilience is best thought of as a dynamic response to unforeseen events than in a classic reliability sense.  It is more than the Mean Time Between Failures (MTBF) and is concerned with how the system performs before, during, and after a disruption.

Resilience is often scenario-based.  For example, in a Defense application, an enemy unexpectedly jamming the signal frequencies for certain wireless transmissions.

In these scenarios, key metrics are often focused on the Time to Recovery or Service Restoration.  One common measurement for this is Mean Time To Recovery (MTTR).

Reliability, Robustness, and Resiliency are critical and disparate elements of modern communications systems.  Understanding the design factors and metrics of each element is essential in evaluating, deploying, and maintain these systems.