1. Cyber Physical Systems
Adam Dettenwanger, Charlie Carlton, Scott Williams
CS 455: Introduction to Distributed Systems
Computer Science Department, Colorado State University

2. Why are Cyber Physical Systems Important?
Most of us interact with a CPS every day
Example: the modern vehicle
Creation of complex systems with new capabilities
Systems that wouldn’t be feasible without CPS
CPS has major economic implications
Advanced manufacturing techniques - economic advantage
Efficiently managed civil infrastructure (power grid, traffic control)

3. Problem Characterization
The CPS feedback loop
Network of sensors transmit current state of the system to controller
Controller uses system modeling algorithms to decide next state
Controller sends control signals to the appropriate actuators
Actuators modify state of the physical system
The cycle repeats
Implementation
Controllers are often embedded systems
Can communicate over private or public networks

4. Trade-off Space for Solutions
Inherently multidisciplinary
Specialized systems on top of specialized embedded hardware require professional knowledge from a variety of fields
Diversity vs. Homogeneity
Balancing ease of use and system impenetrability
Security vs. Performance
Encryption & Gaussian Noise
Hard real-time obligations

5. Dominant Approaches: Part 1
Analyzing continuous, analog reality with discrete computation
Sampling at set intervals
Event-driven, self-triggering
Resiliency
Redundancy
System diversity
Partitioning
Least privilege
Intrusion detection
System monitoring
Strategic information sharing, gossip

6. Dominant Approaches: Part 2
Contracts
Simplified standards for node behavior
Assumption and Guarantee
Specified time quantum or message content
Breach of contract leads to defensive behavior from node holding assumption
Standards, protocols, and best practices
Necessary for the growth and success for any new technology
Law enforcement and physical protection of highly critical nodes

7. Insights Gleaned CPSs face network problems
Balance performance and security
No easy solution for synchronization issue
Suggested solutions
Traditional
redundancy
encryption (may not be feasible in all cases)
network security best practices
CPS face the same core issues that networks and other distributed systems face today:
1. Protecting the system against attack
2. Ensuring the confidentiality, integrity, and authenticity of data
3. The need for efficient communication protocols
4. Require resiliency in the system
Need to be able to handle the loss/malfunction of a single/group of sensors
Need to be able to cope with the loss of the computing layer
As with any network, there is an inherent balance that must be struck between the robustness of your security apparatus and the efficient performance of the system.
We saw that the issue of time/synchronization can be huge is CPS. The solutions of interval sampling, and “event” driven sampling sacrifice data and autonomy, for some level of synchronization.
The suggested solutions to the problems we investigated were ones that we’re all already familiar with:
1. Resiliency - redundancy of sensors, and computational systems
2. Security
encryption of data, may not be feasible for sensors with no computational component
i. New idea - gaussian noise solution
b. use network security best practices
i. isolation, least privilege, authentication

8. The Future Problem Space of CPS
Cyber Physical Highway System
Pressures
Population, roadway congestion, safety
Layers
Intra-vehicle, inter-vehicle, highway control layer
Challenges
Security
Resiliency
We modeled our future problem space around a hypothetical Cyber Physical Highway System.
We thought this system may be viable because of the recent interest and research into autonomous or assisted driving vehicles as well as these societal factors:
population growth
roadway congestion - cost of continuous lane expansions
roadway safety
The Cyber Physical Highway system is a CPS within a CPS within a CPS.
Intra-vehicle: your car itself
inter-vehicle: car to car
highway control layer: traffic pattern analysis and decision making
After considering this system we decided on two major problems that would need to be addressed:
security: at every layer
resiliency: how to make each layer robust, as well as how the system reacts to failures

9. Trade-off Space and Future Solutions
Similar to Present Day
Resiliency
Redundancy
Security
Isolation
Encryption
Gaussian numerical noise
The problem space that we defined overlaps the problem space that present day CPSs face.
Resiliency
Redundancy at layer of the system:
intracar: -redundant sensors monitor all of the vehicles critical components
-like the namenode/secondary namenodes we used in our hadoop clusters have a similar system setup for the onboard controller
- establish an emergency protocol when systems/sensors fail
intercar: -alway have a backup communication module
-emergency failure protocols
highway controller:
-redundant onsite system, as well as geographically separated system
-emergency protocols
Security
intracar:
-isolate the sensors from any external network
intercar:
-wireless communication by necessity
-encryption/gaussian noise
-wired networks where possible
-again use encryption/gaussian noise where possible