CAS CAS Automation Specialist Network Communications & Protocols 2 — Questions and Answers
Question 1: In a DeviceNet network, what is the maximum number of nodes allowed on a single network segment?
- 64 (Correct answer)
- 32
- 128
- 256
Correct answer: 64
DeviceNet supports a maximum of 64 nodes (MAC IDs 0–63) on a single network segment.
Question 2: Which layer of the OSI model does an IP router primarily operate at?
- Network (Layer 3) (Correct answer)
- Data Link (Layer 2)
- Transport (Layer 4)
- Physical (Layer 1)
Correct answer: Network (Layer 3)
Routers operate at OSI Layer 3 (Network layer), using IP addresses to determine the best path for forwarding packets between networks.
Question 3: What does the term 'determinism' mean in the context of industrial communication protocols?
- Data delivery occurs within a guaranteed, predictable time frame (Correct answer)
- Data is encrypted using a fixed algorithm
- All nodes on the network have equal access priority
- The network automatically reconfigures after a fault
Correct answer: Data delivery occurs within a guaranteed, predictable time frame
Determinism in industrial networks means that message delivery times are bounded and predictable, which is critical for real-time control applications.
Question 4: AS-Interface (AS-i) is primarily designed for connecting which type of devices at the lowest level of the automation hierarchy?
- Binary sensors and actuators (Correct answer)
- High-speed servo drives
- SCADA servers
- Engineering workstations
Correct answer: Binary sensors and actuators
AS-Interface is a low-cost, simple two-wire fieldbus specifically designed to connect binary (on/off) sensors and actuators at the field level.
Question 5: Which wireless protocol standard, operating in the 2.4 GHz ISM band, is most commonly used for industrial wireless sensor networks (WirelessHART)?
- IEEE 802.15.4 (Correct answer)
- IEEE 802.11n
- IEEE 802.3
- Bluetooth 5.0
Correct answer: IEEE 802.15.4
WirelessHART is built on the IEEE 802.15.4 physical and data link layer standard, which provides low-power, low-data-rate mesh networking in the 2.4 GHz band.
Question 6: In Modbus TCP/IP, what is the default port number used for communication?
- 502 (Correct answer)
- 102
- 44818
- 2222
Correct answer: 502
Modbus TCP/IP uses TCP port 502 as the well-known port for all Modbus client-server transactions over Ethernet.
Question 7: What is the purpose of a 'terminating resistor' at each end of a PROFIBUS or RS-485 network?
- To absorb signal reflections and prevent data corruption (Correct answer)
- To limit current and protect devices from overvoltage
- To provide power to the bus devices
- To convert RS-485 signals to RS-232
Correct answer: To absorb signal reflections and prevent data corruption
Terminating resistors match the cable's characteristic impedance, absorbing signal energy at the cable ends to prevent reflections that would corrupt data.
CAS CAS Automation Specialist Network Communications & Protocols 2
In a DeviceNet network, what is the maximum number of nodes allowed on a single network segment?