CTE System Architecture & Design 2 — Questions and Answers
Question 1: In a carrier-grade telecom architecture, what does the term 'five nines' availability mean?
- 99.999% uptime, allowing ~5.26 minutes downtime per year (Correct answer)
- 99.99% uptime, allowing ~52.6 minutes downtime per year
- 99.9% uptime, allowing ~8.76 hours downtime per year
- 99.995% uptime, allowing ~26.3 minutes downtime per year
Correct answer: 99.999% uptime, allowing ~5.26 minutes downtime per year
Five nines (99.999%) availability equates to approximately 5.26 minutes of allowable downtime per year, the standard benchmark for carrier-grade systems.
Question 2: Which architectural pattern best supports independent scaling of individual telecom microservices like billing, provisioning, and routing?
- Monolithic architecture
- Service-oriented architecture (SOA)
- Microservices architecture with containerization (Correct answer)
- Client-server two-tier architecture
Correct answer: Microservices architecture with containerization
Microservices architecture with containerization allows each telecom function to be deployed, scaled, and updated independently, reducing blast radius of failures.
Question 3: A telecommunications company is designing a network that must survive the loss of an entire geographic region. Which design principle should be prioritized?
- Load balancing across servers in a single data center
- Geographic redundancy with active-active or active-passive failover (Correct answer)
- Increasing bandwidth capacity at the primary site
- Deploying additional edge caches
Correct answer: Geographic redundancy with active-active or active-passive failover
Geographic redundancy ensures that regional disasters do not cause a total outage, using active-active or active-passive configurations across dispersed sites.
Question 4: What is the primary function of a Session Border Controller (SBC) in a VoIP network architecture?
- To route IP packets between autonomous systems
- To manage and secure real-time communication sessions at network borders (Correct answer)
- To compress voice traffic for efficient WAN utilization
- To convert analog signals to digital formats
Correct answer: To manage and secure real-time communication sessions at network borders
An SBC controls the signaling and media streams of VoIP calls at network borders, providing security, interoperability, and QoS enforcement.
Question 5: In telecom network design, what is the role of a Policy and Charging Rules Function (PCRF)?
- To physically route fiber optic cables between nodes
- To define and enforce QoS policies and charging rules for data sessions (Correct answer)
- To authenticate subscribers using SIM credentials
- To manage DNS resolution for telecom domains
Correct answer: To define and enforce QoS policies and charging rules for data sessions
PCRF is a core component of the LTE/4G architecture that determines QoS policies and charging rules for subscriber data sessions in real time.
Question 6: Which transmission architecture uses a single fiber strand to carry multiple wavelengths of light simultaneously, multiplying capacity?
- SONET/SDH
- Dense Wavelength Division Multiplexing (DWDM) (Correct answer)
- Time Division Multiplexing (TDM)
- Orthogonal Frequency Division Multiplexing (OFDM)
Correct answer: Dense Wavelength Division Multiplexing (DWDM)
DWDM transmits multiple optical signals on a single fiber by assigning each signal a different wavelength (color), dramatically increasing fiber capacity.
Question 7: When designing a telecom OSS/BSS architecture, what does 'northbound interface' refer to?
- Physical connections running north-to-south in a data center
- APIs exposed by a network element to higher-level management systems (Correct answer)
- Redundant links pointing toward the carrier backbone
- Interfaces between OSS and billing systems only
Correct answer: APIs exposed by a network element to higher-level management systems
Northbound interfaces are APIs exposed upward toward higher-layer management or orchestration systems, while southbound interfaces communicate downward to network elements.
CTE System Architecture & Design 2
In a carrier-grade telecom architecture, what does the term 'five nines' availability mean?