Cisco Certified Support Technician (CCST) NetworkingIP ServicesHard
A company is deploying a new application that requires very low latency and minimal jitter, such as real-time financial trading data. The network team decides to implement QoS. Which DiffServ Per-Hop Behavior (PHB) is specifically designed to provide a low-loss, low-latency, low-jitter service, making it ideal for such time-sensitive traffic?
- AAssured Forwarding (AF)
- BClass Selector (CS)
- CDefault Forwarding (DF)
- DExpedited Forwarding (EF)
Show answer & explanationAnswer & explanation
Correct answer: D. Expedited Forwarding (EF)
Expedited Forwarding (EF) PHB is designed to provide a premium, low-loss, low-latency, low-jitter service, often described as a 'virtual leased line'. This makes it highly suitable for real-time applications like VoIP and financial trading.
Why the other options are wrong
- A. Assured Forwarding (AF) provides differentiated services with varying levels of drop precedence, but not the strict low-latency guarantees of EF.
- B. Class Selector (CS) is a backward-compatible mapping of IP Precedence values to DiffServ, not a PHB itself that defines service characteristics.
- C. Default Forwarding (DF) is best-effort and offers no QoS guarantees.
DiffServ Expedited Forwarding (EF)
A DiffServ Per-Hop Behavior (PHB) that provides a low-loss, low-latency, low-jitter service, suitable for real-time and mission-critical applications.
- Often implemented with strict priority queuing.
- Designed for 'virtual leased line' effect.
- Typically used for VoIP, video conferencing, real-time data.
Memory trick: EF is 'Extra Fast' for critical traffic.