Unit IV Key Takeaways

• IntServ relies on RSVP and per-flow state, providing rigid "hard" QoS.
• DiffServ uses DSCP aggregate marking (EF, AF) to provide scalable "soft" QoS for massive cores.
• GPS is the fluid-flow ideal; WFQ is the packet-level reality using Virtual Finish Times.
• RED mathematically prevents global synchronization by using EWMA queue averages to perform proactive random drops.
• Token Buckets are the fundamental tool for metering and marking traffic class compliance.
• Scalability remains the primary reason DiffServ dominates the modern Internet backbone.

--- Unit IV Checklist:

• [x] Explain the RSVP PATH/RESV signaling sequence.
• [x] Calculate the Virtual Finish Time ($F_k$) for a flow in a WFQ scheduler.
• [x] Describe the difference between Guaranteed and Controlled Load service in IntServ.
• [x] Map EF and AF Per-Hop Behaviors to their target application types.
• [x] Calculate the RED drop probability ($P_b$) given $min_{th}, max_{th}$, and $avg$.
• [x] Identify the 6-bit DSCP field versus the 2-bit ECN field.
• [x] Differentiate between Bit-Round Fair Queuing and Deficit Round Robin (DRR).
• [x] Understand the purpose of a Classifier and a Meter in a DiffServ conditioner.
• [x] Explain why "Tail Drop" causes global synchronization in TCP.