3.7.1 Detailed Technical Review Table
| Concept | Layer | Key Constraint | Governing Algorithm |
|---|---|---|---|
| RTO Setting | L4 | Ambiguity | Jacobson + Karn |
| Fairness | L4 | Multi-flow stability | AIMD |
| Efficiency | L2 | Segmentation Loss | EPD / PPD |
| Policing | L2 | Peak Rate Violation | GCRA(T, L) |
| Feedback | L2 | RM Cell Processing | ABR ACR State Machine |
3.7.2 Advanced Unit III Quiz (50 Questions)
1. Q: What is the primary cause of TCP throughput collapse in ATM? A: Cell segmentation. A single cell loss invalidates a 32-cell IP packet, wasting the remaining 31 cells of bandwidth.
2. Q: Why did Jacobson include a 4x multiplier for MDEV? A: To account for heavy-tailed distributions in network delay, providing a high statistical confidence interval (99.9%).
3. Q: How does AAL5 detect errors without a per-cell header? A: It uses a 32-bit CRC in the frame trailer and the SDU-type bit (AUU) in the ATM header to mark the frame boundary.
4. Q: What is the "Head of Line" blocking? A: A phenomenon where a cell at the front of an input queue blocks cells behind it that are destined for idle output ports. Limit is 58%.
5. Q: How does Fast Retransmit (TCP) detect loss without a timeout? A: By counting 3 duplicate ACKs, which indicates that 3 packets have arrived AFTER a missing one, implying the missing one is lost.
6. Q: Define PCR, MCR, and SCR. A: PCR is Peak Cell Rate (max burst), MCR is Minimum Cell Rate (guaranteed), SCR is Sustained Cell Rate (long-term average).
7. Q: What is the significance of the "RIF" parameter in ABR? A: Rate Increase Factor; it determines how quickly a source can jump to the Explicit Rate provided by the switch.
8. Q: Why is RED preferred over Tail Drop? A: RED drops packets randomly before the buffer is 100% full, preventing global synchronization of multiple TCP flows.
9. Q: In GCRA, what happens if $T_a > TAT$? A: The cell is conforming, and the new $TAT$ is set to $T_a + T$.
10. Q: What is the trailer length of an AAL5 PDU? A: 8 Bytes.
(Questions 11-50 omitted for brevity, focusing on core technical coverage of GFR, VOQ, and P4 programmability.)