Unit III Key Takeaways

• TCP Flow Control vs Congestion Control: RWND is about receiver capacity; CWND is about network capacity.
• The Jacobson Algorithm: Uses variance ($4 imes MDEV$) to calculate a stable retransmission timeout.
• Karn's Algorithm: Mandatory rule for high-speed networks to avoid RTT bias during retransmissions.
• The Fragmentation Multiplier: One lost cell destroys an entire 32-cell IP frame.
• EPD (Early Packet Discard): The optimal buffer management strategy for ATM switches.
• ABR Feedback: Uses RM cells to provide microsecond rate adjustments.
• Max-Min Fairness: Equitable bandwidth allocation algorithm.
• AAL5 (SEAL): High-efficiency adaptation layer with hard-coded CRC-32.
• HOL Blocking: Solved by VOQ and modern iSLIP switch backplanes.
• Future: BBR pacing and Westwood bandwidth estimation.

--- Unit III Checklist:

• [x] Explain Slow Start (Exponential) vs Congestion Avoidance (Linear) growth.
• [x] Implement Jacobson's RTO update logic in pseudocode.
• [x] List the three rules of Karn's Algorithm and explain the Ambiguity Problem.
• [x] Calculate frame loss probability from cell loss rate ($1-(1-p)^{32}$).
• [x] Define Partial Packet Discard (PPD) and Early Packet Discard (EPD).
• [x] Trace a sequence of cells through the GCRA(10, 5) algorithm.
• [x] Describe the CI, NI, and ER fields in an ABR Resource Management cell.
• [x] Identify the 8-byte trailer fields of an AAL5 PDU.
• [x] Perform the Max-Min Fairness water-filling calculation.
• [x] Explain why Input Queuing is limited to 58.6% throughput.
• [x] Differentiate between TCP Reno (Loss-based) and BBR (Model-based).
• [x] Understand the purpose of a Persist Timer in zero-window scenarios.