Stanford CS144 - Introduction to Computer Networks (Advanced)

The standard architectural framework for computer networks:
1. Application: High-level network protocols (HTTP, DNS, FTP).
2. Transport: Host-to-host communication and multiplexing (TCP, UDP).
3. Network: Datagram routing across disparate networks (IP).
4. Link: Data transfer between adjacent network nodes (Ethernet, Wi-Fi).
5. Physical: Transmission of raw bits over physical media (copper, optical fiber, wireless).

A foundational network architecture design guide stating that application-specific features (e.g., error checking, encryption, reliable delivery) should be implemented at the end hosts rather than in intermediate network nodes (routers), keeping the network core simple, stateless, and scalable.

The connection establishment phase in TCP:
1. Client $\to$ Server: SYN packet sent with initial sequence number seq = x.
2. Server $\to$ Client: SYN-ACK packet returned with seq = y and ack = x + 1.
3. Client $\to$ Server: ACK packet sent with ack = y + 1.

A sliding window protocol where the sender can transmit up to $N$ unacknowledged packets. The receiver uses cumulative ACKs and discards out-of-order packets. If a loss timeout occurs, the sender retransmits all unacknowledged packets starting from the lost sequence number.

A sliding window protocol where the receiver individually acknowledges each correctly received packet and buffers out-of-order frames. The sender maintains independent timers for each packet and retransmits only unacknowledged packets upon timeout.

While Stop-and-Wait utilization is $U=\frac{L/R}{RTT+L/R}$, a sliding window protocol with window size $N$ increases sender utilization to:
$$U_{\text{window}}=\min \left(1,\frac{N\cdot (L/R)}{RTT+L/R}\right)$$
where $L$ is packet length in bits and $R$ is link transmission rate in bps.

The maximum amount of unacknowledged data a TCP sender can transmit is bounded by the minimum of the congestion window and receive window:
$$\text{Effective Window}=\min (\text{cwnd},\text{rwnd})$$