This repository contains my solutions for the assignments from Stanford CS144: Computer Networking (Winter 2025) which I self-studied during Summer 2025. The course gradually builds a simplified TCP/IP stack from scratch, providing a deep understanding of how networking works under the hood.

Implemented a finite, flow-controlled byte stream abstraction:

• Supports writing from an input end and reading from an output end.
• Flow-controlled: enforces a strict capacity limit (number of bytes held in memory).
• Handles end-of-input (EOF) signaling.
• Can carry streams of arbitrary length even with tiny memory capacity.

Constructed a Reassembler:

• Accepts out-of-order substrings with indices.
• Reassembles them into the original byte stream in order.
• Writes to the same ByteStream built in Assignment 0.

Built the TCPReceiver:

• Translates received segments into reassembled streams.
• Tracks:
  • acknowledgment number (ackno): first missing byte index.
  • window size: how much more data the receiver can accept.
• Integrates the TCP view of sequencing with our previous byte stream and reassembler.

Implemented the TCPSender:

• Reads from the ByteStream and generates outgoing segments.
• Manages:
  • Receiver window (acknowledgment and size).
  • Sending new data (including SYN/FIN).
  • Retransmitting unacknowledged ("outstanding") segments.

Built the NetworkInterface to support Ethernet + ARP:

• Maintains a cache from IP → MAC (ARP cache).
• Sends ARP requests when the MAC of the next hop is unknown.
• Queues outgoing datagrams until ARP resolution completes.
• Responds to ARP requests and updates cache with ARP replies.
• Cleans up expired ARP entries.

Implemented a multi-interface IP router:

• Maintains a routing table: each rule defines a prefix, prefix_length, optional next_hop, and interface_num.
• Forwards datagrams based on longest-prefix matching.
• Drops packets if TTL reaches 0.
• Uses NetworkInterface to send datagrams to next hop or destination.

• Language: C++20
• Build System: CMake

Course: CS144: Computer Networking (Stanford University)
Quarter: Winter 2025