feat: complete part 1 of assignment 1

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@@ -183,7 +183,68 @@ The conditional GET mechanism solves the problem of **cache consistency** - ensu
 
 ### 1.6 Email Protocol Analysis (5%)
 
-[To be completed]
+**Scenario:** Web-based email (Gmail) sent to Alice who accesses email via IMAP on smartphone over Wi-Fi.
+
+#### Network Protocols Involved:
+
+**Sender Side (Web-based Gmail):**
+- **HTTP/HTTPS:** Communication between browser and Gmail web server
+- **SMTP:** Gmail server sending email to Alice's mail server
+- **DNS:** Domain name resolution for Alice's mail server
+- **TCP:** Reliable transport for HTTP and SMTP
+- **IP:** Network layer routing
+- **Wi-Fi (802.11):** Wireless LAN protocol
+- **Ethernet:** If Wi-Fi access point connects via wired network
+
+**Receiver Side (Alice's IMAP access):**
+- **IMAP:** Alice's smartphone retrieving email from her mail server
+- **TCP:** Reliable transport for IMAP
+- **IP:** Network layer routing
+- **Wi-Fi (802.11):** Wireless connection to home network
+- **DNS:** Resolving mail server address
+
+#### Detailed Message Flow Through Protocol Layers:
+
+**Phase 1: Sending Email (Your Smartphone → Gmail Server)**
+
+1. **Application Layer:** You compose email in Gmail web interface
+2. **HTTP/HTTPS:** Browser sends POST request with email data to Gmail server
+3. **Transport Layer:** TCP segments the HTTP request, adds port numbers (443 for HTTPS)
+4. **Network Layer:** IP adds source/destination IP addresses (your phone → Gmail server)
+5. **Link Layer:** Wi-Fi frames the IP packets with MAC addresses (phone → router)
+6. **Physical Layer:** Radio waves transmit frames to Wi-Fi access point
+
+**Phase 2: Gmail Processing and SMTP Delivery**
+
+1. **Gmail Server Processing:** Receives HTTP request, extracts email, prepares for SMTP delivery
+2. **DNS Resolution:** Gmail server queries DNS to find Alice's mail server IP address
+3. **SMTP Connection:** Gmail establishes TCP connection to Alice's mail server (port 25/587)
+4. **Application Layer:** SMTP protocol transfers email from Gmail to Alice's mail server
+5. **Transport Layer:** TCP ensures reliable delivery of SMTP commands and email content
+6. **Network Layer:** IP routes packets through internet infrastructure
+7. **Link Layer:** Various link technologies (Ethernet, fiber, etc.) carry packets
+
+**Phase 3: Alice Retrieving Email (Alice's Mail Server → Smartphone)**
+
+1. **IMAP Request:** Alice's email app sends IMAP commands to check for new messages
+2. **Transport Layer:** TCP establishes connection (port 143/993), segments IMAP requests
+3. **Network Layer:** IP routes packets from Alice's phone to her mail server
+4. **Link Layer:** Wi-Fi frames carry IP packets (phone → Wi-Fi router → ISP)
+5. **Physical Layer:** Radio waves and various physical media transmit signals
+
+**Phase 4: Email Delivery to Alice's Phone**
+
+1. **IMAP Response:** Mail server responds with email content via IMAP protocol
+2. **Transport Layer:** TCP reliably delivers email data to Alice's phone
+3. **Network Layer:** IP routes response packets back to Alice's phone
+4. **Link Layer:** Wi-Fi receives and processes frames at Alice's phone
+5. **Physical Layer:** Radio signals converted back to digital data
+6. **Application Layer:** Email app displays the received message
+
+**Key Protocol Stack Traversals:**
+- **Downward:** Each device processes from Application → Physical when sending
+- **Upward:** Each device processes from Physical → Application when receiving
+- **Multiple Hops:** Email traverses multiple network devices (routers, switches) between sender and receiver, each processing up to Network layer and back down
 
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