fixup assignment 1

1 files changed, 38 insertions, 14 deletions

diff --git a/assignments/1/README.md b/assignments/1/README.md
index 334f69f..79a7363 100644
--- a/assignments/1/README.md
+++ b/assignments/1/README.md
@@ -163,7 +163,8 @@ Reference: Kurose & Ross, 8th ed., Ch. 1 (Internet structure and protocol stack
 
 ## 1.3 Packet-Switched vs Circuit-Switched Networks (5%)
 
-> (5%) What are packet-switched network and circuit-switched network, respectively? Develop a table to summarise their features, pros, and cons.
+> (5%) What are packet-switched network and circuit-switched network,
+respectively? Develop a table to summarise their features, pros, and cons.
 
 | Aspect              | Packet-Switched                     | Circuit-Switched                        |
 | ------------------- | ----------------------------------- | --------------------------------------- |
@@ -184,7 +185,10 @@ Reference: Kurose & Ross, 8th ed., Sec. 1.3 (circuit vs packet switching).
 
 ## 1.4 Network Delays and Traffic Intensity (5%)
 
-> (5%) What are processing delay, queuing delay, transmission delay, and propagation delay, respectively? Where does each delay occur? What is traffic intensity? Why should the traffic intensity be no greater than one (1) when designing a computer network?
+> (5%) What are processing delay, queuing delay, transmission delay,
+and propagation delay, respectively? Where does each delay occur? What
+is traffic intensity? Why should the traffic intensity be no greater
+than one (1) when designing a computer network?
 
 | Delay        | Label     | Location                  | Description                                     |
 | -----        | -----     | --------                  | -----------                                     |
@@ -193,7 +197,8 @@ Reference: Kurose & Ross, 8th ed., Sec. 1.3 (circuit vs packet switching).
 | Transmission | `d_trans` | each sender on a link     | Time to push all bits onto the link             |
 | Propagation  | `d_prop`  | on the medium of delivery | Time for signal to travel                       |
 
-> What is traffic intensity? Why should the traffic intensity be no greater than one (1) when designing a computer network?
+> What is traffic intensity? Why should the traffic intensity be no
+greater than one (1) when designing a computer network?
 
 Traffic intensity is the ratio of the bit arrival rate to the link's transmission capacity, representing the fraction of time the link is busy.
 
@@ -218,7 +223,8 @@ Reference: Kurose & Ross, 8th ed., Sec. 1.4 (delays in packet switching and traf
 
 ## 1.5 Web Caching and Conditional GET (5%)
 
-> (5%) What is Web-caching? When may Web-caching be more useful in a university? What problem does the conditional GET in HTTP aim to solve?
+> (5%) What is Web-caching? When may Web-caching be more useful in a
+university? What problem does the conditional GET in HTTP aim to solve?
 
 Web caching comes in a few forms. One form is client side caching that allows
 browser to cache content and re-serve that content to end users if specific
@@ -250,20 +256,38 @@ Reference: Kurose & Ross, 8th ed., Sec. 2.2 (HTTP, Web caching, conditional GET)
 
 ## 1.6 Email Protocol Analysis (5%)
 
-> (5%) Suppose you have a Web-based email account, such as Gmail, and you have just sent a message to a friend, Alice, who accesses her mail from her mail server using IMAP. Assume that both you and Alice are using a smartphone to access emails via Wi-Fi at home. List all the network protocols that may be involved in sending and receiving the email. Discuss in detail how the message went from your smartphone to Alice's smartphone - that is, how the message went through all the network protocol layers on each of the network devices involved in the communication. Ignore everything between your ISP and Alice's ISP.
+> (5%) Suppose you have a Web-based email account, such as Gmail,
+and you have just sent a message to a friend, Alice, who accesses her
+mail from her mail server using IMAP. Assume that both you and Alice
+are using a smartphone to access emails via Wi-Fi at home. List all
+the network protocols that may be involved in sending and receiving
+the email. Discuss in detail how the message went from your smartphone
+to Alice's smartphone - that is, how the message went through all the
+network protocol layers on each of the network devices involved in the
+communication. Ignore everything between your ISP and Alice's ISP.
 
-Scenario: You send via Gmail web interface; Alice reads with IMAP on her phone. Both on home Wi-Fi. Ignore transit between ISPs.
+The protocols that are likely involved are:
 
-Protocols likely involved:
-- Application: HTTPS (your browser to Gmail), SMTP (Gmail to Alice's server), IMAP (Alice's phone to her server), DNS
+- Application: HTTPS, SMTP, IMAP, DNS
 - Transport: TCP
-- Network: IP; ICMP for diagnostics
-- Link/Physical: Wi-Fi at each home; possibly Ethernet on LAN/backhaul
+- Network: IP
+- Link/Physical: Wi-Fi, Ethernet
 
-How the message flows:
-- Your phone to Gmail: App -> HTTPS over TCP/443 -> IP -> Wi-Fi frames to your router -> ISP uplink
-- Gmail to Alice's server: DNS lookup of MX, then SMTP over TCP to deliver message
-- Alice's phone to her server: IMAP over TCP/993 via her Wi-Fi/router/ISP; server returns the new message; her app displays it
+Sending Email:
+
+1. Open Web-based email account in browser. This will require HTTP over TLS
+   which implicitly uses TCP/IP or QUIC/IP depending on the vendor and browser.
+2. The browser will POST to an HTTP endpoint hosted on a web server.
+3. The web server will receive the email message and deliver it via SMTP to the
+   recipients mail server. This may get relayed multiple times before eventually
+   landing in the recipients mailbox on the mail server.
+
+Receiving Email:
+
+1. Alice will open their preferred mail user agent (MUA) to connect to their
+   IMAP server to retrieve the new mail message.
+2. The MUA will download the mail message to the device and synchronize any
+   changes via IMAP with the mail server.
 
 Reference: Kurose & Ross, 8th ed., Sec. 2.2 (HTTP/HTTPS basics), Sec. 2.3 (Electronic mail: SMTP, IMAP/POP), Sec. 2.5 (DNS).