small edits

1 files changed, 51 insertions, 59 deletions

diff --git a/assignments/1/README.md b/assignments/1/README.md
index 6314e48..320a8ed 100644
--- a/assignments/1/README.md
+++ b/assignments/1/README.md
@@ -19,41 +19,29 @@ linestretch: 1.0
 >
 > If you are not familiar with the utility, read the Microsoft article, "How to Use TRACERT".
 
-Destination: www.athabascau.ca (Athabasca University website)
-Location: Calgary, Alberta, Canada
-Tool: traceroute (default ICMP/UDP probes)
-
-I ran traceroute at three different times of day and include the full outputs below. The destination did not reply to probes; many intermediate routers also filtered probes. In such cases, I use the last responding hop as the end-to-end RTT proxy and clearly state this in the summary.
+I ran traceroute at three different times of day and I included the full
+output below. The destination host didn't reply to my probes.
+I used the last responding hop as the end-to-end RTT and included that in my
+summary.
 
 Summary (using hop 7 as last responding hop):
 
-| Run | Visible hops (last responding hop index) | RTT used (ms) |
-| --- | ---------------------------------------- | ------------- |
-| 1   | 7                                        | 18.50         |
-| 2   | 7                                        | 18.92         |
-| 3   | 7                                        | 18.88         |
+| Run | Visible hops  | RTT used (ms) |
+| --- | ------------- | ------------- |
+| 1   | 7             | 18.50         |
+| 2   | 7             | 18.92         |
+| 3   | 7             | 18.88         |
 
 - Average RTT across runs: (18.50 + 18.92 + 18.88) / 3 = 18.77 ms
-- Standard deviation (sample): ~0.23 ms
-- Number of routers observed in the path: at least 7 (later hops did not reply due to filtering)
-- Note: These RTTs are for the last responding hop (Telus backbone node). The destination and later hops likely rate-limit or drop probes; this is common.
-
-Reference: Kurose & Ross, 8th ed., Ch. 1 (tools and measurement; traceroute concepts), Sec. 6.7 (example path behavior).
-
-Full traceroute outputs
+- Standard deviation (sample): sqrt((0.0729 + 0.0225 + 0.0121) / 2) = ~0.23 ms
+  - (18.50 - 18.77)^2 = 0.0729
+  - (18.92 - 18.77)^2 = 0.0225
+  - (18.88 - 18.77)^2 = 0.0121
+- Number of routers observed in the path: at least 7
 
-Run 1
+Trace 1
 
 ```
-Retrieving speedtest.net configuration...
-Testing from TELUS (108.173.195.49)...
-Retrieving speedtest.net server list...
-Selecting best server based on ping...
-Hosted by Shaw Communications (Calgary, AB) [5.10 km]: 14.384 ms
-Testing download speed................................................................................
-Download: 374.18 Mbit/s
-Testing upload speed......................................................................................................
-Upload: 496.73 Mbit/s
 traceroute to www.athabascau.ca (3.175.64.80), 30 hops max, 60 byte packets
  1  _gateway (192.168.0.1)  3.364 ms  3.332 ms  3.316 ms
  2  10.139.230.1 (10.139.230.1)  4.615 ms  4.601 ms  4.588 ms
@@ -87,18 +75,9 @@ traceroute to www.athabascau.ca (3.175.64.80), 30 hops max, 60 byte packets
 30  * * *
 ```
 
-Run 2
+Trace 2
 
 ```
-Retrieving speedtest.net configuration...
-Testing from TELUS (108.173.195.49)...
-Retrieving speedtest.net server list...
-Selecting best server based on ping...
-Hosted by TELUS Mobility (Calgary, AB) [5.29 km]: 14.111 ms
-Testing download speed................................................................................
-Download: 505.75 Mbit/s
-Testing upload speed......................................................................................................
-Upload: 390.19 Mbit/s
 traceroute to www.athabascau.ca (3.175.64.80), 30 hops max, 60 byte packets
  1  _gateway (192.168.0.1)  2.602 ms  2.580 ms  2.573 ms
  2  10.139.230.1 (10.139.230.1)  6.959 ms  6.953 ms  6.947 ms
@@ -132,18 +111,9 @@ traceroute to www.athabascau.ca (3.175.64.80), 30 hops max, 60 byte packets
 30  * * *
 ```
 
-Run 3
+Trace 3
 
 ```
-Retrieving speedtest.net configuration...
-Testing from TELUS (108.173.195.49)...
-Retrieving speedtest.net server list...
-Selecting best server based on ping...
-Hosted by TELUS Mobility (Calgary, AB) [5.29 km]: 14.617 ms
-Testing download speed................................................................................
-Download: 481.44 Mbit/s
-Testing upload speed......................................................................................................
-Upload: 402.87 Mbit/s
 traceroute to www.athabascau.ca (3.175.64.80), 30 hops max, 60 byte packets
  1  _gateway (192.168.0.1)  2.449 ms  3.640 ms  3.633 ms
  2  10.139.230.1 (10.139.230.1)  4.962 ms  4.955 ms  4.925 ms
@@ -181,13 +151,13 @@ traceroute to www.athabascau.ca (3.175.64.80), 30 hops max, 60 byte packets
 
 > (5%) What are the five layers in the Internet protocol stack? Develop a table to summarise what each layer does.
 
-| Layer | Name        | What it does                                                      |
-| ----- | ----------- | ---------------------------------------------------------------- |
-| 5     | Application | App protocols and data (HTTP, SMTP, IMAP, DNS, etc.)            |
-| 4     | Transport   | Process-to-process delivery (TCP reliable, UDP best-effort)      |
-| 3     | Network     | Host-to-host routing and addressing (IP, ICMP)                   |
-| 2     | Link        | Node-to-node delivery on a link (Ethernet, Wi-Fi)               |
-| 1     | Physical    | Bits on the wire/air (signals over copper, fiber, radio)         |
+| Layer | Name        | PDU      | Function                                                        | Key Protocols        |
+| ----- | ----        | ---      | --------                                                        | -------------        |
+| 5     | Application | Message  | End-user services and data exchange                             | HTTP, DNS, SMTP, FTP |
+| 4     | Transport   | Segment  | Process-to-process delivery with error control and flow control | TCP, UDP             |
+| 3     | Network     | Datagram | Host-to-host routing across networks using logical addressing   | IP, ICMP, IGMP       |
+| 2     | Link        | Frame    | Node-to-node transfer over a physical link with error detection | Ethernet, Wi-Fi, PPP |
+| 1     | Physical    | Bit      | Transmission of raw bits over physical medium                   | IEEE 802.3, 802.11   |
 
 Reference: Kurose & Ross, 8th ed., Ch. 1 (Internet structure and protocol stack overview).
 
@@ -216,11 +186,33 @@ Reference: Kurose & Ross, 8th ed., Sec. 1.3 (circuit vs packet switching).
 
 > (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?
 
-- Processing delay: Time to examine header/make forwarding decision (at routers/switches)
-- Queuing delay: Time waiting in the output queue (at routers/switches; depends on load)
-- Transmission delay: Time to push all bits onto the link = L/R (at each sender on a link)
-- Propagation delay: Time for signal to travel = distance/speed (on the medium)
-- Traffic intensity: rho = L a / R. Design requires rho <= 1 (preferably well below) so queues do not grow without bound.
+| Delay        | Label     | Location                  | Description                                     |
+| -----        | -----     | --------                  | -----------                                     |
+| Processing   | `d_proc`  | routers/switches          | Time to examine header/make forwarding decision |
+| Queuing      | `d_queue` | routers/switches          | Time waiting in the output queue                |
+| 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?
+
+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.
+
+Formula: `p = La/R`
+
+Where:
+
+- L = packet size (bits)
+- a = average arrival rate (packets/sec)
+- R = link transmission rate (bits/sec)
+
+When p > 1, bits arrive faster than they can be transmitted (La > R).
+This causes the queue to grow unbounded, leading to:
+
+- Infinite queuing delays
+- Buffer overflow and packet loss
+- Network instability
+
+When p <= 1, the system can keep up with arrivals.
 
 Reference: Kurose & Ross, 8th ed., Sec. 1.4 (delays in packet switching and traffic intensity).