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| -rw-r--r-- | assignments/2/README.md | 30 | ||||
| -rw-r--r-- | assignments/3/README.md | 77 |
3 files changed, 110 insertions, 24 deletions
diff --git a/assignments/1/README.md b/assignments/1/README.md index 0ee9636..6314e48 100644 --- a/assignments/1/README.md +++ b/assignments/1/README.md @@ -1,6 +1,6 @@ --- title: "COMP-347: Computer Networks" -author: "munir khan - 3431709" +author: "Munir Khan (ID: 3431709)" date: "September 2025" subtitle: "Assignment 1" institute: "Athabasca University" @@ -38,6 +38,8 @@ Summary (using hop 7 as last responding hop): - 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 Run 1 @@ -187,6 +189,8 @@ traceroute to www.athabascau.ca (3.175.64.80), 30 hops max, 60 byte packets | 2 | Link | Node-to-node delivery on a link (Ethernet, Wi-Fi) | | 1 | Physical | Bits on the wire/air (signals over copper, fiber, radio) | +Reference: Kurose & Ross, 8th ed., Ch. 1 (Internet structure and protocol stack overview). + ## 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. @@ -206,6 +210,8 @@ traceroute to www.athabascau.ca (3.175.64.80), 30 hops max, 60 byte packets | Performance | Variable delay and jitter possible | Predictable, consistent latency | | Examples | Internet, Ethernet | PSTN, leased lines | +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? @@ -216,6 +222,8 @@ traceroute to www.athabascau.ca (3.175.64.80), 30 hops max, 60 byte packets - 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. +Reference: Kurose & Ross, 8th ed., Sec. 1.4 (delays in packet switching and traffic intensity). + ## 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? @@ -224,6 +232,8 @@ traceroute to www.athabascau.ca (3.175.64.80), 30 hops max, 60 byte packets - More useful at a university because many users request the same resources, raising cache hit rate and lowering Internet link load. - Conditional GET (If-Modified-Since or If-None-Match) lets caches validate freshness without re-downloading unchanged objects (304 Not Modified vs 200 OK). +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. @@ -241,6 +251,8 @@ How the message flows: - 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 +Reference: Kurose & Ross, 8th ed., Sec. 2.2 (HTTP/HTTPS basics), Sec. 2.3 (Electronic mail: SMTP, IMAP/POP), Sec. 2.5 (DNS). + # Part 2: Long Answer Questions (70%) I provide short, clear answers first, then 1-2 sentences of reasoning. @@ -292,6 +304,8 @@ e) Time when the last packet arrives at the server Method note on traceroute filtering - Many networks de-prioritize or block ICMP/UDP TTL-expired replies. This can hide intermediate and destination hops even when the path is fine. Using TCP to port 443 often elicits more replies, but the assignment requires traceroute; therefore I report the last responding hop and include the full outputs for verification. +Reference: Kurose & Ross, 8th ed., Ch. 1 (delays, throughput, store-and-forward; traceroute context). + ## 2.2 Propagation Delay and Bandwidth-Delay Product (20%) > (20%) Consider that you are submitting another assignment from your home computer to the university server, and you have worked out a list of network links between your computer and the university server. @@ -320,6 +334,8 @@ d) Max bits in links at any time (continuous send) e) What the product implies - Answer: Minimum in-flight/window size of ~3.9 Mb to fully use the path at ~430 Mb/s across a 9 ms one-way path; sets buffer/window requirements. +Reference: Kurose & Ross, 8th ed., Sec. 1.4 (propagation delay) and Ch. 3 (BDP intuition via TCP throughput/window sizing). + ## 2.3 Web Cache Implementation and Performance (20%) > (20%) You have learned that a Web cache can be useful in some cases. In this problem, you will investigate how useful a Web cache can be at a home. First, you need to download Apache server and install and run it as a proxy server on a computer on your home network. Then, write a brief report on what you did to make it work and how you are using it on all your devices on your home network. @@ -346,6 +362,8 @@ Answers with measured average R: - c) beta = 1.763 / (1 - 0.088) ~ 1.763 / 0.912 ~ 1.932 s - d) Total average response time with miss rate 0.5: 0.5 x (5 + 1.932) + 0.5 x (approx 0) ~ 3.466 s +Reference: Kurose & Ross, 8th ed., Sec. 2.2 (Web caching), Sec. 1.4 (M/M/1 intuition for access delay). + ## 2.4 File Distribution: Client-Server vs P2P (10%) > (10%) You have learned that a file can be distributed to peers in either client-server mode or peer-to-peer (P2P) mode. Consider distributing a large file of F = 21 GB to N peers. The server has an upload rate of Us = 1 Gbps, and each peer has a download rate of Di = 20 Mbps and an upload rate of U. For N = 10, 100, and 1,000 and U = 300 Kbps, 7000 Kbps, and 2 Mbps, develop a table giving the minimum distribution time for each of the combination of N and U for both client-server distribution and P2P distribution. Comment on the features of client-server distribution and P2P distribution and the differences between the two. @@ -370,6 +388,11 @@ Takeaways: - Client-server grows linearly with N; the server is the bottleneck. - P2P scales with total peer upload (N x U). With enough peer upload, P2P is much faster and often bounded by each peer’s 20 Mb/s download (8,400 s minimum). +Reference: Kurose & Ross, 8th ed., Sec. 2.6 (P2P file distribution model and formulas). + # References -Kurose, J. F., and Ross, K. W. Computer Networking: A Top-Down Approach (8th ed.). Pearson. +- Kurose, J. F., and Ross, K. W. Computer Networking: A Top-Down Approach (8th ed.). Pearson. + - Ch. 1 The Internet and the Network Edge (delays, switching, traceroute) + - Ch. 2 Application Layer (HTTP/caching, E-mail/SMTP/IMAP, DNS, P2P distribution) + - Ch. 3 Transport Layer (BDP intuition via TCP window/throughput) diff --git a/assignments/2/README.md b/assignments/2/README.md index 6884c34..c7a4d32 100644 --- a/assignments/2/README.md +++ b/assignments/2/README.md @@ -24,12 +24,16 @@ TCP provides reliable data transfer over IP's best-effort service using: - Reordering/in-order delivery: Out-of-order segments are buffered and reassembled before delivery to the application. - Connection management: Three-way handshake establishes state; graceful close ensures all data delivered. +Reference: Kurose & Ross, 8th ed., Ch. 3 (Transport Layer: TCP services, checksums, reliable data transfer, flow control, fast retransmit/recovery). + ## 1.2 Go-Back-N Protocol (5%) > (5%) While the RDT protocols are essentially stop‑and‑wait protocols, the GBN protocol allows the sender to send multiple packets without waiting for acknowledgement from the receiving parties. How does GBN achieve that? GBN achieves higher throughput than stop-and-wait via a sliding window that allows up to N unacknowledged packets in flight. The sender maintains base (oldest unACKed) and nextseqnum, uses a single timer for the oldest unACKed packet, and the receiver sends cumulative ACKs. On timeout, the sender retransmits from base ("goes back N"). This pipelining avoids per-packet waiting. +Reference: Kurose & Ross, 8th ed., Ch. 3 (Pipelined reliable data transfer: Go‑Back‑N). + ## 1.3 IPv6 Transition (5%) > (5%) Invention and adoption of IPv6 is a big advance in computer networking. What problems was IPv6 intended to solve? With the large number of networking devices and applications using IPv4 still in use, how is the transition from IPv4 to IPv6 being resolved? @@ -38,6 +42,8 @@ Motivation: Vast address space (no exhaustion), fewer routing entries via hierar Transition: Dual stack (IPv4+IPv6), tunneling (e.g., 6in4/6to4/Teredo), and translation (NAT64/DNS64) allow coexistence while IPv6 adoption increases. +Reference: Kurose & Ross, 8th ed., Ch. 4 (The Internet Protocol (IP): IPv4, Addressing, IPv6, and More; transition mechanisms). + ## 1.4 SNMP Protocol (5%) > (5%) SNMP is a protocol for network management. It has seven message types. What are the purposes of the SNMP GetRequest and SetRequest messages? Why were UDP datagrams chosen to transport SNMP messages? @@ -46,6 +52,8 @@ Transition: Dual stack (IPv4+IPv6), tunneling (e.g., 6in4/6to4/Teredo), and tran - SetRequest: Manager changes configuration parameters on an agent. - Why UDP: Low overhead and no connection setup; scalable for polling many devices; SNMP defines its own retry/timeout; resilient during control-plane stress when maintaining TCP connections is harder. +Reference: Kurose & Ross, 8th ed., Ch. 5 (Network management and SNMP). + ## 1.5 SDN-Enabled Devices (5%) > (5%) In today’s market and its applications, there are many SDN-enabled networking devices. What are the preferrable features that an SDN-enabled networking device usually has? @@ -57,6 +65,8 @@ Preferable features: - Northbound APIs/integration for centralized policy and automation. - Security via centralized policy (ACLs, microsegmentation). +Reference: Kurose & Ross, 8th ed., Ch. 5 (SDN control plane, generalized forwarding). + ## 1.6 BGP Loop Detection (5%) > (5%) BGP is a routing protocol used for routing among ISPs. One problem that BGP faces is detecting loops in paths. What are the loops? Why should loops be avoided? How does BGP detect the loops in paths? @@ -65,6 +75,8 @@ Preferable features: - Avoidance: Loops waste bandwidth, add delay, and cause instability. - Detection: AS_PATH attribute lists traversed ASes; if a received route’s AS_PATH contains the local AS, discard it. Policies/filters and max-path-length provide additional safeguards. +Reference: Kurose & Ross, 8th ed., Ch. 5 (Inter-AS routing: BGP; loop prevention via AS_PATH). + --- # Part 2: Long Answer Questions (70%) @@ -98,6 +110,8 @@ c) Receiver detection: Add all bytes including the checksum using 1’s-compleme d) Error coverage: Detects all single-bit errors and most multi-bit errors. Certain balanced multi-bit patterns can evade detection (so some 2-bit errors may go undetected). +Reference: Kurose & Ross, 8th ed., Ch. 3 (Internet checksum in UDP/TCP) and Ch. 6 (parity/checksum context at link layer). + ## 2.2 Dijkstra's Shortest Path Algorithm (20%) > (20%) The following table is used to compute the shortest path from A to all other nodes in a network, according to the link‑state algorithm, which is better known as Dijkstra’s shortest path algorithm. @@ -121,6 +135,8 @@ b) Apply Dijkstra from source x (see figure). The following table shows the iter Final shortest-path costs from x: w=3; u=4 (x->w->u); s=5 (x->s); y=5 (x->y); v=5 (x->w->u->v); t=6 (x->s->t); z=9 (x->s->t->z). +Reference: Kurose & Ross, 8th ed., Ch. 5 (Routing algorithms: Dijkstra/Link-State). + ## 2.3 CIDR Routing (20%) > (20%) A router running classless interdomain routing (CIDR) has the following entries in its routing table: @@ -144,6 +160,8 @@ Decisions: - 192.53.40.6 → matches 192.53.40.0/23 (covers 40.0–41.255) → Router 2 - 192.53.56.7 → no match → Default → Router 3 +Reference: Kurose & Ross, 8th ed., Ch. 4 (IP addressing, CIDR, and longest‑prefix matching). + ## 2.4 TCP Congestion Control (20%) > (20%) Consider that only a single TCP connection uses a 1 Gbps link, which does not buffer any data. Suppose that this link is the only congested link between the sending and receiving hosts. Assume that the TCP sender has a huge file to send to the receiver and the receiver’s receive buffer is much larger than the congestion window. Further assume that each TCP segment size is 1,500 bytes; the two-way propagation delay of this connection is 15 msec; and this TCP connection is always in the congestion avoidance phase (ignore slow start). @@ -169,3 +187,15 @@ c) Time to recover to W_max after a loss: d) Buffer sizing to keep the link busy: - For a single flow, provision on the order of the BDP to absorb bursts and maintain full utilization despite window dynamics: ≈ 15 Mb ≈ 1.875 MB ≈ ~1,250 MSS-sized segments. - With many flows, smaller buffers (≈ BDP/sqrt(N)) can suffice, but for N=1, BDP is the safe choice. + +Reference: Kurose & Ross, 8th ed., Ch. 3 (TCP congestion control: AIMD, sawtooth behavior; throughput/window relations). + +--- + +# References + +- Kurose, J. F., & Ross, K. W. (8th ed.). Computer Networking: A Top‑Down Approach. + - Ch. 3 Transport Layer (TCP reliability, checksum, and congestion control) + - Ch. 4 Network Layer: Data Plane (IP addressing, IPv6, CIDR, forwarding) + - Ch. 5 Network Layer: Control Plane (routing algorithms, BGP, SDN control plane, network management/SNMP) + - Ch. 6 Link Layer and LANs (error detection/correction context) diff --git a/assignments/3/README.md b/assignments/3/README.md index fbc9d34..27724f4 100644 --- a/assignments/3/README.md +++ b/assignments/3/README.md @@ -15,37 +15,44 @@ linestretch: 1.0 > (5%) What is the role of the anchor MSC in GSM networks? -The anchor MSC (Mobile Switching Center) keeps a call "anchored" to a single MSC for its entire duration while the mobile moves. It: +The anchor MSC (Mobile Switching Center) keeps a call anchored to a single MSC for its entire duration while the mobile moves. It: - Coordinates with HLR/VLR for authentication, location, and subscriber data. - Manages intra- and inter-MSC handovers by setting up and tearing down trunks to visited MSCs while keeping the original call leg. - Maintains continuity so numbering, charging, and signaling remain stable as the user roams. +Reference: 3GPP TS 23.002; TS 23.009 (high-level architecture and handover procedures in GSM/UMTS networks). + ## 1.2 LTE Network Characteristics (5%) > (5%) What are the main characteristics of LTE radio access networks? How does LTE network differ from previous generations of cellular networks? -- E-UTRAN with a flat architecture: eNodeBs handle radio and many control functions; no RNC. -- Air interface: OFDMA (DL), SC-FDMA (UL); flexible channel bandwidths (1.4 to 20 MHz). -- MIMO and advanced scheduling; adaptive modulation and coding; HARQ; 1 ms TTI. -- All-IP core (EPC); low latency, high throughput, QoS bearers and dedicated/default EPS bearers. +- E-UTRAN with a flat architecture: eNodeBs handle radio and many control functions; no RNC. All-IP core (EPC). +- Air interface: OFDMA (DL), SC-FDMA (UL); flexible channel bandwidths (1.4 to 20 MHz). HARQ; 1 ms TTI. +- MIMO and advanced scheduling; adaptive modulation and coding; QoS bearers (default/dedicated EPS bearers). - Compared to 3G (UMTS/WCDMA): LTE moves from wideband CDMA to OFDM-based access, eliminates circuit-switched core (CS services via IMS/VoLTE), reduces latency, increases spectral efficiency, and simplifies the RAN. +Reference: 3GPP TS 36.300 (E-UTRAN overall description); Kurose & Ross, 8th ed., Ch. 7 (cellular overview). + ## 1.3 CSMA/CD Protocol (5%) > (5%) What does CSMA/CD stand for? How does the protocol work? Explain why RTT on an Ethernet LAN is an important parameter for the CSMA/CD protocol to work properly. - CSMA/CD: Carrier Sense Multiple Access with Collision Detection. -- Operation: Sense channel idle, transmit; detect collision (voltage anomalies), send jam signal; back off using binary exponential backoff (K slots; slot = 512 bit times); retry. -- RTT importance: To guarantee any collision is detected while transmitting, frames must be at least 512 bits so transmission lasts at least one round-trip propagation time (including repeater delays). If frames were shorter than the slot time, a station could finish sending without detecting a collision. +- Operation: Sense channel idle, transmit; while transmitting, detect collision (signal energy). On collision, send jam signal and abort; back off using binary exponential backoff (choose K in {0..2^n-1} slots; slot = 512 bit times); retry. +- RTT/slot-time importance: To guarantee any collision is detected while transmitting, frames must be at least 512 bits so transmission lasts at least one round-trip propagation time (including repeater delays). If frames were shorter than the slot time, a station could finish sending without detecting a collision. + +Reference: Kurose & Ross, 8th ed., Sec. 6.3.2 (CSMA/CD), Sec. 6.4.2 (Ethernet frame and slot time). ## 1.4 CSMA/CA Protocol (5%) > (5%) What does CSMA/CA stand for? How does the protocol work? How can collisions be avoided in the protocol? - CSMA/CA: Carrier Sense Multiple Access with Collision Avoidance (802.11 DCF). -- Operation: After sensing idle for DIFS, choose random backoff; decrement timer while idle; transmit when backoff reaches zero; receiver sends ACK after SIFS. Collisions inferred by missing ACK. +- Operation: After sensing idle for DIFS, choose random backoff; decrement timer while idle; transmit when backoff reaches zero; receiver sends ACK after SIFS. Collisions are inferred by missing ACK. - Avoidance: Random backoff spaces transmissions; RTS/CTS reserves the channel and mitigates hidden terminals; interframe spacing (SIFS/DIFS) prioritizes control/ACK. +Reference: Kurose & Ross, 8th ed., Ch. 7 (802.11 MAC/DCF, RTS/CTS). + ## 1.5 Data Link Layer Error Detection/Correction (5%) > (5%) What techniques can be used for error-detection and error-correction, respectively, on the data link layer? @@ -53,15 +60,19 @@ The anchor MSC (Mobile Switching Center) keeps a call "anchored" to a single MSC - Detection: Parity (single, two-dimensional), checksum (1's complement), CRC. - Correction: Hamming codes, Reed-Solomon, convolutional/turbo/LDPC codes. ARQ/HARQ combine FEC with retransmissions. +Reference: Kurose & Ross, 8th ed., Sec. 6.2 (parity, checksum, CRC). + ## 1.6 Wi-Fi Network Standards (5%) -> (5%) What wireless (Wi-Fi) network standards are used in today’s industries? What are the characteristics of the link specified in each standard? +> (5%) What wireless (Wi-Fi) network standards are used in today's industries? What are the characteristics of the link specified in each standard? - 802.11n (Wi-Fi 4): 2.4/5 GHz, 20/40 MHz channels, MIMO, up to 600 Mbps PHY. - 802.11ac (Wi-Fi 5): 5 GHz, 20/40/80/160 MHz, MU-MIMO (DL), higher-order QAM, multi-Gbps PHY. - 802.11ax (Wi-Fi 6/6E): 2.4/5/6 GHz, OFDMA, MU-MIMO (UL/DL), BSS coloring, TWT; higher efficiency and capacity. - 802.11be (Wi-Fi 7, emerging): 2.4/5/6 GHz, 320 MHz channels, multi-link operation, higher-order MIMO and QAM; very high throughput. +Reference: IEEE 802.11 standard family (e.g., 802.11-2016 and amendments); Kurose & Ross, 8th ed., Ch. 7. + --- # Part 2: Long Answer Questions (70%) @@ -72,15 +83,16 @@ The anchor MSC (Mobile Switching Center) keeps a call "anchored" to a single MSC Chosen scheme: UMTS W-CDMA (FDD). - Spreading: User data is spread by orthogonal variable spreading factor (OVSF) channelization codes to a common chip rate (3.84 Mcps). Scrambling codes separate cells/users at the cell and UE level. -- Power control: Fast closed-loop power control combats near-far and fading (e.g., 1500 Hz DL commands). +- Power control: Fast closed-loop power control combats near-far and fading (e.g., 1500 Hz downlink commands). - Receiver: RAKE combining aligns and coherently combines energy from multipath components (fingers), exploiting multipath diversity. - Handover: Soft/softer handover maintains simultaneous links to multiple cells/sectors; diversity improves robustness. - Advantages over TDM/FDM: Interference averaging (soft capacity), graceful degradation as load increases, strong multipath resilience via RAKE, flexible rate adaptation by varying spreading factor and coding, inherent security through spreading. Sources consulted: -- 3GPP TS 25.213, Spreading and Modulation (FDD), v. specify latest. -- K. Holma and A. Toskala, WCDMA for UMTS: HSPA Evolution and LTE, Wiley. -- J. G. Proakis and M. Salehi, Digital Communications, McGraw-Hill. +- 3GPP TS 25.213, Spreading and Modulation (FDD). +- Holma & Toskala, WCDMA for UMTS: HSPA Evolution and LTE. +- Proakis & Salehi, Digital Communications. +- Kurose & Ross, 8th ed., Ch. 7 (high-level cellular/CDMA context). ## 2.2 Two-Dimensional Checksum (15%) @@ -107,9 +119,11 @@ Why shortest: For an m x n arrangement, checksum length is m + n + 1. For 16 bit 1-bit detect/correct: A single flipped data bit causes exactly one row parity and one column parity to fail, and toggles overall parity (odd). The intersection of the failing row and column identifies the bit to correct. If a parity bit flips, overall parity detects it while rows/columns localize which parity bit erred. +Reference: Kurose & Ross, 8th ed., Sec. 6.2.1 (two-dimensional parity). + ## 2.3 CSMA/CD Ethernet Analysis (20%) -> (20%) Assume a 1 Gbps Ethernet has two nodes, A and B, connected by a 180 m cable with three repeaters in between, and they each have one frame of 1,024 bits to send to each other. Further assume that the signal propagation speed across the cable is 2*10^8 m/sec;, CSMA/CD uses back-off intervals of multiples of 512 bits; and each repeater will insert a store-and-forward delay equivalent to 20-bit transmission time. At time t = 0, both A and B attempt to transmit. After the first collision, A draws K = 0 and B draws K = 1 in the exponential backoff protocol after sending the 48 bits jam signal. +> (20%) Assume a 1 Gbps Ethernet has two nodes, A and B, connected by a 180 m cable with three repeaters in between, and they each have one frame of 1,024 bits to send to each other. Further assume that the signal propagation speed across the cable is 2*10^8 m/sec; CSMA/CD uses back-off intervals of multiples of 512 bits; and each repeater will insert a store-and-forward delay equivalent to 20-bit transmission time. At time t = 0, both A and B attempt to transmit. After the first collision, A draws K = 0 and B draws K = 1 in the exponential backoff protocol after sending the 48 bits jam signal. > a) What is the one-way propagation delay (including all repeater delays) between A and B in seconds? At what time is A's packet completely delivered at B? > b) Now suppose that only A has a packet to send and that the repeaters are replaced with switches. Suppose that each switch has an 8-bit processing delay in addition to a store-and-forward delay. At what time, in seconds, is A's packet delivered at B? > In your calculations for a and b, you must include all the delays that occur according to CSMA/CD, and you must show the details of your work. @@ -117,30 +131,32 @@ Why shortest: For an m x n arrangement, checksum length is m + n + 1. For 16 bit Given: - Rate = 1e9 bps. Frame length = 1024 bits. Jam = 48 bits. Slot = 512 bits. - Cable propagation = 180 m / (2e8 m/s) = 0.9 microseconds. -- 3 repeaters x 20-bit times = 60 ns = 0.06 microseconds (treated as store-and-forward delays in a collision domain per problem statement). +- 3 repeaters x 20-bit times = 60 ns = 0.06 microseconds (treated as added delay per the problem statement). - One-way propagation including repeaters: 0.9 + 0.06 = 0.96 microseconds. -a) Timeline with collision at t=0: -- Both start transmitting at t=0. -- Each detects collision when the other’s signal arrives: t = 0.96 microseconds. +a) Timeline with collision at t = 0: +- Both start transmitting at t = 0. +- Each detects collision when the other's signal arrives: t = 0.96 microseconds. - Each sends 48-bit jam: duration 48 ns = 0.048 microseconds. Local jam ends at 1.008 microseconds. - The last bit of B's jam arrives at A at 1.008 + 0.96 = 1.968 microseconds (channel becomes idle then). -- Backoff: A draws K=0, B draws K=1. A begins retransmission immediately when idle; B would attempt after 1 slot (0.512 microseconds) but will sense busy and defer. -- A’s frame transmission time: 1024 bits / 1e9 = 1.024 microseconds. Last bit leaves A at 1.968 + 1.024 = 2.992 microseconds. +- Backoff: A draws K = 0, B draws K = 1. A begins retransmission immediately when idle; B would attempt after 1 slot (0.512 microseconds) but will sense busy and defer. +- A's frame transmission time: 1024 bits / 1e9 = 1.024 microseconds. Last bit leaves A at 1.968 + 1.024 = 2.992 microseconds. - Last bit arrives at B after one-way propagation: 2.992 + 0.96 = 3.952 microseconds. Answer (a): one-way delay = 0.96 microseconds; A's packet completely delivered at B at about 3.952 microseconds. b) Replace 3 repeaters with 3 store-and-forward switches (8-bit processing per switch): - Per switch delay = frame time + processing = 1.024 microseconds + 8 ns = 1.032 microseconds. -- End-to-end: A transmits 1.024 microseconds, then 3 switches each add 1.032 microseconds, plus cable propagation (0.9 microseconds). Delivery time (from t=0): +- End-to-end: A transmits 1.024 microseconds, then 3 switches each add 1.032 microseconds, plus cable propagation (0.9 microseconds). Delivery time (from t = 0): 1.024 + 3*(1.032) + 0.9 = 1.024 + 3.096 + 0.9 = 5.020 microseconds. Answer (b): about 5.020 microseconds. +Reference: Kurose & Ross, 8th ed., Sec. 6.3.2 (CSMA/CD timing, jam, backoff) and Sec. 6.4.3 (store-and-forward switching). + ## 2.4 802.11 RTS/CTS Transmission (10%) -> (10%) Suppose an 802.11 station is configured to always reserve the channel with RTS/CTS. At t=0 it wants to transmit 1024 bytes. All other stations are idle. At what time will the station complete the transmission? At what time can the station receive the acknowledgement? +> (10%) Suppose an 802.11 station is configured to always reserve the channel with RTS/CTS. At t = 0 it wants to transmit 1024 bytes. All other stations are idle. At what time will the station complete the transmission? At what time can the station receive the acknowledgement? Assumptions (matching common textbook values and ignoring PHY preamble/PLCP overheads unless specified): - Data rate = 11 Mbps. DIFS = 50 microseconds. SIFS = 10 microseconds. @@ -160,6 +176,8 @@ Totals: - Data transmission complete at: 50 + 14.545 + 10 + 10.182 + 10 + 765.091 = 859.818 microseconds. - ACK received at: 859.818 + 10 + 10.182 = 880.000 microseconds. +Reference: Kurose & Ross, 8th ed., Ch. 7 (802.11 timing and RTS/CTS). + ## 2.5 Bluetooth Frame Format Analysis (10%) > (10%) Conduct research about Bluetooth technology and describe and comment on the format of the Bluetooth frame. Focus on its features and limitations. Is there anything in the frame format that inherently limits the number of active nodes in a network to eight active nodes? Explain. @@ -173,3 +191,18 @@ Features and limitations: - Robust short-range links with FEC, ARQ, fast frequency hopping; low power design. - Payload and slot structure constrain throughput; tight timing and hopping sequence complexity. - Piconet concurrency: AM_ADDR is 3 bits, yielding up to 7 active slaves addressed by the master (plus the master itself). Additional devices can be parked (no AM_ADDR) and polled in/out, and multiple piconets can form scatternets, but a single piconet supports at most 7 active slaves concurrently due to the 3-bit address field in the frame header. + +References: Bluetooth Core Specification (e.g., v5.x); Kurose & Ross, 8th ed., Ch. 6/7 (MAC/link framing context). + +--- + +# References + +- Kurose, J. F., & Ross, K. W. (8th ed.). Computer Networking: A Top-Down Approach. (See Ch. 6: Link Layer and LANs; Ch. 7: Wireless and Mobile Networks.) +- 3GPP TS 23.002: Network Architecture; 3GPP TS 23.009: Handover Procedures. +- 3GPP TS 36.300: E-UTRAN Overall Description. +- 3GPP TS 25.213: Spreading and Modulation (FDD) for W-CDMA. +- IEEE 802.11 Standard (e.g., 802.11-2016 and amendments for 11n/ac/ax/be context). +- Bluetooth SIG, Bluetooth Core Specification (e.g., v5.x). +- Proakis, J. G., & Salehi, M. Digital Communications. (CDMA fundamentals.) +- Holma, H., & Toskala, A. WCDMA for UMTS: HSPA Evolution and LTE. |