Q: In most data link protocols that retransmit damaged frames, if the probability that a frame is damaged is p (0 ≤ p < 1) and acknowledgments are never lost, what is the mean number of transmissions required to successfully send one frame?

Introduction / Context: Many link-layer protocols use ARQ (Automatic Repeat reQuest): a sender retransmits a frame when it is detected as damaged or lost. When acknowledgments are assumed reliable (never lost) and only data frames can be damaged with probability p, the number of transmissions per successfully delivered frame follows a geometric pattern. Given Data / Assumptions: Each attempt to send the frame succeeds with probability (1 − p). Failures (damage) occur independently with probability p. Acknowledgments are never lost or corrupted. Retransmissions continue until success. Concept / Approach: Let X be the number of transmissions needed for success. X is a geometric random variable with success probability q = (1 − p). The expected value of a geometric distribution (counting the successful trial) is E[X] = 1 / q = 1 / (1 − p). This captures the average total sends per successfully delivered frame, including necessary retries. Step-by-Step Solution: Define success probability: q = 1 − p.Recognize X ~ Geometric(q) (first success model).Compute expectation: E[X] = 1 / q = 1 / (1 − p).Interpretation: if p = 0.1, E[X] ≈ 1 / 0.9 ≈ 1.111… transmissions per successfully delivered frame. Verification / Alternative check: Series method: E[X] = Σ_{k≥1} k * p^{k−1} * (1 − p) = (1 − p) * Σ k p^{k−1} = 1 / (1 − p). This matches the standard geometric expectation. Why Other Options Are Wrong: 1 / p: Grows unbounded as p → 0; contradicts intuition. 1 + p: Linear, underestimates retries for larger p. 1 − p: This is the success probability, not the expectation. p / (1 − p): Expected number of failures before success; missing the final successful transmission. Common Pitfalls: Forgetting to include the successful final transmission; confusing the expected count of failures p/(1−p) with total transmissions 1/(1−p); assuming acknowledgments can also fail, which would change the model. Final Answer: 1 / (1 − p)

Q: Under the historical IPv4 classful scheme, which address class provides the fewest usable host addresses per network?

Introduction / Context: Although modern networks use CIDR, many exams reference classful IPv4 addressing. Knowing the relative host capacities per class clarifies why classful addressing was wasteful. Given Data / Assumptions: Class A: /8 networks. Class B: /16 networks. Class C: /24 networks. Class D and E are not used for ordinary unicast hosts. Concept / Approach: Usable host addresses per network (ignoring modern VLSM/CIDR): Class A has roughly 16 million minus 2, Class B about 65,534, and Class C about 254. Therefore, among unicast classes A/B/C, Class C has the fewest hosts per network. Step-by-Step Solution: Recall default masks: A=/8, B=/16, C=/24.Compute host counts: 2^(host bits) − 2.For /24: 2^8 − 2 = 254 usable hosts → fewest among A/B/C. Verification / Alternative check: Compare: A (2^24 − 2), B (2^16 − 2), C (2^8 − 2). The ranking is clear: C has the smallest host pool. Why Other Options Are Wrong: Class D/E: Not for general host assignment (multicast/experimental). Class A/B: Far more hosts per network than Class C. Common Pitfalls: Confusing “fewest networks” with “fewest hosts per network.” Class C has many networks but few hosts per network. Final Answer: Class C

Q: For connecting a modem, a computer uses a serial interface defined by the EIA/Telecommunications Industry Association standard RS-232. What do the letters “RS” stand for in RS-232?

Introduction / Context: RS-232 is one of the most widely known serial communication standards used historically for modems and many peripherals. Understanding its naming clarifies the lineage of serial interface specifications from industry bodies such as EIA/TIA. Given Data / Assumptions: Standard in question: RS-232. Context: PC-to-modem serial communication. Abbreviation “RS” must be expanded. Concept / Approach: “RS” in RS-232 originally stood for “Recommended Standard,” a designation from the Electronic Industries Association before the transition to EIA/TIA naming conventions (e.g., EIA-232). The standard defines electrical characteristics, signaling levels, and connector pinouts for serial interfaces. Step-by-Step Solution: Identify the authority: EIA (later EIA/TIA).Recall RS prefix meaning: Recommended Standard.Hence, RS-232 expands to Recommended Standard-232. Verification / Alternative check: Later documents often rename RS-232 to EIA-232, but the “RS” expansion remains historically accurate. Why Other Options Are Wrong: Recognised standard / Registered source / Regulatory specification: Not the historical expansion used by EIA. Random sequence: Nonsense distractor. Common Pitfalls: Assuming RS = “Registered jack” (that applies to RJ-series phone connectors, e.g., RJ-11/RJ-45), not RS-232. Final Answer: Recommended standard

Q: In a typical PC-to-telephone long-distance data connection, where is the modem placed in relation to the computer’s I/O—between the telephone line and which computer interface?

Introduction / Context: Traditional dial-up connectivity used modems to convert digital serial data to analog waveforms suitable for telephone networks. PCs interfaced with external modems through serial ports implementing RS-232, which are asynchronous serial interfaces. Given Data / Assumptions: External modem used for telephone line connection. PC provides standard legacy serial ports (COM1/COM2) using RS-232. Interface timing is asynchronous (start/stop bits), not synchronous clocked serial. Concept / Approach: External dial-up modems connect to the PC via an asynchronous serial port (UART-based), typically exposed as a COM port. The other side of the modem connects to the analog telephone line (POTS). Synchronous serial ports exist but are not typical for consumer PC modem connections. Step-by-Step Solution: Identify the PC-modem link: RS-232 serial (UART) → asynchronous.Identify the modem-line link: analog POTS line via RJ-11.Therefore, the modem sits between the phone line and the PC’s asynchronous serial port. Verification / Alternative check: Common external modems used DB-9/DB-25 RS-232 connectors to COM ports; internal modems implemented the same interface on an expansion card but still presented an asynchronous interface to the OS. Why Other Options Are Wrong: PC (internal bus directly): Internal modems do, but the question states a PC-to-telephone hookup—external modem context. Synchronous port: Not the usual interface for consumer dial-up modems. Crossover cable: Ethernet wiring concept, irrelevant here. Parallel printer port: Not used for standard modems. Common Pitfalls: Confusing “serial” with “synchronous.” RS-232 modems use asynchronous framing (start/stop bits) at the PC side. Final Answer: asynchronous port

Q: Between email servers on the Internet, which protocol is used to transfer messages from one server to another?

Introduction / Context: Internet email delivery relies on a standard server-to-server transport protocol. Understanding the division of responsibilities among SMTP, POP3, and IMAP clarifies how a message moves from the sender’s domain to the recipient’s server and then to end users. Given Data / Assumptions: We focus on inter-server transfer over the public Internet. End-user retrieval protocols are out of scope for this hop. Standard ports and roles apply. Concept / Approach: SMTP (Simple Mail Transfer Protocol) is the application-layer protocol used for message submission and relay between mail transfer agents (MTAs). POP3 and IMAP are for client retrieval from a mailbox. FTP transfers files, not email messages; SNMP is for network management. Step-by-Step Solution: Identify the hop in question: server A → server B.Match to protocol: SMTP handles relay using DNS MX records and TCP (commonly port 25).Exclude client retrieval protocols (POP3/IMAP) and unrelated ones (FTP/SNMP). Verification / Alternative check: Inspect message headers (Received: lines) to see SMTP handoffs between MTAs during delivery. Why Other Options Are Wrong: POP3 / IMAP: Used after delivery for users to access their mailboxes. FTP: General file transfer, not email relay. SNMP: Monitoring/management, not message transport. Common Pitfalls: Confusing message submission (SMTP) with retrieval (POP3/IMAP). Both involve email but different directions and roles. Final Answer: SMTP

Q: Which of the following devices produce a hard copy (physical output on paper or media) in typical computer systems?

Introduction / Context: Hard copy refers to physical output that can be read without a computer—ink or marks on paper or other tangible media. Multiple output devices historically and presently serve this function in computing and technical drawing. Given Data / Assumptions: Typewriter terminal: impact device that prints characters on paper. Line printer: high-speed impact or laser device printing entire lines at once. Plotter: vector-drawing device that creates line art on paper using pens or modern inkjet mechanisms. Concept / Approach: Any device that renders computer-generated output in physical form is a hard-copy device. Typewriter terminals (teleprinters/TTYs), classic line printers, and plotters each produce tangible output that persists independently of the screen. Step-by-Step Solution: Evaluate each device’s output medium.Confirm that all three put marks on paper.Conclude that “All of the above” is correct. Verification / Alternative check: Historical computing labs used TTYs and line printers for logs and listings; engineering shops used pen plotters for CAD drawings—each a prototypical hard-copy workflow. Why Other Options Are Wrong: None of the above: Incorrect because all listed devices produce physical output. Individual picks (a, b, or c) alone: Incomplete; all apply. Common Pitfalls: Confusing “hard copy” with “hard drive”; hard copy is about physical printed output, not storage media. Final Answer: All of the above

Q: Which of the following media and links are considered broadband communications channels under common networking usage?

Introduction: “Broadband” broadly denotes high-capacity communications capable of carrying wide frequency ranges or multiple channels simultaneously. In practical networking, several physical media and radio links meet this description, enabling high data rates for access networks, backbones, and intercontinental connectivity. Given Data / Assumptions: We consider common infrastructure technologies used for high-rate data carriage. Broadband implies high bandwidth compared to legacy narrowband links (e.g., voice-grade lines). Examples include coaxial systems, optical fiber, terrestrial microwave, and satellite links. Concept / Approach: Coaxial cable supports high symbol rates and multi-channel modulation (e.g., DOCSIS). Fiber optic cable provides extremely high bandwidth with low loss, supporting dense wavelength division multiplexing (DWDM). Microwave circuits offer high-throughput, line-of-sight backhaul using wide channels and advanced modulation. Satellite systems use microwave and millimeter-wave bands for broadband backhaul and access. All qualify as broadband under typical definitions used by service providers and standards bodies. Step-by-Step Solution: 1) Evaluate each option’s capacity characteristics.2) Recognize that each supports multi-MHz to multi-GHz bandwidths or multiplexed channels.3) Conclude that all listed media are categorized as broadband in practice. Verification / Alternative check: Regulatory and industry documents (e.g., DOCSIS for cable, ITU-T for fiber systems, ETSI for microwave, and satellite operator specs) consistently treat these as broadband platforms. Why Other Options Are Wrong: Options A–D are each valid, so the composite All of the above is the only correct response. Common Pitfalls: Equating “broadband” only with consumer last-mile services; in fact, the term applies across access, metro, backhaul, and core networks. Final Answer: All of the above

Q: In Internet mail protocols, what is the default TCP port number used by POP3 (Post Office Protocol version 3) for retrieving emails from a server?

Introduction: Mail clients commonly use standardized Transmission Control Protocol (TCP) ports to connect to servers. POP3 (Post Office Protocol v3) is one such protocol used to download messages from a mailbox. Knowing the default port numbers helps with firewall rules, troubleshooting, and exam readiness. Given Data / Assumptions: We are concerned with the default port for POP3 without TLS implicit wrapping. Other mail protocols (IMAP, SMTP) use different well-known ports. Security variants may use alternate ports. Concept / Approach: POP3 operates by default on TCP port 110. If using implicit TLS (“POP3S”), servers typically listen on TCP port 995. IMAP uses port 143 (and IMAPS 993), and SMTP servers commonly accept message submissions on ports 25, 465 (implicit TLS), or 587 (submission). Recognizing these distinctions prevents misconfiguration during client setup. Step-by-Step Solution: 1) Identify the protocol: POP3 for message retrieval.2) Recall well-known port mapping: POP3 → 110.3) Differentiate from IMAP (143) and HTTP (80), which are often confused by beginners.4) Provide context about secure variants (995) without changing the default answer. Verification / Alternative check: Mail client documentation and IANA port assignments list POP3 with default TCP port 110, confirming the mapping. Why Other Options Are Wrong: 90: not a standard mail protocol port. 80: HTTP default port. 49: historically used by TACACS, not POP3. 143: IMAP default port, not POP3. Common Pitfalls: Confusing POP3 with IMAP or assuming the secure variant (995) is the “default.” Unless the question explicitly asks for the implicit TLS port, 110 is the correct default. Final Answer: 110

Question 1

In a sliding window protocol where 4 bits are used for sequence numbers, what is the maximum sender window size? (Assume Go-Back-N unless otherwise specified.)

Accepted Answer

Introduction / Context: Sliding window protocols use a finite sequence number space. The chosen ARQ variant—Go-Back-N (GBN) or Selective Repeat (SR)—determines the maximum permissible sender window to avoid ambiguity when sequence numbers wrap around. Given Data / Assumptions: Number of sequence bits m = 4 → sequence space size = 2^m = 16. Assume Go-Back-N unless otherwise specified. Acknowledgments are reliable and eventually arrive. Concept / Approach: For Go-Back-N, the maximum sender window W_max is 2^m − 1. This ensures that when sequence numbers wrap, outstanding frames cannot be confused with newly sent frames. For Selective Repeat, to avoid overlap between outstanding and future frames, W_max is 2^(m−1). The problem statement does not specify SR, so the common default is GBN. Step-by-Step Solution: Compute sequence space: 2^4 = 16 distinct numbers.Apply GBN rule: W_max = 2^m − 1 = 16 − 1 = 15.Validate no ambiguity at wrap-around with this bound. Verification / Alternative check: If it were Selective Repeat, W_max would be 2^(4−1) = 8. Many textbooks explicitly state the default unspecified case as Go-Back-N, yielding 15. Why Other Options Are Wrong: 16: Equals the entire sequence space; would cause ambiguity in GBN. 8: Correct only for Selective Repeat, which was not specified. 4: Too small relative to the allowable window. It depends on RTT only: RTT influences throughput, not the protocol limit. Common Pitfalls: Mixing up GBN and SR window bounds; forgetting that sequence wrap-around safety drives these limits, not bandwidth-delay product. Final Answer: 15

Question 2

When you send traffic to the loopback address (127.0.0.1), assuming TCP/IP is installed correctly and the stack is functioning locally, when should you receive a response?

Accepted Answer

Introduction / Context: The loopback interface is a virtual network interface that routes packets back to the local host. It is essential for testing whether the TCP/IP stack is correctly installed and operational without relying on any physical network hardware. Given Data / Assumptions: Destination is 127.0.0.1 (or ::1 for IPv6). TCP/IP stack is properly installed and active. No external network path is involved. Concept / Approach: Packets addressed to 127.0.0.0/8 are handled entirely within the host kernel’s networking stack. As there is no physical transmission or ARP/neighbor discovery needed, responses are generated as soon as the local IP layer processes the packets. Therefore, successful pings or TCP connections to loopback return immediately, constrained only by local processing. Step-by-Step Solution: Initiate a local ping or TCP connect to 127.0.0.1.The OS routes the packet to the loopback interface.The local TCP/IP stack receives and replies internally.The application sees the response with minimal delay (no wire involved). Verification / Alternative check: Disabling the NIC or unplugging the cable does not affect loopback. If loopback fails, the problem lies within the local stack configuration or firewall, not the external network. Why Other Options Are Wrong: Only if the address fails: Nonsense; if it fails, there is no response. After the next host comes online: Loopback is local; other hosts are irrelevant. Within two minutes: No reason for such a delay locally. No response is expected: Incorrect; loopback is designed to respond when healthy. Common Pitfalls: Confusing loopback with localhost name resolution issues; even if DNS fails, direct 127.0.0.1 should still work. Final Answer: Immediately

Question 3

In most data link protocols that retransmit damaged frames, if the probability that a frame is damaged is p (0 ≤ p < 1) and acknowledgments are never lost, what is the mean number of transmissions required to successfully send one frame?

Accepted Answer

Introduction / Context: Many link-layer protocols use ARQ (Automatic Repeat reQuest): a sender retransmits a frame when it is detected as damaged or lost. When acknowledgments are assumed reliable (never lost) and only data frames can be damaged with probability p, the number of transmissions per successfully delivered frame follows a geometric pattern. Given Data / Assumptions: Each attempt to send the frame succeeds with probability (1 − p). Failures (damage) occur independently with probability p. Acknowledgments are never lost or corrupted. Retransmissions continue until success. Concept / Approach: Let X be the number of transmissions needed for success. X is a geometric random variable with success probability q = (1 − p). The expected value of a geometric distribution (counting the successful trial) is E[X] = 1 / q = 1 / (1 − p). This captures the average total sends per successfully delivered frame, including necessary retries. Step-by-Step Solution: Define success probability: q = 1 − p.Recognize X ~ Geometric(q) (first success model).Compute expectation: E[X] = 1 / q = 1 / (1 − p).Interpretation: if p = 0.1, E[X] ≈ 1 / 0.9 ≈ 1.111… transmissions per successfully delivered frame. Verification / Alternative check: Series method: E[X] = Σ_{k≥1} k * p^{k−1} * (1 − p) = (1 − p) * Σ k p^{k−1} = 1 / (1 − p). This matches the standard geometric expectation. Why Other Options Are Wrong: 1 / p: Grows unbounded as p → 0; contradicts intuition. 1 + p: Linear, underestimates retries for larger p. 1 − p: This is the success probability, not the expectation. p / (1 − p): Expected number of failures before success; missing the final successful transmission. Common Pitfalls: Forgetting to include the successful final transmission; confusing the expected count of failures p/(1−p) with total transmissions 1/(1−p); assuming acknowledgments can also fail, which would change the model. Final Answer: 1 / (1 − p)

Question 4

Under the historical IPv4 classful scheme, which address class provides the fewest usable host addresses per network?

Accepted Answer

Introduction / Context: Although modern networks use CIDR, many exams reference classful IPv4 addressing. Knowing the relative host capacities per class clarifies why classful addressing was wasteful. Given Data / Assumptions: Class A: /8 networks. Class B: /16 networks. Class C: /24 networks. Class D and E are not used for ordinary unicast hosts. Concept / Approach: Usable host addresses per network (ignoring modern VLSM/CIDR): Class A has roughly 16 million minus 2, Class B about 65,534, and Class C about 254. Therefore, among unicast classes A/B/C, Class C has the fewest hosts per network. Step-by-Step Solution: Recall default masks: A=/8, B=/16, C=/24.Compute host counts: 2^(host bits) − 2.For /24: 2^8 − 2 = 254 usable hosts → fewest among A/B/C. Verification / Alternative check: Compare: A (2^24 − 2), B (2^16 − 2), C (2^8 − 2). The ranking is clear: C has the smallest host pool. Why Other Options Are Wrong: Class D/E: Not for general host assignment (multicast/experimental). Class A/B: Far more hosts per network than Class C. Common Pitfalls: Confusing “fewest networks” with “fewest hosts per network.” Class C has many networks but few hosts per network. Final Answer: Class C

Question 5

For connecting a modem, a computer uses a serial interface defined by the EIA/Telecommunications Industry Association standard RS-232. What do the letters “RS” stand for in RS-232?

Accepted Answer

Introduction / Context: RS-232 is one of the most widely known serial communication standards used historically for modems and many peripherals. Understanding its naming clarifies the lineage of serial interface specifications from industry bodies such as EIA/TIA. Given Data / Assumptions: Standard in question: RS-232. Context: PC-to-modem serial communication. Abbreviation “RS” must be expanded. Concept / Approach: “RS” in RS-232 originally stood for “Recommended Standard,” a designation from the Electronic Industries Association before the transition to EIA/TIA naming conventions (e.g., EIA-232). The standard defines electrical characteristics, signaling levels, and connector pinouts for serial interfaces. Step-by-Step Solution: Identify the authority: EIA (later EIA/TIA).Recall RS prefix meaning: Recommended Standard.Hence, RS-232 expands to Recommended Standard-232. Verification / Alternative check: Later documents often rename RS-232 to EIA-232, but the “RS” expansion remains historically accurate. Why Other Options Are Wrong: Recognised standard / Registered source / Regulatory specification: Not the historical expansion used by EIA. Random sequence: Nonsense distractor. Common Pitfalls: Assuming RS = “Registered jack” (that applies to RJ-series phone connectors, e.g., RJ-11/RJ-45), not RS-232. Final Answer: Recommended standard

Question 6

In a typical PC-to-telephone long-distance data connection, where is the modem placed in relation to the computer’s I/O—between the telephone line and which computer interface?

Accepted Answer

Introduction / Context: Traditional dial-up connectivity used modems to convert digital serial data to analog waveforms suitable for telephone networks. PCs interfaced with external modems through serial ports implementing RS-232, which are asynchronous serial interfaces. Given Data / Assumptions: External modem used for telephone line connection. PC provides standard legacy serial ports (COM1/COM2) using RS-232. Interface timing is asynchronous (start/stop bits), not synchronous clocked serial. Concept / Approach: External dial-up modems connect to the PC via an asynchronous serial port (UART-based), typically exposed as a COM port. The other side of the modem connects to the analog telephone line (POTS). Synchronous serial ports exist but are not typical for consumer PC modem connections. Step-by-Step Solution: Identify the PC-modem link: RS-232 serial (UART) → asynchronous.Identify the modem-line link: analog POTS line via RJ-11.Therefore, the modem sits between the phone line and the PC’s asynchronous serial port. Verification / Alternative check: Common external modems used DB-9/DB-25 RS-232 connectors to COM ports; internal modems implemented the same interface on an expansion card but still presented an asynchronous interface to the OS. Why Other Options Are Wrong: PC (internal bus directly): Internal modems do, but the question states a PC-to-telephone hookup—external modem context. Synchronous port: Not the usual interface for consumer dial-up modems. Crossover cable: Ethernet wiring concept, irrelevant here. Parallel printer port: Not used for standard modems. Common Pitfalls: Confusing “serial” with “synchronous.” RS-232 modems use asynchronous framing (start/stop bits) at the PC side. Final Answer: asynchronous port

Question 7

Between email servers on the Internet, which protocol is used to transfer messages from one server to another?

Accepted Answer

Introduction / Context: Internet email delivery relies on a standard server-to-server transport protocol. Understanding the division of responsibilities among SMTP, POP3, and IMAP clarifies how a message moves from the sender’s domain to the recipient’s server and then to end users. Given Data / Assumptions: We focus on inter-server transfer over the public Internet. End-user retrieval protocols are out of scope for this hop. Standard ports and roles apply. Concept / Approach: SMTP (Simple Mail Transfer Protocol) is the application-layer protocol used for message submission and relay between mail transfer agents (MTAs). POP3 and IMAP are for client retrieval from a mailbox. FTP transfers files, not email messages; SNMP is for network management. Step-by-Step Solution: Identify the hop in question: server A → server B.Match to protocol: SMTP handles relay using DNS MX records and TCP (commonly port 25).Exclude client retrieval protocols (POP3/IMAP) and unrelated ones (FTP/SNMP). Verification / Alternative check: Inspect message headers (Received: lines) to see SMTP handoffs between MTAs during delivery. Why Other Options Are Wrong: POP3 / IMAP: Used after delivery for users to access their mailboxes. FTP: General file transfer, not email relay. SNMP: Monitoring/management, not message transport. Common Pitfalls: Confusing message submission (SMTP) with retrieval (POP3/IMAP). Both involve email but different directions and roles. Final Answer: SMTP

Question 8

Which of the following devices produce a hard copy (physical output on paper or media) in typical computer systems?

Accepted Answer

Introduction / Context: Hard copy refers to physical output that can be read without a computer—ink or marks on paper or other tangible media. Multiple output devices historically and presently serve this function in computing and technical drawing. Given Data / Assumptions: Typewriter terminal: impact device that prints characters on paper. Line printer: high-speed impact or laser device printing entire lines at once. Plotter: vector-drawing device that creates line art on paper using pens or modern inkjet mechanisms. Concept / Approach: Any device that renders computer-generated output in physical form is a hard-copy device. Typewriter terminals (teleprinters/TTYs), classic line printers, and plotters each produce tangible output that persists independently of the screen. Step-by-Step Solution: Evaluate each device’s output medium.Confirm that all three put marks on paper.Conclude that “All of the above” is correct. Verification / Alternative check: Historical computing labs used TTYs and line printers for logs and listings; engineering shops used pen plotters for CAD drawings—each a prototypical hard-copy workflow. Why Other Options Are Wrong: None of the above: Incorrect because all listed devices produce physical output. Individual picks (a, b, or c) alone: Incomplete; all apply. Common Pitfalls: Confusing “hard copy” with “hard drive”; hard copy is about physical printed output, not storage media. Final Answer: All of the above

Question 9

In TCP/IP networking, which item explicitly identifies both the network portion (network ID) and the host portion (host ID) assigned to a computer for end-to-end communication on an IP network?

Accepted Answer

Introduction: Every device on an Internet Protocol (IP) network needs a way to be uniquely identified so it can send and receive packets. Conceptually, an IP address contains two parts: a network identifier that tells routers which logical network a host belongs to, and a host identifier that distinguishes the specific device within that network. Understanding which configuration element conveys these two identifiers is a fundamental networking skill and frequently appears in certification and interview questions. Given Data / Assumptions: A host participates in an IPv4 network using standard TCP/IP settings. Common settings include IP address, subnet mask, and default gateway. We are asked which item specifies the network and host address of the computer. Concept / Approach: The IP address assigned to a host encodes both the network ID and the host ID. Historically, classful addressing implied fixed boundaries, but in modern Classless Inter-Domain Routing (CIDR), the network/host split is determined by a prefix length (or mask). While the subnet mask (or prefix) tells where the boundary lies, the actual values of the network and host portions are carried in the IP address itself. The default gateway is merely the next-hop router used for off-subnet traffic and does not encode the host’s identity. Step-by-Step Solution: 1) Identify the items: IP address, subnet mask, default gateway.2) Recognize that the IP address is a 32-bit value whose high-order bits (per mask) denote network ID and remaining bits denote host ID.3) Note that the subnet mask is a boundary indicator, not an address; it does not by itself identify a host.4) Conclude that the IP address uniquely specifies both the network and host identifiers for the machine. Verification / Alternative check: Given an IP (e.g., 192.168.10.34) and a mask (/24), routers compute the network ID (192.168.10.0) by applying the mask to the IP address and infer the host ID (.34) from the remaining bits. This confirms that the IP address carries both values. Why Other Options Are Wrong: The TCP address: no such configuration parameter exists; TCP is a transport-layer protocol. The subnet mask: identifies the split position but not the host’s numeric identity. The default gateway: a routing next-hop, not an identity descriptor. None of the above: incorrect because the IP address is the right choice. Common Pitfalls: Students sometimes choose the subnet mask because it “determines” the split. Remember: the mask defines boundaries; the address carries the actual network and host values. Final Answer: The IP address

Question 10

In operating systems and data processing, the term “remote job entry (RJE)” most closely relates to which style of workload submission and execution?

Accepted Answer

Introduction: Remote Job Entry (RJE) is a historical yet important concept from mainframe and minicomputer eras that still informs modern workload orchestration. RJE enabled users at remote terminals or sites to submit entire jobs—often containing multiple programs, datasets, and control statements—to a centralized host system for later execution. Understanding RJE clarifies the differences between batch, real-time, and transaction-oriented paradigms. Given Data / Assumptions: RJE involves sending job control and input data to a central computer. Results are returned after the job has been scheduled and executed. There is no requirement for immediate, sub-second response to each individual user action. Concept / Approach: Batch processing groups work into jobs that run under the control of a scheduler, typically without interactive user oversight during execution. RJE fits this paradigm: jobs are queued, prioritized, executed, and output is delivered (often as printouts or files) later. In contrast, realtime processing must meet strict timing constraints for each event, and transaction processing focuses on short, atomic requests (e.g., bank account updates) with immediate acknowledgments. RJE is not about distributing computation across peers; it is about remote submission to a central batch system. Step-by-Step Solution: 1) Identify RJE elements: remote submission, queued execution, later retrieval of output.2) Compare to paradigms: batch = queued jobs; realtime = immediate deadlines; transaction = short requests with quick commits.3) Map RJE to batch processing due to its non-interactive execution model.4) Conclude that “batch processing” is the best fit. Verification / Alternative check: Classic systems (e.g., IBM JES/RJE/SJE) explicitly describe remote job submission and spooling for batch workloads, reinforcing the association. Why Other Options Are Wrong: Realtime processing: RJE does not guarantee deterministic deadlines per event. Transaction processing: RJE jobs are larger units than a single transaction and are not interactive. Distributed processing: RJE centralizes execution; it does not distribute computation among peers. None of the above: invalid because “batch processing” fits precisely. Common Pitfalls: Confusing RJE terminals with interactive timesharing. Timesharing sessions are conversational; RJE queues whole jobs for later execution. Final Answer: batch processing

Question 11

In computer data communications, inter-computer links for data exchange are almost always implemented using which transmission mode?

Accepted Answer

Introduction: Modern digital communication between computers—whether across copper, fiber, or radio—overwhelmingly uses serial transmission. Even when internal buses may be parallel, links between devices and systems favor serial signaling for distance, cost, and electromagnetic performance reasons. Recognizing why serial dominates clarifies design choices from USB and PCIe to Ethernet and optical transport networks. Given Data / Assumptions: We are discussing inter-computer communication (cables, fiber, wireless), not on-chip or very short PCB buses. Physical channels must manage clocking, skew, crosstalk, attenuation, and cost. High throughput and reliability are required over practical distances. Concept / Approach: Serial links send bits sequentially over one (or a few differential) pairs, enabling simpler connectors, tighter impedance control, and better immunity to skew than wide parallel ribbons. Techniques like differential signaling, clock recovery, encoding (e.g., 8b/10b, 64b/66b), and equalization unlock very high data rates per lane. Parallel signaling suffers from inter-pair skew and crosstalk that grow with frequency and distance, making it impractical for long or fast off-board connections. Step-by-Step Solution: 1) Compare physical constraints: long parallel buses require tight skew control; serial avoids this by using few conductors.2) Note standards: Ethernet, USB, SATA, PCIe, Thunderbolt, and optical systems all employ serial lanes.3) Consider scalability: aggregate bandwidth is achieved by lane bonding (x4, x8, x16) while retaining serial advantages.4) Conclude that serial transmission is the near-universal choice for inter-computer links. Verification / Alternative check: Observe that once-parallel interfaces (e.g., PATA) were replaced by serial counterparts (SATA) to overcome speed and cabling limitations. Why Other Options Are Wrong: Parallel: reserved for very short on-board buses; impractical for distance and very high speeds. Series parallel / direct: not standard transmission mode terms. None of the above: invalid because serial is correct. Common Pitfalls: Assuming “parallel is always faster”; at scale and distance, serial with proper coding and equalization wins decisively. Final Answer: serial

Question 12

Which of the following media and links are considered broadband communications channels under common networking usage?

Accepted Answer

Introduction: “Broadband” broadly denotes high-capacity communications capable of carrying wide frequency ranges or multiple channels simultaneously. In practical networking, several physical media and radio links meet this description, enabling high data rates for access networks, backbones, and intercontinental connectivity. Given Data / Assumptions: We consider common infrastructure technologies used for high-rate data carriage. Broadband implies high bandwidth compared to legacy narrowband links (e.g., voice-grade lines). Examples include coaxial systems, optical fiber, terrestrial microwave, and satellite links. Concept / Approach: Coaxial cable supports high symbol rates and multi-channel modulation (e.g., DOCSIS). Fiber optic cable provides extremely high bandwidth with low loss, supporting dense wavelength division multiplexing (DWDM). Microwave circuits offer high-throughput, line-of-sight backhaul using wide channels and advanced modulation. Satellite systems use microwave and millimeter-wave bands for broadband backhaul and access. All qualify as broadband under typical definitions used by service providers and standards bodies. Step-by-Step Solution: 1) Evaluate each option’s capacity characteristics.2) Recognize that each supports multi-MHz to multi-GHz bandwidths or multiplexed channels.3) Conclude that all listed media are categorized as broadband in practice. Verification / Alternative check: Regulatory and industry documents (e.g., DOCSIS for cable, ITU-T for fiber systems, ETSI for microwave, and satellite operator specs) consistently treat these as broadband platforms. Why Other Options Are Wrong: Options A–D are each valid, so the composite All of the above is the only correct response. Common Pitfalls: Equating “broadband” only with consumer last-mile services; in fact, the term applies across access, metro, backhaul, and core networks. Final Answer: All of the above

Question 13

In Internet mail protocols, what is the default TCP port number used by POP3 (Post Office Protocol version 3) for retrieving emails from a server?

Accepted Answer

Introduction: Mail clients commonly use standardized Transmission Control Protocol (TCP) ports to connect to servers. POP3 (Post Office Protocol v3) is one such protocol used to download messages from a mailbox. Knowing the default port numbers helps with firewall rules, troubleshooting, and exam readiness. Given Data / Assumptions: We are concerned with the default port for POP3 without TLS implicit wrapping. Other mail protocols (IMAP, SMTP) use different well-known ports. Security variants may use alternate ports. Concept / Approach: POP3 operates by default on TCP port 110. If using implicit TLS (“POP3S”), servers typically listen on TCP port 995. IMAP uses port 143 (and IMAPS 993), and SMTP servers commonly accept message submissions on ports 25, 465 (implicit TLS), or 587 (submission). Recognizing these distinctions prevents misconfiguration during client setup. Step-by-Step Solution: 1) Identify the protocol: POP3 for message retrieval.2) Recall well-known port mapping: POP3 → 110.3) Differentiate from IMAP (143) and HTTP (80), which are often confused by beginners.4) Provide context about secure variants (995) without changing the default answer. Verification / Alternative check: Mail client documentation and IANA port assignments list POP3 with default TCP port 110, confirming the mapping. Why Other Options Are Wrong: 90: not a standard mail protocol port. 80: HTTP default port. 49: historically used by TACACS, not POP3. 143: IMAP default port, not POP3. Common Pitfalls: Confusing POP3 with IMAP or assuming the secure variant (995) is the “default.” Unless the question explicitly asks for the implicit TLS port, 110 is the correct default. Final Answer: 110

Question 14

In data communications hardware, which device performs both modulation and demodulation to convert between digital data and carrier-based analog signals for transmission?

Accepted Answer

Introduction: Digital systems often need to transmit data across channels optimized for analog waveforms, such as radio or legacy telephone circuits. The component that bridges this gap is responsible for modulating a carrier at the transmitter and demodulating it at the receiver—hence the portmanteau “modem.” Given Data / Assumptions: We are discussing physical-layer signal conversions for data transport. Digital endpoints must communicate over analog channels in many scenarios. Terminology distinguishes medium (fiber, coax) from active signal-processing equipment (modem). Concept / Approach: A modem transforms baseband digital data into a passband analog signal by varying a carrier’s amplitude, frequency, or phase (ASK, FSK, PSK, QAM). At the far end, another modem performs the inverse operation to recover the digital bitstream. Cables and satellites are media or platforms, not the active devices that execute modulation/demodulation. Step-by-Step Solution: 1) Identify the function: convert digital data ↔ analog carrier.2) Map this function to the device class called a “modem.”3) Distinguish from transmission media (fiber, coax) and platforms (satellite), which merely carry signals.4) Conclude that “modem” is the correct answer. Verification / Alternative check: Examples include DSL/cable modems, cellular modems, and radio modems—all explicitly named for their modulation/demodulation roles. Why Other Options Are Wrong: Fiber optic / coaxial cable: physical media, not active mod/demod devices. Satellite: a communications relay platform; the ground segment still uses modems for waveform conversion. None of the above: invalid because a modem fits perfectly. Common Pitfalls: Confusing the medium (what the signal travels through) with the modem (what transforms the signal at the endpoints). Final Answer: modem

Question 15

Which statement about satellites and their transponders is correct when comparing spin-stabilized designs and frequency usage for uplink and downlink?

Accepted Answer

Introduction: Satellite platforms employ different stabilization methods (spin-stabilized vs. three-axis stabilized) and follow well-defined transponder frequency plans for uplinks and downlinks. Knowing these fundamentals helps interpret satellite diagrams and avoid common misconceptions on how spacecraft point and how frequency translation is arranged in bent-pipe transponders. Given Data / Assumptions: Spin-stabilized buses rotate to maintain gyroscopic stability. Three-axis stabilized buses use active attitude control and often sun-tracking panels. Transponders translate between different uplink and downlink frequency bands to prevent self-interference. Concept / Approach: Spin-stabilized satellites characteristically mount solar cells on a cylindrical body that rotates, averaging incident sunlight and leveraging gyroscopic effects for stability. In contrast, three-axis stabilized spacecraft use articulated solar arrays that track the Sun and do not require whole-body spin. Regarding transponders, standard practice is to receive at a higher frequency (uplink) and transmit at a lower frequency (downlink) to manage link budgets and oscillator plan; using the same frequency for both directions is avoided to prevent feedback and interference. Step-by-Step Solution: 1) Distinguish stabilization types: spinning body (spin-stabilized) vs. non-spinning, gimbaled panels (three-axis).2) Map the description in option A to spin-stabilized behavior (correct).3) Evaluate transponder statements: option C reverses the usual uplink/downlink relationship; option D incorrectly uses a single frequency.4) Conclude that option A is the only correct statement. Verification / Alternative check: Historical spin-stabilized satellites (e.g., early GEO platforms) match the cylindrical, rotating design; modern GEO buses with sun-tracking wings are three-axis stabilized. Why Other Options Are Wrong: Option B: describes three-axis stabilization, not spin stabilization. Option C: uplinks are typically at higher frequencies than downlinks, not lower. Option D: same-frequency operation would cause severe self-interference; frequency translation is mandatory. None of the above: invalid because A is correct. Common Pitfalls: Confusing satellite bus types and assuming arbitrary frequency reuse within a single transponder. Final Answer: A spin-stabilized satellite uses solar cells on a rotating cylindrical body and relies on gyroscopic action of the spin to help maintain orientation toward Earth and the Sun.

Question 16

On a Class C IPv4 network using a subnet mask whose last octet is 192 (/26), how many subnets are available under the legacy convention that disallowed subnet-zero and all-ones subnets?

Accepted Answer

Introduction: Subnetting questions often hinge on whether you assume modern CIDR practices (which allow using all subnets, including subnet-zero) or legacy rules (which historically reserved the all-zeros and all-ones subnets). This problem asks specifically about a Class C network with a mask value of 192 in the last octet, i.e., a /26, and wants the number of subnets available under the older, more restrictive convention. Given Data / Assumptions: Class C base: /24. Subnet mask: 255.255.255.192 → borrows 2 bits (since 192 = 11000000). Legacy rule: do not use subnet-zero or the all-ones subnet. Concept / Approach: With 2 borrowed bits, the total number of theoretical subnets is 2^2 = 4. Under the legacy “no subnet-zero” rule, you must subtract 2 reserved subnets (all-zeros and all-ones), yielding 4 − 2 = 2 usable subnets. Note that hosts per subnet would be 2^6 − 2 = 62 (since 6 host bits remain), but the question is about subnets available, not hosts per subnet. Step-by-Step Solution: 1) Determine borrowed bits: /26 means 2 bits for subnetting.2) Compute theoretical subnets: 2^2 = 4.3) Apply legacy reservation: 4 − 2 = 2 usable subnets.4) Confirm distinction from hosts per subnet (62) to avoid misinterpretation. Verification / Alternative check: Modern practice (allowing all subnets) would yield 4 usable subnets. However, many classic exam items explicitly invoke the old restriction to test historical knowledge. Why Other Options Are Wrong: 254 / 62 / 30 / 14: these are typical host-per-subnet counts for /24, /26, /27, /28 respectively, not the number of subnets under the stated convention. Common Pitfalls: Confusing “subnets” with “hosts per subnet,” or forgetting whether subnet-zero is permitted in the scenario. Final Answer: 2

Question 17

In error control, what is a parity bit and how is it used when appending control information to a string of binary digits?

Accepted Answer

Introduction: Parity is one of the simplest and oldest error-detection schemes. By adding a single bit that reflects the parity (evenness or oddness) of the number of 1s in a data word, systems can detect many single-bit errors with minimal overhead. While modern networks prefer stronger codes (CRC), parity remains pedagogically important and still appears in memory systems and serial protocols. Given Data / Assumptions: A binary string (e.g., a byte) is to be transmitted or stored. We choose either even parity or odd parity convention. We seek a definition of the parity bit itself. Concept / Approach: A parity bit is appended to the data so that the total count of 1s, including the parity bit, satisfies the chosen rule. For even parity, the parity bit is set such that the total number of 1s is even; for odd parity, it is set so that the total is odd. At the receiver, the parity of the received bits is recomputed and compared—if it does not match the expected parity, an error is detected. Parity detects all single-bit errors and some multi-bit patterns, but it cannot correct errors nor detect all multi-bit errors. Step-by-Step Solution: 1) Choose a parity convention (even or odd).2) Count the number of 1s in the data word.3) Set the parity bit so that total 1s (data + parity) matches the convention.4) On reception, recompute parity and compare; mismatch indicates an error. Verification / Alternative check: Practical interfaces like RS-232 allow an optional parity bit in the frame (start, data bits, optional parity, stop), illustrating live usage of this concept. Why Other Options Are Wrong: Checksum (option A): uses multi-byte arithmetic sums, not just a single parity bit. Syntactic codes (option C): relate to language/grammar constraints, not parity. Error rate (option D): a performance metric, not a code definition. None of the above: invalid because option B is correct. Common Pitfalls: Assuming parity can correct errors; it only detects certain error patterns and is weaker than CRCs or Hamming codes. Final Answer: a check bit appended to a binary string to make the total number of 1s conform to a chosen parity (even or odd)

Question 18

In management information systems, the organization that interconnects its internal systems and external partners via the Internet, intranets, and other networks is best described as which of the following?

Accepted Answer

Introduction: Modern organizations rarely operate as isolated islands. Instead, they connect employees, branches, suppliers, and customers using a mesh of internal and external networks. This strategic use of connectivity enables collaboration, end-to-end digital processes, and data-driven decision making across the enterprise and its ecosystem. Given Data / Assumptions: The enterprise uses the public Internet for outward communication. It also employs private intranets and extranets for internal and partner access. The question asks for the best descriptive term for such an organization. Concept / Approach: The term Internetworked enterprise captures an organization whose processes and stakeholders are tightly integrated through networking technologies. It implies seamless information flow across departments and with external partners, often spanning web applications, APIs, VPNs, and cloud services. Other terms in the options either describe a general technology category or a specific architecture pattern and thus are not the best label for the enterprise as a whole. Step-by-Step Solution: 1) Identify scope: not just a single LAN or client/server pattern, but enterprise-wide and partner-facing connectivity.2) Match to terminology: “Internetworked enterprise” denotes organizational structures enabled by interconnected networks.3) Exclude generic or overly broad phrases (e.g., “business applications of telecommunications”).4) Select the most precise descriptor. Verification / Alternative check: Management information systems textbooks routinely use “internetworked enterprise” to describe organizations that leverage Internet, intranets, and extranets for integrated operations. Why Other Options Are Wrong: Information super highway: colloquial phrase for the Internet, not a type of organization. Business applications of telecommunications: category of use cases, not an enterprise descriptor. Client/Server networks: an architecture style, not a holistic enterprise label. None of the above: invalid because option A is the precise term. Common Pitfalls: Choosing a technology buzzword instead of the organizational term the question seeks. Final Answer: Internetworked enterprise

Question 19

In computer networking fundamentals, which one of the following items is typically not required to build or operate a Local Area Network (LAN) within an office or campus environment?

Accepted Answer

Introduction / Context: A Local Area Network (LAN) interconnects devices such as PCs, printers, and servers across a small geographic area like a room, floor, or building. Understanding which components are essential to a LAN—and which belong to wide-area or Internet access—is a foundational skill for IT support and exam preparation. Given Data / Assumptions: Scope is a LAN: limited to a local site, short distances, and high-speed links. Typical LAN media include twisted pair, fiber, and sometimes radio (WLAN). End devices: computers, printers, access points, switches. Concept / Approach: A modem (modulator/demodulator) converts digital signals to analog waveforms (and back) for carriage over legacy telephone circuits or other carrier facilities. That function is associated with WAN or Internet edge connectivity, not with the internal switching of a LAN. Inside a LAN, devices connect through Ethernet switches using digital signaling over copper or fiber; no analog conversion is required. Step-by-Step Solution: Identify LAN essentials: computers and printers (endpoints) and cables (or Wi-Fi) for connectivity.Recognize that switches/routers may exist, but a modem is only needed to reach a public carrier network.Conclude that a modem is not a typical requirement for the LAN itself. Verification / Alternative check: In a common setup, the modem sits at the Internet/WAN edge (e.g., DSL/cable/4G) and connects to a router/firewall; internal LAN segments remain entirely digital and switched without modulation/demodulation steps. Why Other Options Are Wrong: Computer: a standard LAN endpoint.Printer: often networked for shared office use.Cable: a primary LAN medium alongside Wi-Fi.“None of the above”: incorrect because “Modem” is indeed not needed for internal LAN operation. Common Pitfalls: Confusing internal LAN components with Internet-edge equipment; assuming Wi-Fi always removes the need for cabling (switch uplinks and PoE still use cables). Final Answer: Modem.

Question 20

Networking media basics: Which of the following is not a transmission medium for carrying signals between devices?

Accepted Answer

Introduction / Context: A transmission medium is the physical path or propagation environment a signal travels through to carry information from a sender to a receiver. Distinguishing between the medium itself and the devices that interface with it helps prevent design and troubleshooting errors. Given Data / Assumptions: Media can be guided (copper, fiber) or unguided (microwave, satellite links). Interface devices may condition, convert, or modulate signals for transport. We must select the option that is not a medium. Concept / Approach: Telephone lines and coaxial cables are guided media. Microwave and satellite systems describe wireless propagation environments (unguided media). A modem, however, is a device that prepares signals for a medium (e.g., modulates for a telephone line) and therefore is not itself a transmission medium. Step-by-Step Solution: Identify which options are physical paths or propagation environments.Recognize “modem” as equipment that interfaces with a medium.Select “modem” as the choice that is not a transmission medium. Verification / Alternative check: Ask whether the item can exist end-to-end between two sites without active electronics. Media can; a modem cannot—it is an endpoint device, not a path. Why Other Options Are Wrong: Telephone lines: twisted pair copper—classic guided medium.Coaxial cable: guided medium used in LANs, CATV, and RF.Microwave systems: terrestrial line-of-sight radio propagation—an unguided medium.Satellite systems: space segment relays carrying RF paths—function as an unguided medium. Common Pitfalls: Treating system names as devices; mixing up modems (devices) with the copper pair they use; overlooking that “systems” can still denote a medium context here. Final Answer: modem.

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