Question 1

Which transport-layer protocol is connectionless and provides best-effort delivery without built-in reliability?

Accepted Answer

Introduction / Context: Transport-layer protocols provide end-to-end communication services. Some are connection-oriented with sequencing and retransmissions; others are connectionless with minimal overhead, favoring latency over reliability. Given Data / Assumptions: We compare common protocols used in Internet stacks. Focus: whether the transport is connection-oriented or connectionless. Concept / Approach: UDP (User Datagram Protocol) is connectionless and provides best-effort delivery—no session setup, no guaranteed ordering, and no retransmission by the protocol itself. TCP, by contrast, is connection-oriented with reliability features. NVT and FTP are not transport protocols (application concepts/protocols). Step-by-Step Solution: 1) Identify transport-layer candidates: TCP and UDP. 2) Determine connection semantics: TCP is connection-oriented; UDP is connectionless. 3) Therefore, the connectionless transport is UDP. Verification / Alternative check: Refer to IETF standards: UDP is defined with minimal header fields (ports, length, checksum), and lacks sequence numbers and ACKs. TCP includes sequence/ack numbers and a three-way handshake. Why Other Options Are Wrong: NVT: Network Virtual Terminal (a TELNET concept), not transport. FTP: Application-layer file transfer protocol. TCP: Connection-oriented, not connectionless. None: incorrect because UDP is explicitly connectionless. Common Pitfalls: Equating “connectionless” with “unreliable in all senses”; applications can add reliability on top of UDP if needed; also confusing IP (network layer) with UDP (transport layer). Final Answer: UDP

Question 2

Which statement best describes how a statistical multiplexer differs from a fixed (conventional) multiplexer?

Accepted Answer

Introduction / Context: Multiplexing lets multiple sources share one link. In fixed Time Division Multiplexing (TDM), each input gets a time slot whether or not it has data. Statistical multiplexing instead assigns capacity dynamically, based on which inputs have traffic, improving efficiency under bursty loads. Given Data / Assumptions: Fixed (conventional) multiplexers typically allocate resources deterministically (e.g., TDM slots). Statistical multiplexers schedule packets/frames opportunistically. Concept / Approach: Because many data sources are bursty, fixed slots can be idle, wasting capacity. Statistical multiplexers queue incoming data (hence need buffering) and transmit when the link is available, achieving higher utilization across many sources with independent bursts. Step-by-Step Solution: 1) Identify waste in fixed TDM: idle slots occur when a source is silent. 2) Recognize statistical multiplexing dynamically fills the link with active traffic. 3) Conclude that statistical multiplexers optimize link use compared to fixed TDM. Verification / Alternative check: Queueing models show utilization gains with independent, bursty sources. Packet networks (e.g., routers) embody statistical multiplexing by forwarding whichever packets are queued, not reserving fixed slots per source. Why Other Options Are Wrong: No buffering: false—statistical multiplexers require buffers to absorb bursts. X.25 vs Aloha: protocol pairing here is irrelevant and incorrect. TDM vs FDM claim: statistical multiplexing is not defined by FDM; it is about dynamic allocation. None of the above: incorrect because the efficiency statement is accurate. Common Pitfalls: Assuming statistical multiplexing is the same as priority scheduling; conflating it with specific MAC schemes; believing it guarantees zero loss (buffers can overflow under heavy load). Final Answer: Fixed TDM multiplexers may waste link capacity, whereas statistical multiplexers optimize use based on demand

Question 3

Why is error control (reliability) required at the transport layer even when lower layers exist?

Accepted Answer

Introduction / Context: Transport-layer reliability (e.g., in TCP) provides end-to-end error control beyond what data link and physical layers can guarantee. The network core may reorder, drop, or duplicate packets; only the endpoints can fully detect and correct such end-to-end faults across multiple hops. Given Data / Assumptions: Multi-hop packet-switched networks are used. Lower layers reduce but do not eliminate errors, losses, or reordering. Applications expect ordered, reliable byte streams for many use cases. Concept / Approach: End-to-end reliability adds sequence numbers, acknowledgments, retransmissions, and reassembly at the transport layer. This counters drops/duplicates that can occur in queues, during congestion, or due to transient faults that lower layers cannot address across the entire path. Step-by-Step Solution: 1) Recognize that each hop may be reliable locally, yet packets can still be lost between endpoints. 2) Transport adds sequence numbers to detect loss/duplication and maintain order. 3) ACKs and timers trigger retransmissions for missing segments. 4) The receiving transport reorders segments before delivery to the application. Verification / Alternative check: Observe TCP traces: gaps in sequence numbers and resulting retransmissions confirm end-to-end error control responding to network loss, not just physical noise in one link. Why Other Options Are Wrong: Physical noise is often corrected with link-layer checks/retries; transport still needed for multi-hop path issues. Routers do not “routinely corrupt” packets; corruption is rare and checked by link and transport checksums. Applications do not control network packet order; transport ensures in-order delivery to apps. Password encryption is a security concern, not error control. Common Pitfalls: Assuming link-layer ARQ eliminates all losses end-to-end; conflating error control with security; believing reordering equals “error” rather than a normal network behavior that transport must handle. Final Answer: Because packets can be lost or duplicated within the network, requiring end-to-end recovery

Question 4

In signal transmission, what is the term for the decrease in the magnitude of current, voltage, or power between two points?

Accepted Answer

Introduction / Context: Signals lose strength as they propagate through copper, fiber, or free space. Understanding the correct terminology helps when sizing amplifiers, selecting cables, and budgeting optical links. Given Data / Assumptions: We consider electrical or optical signals over distance. Magnitude refers to measurable quantities like voltage, current, or power. Concept / Approach: The correct term for a reduction in signal magnitude is attenuation. It is often quantified in decibels (dB). Excessive attenuation degrades signal-to-noise ratio and can cause bit errors or link failures. Step-by-Step Solution: 1) Identify the phenomenon: signal strength decreases with distance and losses. 2) Map to term: attenuation = loss of magnitude. 3) Recognize related practices: equalization, amplification, or regeneration counter attenuation. Verification / Alternative check: Link budgets compute total attenuation from connectors, splices, and medium loss per unit length, verifying whether received power meets receiver sensitivity. Why Other Options Are Wrong: Amplitude: the value itself, not its decrease over distance. Aloha: a random access MAC protocol, unrelated to signal strength. Carrier: a sinusoidal signal used for modulation, not loss. None: incorrect because the correct term is attenuation. Common Pitfalls: Confusing attenuation with interference or noise; assuming attenuation is linear across frequency (it is often frequency-dependent). Final Answer: Attenuation

Question 5

Which communication service specifically offered message preparation (editing) and electronic transmission facilities in office contexts?

Accepted Answer

Introduction / Context: Prior to modern email standards, organizations used various services to create and send documents electronically. Some were interactive broadcast services; others enabled point-to-point office messaging with document preparation features. Given Data / Assumptions: We want a service that includes message preparation (editing) and electronic transmission. Office communication, beyond mere broadcast pages or raw facsimile, is implied. Concept / Approach: Teletex was an enhanced Telex system designed for office document exchange, supporting message preparation, formatting, and electronic delivery between compatible terminals. It differs from broadcast-oriented Teletext and image-only Fax transmission. Step-by-Step Solution: 1) Identify candidate services and their core capabilities. 2) Match “message preparation + transmission” to Teletex. 3) Exclude broadcast and image facsimile systems. Verification / Alternative check: Historical standards show Teletex specifications supporting typed document exchange with structured formatting across office terminals, not just scanned pages or public information screens. Why Other Options Are Wrong: Teletext: a one-way broadcast of information pages to TVs, not office document exchange. X.400: an email addressing/messaging standard suite; it does not itself define a message-editing terminal service like Teletex. Fax: transmits images of pages; it lacks native text editing facilities. None: incorrect because Teletex matches the description. Common Pitfalls: Confusing Teletext with Teletex due to similar names; equating faxing typed pages with electronic text services that support editing and formatting. Final Answer: Teletex

Question 6

A network that relies on manual (human) intervention to set up and route connections was historically referred to as what type of switched network?

Accepted Answer

Introduction / Context: Early telecommunications used manual switchboards in which human operators physically connected calls by plugging patch cords. This predates automatic electronic or digital switching and required human intervention for routing signals. Given Data / Assumptions: The question refers to networks requiring human intervention for routing signals. We are contrasting with automatic topologies like bus, ring, or star, which describe physical layouts rather than manual switching operations. Concept / Approach: Manual, operator-assisted telephone switching is historically described as a telephony-switched (here denoted “T-switched”) network. Operators established circuits on demand by connecting caller and receiver through a series of manual switchboards. Step-by-Step Solution: 1) Identify that bus/ring/star are topologies, not manual switching systems. 2) Recognize that the defining feature is human intervention in call setup. 3) Select the operator-assisted telephone switching option. Verification / Alternative check: Historical telephony references describe switchboard operators completing calls by inserting plugs into jacks, a clear example of human-routed circuit switching before automated exchanges. Why Other Options Are Wrong: Bus: a broadcast physical topology; no implication of manual routing. Ring: token or ring-based topology; automatic signaling. Star: hub/switch-centered topology; again automatic. None: incorrect because the operator-assisted form is explicitly described. Common Pitfalls: Confusing network topology (physical layout) with switching method (manual vs automatic); assuming all switching has always been automatic. Final Answer: T-switched network (operator-assisted telephone switching)

Question 7

In a UPC (Universal Product Code) checkout system, where is the item’s price typically stored and retrieved from at point of sale?

Accepted Answer

Introduction / Context: UPC barcodes encode an identifier, not the price. Modern point-of-sale (POS) systems scan the UPC, look it up in a database, and retrieve current pricing, discounts, or promotions. This enables dynamic price updates without reprinting every package. Given Data / Assumptions: Retail checkout uses barcode scanners and a central pricing database. UPC symbol encodes manufacturer and item code, not numeric price. Concept / Approach: Because the UPC is an identifier, the price must be stored elsewhere—namely, in computer storage (the POS pricing database). Shelf labels may show human-readable prices, but the authoritative price at checkout comes from the database record tied to the UPC code. Step-by-Step Solution: 1) Scan UPC at POS. 2) POS queries its item database using the UPC key. 3) POS retrieves price, tax rules, and any promotions to compute the total. Verification / Alternative check: Retail systems update prices centrally, and changes take effect immediately at checkout without altering product packaging. Audits compare shelf labels to POS database to ensure consistency. Why Other Options Are Wrong: On the item only: modern barcodes do not embed price values. Item + shelf label: shelf labels are informational; the system of record is the database. Shelf + database simultaneously as the authoritative store: the shelf label is not a storage system. None: incorrect because the price resides in computer storage tied to the UPC. Common Pitfalls: Assuming the barcode encodes the price; confusing human-readable labels with the transactional data source; overlooking price overrides or promotions applied by the POS rules engine. Final Answer: In computer storage (price database linked to the UPC)

Question 8

In Ethernet-based LANs, which device regenerates and forwards electrical signals to extend or interconnect segments without interpreting frames?

Accepted Answer

Introduction / Context: Local networks use different devices at different layers. Some work at the physical layer to extend cable length by regenerating signals; others inspect frames at the data link layer to segment collision domains. Knowing which device merely copies signals is key for design and troubleshooting. Given Data / Assumptions: Ethernet signaling may degrade over distance. We need a device that operates purely at the physical layer. Concept / Approach: A repeater regenerates and re-times electrical (or optical) signals, forwarding them to another segment without examining MAC addresses or frame contents. It extends reach but does not reduce collisions or filter traffic. Bridges and switches operate at Layer 2 and make forwarding decisions based on MAC addresses; hubs are essentially multiport repeaters but still work at the physical layer within one collision domain. Step-by-Step Solution: 1) Identify the requirement: physical-layer copying/regeneration only. 2) Map to device: repeater fits by regenerating signals across segments. 3) Exclude devices that interpret frames (bridges) or that are passive (do not regenerate). Verification / Alternative check: Standards and textbooks define hubs as multiport repeaters; however, the canonical single device that copies electrical signals between Ethernet segments is the repeater. Bridges learn MAC addresses and forward selectively, which is more than just copying signals. Why Other Options Are Wrong: Bridge: reads frames and filters/forwards based on MAC, not mere signal copying. Hub: multiport repeater inside one shared segment; the generic answer asked is “repeater.” Passive hub: provides wiring concentration without regenerating signals. None: incorrect because a repeater exists for this exact purpose. Common Pitfalls: Confusing bridges/switches with repeaters; assuming hubs extend separate segments (they extend the same collision domain); overlooking that repeaters do not manage congestion or errors at higher layers. Final Answer: Repeater

Question 9

In computer networks, devices such as switches, routers, hubs, and gateways are collectively known as specialized communication processors that interconnect and manage traffic across multiple networks. What is the best term for such devices?

Accepted Answer

Introduction: In data communications, several hardware devices collaborate to move bits from one place to another. Switches, routers, hubs, and gateways are often grouped under a single conceptual umbrella because they process frames or packets, apply forwarding/learning rules, and connect different network segments or even different protocol realms. The question asks for the most precise term that collectively describes these hardware elements. Given Data / Assumptions: The examples include switches (Layer 2), routers (Layer 3), hubs (legacy repeaters at Layer 1), and gateways (protocol translation at higher layers). We focus on the role they play: interconnecting and processing traffic across networks or segments. We seek a term for devices, not for a protocol suite or an architectural philosophy. Concept / Approach: A unifying phrase used in traditional networking curricula is “internetwork processor.” It highlights that these devices process traffic between networks (inter-network) rather than simply within a single shared medium. While modern texts often emphasize specific roles (switch vs router), the generic class name that fits all listed examples is the internetwork processor. Step-by-Step Solution: 1) Identify what the listed devices have in common: they connect or segment networks and make forwarding/translation decisions.2) Exclude terms that are not device classes (e.g., protocol names or architectural models).3) Select the established collective term: internetwork processor. Verification / Alternative check: “Internetwork” stresses connectivity across multiple networks, exactly the scope of routers and gateways. Switches and hubs fit historically as processors of frames/signals in multi-segment topologies. Why Other Options Are Wrong: TCP/IP: a protocol suite, not hardware. Protocol: a set of rules for communication, not a device. Open systems: philosophy/standardization approach, not a device class. Network topology: the layout/graph of links and nodes, not hardware. Common Pitfalls: Equating device classes with protocol names; assuming “gateway” alone covers all devices (it does not—switches and hubs are not gateways). Final Answer: Internetwork processor.

Question 10

Which network access standard is classically used for connecting end stations to a public packet-switched network (PSDN)?

Accepted Answer

Introduction: In traditional packet-switched data networks (PSDNs), the ITU-T X-series recommendations defined standards for how terminals and hosts accessed and exchanged packets. The question asks which standard specifically governed user access to a packet-switched network. Given Data / Assumptions: We consider classic public packet networks such as those built on X.25. “Access” means the interface and procedures between a user device (DTE) and the network (DCE). Related X-series recommendations exist for physical interfaces, PAD parameters, and inter-network links. Concept / Approach: X.25 specifies the DTE–DCE interface for packet-level access to a PSDN, including virtual circuits (PVC/SVC), packet formats, flow control, and error handling. Other X-standards play supporting roles but are not the end-station packet access protocol itself. Step-by-Step Solution: 1) Identify which recommendation covers packet-level access: X.25.2) Differentiate supporting standards: X.21 covers physical circuit signaling; X.3 defines PAD parameters; X.75 governs interconnecting packet networks.3) Choose X.25 as the user access protocol to the packet network. Verification / Alternative check: Historical PSDNs (e.g., international X.25 networks) used X.25 at the edge for terminals/hosts while X.75 handled network-to-network interconnect. Why Other Options Are Wrong: X.3: parameter set for PADs, not the packet access protocol itself. X.21: physical interface/signaling recommendation. X.75: inter-PSDN gateway protocol, not user access. None of the above: incorrect because X.25 is correct. Common Pitfalls: Confusing PAD configuration (X.3) or physical interface (X.21) with the end-to-network packet protocol (X.25). Final Answer: X.25.

Question 11

A 4 kHz (voice-band) noiseless channel is PCM sampled once every 125 microseconds (i.e., 8000 samples/s). If standard telephony coding with 8 bits per sample is used (as in CCITT 2.048 Mb/s systems), what is the resulting bit rate for that single ch…

Accepted Answer

Introduction: Telephony Pulse Code Modulation (PCM) encodes analog voice (nominal 300–3400 Hz) by sampling and quantization. The classic public network standard samples at 8000 samples/s (every 125 microseconds) and uses 8 bits per sample, yielding a familiar channel bit rate. This question tests your ability to connect sampling parameters to bit rate, and to recognize the relationship to CCITT (now ITU-T) 2.048 Mb/s E1 framing. Given Data / Assumptions: Channel bandwidth: approximately 4 kHz voice-band. Sampling period: 125 microseconds => sampling rate = 8000 samples/s. Quantization: 8 bits per sample (A-law or μ-law companding in practice). Ideal noiseless channel assumed for rate calculation. Concept / Approach: Bit rate for PCM = samples per second * bits per sample. For a single encoded voice channel, this is independent of framing overhead; framing becomes relevant when multiplexing many channels (e.g., 32 time slots in an E1 line at 2.048 Mb/s). Step-by-Step Solution: 1) Compute sampling rate: 1 / 125 microseconds = 8000 samples/s.2) Multiply by bits per sample: 8000 * 8 = 64,000 bits/s.3) Express in kbps: 64,000 bits/s = 64 Kbps.4) Recognize link to E1: 32 * 64 Kbps = 2.048 Mbps (one time slot for framing/signal depending on system). Verification / Alternative check: Nyquist sampling for a ~3.4 kHz voice passband leads to a standard 8 kHz sampling rate, which aligns with the 64 Kbps channel rate widely used in telephony. Why Other Options Are Wrong: 500 Kbps: far too high for a single PCM voice channel. 32 Kbps: would require 4 bits per sample or sub-PCM compression. 8 Kbps: characteristic of low-rate vocoders, not standard PCM. 16 Kbps: typical of ADPCM profiles, not 8-bit PCM. Common Pitfalls: Confusing the single-channel rate (64 Kbps) with the aggregate E1 rate (2.048 Mb/s); mixing PCM with ADPCM/vocoder assumptions. Final Answer: 64 Kbps.

Question 12

If communication software is the “traffic cop” of a microcomputer communication system (managing control and rules), what role best describes the modem in that system?

Accepted Answer

Introduction: A modem (modulator–demodulator) converts digital signals from data terminal equipment into analog waveforms suitable for telephone lines and converts received analog signals back to digital. The question uses an analogy: if software enforces rules like a “traffic cop,” what is the modem’s comparable functional role? Given Data / Assumptions: Microcomputer with communication software and a modem connected to a telephone or carrier line. Software manages sessions, protocols, and user interaction. We are mapping device function to an intuitive label. Concept / Approach: The modem sits at the boundary between the digital world (DTE) and the analog carrier network (PSTN or similar). Functionally, it is the interface that adapts signal formats, line levels, and timing so that two unlike systems can communicate. Step-by-Step Solution: 1) Identify key modem behavior: modulation/demodulation and line adaptation.2) Translate to analogy: a boundary device enabling interoperation => an interface.3) Eliminate metaphors that imply passive locations or unrelated constructs (e.g., “park”). Verification / Alternative check: Many textbooks call the modem the “interface” between DTE and communication line, emphasizing its conversion function. “Bridge” has a specific LAN meaning that does not fit dial-up modems; “link” describes a connection, not the converter. Why Other Options Are Wrong: Park: a place, not a communications function. Bridge: a Layer-2 LAN device, not the DTE–PSTN converter here. Link: describes the connection itself, not the converting hardware. None of the above: incorrect because interface fits precisely. Common Pitfalls: Confusing network topology terms with device roles; assuming “bridge” generically means any connector. Final Answer: Interface.

Question 13

Enterprise data communication support typically includes a broad set of services. Which list best reflects that breadth?

Accepted Answer

Introduction: Organizations rely on networks to support diverse workflows—from moving files and running transactions to interactive terminal access and messaging. This question asks whether the typical scope of data communications support is narrow or comprehensive across these areas. Given Data / Assumptions: Enterprises operate file services, application servers, databases, email systems, and sometimes voice over IP. “Support” refers to the network and related systems enabling these functions reliably and securely. The three listed groups represent common enterprise use cases. Concept / Approach: Modern enterprise networks are multi-service platforms. They enable bulk transfers (file/backup), transactional workloads (OLTP, web transactions), structured data access (databases), legacy/remote terminal sessions, and asynchronous messaging (email, voice messages). Therefore, a realistic scope encompasses all the listed categories. Step-by-Step Solution: 1) Evaluate each item as a standard enterprise workload.2) Recognize that networks are designed to transport data for all these application types.3) Conclude that the inclusive option reflects real-world breadth. Verification / Alternative check: Enterprise reference architectures (campus/core/data center) explicitly plan for file/DB traffic, transactional systems, email, and voice/video collaboration, confirming wide scope. Why Other Options Are Wrong: Each individual list is only a partial view of typical services. None of the above is false because all the examples are indeed part of enterprise networking. Common Pitfalls: Equating “data communications” with only file transfer; overlooking interactive and transactional traffic. Final Answer: All of the above.

Question 14

In classful IPv4 addressing, what is the default subnet mask for a Class A network block?

Accepted Answer

Introduction: Classful IPv4 addressing once defined fixed mask lengths for Classes A, B, and C. Although CIDR superseded classful addressing, exams still test default masks. The question asks for the default mask for a Class A network. Given Data / Assumptions: Class A first octet range (usable): 1–126 (127 is loopback; 0 reserved historically). Default mask length: /8 for Class A. We distinguish masks from specific addresses like loopback. Concept / Approach: A Class A network reserves 8 bits for the network portion and 24 bits for hosts by default. In dotted-decimal, /8 corresponds to 255.0.0.0. Step-by-Step Solution: 1) Recall class A default prefix length: /8.2) Convert /8 to dotted mask: 255.0.0.0.3) Eliminate distractors that are addresses or malformed masks. Verification / Alternative check: Class B defaults to /16 (255.255.0.0) and Class C to /24 (255.255.255.0), reinforcing that Class A is /8 (255.0.0.0). Why Other Options Are Wrong: 127.0.0.1: loopback address, not a mask. 255.255.255.0.0: invalid, five octets. 255.255.255.0: /24, Class C default. None of the above: incorrect because 255.0.0.0 is correct. Common Pitfalls: Confusing default masks with commonly deployed masks after subnetting; treating loopback as part of Class A usable range. Final Answer: 255.0.0.0.

Question 15

After manually configuring an IPv4 address, subnet mask, gateway, and DNS on a Windows host, which tool provides a definitive view of the current configuration, including the DHCP server field if present?

Accepted Answer

Introduction: Verifying TCP/IP configuration on Windows is a routine administrative task. Command-line tools provide authoritative, detailed views beyond what basic dialogs display. The question asks which method definitively shows the active configuration and related parameters on the host. Given Data / Assumptions: Windows operating system environment. Manual configuration performed (static), though tool also reveals DHCP details if enabled. We need a trustworthy, comprehensive readout. Concept / Approach: The IPCONFIG tool (run as ipconfig /all) enumerates all interfaces and shows IP address, mask, gateway, DNS, WINS (legacy), MAC, DHCP status, DHCP server, lease times, and more. It is widely used for both static and DHCP configurations. Step-by-Step Solution: 1) Choose a tool that exposes low-level adapter data.2) Recognize ipconfig /all as the comprehensive Windows CLI utility.3) Prefer a CLI snapshot over partial GUI views when certainty is required. Verification / Alternative check: Administrators routinely request “send ipconfig /all output” during troubleshooting because it is authoritative and standardized across Windows versions. Why Other Options Are Wrong: Network Properties dialog: limited summary, may omit lease/gateway specifics per adapter. DHCPINFO: not a standard Windows tool. Advanced Properties tab: GUI varies by version; still less complete than the CLI dump. None of the above: incorrect because ipconfig /all is correct. Common Pitfalls: Confusing Windows with Unix/Linux tools (e.g., ifconfig, ip); relying on cached GUI panes that do not reflect the current state. Final Answer: IPCONFIG/ALL.

Question 16

Identify the incorrect statement about common data communication components and control signals.

Accepted Answer

Introduction: Many legacy and modern systems rely on standardized interfaces and control signals for serial communications. Knowing what each signal means and which protocols are synchronous vs. asynchronous helps avoid configuration errors. The question asks you to spot the one statement that is factually incorrect. Given Data / Assumptions: Classical serial interface control uses signals like RTS (Request to Send) and CTS (Clear to Send). HDLC (High-Level Data Link Control) is a synchronous, bit-oriented Layer-2 protocol. Multiplexers combine multiple input streams for transmission over fewer physical lines. Concept / Approach: RTS/CTS implements handshaking for flow control: the DTE asserts RTS to request permission to transmit; the DCE responds with CTS to grant it. Ring indication is typically signaled by the RI (Ring Indicator) line in RS-232, not RTS/CTS. Step-by-Step Solution: 1) Validate statements about multiplexers and HDLC: both are correct as written.2) Recall control line meanings: RTS/CTS manage send/receive readiness; RI indicates ringing.3) Therefore, the statement equating RTS/CTS with ringing is incorrect. Verification / Alternative check: RS-232 pinouts explicitly list RI for ring detection; RTS and CTS serve flow control/handshake functions. Why Other Options Are Wrong: Multiplexer statement: describes standard TDM/aggregate behavior. HDLC statement: reflects a well-known synchronous Layer-2 protocol. RTS/CTS readiness statement: aligns with DTE–DCE handshake usage. None of the above: false because one statement is indeed incorrect. Common Pitfalls: Mixing up RI with RTS/CTS; assuming all control signals are interchangeable. Final Answer: “RTS/CTS is the way the terminal indicates ringing” is incorrect.

Question 17

On a Windows client, how can you display the DHCP server address from which the machine obtained its IP configuration?

Accepted Answer

Introduction: When troubleshooting dynamic addressing, technicians often need to confirm the identity of the DHCP server that leased an address to a Windows host. The command-line provides a concise, authoritative view. This question seeks the correct method to view that server address. Given Data / Assumptions: Windows operating system environment. The client is configured for DHCP or has a DHCP lease history. We want to view the DHCP server address specifically. Concept / Approach: The ipconfig /all output enumerates per-adapter details including DHCP Enabled status, DHCP Server, Lease Obtained, and Lease Expires. This output is the standard artifact requested in support tickets. Step-by-Step Solution: 1) Open Command Prompt with appropriate privileges.2) Run ipconfig /all and locate the active adapter.3) Read the “DHCP Server” field to identify the leasing server. Verification / Alternative check: Network engineers routinely ask for this output to validate DHCP scope, options, and server identity across Windows versions. Why Other Options Are Wrong: Advanced Properties: GUI does not always expose the server address directly and varies by version. DHCPINFO: not a standard Windows utility. Ping the DHCP server: requires knowing the address already; not a discovery method. None of the above: incorrect because ipconfig /all is valid. Common Pitfalls: Looking at the wrong adapter (e.g., virtual NICs); ignoring that a statically configured adapter will not show DHCP fields. Final Answer: Use IPCONFIG/ALL.

Question 18

Which statement correctly describes a satellite transponder used in communications satellites?

Accepted Answer

Introduction: A satellite transponder is the fundamental “bent-pipe” element aboard a communications satellite. It listens to uplink signals, conditions them (filtering, frequency translation, amplification), and retransmits them back toward earth on a designated downlink frequency. Understanding this basic operation helps differentiate correct and incorrect statements about satellite links. Given Data / Assumptions: We consider a conventional bent-pipe communications satellite (not regenerative on-board processing). Standard operation involves receive chain, frequency conversion, amplification, and transmit chain. Uplink and downlink use different frequency bands to avoid interference. Concept / Approach: A transponder includes a receiver (LNA, filtering), a frequency converter/translator, and a power amplifier feeding the transmit chain. It does not “echo” without change; it performs translation and amplification. Also, for most services, the satellite receives at a higher uplink frequency and transmits at a lower downlink frequency (e.g., C-band, Ku-band), contrary to the misleading claim about the direction of frequency change. Step-by-Step Solution: 1) Identify required blocks: receiver + translator + transmitter.2) Recognize purpose: relay (bent-pipe) from uplink beam to downlink beam.3) Compare options: only the statement describing RX + TX relay fits universally. Verification / Alternative check: Industry diagrams show transponders converting uplink to a different downlink frequency while applying gain and filtering, confirming the receiver-transmitter characterization. Why Other Options Are Wrong: Echo without change: ignores frequency translation and amplification. Transforms code: regenerative satellites can process, but basic transponders do not change message coding. Lower RX, higher TX: reversed; satellites typically receive higher-frequency uplinks and transmit lower-frequency downlinks. None of the above: one option is correct. Common Pitfalls: Assuming satellites behave like passive mirrors; confusing regenerative processing with bent-pipe relaying. Final Answer: A satellite transponder contains a receiver and a transmitter that relay microwave transmissions between earth stations.

Question 19

You administer the private network 192.168.10.0 and must subnet it to support up to 12 hosts per subnet while maximizing the number of subnets. Which subnet mask should you choose (standard IPv4 addressing, network and broadcast excluded)?

Accepted Answer

Introduction / Context: Subnet design balances two goals: providing enough host addresses in each subnet and creating as many subnets as possible from a given block. Here the base block is 192.168.10.0/24 and each subnet must support up to 12 hosts. Given Data / Assumptions: Base network: 192.168.10.0/24. Required: at least 12 usable host addresses per subnet. Objective: maximize number of subnets. Usable hosts = total addresses per subnet − 2 (network and broadcast). Concept / Approach: For a /n mask, total addresses per subnet are 2^(32 − n). Usable hosts are that total minus 2. We must find the smallest subnet that still gives ≥ 12 usable hosts; that choice maximizes the number of subnets within the /24 space. Step-by-Step Solution: Check /29 (255.255.255.248): 2^(32−29) = 8 total → 6 usable (too few).Check /28 (255.255.255.240): 2^(32−28) = 16 total → 14 usable (meets ≥ 12).Check /27 (255.255.255.224): 32 total → 30 usable (meets, but larger than needed, so fewer subnets).Therefore choose /28 to maximize subnets while meeting host requirement. Verification / Alternative check: In a /24, /28 yields 16 addresses per subnet and 14 usable. The /24 can be divided into 16 such subnets (0, 16, 32, …, 240). A /27 would produce only 8 subnets; a /26 only 4. Thus /28 best satisfies “maximum subnets.” Why Other Options Are Wrong: 255.255.255.248 (/29): Only 6 usable hosts; fails the ≥ 12 requirement. 255.255.255.224 (/27): Works, but produces fewer subnets than /28. 255.255.255.192 (/26): Far more hosts than needed; fewest subnets among listed valid masks. 255.255.255.252 (/30): Only 2 usable hosts; typical for point-to-point links. Common Pitfalls: Forgetting to subtract network and broadcast when counting usable hosts; mixing up total vs usable; choosing a larger subnet than necessary, which reduces how many subnets you can create. Final Answer: 255.255.255.240 (/28)

Question 20

In email systems, which protocol primarily provides a simple mailbox (server-side storage) and downloads whole messages to the client without rich, selective, server-side management features?

Accepted Answer

Introduction / Context: Internet email involves multiple protocols. SMTP moves mail between servers and from clients to servers; POP3 and IMAP retrieve mail from a mailbox for end users. This question contrasts simple download models with more advanced server-side management. Given Data / Assumptions: We want a protocol that offers a basic mailbox and straightforward retrieval. “Does not allow a user to download messages selectively” contrasts with richer capabilities like server-side folders and partial fetch. Legacy/typical behavior is considered. Concept / Approach: POP3 (Post Office Protocol v3) provides a simple model: connect, authenticate, list, retrieve, optionally delete. While POP3 has commands like LIST and RETR, typical workflows lack sophisticated server-side filtering, partial fetch, and folder management inherent to IMAP. IMAP excels at selective, synchronized access across devices. Step-by-Step Solution: Identify protocols: SMTP (transport), POP3 (basic retrieval), IMAP (advanced retrieval).Match the described behavior—simple mailbox and non-rich selection—to POP3.Exclude unrelated protocols (DHCP assigns IPs; NNTP is for Usenet). Verification / Alternative check: Standard client settings: “POP3 account” downloads and typically stores mail locally with minimal server-side state; “IMAP account” keeps messages server-side with folders, flags, and selective sync/partial fetch. Why Other Options Are Wrong: SMTP: Pushes mail between servers and client-to-server; not for end-user retrieval. IMAP: Designed for selective, server-managed access (opposite of the prompt). DHCP: Address configuration, unrelated to email. NNTP: Network News, not email retrieval. Common Pitfalls: Assuming POP3 equals “no selection at all.” It can list message numbers, but compared to IMAP it lacks selective, folder-aware, partial, server-resident workflows. Final Answer: POP3

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