Question 1

You must capture, inspect, and store TCP/IP packets to analyze a networking problem on a Microsoft environment. Which built-in utility is best suited for packet capture and deep inspection?

Accepted Answer

Introduction: Troubleshooting TCP/IP problems often requires visibility into actual packets on the wire. Tools differ in purpose: some summarize counters, some manage services, and some capture frames for decode. This question asks you to pick the Microsoft utility historically designed to capture and analyze packets in detail. Given Data / Assumptions: Windows/ Microsoft ecosystem context. Goal is packet capture and storage, not just connection listings or counters. Administrative access is available if required for capture. Concept / Approach: Network Monitor (NetMon) was Microsoft’s packet sniffer, capable of capturing frames, applying filters, and decoding numerous protocols. By contrast, NETSTAT lists active connections and ports; NBTSTAT displays NetBIOS name information; Performance Monitor tracks system and network counters; and the DHCP Management Console configures DHCP servers rather than inspecting packets. Therefore, for deep packet inspection and saving trace files, Network Monitor is the correct choice among the listed utilities. Step-by-Step Solution: Clarify requirement: capture and decode packets.Map tool capabilities: only Network Monitor performs wire-level capture and protocol decode.Eliminate utilities for stats/config (NETSTAT, NBTSTAT, PerfMon, DHCP MMC).Select Network Monitor. Verification / Alternative check: Microsoft later offered Message Analyzer and today many admins use Wireshark; however, within the classic Microsoft tooling list here, Network Monitor is the packet capture tool designed for precisely this task. Why Other Options Are Wrong: NBTSTAT: NetBIOS name table/status, not capture. Performance Monitor: counters and trends, no packet decode. NETSTAT: shows sockets/ports and routing, not frames. DHCP Management Console: server configuration, not packet analysis. Common Pitfalls: Assuming NETSTAT can capture traffic; confusing service management with wire-level analysis; overlooking permission requirements for capture on some NICs. Final Answer: Network Monitor.

Question 2

When connecting to an online information service, you submit your user name, account or ID, and a password before access is granted. What is this short, initial exchange called?

Accepted Answer

Introduction: Almost all remote information services require a brief dialogue at the start of a session to verify who you are and whether you may proceed. This is a fundamental aspect of access control and accountability. The question asks for the commonly accepted name of that initial, short exchange in which credentials are presented. Given Data / Assumptions: User provides an identifier (name, account, or user ID). User supplies a secret (password, passphrase, or equivalent factor). System validates the credentials before granting a session. Concept / Approach: The standard term is the log-on procedure (also written login or log in). This encompasses both identification (claiming an identity) and authentication (proving that identity), typically via a password. While “security procedure” and “safeguard procedure” describe the larger domain, they are not the precise, conventional label for this short credential exchange. “Identification procedure” is incomplete because it omits the authentication step that actually verifies the claim. Step-by-Step Solution: Recognize the scenario: providing user ID and password to start a session.Match to the standard label used in systems and documentation: log-on (login) procedure.Eliminate broader or incomplete terms that do not name the specific exchange. Verification / Alternative check: Operating systems, databases, and SaaS portals uniformly label this step “log on” or “sign in,” reinforcing the conventional name for the process described. Why Other Options Are Wrong: Security procedure: too broad, not the specific exchange name. Safeguard procedure: vague; not a standard term. Identification procedure: misses authentication; identification alone is insufficient. None of the above: incorrect because log-on procedure is correct. Common Pitfalls: Confusing identification with authentication; assuming “registration” (creating credentials) is the same as logging on (using them). Final Answer: Log-on procedure.

Question 3

In data communications terminology, what does “baseband” transmission mean, and which description best fits the term in contrast to modulated carrier systems?

Accepted Answer

Introduction: The term baseband distinguishes direct, unmodulated signaling from modulated carrier transmission (passband). Classic Ethernet on copper, for example, is baseband: the digital waveform is placed directly on the wire without up-conversion to a high-frequency carrier. This item asks you to pick the description that accurately captures baseband in communications contexts. Given Data / Assumptions: We contrast baseband versus passband (carrier-modulated) systems. Baseband examples include early 10BASE-T/2/5 Ethernet and many serial links. We are looking for the most precise definition, not related but different concepts. Concept / Approach: Baseband transmission sends the original low-frequency (baseband) signal directly over the medium using a line code (e.g., NRZ, Manchester). No separate sinusoidal carrier is used for up/down conversion. In contrast, passband systems (radio, cable TV) modulate the baseband onto a carrier (AM, FM, QAM). While a baseband signal is indeed bandlimited, “bandlimited” is a more general term that applies to many signals (baseband or passband) and is not the definition of baseband itself. Likewise, “simultaneous transmission to many stations” describes broadcast/multicast behavior, not baseband. Step-by-Step Solution: Identify the essential property: no modulation onto a separate carrier.Map to examples: 10BASE-T uses line coding directly on twisted pair.Eliminate descriptions that are true of other concepts (bandlimited, broadcast).Select the definition that explicitly says “without modulation.” Verification / Alternative check: Standards documents label early Ethernet as “BASE” (baseband) in names like 10BASE-T, distinguishing it from broadband coax systems that carry multiple RF channels simultaneously via modulation. Why Other Options Are Wrong: Bandlimited signal: true for many signals but not the definition of baseband. Simultaneous transmission: broadcast/multicast concept unrelated to baseband vs passband. All of the above: incorrect since the other items are not definitions of baseband. None of the above: incorrect because one option matches exactly. Common Pitfalls: Confusing “baseband” with “unfiltered DC content” (some line codes are DC-balanced); thinking baseband implies single-user only—multiple access can be achieved with time slots even at baseband. Final Answer: Transmission of signals without modulation onto a separate carrier.

Question 4

LAN design question: which physical topology typically provides the greatest flexibility for adding, moving, or replacing devices and cabling in practice?

Accepted Answer

Introduction: Physical topology affects how easy it is to expand or reconfigure a local area network. Flexibility means minimal disruption when adding or relocating devices, straightforward troubleshooting, and limited impact from a single link failure. This question asks which topology generally offers the best flexibility for wiring changes in modern LANs. Given Data / Assumptions: Focus is on physical cabling and ease of change management. Common topologies considered: bus, ring, and star. Assume typical Ethernet implementations (e.g., twisted-pair to a switch). Concept / Approach: In a star topology, each device connects via a dedicated cable to a central hub/switch. Adding or moving a device usually involves terminating a new cable at the patch panel and switch—no interruption to other links. In a bus topology (thin coax), inserting a new node requires cutting into the shared cable and carefully maintaining impedance/terminations, risking downtime for the entire segment. In a ring, breaking the ring impacts all nodes unless special MAUs or protections are used. Thus, star provides the greatest practical flexibility and fault isolation. Step-by-Step Solution: Compare per-node cabling: star uses independent home runs; bus/ring share a path.Assess change impact: star changes affect only the link being worked on.Assess fault isolation: star localizes failures to a single port/cable.Select star networks as the most flexible topology. Verification / Alternative check: Modern enterprise and home Ethernet overwhelmingly use a star (switched) topology; structured cabling standards are built around this model, confirming its flexibility and maintainability. Why Other Options Are Wrong: Bus: difficult expansions; a single fault can drop the whole segment. Ring: link changes interrupt the loop; specialized hardware needed for resilience. Circuit-switched (T-switched): describes WAN service type, not a LAN physical topology choice. None of the above: incorrect because star is correct. Common Pitfalls: Assuming “fewer cables” equals “more flexible”; in practice, manageability and fault isolation dominate, favoring star. Final Answer: Star networks.

Question 5

Communication modes: which mode supports transmission of data in both directions at the same time between two endpoints?

Accepted Answer

Introduction: Communication systems are often described by their directionality: whether information can flow one way only, both ways but not simultaneously, or both ways at the same time. Knowing these distinctions is foundational for configuring serial links, Ethernet links, and wireless channels. This question asks you to identify the mode that permits simultaneous two-way transmission. Given Data / Assumptions: Two endpoints exchange data. We compare simplex, half-duplex, and full-duplex modes. Ignore unrelated terms that describe capacity sharing (multiplexing). Concept / Approach: Simplex permits one-way flow only (e.g., broadcast paging). Half-duplex allows both directions but not at the same time; the channel alternates (e.g., push-to-talk radios, legacy shared Ethernet). Full-duplex supports concurrent transmission and reception, often by using separate physical pairs/frequencies or echo cancellation (e.g., modern Ethernet over twisted pair, many telephony systems). Therefore, the correct answer is full-duplex. Step-by-Step Solution: Define each mode succinctly: simplex, half-duplex, full-duplex.Identify requirement: simultaneous bi-directional operation.Match requirement to full-duplex. Verification / Alternative check: 1000BASE-T Ethernet operates full-duplex using echo cancellation across all pairs; serial links can achieve full-duplex by dedicating separate TX/RX conductors, confirming concurrency in both directions. Why Other Options Are Wrong: Simplex: one way only. Half-duplex: alternates direction, not simultaneous. Multiplex: refers to sharing medium among signals (time/frequency), not directionality. None of the above: incorrect because full-duplex is correct. Common Pitfalls: Confusing multiple access or multiplexing with duplex modes; assuming “collision-free” implies full-duplex (it does not necessarily). Final Answer: Full-duplex.

Question 6

Microsoft TCP/IP troubleshooting: which command-line tool is universally included and used to test basic IP reachability to a host?

Accepted Answer

Introduction: When diagnosing network connectivity, the first step is often verifying whether a target host responds at the IP layer. Microsoft clients include a small utility that sends ICMP Echo Request messages and reports responses to confirm basic reachability and round-trip time. This question asks you to identify that universal, built-in tool. Given Data / Assumptions: Environment: Microsoft TCP/IP clients across versions. Goal: verify IP connectivity quickly from the command line. We are not configuring services—just testing reachability. Concept / Approach: PING is the ubiquitous command that uses ICMP Echo Request/Reply to test reachability. It is present across Windows versions (with minor syntax variations) and is among the first tools admins run. By contrast, WINIPCFG existed on Windows 9x but not on all versions; DHCP and WINS are services/protocols, not command-line tools. Therefore, PING is the correct choice for a universally included test utility. Step-by-Step Solution: State requirement: command-line, always available, checks reachability.Map to tool: PING meets all criteria via ICMP Echo.Eliminate non-tool answers and version-specific utilities. Verification / Alternative check: Typical troubleshooting sequences begin with ping, followed by ipconfig, tracert, and others. The presence of ping on Windows, Linux, and macOS underscores its universality. Why Other Options Are Wrong: DHCP: a protocol/service, not a command-line reachability tool. WINS: a name-resolution service, not a ping utility. WINIPCFG: legacy Windows 9x GUI; not universal. None of the above: incorrect because PING is correct. Common Pitfalls: Interpreting a lack of ping replies as proof the host is down (ICMP can be filtered); forgetting to test DNS separately with nslookup or ping by IP vs name. Final Answer: PING.

Question 7

ARCNET hub architecture: which characteristic is a key feature of ARCNET's design for coordinated medium access and addressing?

Accepted Answer

Introduction: ARCNET is a legacy LAN technology known for using a star or bus topology with a deterministic token-passing access method. Understanding its architectural features helps contrast it with Ethernet and Token Ring. This question focuses on the notable characteristic provided by ARCNET's hub-based approach: orderly access and addressing. Given Data / Assumptions: ARCNET employed token passing and centralized hubs in many deployments. Deterministic access and explicit addressing were part of its strengths. We are not considering 802.1Q VLANs or dynamic routing features (not part of classic ARCNET). Concept / Approach: ARCNET assigns node addresses and uses a token to control who may transmit, providing access control and addressing integral to the network's operation. Directionalized transmission, VLAN partitioning, or advanced alternative routing were not signature features of ARCNET hub architecture. Instead, its appeal lay in predictable access and simple, robust operation across relatively modest data rates by today's standards. Step-by-Step Solution: Recall ARCNET fundamentals: token based, addressable nodes, hub/star wiring common.Identify key property: orderly access to the medium with addressing to deliver frames.Exclude unrelated features (VLANs, dynamic routing).Select “access control and addressing.” Verification / Alternative check: Historical ARCNET documentation highlights deterministic token access and node addressing as core elements, often cited for industrial control due to predictability compared to early Ethernet contention systems. Why Other Options Are Wrong: Directionalized transmission: not a defining ARCNET property. Multiple virtual networks: VLANs are an 802.1Q/bridging feature, not ARCNET's. Alternative routing: requires layer-3 or specialized redundancy beyond standard ARCNET hubs. None of the above: incorrect because one option is correct. Common Pitfalls: Projecting modern Ethernet features onto ARCNET; assuming any hub architecture implies VLANs or routing capabilities. Final Answer: Access control and addressing.

Question 8

UNIX utilities: which program traditionally copies files to or from another UNIX time-sharing system over a single communication link?

Accepted Answer

Introduction: Before always-on IP networking was common, UNIX systems often exchanged files, emails, and news via dial-up or direct serial links. A classic utility automated these transfers with scheduled jobs and store-and-forward routing. This question asks you to identify the program historically used to copy files between UNIX systems over a single link. Given Data / Assumptions: Environment: classic UNIX to UNIX communication. Transport: single serial or dial-up link, possibly scheduled. Goal: copy files between hosts reliably. Concept / Approach: UUCP (Unix-to-Unix Copy Program) provided command-line tools and daemons for file transfer, remote command execution, and email/news forwarding across point-to-point links, building store-and-forward networks (e.g., UUCPNET). TFTP is a simple UDP/IP file protocol used on IP networks, not over arbitrary single serial links. VMTP is a historical transport protocol (Versatile Message Transaction Protocol), not a file-copy utility. UART is a hardware component (Universal Asynchronous Receiver/Transmitter), not software for file transfers. Step-by-Step Solution: Identify requirement: copy files between UNIX hosts over a single link.Map to the tool designed for dial-up/serial scheduling and transfer: UUCP.Eliminate IP-dependent or hardware-only distractors (TFTP, UART, VMTP).Select UUCP as the traditional solution. Verification / Alternative check: Historical references to Usenet and early email systems show UUCP scripts dialing neighbors nightly to exchange content, confirming UUCP’s role in single-link, store-and-forward operations. Why Other Options Are Wrong: TFTP: requires IP; lacks authentication/robustness for dial-up serial links. VMTP: a protocol, not a UNIX file-copy tool. UART: hardware interface, not a program. None of the above: incorrect because UUCP is correct. Common Pitfalls: Confusing modern IP-based tools (SCP, rsync) with historical pre-IP mechanisms; mistaking hardware components for software utilities. Final Answer: UUCP.

Question 9

In data communications, the error-detecting code field inserted into a frame before transmission is called what?

Accepted Answer

Introduction / Context: At the data link layer, frames include a dedicated field used to detect accidental bit errors introduced by noise, attenuation, or interference. This field lets the receiver verify integrity before passing data up the stack or requesting a retransmission. Knowing the correct term used in standards and textbooks prevents confusion with related ideas such as checksums and general error-control concepts. Given Data / Assumptions: The question asks for the name of the specific field placed in a frame to detect errors. We are at the data link (layer 2) level, dealing with frames, not packets or segments. Typical LAN/WAN technologies include Ethernet, PPP, and HDLC-like links. Concept / Approach: Most layer-2 protocols append a field called the Frame Check Sequence (FCS). The FCS is the container that carries check bits computed over the frame—commonly using a Cyclic Redundancy Check (CRC) polynomial. While the underlying math might be CRC, the on-the-wire field in the frame trailer is formally named FCS in many standards (for example, IEEE 802 LANs). Step-by-Step Solution: Identify the OSI layer and unit: layer 2 and “frame.”Recall the standardized trailer field name: Frame Check Sequence.Understand that the FCS usually contains CRC bits used to detect errors.Therefore, the field inserted for error detection is the Frame Check Sequence. Verification / Alternative check: In Ethernet, the 32-bit CRC value is placed in the FCS field at the end of each frame. PPP and HDLC use a Frame Check Sequence of configurable length (often 16 or 32 bits) to provide similar integrity checks. Why Other Options Are Wrong: Error-detecting code: A generic phrase; the field’s standardized name is FCS. Checksum: Another integrity mechanism, but Ethernet and many L2 links use CRC in an FCS, not a simple checksum. Flow control: Regulates sending rate/windowing; not error detection. Cyclic Redundancy Check field: Describes the math, but the proper frame-field name is FCS in common standards. Common Pitfalls: Mixing the algorithm (CRC) with the frame field name (FCS). Also, confusing higher-layer checksums (e.g., TCP checksum) with link-layer FCS. Final Answer: Frame Check Sequence

Question 10

In telecommunications, ITU-T X.21 defines what type of interface/standard for connecting data terminal equipment (DTE) to a circuit-switched digital network?

Accepted Answer

Introduction / Context: Several legacy standards describe how user equipment attaches to carrier networks. Understanding which specification covers the physical/electrical and signaling interface to a circuit-switched digital network helps distinguish access standards from media access control or higher-layer protocols. Given Data / Assumptions: Standard referenced: ITU-T X.21. Environment: circuit-switched digital networks. Objective: identify what X.21 specifies. Concept / Approach: X.21 defines the DTE/DCE interface (pin-out, signaling, and call control) for attaching terminals or computers to a circuit-switched public data network. It is not a shared-medium MAC method, nor a bit-oriented data link protocol like HDLC/SDLC, and it is not an ISO LAN standard. It focuses on access to carrier circuits (e.g., switched virtual circuits in early PDNs). Step-by-Step Solution: Recognize X.21 as an ITU-T access specification.Link it to DTE/DCE interface on circuit-switched digital PDNs.Exclude MAC methods and generic data link protocols.Select the description matching a network access standard. Verification / Alternative check: X.21 complements other X-series interfaces (e.g., X.25 packet layer with LAPB at link layer); together they enabled connections over carrier-provided circuits before widespread IP. Why Other Options Are Wrong: Media access methods (a, b) relate to LAN contention/token techniques, not carrier access interfaces. Bit-oriented link protocol (c) describes HDLC/SDLC, not X.21. None of the above: Incorrect because X.21 is indeed a circuit-switched access standard. Common Pitfalls: Confusing X.21 (access) with X.25 (packet layer) or HDLC (link control); each addresses different layers/responsibilities. Final Answer: A network access standard for connecting stations to a circuit-switched network

Question 11

Wide Area Network (WAN) operation commonly uses which transmission facilities? Select the best overall choice.

Accepted Answer

Introduction / Context: A Wide Area Network spans cities, countries, or continents. To cover such distances and diverse terrains, WANs rely on different carrier media and technologies—from terrestrial copper/fiber to microwave relays and satellite links. Recognizing the breadth of possible media clarifies why WAN design involves latency, availability, and cost trade-offs. Given Data / Assumptions: WANs interconnect geographically distant sites. Media choices include wired and wireless carrier infrastructure. The question asks for the most inclusive correct choice. Concept / Approach: WANs may use public switched telephone networks, leased lines over copper/fiber, microwave line-of-sight backhaul, and satellite links (GEO, MEO, LEO). Modern WANs also overlay VPNs on the Internet and carrier Ethernet/MPLS backbones. Because multiple technologies are routinely used in combination, the correct answer aggregates these options. Step-by-Step Solution: Identify common WAN media: PSTN/leased lines, microwave, satellite.Acknowledge that many WANs mix these for redundancy or reach.Choose the inclusive option covering all. Verification / Alternative check: Real deployments often pair terrestrial fiber with microwave as backup and add satellite for remote/mining/oceanic locations where terrestrial build-out is impractical. Why Other Options Are Wrong: Single-medium choices (telephone, microwave, satellite) are incomplete. None of the above: Incorrect because all listed media are valid WAN options. Common Pitfalls: Assuming WANs are always fiber only; last-mile and contingency links frequently use microwave or satellite where fiber is unavailable or cost-prohibitive. Final Answer: All of the above

Question 12

Identify the incorrect statement about OSI layer responsibilities (focus on formatting/translation vs link transfer). Which statement below is wrong?

Accepted Answer

Introduction / Context: The OSI model separates concerns so that each layer has clear responsibilities. Distinguishing between the Presentation layer (format/translation) and the Transport layer (end-to-end delivery) helps avoid common misconceptions when mapping protocols and services to layers. Given Data / Assumptions: Option (a) assigns translation/formatting to the Transport layer. Option (b) assigns translation/formatting to the Presentation layer. Option (c) describes the Data Link layer’s role on a single physical link. Concept / Approach: Presentation (Layer 6) is responsible for data representation: character set translation, encryption/decryption, compression, and syntax marshaling. Transport (Layer 4) provides end-to-end delivery services: segmentation, sequencing, flow and error control, and retransmission. Data Link (Layer 2) manages framing and reliable transfer across a local link between adjacent nodes. Step-by-Step Solution: Compare option (a) with the OSI definitions: its functions belong to Presentation, not Transport.Confirm option (b) correctly describes the Presentation layer.Confirm option (c) correctly captures the Data Link layer’s responsibility.Therefore, (a) is the incorrect statement. Verification / Alternative check: Mapping to real protocols: TLS record encoding and content-encoding transformations align with Presentation-layer concepts; TCP’s sequencing and congestion control exemplify Transport-layer duties. Why Other Options Are Wrong: “All of the above”: Not true because (b) and (c) are correct. “None of the above”: Not true because (a) is demonstrably incorrect. Common Pitfalls: Attributing encryption and data format conversion to Transport; while some stacks blur layers, in OSI these are Presentation functions. Final Answer: The transport layer provides for any format, translation or code conversion necessary to put the data into an intelligible format.

Question 13

You purchased a Multistation Access Unit (MAU) for your network. Which type of network interface card (NIC) should the workstations use to connect to this MAU?

Accepted Answer

Introduction / Context: Different LAN technologies use different concentrators and cabling conventions. In classic IBM-style networks, a Multistation Access Unit (MAU) serves as the hub for Token-Ring stations. Identifying the appropriate NIC type prevents mismatches between endpoint interfaces and wiring centers. Given Data / Assumptions: A MAU has been purchased to interconnect client machines. We must choose the correct NIC type for workstations. Options include storage buses, backup software, and other unrelated items intended as distractors. Concept / Approach: MAUs are specific to Token-Ring networks (IEEE 802.5). They create a logical ring by internally wiring stations in sequence while providing bypass/relay mechanisms to keep the ring intact if a station disconnects. Therefore, the NICs must speak Token-Ring, not Ethernet or storage interfaces. Step-by-Step Solution: Identify what a MAU is used for: Token-Ring wiring center.Match workstation NICs to the MAU’s technology.Select Token-Ring NICs as the appropriate choice. Verification / Alternative check: IBM 8228 and similar MAUs historically connected Token-Ring stations at 4 or 16 Mbps; Ethernet uses hubs/switches rather than MAUs, and storage (SCSI) or backup software (ArcServe) are unrelated to NIC selection. Why Other Options Are Wrong: Fast SCSI Wide: Storage interconnect, not a LAN NIC. ArcServe: Backup software, not a NIC. Ethernet: Uses hubs/switches; not compatible with Token-Ring MAUs. None of the above: Incorrect because Token-Ring is correct. Common Pitfalls: Assuming “hub-like device” implies Ethernet; MAUs are specifically for Token-Ring. Final Answer: Token-Ring

Question 14

In distributed data processing, the orderly method where a controller systematically queries each remote device or small computer for service is called what?

Accepted Answer

Introduction / Context: When many subordinate devices share a controller or communication line, the system needs an orderly access method. One classic approach has the master ask each device in turn whether it has data to send or needs service, ensuring fairness and preventing collisions on shared media. Given Data / Assumptions: Multiple remote devices or small computers participate in a shared system. Access is coordinated by a central controller. The method is systematic and cyclical. Concept / Approach: Polling is a master-driven access method wherein the controller sequentially queries (“polls”) each device. If a device has traffic, it transmits during its turn; otherwise, the controller moves on. Variants include roll-call polling and hub-go-ahead strategies. Polling contrasts with contention (e.g., CSMA) and scheduled token passing. Step-by-Step Solution: Identify the need for orderly, centrally coordinated access.Map this to the technique where the master queries subordinates in sequence.Conclude that the described method is polling. Verification / Alternative check: Legacy multidrop serial lines and many industrial fieldbuses used polling to guarantee deterministic behavior, especially where collisions or random access were unacceptable. Why Other Options Are Wrong: Dialed service: Refers to connection establishment, not access scheduling. Multiplexing: Combines multiple signals/streams on one medium; not a query-based access protocol. Conversational mode: Describes interactive behavior, not an access algorithm. None of the above: Incorrect because polling is the standard term. Common Pitfalls: Confusing polling with interrupt-driven access; in polling, the master dictates timing rather than devices interrupting spontaneously. Final Answer: Polling

Question 15

In the classic X.25 protocol stack, how many OSI layers does the standard encompass directly (considering the physical, data link, and packet layers)?

Accepted Answer

Introduction / Context: X.25 is an early packet-switched networking standard that predated today’s IP-based Internet. It defined how user equipment connects and exchanges packets over public data networks. Understanding where X.25 sits in the OSI model clarifies its scope and how it relates to higher-layer services. Given Data / Assumptions: X.25 comprises: physical interface, link-layer control, and packet layer protocol. OSI layering reference is assumed. We count the layers that X.25 directly specifies. Concept / Approach: X.25 spans three OSI layers: Layer 1 (physical interface, often via X.21 or V-series), Layer 2 (LAPB — Link Access Procedure, Balanced), and Layer 3 (Packet Layer Protocol for virtual circuits). It does not define transport, session, presentation, or application functions. Step-by-Step Solution: Map X.25 physical attachment to OSI Layer 1.Map LAPB link control to OSI Layer 2.Map packet layer virtual circuits to OSI Layer 3.Total layers covered: three. Verification / Alternative check: Classic diagrams show X.25’s packet layer offering a network service to higher layers while relying on LAPB and a carrier physical interface below. Why Other Options Are Wrong: two: Omits one of the layers X.25 specifies. seven or six: Overstate X.25’s scope beyond the network service boundary. None of the above: Incorrect because “three” is correct. Common Pitfalls: Confusing X.25 end-to-end application services with its network-service role; transport and above are out of scope for the standard. Final Answer: three

Question 16

A digital system uses a 6-MHz channel and 4-level signaling (M = 4). Assuming the ideal Nyquist criterion for a noiseless baseband channel, what is the maximum symbol rate achievable?

Accepted Answer

Introduction / Context: The Nyquist criterion sets a theoretical upper bound on symbol rate for intersymbol-interference-free transmission over an ideal baseband channel with limited bandwidth. Separating symbol rate (baud) from bit rate (bit/s) is essential, especially when multi-level signaling is used. Given Data / Assumptions: Channel bandwidth B = 6 MHz. Signal levels M = 4 (2 bits per symbol if used for bit rate computation). Assume ideal, noiseless baseband with perfect Nyquist pulses. Question asks explicitly for symbol rate (baud), not bit rate. Concept / Approach: For an ideal baseband channel, the Nyquist maximum symbol rate is R_s,max = 2 * B symbols per second. With B = 6e6 Hz, the maximum symbol rate is 12e6 symbols/s, i.e., 12 Mbaud/s. If we were asked for bit rate, we would multiply by log2(M): R_b,max = R_s,max * log2(4) = 12e6 * 2 = 24 Mb/s. Step-by-Step Solution: Write Nyquist formula for baud: R_s,max = 2 * B.Substitute B = 6 MHz → R_s,max = 12 MHz in baud.Match to options: 12 Mbaud/s. Verification / Alternative check: Cross-check using bit rate notion: with M = 4, each symbol carries 2 bits, giving 24 Mb/s maximum in the same conditions—consistent with 12 Mbaud/s symbol rate. Why Other Options Are Wrong: 1.5 or 6 Mbaud/s: Below the Nyquist limit for 6 MHz. 24 Mbaud/s: Would require >12 MHz bandwidth for ideal Nyquist signaling. None of the above: Incorrect because 12 Mbaud/s fits. Common Pitfalls: Confusing bit rate with baud; multi-level signaling increases bits per symbol but not the maximum symbol rate allowed by Nyquist for a given bandwidth. Final Answer: 12 Mbaud/s

Question 17

For a basic serial communications link (e.g., RS-232 style asynchronous), what is the minimum number of wires required to send data reliably between two devices?

Accepted Answer

Introduction / Context: Serial links can use many control signals, but at minimum they need a shared reference and one path in each direction if two-way data is required. Understanding the minimal wiring helps troubleshoot cabling and set expectations for simple null-modem or point-to-point connections. Given Data / Assumptions: Consider a typical asynchronous serial link between two devices. No modem control (RTS/CTS, DTR/DSR) is strictly required. Goal is basic, reliable data exchange. Concept / Approach: Minimal RS-232-style links use three wires: Transmit Data (TXD), Receive Data (RXD), and Signal Ground (GND). TXD of one device connects to RXD of the other (and vice versa), with a shared ground to establish a reference. Although some current-loop or differential interfaces use pairs differently, the canonical minimum for classic single-ended serial is three conductors. Step-by-Step Solution: Identify necessary signals: TX, RX, and a common ground.Cross-connect TX↔RX between devices.Confirm that additional hardware flow-control lines are optional for basic operation. Verification / Alternative check: Count typical DB-9 connections: pin 2 (RXD), pin 3 (TXD), pin 5 (GND) suffice for simple terminal-to-host links when software flow control (XON/XOFF) is used or flow control is disabled. Why Other Options Are Wrong: 1 wire: Cannot carry bidirectional data nor establish a reference. 2 wires: Lacks a shared ground in single-ended RS-232; unreliable. 4 wires: Works (adds hardware flow control) but is not the minimum. None of the above: Incorrect because three wires suffice. Common Pitfalls: Confusing RS-232 with differential standards like RS-485 (which use pairs) or assuming hardware flow control is mandatory. For many simple setups, 3-wire null-modem works. Final Answer: 3

Question 18

In digital communications, what conversion does a modulator perform when preparing data for transmission over passband channels such as radio or telephone circuits?  Choose the pair that correctly fills the blanks: A modulator converts a _____ signa…

Accepted Answer

Introduction: A core task at the physical layer is adapting the form of information to suit the channel. Computers generate discrete-time, discrete-amplitude data (bits), but many practical channels—especially legacy copper loops and radio links—are optimized for band-limited, continuous-time waveforms. This question tests whether you know the direction of conversion performed by a modulator before transmission. Given Data / Assumptions: Source data is digital (bits from a computer or digital interface). The transmission medium favors continuous, band-limited signals (for example, voice-band telephone line or RF channel). A modulator is used on the transmit side; a demodulator is used on the receive side. Concept / Approach: Modulation maps digital symbols onto the parameters of a carrier—amplitude, frequency, or phase—creating an analog passband waveform. Common schemes include ASK, FSK, PSK, and QAM. The receiver applies demodulation to recover the original symbols. This pair of operations (modulate/demodulate) explains the portmanteau “modem.” Therefore, the correct fill-in is: a modulator converts a digital signal to an analog signal suitable for the channel. Step-by-Step Solution: Identify the domain mismatch: digital source vs. analog-friendly channel.Recall the role of a modulator: map bits/symbols to carrier waveform parameters.State the transformation: digital → analog at the transmitter.Conclude that the correct pair is “digital; analog.” Verification / Alternative check: Consider a classic telephone-line modem: it accepts serial digital data and outputs audio-frequency tones. Similarly, cellular “modems” produce RF waveforms from digital packets. Why Other Options Are Wrong: FSK; PSK and PSK; FSK (A, B): these are two types of analog modulation, not input/output categories. analog; digital (C): this describes demodulation, not modulation. None of the above (E): invalid because “digital; analog” is correct. Common Pitfalls: Confusing the direction of conversion (mixing up modulator vs. demodulator) or treating specific schemes (FSK, PSK) as if they described the input/output domains. Final Answer: digital; analog

Question 19

Historically, who originally sponsored and designed the TCP/IP suite that underpins today’s Internet architecture?

Accepted Answer

Introduction: Understanding the origins of TCP/IP provides context for why the protocols emphasize robustness, internetworking across heterogeneous links, and end-to-end reliability. The question asks for the organization that originally sponsored and oversaw development of the Transmission Control Protocol/Internet Protocol suite. Given Data / Assumptions: We are referring to the initial design and standardization era (1970s–early 1980s). TCP/IP became the foundation of ARPANET’s transition and later the global Internet. The answer seeks the sponsoring institution, not individual researchers (e.g., Vint Cerf, Bob Kahn). Concept / Approach: TCP/IP was initiated under the auspices of the U.S. Department of Defense’s Advanced Research Projects Agency (ARPA, later DARPA). The design mandate prioritized survivable, interoperable networking across diverse media. Universities, research labs, and contractors participated, but the overarching sponsor and steward was the Department of Defense via ARPA/DARPA. Step-by-Step Solution: Identify the era and program: ARPA networking projects in the 1970s.Link key contributors (Cerf, Kahn) to ARPA/DARPA funding and coordination.Recall the 1983 ARPANET flag day cutover to TCP/IP, a DoD-directed milestone.Conclude that the Department of Defense is the correct institutional answer. Verification / Alternative check: Historical timelines document DARPA’s role in funding and guiding the Internet Program, including TCP/IP specifications and early implementations (e.g., BBN, Stanford, ISI). Why Other Options Are Wrong: Novell: developed IPX/SPX and NetWare, not TCP/IP’s original design. IBM: advanced SNA; later supported TCP/IP but did not originate it. Xerox: created XNS; influential, but distinct from TCP/IP’s origin. None of the above: invalid because DoD (via ARPA/DARPA) is correct. Common Pitfalls: Confusing corporate protocol suites (IPX/SPX, SNA, XNS) with the DoD-sponsored TCP/IP lineage. Final Answer: The Department of Defense

Question 20

For setting up a classic dial-up Bulletin Board System (BBS), which items are required at the host end to receive and serve callers?

Accepted Answer

Introduction: Before the modern Internet, hobbyists and small organizations used Bulletin Board Systems (BBS) to share files, messages, and announcements. Understanding the minimal hardware and connectivity required to host a BBS clarifies how dial-up access worked and why certain capabilities were critical. Given Data / Assumptions: The BBS is reachable by callers over the public switched telephone network (PSTN). The host needs to answer incoming calls automatically, without manual intervention. Basic computing resources are needed to run the BBS software and store content. Concept / Approach: A functioning BBS requires: (1) a personal computer to run the BBS application and manage storage; (2) a telephone line so remote users can dial in; and (3) a smart modem with auto-answer capability so the system can detect incoming rings and negotiate a data connection automatically. Without any one of these, the BBS cannot accept unattended calls reliably. Step-by-Step Solution: List necessary components: PC + phone line + auto-answer modem.Confirm each item’s role: compute, connectivity, call negotiation.Recognize that all three are jointly necessary for a dial-up BBS.Select “All of the above.” Verification / Alternative check: Classic BBS guides specify modem initialization strings and auto-answer settings (e.g., ATS0=1) to pick up after a set number of rings. Why Other Options Are Wrong: Single components (A, B, or C) are insufficient alone. None of the above: invalid because all listed items are required. Common Pitfalls: Overlooking auto-answer; manual pickup would defeat unattended access by remote users. Final Answer: All of the above

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