Question 1

You manage 192.168.10.0 (a /24 network) and require at least nine subnets while keeping the maximum possible hosts per subnet. Which subnet mask should you choose?

Accepted Answer

Introduction: Subnetting divides an address block into smaller networks. The design target here is to obtain at least nine subnets from a /24 while preserving as many host addresses per subnet as possible. Given Data / Assumptions: Base: 192.168.10.0/24 (default mask 255.255.255.0). Required subnets: ≥ 9. Goal: maximize hosts per subnet subject to the subnet count constraint. Concept / Approach: Borrow the fewest bits that still meet the subnet-count requirement. From a /24, borrowing n bits yields 2^n subnets. For ≥9 subnets, n must be 4 because 2^3 = 8 (insufficient) and 2^4 = 16 (sufficient). A /24 + 4 bits = /28, whose mask is 255.255.255.240. Hosts per /28 = 2^(32-28) - 2 = 14 per subnet, which is the maximum host count achievable while still having at least nine subnets from the /24 block. Step-by-Step Solution: 1) Determine bits needed: need ≥9 → n = 4.2) New prefix: /24 + 4 = /28.3) Mask: 255.255.255.240.4) Verify: 16 subnets, 14 hosts each. Verification / Alternative check: Trying /27 gives only 8 subnets; trying /29 gives 32 subnets but fewer hosts per subnet, violating the “maximize hosts” objective. Why Other Options Are Wrong: /26 (255.255.255.192): 4 subnets (if using old rules) or 64 subnets in CIDR context across larger blocks, but within this /24 borrowing only 2 bits gives only 4 distinct /26s (insufficient for ≥9 from a single /24). /27 (255.255.255.224): 8 subnets, still short of 9. /29 and beyond: meet subnet count but reduce hosts further than necessary. Common Pitfalls: Mixing legacy “no subnet-zero” conventions with modern usage; today subnet-zero is allowed, but the math above already ensures ≥9 using /28. Final Answer: 255.255.255.240

Question 2

Among common media and carriers, which typically provides the slowest data transmission speeds under comparable conditions?

Accepted Answer

Introduction: Physical media differ in bandwidth, attenuation, and interference immunity. Knowing which media are inherently faster or slower helps in selecting appropriate links for LANs, access networks, and backbones. Given Data / Assumptions: “Twisted-pair wire” refers to copper pairs (e.g., Cat3–Cat6) without special conditioning. “Coaxial cable” offers better shielding and bandwidth than unshielded twisted pair of similar vintage. “Fiber-optic cable” supports very high data rates and long reach. “Microwaves” refers to point-to-point RF links capable of high throughput under line-of-sight conditions. Concept / Approach: Under comparable generations of technology, unshielded twisted pair (especially older categories) provides lower usable bandwidth and higher susceptibility to noise than coaxial or fiber. Microwave links, though variable, can achieve high aggregate throughput using modern modulation and channel widths. Therefore, the slowest typical baseline is twisted-pair copper. Step-by-Step Solution: 1) Compare inherent bandwidth: fiber » microwave/coax » twisted pair.2) Consider attenuation and noise: UTP suffers more than coax; fiber is immune to EMI.3) Account for practical deployments: legacy UTP (e.g., Cat3) was limited to low Mbps; modern fiber/coax/microwave routinely exceed this. Verification / Alternative check: Enterprise networks use fiber for backbones and high-speed access, while twisted pair is used for desktop drops where ultra-high bandwidth is not always required—evidence of its relatively lower capacity. Why Other Options Are Wrong: Coaxial: higher bandwidth and better shielding than basic UTP. Fiber-optic: far higher data rates and distances. Microwaves: high capacities with modern radios and channel aggregation. Common Pitfalls: Assuming “wireless is slow.” With modern microwave radios, that assumption is not generally true compared to old copper pairs. Final Answer: twisted-pair wire

Question 3

In the OSI reference model, which layer defines the interface with end users and provides services such as file transfer, email, network management applications, and resource sharing?

Accepted Answer

Introduction: The OSI model organizes network functionality into seven layers. Understanding which layer directly supports end-user applications clarifies where protocols like HTTP, FTP, SMTP, and SNMP conceptually reside. Given Data / Assumptions: OSI layers: 7 Application, 6 Presentation, 5 Session, 4 Transport, 3 Network, 2 Data Link, 1 Physical. Examples of user-facing services include file transfer, email, and management consoles. Concept / Approach: The Application layer (Layer 7) provides network services directly to application software, defining how applications request and present network data. Presentation (Layer 6) handles representation (encryption/translation), and Session (Layer 5) manages dialogues; neither is the primary user-facing service endpoint. Step-by-Step Solution: 1) Map sample services (FTP, SMTP, HTTP, SNMP) to Layer 7.2) Distinguish lower layers: they enable delivery, not application semantics.3) Conclude that user-facing network functions belong to Layer 7. Verification / Alternative check: In TCP/IP, the “application layer” similarly hosts application protocols, even though the model collapses OSI layers. Why Other Options Are Wrong: Network: routing and addressing. Data-link: framing and MAC addressing. Session: dialog setup/teardown, not end-user services. Common Pitfalls: Assuming encryption means Application layer; encryption can be at Presentation or Transport (e.g., TLS) depending on the stack abstraction. Final Answer: Application layer

Question 4

Classic Ethernet (IEEE 802.3) design rule: what is the maximum number of cable segments that may separate any two nodes on a shared coax/repeater-based network?

Accepted Answer

Introduction: Legacy shared-media Ethernet (before modern switches) followed physical-layer rules to ensure collision detection and timing integrity. A well-known guideline is the “5-4-3” rule, which constrains the number of segments and repeaters between any two stations. Given Data / Assumptions: Topology uses repeaters/hubs and coax or copper segments (not modern full-duplex switching). CSMA/CD timing must be preserved for reliable collision detection. Propagation delay across the path must remain within limits. Concept / Approach: The 5-4-3 rule states that along the maximum path between two stations you can have up to 5 segments connected by 4 repeaters, with at most 3 of those segments populated by active nodes (the other 2 are inter-repeater links). This bound maintains the slot-time window needed for CSMA/CD to function as specified. Step-by-Step Solution: 1) Identify constraints: collision domains must meet round-trip timing.2) Apply the rule: ≤5 segments, ≤4 repeaters, ≤3 populated segments.3) Conclude the maximum number of segments between two nodes is five. Verification / Alternative check: Design guides for 10BASE5/10BASE2 and early 10BASE-T hubs cite 5-4-3 explicitly for compliant paths. Why Other Options Are Wrong: Two/Three/Four/Six: these violate or understate the canonical 5-4-3 constraint for classic shared Ethernet topologies. Common Pitfalls: Applying this rule to switched Ethernet; with full-duplex switches, CSMA/CD no longer bounds segment counts in the same way. Final Answer: Five

Question 5

According to the X.25 architecture, how many distinct protocol layers are specified at the serial interface gateway between user equipment and the packet-switched network?

Accepted Answer

Introduction: X.25 defined a complete suite for connecting Data Terminal Equipment (DTE) to a packet-switched network via a serial interface. Its layering mirrors the lower portion of the OSI model and clarifies responsibilities at the network edge. Given Data / Assumptions: We are concerned with the DTE–DCE interface (user equipment to network). Physical, link, and network functions are required. Higher-layer transport/session logic is outside X.25’s lower-layer scope. Concept / Approach: X.25 specifies three layers: (1) Physical layer (e.g., X.21, V.24/V.28) provides electrical/connector characteristics; (2) Data link layer uses LAPB for reliable framing and error control; (3) Packet layer provides virtual circuits and network addressing/flow control. Together they deliver reliable packet service to higher layers. Step-by-Step Solution: 1) Identify physical signaling needs → Physical layer.2) Ensure reliable frame transport → Data link via LAPB.3) Provide virtual circuit services → Packet layer (level 3) of X.25. Verification / Alternative check: Host stacks historically implemented these three levels to reach PDNs, with higher-layer protocols (transport/session) riding above the packet layer. Why Other Options Are Wrong: 2 or 4 or 6: do not match the standardized three-layer decomposition in X.25 at the interface. None of the above: invalid because three is correct. Common Pitfalls: Confusing X.25’s three-layer model with the full seven-layer OSI model or with TCP/IP layering. Final Answer: 3

Question 6

In the EIA-232 (RS-232) serial interface, which line coding is specified for representing mark and space at the electrical level?

Accepted Answer

Introduction: EIA-232 (often called RS-232) is a classic point-to-point serial interface standard widely used for terminals, modems, and instrumentation. Understanding its electrical signaling and line coding is fundamental for debugging and interfacing legacy serial equipment. Given Data / Assumptions: RS-232 defines voltage levels for logical states called mark and space. We are focused on how bits are represented on the wire over time. No clock is embedded (as in Manchester) because asynchronous framing supplies timing. Concept / Approach: RS-232 uses NRZ-L coding, where a constant voltage level over a bit interval indicates the bit value (mark/space). There is no guaranteed transition each bit period, unlike Manchester or Differential Manchester line codes used for self-clocking links. Because NRZ-L lacks inherent clock recovery, RS-232 relies on start/stop bits and agreed baud rate for timing. Step-by-Step Solution: 1) Identify logical states: mark and space correspond to specified positive/negative voltage ranges.2) Recognize that bit values are conveyed by sustained levels (NRZ-L), not by transitions (NRZ-I) or mid-bit flips (Manchester).3) Confirm asynchronous framing supplies timing instead of a self-clocking code. Verification / Alternative check: Equipment datasheets and scopes show constant-level signaling for each bit interval with start and stop bits bracketing data bytes, consistent with NRZ-L. Why Other Options Are Wrong: NRZ-I: information encoded by transitions; not RS-232. Manchester/Differential Manchester: self-clocking codes used in Ethernet/Token Ring, not in RS-232. Bipolar-AMI: alternate mark inversion used in T-carrier systems, not RS-232. Common Pitfalls: Assuming all serial links embed a clock; RS-232 does not and therefore depends on accurate baud configuration at both ends. Final Answer: NRZ-L (Non-Return-to-Zero Level)

Question 7

You have Class B network 134.57.0.0 and need subnets that each support at least 600 hosts. To maximize the number of subnets while meeting this host requirement, which mask should you assign (choose from the options provided)?

Accepted Answer

Introduction: For a Class B block (default /16), choosing a subnet mask requires balancing the number of hosts per subnet against the number of available subnets. The goal here is to meet at least 600 hosts per subnet while maximizing the number of subnets given the answer choices provided. Given Data / Assumptions: Base: 134.57.0.0 (Class B, /16). Required hosts per subnet: ≥ 600. We must pick from the listed masks only. Concept / Approach: Hosts per subnet = 2^(host_bits) - 2. To support ≥600 hosts, host_bits must be at least 10 (2^10 - 2 = 1022). That implies a /22 prefix (since 32 - 22 = 10). A /22 mask is 255.255.252.0, which would maximize subnets while meeting the host requirement. Although /22 is not offered in the options, the next longest prefix among the choices that still satisfies ≥600 hosts is /21 (255.255.248.0) with 2^(11) - 2 = 2046 hosts per subnet. /21 yields more subnets than /20 or /19, and /24 is too small for 600 hosts. Step-by-Step Solution: 1) Compute minimum host bits: need ≥600 → host_bits = 10.2) Ideal mask: /22 (255.255.252.0) → not in options.3) Choose longest available prefix that still meets hosts: /21 (255.255.248.0).4) Validate: 2046 hosts/subnet ≥ 600; more subnets than /20 or /19. Verification / Alternative check: Check other options: /24 (254 hosts) fails; /19 and /20 allow many hosts but fewer subnets than /21, contradicting the “maximize subnets” goal. Why Other Options Are Wrong: 255.255.224.0 (/19) and 255.255.240.0 (/20): satisfy hosts but yield fewer subnets than /21. 255.255.255.0 (/24): only 254 hosts; insufficient. 255.255.255.255 (/32): no host capacity. Common Pitfalls: Forgetting that to maximize subnets you choose the longest allowable prefix that still meets the host requirement; if the ideal mask is missing from options, select the closest longer prefix that remains valid. Final Answer: 255.255.248.0

Question 8

In a synchronous modem, which functional section typically contains the scrambler used to randomize the data stream for clock transparency and spectrum shaping?

Accepted Answer

Introduction: Scramblers are applied to digital data streams to break up long runs of identical bits, aiding timing recovery, reducing spectral lines, and improving performance over certain channels. In synchronous modems, scramblers help maintain clock transparency prior to modulation. Given Data / Assumptions: We are discussing internal modem functions, not higher-layer encryption. Goal is to condition the bitstream before it drives the modulator. Descrambling must occur at the far-end receiver to recover the original data. Concept / Approach: The scrambler operates in the transmit path so that the signal entering the modulator has randomized bit patterns. At the receiving modem, a descrambler in the receive path restores the original data. This pair preserves data integrity while improving timing and spectral properties during transmission. Step-by-Step Solution: 1) Identify where bit preparation is needed → before modulation.2) Place scrambler in the transmission section so the modulator sees randomized bits.3) Complement with a receiver-side descrambler to reconstruct the original stream. Verification / Alternative check: Block diagrams of synchronous modems show the scrambler inline with the transmit chain and the descrambler inline with the receive chain, confirming the placement. Why Other Options Are Wrong: Terminal section: refers to the attached DTE, not internal modem conditioning. Receiver section: contains the descrambler, not the scrambler. Control section: manages settings; it does not process the data stream. None of the above: invalid because the transmission section is correct. Common Pitfalls: Confusing scrambling (for spectral/randomization purposes) with encryption (for confidentiality). They are conceptually different processes. Final Answer: Transmission section contains the scrambler

Question 9

Small office networking scenario: Stephanie needs a simple yet secure setup where each user keeps full control over their own workstation data while still being able to share files with others in the office. With only basic networking knowledge amon…

Accepted Answer

Introduction / Context: Small offices often need to balance simplicity, basic security, and low administrative overhead. When users want to retain direct control over their local data but also share folders or printers with coworkers, a peer-to-peer design aligns with these goals without demanding advanced server administration skills. Given Data / Assumptions: User group has only basic networking knowledge. Goal is “simple but secure,” not enterprise-grade directory services. Users want control over their own data and selective sharing. Cost and complexity should be minimal. Concept / Approach: In a peer-to-peer network, each workstation can publish shared resources and set permissions locally. This matches environments where centralized authentication, roaming profiles, and group policies are not mandatory. Basic OS-native sharing (with passwords or user accounts) and a modest firewall/antivirus posture can deliver acceptable security for a very small office. Step-by-Step Solution: 1) Identify the control requirement: users want local control over their files.2) Map skill level to solution: basic skills favor a peer-to-peer arrangement.3) Ensure sharing capability: OS file/print sharing suffices for small groups.4) Add simple safeguards: strong passwords, least-privilege shares, and endpoint protection.5) Optionally introduce a lightweight NAS for common shares without adding domain complexity. Verification / Alternative check: If future needs grow (centralized login, audit, compliance), the office can later migrate to a server-based or cloud directory model. For now, peer-to-peer keeps setup and maintenance straightforward. Why Other Options Are Wrong: Master domain / Server-based: adds complexity, requires admin skills; centralizes control away from users.WAN: refers to long-distance connectivity, not a local design choice for one office.Share-level (as a distinct “network”): describes a permission style, not an overall architecture choice. Common Pitfalls: Over-sharing folders with “everyone,” using weak passwords, and neglecting regular updates. Document share locations and teach users how to map drives safely. Final Answer: Peer-to-peer.

Question 10

In computer architecture, “microprogramming” refers to programming at the control-unit level to define how machine instructions are executed by sequencing low-level control signals. What is microprogramming best described as?

Accepted Answer

Introduction / Context: Microprogramming is a classic technique used in many CISC-style CPUs and some microcontrollers to implement the processor’s instruction set. Instead of hardwiring every control path, designers encode sequences of control signals—microinstructions—stored in a control store. Executing a machine instruction then becomes interpreting a short sequence of micro-operations. Given Data / Assumptions: We are discussing internal CPU control, not user-level programming. Microinstructions generate signals: register enables, ALU function selects, memory read/write, bus gating, etc. Control store can be ROM, PLA, or writable control memory. Concept / Approach: The essence of microprogramming is control unit programming. A microprogram specifies how to orchestrate datapath components over successive cycles to realize each ISA instruction. This separates the “what” (architectural instruction semantics) from the “how” (micro-operations that drive hardware signals). Step-by-Step Solution: 1) Recognize the level: micro-operations live below assembly language.2) Identify artifacts: microinstruction fields control ALU ops, source/destination registers, condition tests, and next-address sequencing.3) Map ISA instructions to microcode routines stored in the control store.4) CPU control unit fetches/executes microinstructions to realize machine instructions. Verification / Alternative check: Compare hardwired control (fixed logic) vs. microprogrammed control (table-driven). The latter eases ISA changes and complex instruction sequencing at the cost of potential speed overhead. Why Other Options Are Wrong: Assembly language is architectural instruction-level, not micro-operations.Programming minicomputers is unrelated to the control store concept.Macro programming is a source-level text substitution concept, not control hardware sequencing.“None of the above” is wrong because control unit programming is correct. Common Pitfalls: Confusing microcode with firmware visible to users, assuming microcode equals assembly, and overlooking that RISC cores often use more hardwired control. Final Answer: Control unit programming.

Question 11

IPv4 subnetting design: For network 172.16.0.0, you need 25 subnets for your company now and an additional 30 after a merger (total 55). Each subnet must support about 600 hosts. What single subnet mask will satisfy these requirements?

Accepted Answer

Introduction / Context: Subnet mask selection must satisfy two constraints simultaneously: number of required subnets and number of hosts per subnet. For a Class B private block (172.16.0.0/16), borrowing bits from the host field increases subnet count while reducing hosts per subnet. The chosen mask must meet or exceed both the subnet and host requirements. Given Data / Assumptions: Base network: 172.16.0.0 with default mask /16. Required subnets: 25 now + 30 later = 55 total. Hosts per subnet ≈ 600 (usable addresses need to exceed this). Standard IPv4 addressing with CIDR. Concept / Approach: Let s = subnet bits borrowed from the /16 host field. Subnets available = 2^s. Hosts per subnet (usable) = 2^(16 - s) - 2. We need 2^s ≥ 55 and 2^(16 - s) - 2 ≥ 600. Find the smallest s that satisfies both. Step-by-Step Solution: 1) 2^5 = 32 (not enough subnets); 2^6 = 64 (enough).2) With s = 6, host bits = 16 - 6 = 10.3) Usable hosts = 2^10 - 2 = 1024 - 2 = 1022 ≥ 600 (satisfies host requirement).4) New prefix = /16 + 6 = /22 → mask 255.255.252.0. Verification / Alternative check: Check neighboring masks: /21 (255.255.248.0) gives 2^5 = 32 subnets (too few). /23 (255.255.254.0) would give more hosts than needed but still only 2^7 = 128 subnets if taken from /16? (That would be /23 = s = 7, but then hosts per subnet = 510, which fails the ~600 requirement.) /22 is the smallest mask that simultaneously satisfies both bounds. Why Other Options Are Wrong: 255.255.192.0 (/18): only 2^(18-16)=4 subnets; hosts per subnet large, but subnet count fails.255.255.224.0 (/19): 8 subnets; still too few.255.255.240.0 (/20): 16 subnets; still too few.255.255.248.0 (/21): 32 subnets; still too few. Common Pitfalls: Forgetting to satisfy both constraints, miscounting usable hosts by ignoring the network and broadcast addresses, and mixing classful intuition with CIDR math. Final Answer: 255.255.252.0.

Question 12

Digital communications over telephone lines: What is the device that converts a computer’s digital signals into a form suitable for transmission over an analog telephone line and back again at the other end?

Accepted Answer

Introduction / Context: Traditional public switched telephone networks were designed for analog voice. Computers generate digital signals, so a specialized device is required to modulate digital data into an analog waveform for transport and demodulate it back into digital data at the destination. Given Data / Assumptions: Medium: analog telephone line. Endpoints: digital computers. Need: bidirectional conversion between digital and analog domains. Concept / Approach: A modem (MOdulator/DEModulator) maps digital bits to analog symbols (tones, phases, amplitudes) and reverses the process on receive. Standards (e.g., V.34, V.90) defined symbol rates and encoding to approach channel capacity limits on voice-grade lines. Step-by-Step Solution: 1) Transmit side: digital bits → modulator → analog waveform on copper pair.2) Network carries analog signal over the voice channel.3) Receive side: analog waveform → demodulator → digital bits.4) Handshaking negotiates rates and error correction as line conditions dictate. Verification / Alternative check: Observe that without modulation/demodulation, raw digital levels would not be preserved over analog-only facilities. Modern broadband replaces analog modulation with DSL or all-digital links, but the principle remains. Why Other Options Are Wrong: Teleport: not a networking device term.Multiplexer: combines multiple channels, does not convert digital-to-analog for PSTN voice channels.Concentrator: aggregates many lines to fewer trunk connections, not a modem.“None of the above” is wrong because modem is correct. Common Pitfalls: Confusing multiplexing with modulation, or assuming Ethernet-to-PSTN works without conversion. Final Answer: Modem.

Question 13

Hypermedia-based file retrieval on the Internet: Which of the following methods uses hypermedia (documents with links that may include text, images, and other media)?

Accepted Answer

Introduction / Context: Hypermedia extends hypertext by incorporating multiple media types (text, images, audio, video) linked together. On today’s Internet, the World Wide Web delivers hypermedia primarily using HTTP to transfer and render resources that embed links and media. Given Data / Assumptions: Hypermedia implies navigable links among heterogeneous media. We compare classic retrieval systems: HTTP, WAIS, Veronica, Archie. Focus is on protocol or service used for hypermedia documents. Concept / Approach: HTTP (Hypertext Transfer Protocol) is the application protocol for fetching linked web resources (HTML, images, video). HTML/HTTP enables embedding and traversing links—defining modern hypermedia. WAIS, Veronica, and Archie historically indexed documents/FTP archives but did not themselves deliver rich hypermedia pages as the Web does. Step-by-Step Solution: 1) Identify which system underpins the Web’s hypermedia model: HTTP.2) Recognize WAIS as a search/access system for text databases.3) Recognize Veronica as an indexer for Gopher menus (text-oriented).4) Recognize Archie as an FTP archive indexer. Verification / Alternative check: Modern browsers use HTTP/HTTPS to fetch HTML, CSS, JS, images, and video, enabling rich hypermedia experiences. Legacy systems predate and do not natively provide comparable hypermedia navigation. Why Other Options Are Wrong: WAIS: full-text search service; not a hypermedia delivery protocol.Veronica: Gopher index; menu-driven, not general hypermedia.Archie: FTP file listings; no hypermedia structure.“None of the above” is wrong because HTTP is correct. Common Pitfalls: Confusing search/index services with content delivery protocols; conflating “hypertext” with any text retrieval system. Final Answer: HTTP.

Question 14

NetBEUI (NetBIOS Extended User Interface) characteristics: Which of the following statements is not true about NetBEUI?

Accepted Answer

Introduction / Context: NetBEUI is a lightweight transport once common on small Windows LANs. It emphasizes simplicity and low overhead but does not scale across routers. Understanding its traits helps compare it with routable protocols like TCP/IP and IPX/SPX used in larger or segmented networks. Given Data / Assumptions: Scope: small, flat LANs without routing. Priority: ease of setup and minimal tuning. Historically used for quick peer-to-peer file and printer sharing. Concept / Approach: The defining limitation of NetBEUI is that it is not routable. It broadcasts for name resolution and relies on a single broadcast domain. While quick and self-configuring, it cannot traverse IP routers, making it unsuitable for multi-subnet or wide-area environments. Step-by-Step Solution: 1) Identify the false property in the list relative to NetBEUI behavior.2) Note that “routable” contradicts NetBEUI’s design.3) Confirm that the remaining traits (easy setup, fast for small LANs, minimal tuning) align with NetBEUI’s strengths.4) Conclude that the “not true” statement is “Routable.” Verification / Alternative check: In multi-subnet designs, NetBEUI traffic does not pass through IP routers. Administrators historically migrated to TCP/IP to enable routing, centralized services, and Internet connectivity. Why Other Options Are Wrong: Highly-customizable: comparatively less need for configuration; but this is not the key falsehood when compared to routability.Little configuration required: true for small plug-and-play setups.Fast/self-tuning: true within small broadcast domains.Optimized for small non-routed LANs: true description of NetBEUI use. Common Pitfalls: Assuming NetBEUI can be routed like TCP/IP; overlooking broadcast overhead as LANs grow. Final Answer: Routable.

Question 15

Choosing a versatile LAN architecture: Jim wants the network architecture that offers the most cabling/topology flexibility and multiple data rates for growth. Which architecture provides the widest range of options?

Accepted Answer

Introduction / Context: Selecting a LAN architecture involves considering topology flexibility, media options, and upgrade paths. Over time, Ethernet has evolved from shared coaxial bus to switched star topologies on copper and fiber, scaling through multiple speed generations while remaining widely interoperable and cost-effective. Given Data / Assumptions: Desire for flexibility in physical layout (star, tree, aggregations with switches). Need for multiple speed options for future growth. Broad availability of components and support. Concept / Approach: Modern Ethernet supports twisted pair and fiber, structured cabling (star with switches), and speeds ranging from 10/100/1000 Mbps to multi-gig and 10G/40G/100G+. Its ubiquity ensures diverse NICs, switches, and transceivers. Token-Ring, by contrast, depends on ring/MAU topology and is largely obsolete. Step-by-Step Solution: 1) Compare topologies: Ethernet works best in switched star and scales hierarchically.2) Compare speeds: Ethernet supports many standardized rates.3) Compare ecosystem: Ethernet dominates the market, ensuring interoperability and availability.4) Choose Ethernet for maximum options. Verification / Alternative check: Review common enterprise deployments: structured cabling with Ethernet switches is the norm, from small offices to data centers. Why Other Options Are Wrong: Token-Ring at 4/16 Mbps does not “fit any topology” and is obsolete.Ethernet is not fiber-only; copper is common (Cat5e/Cat6/Cat6A).Using a MAU does not make Token-Ring broadly flexible.ARCnet is niche and dated, not the preferred universal choice. Common Pitfalls: Equating legacy coax bus with modern Ethernet; overlooking that switching eliminated collisions and expanded topological flexibility. Final Answer: Ethernet with multiple topologies and speeds.

Question 16

Commercial data communications monitors (software tools for analyzing protocol traffic and sessions) include which of the following?

Accepted Answer

Introduction / Context: A data communications monitor is software that observes, captures, and analyzes traffic and protocol exchanges—often used for troubleshooting, performance tuning, or session auditing. Historically, various commercial tools targeted mainframe, minicomputer, and LAN environments to decode and summarize sessions across terminal and network protocols. Given Data / Assumptions: We are identifying examples of software products (not carriers or generic terms). Legacy/mainframe ecosystems had proprietary monitoring suites. Only one option is to be selected as the best-known example. Concept / Approach: Among the listed names, ENVIRON/1 is a recognized commercial communications monitor package from historical enterprise environments. The other choices either do not clearly map to established monitoring products or refer to a service provider rather than a software monitor. Step-by-Step Solution: 1) Filter names that correspond to known software monitor products.2) Identify Telenet as a network service provider brand, not a monitor.3) Select ENVIRON/1 as a valid example of a comms monitor.4) Conclude that ENVIRON/1 best fits the definition in this list. Verification / Alternative check: Historical catalogs and enterprise software references list ENVIRON/1 among communications/transaction monitors. The other labels are ambiguous or unrelated to monitoring software. Why Other Options Are Wrong: TOTAL: ambiguous; not a clearly identified communications monitor product in this context.BPL: vague acronym; not a standard monitor product name here.Telenet: a packet-switched network service, not monitoring software.“None of the above” is wrong because ENVIRON/1 is a valid example. Common Pitfalls: Confusing service/network brands with software tools; assuming any acronym implies a monitor. When in doubt, prefer the option with clear historical association to comms monitoring. Final Answer: ENVIRON/1.

Question 17

Collision avoidance requirement: You need a LAN technology that inherently prevents collisions on the medium while providing orderly access. Which option best satisfies this requirement?

Accepted Answer

Introduction / Context: Media access control determines how multiple nodes share a LAN without interfering. Some methods allow contention (collisions may occur and are handled), while others serialize access so collisions do not occur in the first place. Choosing a collision-free method can be important for deterministic latency and legacy equipment compatibility. Given Data / Assumptions: Goal: avoid collisions on the shared medium. Consider classic wired LAN technologies and access methods. Deterministic token-passing is acceptable. Concept / Approach: Token-Ring uses a circulating token; only the station holding the token transmits. Because at most one station transmits at a time, collisions are inherently prevented. In contrast, CSMA/CD (legacy shared Ethernet) allows collisions and resolves them with backoff, while CSMA/CA (wireless) reduces—but does not entirely eliminate—collisions due to hidden nodes and timing limits. ARCnet also uses token passing, but Token-Ring is the canonical answer in common curricula. Step-by-Step Solution: 1) Identify which protocols are contention-based (CSMA/CD, many Ethernet variants) vs. token-based.2) Token-passing implies single-transmitter at any instant → no collisions.3) Choose Token-Ring as the most recognized collision-free LAN method. Verification / Alternative check: Textbooks consistently categorize Token-Ring as collision-free by design. Modern switched Ethernet also avoids collisions per port, but the protocol family historically relied on CSMA/CD for shared segments. Why Other Options Are Wrong: CSMA/CD: collisions are part of the algorithm; they are detected, not prevented.Ethernet: historically used CSMA/CD on shared media; switched Ethernet removes collisions but is not described as a “collision avoidance method.”CSMA/CA: attempts to avoid collisions but cannot guarantee none on a shared wireless medium.ARCnet: also token-based, but far less common; the best single answer in standard curricula is Token-Ring. Common Pitfalls: Assuming modern Ethernet never collides due to switches, which is true per-port but not the same as a token-based MAC that enforces serialized access. Final Answer: Token-Ring.

Question 18

Private-to-public network interconnection via gateways: Which fundamental requirements should such gateways provide to support enterprise DTE access and administration?

Accepted Answer

Introduction / Context: Gateways that connect private enterprise networks to public carriers must allow authorized devices to reach public services while giving administrators the tools to manage access, usage, and expenses. The design focus is on controlled, universal reachability and accountable use—not necessarily on readdressing internal endpoints. Given Data / Assumptions: Enterprises wish to interconnect private LAN/WANs with public networks. Gateways mediate protocol, addressing, authentication, and policy. Administration requires visibility and control over cost and usage. Concept / Approach: Two fundamental needs are: (1) universal accessibility for approved DTEs—ensuring endpoints can reach required external destinations subject to policy—and (2) adequate cost control mechanisms, such as metering, accounting, quotas, and policy enforcement. Address assignment for private DTEs is typically an internal function (e.g., DHCP), not a public gateway obligation, though gateways may perform translation (e.g., NAT) rather than assignment. Step-by-Step Solution: 1) Identify core capabilities that are gateway-centric: accessibility and administrative control.2) Confirm that address assignment for private devices is out-of-scope or handled by internal servers, not mandated by the public interconnect gateway.3) Select the combined option that includes accessibility and cost control. Verification / Alternative check: Real-world deployments include firewalls, NAT/ALG, AAA integration, and usage logging—features aligned with accessibility plus cost/usage control, not device address assignment. Why Other Options Are Wrong: Option a alone omits administrative control and accounting.Option b alone omits the baseline requirement of reachability.Option c misstates a typical gateway role; address assignment is an internal DHCP/DNS task.“None of the above” ignores the dual requirement embodied by option d. Common Pitfalls: Confusing NAT (translation) with DHCP (assignment), and assuming public gateways must manage internal address plans. Final Answer: a and b both.

Question 19

In data communications, what does MAC (Media Access Control) refer to on a shared transmission medium?

Accepted Answer

Introduction / Context: In computer networking, MAC stands for Media Access Control. It addresses the fundamental problem of how multiple devices share a common communication channel (for example, Ethernet). A solid grasp of MAC helps explain collisions, fairness, throughput, and why different LAN technologies behave differently. Given Data / Assumptions: We are discussing local networks with a shared medium or a logical shared medium (e.g., switched Ethernet still applies MAC rules). Focus is on how access to the medium is coordinated, not on higher-layer protocols or physical cabling details. Concept / Approach: MAC defines the rules devices follow to transmit frames so that only one station effectively uses the channel at a time. Classic examples include contention-based schemes (CSMA/CD in early Ethernet) and controlled access (token passing in Token Ring). MAC is Layer 2 (data link) sublayer logic; it does not encrypt, route, or define telephony standards. Step-by-Step Solution: 1) Identify the layer: MAC is part of the data link layer, specifically the MAC sublayer. 2) Identify the problem: multiple stations share a medium; simultaneous transmissions would interfere. 3) Provide the rule set: a MAC method decides who transmits next and when. 4) Result: orderly access, reduced collisions, improved throughput under load. Verification / Alternative check: Consult IEEE 802 standards: 802.3 (Ethernet) defines MAC framing, addresses, and access rules. Token Ring (IEEE 802.5) used token passing. These are classical MAC mechanisms. Why Other Options Are Wrong: A transport-layer encryption scheme: encryption is not MAC; that is a Layer 4/7 security concern. Bit-oriented ISO protocol (e.g., HDLC): that is a specific data link protocol, not the generic concept of media access control. Circuit-switched access standard: telephony access differs from MAC on packet LANs. None of the above: incorrect because a MAC method is exactly the right description. Common Pitfalls: Confusing MAC with physical wiring; assuming MAC implies collisions only (token-based systems are collision-free); mixing MAC with cryptographic Message Authentication Codes (same acronym, different meaning). Final Answer: A method that determines which device may access the medium at a given time

Question 20

Which network application lets a user access and modify remote files as if they were local, without explicit upload/download steps?

Accepted Answer

Introduction / Context: Users often need to work with files that reside on a remote server. Some technologies require explicit transfers, while others provide transparent, mountable access so that applications can open, save, and modify files as if they were local. Given Data / Assumptions: Goal: seamless remote file access and changes. Expectation: no manual upload/download cycle for each change. Concept / Approach: Network File System (NFS) allows a client to mount a remote directory over the network. Once mounted, the remote files appear within the local file system namespace, enabling standard operations (open, read, write) transparently. This differs from file transfer protocols that require discrete copy operations. Step-by-Step Solution: 1) Identify which option offers transparent file access: NFS. 2) TELNET provides remote interactive login, not file mounting. 3) FTP copies files back and forth but does not mount them. 4) DNS resolves names to IP addresses and has nothing to do with file access. Verification / Alternative check: System administrators mount NFS exports (e.g., /srv/share) on clients (e.g., /mnt/share). Standard tools (cp, editors, IDEs) then operate on remote files transparently via the kernel’s NFS client. Why Other Options Are Wrong: TELNET: remote terminal only. FTP: explicit transfers, not transparent editing. DNS: name resolution service, unrelated to files. None: incorrect because NFS fits exactly. Common Pitfalls: Confusing “can edit remote files” via an editor over TELNET/SSH with actual file system mounting; mixing SMB/CIFS and NFS (both provide similar transparency but NFS is the Unix-centric answer here). Final Answer: NFS

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