1What is the main purpose of the Domain Name System (DNS)?
Domain Name System
Easy
A.To encrypt messages sent by email
B.To translate domain names into IP addresses
C.To transfer files between computers
D.To connect Bluetooth devices
Correct Answer: To translate domain names into IP addresses
Explanation:
DNS translates human-readable domain names, such as example.com, into IP addresses.
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2Which DNS record maps a domain name to an IPv4 address?
Domain Name System
Easy
A.MX record
B.A record
C.CNAME record
D.NS record
Correct Answer: A record
Explanation:
An A record associates a domain name with an IPv4 address.
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3Which protocol is commonly used to send email from a client to a mail server?
Email
Easy
A.SMTP
B.DNS
C.FTP
D.HTTP
Correct Answer: SMTP
Explanation:
Simple Mail Transfer Protocol (SMTP) is used to send and relay email messages.
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4Which email protocol normally keeps messages on the server and synchronizes them across devices?
Email
Easy
A.IMAP
B.FTP
C.SMTP
D.ARP
Correct Answer: IMAP
Explanation:
IMAP keeps email on the server and synchronizes mailboxes across multiple devices.
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5What is the primary purpose of FTP?
FTP
Easy
A.To send wireless radio frames
B.To resolve names into addresses
C.To transfer files over a network
D.To manage email mailboxes
Correct Answer: To transfer files over a network
Explanation:
File Transfer Protocol (FTP) is used to upload and download files between networked systems.
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6Which two connections are traditionally used by FTP?
FTP
Easy
A.Control and data connections
B.Local and remote connections
C.Input and output connections
D.Voice and video connections
Correct Answer: Control and data connections
Explanation:
FTP uses a control connection for commands and a separate data connection for file transfers.
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7What medium is commonly used to transmit data in a wireless network?
Introduction to Wireless Networks
Easy
A.Coaxial cables
B.Radio waves
C.Copper wires
D.Fiber strands
Correct Answer: Radio waves
Explanation:
Wireless networks commonly transmit data through the air using radio waves.
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8Which device commonly connects wireless clients to a wired local network?
Introduction to Wireless Networks
Easy
A.Network repeater
B.DNS resolver
C.Email server
D.Wireless access point
Correct Answer: Wireless access point
Explanation:
A wireless access point allows Wi-Fi devices to connect to a wired local network.
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9The IEEE 802.11 standards are mainly associated with which technology?
IEEE 802.11
Easy
A.Satellite television
B.Wireless LAN
C.Wired Ethernet
D.Cellular voice
Correct Answer: Wireless LAN
Explanation:
IEEE 802.11 defines standards for wireless local area networks, commonly called Wi-Fi.
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10What does SSID identify in an IEEE 802.11 network?
IEEE 802.11
Easy
A.The device hardware address
B.The Internet protocol version
C.The email account name
D.The wireless network name
Correct Answer: The wireless network name
Explanation:
The Service Set Identifier (SSID) is the name used to identify a Wi-Fi network.
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11Which frequency band is used by IEEE 802.11a?
802.11a
Easy
A.60 GHz
B.900 MHz
C.5 GHz
D.2.4 GHz
Correct Answer: 5 GHz
Explanation:
IEEE 802.11a operates in the 5 GHz frequency band.
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12What is the maximum theoretical data rate of IEEE 802.11b?
802.11b
Easy
A.150 Mbps
B.11 Mbps
C.54 Mbps
D.24 Mbps
Correct Answer: 11 Mbps
Explanation:
IEEE 802.11b provides a maximum theoretical data rate of 11 Mbps.
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13What is the maximum theoretical data rate of IEEE 802.11g?
802.11g
Easy
A.11 Mbps
B.24 Mbps
C.54 Mbps
D.150 Mbps
Correct Answer: 54 Mbps
Explanation:
IEEE 802.11g supports a maximum theoretical data rate of 54 Mbps.
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14Which technology is a major feature of IEEE 802.11n?
802.11n
Easy
A.Token passing
B.Frequency dialing
C.MIMO
D.Circuit switching
Correct Answer: MIMO
Explanation:
802.11n uses Multiple Input Multiple Output (MIMO) to improve speed and reliability.
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15What is a small Bluetooth network with one central device and connected devices called?
Bluetooth Architecture
Easy
A.Subnet
B.Piconet
C.Intranet
D.Ethernet
Correct Answer: Piconet
Explanation:
A piconet is a small Bluetooth network formed by one central device and connected peripheral devices.
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16What is formed when multiple Bluetooth piconets are interconnected?
Bluetooth Architecture
Easy
A.Scatternet
B.Metropolitan network
C.Broadcast domain
D.Virtual circuit
Correct Answer: Scatternet
Explanation:
A scatternet is formed when devices connect two or more Bluetooth piconets.
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17Bluetooth is mainly designed for which type of communication?
Bluetooth Architecture
Easy
A.Underwater cable communication
B.Short-range wireless communication
C.Long-range satellite communication
D.Wide-area cellular communication
Correct Answer: Short-range wireless communication
Explanation:
Bluetooth is designed for short-range wireless communication between nearby devices.
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18Which Bluetooth layer handles radio transmission and reception?
Bluetooth Layers
Easy
A.Application layer
B.Radio layer
C.Service layer
D.L2CAP layer
Correct Answer: Radio layer
Explanation:
The Bluetooth radio layer defines how data is transmitted and received using radio signals.
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19Which Bluetooth layer adapts upper-layer protocols to the lower baseband layer?
Bluetooth Layers
Easy
A.DNS
B.SMTP
C.L2CAP
D.HTTP
Correct Answer: L2CAP
Explanation:
L2CAP provides adaptation and multiplexing services between upper-layer protocols and the baseband.
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20Which Bluetooth protocol emulates a serial cable connection?
Bluetooth Layers
Easy
A.Baseband
B.L2CAP
C.Link Manager
D.RFCOMM
Correct Answer: RFCOMM
Explanation:
RFCOMM provides serial port emulation for Bluetooth applications.
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21A DNS resolver has cached an address record with a TTL of 900 seconds. A client requests the same record 600 seconds later. What should the resolver normally do?
Domain Name System
Medium
A.Discard the record because half its TTL has passed
B.Contact the root server before returning the record
C.Return the cached record with 300 seconds remaining
D.Query the authoritative server and reset the TTL
Correct Answer: Return the cached record with 300 seconds remaining
Explanation:
A cached DNS record remains valid until its TTL expires. After 600 seconds, the record can be returned with seconds remaining.
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22An administrator wants email for example.com to be delivered to mail.example.com. Which DNS record should be configured for example.com?
Domain Name System
Medium
A.An MX record referencing mail.example.com
B.A PTR record referencing mail.example.com
C.A CNAME record referencing mail.example.com
D.An NS record referencing mail.example.com
Correct Answer: An MX record referencing mail.example.com
Explanation:
An MX record identifies the mail server responsible for accepting email on behalf of a domain.
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23A network administrator needs to determine the hostname associated with the IP address 192.0.2.25. Which DNS operation is required?
Domain Name System
Medium
A.A mail lookup using an MX record
B.A forward lookup using an A record
C.An alias lookup using a CNAME record
D.A reverse lookup using a PTR record
Correct Answer: A reverse lookup using a PTR record
Explanation:
Reverse DNS maps an IP address to a hostname using a PTR record, typically under the in-addr.arpa domain for IPv4.
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24A user wants messages and folder changes to remain synchronized across a laptop and a phone. Which protocol is most appropriate for retrieving the messages?
Email
Medium
A.IMAP because it maintains server-side mail state
B.FTP because it preserves mailbox folder structure
C.POP3 because it always synchronizes server folders
D.SMTP because it retrieves and organizes messages
Correct Answer: IMAP because it maintains server-side mail state
Explanation:
IMAP keeps messages and folders on the server, allowing read status, deletions, and folder changes to remain synchronized across devices.
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25An email containing a JPEG attachment must travel through systems originally designed for text messages. Which mechanism enables the attachment to be represented correctly?
Email
Medium
A.SMTP with an appropriate DNS address record
B.IMAP with an appropriate mailbox and folder
C.POP3 with an appropriate retrieval transaction
D.MIME with an appropriate content type and encoding
Correct Answer: MIME with an appropriate content type and encoding
Explanation:
MIME extends email by describing content types and encodings, allowing binary files such as JPEG images to be transmitted safely.
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26An FTP client is behind a firewall that blocks unsolicited incoming connections. Which FTP mode is generally more suitable?
FTP
Medium
A.Active mode, because the server opens both connections
B.Passive mode, because it uses only a control connection
C.Active mode, because it uses only a data connection
D.Passive mode, because the client opens both connections
Correct Answer: Passive mode, because the client opens both connections
Explanation:
In passive FTP, the client initiates both the control and data connections, which works better through firewalls and NAT devices.
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27During an FTP session, a large file is being transferred while the client sends a command to list another directory. Which FTP feature supports this behavior?
FTP
Medium
A.A shared TCP connection with fixed time slots
B.Separate request and response UDP datagrams
C.Separate control and data TCP connections
D.A shared UDP connection with numbered commands
Correct Answer: Separate control and data TCP connections
Explanation:
FTP uses one TCP connection for commands and replies and a separate TCP connection for file transfers or directory listings.
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28Stations A and C can both reach station B but cannot hear each other. Their simultaneous transmissions repeatedly collide at B. Which technique most directly reduces this hidden-terminal problem?
Introduction to Wireless Networks
Medium
A.Using frequency-independent signal amplification
B.Using RTS and CTS before transmitting data
C.Using full-duplex Ethernet collision detection
D.Using DNS caching before resolving addresses
Correct Answer: Using RTS and CTS before transmitting data
Explanation:
RTS/CTS reserves the wireless medium around the receiver, helping stations that cannot hear one another avoid transmitting simultaneously.
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29A company wants wireless clients to communicate with each other and access its wired LAN through a central device. Which network arrangement should it deploy?
Introduction to Wireless Networks
Medium
A.Ad hoc mode with no wireless access point
B.Infrastructure mode with a wireless access point
C.Mesh mode with no connection to the wired LAN
D.Peer mode with a dedicated Bluetooth controller
Correct Answer: Infrastructure mode with a wireless access point
Explanation:
Infrastructure mode uses an access point to coordinate wireless communication and bridge clients to a wired network.
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30A wireless station detects that an IEEE 802.11 channel is busy. Under CSMA/CA, what should it normally do before attempting transmission?
IEEE 802.11
Medium
A.Transmit immediately and detect any resulting collision
B.Send data continuously until an acknowledgment arrives
C.Switch permanently to another channel without listening
D.Wait for the channel and then use a random backoff
Correct Answer: Wait for the channel and then use a random backoff
Explanation:
IEEE 802.11 uses carrier sensing and a random backoff to reduce collision probability because reliable collision detection is impractical over wireless links.
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31A unicast IEEE 802.11 data frame is received correctly, but the sender does not receive the expected acknowledgment. What will the sender normally infer?
IEEE 802.11
Medium
A.The transmission failed and may need retransmission
B.The transmission succeeded and should not be repeated
C.The access point has changed the network's SSID
D.The receiver has permanently left the wireless network
Correct Answer: The transmission failed and may need retransmission
Explanation:
IEEE 802.11 uses acknowledgments for unicast delivery. If an ACK is missing, the sender treats the frame as unsuccessful and may retransmit it.
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32An office has heavy interference from older 2.4 GHz devices and uses only clients compatible with both bands. Why might 802.11a be selected?
802.11a
Medium
A.It operates in 5 GHz and supports up to 11 Mbps
B.It operates in 5 GHz and supports up to 54 Mbps
C.It operates in 2.4 GHz and supports up to 54 Mbps
D.It operates in 2.4 GHz and supports up to 11 Mbps
Correct Answer: It operates in 5 GHz and supports up to 54 Mbps
Explanation:
802.11a operates in the 5 GHz band and has a nominal maximum rate of 54 Mbps, avoiding much of the interference found in 2.4 GHz.
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33An 802.11b client moves farther from its access point and experiences a weaker signal. Which rate adaptation is consistent with the standard's supported data rates?
802.11b
Medium
A.Increase the rate from 11 Mbps to 54 Mbps
B.Reduce the rate from 11 Mbps to 5.5 Mbps
C.Increase the rate from 5.5 Mbps to 150 Mbps
D.Reduce the rate from 54 Mbps to 24 Mbps
Correct Answer: Reduce the rate from 11 Mbps to 5.5 Mbps
Explanation:
802.11b supports rates including 11, 5.5, 2, and 1 Mbps. A client may select a lower rate when signal quality decreases.
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34An 802.11g access point permits an 802.11b client to join the network. What is a likely consequence for the wireless cell?
802.11g
Medium
A.Compatibility is lost, but overall efficiency must increase
B.Compatibility is maintained, but overall efficiency may decrease
C.The access point automatically changes to the 5 GHz band
D.The client automatically gains the full 802.11g data rate
Correct Answer: Compatibility is maintained, but overall efficiency may decrease
Explanation:
802.11g is backward compatible with 802.11b, but protection mechanisms and slower client transmissions can reduce overall network efficiency.
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35An 802.11n access point uses multiple antennas to transmit independent data streams at the same time. Which feature is being applied?
802.11n
Medium
A.Bluetooth frequency hopping
B.CSMA collision detection
C.DNS query multiplexing
D.MIMO spatial multiplexing
Correct Answer: MIMO spatial multiplexing
Explanation:
MIMO spatial multiplexing uses multiple antennas and spatial streams to increase throughput over the same radio channel.
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36An administrator configures an 802.11n access point to combine two adjacent 20 MHz channels. What is the main intended benefit?
802.11n
Medium
A.Higher throughput through a 40 MHz channel
B.Greater security through a 60 MHz channel
C.Lower latency through a 5 MHz channel
D.Longer range through a 10 MHz channel
Correct Answer: Higher throughput through a 40 MHz channel
Explanation:
Channel bonding combines two 20 MHz channels into one 40 MHz channel, increasing available bandwidth and potential throughput.
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37Eight Bluetooth devices must participate actively in a single piconet. How should their roles normally be arranged under classic Bluetooth?
Bluetooth Architecture
Medium
A.Two masters and six active slaves
B.One master and seven active slaves
C.Eight masters with no active slaves
D.Four masters and four active slaves
Correct Answer: One master and seven active slaves
Explanation:
A classic Bluetooth piconet has one master and can support up to seven active slave devices.
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38A Bluetooth device participates in one piconet and also connects to devices in another piconet. What larger arrangement is formed?
Bluetooth Architecture
Medium
A.A basic service set linking access points
B.A collision domain linking Ethernet segments
C.A DNS zone linking authoritative servers
D.A scatternet linking multiple piconets
Correct Answer: A scatternet linking multiple piconets
Explanation:
A scatternet is formed when Bluetooth devices link two or more piconets, with a shared device participating in multiple piconets.
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39Several upper-layer Bluetooth protocols need to share one lower-layer connection, and large packets may require segmentation. Which layer provides these functions?
Bluetooth Layers
Medium
A.Radio
B.RFCOMM
C.L2CAP
D.Baseband
Correct Answer: L2CAP
Explanation:
L2CAP multiplexes upper-layer protocols and performs segmentation and reassembly of packets over Bluetooth logical links.
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40A legacy application expects an RS-232-style serial connection, but it must communicate over Bluetooth. Which Bluetooth protocol is designed for this purpose?
Bluetooth Layers
Medium
A.Service Discovery Protocol
B.L2CAP
C.Baseband
D.RFCOMM
Correct Answer: RFCOMM
Explanation:
RFCOMM emulates serial cable communication over Bluetooth, allowing applications designed for serial ports to operate over a wireless link.
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41A recursive resolver receives an authoritative NXDOMAIN response for api.example.com with a negative-cache TTL of seconds. After seconds, the zone administrator creates an A record for that name, but the resolver is not notified. What response may the resolver legitimately return at seconds?
Domain Name System
Hard
A.A. The new A record, because positive data overrides negative cache entries
B.D. A referral to the authoritative server, because negative answers cannot be reused
C.B. NXDOMAIN, because the cached negative response has not expired
D.C. SERVFAIL, because the authoritative zone changed during the TTL
Correct Answer: B. NXDOMAIN, because the cached negative response has not expired
Explanation:
DNS resolvers may cache an authoritative negative response for its negative TTL. Until , the resolver can return NXDOMAIN without querying the updated authoritative server.
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42A parent zone delegates child.example to ns1.child.example and ns.outside.net. Which handling of address records in the referral is correct?
Domain Name System
Hard
A.A. Include required glue for ns1.child.example; resolve ns.outside.net separately
B.B. Include authoritative glue for both servers because both appear in the NS set
C.C. Omit all glue because recursive resolvers must query every server name independently
D.D. Copy the complete address and alias chains of both name servers into the parent zone so that the referral remains authoritative even if either external zone is unavailable
Correct Answer: A. Include required glue for ns1.child.example; resolve ns.outside.net separately
Explanation:
ns1.child.example is in-bailiwick, so glue is needed to avoid a resolution loop. The address of the out-of-bailiwick ns.outside.net should be obtained through normal DNS resolution.
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43A zone contains both pay.example. CNAME host.vendor.net. and pay.example. MX 10 mail.example.. Ignoring DNSSEC-generated records, what is the fundamental configuration error?
Domain Name System
Hard
A.C. A CNAME cannot coexist with an MX record at the same owner name
B.B. A CNAME target must reside inside the same authoritative DNS zone
C.D. An MX preference value cannot be used when the owner has an alias
D.A. An MX record must always point to the same target as a CNAME record
Correct Answer: C. A CNAME cannot coexist with an MX record at the same owner name
Explanation:
An owner name containing a CNAME generally cannot contain other ordinary resource-record data. The alias and mail-routing records must use different owner names.
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44An SMTP message body contains the logical lines alpha, ., and ..beta. Which sequence must be transmitted after DATA, including the SMTP end marker?
Email
Hard
A.C. alpha\r\n...\r\n....beta\r\n.\r\n
B.A. alpha\r\n..\r\n...beta\r\n.\r\n
C.B. alpha\r\n.\r\n..beta\r\n.\r\n
D.D. alpha\r\n..\r\n..beta\r\n..\r\n
Correct Answer: A. alpha\r\n..\r\n...beta\r\n.\r\n
Explanation:
SMTP dot-stuffing adds one dot to every body line beginning with a dot. A separate line containing one dot terminates the DATA transfer.
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45A forwarder retransmits a message without changing its signed headers or body. SPF fails because the forwarder's IP is not authorized for the original envelope-sender domain. Under what condition can DMARC still pass?
Email
Hard
A.B. A valid DKIM signature has a domain aligned with the visible From domain
B.A. The original SMTP server used port 587 rather than port 25
C.D. DMARC automatically ignores SPF after forwarding and accepts the message whenever its MIME structure and all original Received headers remain unchanged
D.C. The forwarder replaces the envelope sender with any locally valid address
Correct Answer: B. A valid DKIM signature has a domain aligned with the visible From domain
Explanation:
DMARC passes when either aligned SPF or aligned DKIM passes. Unmodified forwarding can preserve a valid DKIM signature even when SPF fails.
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46An IMAP client caches messages by UID. On reconnecting, it finds that the mailbox's UIDVALIDITY value has changed, although several old UID numbers are still present. What is the correct action?
Email
Hard
A.A. Continue using the cache because UIDs are globally permanent
B.D. Retain only entries whose UIDs are smaller than UIDNEXT
C.C. Invalidate the UID-based cache and rebuild mailbox mappings
D.B. Match cached messages using their current sequence numbers
Correct Answer: C. Invalidate the UID-based cache and rebuild mailbox mappings
Explanation:
An IMAP UID is persistent only within a mailbox while UIDVALIDITY remains unchanged. A changed value means old UID-to-message mappings are no longer trustworthy.
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47A client behind a NAT successfully establishes an FTP control connection but sends a PORT command containing its private address. The directory listing then fails. Which change most directly addresses the problem?
FTP
Hard
A.B. Use ASCII transfer mode so the NAT can inspect the listing
B.A. Use passive mode so the client initiates the data connection
C.C. Move the control connection from port 21 to port 20
D.D. Send REST 0 before every command that transfers directory data
Correct Answer: A. Use passive mode so the client initiates the data connection
Explanation:
In active FTP, the server opens the data connection to the address supplied by the client, which fails with an untranslated private address. Passive FTP makes the client initiate both connections.
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48A compressed archive is uploaded through FTP using TYPE A. Its byte count changes and its checksum no longer matches the source. Which explanation and remedy are correct?
FTP
Hard
A.C. Passive mode compressed the data; repeat using active mode
B.D. The server removed FTP framing bytes; repeat using stream mode
C.B. ASCII conversion changed byte sequences; repeat using TYPE I
D.A. Control-channel replies entered the file; use a separate login account
Correct Answer: B. ASCII conversion changed byte sequences; repeat using TYPE I
Explanation:
TYPE A permits text-oriented representation conversions such as line-ending translation. Binary archives must be transferred using image/binary mode, selected with TYPE I.
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49Stations A and C cannot hear each other, but both can communicate with access point B. They simultaneously send RTS frames to B. What limitation of RTS/CTS is illustrated?
Introduction to Wireless Networks
Hard
A.B. Hidden stations become exposed only after receiving an ACK
B.C. The RTS frames can still collide at B, requiring contention and retry
C.A. RTS frames are never subject to collisions because they are short
D.D. The access point combines both overlapping RTS frames, decodes their duration fields, and allocates separate collision-free channels for the subsequent data transmissions
Correct Answer: C. The RTS frames can still collide at B, requiring contention and retry
Explanation:
RTS/CTS reduces the cost and likelihood of hidden-terminal data collisions, but simultaneous RTS transmissions can still collide at the receiver.
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50A transmits to B. Station C hears A and therefore defers, even though C could transmit to D without interfering with reception at B. Which phenomenon is present?
Introduction to Wireless Networks
Hard
A.B. The exposed-terminal problem caused by conservative carrier sensing
B.D. The near-far problem caused by different spreading-code correlations at D
C.C. The capture effect caused by unequal received signal powers
D.A. The hidden-terminal problem caused by asymmetric reachability
Correct Answer: B. The exposed-terminal problem caused by conservative carrier sensing
Explanation:
C is exposed because it unnecessarily suppresses a transmission that would not cause a harmful collision at the intended receivers.
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51In an IEEE 802.11 RTS/CTS exchange, a station cannot hear the sender's RTS but does hear the receiver's CTS. Why should it still defer?
IEEE 802.11
Hard
A.A. The CTS duration updates its NAV for the remaining reserved exchange
B.B. The CTS permanently marks the channel as controlled by the receiver
C.D. Receiving a CTS changes the station's physical carrier-sensing threshold
D.C. Every CTS forces all stations to reset their contention windows to zero
Correct Answer: A. The CTS duration updates its NAV for the remaining reserved exchange
Explanation:
The CTS carries a Duration value covering the remaining data and acknowledgment exchange. A station hearing it sets its Network Allocation Vector and defers virtually.
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52An 802.11 DCF station selects a backoff of slots. It counts down idle slots, then another transmission makes the medium busy. Assuming its own frame has not yet been transmitted, what happens after the medium becomes idle again?
IEEE 802.11
Hard
A.A. It waits one DIFS and resumes with remaining slots
B.D. It immediately transmits because the original DIFS was already observed
C.B. It waits one SIFS and resumes with remaining slots
D.C. It waits one DIFS and draws a new backoff from a doubled window
Correct Answer: A. It waits one DIFS and resumes with remaining slots
Explanation:
The backoff counter freezes while the medium is busy and resumes after the channel is idle for DIFS. A new enlarged contention window is associated with a failed transmission, not ordinary freezing.
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53Why does an 802.11 sender normally not retransmit a broadcast data frame at the MAC layer when one receiver misses it?
IEEE 802.11
Hard
A.C. Broadcast frames receive no per-recipient ACK that could trigger retry
B.B. Broadcast frames are delivered through the access point's wired interface
C.A. Broadcast frames are protected by mandatory RTS/CTS exchanges
D.D. Every receiver sends a delayed cumulative acknowledgment containing reception state for all broadcast frames observed during the current beacon interval
Correct Answer: C. Broadcast frames receive no per-recipient ACK that could trigger retry
Explanation:
802.11 broadcast and multicast data frames are not individually acknowledged. Consequently, the sender lacks MAC feedback for selective retransmission.
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54An 802.11a-only access point transmits beacons normally, but an 802.11b-only client does not discover it. What is the primary reason?
802.11a
Hard
A.C. 802.11b clients reject all access points whose maximum rate exceeds 11 Mbps
B.B. 802.11a suppresses beacon frames unless an 802.11a client probes first
C.A. 802.11a uses a 5 GHz OFDM PHY that the 2.4 GHz client cannot receive
D.D. 802.11a encrypts management frames using a modulation-specific mandatory key
Correct Answer: A. 802.11a uses a 5 GHz OFDM PHY that the 2.4 GHz client cannot receive
Explanation:
802.11a and 802.11b use incompatible PHYs and different frequency bands. Protocol similarity at the MAC layer does not provide radio-level interoperability.
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55Which mapping of legacy 802.11b data rates to physical-layer coding is correct?
802.11b
Hard
A.B. 1 and 2 Mbps use CCK; 5.5 and 11 Mbps use OFDM
B.D. All four rates use OFDM with different convolutional coding rates
C.A. 1 and 2 Mbps use Barker spreading; 5.5 and 11 Mbps use CCK
D.C. 1 and 5.5 Mbps use Barker spreading; 2 and 11 Mbps use OFDM
Correct Answer: A. 1 and 2 Mbps use Barker spreading; 5.5 and 11 Mbps use CCK
Explanation:
Legacy 802.11b uses DSSS with Barker-code signaling at 1 and 2 Mbps, while Complementary Code Keying supports the higher 5.5 and 11 Mbps rates.
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56An 802.11g network's throughput falls after a legacy 802.11b station associates, even though that station sends little application data. What is the best explanation?
802.11g
Hard
A.C. OFDM becomes prohibited for every associated 802.11g station
B.A. The access point must move all traffic from 2.4 GHz to 5 GHz
C.B. Protection exchanges and legacy timing add airtime overhead
D.D. The contention window is permanently doubled for all stations
Correct Answer: B. Protection exchanges and legacy timing add airtime overhead
Explanation:
Mixed 802.11b/g operation may use RTS/CTS or CTS-to-self protection and legacy-compatible timing. These mechanisms consume airtime even when high-rate stations still use OFDM.
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57On an error-prone 802.11n link, which aggregation method permits successful subframes to remain accepted while only corrupted MPDUs are retransmitted using Block ACK information?
802.11n
Hard
A.A. A-MSDU, because all MSDUs have independent PHY preambles
B.B. A-MPDU, because each aggregated MPDU retains its own FCS
C.C. Channel bonding, because each 20 MHz half is acknowledged separately
D.D. Spatial multiplexing, because each spatial stream has an independent ACK
Correct Answer: B. A-MPDU, because each aggregated MPDU retains its own FCS
Explanation:
An A-MPDU contains multiple independently protected MPDUs. Block ACK identifies which MPDUs succeeded, allowing selective retransmission; an A-MSDU is carried inside one MPDU.
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58A Bluetooth device bridges two classic piconets whose masters use different hopping sequences. How does the bridge normally participate?
Bluetooth Architecture
Hard
A.D. It forces both piconet masters to adopt the bridge's native clock
B.C. It merges both masters' addresses into a single scatternet hop sequence
C.A. It time-shares participation and resynchronizes when switching piconets
D.B. It follows both hopping sequences simultaneously on one classic radio
Correct Answer: A. It time-shares participation and resynchronizes when switching piconets
Explanation:
Each piconet has its own timing and hopping pattern. A scatternet bridge participates in multiple piconets by switching context rather than using both hop sequences simultaneously.
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59In a classic Bluetooth piconet, which information primarily determines the channel-hopping sequence and phase followed by connected slave devices?
Bluetooth Architecture
Hard
A.A. The master's device address and native clock
B.C. The strongest slave's address and received signal strength
C.D. The service UUID and L2CAP channel identifier of the active application
D.B. The slaves' averaged clocks and logical transport addresses
Correct Answer: A. The master's device address and native clock
Explanation:
Classic Bluetooth derives piconet hopping behavior from the master's address and clock. Slaves synchronize to the master's piconet timing and hopping sequence.
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60A classic Bluetooth application must discover a remote serial-port service and then exchange a serial-style byte stream. Which protocol sequence is appropriate?
Bluetooth Layers
Hard
A.A. Use SDP for discovery, then RFCOMM over L2CAP for the stream
B.D. Use L2CAP to query every remote application process directly, then bypass RFCOMM and transmit the serial stream as unframed inquiry packets on the physical radio
C.B. Use RFCOMM for discovery, then SDP directly over the baseband
D.C. Use HCI for discovery, then SCO as a reliable serial byte stream
Correct Answer: A. Use SDP for discovery, then RFCOMM over L2CAP for the stream
Explanation:
SDP locates and describes the remote service. RFCOMM provides serial-port emulation and is commonly carried over L2CAP on an ACL logical transport.
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