Networks

A LAN is a network connecting devices within a limited area such as a single building or premises, so the first option is correct. The second describes a WAN, which links distant sites, and the third describes the Internet. The fourth is closer to an extranet, a different notion from LAN, which is a classification by area.

The data amounts to 1×1,000×1,000,000×8 = 8,000,000,000 bits. The effective speed is 100Mbits per second × 50% = 50,000,000 bits per second, so 8,000,000,000 ÷ 50,000,000 = 160 seconds, and the second option is correct. 80 seconds forgets to apply the transmission efficiency, and 320 and 640 seconds underestimate the effective speed even further.

The network name given to a wireless LAN access point is the SSID, and users choose this name to specify where to connect, so the second option is correct. The first is the 48-bit identifier assigned to a NIC, the third is the IP address of the device serving as the exit to outside networks, and the fourth is a name representing an organization on the Internet; none is the connection name of a wireless LAN.

The data amounts to 300×1,000,000×8 = 2,400,000,000 bits. The effective speed is 20Mbits per second × 80% = 16,000,000 bits per second, so 2,400,000,000 ÷ 16,000,000 = 150 seconds, and the third option is correct. 120 seconds forgets to apply the transmission efficiency, 18.75 seconds forgets to convert bytes to bits, and 240 seconds wrongly shrinks the effective speed.

It is the router that looks at IP addresses and selects and forwards along routes between different networks, so the fourth option is correct. A repeater amplifies signals to extend distance, a NIC is the component connecting a computer to a LAN, and a switching hub looks at MAC addresses and sends data only to the destination port within the same network; none of these selects routes between networks.

The data amounts to 600×1,000,000×8 = 4,800,000,000 bits. To send it in 60 seconds requires an effective speed of 4,800,000,000÷60 = 80,000,000 bits per second, and with 80% transmission efficiency the line speed must be 80÷0.8 = 100Mbits per second, so the third option is correct. 80 ignores the transmission efficiency, 64 wrongly multiplies by 0.8 instead, and 125 mixes up the denominator in the calculation.

The data amounts to 512×1,024×1,024×8 = 4,294,967,296 bits. The M in the communication speed means 1,000,000, so the effective speed is 200,000,000×50% = 100,000,000 bits per second, and 4,294,967,296÷100,000,000 is about 42.9 seconds, making the third option correct. About 41 seconds treats 1Mbyte as 1,000,000 bytes, about 21 seconds forgets to apply the transmission efficiency, and about 86 seconds wrongly halves the effective speed.

What may be freely assigned within an organization and cannot communicate on the Internet as is, is a private IP address, so the first option is correct. A global IP address is managed to avoid duplication and can communicate directly on the Internet, a MAC address is the identifier assigned to a NIC at manufacture, and a domain name is a name given for human readability; none of these applies.

The mechanism that converts between names and IP addresses is DNS, so the fourth option is correct. DHCP automatically distributes settings such as IP addresses to connected devices, NAT converts between private and global IP addresses, and NTP sets devices' clocks to the correct time; none of them performs name conversion.

It is DHCP that automatically assigns settings such as IP addresses to connected devices, so the second option is correct. DNS converts between names and IP addresses, FTP is a protocol for transferring files, and NTP is a protocol for synchronizing device clocks; none of them assigns addresses.

A router looks at IP addresses and chooses the route to the destination network, which is the work of the network layer, so the first option is correct. Bridges and switching hubs operate at the data link layer, and repeaters and repeater hubs at the physical layer. A gateway is what handles layers up beyond the transport layer.

A MAC address is a 48-bit identification number assigned to a NIC at manufacture and as a rule does not change, so the third option is correct. The first option describes an IP address, the second a port number, and the fourth a cookie. Staying the same even when the network changes is the big difference from an IP address.

It is HTTPS that combines HTTP with encryption to prevent eavesdropping on and tampering with the communication, so the fourth option is correct. HTTP is the basic protocol for exchanging Web pages but does not encrypt. FTP is for file transfer and POP3 for receiving mail; neither plays the role of encrypted Web communication.

NAT is the mechanism that converts between the private IP addresses used inside the company and the global IP addresses used on the Internet, so the second option is correct. The first describes DNS, the third DHCP, and the fourth a VPN. NAT lets many devices use the Internet with only a few global IP addresses.

It is SMTP that is used for sending mail, so the first option is correct. POP3 and IMAP4 are both protocols for receiving mail: POP3 downloads it to the device for reading, while IMAP4 reads it while it stays on the server. FTP is a protocol for file transfer and is not used for sending or receiving mail.

IMAP4 handles mail while it remains on the server, with read status and folder organization also managed on the server, so it can be read in the same state from multiple devices such as a PC and a smartphone, making the fourth option correct. Encryption and skipping authentication are not IMAP4 features. The third option describes POP3, which downloads to the device.

Addresses entered in Bcc are not shown to the other recipients, so the first option is correct. Addresses entered in Cc or To are visible to all recipients, which would leak the addresses. Reply-To is a field for specifying where replies go and does not change how addresses appear to recipients.

The small data stored in the browser and sent back to the server on the next access is a cookie, used for things like keeping you logged in, so the second option is correct. An RSS feed is a mechanism for distributing site update information, a CMS is a mechanism for managing Web pages without specialist knowledge, and SEO is the effort to rank higher in search results.

The technology that creates a virtual dedicated line over public lines with encryption and authentication is a VPN, so the fourth option is correct. VoIP carries voice over IP networks, LPWA is a low-power wide-area wireless scheme for IoT, and SDN is a technology for flexibly controlling network configuration in software; none creates a secure virtual dedicated line.

Since the other PCs connect normally, the sensible suspicion is a cause specific to that one machine rather than the shared router or line, so checking the cable or wireless connection and the settings, the third option, is the right first step. The first and fourth options contradict the symptoms, which would then affect everyone or other PCs too. The second drags normal users into an outage and is inappropriate.