Field connectivity, power, networks and IT security

Explanation : WFP leads the ETC at global level, which provides data, secure radio and user support services in emergencies. The ITU is a specialised agency that does not have this lead role.

Explanation : 10 Mbit/s = 10,000 kbit/s; 10,000 / 40 = 250 kbit/s per user, not counting protocol overhead. Hence the value of limiting updates and video streaming during working hours.

Explanation : Stored energy: 4 × 12 V × 200 Ah = 9,600 Wh; usable energy at 50%: 4,800 Wh; autonomy: 4,800 / 400 = 12 hours. 24 hours would assume a full discharge, which damages the batteries.

Explanation : Peak power = 3,000 Wh / (5 h × 0.75) = 3,000 / 3.75 = 800 Wp. 600 Wp ignores system losses (3,000 / 5).

Explanation : HF (3 to 30 MHz) can reach hundreds or thousands of kilometres thanks to ionospheric propagation. VHF is limited by the radio horizon, unless repeaters are used.

Explanation : “Out” ends the communication. “Over” invites the other station to reply; “Over and out” is contradictory and must not be used. “Roger” means the message has been received.

Explanation : A /26 leaves 32 - 26 = 6 bits for hosts: 2^6 = 64 addresses, minus the network address and the broadcast address, i.e. 62 usable addresses.

Explanation : The private ranges are 10.0.0.0/8, 172.16.0.0/12 (172.16.0.0 to 172.31.255.255) and 192.168.0.0/16. 172.32.5.10 is outside 172.16.0.0/12: it is a public address.

Explanation : 2,000 MB × 8 = 16,000 Mbit; 16,000 / 0.512 Mbit/s = 31,250 seconds, i.e. about 8.7 hours. The classic mistake is to forget to convert bytes to bits (factor of 8).

Explanation : The 3-2-1 rule combines redundancy (3 copies), media diversity (2) and protection against a local disaster, theft or fire (1 copy off site or in the cloud).

Explanation : The signal travels about 36,000 km up to the geostationary satellite and the same distance back down, in each direction: round-trip latency generally exceeds 500 ms, which degrades interactive voice. Low Earth orbit constellations greatly reduce this latency.

Explanation : This is typical phishing (impersonation of a senior manager and urgency). Credentials are never sent by email; verify through an independent channel and report it so that the team can block the sender. Forwarding the message spreads the risk.

Explanation : Active power = apparent power × power factor = 1,500 × 0.6 = 900 W. A 1,200 W load would overload this UPS even though it is below 1,500.

Explanation : Least privilege limits the damage if an account is compromised. Multi-factor authentication and defence in depth are complementary but refer to other measures.

Explanation : A copper Ethernet channel is limited to 100 metres. Beyond that, an intermediate switch, optical fibre or a radio link is needed.

Explanation : Channels in the 2.4 GHz band are spaced 5 MHz apart while a signal occupies about 20 MHz: only 1, 6 and 11 do not overlap under most regulations. Adjacent channels cause interference.

Explanation : Iridium uses a low Earth orbit constellation covering the entire globe. Thuraya and Inmarsat rely on geostationary satellites whose coverage is regional or does not reach the polar regions.

Explanation : In RAID 5, the equivalent of one disk is used for parity: (4 - 1) × 2 TB = 6 TB. The volume can withstand the failure of a single disk; RAID does not replace a backup.

Explanation : Without encryption, the disk can be read by connecting it to another computer, whatever the session password. Full disk encryption makes the data unreadable without the key. Antivirus software does not protect against physical theft.

Explanation : A 169.254.x.x address is self-assigned when no DHCP server responds. The DHCP server or router and the cabling must be checked. A DNS or satellite link problem does not prevent a local address from being obtained.