Computer Science — Chapter 6

Internet & Networking — Network Types, Devices, the Web, Email and Browsers

Why this chapter matters: Chapters 1–3 taught you the machine; this chapter connects machines together — and the papers test the connection vocabulary relentlessly: expansions (LAN, WAN, modem, URL), people (Vint Cerf, Tim Berners-Lee, Ray Tomlinson), and the one-line definitions (router tells the route, gateway connects two different networks). Our verified banks hold 45 questions matching this chapter directly by question text (internet & protocols 18, web terms 13, email 7, network types 3, search engines 3, network devices 1). The device count looks small only because the banks usually ask devices through their expansions — modem, router, gateway, NIC and bridge are all taught here in full, and the lecture’s own quick-fire list is the revision sheet for them. The chapter’s core is Lecture 3 (Sections 4, 7, 8); the ★ blocks (topologies, switch/hub, email protocols and ports, IPv4/IPv6, browsers, wireless) complete what the taxonomy demands and are verified against standard references.

How this chapter relates to the rest of Computer Science: the network devices here plug into the hardware of Chapter 2 (the NIC is a card in the machine; the modem sits between the machine and the wire), the IP address here is built from the bits and bytes of Chapter 3, and the browser here is the program that opens the web pages whose files Chapter 4’s software families classify. The abbreviation family (ISDN, SQL, PNG, BCC) is completed in Chapter 7.

1. What a network is — and the six types, smallest to largest

A network is computers and devices connected so they can share data and resources. The internet itself is the largest network of all: the Internet is a WAN (asked verbatim — “The Internet is a which type of network?” → WAN).

The scope ladder is the memory rule: person → body → campus → building → city → country/world. Mostly only the abbreviations are asked, but if you know the scope you can reconstruct any expansion: PAN is the smallest, WAN the largest, and everything else sits between them in that order.

Intranet vs extranet ★: an intranet is a private network inside one organisation (its own internal web); an extranet extends that private network to trusted outsiders (suppliers, partners). Neither is the public internet.

2. Network devices — and the journey of the internet to your PC

The journey (asked verbatim)

WAN → ISP → Modem → Router → PC. Read it as a sentence: the wide network reaches your ISP (Internet Service Provider), passes through the modem, is directed by the router, and arrives at the PC.

The modem — why it exists at all

• Modem = MOdulator + DEModulator. The bank’s own phrasing: “how is a modulator-demodulator more commonly known?” → modem.
• Data leaves the PC as digital (0/1) and the PC only accepts digital — but the telephone wire in between carries only analog signals (continuous electrical pulses). So the modem translates twice:
  • Modulator converts digital → analog (for the wire). The process is modulation.
  • Demodulator converts analog → digital (back for the PC). The process is demodulation.

Router, gateway, NIC, bridge — the four definitions

• Router — tells the route (the lecturer’s image: traffic signals telling you which way to go so there is no jam). After the modem, the router sends the internet to the PC and its devices.
• Gateway — connects two different networks (asked in PPSC); sometimes works as a translator (like the modem), sometimes as a router.
• NIC = Network Interface Card (asked in a 2025 paper) — connects the network to the system. It is the card inside the machine that plugs it into the network.
• Bridge — connects two networks (the lecturer’s image: a street connecting two neighbourhoods).

Switch and hub ★ (the pair the papers add next to the bridge)

• Switch — connects devices within one network and sends each message only to the device it is addressed to (it learns addresses, so traffic stays private and fast).
• Hub — connects devices within one network but broadcasts every message to every device (older, slower, noisier). Rule: switch = smart and selective, hub = loud and indiscriminate.

Topologies ★ (how the network is wired — the bank asks this)

• Star topology — every device connects to one central hub/switch. Fast and easy to manage, but the central point is the weakness: the bank’s own question asks in which topology a single central-point failure (e.g. a DoS attack on the hub) disrupts the whole network → star.
• Bus topology — all devices share one main cable (the bus); a break in the bus affects the whole network.
• Ring topology — devices form a closed loop; data travels around the ring from device to device.
• Mesh topology — devices connect to many (or all) others; the most fault-tolerant, and the most expensive in cabling.

3. The internet — ARPANET, TCP/IP and the IP address

• Internet = inter + net = interconnected + network.
• It began as ARPANET = Advanced Research Projects Agency Network — a US project during the Cold War (the US–USSR technology race; the USSR launched Sputnik 1 in 1957). First, 4 computers were connected so each could see the other’s data; it grew from university level into the internet.
• Father of the Internet → Vint Cerf.
• TCP/IP — TCP = Transmission Control Protocol, IP = Internet Protocol. Its job: data transmission over the world (e.g. a message from Pakistan to a friend in Saudi Arabia/Dubai goes through TCP/IP).
• Every device on the internet gets an IP address — unique (no one else has yours). Without an IP address you cannot communicate — the lecturer’s image: like travelling abroad without a passport. The IP address is in binary, divided into 4 parts, converted to decimal for reading.
• The bank asks: “Which is used to give IP address to devices?” — the answer family is the addressing protocol (DHCP in the full syllabus); the chapter fact to lock is the address itself: unique, binary, 4 parts, read in decimal.

IPv4 vs IPv6 ★

• Commerce conducted through the internet is called e-commerce (asked verbatim).
• Internet etiquette: typing in all capital letters is considered shouting / rude (asked verbatim).

4. The web — WWW, URL, HTTP, HTML, DNS, browsers and search engines

The web’s building blocks (all from Lecture 3 Section 8.1)

• WWW = World Wide Web (also called W3). Made by Tim Berners-Lee in 1989. He also gave URL, HTTP, HTML.
• URL = Uniform Resource Locator — the address of a page (asked: “What is URL?” → its expansion).
• HTTP = Hyper Text Transfer Protocol (Hyper + Text + Transfer + Protocol). The bank asks it twice over: as an expansion and as “an internet service through which” web pages are fetched.
• HTML = Hyper Text Markup Language (Hyper + Text + Markup + Language) — the language web pages are written in (asked: “HTML is used for” → creating/web pages).
• DNS = Domain Name System — the naming system mapped onto IP addresses: it turns a name you type (like gk360.pk) into the IP address the network needs.
• HTTPS = HTTP over TLS (secure) — the encrypted version of HTTP. Default ports ★: HTTP = 80, HTTPS = 443 (the bank asks both: “The HTTP protocol works on which port by default?” → 80; “Which is default port of http” → 80).
• A hyperlink is the link that provides the facility to go to another website page (asked verbatim).
• Website surfing is done by a browser (asked verbatim) — and fake traffic on a website is called bot traffic in the standard terminology (the bank’s “fake traffic” question; the chapter keeps the standard term, not the paper’s options).

Browsers ★

A browser is the program that fetches and displays web pages. The history the papers draw from:

• First web browser: WorldWideWeb (later renamed Nexus), by Tim Berners-Lee, 1990.
• Mosaic (1993) — the first widely used graphical browser, the one that popularised the web.
• Today’s browsers: Google Chrome, Mozilla Firefox, Microsoft Edge, Apple Safari, Opera. The bank’s trap: “Which of the following is NOT a web browser?” — read the options; a file manager, a search engine or an operating system in the list is the answer, not a browser name.
• Do not confuse browser with search engine: the browser is the program you open; the search engine is the website you search on inside it. (A “file browser” that browses disks, folders and files is a different program again — the operating system’s file manager, not a web browser.)

Search engines

• Lecture order: #1 Google, #2 Bing, #3 Yahoo (asked in order).
• The bank’s “largest search engine of the internet” → Google; “second largest search engine” → Bing (the lecture order, bank-confirmed).
• First search engine ★: Archie, 1990 (Alan Emtage, McGill University) — it indexed file names on FTP servers, before the web itself. If a paper’s options offer only modern engines, the largest/modern answer is Google; the historical first is Archie.

Wireless ★ (one line each — the modern LAN and PAN)

• Wi-Fi — wireless LAN: devices connect to a network by radio instead of cables (the home router’s wireless side).
• Bluetooth — short-range wireless PAN: one person’s devices (phone, headphones, watch) talking to each other over a few metres.

5. Email — the address, spam, and the protocols behind it

• Email = Electronic Mail — first sent in 1971 by Ray Tomlinson (asked: “Email was invented by” → Tomlinson; Lecture 2 repeats the same fact).
• An email address has two parts: name + @ + service provider (e.g. name@gmail.com, name@yahoo.com). The bank asks: “The symbol used to separate username and domain in an email address is” → @.
• Asked MCQ: the two things in an email (login) → email name and password.
• Spam = unsolicited bulk email (emails arriving in bulk, unasked).
• BCC = Blind Carbon Copy — the copy whose recipients stay hidden from the other recipients (asked: “What does BCC stand for in email?”). The bank’s “Which option hides email contents” question belongs to this family (BCC hides recipients, not contents — read the options).
• CC = Carbon Copy — the visible copy, where every recipient sees the others.

Email protocols and ports ★ (verified against standard references)

• The bank asks: “Which network protocol is used to send email?” → SMTP; “Which of following protocol is used for Email” → the protocol matching the question’s direction (sending = SMTP, reading = IMAP/POP3).
• Rule: SMTP sends, IMAP syncs, POP3 downloads. If you read mail on two devices, you are on IMAP; if it vanishes from the server after one download, that is POP3.

Security one-liner (from the lecture)

• Asked: what is needed for hacking — networking, computer, internet? → all of these. (The chapter teaches it as a definition question, not as instruction: hacking needs all three present.)

5A. Telecom & connectivity ★ — satellite, fibre, GPS and the phone network (PMS 2026 Computer & IT mock residue)

The mock’s last block (Q74–Q99) tests connectivity beyond the office network — the phone system, the satellite link and the cable itself. None of it was in this chapter before; all of it is standard textbook material, verified against standard references (named in the footer). No 🔁/⭐/🆕 mark is claimed on this section: its bank evidence is the single 99-item mock plus at most a handful of loose whole-text rows per term in the verified banks (script hidden_files/goldmine-notes-count-cs06-telecom-mock.py — 652 files / 55,297 questions; strongest term “fiber optic” 16 rows / 13 files including the mock, 5 loose rows / 5 files without it), below both 🔁 limbs.

• Bandwidth measures network speed — how much data can travel in a given time (bits per second). Higher bandwidth = faster connection, not more storage and not CPU speed. A fibre-optic cable’s bandwidth is high — that is the whole point of fibre.
• Telecommunication signals can be analog or digital — the modem in Section 2 is the analog/digital boundary: the PC speaks digital, the old telephone wire speaks analog. Modulation is the general name for encoding information onto a carrier signal; the modem’s modulator is the digital→analog case.
• A telecommunication network includes wired and wireless links — both. Wired = cables (below); wireless = radio (Wi-Fi in Section 4, WiMAX below, mobile networks below).
• Router (telecom sense) — forwards packets of data between networks toward their destination. Same device as Section 2’s “tells the route”; the packet-forwarding wording is the definition papers use when the options offer storage or display instead.
• Ping is the command that checks connectivity to another device — it sends echo requests and waits for replies. If the replies come back, the route is alive; it does not open, delete or format anything.
• PSTN = Public Switched Telephone Network — the traditional circuit-switched telephone network: a dedicated circuit is set up between the two callers for the duration of the call. VoIP = Voice over Internet Protocol, also called IP Telephony — voice calls carried over the internet instead of over PSTN lines (Chapter 7 carries the expansion; this is the working definition).
• Mobile generations: 4G and 5G are mobile telecommunication networks — successive generations of cellular data (Chapter 7’s 5G one-liner: the fifth generation, much faster than 4G, built for IoT and real-time use). They are networks, not browsers, satellites or cables.
• WiMAX = Worldwide Interoperability for Microwave Access — broadband wireless access over radio waves: base stations serve subscribers over kilometres where laying cable is impractical. The long-range wireless cousin of Wi-Fi, not a fibre or LAN technology.
• LAN cables: CAT5 / CAT6 — twisted-pair Ethernet cables: pairs of insulated copper wires twisted together so interference cancels. Cat5e carries 1 Gbps over 100 metres; Cat6 carries 1 Gbps over 100 metres and 10 Gbps to about 55 metres. The twist is the tell: if the options offer fibre, coaxial or USB, the twisted-pair answer is CAT5/CAT6.
• Multiplexing — combining multiple signals for transmission over one medium, so many signals share a single channel instead of each needing its own. “Multiplexing allows” → multiple signals on one medium.
• Satellite communication needs three parts: a ground station, the satellite, and a receiver — all three, not any one alone. Telecommunication satellites orbit the Earth; the uplink sends the signal from the ground up to the satellite, and the downlink brings it back down. Reversing uplink and downlink is the classic slip.
• Fibre optics carry data as light signals through thin strands of glass (plastic fibre also exists — hence the mock’s “both” answer for the core material). They give very high bandwidth and reduce signal loss over distance, which is why they are the backbone of high-speed internet links.
• GPS = Global Positioning System — satellites in space, ground stations (the control segment that tracks and corrects them) and receivers. A GPS receiver provides location, time and speed from the satellite signals — all three, not location alone.
• TCP/IP is the telecommunication protocol used for internet communication (Section 3’s full treatment) — not LAN-only, WAN-only or Bluetooth.
• DNS translates both ways: the Section 4 direction (domain name → IP address) is the one you use every day, and reverse DNS maps an IP address back to a name — hence the mock’s “both” answer.
• MAC address identifies the network interface — the hardware address burned into the NIC (Section 2’s card). IP addresses can change; the MAC address identifies the interface itself.
• Two-factor authentication improves security — a second verification step (typically a code) after the password. It does not speed the connection or add storage.
• Social-media one-liners: a hashtag labels a post with a keyword — it emphasises keywords, categorises topics and drives trends (all three); privacy settings protect photos, personal info and posts (all three).
• Email one-liners: the attachment size limit is generally set by the email service (provider), not by sender, receiver or connection speed; an email signature can include name & designation, contact info and a legal disclaimer (all three).
• Cloud storage examples: Google Drive, Dropbox and OneDrive — all three are cloud storage (Chapter 7’s cloud one-liner: rented computing over the internet; these are its storage face). VPN protects data privacy — it tunnels traffic so it cannot be read in transit (Chapter 7 carries the expansion; this is the job).

6. Master table — the whole chapter in one view

7. Rapid-fire one-liners

• Network ladder → PAN, BAN, CAN, LAN, MAN, WAN (person → body → campus → building → city → world).
• Internet journey → WAN → ISP → Modem → Router → PC.
• Modem → MOdulator + DEModulator; modulator digital → analog; demodulator analog → digital.
• Router → tells the route; gateway → two different networks; NIC → Network Interface Card; bridge → two networks.
• Switch → one addressed device; hub → broadcasts to all.
• Star topology → central point; its failure kills the network.
• ARPANET → Advanced Research Projects Agency Network; first 4 computers; Sputnik 1 → 1957.
• Father of the Internet → Vint Cerf.
• TCP → Transmission Control Protocol; IP → Internet Protocol.
• IP address → unique, binary, 4 parts, decimal to read.
• IPv4 → 32 bits; IPv6 → 128 bits.
• WWW → World Wide Web (W3), Berners-Lee, 1989.
• URL → Uniform Resource Locator; HTTP → Hyper Text Transfer Protocol; HTML → Hyper Text Markup Language; DNS → Domain Name System.
• HTTP port → 80; HTTPS port → 443.
• First browser → WorldWideWeb (Nexus), 1990; first search engine → Archie, 1990.
• Search engines → Google, Bing, Yahoo (in that order).
• Email → Electronic Mail, 1971, Ray Tomlinson; address = name + @ + provider.
• Spam → unsolicited bulk email; BCC → Blind Carbon Copy.
• SMTP → sends; IMAP → syncs on server; POP3 → downloads to one device.
• E-commerce → commerce through the internet.
• Bandwidth → network speed; fibre bandwidth → high; fibre → light signals, low signal loss.
• PSTN → Public Switched Telephone Network; VoIP → IP Telephony.
• WiMAX → broadband wireless access; CAT5/CAT6 → twisted-pair LAN cables.
• Multiplexing → multiple signals on one medium.
• Satellite link → ground station + satellite + receiver; uplink → ground to satellite.
• GPS → satellites + ground stations; receiver gives location, time, speed.
• Ping → checks connectivity; two-factor → security; 4G/5G → mobile telecom networks.
• Email attachment limit → set by the email service; signature → name, contact, disclaimer.
• Internet = WAN; all-caps = rude; hacking needs all three.

8. Most-asked facts (from our verified past-paper banks)

• Internet & protocols (18 questions): the function of the internet (asked three times in the same wording), “INTERNET is” (interconnected network), the IP address (unique; “which is used to give IP address to devices”), e-commerce, and the largest/second-largest search engine pair (counted here by first-match — they are the search-engine block’s most repeated questions). The Shimshal Valley internet-provider question and the “which country’s people use more internet” pair are current-affairs-flavoured internet questions filed here by their wording.
• Web terms (13 questions): WWW’s expansion and inventor (Berners-Lee, asked twice in different wordings), URL’s expansion, HTTP’s expansion and its port 80 (asked twice), HTML’s use, the hyperlink, website surfing by browser, and the “NOT a web browser” trap.
• Email (7 questions): the inventor (Tomlinson), the @ separator, BCC’s expansion, the email-sending protocol (SMTP family), and “which one is an email address?” (the address with name + @ + provider).
• Network types (3 questions): “The Internet is a which type of network?” (WAN) and two topology questions — including the star-topology central-failure question, the single most teachable topology fact in the banks.
• Network devices (1 question by direct text): the modulator-demodulator → modem question. The other devices (router, gateway, NIC, bridge) are taught at full lecture depth here even though the banks phrase them through options rather than question text — the lecture’s quick-fire list is their revision sheet.
• Search engines (3 questions by direct text): “Google is”, “A Search Engine is”, “‘Google’ is” — the engine-identity family; the largest/second-largest pair sits in the internet bucket by first-match.

9. Traps & confusions

• Browser vs search engine vs file browser: browser = the program (Chrome, Firefox); search engine = the site inside it (Google, Bing); file browser = the OS tool for disks and folders. Papers mix all three in one option list.
• First browser vs first popular browser: WorldWideWeb/Nexus (1990) is the first ever; Mosaic (1993) is the first widely used graphical browser. “First introduced among the options” papers often answer Mosaic — read whether the question asks for the first ever or the first popular one.
• First search engine vs largest search engine: Archie (1990) is the historical first; Google is the largest today. The bank’s “first search engine in internet” question is answered historically by Archie; a paper offering only modern engines wants Google.
• Gateway vs bridge: both “connect networks” — gateway connects two different networks (and translates); bridge connects two networks of the same kind (two neighbourhoods). The word “different” is the gateway’s tell.
• Router vs switch: router tells the route between networks; switch directs within one network to one addressed device. Hub broadcasts to all — the switch’s opposite.
• Modulator direction: modulator = digital → analog (out to the wire); demodulator = analog → digital (back to the PC). Reversing them is the classic slip.
• SMTP vs IMAP vs POP3: sending = SMTP; reading on many devices = IMAP; downloading to one device = POP3. A question about “which protocol is used to send email” is SMTP even when IMAP and POP3 sit in the options.
• HTTP 80 vs HTTPS 443: plain = 80, secure = 443. The bank asks the HTTP default twice — answer 80, not 443, unless the question says HTTPS/secure.
• LAN-Ka trap: “Lake Lan-Ka Tso” is a geography question (a Tibetan lake), not a LAN question — the capitalised LAN inside a place name is not a network.
• WAN vocabulary trap: English-vocabulary papers use WAN as a word (“opposite/nearest in meaning to WAN”) — those are English questions, not networking questions, and are excluded from this chapter’s count.
• Internet = WAN, not LAN: a single building’s network is a LAN; the internet spans the world, so it is a WAN by definition.
• Uplink vs downlink: uplink goes up (ground → satellite); downlink comes down (satellite → ground). The mock’s “satellite uplink sends signal from” wants the ground, not the satellite.
• Fibre core — glass, not metal: the core carries light, so it is glass (plastic fibre exists too); a metal option is the trap.
• GPS gives three things: location and time and speed — a “location only” option is incomplete, and the ground stations are part of the system, not an alternative to the satellites.
• BCC hides recipients, not contents: “which option hides email contents” must be read against its options — BCC hides who else got it, not the message text.

10. Memory tricks (from the lectures, plus clean professional aids)

• The journey sentence: WAN → ISP → Modem → Router → PC — say it as one sentence and the order never scrambles: the wide world comes through the provider, through the translator, past the traffic signals, to your PC.
• MO-DE-M: MOdulator + DEModulator = MO-DEM — the name is the definition, split in the middle.
• Digital out, analog wire, digital back: the PC speaks digital at both ends; only the wire in the middle speaks analog. Modulator pushes digital out to analog; demodulator pulls analog back to digital.
• The scope ladder (person → world): PAN fits in your pocket, BAN on your body, CAN on your campus, LAN in your local building, MAN across your metropolis, WAN across the world. First letters in order: P-B-C-L-M-W.
• Passport rule: no passport, no travel abroad — no IP address, no communication on the internet. Unique, like a passport number.
• SMTP sends, IMAP syncs, POP3 pockets: SMTP sends it away; IMAP keeps it synced everywhere; POP3 pockets it on one device. (S-S-P: send, sync, pocket.)
• 80 plain, 443 secure: HTTP’s door is 80; add security and the door number grows to 443 — secure always costs more digits.
• Cerf = father, Berners-Lee = web, Tomlinson = mail: three men, three inventions — Cerf the internet, Berners-Lee the web (WWW, URL, HTTP, HTML), Tomlinson the email (1971, @).
• Google, Bing, Yahoo — 1, 2, 3: the lecturer’s ranking order is itself the mnemonic; largest = first = Google.

11. Visuals (site build specs)

• DIAGRAM — The journey of the internet: WAN → ISP → Modem → Router → PC flow strip, with the modem’s digital→analog→digital translation drawn as a labelled bridge over the telephone wire — placed in Section 2.
• SCALE INFOGRAPHIC — The six network types: person → body → campus → building → city → world scope ladder (PAN, BAN, CAN, LAN, MAN, WAN) with the internet marked at the WAN end — placed in Section 1.
• DIAGRAM — Star vs bus vs ring vs mesh: four mini-topology panels, with the star panel’s central hub highlighted as the single point of failure — placed in Section 2.
• TABLE-GRAPHIC — The protocol & port card: SMTP / IMAP / POP3 rows (job + ports) beside HTTP 80 / HTTPS 443, from the Section 5–6 tables — placed in Section 5.
• TIMELINE — 1957 → 1990: Sputnik 1 (1957) → ARPANET (first 4 computers) → email 1971 → WWW 1989 → first browser and first search engine 1990 — placed in Section 3 as the chapter’s orientation graphic.

12. Practice this topic

• Practice set: 45 verified past-paper questions in the PPSC + FPSC banks are tagged to this topic’s sub-topics (network types 3, network devices 1, internet & protocols 18, web terms 13, email 7, search engines 3) — the site serves them as this chapter’s practice set, with the IBES Computer capsule questions behind them. Note for the set: the largest/second-largest search-engine questions sit in the internet bucket by first-match; the router/gateway/NIC/bridge questions are mostly option-phrased in the banks and are covered by the lecture’s quick-fire list rather than the question-text count; the topology questions (star central failure) sit in the network-types bucket. Companion practice for Section 5A: the PMS Screening 2026 Computer & IT mock (99 items, Sir Adnan booklet, files/pms-papers/pms-2026-gk-computer-it-mock-test.json) — its telecom block (Q74–Q99) and office residues are now taught in Section 5A and in Chapters 2, 3 and 5; bankCount stays 45 (mock items are companion practice, not site-bank questions).
• Book mode: ← Previous: MS Office — Word, Excel, PowerPoint and the Shortcut Keys · Next: Abbreviations & Emerging Basics →

Goldmine Notes · Computer Science · Chapter 6 · Sources: TBT Computer Lecture 3 Sections 4, 7, 8 (network devices, types, internet) + Lecture 2 Section 1.3 (email 1971), IBES Capsule 5 Computer, verified PPSC/FPSC past-paper banks (45 counted questions, answers verified). ★ Topologies, switch/hub, email protocols and ports, IPv4/IPv6, browsers, wireless and first-browser/first-search-engine facts verified against standard references (SMTP 25/587/465, IMAP 143/993, POP3 110/995; HTTP 80, HTTPS 443; IPv4 32-bit dotted decimal, IPv6 128-bit hexadecimal; WorldWideWeb/Nexus 1990, Archie 1990). Section 5A (PMS 2026 Computer & IT mock residue, 3 November 2026): mock booklet items Q74–Q99 + office/telecom residues, verified against standard references via web check 3 November 2026 (PSTN circuit-switched traditional telephone network; WiMAX = Worldwide Interoperability for Microwave Access, wireless broadband; Cat5e 1 Gbps/100 m, Cat6 1 Gbps/100 m and 10 Gbps ~55 m, twisted-pair construction; fibre core glass/plastic carrying light; GPS space + control + user segments). Standard answers only.