Which of the following statements about URIs are correct? Select all that apply.

A URL is a URI that locates a resource by its access mechanism

A URN names a resource independently of its location

A URL never changes once published

A URL is a URI that locates a resource by its access mechanism

A URN names a resource independently of its location

URI stands for Universal Retrieval Index

Assertion (A): In a star topology, the failure of the central switch disconnects every node. Reason (R): In a star topology, every node is connected only to the central device. Choose the correct option.

Both A and R are true, and R is the correct explanation of A

Both A and R are true, but R is not the correct explanation of A

Which of the following are ways an intrusion detection system identifies attacks? Select all that apply.

Matching known attack signatures

Detecting departures from normal behaviour

Assigning IP addresses to hosts

Matching known attack signatures

Detecting departures from normal behaviour

Encrypting all traffic with AES

How did S-HTTP differ from HTTPS?

S-HTTP secured individual HTTP messages, whereas HTTPS encrypts the whole connection with TLS

S-HTTP is the newer standard that replaced HTTPS

They are two names for the same protocol

S-HTTP secured individual HTTP messages, whereas HTTPS encrypts the whole connection with TLS

S-HTTP transfers files while HTTPS sends e-mail

ICT in Libraries II: Computer Networks and Topologies; the Internet, Browsers, the Web, E-mail and Search Engines; Internet Protocols and Standards; Hypertext, Multimedia, Video Conferencing and Virtual and Augmented Reality; and Data and Network Security

The second chapter of Unit VII covers items 6 to 10, the networked side of library technology: network topologies and types; the internet, web browsers, the World Wide Web, e-mail, search engines and meta and entity search engines; the protocols and standards the syllabus names, HTTP, S-HTTP, FTP, SMTP, TCP/IP, URI and URL; hypertext, hypermedia, multimedia, video conferencing, virtual reality and augmented reality (the syllabus's "Augmented Technologies"); and data and network security, firewalls, cryptography, anti-virus and anti-spyware software and intrusion detection. As in the previous chapter, the treatment is what a librarian needs to run and protect library systems; the NET Computer Science course goes deeper.

1. Computer networks: topologies and types

Topology	Layout	Strength and weakness
Bus	All nodes on one shared backbone cable	Cheap and simple; a backbone fault stops the network and traffic collides
Star	Every node linked to a central hub or switch	Easy to manage and extend, and one cable fault affects one node; the central device is a single point of failure; the usual LAN layout
Ring	Nodes in a closed loop, data passing round (token ring)	Orderly access; one break can disrupt the ring unless it is dual
Mesh	Nodes interconnected; a full mesh of n nodes needs n(n − 1) / 2 links	Highly reliable with redundant paths; costly to cable
Tree and hybrid	Hierarchies of stars, or combinations	Scales across buildings and campuses

By extent, networks are personal area networks (PAN, a few metres), local area networks (LAN, a building or campus, usually Ethernet under IEEE 802.3 plus Wi-Fi), metropolitan area networks (MAN, a city) and wide area networks (WAN, a country or the world, of which the internet is the largest). Devices include the repeater (regenerates the signal), hub (repeats to all ports), switch (forwards to the right port by hardware address), bridge (joins two LAN segments), router (forwards packets between networks by IP address) and gateway (connects networks using different protocols). The OSI reference model (ISO) describes seven layers, physical, data link, network, transport, session, presentation and application; the internet's TCP/IP model uses four, link, internet, transport and application. A full mesh of 8 library branches would need 8 × 7 / 2 = 28 links, which is why real networks use star and tree layouts.

2. The internet: browsers, the World Wide Web, e-mail and search engines

The internet grew from ARPANET (1969), which adopted TCP/IP on 1 January 1983. Public internet access in India began through VSNL on 15 August 1995. The World Wide Web, a system of hyperlinked documents on the internet, was proposed by Tim Berners-Lee at CERN in 1989; he wrote the first browser and server in 1990, and the web opened publicly in 1991. Browsers render web pages: the graphical Mosaic (1993) popularised the web, followed by Netscape Navigator, Internet Explorer, Firefox, Chrome, Safari and Edge. E-mail predates the web: Ray Tomlinson sent network e-mail in 1971 and chose the @ sign. A search engine has a crawler (spider) that follows links and fetches pages, an indexer that builds an inverted index of words, and a query processor that matches queries and ranks results, as Google's PageRank (1998) did by counting links as votes. A meta search engine sends one query to several search engines and merges their results (examples are Dogpile and MetaCrawler). An entity search engine returns facts about entities, people, places, organisations or products, rather than a list of documents, drawing on knowledge graphs, as in the knowledge panels of major search engines.

⚠️ The internet is not the web

The internet is the global network of networks (1969 onwards); the web (1989-91) is one service that runs on it, alongside e-mail, file transfer and others. A library catalogue reached by a web browser uses the web; a Z39.50 search between two library systems uses the internet without the web.

3. Internet protocols and standards: HTTP, S-HTTP, FTP, SMTP, TCP/IP, URI and URL

Protocol or standard	Function
TCP/IP	The internet's core suite: IP addresses and routes packets (IPv4 uses 32-bit addresses, about 4.3 billion; IPv6 uses 128-bit addresses); TCP provides reliable, ordered, connection-oriented delivery
HTTP	Hypertext Transfer Protocol: the request-response protocol of the web between browser and server; stateless; port 80
HTTPS and S-HTTP	HTTPS runs HTTP over an encrypted TLS connection (port 443) and is now standard; S-HTTP (Secure HTTP), designed in the mid-1990s, instead secured individual messages, and lost out to HTTPS
FTP	File Transfer Protocol for uploading and downloading files (ports 20 and 21); secure variants SFTP and FTPS
SMTP, POP3 and IMAP	SMTP (Simple Mail Transfer Protocol, port 25) sends and relays e-mail; POP3 and IMAP retrieve it from the mail server
URI, URL and URN	A URI (Uniform Resource Identifier) identifies a resource; a URL locates it by its access mechanism, scheme://host:port/path?query#fragment; a URN names it persistently regardless of location, such as urn:isbn:9780306406157

🎯 Why librarians care about URLs breaking

URLs change when sites are reorganised, so citations and catalogue links rot. Persistent identifiers, the DOI, the Handle System, ARKs and PURLs (Unit VIII), add a stable name that resolves to the current URL, which is why citation styles now ask for DOIs.

4. Hypertext, hypermedia, multimedia, video conferencing, virtual reality and augmented reality

Vannevar Bush's essay "As We May Think" (1945) imagined the Memex, a desk that stored a person's records and linked them by associative trails. Ted Nelson coined "hypertext" in the mid-1960s for non-linear text with links, and "hypermedia" when the linked nodes include images, sound and video. Multimedia combines text, graphics, audio, video and animation, often interactively. Video conferencing links participants by live audio and video over networks (standards include H.323 and SIP; everyday platforms carry most of it); libraries use it for webinars, virtual reference, training and remote meetings. Virtual reality immerses the user in a computer-generated environment, usually through a headset; augmented reality overlays digital information on the real world through a phone or glasses; mixed reality lets virtual and real objects interact. The syllabus's "Augmented Technologies" refers to augmented reality technologies: in libraries, AR shelf navigation, interactive exhibits and virtual tours.

5. Data security, network security, firewalls, cryptography, anti-virus, anti-spyware and intrusion detection

Information security protects confidentiality (only authorised people see data), integrity (data are not altered improperly) and availability (systems work when needed), the CIA triad. Threats include malware (viruses that attach to files, worms that spread by themselves, trojan horses disguised as useful programs, ransomware that encrypts data for ransom, spyware and adware), phishing, denial-of-service attacks and exploitation of unpatched software. A library holds patron records and licensed content, so data security measures matter: regular backups kept off-site (the 3-2-1 rule: three copies, on two kinds of media, one elsewhere), access control with least privilege, strong authentication with multi-factor login, encryption, patching and staff awareness. India's CERT-In, the national computer emergency response team under the Ministry of Electronics and IT, issues advisories and handles incidents.

Tool	How it works
Firewall	Filters traffic between networks by rules: packet-filtering (by address and port), stateful inspection (tracks connections), proxy or application-level gateways, and next-generation firewalls that inspect content
Symmetric cryptography	One shared secret key encrypts and decrypts; fast; examples DES and its successor AES
Asymmetric (public-key) cryptography	A public key encrypts and only the matching private key decrypts (Diffie and Hellman, 1976; RSA, 1977); underlies TLS and digital signatures
Hash functions and digital signatures	A hash (such as SHA-256) is a fixed-length fingerprint that changes if the data change, used to check integrity (fixity checks in digital preservation); a digital signature encrypts a hash with the signer's private key, recognised under the IT Act with certificates from licensed Certifying Authorities
Anti-virus and anti-spyware	Detect and remove malware by signatures of known threats and by heuristic or behavioural analysis; must be updated continuously
Intrusion detection system (IDS)	Monitors network (NIDS) or host (HIDS) activity and raises alerts, by matching attack signatures (misuse detection) or spotting departures from normal behaviour (anomaly detection); an intrusion prevention system also blocks

⚠️ A firewall is not an anti-virus

A firewall decides which traffic may pass between networks; it does not clean an infected file that a user opens. Anti-virus software examines files and programs; an IDS watches for attacks in progress. Defence in depth uses all three.

Key takeaways

Topologies are bus, star (the usual LAN), ring, mesh (n(n − 1)/2 links, so 28 for 8 nodes) and tree; networks are PAN, LAN, MAN and WAN; OSI has seven layers and TCP/IP four.
ARPANET (1969) adopted TCP/IP in 1983; India's public internet began on 15 August 1995; Berners-Lee proposed the web in 1989; Mosaic (1993) popularised browsers; Tomlinson sent e-mail in 1971; search engines crawl, index and rank; meta search engines merge several engines; entity search returns facts about entities.
TCP/IP (IPv4 32-bit, IPv6 128-bit), HTTP (port 80), HTTPS (TLS, port 443) versus the older message-level S-HTTP, FTP (20, 21), SMTP (25); a URI identifies, a URL locates, a URN names persistently.
Bush's Memex (1945) and Nelson's hypertext led to hypermedia and multimedia; video conferencing, VR and AR (the syllabus's "Augmented Technologies") support library outreach and navigation.
Security protects confidentiality, integrity and availability with backups (3-2-1), access control, firewalls, symmetric (AES) and public-key (RSA) cryptography, hashes and digital signatures, anti-virus and anti-spyware, and IDS by signature or anomaly.

Practice questions (10)

Attempt each one before opening the answer. Every explanation names the tempting wrong option as well as the right one, because that is where marks are lost.

How many point-to-point links are needed to connect 8 library branches in a full mesh topology? Type the number.
Numerical answer — type the value.
Show answer
Answer: 28
A full mesh of n nodes needs n(n − 1) / 2 links: 8 × 7 / 2 = 56 / 2 = 28. The number grows quickly with n, which is why large networks use star or tree layouts instead.
How many bits long is an IPv6 address? Type the number.
Numerical answer — type the value.
Show answer
Answer: 128
IPv6 addresses are 128 bits long, against 32 bits for IPv4, whose roughly 4.3 billion addresses ran out as devices multiplied.
Which protocol is used to send and relay e-mail between mail servers?
1. HTTP
2. IMAP
3. SMTP
4. FTP
Show answer
Answer: C — SMTP
SMTP (Simple Mail Transfer Protocol) sends and relays mail. IMAP and POP3 retrieve mail from a server to the user, FTP transfers files, and HTTP carries web pages.
A search tool that sends one query to several search engines at once and merges their results is:
1. A subject gateway
2. A meta search engine
3. An entity search engine
4. A web crawler
Show answer
Answer: B — A meta search engine
A meta search engine, such as Dogpile or MetaCrawler, has no index of its own and relays queries to other engines. An entity search engine returns facts about entities, a subject gateway is a human-selected catalogue, and a crawler is the part of a search engine that fetches pages.
Which of the following statements about URIs are correct? Select all that apply.
1. A URL never changes once published
2. A URL is a URI that locates a resource by its access mechanism
3. A URN names a resource independently of its location
4. URI stands for Universal Retrieval Index
Show answer
Answer: B — A URL is a URI that locates a resource by its access mechanism; C — A URN names a resource independently of its location
URI (Uniform Resource Identifier) is the umbrella: URLs locate, URNs name persistently. URLs change often when sites are reorganised, which is why persistent identifiers exist, and URI does not stand for Universal Retrieval Index.
Assertion (A): In a star topology, the failure of the central switch disconnects every node. Reason (R): In a star topology, every node is connected only to the central device. Choose the correct option.
1. Both A and R are true, and R is the correct explanation of A
2. Both A and R are true, but R is not the correct explanation of A
3. A is true, but R is false
4. A is false, but R is true
Show answer
Answer: A — Both A and R are true, and R is the correct explanation of A
Both are true and R explains A. Because each node's only link is to the central switch, its failure leaves every node without a path to the others; a single cable fault, by contrast, isolates only one node.
Public-key cryptography was introduced by Diffie and Hellman in:
1. 2001
2. 1991
3. 1945
4. 1976
Show answer
Answer: D — 1976
Whitfield Diffie and Martin Hellman published the idea of public-key cryptography in 1976, and RSA followed in 1977. 1945 is Bush's Memex essay, 1991 the public opening of the web, and 2001 the adoption of AES.
Which of the following are ways an intrusion detection system identifies attacks? Select all that apply.
1. Assigning IP addresses to hosts
2. Matching known attack signatures
3. Detecting departures from normal behaviour
4. Encrypting all traffic with AES
Show answer
Answer: B — Matching known attack signatures; C — Detecting departures from normal behaviour
An IDS uses signature (misuse) detection and anomaly detection. Encryption protects confidentiality but does not detect intrusions, and assigning IP addresses is the job of DHCP, not an IDS.
How did S-HTTP differ from HTTPS?
1. S-HTTP is the newer standard that replaced HTTPS
2. They are two names for the same protocol
3. S-HTTP secured individual HTTP messages, whereas HTTPS encrypts the whole connection with TLS
4. S-HTTP transfers files while HTTPS sends e-mail
Show answer
Answer: C — S-HTTP secured individual HTTP messages, whereas HTTPS encrypts the whole connection with TLS
S-HTTP, from the mid-1990s, applied security at the level of each message; HTTPS wraps all HTTP traffic in an encrypted TLS session and became the standard, so S-HTTP is now little used. Neither is a file-transfer or e-mail protocol.
Who proposed the World Wide Web at CERN in 1989?
1. Tim Berners-Lee
2. Vannevar Bush
3. Ray Tomlinson
4. Ted Nelson
Show answer
Answer: A — Tim Berners-Lee
Tim Berners-Lee proposed the web in 1989 and built the first browser and server in 1990. Tomlinson sent the first network e-mail, Nelson coined hypertext, and Bush imagined the Memex.