SENG1050 Chap.1 The Internet, Networks and Protocols
The Internet, Networks and Protocols
This chapter follows the Week 1 lecture on how the Internet carries data. It defines a network and the Internet as a network of networks, compares local and wide area networks, and sets out the shapes a LAN can take.
It then compares the switching methods, separates routing from forwarding, and explains TCP, IP addressing in binary and CIDR notation, DNS, SMTP and the HTTP request and response lines, ending with why the Web is not the Internet. Lab 1, which runs in Week 2, turns the same ideas into practice by reading HTTP headers and finding the addresses a computer uses.
What this chapter covers
- 01
Networks and the network of networks
- 02
LAN versus WAN and the five topologies
- 03
Intranet, extranet and VPN
- 04
Circuit, message and packet switching
- 05
Routing versus forwarding and overrun
- 06
TCP, IP and port numbers
- 07
IPv4 in binary, CIDR and IPv6
- 08
DNS, SMTP and HTTP status classes
Worked example · free
Compare star and mesh topologies for a small office
- 1In a star, every computer connects to one central switch, so four computers need four cables, one each.
- 1In a full mesh, every pair of computers has its own link. Four computers form six pairs, so six cables are needed.
- 1The star depends on its central device: if the switch fails, every computer loses its connection. A mesh has no single central point.
- 1For a budget office the star is the sensible choice, because it is cheaper to cable and easier to manage, accepting the risk of the central switch.
Key terms
- Network
- A network is a group of connected computing devices that can transfer information between them rapidly.
- Internet backbone
- The Internet backbone is the core where the largest, fastest networks meet over fibre links and high-performance routers.
- Datagram packet switching
- Datagram packet switching sends each packet independently along its own path, which is the method the Internet uses.
- Router
- A router is a device connected to several networks that chooses paths by routing and moves packets by forwarding.
- IP address
- An IP address is a 32-bit IPv4 identifier, written as four 8-bit decimals, that names one device's connection.
- CIDR notation
- CIDR notation writes an address as a.b.c.d/x, where x is the number of leading bits that identify the network.
- Domain Name System
- The Domain Name System maps memorable names to the numeric IP addresses that routers need.
- Port number
- A port number identifies the application on a host that should receive traffic, such as 80 for HTTP or 443 for HTTPS.
The Internet, Networks and Protocols FAQ
What is the difference between routing and forwarding?
Routing is the work of choosing a path from source to destination, done by an algorithm that builds the router's table. Forwarding is the local step of moving one arriving packet to the correct output, using its header and that table. Answers that merge the two lose marks.
Why does the Internet use datagram packet switching?
Each packet travels independently, so nothing is reserved or blocked, the network stays cheap, and traffic can be re-routed around failures. The cost is that packets can be lost or arrive out of order, so every packet carries a header used to reassemble the message.
How do I convert an IP address to binary?
Treat each of the four decimal blocks separately and write it as eight bits using the place values 128, 64, 32, 16, 8, 4, 2 and 1, padding with leading zeros. Repeated division by two, reading the remainders upwards, gives the same result.
What do the HTTP status code classes mean?
The first digit gives the class. Codes starting with 1 are informational, 2 means success, 3 means redirection, 4 means a client error such as 403 Forbidden or 404 Not Found, and 5 means a server error such as 500 Internal Server Error. Name the class before the specific code.
How is an intranet different from an extranet?
An intranet works like the Internet but is reachable only from inside an organisation, as a private network for staff. An extranet is the part of that network opened to selected outsiders such as suppliers or customers. A virtual private network lets staff reach the intranet securely from outside.
Exam move
Draw the five topologies from memory and write one advantage and one weakness under each. Build a four-row table for the switching methods without looking, then check it. Practise converting two or three IP addresses to binary each day until every block comes out as exactly eight bits. Finish by writing a request line and naming the class of any status code you are given.
When you revise, say aloud why the Web is not the Internet, since the annotated slides repeat that warning.
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