Communication

The internet, WWW and bit streaming

Networks including the internet AS Level 15 min read

On this page

What you need to be able to do
The internet and the World Wide Web
Hardware that supports the internet
Bit streaming
Mark-scheme focus
Worked examples
Summary
Can I do this?
Quiz

What you need to be able to do

Syllabus 2.1 Networks including the internet

2.1Explain the difference between the internet and the World Wide Web (WWW).
2.1Describe the hardware that supports the internet: modems, PSTN, dedicated lines, the cell phone network.
2.1Explain bit streaming, real-time and on-demand, and the importance of bit rates and broadband speed.

You need: LAN hardware and routers. Next: IP addresses.

The internet and the World Wide Web

	The internet	The World Wide Web (WWW)
What it is	the global network of interconnected networks: the infrastructure (cables, routers, satellites, protocols such as TCP/IP)	a collection of websites / web pages (and other resources) accessed via the internet, linked by hyperlinks
Made of	hardware + communication protocols	information: pages written in HTML, held on web servers, identified by URLs
Used by	the WWW, email, file transfer, video calls, online games, IoT devices…	web browsers using HTTP / HTTPS

So the WWW runs on the internet; email sent from an app is internet without the WWW, while reading a web page uses both.

When asked whether a task uses the internet, the WWW or both, justify each part. Repeating the question (“because her email is accessed through a website”) scored nothing (June 2021). “Internet: the data travels across the internet's infrastructure. WWW: she is using a website stored on a web server.”

Hardware that supports the internet

How a home reaches the internet.

Hardware	What it does
Modem (modulator-demodulator)	converts digital data into analogue signals for transmission down telephone lines, and converts analogue back to digital at the other end
PSTN (Public Switched Telephone Network)	the traditional telephone network: many different types of communication lines, so digital data may need converting to analogue; data is sent in both directions at once (duplex); connections pass through switching centres / ISPs. Dial-up and DSL broadband use it
Dedicated (leased) line	a direct, private connection between two sites, rented from a telecoms company, not shared, so it provides faster, more reliable and more secure transmission; expensive
Cell phone network	the land is split into cells, each with a tower (base station) and antenna that receives and transmits data; data travels between the tower and the phone wirelessly using low-power radio signals; many devices can communicate with the same tower at once; as a phone moves, it is handed over to the next cell; the towers are linked to the wider network by cables or microwave links

Bit streaming

Bit streaming: a continuous ordered flow of bits over a communication path: the user watches or listens while the data is still arriving, instead of downloading the whole file first.

The video / audio is compressed and uploaded to a media server.
The server sends the data continuously as a series of bits.
On arrival the data goes into a buffer (temporary memory) on the user's device.
The buffer stores data from the server until the device can play it; it smooths out differences between the transmission speed and the playback speed.
The player plays the bit stream from the buffer. If the buffer empties (the connection is too slow), playback stops: buffering.

	Real-time streaming	On-demand streaming
Source	live, direct from the source as it happens (a live match, a video call, a concert)	pre-recorded, stored on the server, watched whenever the user chooses
Control	cannot be paused / rewound / skipped ahead beyond what has happened	can be paused, rewound, fast-forwarded, re-watched
Delivery	plays continually: the data is sent as it is produced; must keep up with real time	the file is sent in sections / blocks; playback can wait for the next block
Compression	usually lossy and fast, so it keeps up	can be compressed in advance, at several qualities

Bit rates and broadband speed

The bit rate of a stream is how many bits per second it needs (e.g. HD video about 5 Mbps). The broadband speed is how many bits per second the connection can deliver. For smooth streaming, the broadband speed must be at least the stream's bit rate (with spare for other users on the same connection); otherwise the buffer empties and the video pauses. Services adapt by sending a lower-quality (lower bit rate) stream when the connection is slow.

1 Can this connection stream it?

A film streams at 8 Mbps. A home connection gives 6 Mbps. What happens?

AskedoutcomeKnowneeds 8, gets 6Routecompare bit rate and speed

Data arrives slower than it is played, so the buffer empties
playback pauses to buffer, or the service switches to a lower-quality (lower bit rate) stream

2 Data used by a stream

A user streams a 5 Mbps video for 1 hour. How many gigabytes is that?

AskedGBKnowbit rate × timeRoutebits → bytes → GB

5 Mbps × 3600 s = 18 000 megabits
÷ 8 = 2250 megabytes = 2.25 GB

3 Download time

How long does a 1.5 GB file take to download at 20 Mbps?

AskedsecondsKnowbytes vs bitsRoute× 8 then ÷ rate

1.5 GB = 1500 MB = 12 000 megabits
12 000 ÷ 20 = 600 s (10 minutes)

Broadband speeds are in bits per second; file sizes in bytes. Multiply by 8 before dividing.

Mark-scheme focus

Define bit streaming; two differences between real-time and on-demand (3 marks)

A video doorbell records video and transmits it to a smartphone. (e) The video doorbell allows both real-time and on-demand bit streaming. (i) State what is meant by bit streaming. [1] (ii) Give two differences between real-time and on-demand bit streaming. [2] — 9618/11/M/J/24 Q2Paper 1 · Theory fundamentalsPart (e)3 marksFull size

Credited

(i) Continuous ordered flow of bits over a communication path B1
(ii) Real-time is direct from source, on-demand is pre-recorded / downloaded to view later B1; real-time cannot be re-watched, on-demand can be paused / re-watched // real-time plays continually, on-demand downloads blocks B1

Not credited

(i) “streaming bits” / “watching videos online”
(ii) one-sided statements (“real-time is live”) with no comparison

From: 9618/11/M/J/24 Q2(e)

Internet, WWW or both? (3 marks)

(d) Melinda sends emails from her webmail account (email account accessed through a website). Explain whether Melinda is using the internet, or the World Wide Web (WWW), or both. [3] — 9618/11/M/J/21 Q4Paper 1 · Theory fundamentalsPart (d)3 marksFull size

Credited

Both B1
Internet: sending data on the infrastructure B1
WWW: accessing a website (stored on the webmail's web server) that is part of the WWW B1

Not credited

“Because her email account is accessed through a website” (repeats the question)
“Both” with only one part justified

From: 9618/11/M/J/21 Q4(d)

Bit streaming: define (1), real-time vs on-demand (2), explain how it works in a video conference (4).
Internet hardware: modems / dedicated lines (2), PSTN (2), cell network (4).

Worked examples

Example 1 · Real-time streaming in a video conference; modems and dedicated lines (Paper 1, 6 marks) ★★ Medium

Programmers take part in live video conferences using real-time bit streaming; the video is compressed before transmission. (a) Explain how data is transferred using real-time bit streaming. [4] (c) The video conference is accessed over the internet. Complete the table by stating how modems and dedicated lines are used when data is transmitted over the internet. [2] — 9618/11/M/J/25 Q2Paper 1 · Theory fundamentalsParts (a) and (c)6 marksFull size

1 Read it with me what is actually happening?

(a) the streaming story: continuous bits → media server → buffer → viewer. (c) one use for each piece of hardware.

real-time bit streaminglive, continuous
how … usedwhat each device does to the data

2 What is it asking for? the target, part by part

(a)4 steps4
(c)modem, dedicated line2

3 What do we know? everything the question gives us

4 Plan the route work backwards from what we want

FindKey ideaAlready have itWork out firstTrap

(a)
- 1transmitted continuously as bits
- 2media server
- 3buffer on the device
- 4viewer plays from the buffer

Why the buffer?

Transmission and playback speeds differ; it stores data until the device can use it.

5 Now solve it have a go on paper first, then open the worked solution

(a) Video is transmitted continuously as a series of bits B1; it is uploaded to a media server and users download from the media server B1
The server sends the data to a buffer on the user's device B1; the buffer stores data until the recipient can receive it (speeds differ) and the recipient views the bit stream from the buffer B1
(c) Modems: convert digital data to analogue for transmission down phone lines (and back) B1; dedicated lines: a direct / private connection, so faster transmission B1

6 Check it does the answer make sense?

(a) is in time order, source to screen ✓.

Example 2 · Bit streaming in a video conference (Paper 1, 4 marks) ★ Easy

(c) The computer on the LAN is used for real-time video conferences, where people communicate in real-time using video and audio. Explain how bit streaming is used in a real-time video conference. [4] — 9618/13/O/N/24 Q9Paper 1 · Theory fundamentalsPart (c)4 marksFull size

1 Read it with me what is actually happening?

The same chain as Example 1 - and compression is credited here as the first step.

2 What is it asking for? the target, part by part

3 What do we know? everything the question gives us

4 Plan the route work backwards from what we want

FindKey ideaAlready have itWork out firstTrap

5 Now solve it have a go on paper first, then open the worked solution

Data is compressed before transmitting B1
The video and audio are transmitted continuously as a series of bits B1
On download, the media server sends the data to a buffer B1
The buffer stores data until the receiving device can process it; the device receives the bit stream from the buffer B1

6 Check it does the answer make sense?

Each point is one link in the chain ✓.

Example 3 · How the cell phone network carries data (Paper 1, 4 marks) ★★ Medium

(b) The smartphones use the cell phone network to connect to the WAN. Explain how data is transmitted using the cell phone network. [4] — 9618/12/M/J/25 Q6Paper 1 · Theory fundamentalsPart (b)4 marksFull size

1 Read it with me what is actually happening?

Cells, towers, radio, many users per tower.

2 What is it asking for? the target, part by part

(b)4 points4

3 What do we know? everything the question gives us

4 Plan the route work backwards from what we want

FindKey ideaAlready have itWork out firstTrap

5 Now solve it have a go on paper first, then open the worked solution

Land is split into cells (designed for maximum line of sight) B1
Each cell has a tower with an antenna which receives and transmits data B1
Data is transmitted between the tower and the phone wirelessly using low-power radio signals B1
Multiple devices can communicate simultaneously with the same tower B1

6 Check it does the answer make sense?

Four separate facts, none repeating “it uses the cell network” ✓.

Example 4 · The role of the PSTN (Paper 1, 2 marks) ★ Easy

(c)(ii) Describe the role of the PSTN (Public Switched Telephone Network) in the transmission of data through the internet. [2] — 9618/12/M/J/24 Q3Paper 1 · Theory fundamentalsPart (c)(ii)2 marksFull size

1 Read it with me what is actually happening?

What the telephone network does to internet data as it passes through.

2 What is it asking for? the target, part by part

(c)(ii)2 points2

3 What do we know? everything the question gives us

4 Plan the route work backwards from what we want

FindKey ideaAlready have itWork out firstTrap

5 Now solve it have a go on paper first, then open the worked solution

The PSTN consists of many different types of communication lines B1 … so digital data may need to be converted to analogue B1
(also: duplex - both directions at once; passes through different switching centres / ISPs)

6 Check it does the answer make sense?

✓

Summary

Internet = the infrastructure (network of networks). WWW = websites and web pages accessed over it.
Modem: digital ↔ analogue. PSTN: telephone network, switching centres, duplex. Dedicated line: private, fast. Cell network: cells, towers, low-power radio.
Bit streaming: continuous flow of bits via a media server into a buffer. Real-time (live, no rewind) vs on-demand (pre-recorded, pause / rewind). Broadband speed must exceed the bit rate.

If you see…	do this
“internet or WWW?”	infrastructure vs websites, justify both parts
“explain bit streaming”	compress → continuous bits → media server → buffer → play
“real-time vs on-demand”	live / pre-recorded; no rewind / rewind; continual / blocks
Mbps and MB	× 8 or ÷ 8 between bits and bytes

Can I do this?

I can explain the difference between the internet and the WWW, and justify which a task uses.
I can describe modems, the PSTN, dedicated lines and the cell phone network.
I can explain how bit streaming works, including the buffer.
I can compare real-time and on-demand streaming and explain why bit rate matters.

Anything unticked: revise that section first. All ticked: take the quiz.

Quiz

The multiple-choice and guided questions need JavaScript. The concept checks and exam practice below work without it.

Concept checks

Answer each one in your head first, then open it.

1Does a video call use the WWW?Show answer

Not necessarily: a video-call app uses the internet's infrastructure and protocols without web pages; a browser-based call uses both.

2Why can't you skip ahead in a live stream?Show answer

The future part hasn't been recorded yet: the data is sent as it is produced.

3Why do streaming services drop the quality when your connection slows?Show answer

A lower quality needs a lower bit rate, which the slower connection can keep up with, so the buffer doesn't run dry.

Exam-style practice

New questions, not used above. Do them on paper, then mark your work against the official mark scheme.

Q1Past-paper style4 marks

A sports club streams its matches live, and also puts recordings online to watch later.

(a)
Give two differences between the live stream and the recordings.
[2]
(b)
Explain the purpose of the buffer on a viewer's device.
[2]

Show the mark scheme

Part	Answer / working	Marks
(a)	Live is direct from the source as it happens; recordings are pre-recorded	B1
	Live can't be paused / re-watched (beyond the present); recordings can be paused / rewound	B1
(b)	Temporarily stores data received from the server …	B1
	… until the device can play it, because the transmission speed and playback speed differ / so playback is smooth	B1
Total: 4 marks

Q2Past-paper style2 marks

Explain the difference between the internet and the World Wide Web.

Show the mark scheme

Part	Answer / working	Marks
	The internet is the global network of interconnected networks / the infrastructure	B1
	The WWW is the collection of websites / web pages accessed using the internet	B1
Total: 2 marks

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