Chapter 2.2 - The internet (AS + A2)

Question 1

list the differences between the following:

the internet and WWW

(hint: think of the former as one big WAN)

Answer 1

1. the internet’s a large WAN of interconnected LANs whereas the WWW’s just a subset of it
2. the internet also uses TCP/IP whereas the WWW uses HTTP(S) written with HTML via web browsers

(more on TCP/IP, HTTP(S), and HTML later)

Question 2

compare the following telephoning methods with each other:

PSTNs and VoIP

(hint: the former uses phone lines whereas the latter uses the internet)

Answer 2

• PSTNs: involve telephone-connected phone lines that stay active until both sides of the connection have hung up (including during a power cut) thanks to circuit-switching w/ modern digitized phone systems using fiber optic cables
• VoIP: involves internet usage booted by packet switching over a non-dedicated line + file compression that makes a VoIP call more efficient than a PSTN one

(more on packet switching later)

Question 3

list the three main types of the following:

satellites

(hint: the mobile nets of today tend to use lower-orbit satellites)

Answer 3

1. GEOs (geostationary satellites that orbit up to 35.8K kms above the Earth’s surface and provide long-distance networking/telecoms over a 24h orbital period)
2. MEOs (~10mid-atmosphere satellites that orbit up to 12K kms above the Earth’s surface and provide GPS services over a 2-12h orbital period)
3. LEOs (>100 lower-atmosphere satellites that orbit up to 2.5K kms above the Earth’s surface and provide mobile networking over a 1-2h orbital period)

(goes to show that satellites can give coverage w/ less signal cutoffs)

Question 4

describe the structure of the following:

IPv4 addresses

(hint: try finding out what your IP address is online)

Answer 4

they contain 4 period-separated octets that altogether make up 32 bits + can be represented in either hexadecimal (e.g. b1.a4.39.c9) or denary (e.g. 177.164.57.201)

(next up: IPv4 network classes~)

Question 5

list the following in terms of address ranges and bit allocation:

IPv4 network classes

(hint: the first three are for general networking)

Answer 5

1. class A (for large networks w/ IP addresses up to 127.255.255.255 + an 8:24 netID:hostID bit allocation ratio)
2. class B (for midsized networks w/ IP addresses up to 191.255.255.255 + a 16:16 netID:hostID bit allocation ratio)
3. class C (for smaller networks w/ IP addresses up to 223.255.255.255 + a 24:8 netID:hostID bit allocation ratio)
4. class D (for multicasting w/ IP addresses up to 239.255.255.255)
5. class E (for experimental networks w/ IP addresses up to 255.255.255.255)

(this is insufficient in terms of range thus leading to CIDR usage)

Question 6

explain how the following makes up for the narrower IPv4 address ranges:

CIDR (classless interdomain routing)

(hint: consider the slash after the 4th octet in some IP addresses)

Answer 6

by flexibly using suffixes to denote the number of bits allocated to the netID (eg. 111.203.12.00/19)

Question 7

describe the structure of the following:

IPv6 addresses

(hint: think back to IPv4’s 32-bit address registers)

Answer 7

they contain 8 colon-separated groups of 4 octets that altogether make up 128 bits + are mainly represented in hexadecimal (eg. B1A4:C9C2:3939:3556:FFF0:C0FE:5E5E:45D0)

(this erases the need for NAT + risk of private IP collisions)

Question 8

how can this IPv6 address be shortened?

a01a:303c:0000:0000:1022:0000:bcde:1973

(hint: look for the zeros in the address)

Answer 8

by zero-compressing it into something like a01a:303c::1022:0000:bcde:1973

Question 9

describe the subnetted basis of the following:

CIDR

(hint: the netIDs are different between subnetworks)

Answer 9

it divides a LAN into subnetworks associated w/ a particular location within a building/campus that each have their own separate netIDs but share the same hostID ranges

Question 10

compare the following IP address types with each other:

public/private

(hint: public IPs are ISP-assigned)

Answer 10

• public IP addresses: ISP-allocated + reachable by normal internet users due to their usage in DNS servers/routers
• private IP addresses: reserved for internal organizational use in 3 classes (A - 10.x.x.x; B - 172.16-32.x.x.x; C - 192.168.x.x) + unreachable by normal internet users as a result of them not taking up public addressing space

Question 11

describe the structure of the following:

URLs

(hint: just look at the address bar of this deck)

Answer 11

protocol://domain/path/filename (protocol - HTTP(S)/FTP/etc.; domain - host.sitename.type(.countrycode); path + filename - webpages + items)

Question 12

list the steps of the following process:

DNS (domain name service)

(hint: web domains tend to be associated with some IP addresses)

Answer 12

1. the browser requests a DNS server for an IP address associated w/ a URL typed in the address bar
2. if the first DNS server can’t find the URL’s associated IP address it forwards the request to another DNS server and so on
3. once the IP address associated w/ the URL’s been found it gets sent back to the computer system the browser’s installed on
4. only with that can the URL’s associated webpages be downloaded through HTML interpretation as required