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Level 2 Diploma
Unit 10 Setting up an IT Network
OSI Layers 1 to 4

OSI Physical layer 1
 Network media – the cables/wireless and adapters

OSI Data link layer 2
 Method of transferring data between network adapters
 Organises data streams into frames
 Uses MAC addresses

OSI Network layer 3
 Routes packets between networks
 Uses IP addresses
OSI (Open Systems Interconnect)
model

7 layers

Each layer provides a
service for the layer above
and uses the services of the
layer below

Each layer (except the
physical) attaches a header

Headers provide control
information
Frames

Address used is the 48 bit unique MAC (Media Access
Control) address hard coded into the adapter
Network Layer 3

Data messages are split into smaller packets
 Better chance of successful delivery
 Easier to resend if lost or damaged

Routers
 Choose the path that packets take around the network
 Packets are given a time to live (TTL) to prevent them travelling for ever

Internet Protocol (IP) and IP addressing
 Provides network identification and addressing
 An IP address is a 32 bit binary value expressed as dotted decimal
00001010.00000001.1010000.00001100 is easier as 10.1.80.12
Restricted addresses
Type
Range
Comment
Private
10.0.0.0 – 10.255.255.255
Class A
169.254.0.0 – 169.254.255.255
172.16.0.0 – 169.254.255.255
Class B
192.168.0.0 – 192.168.255.255
Class C
Loopback 127.0.0.0 – 127.255.255.255
Multicast
224.0.0.0 – 239.255.255.255
Reserved 0.0.0.0 - 0.255.255.255
Tests host function
Broadcast to many hosts
Not permitted
128.0.0.0 – 128.0.255.255
Not permitted
191.255.0.0 – 191.255.255.255
Not permitted
192.0.0.0 – 192.0.0.255
Not permitted
223.255.255.0 – 223.255.255.255 Not permitted
I. P Addresses
•11000000101010000000000100000101
•What is a ’bit’?
•192.168.1.5
•www.
Network Address Translation


Private networks connect to the Internet via a
router
Host’s private address is translated to a valid
public address by the router using NAT
 Easier IP configuration
 Hosts protected from direct internet access
 Can map 1:1 or use port addresses to map n:1
ARP and ICMP

ARP (Address resolution protocol)
 Network layer
 Converts IP addresses to MAC addresses
 Converts MAC addresses to IP addresses

ICMP (Internet control message protocol)
 Used for diagnostic and troubleshooting tools
 PING
 TRACERT
TCP and UDP Layer 4

TCP Transmission Control Protocol
 Reliable
 Connection oriented packet transfer

TCP/IP applications use a unique
identification number called a port
 An IP address and a port make a socket
 Socket to socket connections make a path
 http:215.58.254.252:80 where 80 is the port
number
Common port numbers
Port Number
Process Name
Description
20
FTPDATA
File transfer protocol – Data
21
FTP
File transfer protocol – Control
22
SSH
Secure shell
23
TELNET
Telnet
25
SMTP
Simple Mail Transfer Protocol
53
DNS
Domain Name Service
69
TFTP
Trivial FTP
80
HTTP
Hypertext Transfer Protocol
110
POP3
Post Office Protocol 3
119
NNTP
Network News Transfer Protocol
123
NTP
Network Time Protocol
139
NetBIOS
Session port
143
IMAP4
Internet Mail Access Protocol
389
LDAP
Directory Access Protocol
443
HTTPS
HTTP Secure
HTTP and HTML

Hypertext transfer protocol
 Web browsers request resources from web
servers by
○ connecting to port 80
○ Using a Uniform Resource Identifier (URI)
 Common web servers are
○ Apache (open source)
○ Microsoft Internet Information Server (IIS)
 HTTP is used to serve HTML (Hypertext MarkUp
language) pages which describe how the text
should be displayed
SSL/TLS
HTTP is not encrypted and does not
authenticate
 SSL (Secure sockets layer) and TLS
(Transport Layer Security)

 Provide cryptographic security
 Used with HTTPS
○ Uses port 443
○ Puts https:// in the URI
○ Adds a padlock icon in the browser
E-mail
Plain text
 File attachments encoded in MIME
(multipurpose internet mail extensions)
 Send mail out using SMTP

 Simple mail transfer protocol

Receive mail using
 POP3 or IMAP4

Can be secured using PGP (Pretty Good
Privacy or Secure MIME
FTP

File transfer protocol
 More efficient then e-mail
 Plain text transfer
 Most browsers include an FTP client
○ ftp://ftp.microsoft.com/
Instant Messaging

Exchange of
text messages
with contacts
Domain names




Every host on the internet has a unique, 32 bit IP address
For convenience each host also has a Fully Qualified
Domain Name (FQDN)
Domain Name Servers cross reference between domain
names and IP addresses
An FQDN is hierarchical
 www.google.com
local domain
Top level domain
Subdomain
www as a local domain indicates the resource is a web server
 A Subdomain has to be registered and identifies a company,
organisation or individual
Top level domain names
Domain Name
Description
edu
Educational and research institutes
gov
Government agencies
mil
Military institutions
net
Network companies (ISPs)
com
Commercial organisations
org
Other organisations
uk
United Kingdom
au
Australia
jp
Japan
Uniform Resource Identifier

A URI (sometimes known as a URL):
 Has all the information to identify a resource
 http://news.bbc.co.uk/1/hi/sci/tech/8013709.
stm
○ http:// is the protocol being used
○ News.bbc.co.uk is the FQDN
○ /1/hi/sci/tech/8013709.stm is the file path on
the server
email address

An email address consists of:
 The user name
 A separator symbol (@)
 A domain name
○ [email protected]
Task (criteria P5)

You have been asked by a friend to explain
how network communications work in a
company. Describe how hardware, software
and addressing combine to use a web browser
to send an e-mail to another system.
 Include a diagram making sure you show how the
components are connected together
 Make sure you explain:
○ NIC, cable, switches, routers, modems, servers
○ NOS, E-mail client, web browser
○ IP and MAC addresses