GCSE Computing - Computer Networks 3

1. © GCSE Computing
Candidates should be able to:
 explain the terms:
 IP addressing
 MAC addressing
 Network packets
 Network protocols
Slide 1
GCSE Computing - 1.6 Computer
communications and networking (3)

2. © GCSE Computing
 An Internet Protocol (IP) address is a unique reference number that is
allocated to devices on a computer network that uses the Internet
Protocol.
 It is used to identify the device that sends data over the network AND
the device that is to receive the data.
 An IP address can be private, (for use on a LAN) or public (for use on
the Internet or another WAN).
 The IP address allocated to a device on a network can be static
(assigned by a system administrator) or dynamic, (assigned by another
device on the network and different each time the connection is made).
Slide 2
What is IP addressing?

3. © GCSE Computing
 Using IPv4, IP addresses are stored as 32-bit numbers, although for our
convenience they are usually displayed as a series of 4 decimal
numbers, each one representing 8 bits of the original binary address.
 Binary version (32-bit):
11001001 0100000 010110100 11111111
 Decimal version:
201.64.182.255
 The new IPv6 IP address system uses 128-bit numbers but for our
convenience they are usually displayed as a series of 8 hexadecimal
numbers, each one representing 16 bits of the original binary address.
 Binary version (128-bit):
001000011101101000000000110100110000000000000000
001011110011101100000010101010100000000011111111
11111110001010001001110001011010
 Hexadecimal version:
21DA:00D3:0000:2F3B:02AA:00FF:FE28:9C5A
Slide 3
What do IP address look like?

4. © GCSE Computing
 In computer networking, a Media Access Control address (MAC
address) is a unique 48-bit number assigned to a network interface
card (NIC) to identify it on a LAN.
 Because they are so long, MAC addresses are usually displayed in
hexadecimal, for example 00-0C-E7-5D-A8-AD.
 MAC addresses are limited to being used on a LAN but IP addresses can
be used on multiple types of networks including the Internet.
 On a LAN, data packets that use a protocol such as TCP/IP will be
packaged inside data packets that use the MAC address to deliver them
correctly.
 Another use for the MAC address is as a security feature on cabled and
wireless systems, only allowing computers with authorised MAC
addresses to have access to the network.
 This works by inspecting the data packet that is sent from a computer to
see if its MAC address matches one of the approved ones in a a pre-
defined table.
Slide 4
What is MAC addressing?

5. © GCSE Computing
Modern computer networks, including the Internet, carry data by breaking it
down into a series of distinct units called packets, rather than sending it
as a continuous stream of data.
A typical packet might contain 1,000 to 1,500 bytes and has two parts:
 Payload
 This is the user data that is to be delivered and is located between the packet
headers and footers.
 Control information
 This provides the data that the network needs to deliver the payload, for
example the source and destination addresses.
 It will also have error checking data such as checksums and the number of
the packet so they can be reassembled in the correct order.
 The control information is found
in the packet headers
Slide 5
What is a Data Packet?

6. © GCSE Computing
 In complex networks such as the Internet, a series of packets sent from
one computer to another may follow different routes to reach the same
destination.
 This technology is called packet switching and makes the network
more efficient because the network can balance the load across various
pieces of equipment and if there is a problem with one piece of
equipment in the network then packets can be routed around it.
 Data packets can be nested inside each other, for example on a LAN, IP
packets are held inside Ethernet packets (that use the MAC address) to
route the packet to the correct destination computer.
 If a packet is destined for the Internet then the Ethernet packet is
discarded when it leaves the LAN.
 When the IP packet returns to the LAN from the Internet then it is placed
inside another Ethernet packet for final delivery to the computer with the
MAC address that requested the information.
Slide 6
What is a Data Packet?

7. © GCSE Computing
 A protocol is a formal description of the format that data has to be in and the
rules for exchanging this data.
 There may also be rules for error checking and error correction. As long as
different computers on a network are using the same protocol then they will be
able to exchange data correctly.
 The Internet Protocol Suite is the set of communications protocols used for the
Internet and other similar networks. It is commonly also known as TCP/IP, named
from two of the most important protocols in it:
 the Transmission Control Protocol (TCP)
 the Internet Protocol (IP).
 The TCP provides the service of exchanging data directly between two
networked computers while the IP is used to route data packets between
networks and over the Internet.
 Some other common Internet Protocols:
 HTTP (HyperText transfer Protocol): used on the World Wide Web for transferring web
pages and files contained in web pages such as images.
 FTP (File Transfer protocol): employed for transferring files between computers.
 SMTP (Simple Mail Transport Protocol): used for email.
Slide 7
What is a Protocol?