Transcript Computer communication

Computer communication
Networks
Protocols
Protocol
Meaning
Application
DNS
Domain Name System (Server)
Translates domain names such
as ocr.org.uk into IP Addresses
TLS/SSL
Transport Layer Security /
Secure Sockets Layer
Cryptographic protocols
designed for secure
communications
FTP
File transfer Protocol
For copy files from one host to
another
HTTP
Hypertext Transfer Protocol
For distributing hypermedia files
– essentially web pages
IMAP
Internet Message Access
Protocol
One method for accessing
emails.
POP3
Post Office Protocol (V3)
Another method for accessing
emails – used by webmail
services
Telnet
Allows bi-directional text
communications on a network
Addressing
IP Addresses
• 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).
Addressing
IP Addresses
•
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
Addressing
MAC Addresses
• 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.
Packets
Packets
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.
•
Header
– 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.
– It will also contain the packet sequence number so the packet can be
reassembled in the correct order.
Packets
Packets
Source
Address
Destination
Address
Packet
Sequence
Number
Data
Checksum
Packets
The data is split into
a number of smaller
packets that may take
different routes to
reach the destination.