The server is a
powerful computer
which provides services
or resources required
by any of the clients
A client is a computer
which requests the
services or resources
provided by the server
Different
types of
servers
A file server holds all the data files and
databases and manages backups A print server
may organise printing on different printers An
email server may receive emails, detect and
block spam, distribute emails to users A web
server may host the school’s external website
Roles on
the
network
The client sends
requests to the
server Waits for a
reply Receives the
reply
The server waits for requests from a client
Acknowledges the request The server may need
to pass the request (e.g. for a web page) to
another server – in which case, it becomes the
“client” The data is sent back to the client.
VS
A central backing store is available to
all computers Security is controlled by
the central computer Backup is done
centrally on the server All users are
reliant on the central server Can
support hundreds or even thousands of
users and grow with an organisation.
Requires IT staff to administer and
control
Storage facilities are distributed across all
computers Security is not centrally
controlled Backup must be done
separately for each computer No central
server Easy to set up but most suited to
homes and small businesses. Viruses
easily spread. If one link goes down, then
nothing else is damaged, but computers
are unable to access anything from that
peer.
Peer2Peer
Used for BBC Iplayer and
illegal file sharing sites
as they are difficult to
close down
Cloud
networking
All data is kept on remote
server, to be accessed by
wireless or cabled connections
Each application has
a(some) dedicated
server(s)
If you have Gmail or
Hotmail, you are using
it
Typically on a subscription
basis No need to have the
software installed on a local
machine Can access the
software (and your data) from
any Internet-connected
computer, including mobile
phone applications
Everything backed up by service
provider.Applications can be
accessed from anywhere with
connection
Giving sensitive or important
data to someone else to
look after.
More
vunerable
to hacking
Paymnent needed for
more than an allowed
amount of data
Transmission
methods
Copper cables
Tried and
trusted
Lots of energy
needed, and
signal boosters
needed
Heavy
cables
low
bandwidth
Affected by
electric and
magnetic fields
Fibre opics
Safer
Higher data
transmission
High cost
Low
energy
Not affected by
electric or
magnetic fields
Wireless
Less
secure
Can get it
anywhere
with signal
Easy to
add
devices
Lower data
transmission
Signal can be
blocked easily
Bandwidth: the
amount of data that
can be carried at once,
like water in a ipe
Latency: the delay
between the first
packet of data being
sent, and the first
packet being collected
at the other side
Sometimes packets collide because of
large amounts of data on the line. WHen
this happens, they are corrupted or
lost, then resent
The
internet
A series of
interconnected
networks
Any network in which the
computers communicate using
resources supplied by a “third
party carrier”, such as British
Telecom, is a WAN . It is usually
spread over a large geographical
area
A Media Access Control (MAC) address
is assigned to each Network Interface
Card (NIC) by the manufacturer Your
computer may have more than one
MAC address, e.g. one for ethernet and
one for wireless And a mobile phone
may have two different MAC addresses
– one for wireless and one for
bluetooth
Internet of things:Mobile
devices, parking meters,
thermostats, roads, cars,
supermarket shelves, kitchen
appliances, dogs, cats, contact
lenses, glasses, us, drinks,
clothes, paper
IPV^ is the new
version of IPV4.
IPV4 is currently
running out. These
are like addresses
for your mobile
device
There are 13 DNS “root” servers
worldwide which keep a complete
database of all names and IP addresses
Other DNS servers lower down the
hierarchy hold parts of the database
When a DNS server receives a request
not in its database, it will pass the
request on to another server until it
reaches one with the matching name and
IP address
Phone calls use
circuit switching,
with a dedicated
connection
between the two
callers
The internet uses packet
switching, where data is split
into chunks, and sent down
their individual fastest route
Each packet contains where it is
going, where from, and the
infomation, and some error
checking info
They are all sent with the
same amount of bytes in,
the umber of packets
there are and thier packet
number
IP
addresses
change
whilst
moving
from place
to place
If the client requests it, or if
the server does not recieve
an acknowledgement after a
certain time, packeages are
resent
Routers move packets
along their fastest
route to the
destination
The actual geographical location of a
networked device can be determined by its IP
address If you take your laptop to another
part of town, or to another country, its IP
address will change When you request a web
page, each router along the way uses the
MAC address of the next router to send the
data packet on the next leg of its journey The
MAC address of a NIC never changes
Domain Name System
(DNS) allows web addresses
to be converted to IP
addresses
Wireless
networking
Data
transmission
Commonly uses radio waves
Data should be encrypted
because it is easily
intercepted on wireless
networks
Wireless encryption
standards
Wired equivalent
privacy
Wi-Fi Protected Access (WPA) .
WPA2 Most secure
Wireless hardware
Network Interface Card.
Everything needs these to connect.
Wireless Access Point. Everything needs one of
these to send out an internet signal
Frequencies and channels
802.11
standard
2.4 Ghz, 3.6Ghz, 5Ghz,
4.9Ghz,
5.9Ghz
Each frequency is subdivided into
channels
5Ghz higher data
transmission as fewer
networks on it.
2.4 Ghz is better at moving through
objects and has a wider range.
Encryption
Symetric
Uses the same key to decode and
encode
Asymetric
Public key, used to encode
Private key, used to decode. Only the person the
message is sent to knows the private key.
Two large prime numbers are multiplied
together. The larger the primes, the more
difficult it is to work out the original numbers.
I Know everything I need to about codes
Local area
networks
Generally used in schools
or short range computer
groups
Advantages and
disadvantages
Advantage
Sharing resources like printers saves money
Access files from any computer on the
network
Data is easy to back up, as it is stored on a central
server
Disadvantage
Expensive to purchase the network
hardware
managing a large network is
complicated
Viruses spread more easily throughout the network
Layout
Mesh
Partial
Most computers connected
FUll
All computers connected
Nodes act as routers for each other
Advantages
No single point of failure – It is a self-healing network
Expansion and modification can be done without disrupting the network
Data can be transmitted from different devices simultaneously
Disadvantages
Can involve redundant connections
Expensive to install cabling if using wired connections
Network maintenance and administration is difficult
Star
Advantages
Faster data transfer as there are fewer collsions
If one cable fails then no other computers are
affected
Disadvantages
Requires additional hardware such as central switch
If the central device fails the whole network goes down
Extended star
Star and mesh topologies usually used
together
Wireless mesh networks
In a wireless mesh network, only one node would
need a wired connection. After this, they could be
connected wirelessly. The more nodes using the
network, the more the signal travels. If a node is
within range of three other nodes, it will get three
times the normal broadband. As the distance
betwwen two nodes is halved, the signal becomes four
times stronger
Hardware
Router-Directs packets down the fastest
route
Hub- Sends all incoming packets to all computers on the
network
Switch-Sends all packets to the intended reciever using MAC
addresses
ethernet
Etherernet is a set of rules, or protocols, which which format data for transmission
between computers on the same network
Nodes will wait until a connection is quiet before attempting to send a
message along the connection themselves
Two nodes attempting to transmit simultaneously will stop and each wait a random period before
reattempting
It splits packets into frames, similar to packets, each
containing source and destination adresses and error
checking data
Frames are broadcast to all nodes – only the intended recipient will
open the frame. Others will be discarded
Frames which are detected to contain transmission errors are dropped or resent
Protocols and layers
APPLICATION
TRANSPORT
NETWORK
LINK
The link layer involves all of the
physical hardware connecting
the two hosts.
HTTP HyperText
Transfer Protocol.
Used to access and
receive web pages in
the form of HTML
files on the internet.
FTP File Transfer
Protocol.Used in
the same way as
HTTP
IP Routes the individual packets
The transport layer creates a
connection between two host
computers
TCP Transmission Control Protocol: Breaks up
messages sent over the internet into packets.
It re-assembles the packets at the other end.
Detects errors. Re-sends lost Messages
SMTP Simple Mail Transfer Protocol. Used for
transferreing mail between remote servers.Client
email software sends message to outgoing mail
server Mail server contacts destination mail
server to pass on email using SMTP
PROTOCOL
LAYER
Advantages
Self contained-One layer
can be affected without
having to alter others
All hardwares and
softwares conform to the
same protocols, so are all
compatible