3.3 Networks Flashcards
What is a network?
Two or more computers connected together so that they can transmit data between each other.
What are 2 types of network?
local area network LAN
wide area network WAN
What are the characteristics of a LAN?
hardware is privately owned
small geographic area
MAC addresses used to communicate between LAN devices
What are the characteristics of a WAN?
makes use of external or third party hardware
large geographic area
connects to other networks
IP addresses are used for routers to connect networks together
What is the difference between the physical and logical topology?
The physical topology is the layout of the wires or the way in which components are connected whereas logical is about how the data flows and is transmitted.
What are 3 physical network topologies?
bus
star
mesh
What is a bus topology?
A layout where all terminals/devices are connected to a backbone cable. The ends of the cable are plugged into a terminator.
What are the advantages of a bus topology?
cheap to set up
doesn’t require additional hardware
What are the disadvantages of a bus topology?
entire network disconnects if the backbone cable fails
all computers have access to the data transmission
heavy traffic reduces performance and is all transmitted through one cable
What is a star topology?
A layout where all devices are connected to a central node which is typically a switch. MAC addresses are used to uniquely identify each device on the network.
What does MAC stand for?
media access control
What is a switch?
A physical device that receives and forwards data packets between computers/network devices on a LAN to connect them. Recipient’s MAC address is stored in packet headers.
What are the advantages of a star topology?
if one cable fails, only that device is affected
transmits data faster than a bus topology
easy to add new devices
no data collisions
What are the disadvantages of a star topology?
more expensive than a bus topology
if the central switch fails, the entire network disconnects
What is a mesh topology?
A network layout where any node can be connected to any other node. A full mesh is where every node is connected to every other node, otherwise its a partial mesh.
What are the advantages of a mesh topology?
as the number of nodes increases, the speed and reliability of data transmission improves
no single point of failure
What are the disadvantages of a mesh topology?
if wired, lots of cables which is expensive
if wireless, data transmission may be slower or less reliable
network maintenance is difficult and expensive
difficult to add new nodes
What is a protocol?
A set of rules that governs the transmission of data and communication across a network.
Why are protocols important?
So that devices know how to communicate between each other despite having different hardware/software architectures.
What is HTTP(s)?
hypertext transfer protocol (secure) - used for web pages
What is TCP/IP?
transmission control protocol/internet protocol - used for forwarding packets through networks
What is POP3?
post office protocol - used for downloading email
What is IMAP?
internet message access protocol - used for accessing emails on a web server
What is FTP?
file transfer protocol - used for transmission of files through networks
What is the internet?
A network of networks spanning across the world.
What are the 4 layers of the TCP/IP stack?
application layer
transport layer
internet layer
network access or data link layer
What are the advantages of layering?
Each layer performs a specialised function and can be changed without an impact on the rest of the TCP/IP stack as each layer is isolated from the rest.
What happens on the application layer?
Specifies what protocol needs to be used related to the application that’s being sent i.e. HTTP SMTP IMAP POP3 FTP
Encrypts/decrypts messages and transfers to/from the to transport layer when sending/receiving messages.
What happens on the transport layer?
TCP establishes an end-to-end connection between the source and recipient computer
data is split into packets that are labelled with a packet number and port number
this layer requests retransmission of any lost packets
What happens on the internet layer?
the packets are labelled with source and destination IP addresses
routers forward and receive data packets
What happens on the link layer?
adds the MAC address of the source and destination computers to enable the physical connection between the network nodes
if the recipient is in a separate network to the sender, the destination MAC address is the MAC address of the router
What does DNS stand for?
domain name system
What is the purpose of the domain name system?
Translates an easy to remember domain name into the IP address for the website.
What are packets?
Segments of data
What are 3 parts of a packet?
header
payload
trailer
What is the header?
The label that shows the IP addresses, protocol, packet order and time to live (expiry date)
What is the payload?
the raw data
What is the trailer?
A checksum used to detect if errors have happened during transmission
What are the 2 techniques that networks use to exchange data?
packet switching
circuit switching
How does packet switching work?
Data is split into packets which are then each sent on the most efficient route.
What are the advantages of packet switching?
can use checksums to ensure data arrives intact
multiple routes can be used between devices
packets can be transferred over very large networks allowing for global communication
What are the disadvantages of packet switching?
time is spent splitting up data and reconstructing packets
data can’t be reconstructed until all packets have been received without errors
How does circuit switching work?
A direct link is created between two devices. This link is maintained for the entire duration of data transmission. The devices must transfer and receive data at the same rate.
What are the advantages of circuit switching?
data arrives in a logical order so it is quicker to reconstruct
enables 2 users to hold a call without delays in speech
What are the disadvantages of circuit switching?
bandwidth is wasted during periods of time where data isn’t being sent
devices must send/receive at an equal rate
switches can produce electrical interference that corrupts data
What is the purpose of a firewall?
Preventing unauthorised access to a computer network.
How do firewalls work?
Data packets are compared against a set of premade rules to decide whether the traffic should be accepted or rejected/blocked.
What is a proxy?
A server that acts as an intermediary between 2 devices, collecting and sending data on their behalf.
What is a WAP?
wireless access point - device that allows a wireless device to connect to a wired network
What are the advantages of proxies?
user’s privacy is protected so that they can remain anonymous
proxy server can cache frequently used website data making it load faster
can be used by administrators to prevent access to sensitive or irrelevant data
What is a NIC?
network interface card - a device that is built into a computer so it can connect to a network, this assigns the computer a MAC address
What is the format of a MAC address?
48-bit value written as 12 hex numbers
What is a router?
A device that connects together two or more networks and forwards/receives data packets.
What is a gateway?
A device that can translate between protocols allowing networks to communicate even if they don’t use the same protocol.
What is a client-server network?
A network that consists of clients which can request access to data from a central server that stores it.
What are the advantages of client-server?
more secure as data is stored in a secure server (1 location)
only 1 location needs to be backed up
data and resources can be shared between clients
server can manage permissions so different clients can access different data
What are the disadvantages of client-server?
expensive to set up as a server requires a powerful central computer with high processing power
server may require maintenance
all network performance depends on the speed of the server
What is a peer-peer network?
A network in which computers are directly connected to each other and can share files. Each device can both provide and request data.
What are the advantages of peer-peer?
cheaper to set up
allows users to share resources
easy to maintain
not dependent on a central server
no specialist staff requiredWH
What are the disadvantages of peer-peer?
impossible to trace the origin of files
each device must be backed up separately
poorer security
may be difficult to locate resources as they could be on any device
