Unit 6 - Communications and Networks Flashcards
What are the two types of cables?
Serial and parallel
What are the advantages of serial cables?
- Reliable over long distance
- Reliable with high frequencies
- Smaller connectors
- Cheaper as fewer wires are needed
What is skew?
Data on different cables within a parallel wire moving at different speeds so that they arrive at their destination at different times, this causes latency and data can be lost
What is crosstalk?
Electromagnetic interference between two cables within a parallel wire causing data to be lost or corrupted meaning it has to be resent
What happens to crosstalk as the frequency is increased?
Becomes more pronounced
What are the disadvantages of serial transmission?
- Two cables have to be added for two way transmission
- Slow as data has to be sent one after the other
What are the two types of data transmission?
Synchronous and asynchronous
Define latency
The time delay that occurs when transmitting data between devices
What is synchronous transmission?
Data is transmitted where the pulse of the clock of the receiving device and the sending devices are in times with one another
What is asynchronous transmission?
Data is transmitted between two devices that do not share a common clock signal
Compare synchronous and asynchronous transmission
Synchronous transmission is quicker and more efficient as asynchronous transmission requires additional bits to be sent which means sending more data and there are gaps between transmission. However, asynchronous transmission is cheaper so it is often used in low speed connections such as between a mouse or a keyboard.
Why are protocols necessary?
All devices involved in communications must agree on the rules of information transfer
What points do protocols cover?
- Standards for physical connection such as cabling
- The rate of transmission
- Data format
- Whether the transmission is synchronous or asynchronous
- Error checking procedures (even or odd parity)
What is bit rate?
The number of bits transmitted in one second over a wired or wireless data link
What is baud rate?
The rate at which the signal in a communications channel changes state
What equation links bit rate and baud rate?
Bit rate = baud rate x number of bits per signal
Why can’t the baud rate ever be higher than the bit rate?
The baud rate is a measure of how many times the signal changes state and the maximum number of times is once for every transition between two bits
What is the difference between baseband and broadband?
Baseband carries one signal at a time, a bit is represented by high or low voltage in the cable.
Broadband carries multiple signals on a fixed carrier wave which means that bits are sent as variations on the wave.
What is broadband?
A measure of the maximum capacity of a communications channel
What is a LAN?
Two or more computers connected together within a small geographic location .e.g. home or office
What is a standalone?
A computer which is not connected to any other computing device
What is a WAN?
Two or more computers connected together and the connection spans a large area .e.g. international
What is a bus topology?
An arrangement where nodes are connected in a daisy chain by a single central communications channel
What is a star topology?
An arrangement where a central switch or hub provides a common connection point for all other nodes and each node has a connection directly to the central hub or switch
What does it mean if nodes are passive?
They do not actively communicate with one another
What happens if two nodes try to transmit at the same time in a bus topology?
CSMA/CA will detect this and halt the transmission from both nodes, each nodes will then have to wait a random amount of time before it can try to transmit again
What are the advantages of a bus topology?
- Cheaper to install than a star topology
- Easier to install than a star topology
- Easy to add new client
What are the disadvantages of a bus topology?
- Not good for large networks
- Low security
- Adding users to the network increases latency
- The main cable failing will affect all the users
- Less reliable than a star network
- More difficult to find faults
What does CSMA/CD stand for and what does it do?
Carrier Sense Multiple Access and Collision Detection. This is a type of software that can be used in wired networks to detect possible collisions and manage transmissions.
What type of software is often used in wireless networks?
CSMA
How does the switch in a star topology send messages to the right device?
Each device contains a Network Interface Card (NIC) and each one of these is encoded with a Media Access Control (MAC) address. The switch will have the MAC address for every device and can cross reference it with the message being sent. It can then send the message to the right computer.
What is the difference between a hub and a switch?
A switch will send messages to individual devices within a star topology where as a hub will broadcast the message to every device within the topology
What are the advantages of a star topology?
- Fast connection as each client has a dedicated cable
- Will not experience the same latency as other topologies when there are many users connected
- It is easier to trace faults
- Each client-server connection is unique so it is relatively secure
- It is easy to add new clients
- A cable failure only affects one client
What are the disadvantages of a star topology?
- Expensive due to extra cables
- A client may not be able to receive data if its cable fails
- Can be difficult to install
- The server can become congested
- The whole network fails if there is a problem with the central server
What is a physical topology?
How the devices in a network are physically connected
What is a logical topology?
The conceptual way data is transmitted around the network and which protocols are used for communications
List the features of a client-server network
- A central server to manage security
- Files held on central server
- Processing tasks performed by central server
- Client issue request to the server for services
- Suitable for many different types of organisation
- May require staff to administer it
List the features of a peer-peer network
- No central server or security
- Suitable for small companies with fewer computers
- All computers can easily access file on others
- All computers communicate directly with one another
- Once a computer is switched off, data cannot be retrieved
Define client
A device which requests services from another device
Define server
A device which provides services to other devices
Describe the process the server takes to provide services to another device
The server waits for a request, acts upon the request by carrying out the necessary processes and then returns the result of these processes to the client
What will happen if a server is unable to perform the processes needed to complete a request?
It will send the request to another server or device to carry out the processes in which case the original server becomes a client
What is cloud computing?
This is a form of computing which employs the use of the internet to store and share files or software which means that it does not have to sit on the user’s hard drive
What are the advantages of cloud computing?
- Does not require any additional software to be downloaded
- Software and data is accessible from any computer
- Software and data are automatically backed up
- Software and data do not take up space on the user’s hard drive
What are the disadvantages of cloud computing?
- If the internet goes down then the cloud goes down too and nothing is accessible
- The cloud is not secure and can be easily hacked
- The ownership of data is unclear once it is uploaded to the cloud
- Little to no customer support
- The cloud management may require their formats and applications to be used
- Can lead to quickly escalating costs as you have to progressively pay for more features
Define Wi-Fi
A wireless networking technology that provides high-speed internet and network connections
What is a WAP?
Wireless Access Point
What does a WAP allow you to do?
Access the internet
What are the advantages of Wi-Fi?
- Access from anywhere
- Easier to set up and inexpensive
- Convenient
- Can handle a large number of users
- Easy information and data transfer (social media)
What are the disadvantages of Wi-Fi?
- Slower than a wired network
- Relies on signal from WAP
- Signals can be easily obstructed
- Less secure
What is a wireless network interface card?
A device component that allows it to establish a connection with the nearest WAP
What hardware is required for a wireless network connection (in order)?
- Wireless network interface card
- Wireless access point
- Router
- Modem
Define SSID
A service set identifier which allows a user to connect to the network
Why are SSID’s useful?
They can be hidden which means that no one can access the network unless they know it, you can add a password or/and change the name yourself
What is a MAC whitelist?
A list that is held by network that details which MAC addresses are allowed to connect to that network
What is the purpose of the start bit in asynchronous transmission?
The start bit is sent so that the receiving device can prepare for incoming data
What is the purpose of the stop bit in asynchronous transmission?
The stop bit is sent to the signal the end of the transmission so that the receiver can process the data accordingly
How are bit rate and bandwidth related?
They are directly proportional
Define a firewall
Hardware or software that monitors ingoing and outgoing traffic to a network and prevents unauthorised access through the use of packet filtering or stateful inspection
Define packet filtering
Checking packet headers against a list of rules (packet filters) to determine whether or not the packet is allowed through .e.g. the packet filter could include an IP address that is blocked from sending packets to the network
Define stateful inspection
Continuously monitoring incoming and outgoing traffic after a connection is established by analysing the packet types and checking the payloads
Define proxy server
Provides anonymity to client devices by sitting between the client and the firewall
How does a proxy server provide anonymity to clients?
The packets that have passed through the firewall will all be passed to the proxy server and the proxy server will then pass the information to the client, this means that the proxy server is the only server that knows which client has made which request
Define serial transmission
Data is transmitted one bit at a time down a single wire
Define parallel transmission
Data is transmitted several bits at a time down multiple wires
What are the disadvantages of parallel transmission?
- Crosstalk
- Skew
- Signal degradation as speed or distance increases
Define bandwidth
A measure of the capacity of the channel data is being sent down
What is the relationship between time and bandwidth?
Bandwidth increases over time meaning the bandwidth available to the user increases each year
How is bandwidth related to carrier wave frequencies?
Bandwidth is another way of expressing the range of frequencies available on a carrier wave
What is the baud rate determined by?
The transmission medium
What are the three types of latency when transmitting data?
Propagation latency, transmission latency and processing latency
What is propagation latency?
The amount of time it takes for a logic gate within a circuit to transmit the data
What is transmission latency?
The amount of time it takes to pass through a communication medium (a wire)
What is processing latency?
The amount of time it takes data to pass around a network which is dependent on the number of servers and devices it has to pass through
What happens if two devices are using synchronous transmission and their transmission rates are not in synch with one another?
Data can be lost
Define protocols
A set of rules
What is a NIC?
A card that enables a devices to connect to a network
What is a network topology?
The layout of a network usually in terms of its conceptual layout rather than physical layout
State four methods of securing a wireless network
- Changing the SSID from the default value and hiding it
- Ensuring that all devices connected to the network are WPA/WPA2 compliant
- Use a string encryption
- Utilise a MAC whitelist
