Communications

Define Baud rate

The number of signal changes in a communication medium per second

What method of data transmission is used for long distances?

Serial data transmission

What unit is used for bandwidth?

Hertz

Define bandwidth

The range of frequencies that a communication medium is capable of transmitting

Define latency

The difference in time between an action being initiated and its effect being noticed

Define protocol

A set of rules relating to communication between devices

Which method of data transmission is suitable for real-time systems?

Synchronous data transmission

What is serial data transmission?

Data sent one bit at a time over a single communication line

How does asynchronous data transmission work?

Sender and receiver synchronise their clocks only for the duration of data transmission

How does parallel data transmission work?

Numerous parallel communication lines send multiple bits between components simultaneously

What is crosstalk?

Signals from tightly packed communication lines leaking into others

What method of data transmission uses start and stop bits?

Asynchronous data

What does network topology mean?

Refers to the structure of a network

What is a physical topology?

The actual architecture of a network

What is a physical star network topology?

Each client had its own direct connection the central hub

What are advantages of a physical star topology

* Failure of one cable does not affect the performance of the rest of the network
* Each cable has just one device communicating over it
* It is easy to add and remove clients

What are disadvantages of physical star topology?

* If central hub fails, all communication stops
* Expensive to install

What is a physical bus topology?

Connects clients to a single cable called a backbone, a device called a terminator is placed at either end

What are advantages of physical bus topology?

* There is no central hub, reducing cost and chances of a network failure
* Inexpensive to install

What are disadvantages of physical bus topology?

* Packets sent through shared backbone
* Risk of collisions
* If backbone fails, network is unusable

What is a logical network topology?

Refers to the flow of data within a network

What is client-server networking?

One or more central servers provide services to the clients on the network.

How does a client-server network work?

Clients request services from the servers, which then respond to the client with the requested service

What is peer-to-peer networking?

Services are provided by the clients themselves and every client has equal status

What are advantages of peer-to-peer?

* More cost effective
* No need for a powerful server
* Easy to set up and maintain

What are wireless networks?

Allow clients to communicate within a network without being physically connected to it

What do wireless networks require?

Wireless access point and a wireless network adapter

What is WiFi?

Wireless local area network that is based on international standards.

How are wireless networks secured?

* Encrypting transmitted data using WPA or WPA2
* Disabling SSID broadcast
* Set up a MAC address whitelist

What does WPA stand for?

WiFi protected access

What does WPA require?

Require new clients to enter a password in order to connect to the network

What does disabling SSID broadcast do?

Stops wireless devices from displaying the network is available

What is MAC address whitelist?

Specify which devices are able to join the network

What does CSMA/CA stand for?

Carrier sense multiple access with collision avoidance

What is CSMA/CA?

A protocol used to avoid data collisions caused by multiple devices communicating simultaneously

List the process that CSMA/CA follows

1. when a frame is ready, transmitting computer checks whether the channel is idle or busy
2. if channel is busy, station waits until channel becomes idle
3. if channel idle, computer waits for inter-frame gap amount of time and then sends the frame
4. otherwise it waits for a back off time period and restarts the algorithm
5. after sending the frame, it sets a timer
6. computer waits for acknowledgement from network access point

What does RTS/CTS stand for?

Request to send/Clear to send

What does RTS/CTS do?

1. device sends an RTS to the network access point
2. a CTS is sent back if network is clear
3. device transmits data until network access point stops it

What is the internet?

defined as a network of interconnected computer networks which use an end-to-end communication protocol

What are internet service providers?

a company that provides its customers with access to the internet

What is a packet?

a container in which data is transmitted over networks

What does a packet contain?

labelled with an address for sender and recipient and contain information intended for recipient

What does a packet switched network mean?

a network in which data is sent in packets

What is a time to live?

number that indicates how many hops the packet can do before it expires

What is the sender’s address?

identifies where the packet was sent from and where the response is sent to

What is the receiver’s address?

identifies the packet’s intended recipient, allowing it to be routed the correct device

What are the packet contents?

where the packet holds the data that is being transferred

What is a sequence number?

contains the number of packets in a message and identifies a packets position

What is a URL?

an address assigned to files on the internet

What is a domain name?

identifies an organisation or individual on the internet

What is a fully qualified domain name?

specified an exact resource and can only be interpreted in one way

What is an IP address?

assigned to every device on the internet

What is a domain name server?

domain name server translates domain name into corresponding IP address

What are internet registries?

responsible for the allocation of IP addresses

What are firewalls?

sits between a device and the internet and regulates the packets that pass through it

What is packet filtering?

accept and block packets based on their source IP address or the protocol that they are using

What is stateful inspection?

examined the contents of a packet before deciding whether to allow it through the firewall

What is a proxy server?

a server that sits between a public network and a private network which manages every packet that passes between the two networks

What is symmetric encryption?

both sender and receiver share the same private key

What is asymmetric encryption?

each device has a private and public key, data encrypted with public key

What are digital signatures?

can be used to verify the sender of a message and to verify that a message has not been tampered with during transmission

What is a digital certificate?

verifies ownership of a key pair used in asymmetric encryption

How is a digital signature used?

1. a digest of message is created
2. digest is encrypted with sender’s private key
3. encrypted digest appended to message
4. message and appended digest are encrypted with recipient’s public key
5. when recipient receives message, decrypt it using private key
6. decrypt digest using sender’s public key, verifies message was sent by sender

What is a worm?

malicious software that can self-replicate between computers

What is a trojan?

malware disguised as a benign file that users can be tricked into opening

What are viruses?

executable files, can lie dormant until host file is opened

What does TCP/IP stand for?

Transmission control protocol / internet protocol

What are the four layers?

1. Application layer
2. Transport layer
3. Network layer
4. Data link layer

What is the application layer?

data stream provides network services for application

Name some protocols in the application layer

1. HTTP
2. HTTP/S
3. IMAP
4. SMTP
5. POP
6. FTP
7. SSH

What is the transport layer?

data split into numbered segments, uses a port number to keep track of conversations

Name the protocol at transport layer

TCP

What is the network layer?

segments put into packets and destination source IP in header

Name protocols at the network layer

1. IPv4
2. IPv6

What is the data link layer?

prepares packet for physical media

Name protocols at data link layer

1. ethernet
2. MAC

What happens after packet is received?

packet stripped of extra information by reversing TCP/IP stack

What port does FTP use and what is its function?

20 & 21, sending files between devices

What port does SSH use and what is its function?

22, remote management of computers

What port does HTTP use and what is its function?

80, receives and renders text files

What does an IP address consist of?

network identifier and host identifier

How many IPv4 address classes are there?

3

How can the network identifier of an IP address be determined?

By using the subnet mask

What is the public IP range of a class A address?

1\.0.0.0 to 127.0.0.0

What is the private IP range of a class A address?

10\.0.0.0 to 10.255.255.255

What is the subnet mask of a class A address?

255\.0.0.0

What is the public IP range of a class B address?

128\.0.0.0 to 191.255.0.0

What is the private IP range of a class B address?

172\.16.0.0 to 172.31.255.255

What is the subnet mask of a class B address?

255\.255.0.0

What is the public IP range of a class C address?

192\.0.0.0 to 223.255.255.0

What is the private IP range of a class C address?

192\.168.0.0 to 192.168.255.255

What is the subnet mask of a class C address?

255\.255.255.0

What does a subnet mask do?

Get rid of host bits

what does dynamic host configuration protocol do?

assigns IP address to devices as they join a network

How does DCHP assign IP address?

1. Client sends DHCP discover
2. DHCP server sends an offer
3. Clients sends a request to DHCP
4. DHCP acknowledges request the request and sends a response

What is network address translation?

* device on the private network needs to communicate with device on the internet, it sends packets through the router which makes a record of the packet before replacing the private IP address with its own routable IP address
* response is received, sent to router’s public IP which then forwards response to private IP address

When is port forwarding used?

when a client needs to communicate with a server that is connected to a private network

How does port forwarding work?

* client sends packets to public IP address of the routers private network
* packets sent by client contain port number of the application running on the server that the client wishes to access

What is the client server model?

client sends request messages to servers which reply to the clients with response messages

What are API’s?

Application programming interface is the name given to a set of protocols relating to how different applications communicate with each other