June Test Flashcards
Key applications of communications in robotics (3 of them)
Telerobotics: semi-autonomous robots controlled remotely via comunication network
Swarm robotics: an approach for coordinating several robots capable of performing simple tasks
Cloud robotics: any robot that relies on data/code from a network to support its operation
Haptic/tactile technology
Haptic: creates an experience of touch through vibrations forces or motions
Tactile: sensors designed to provide feedback to human operators about robots environment
Definition of latency
Acceptable latency for VR (only roughly)
Time it takes for a packet of data to get from one designated point to another
Around 25ms
Calulating latency for a given length of fiber
Ask henry
CPS: what it stands for, what is it and three key components
Cyber physical systems
Integrates the physical and digital processes
Used for communication, control and computation
Definition of IOT
Difference between CPS and IOT
Internet of things-computing devices connected via the internet
All IOT devices are CPS’s but CPS’s are not necessarily connected to the internet
Definition of PAN,LAN
PAN: personal area network, within around 10 metres, computer connected to mouse/printer, bluetooth
LAN: local area network, small geographic area, computers in offices to share resources
Definiton of MAN,WAN, internet
MAN: metropolitan area network, covers between several buildings to a city
WAN: wide area network, covers a country/continent
Internet: WAN that interconnects billions of devices
Name for the link from source-to-destination and vice versa
Three categories of equipment in networks
Uplink/upstream
Downlink/downstream
1. End systems (hosts): client/server devices
2. Intermediate devices: devices capable of directing packets or performing other functions on the packets
3. Network media: medium providing a channel for communication (fiber cable etc)
Definition of:
Transmission latency
Link throughput
Hop count
TL: delay between transmission and reception on a communication link
LT: number of bits per second
HC: number of communication links traversed in a path
Things to consider about network media
Distance of each link dictated by media
Impairments associated with media
Maximum sustained throughput
Cost
Key challenges to do with networking (5 of them)
Sender and reciever locating each other over a network
Accomodating multiple senders and receivers simultaneously
Avoiding errors i.e. missage mix ups
Maintaining communication path between reciever and sender
Stopping eavesdropping
OSI model: what it stands for, all the layers, good mnemonic to remember
Open systems interconnection
Application, presentation, session, transport, network, data link, physical
All people seem to need data processing
Description of 1-3 OSI layers (what they do)
Application: implement human machine interface
Presentation: encode and compress data in appropriate form
Encrypt/decrypt data
Session: manages sessions for different host applications
Description of 4-5 OSI layers
Transport: enables error correction and flow control
Network: structure and manage network using logical addressing
Manage message priority and scheduling
Description of 6-7 OSI layers
Data link: manages reliable transmission and sharing of physical media
Physical: encodes data in to voltages/waveforms
Protocol multiplexing and de-multiplexing (specifically how to de-multiplex)
Multiple overlying (higher) protocols can use same underlying (lower) protocols. E.g. Multiple transport protocols can use the same networking one Protocol headers: each layer attaches a label/tag. Lower layers remove tags before forwarding payload upwards
Differences between OSI and TCP/IP
OSI is reference architecture, TCP/IP is based on the specific standardized internet protocols
In TCP/IP the first three layers are merged into one application layer
The three properties of layers
Service: functionality of the layer
Service interface: how to access the service
Protocol interface: how peers communicate to implement service
Rules and formats about communication between two internet hosts
Hub: layers involved, how they work and collision/broadcast domains
Only has physical layer
Sends incoming signal to all outgoing ports
1 collision domain, 1 broadcast domain
Switch: layers involved, how they work and collision/broadcast domains
Switch: physical and data link layers.
Knows specific address of messages and can send directly to the right computer
0 collision domain so can receive from multiple PC’s.
1 broadcast domain
Router: layers involved, how they work and collision/broadcast domains
Physical, data and network layers
Usually connects two networks
0 collsion and broadcast domain so can send and receive from multiple PC’s
What is collision and broadcast domain?
CD: the part of the network where collisions can occur
Collision: when two devices send a packet at the same time on the same network segment
BD: the domain in which a broadcast is forwarded
All ports on a hub/switch are in the same broadcast domain
All ports on a router are in different broadcast domains
Packet switching equations: time required to complete transmission
T = L/R T= time L = packet length R = bits per second
What is store-and-forward transmission?
What’s the equation for transmitting time for switches/routers?
SFT: switches and routers must receive complete packet before the first bit can be retransmitted
τ = 4L/R
L = packet length
R = bits per second
What’s the general equation for sending one packet over a path with multiple N links
τ = N*L/R N = number of links between source and destination Means theres N-1 routers L = packet length R = bits per second rate of the links
Circuit switching: description, pros and cons
Reserves the resources required for the duration of communication session
Pros: guaranteed good service and no delays
Cons: wasted bandwidth, static single path to follow
Packet switching: description, pros and cons
No prior reservation of resources. Instead they are allocated on demand so messages may have to wait in queues
Pros: enables data transmission on multiple paths simultaneously
Cons: wasted bandwidth when source bit rate is lower than link bit rate
Congestion occurs under heavy traffic
Multiplexing: frequency division vs time division
What’s a frame?
Equation for transmission rate of a circuit
Frequency division: multiple packets being transmited at the same time at different frequencies
Time division: packets sent one at time at all frequencies
Frame: a unit of data
TRC = Frame rate (No. of frames per second) * Number of bits in each slot
What is source coding?
What is the equation to calculate the number of bits required for a source code?
Converting any type of data into binary form
2^L = M
M = number of distinct characters (aka not repeated)
L = number of bits
How to synchronise a message?
What is a fix length code?
Send code that identifies the start and end of a message
The number of bits used for all symbols/data in a source code is the same i.e. if theres 8 symbols use 3 bits
What is a variable length code? What is the benefit?
Symbols that appear more often have fewer number of bits than symbols that appear more often.
Saves data but requires carefully designed source code
How to use the huffman algorithm?
- List all letters and how often they appear. REMEMBER SPACES
- Combine them into nodes with a combined value. Do this in order from lowest frequency to highest
- List them in a tree. One side gets a 0, other side gets a 1
- To list off values follow the tree
What is required for variable length code?
Needs to be uniquely decodable. Achieved by prefix free code
What does uniquely decodable mean/prefix free mean?
When variable length code is put in series, you are able to deode and identify each letter individually