Week 3 - Lecture 5 Flashcards
What are the layers of the OSI Reference Model?
Application Layer
Presentation Layer
Sessions Layer
Transport Layer
Network Layer
Data Link Layer
Physical Layer
The all the way back up on the other end
What is a PAN?
Personal Area Network (About a square meter - around a single person)
What is a MAN?
about 10km - A city
What is a WAN?
Around 100 - 1000km - A country or a continent
What is a LPWAN?
Low power wide area network
What is the internet of things stack (Vs OSI stack)?
Application Layer
Transport layer
Network layer / IP
Link Layer
Physical Layer
Why can’t we use OSI for IoT?
OSI created based on assumption of single technology stacks. IoT is characterised by high technology heterogeneity
The internet stack abstracts the physical layer due to, typically, fully homogeneous networks but this is not the case for IoT where different power constrained devices at the edge are utilised
Many of the low-level IoT devices used in constrained networks do not fully support IP compliant communication.
What aspects should be considered for IoT protocol stacks?
Physical aspect
- Don’t exclude any available technology.
- For example, consider that a device with radio capabilities employs the Zigbee protocol while an application for a smartphone using the data produced by the device at the edge communicates with the database on cloud services through Wi-Fi or 3G cellular communication
Link Aspect
Should support heterogeneity (although more limited than in the physical layer) and underpin security solutions as well. In addition, this layer must provide upper layers with standardised capabilities and interfaces. Again the idea is not to limit the implementation of data link layer but rather ensure the coexistence of several solutions for the link layer
Network and ID aspects
- Provide functionalities as required by the network layer of the OSI stack. Providing a common communication platform for every possible networking solution can be the bottleneck for IoT systems. Alternatively, the ID aspect should provide identification functionalities and where necessary resolution functionalities between locators (descriptors of the location of a given IoT element in the network) and identifiers (unique descriptors of the Digital Artefact; either active or passive).
Consequently, this interoperability aspect takes care of the addressing issue in between any two systems irrespective of the particular technologies they utilize
End-to-end aspect
Reliability, transport issues, translation, proxy/gateway support and parameter configuration when the communication crosses different networking environments. This aspect is the final component for achieving a global M2M (machine-to-machine) communication model
Data aspect
Needs to model:
- Capability of providing structured attributes for data description
- Capability of being translated (possibly by compression / decompression) one to each other, e.g. COAP to HTTP by decompression or XML to EXI by compression, IPv4 to IPv6 by mapping
What is an unconstrained network?
High-speed communication links (Mbit\s or higher). Wired internet we all know is an example. Link-level transfer latencies are also small and mainly affected by congestion events in the network rather than by the technology utilised for the physical layer
What is a constrained network?
Relatively low transfer rates, typically smaller than 1 Mbit\s. These networks typically involve large latencies. These latencies are due to several factors including:
- Low-bitrate supported by the physical layer technology
- Power saving policies and mechanisms of the terminals populating these networks. Could be hibernation states or a policy for the periodic power off of their radios
What is the most typical case for IoT communication approaches?
Constrained networks intermediated by an unconstrained network (e.g. the internet)
What three things is communication subject to?
noise, interference and losses
- Each medium is subject to different loss mechanisms
At what speed to signals usually propogate?
The speed of light
c = lambda * f
Where lambda is the wavelength (m) and f is the signal frequency [Hz}
What is 1/4 wave antenna
The physical size of the antenna should be 1/4 of the signal wavelength
Assume signal transmission at 1 MHz. What’s the size of an 1/4 wave antenna?
(310^8) / (1x10^6) / 4 = 310^2/4 = 300/4 = 75m
At ISM band (2.4 GHz)
(310^8)/(2.410^9) / 4 = 1.25*10^-1 / 4 = 0.125/4 = 0.03125m
What does “baseband” frequency typically refer to?
digital circuits producing the “digital information”
Baseband signals are propagated by modulating higher frequency signals (RF carriers)
