L7

Question 1

What are the interaction models of application protocols?

Answer 1

Request/response -> client/server (HTTP)

Publish/subscribe -> publisher/subscriber

Handshaking and data transfer

Question 2

What is the HTTP protocol?

Answer 2

Allows devices to exchange information about their status through standardized CRUD functions

C (POST) R (GET) U (PUT) D (DELETE)

Does not define any QoS (quality of service) levels

Uses the TLS protocol and uses TCP ad the transport layer

Question 3

What is one advantage and one disadvantage of using HTTP?

Answer 3

Pros:
- Enables REST architectures
- TCP guarantees reliable communication
- Appropriate for large data transfer, latency insensitive

Cons:
- Use of TCP and TLS lead to high overheads
- Does not support server push notifications
- Size of header and message payloads depend on the web server

Question 4

What are some characteristics of the CoAP protocol?

Answer 4

(Constrained Application Protocol)

Interoperable with HTTP

Transport protocol is UDP

QoS is enable though CON and NON

Question 5

What are some characteristics of the Mosquito protocol?

Answer 5

MQTT (Message Queuing Telemetry Transport), also called Mosquito

Utilizes the publish/subscribe model

A binary protocol

Header is of at least 2-bytes (size of packet)

Supports 3 QoS levels

Question 6

What are the 3 QoS levels of MQTT?

Answer 6

QoS 0: delivers without confirmation

QoS 1: message confirmation is necessary; resends if not confirmed

QoS 2 (less appropriate for IoT): guarantees that the message will be delivered exactly once without duplications

Question 7

What are some characteristics of the AMQP protocol?

Answer 7

AMQP (Advanced Message Queueing Protocol)
Binary protocol (Fixed headers of 8-bytes)

Heavier than MQTT

Uses TCP for transport protocol and TLS/SSl and SASL for security

Offers two QoS levels

Reliability is one of the core features of AMQP

Question 8

What are some characteristics of the Websocket protocol?

Answer 8

Handshake and a data transfer protocol

Enables two-way communication

Utilizes TCP at the transport layer

Can decrease the latency by a factor of three compared to HTTP

Question 9

Evaluate the 4 protocols: CoAP, MQTT, HTTP, and AMQP

Answer 9

MQTT, AMQP , and HTTP run on TCP, therefore the message overhead is entailed. It also gives a higher latency than other transport protocol.

CoAP runs on UDP does not add connection overheads.

HTTP is the most verbose and heavy-weight protocol.

CoAP and MQTT are designed for low bandwidth and resource-constrained devices.

Ranking for message overhead, message size, power consumption, resource requirement (h to l): HTTP -> AMQP -> MQTT -> CoAP

For reliability, MQTT offers the highest level of Qos.

For interoperability, HTTP is the most interoperable because all that is needed is an HTTP stack.

HTTP has the highest level of standardisation.

Question 10

When would you use AMQP over MQTT?

Answer 10

MQTT was built as a lighteight protocol for devices with limited resources, such as IoT constrained nodes

AMQP is also lightweight but more suited for more powerful devices due its processing power requirements

Question 11

What are the two evaluation metrics for evaluation protocols?

Answer 11

Protocol efficiency: the ratio between the number of useful information bytes and the total number of bytes exchanged

Round Trip Time (RTT)