Observe option for notifications in IOT Protocols - Step-by-Step Execution

Process Flow - Observe option for notifications

Client sends Observe request

↓

Server registers client for resource

↓

Server sends initial resource state

↓

Resource changes?

No→Wait

Yes↓

Server sends notification to client

↓

Client receives updated state

↓

Client may cancel Observe

↓

END

The client asks the server to watch a resource. The server sends updates when the resource changes until the client stops watching.

Execution Sample

IOT Protocols

Client: GET /sensor/temp Observe
Server: 2.05 Content (temp=22C)
...
Server: 2.05 Content (temp=23C)
...
Client: Cancel Observe

Client requests to observe temperature sensor; server sends initial and updated values; client cancels observation.

Process Table

Step	Action	Message Sent	Server State	Client State	Notification Sent
1	Client sends Observe request	GET /sensor/temp with Observe option	Registers client as observer	Waiting for updates	No
2	Server responds with current value	2.05 Content (temp=22C)	Client registered	Received initial value 22C	No
3	Resource changes temperature	None	Temp updated to 23C	Waiting for notification	Yes, sends 2.05 Content (temp=23C)
4	Client receives update	None	Temp 23C	Received updated value 23C	No
5	Client cancels Observe	GET /sensor/temp with Cancel Observe	Removes client from observers	Stops receiving updates	No

💡 Client cancels Observe, so server stops sending notifications.

Status Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	After Step 4	Final
Client State	Idle	Waiting for updates	Received initial value 22C	Waiting for notification	Received updated value 23C	Stopped observing
Server Observers	Empty	Client registered	Client registered	Client registered	Client registered	Client removed

Key Moments - 3 Insights

Why does the server send multiple notifications?

Because the client requested to observe, the server sends updates each time the resource changes (see Step 3 and 4 in execution_table).

What happens if the client does not cancel the Observe?

The server keeps sending notifications whenever the resource changes, as shown by the server state staying with the client registered (Steps 2 to 4).

Does the client get the current resource value immediately after requesting Observe?

Yes, the server sends the current value right after registering the client (Step 2).

Visual Quiz - 3 Questions

Look at the execution_table, what is the client state after Step 2?

A Waiting for updates

B Received initial value 22C

C Stopped observing

D Idle

💡 Hint

Check the 'Client State' column for Step 2 in execution_table.

At which step does the server send a notification due to resource change?

A Step 1

B Step 2

C Step 3

D Step 5

💡 Hint

Look for 'Notification Sent' column showing 'Yes' in execution_table.

If the client never cancels Observe, what happens to the server observers?

A Client remains registered indefinitely

B Client is removed immediately

C Server stops sending notifications

D Client state changes to Idle

💡 Hint

Refer to 'Server Observers' in variable_tracker after Step 4.

Concept Snapshot

Observe option lets a client watch a resource on a server.
Client sends GET with Observe option.
Server replies with current state and sends updates on changes.
Client receives notifications until it cancels Observe.
Useful for real-time updates without repeated polling.

Full Transcript

The Observe option in IoT protocols allows a client to request continuous updates from a server about a resource. The client sends a GET request with the Observe option. The server registers the client as an observer and immediately sends the current resource state. When the resource changes, the server sends notifications with the updated state. This continues until the client cancels the Observe request. This mechanism avoids repeated polling and provides real-time updates efficiently.

Practice

1. What is the main purpose of the Observe option in IoT protocols like CoAP?

easy

A. To allow clients to receive automatic updates from the server without repeated requests

B. To encrypt the data sent between client and server

C. To authenticate the client before data transfer

D. To compress the data for faster transmission

Solution

1. Step 1: Understand the Observe option function

   The Observe option enables clients to subscribe to resource changes and get updates automatically.

2. Step 2: Compare with other options

   Encryption, authentication, and compression are different features unrelated to Observe.

3. Final Answer:

   To allow clients to receive automatic updates from the server without repeated requests -> Option A

4. Quick Check:

   Observe = automatic updates [OK]

Hint: Observe means automatic updates without asking repeatedly [OK]

Common Mistakes:

• Confusing Observe with security features
• Thinking Observe compresses data
• Assuming Observe authenticates clients

2. Which of the following is the correct way to include the Observe option in a CoAP GET request?

easy

A. Add option number 14 with value 1 in the request header

B. Add option number 12 with value 1 in the request header

C. Add option number 14 with value 0 in the request header

D. Add option number 15 with value 0 in the request header

Solution

1. Step 1: Identify Observe option number and value

   Observe option in CoAP is option number 14. To register for notifications, value 0 is used.

2. Step 2: Match correct option number and value

   Option 14 with value 0 is the correct way to request observation.

3. Final Answer:

   Add option number 14 with value 0 in the request header -> Option C

4. Quick Check:

   Observe option = 14, value = 0 [OK]

Hint: Observe option number is 14, value 0 to observe [OK]

Common Mistakes:

• Using wrong option number
• Using wrong value for Observe
• Confusing Observe option with other options

3. Given this CoAP client code snippet requesting observation:

GET /sensor/temp
Options: Observe=0

What will the client receive after the initial response?

medium

A. Only the initial temperature value, no updates

B. Initial value plus automatic updates when temperature changes

C. An error because Observe=0 is invalid

D. Only updates without initial value

Solution

1. Step 1: Understand Observe=0 meaning

   Observe=0 means the client wants to register for notifications and receive updates.

2. Step 2: Expected server behavior

   The server sends the initial resource value, then sends notifications when the value changes.

3. Final Answer:

   Initial value plus automatic updates when temperature changes -> Option B

4. Quick Check:

   Observe=0 means subscribe and get updates [OK]

Hint: Observe=0 means subscribe and get updates including initial [OK]

Common Mistakes:

• Thinking Observe=0 disables updates
• Expecting error from Observe=0
• Assuming updates come without initial value

4. A client sends a CoAP GET request with Observe=2 option. The server does not send notifications. What is the likely problem?

medium

A. Client forgot to include URI path

B. Server does not support Observe option

C. Server requires Observe=3 to send notifications

D. Observe=2 is invalid; client must use 0 or 1 to register

Solution

1. Step 1: Check valid Observe values

   Valid Observe values for registration are 0 or 1. Value 2 is not defined for Observe.

2. Step 2: Understand server behavior

   Server ignores invalid Observe values and does not send notifications.

3. Final Answer:

   Observe=2 is invalid; client must use 0 or 1 to register -> Option D

4. Quick Check:

   Observe values must be 0 or 1 [OK]

Hint: Observe option values are only 0 or 1 for notifications [OK]

Common Mistakes:

• Using unsupported Observe values
• Assuming server requires special values
• Ignoring invalid option values

5. You want to monitor a sensor's state changes efficiently using CoAP Observe. Which approach best saves battery and network usage?

hard

A. Use Observe option to get notifications only when sensor state changes

B. Send repeated GET requests every second without Observe

C. Use Observe option but ignore notifications and poll manually

D. Send a single GET request and never update

Solution

1. Step 1: Understand Observe benefits

   Observe lets the client receive updates only when the sensor state changes, avoiding repeated requests.

2. Step 2: Compare with other methods

   Repeated GET requests waste battery and network. Ignoring notifications defeats Observe purpose. Single request never updates.

3. Final Answer:

   Use Observe option to get notifications only when sensor state changes -> Option A

4. Quick Check:

   Observe saves battery by sending updates only on changes [OK]

Hint: Observe sends updates only on changes, saving resources [OK]

Common Mistakes:

• Polling too frequently wasting battery
• Ignoring Observe notifications
• Not using Observe for real-time updates