Q- What happens to messages that get published to topics that no one subscribes to?
A- They are discarded by the broker.
Q-How can I find out what topics have been published?
A- You can’t do this easily as the broker doesn’t seem to keep a list of published topics as they aren’t permanent.
Q- Can I subscribe to a topic that no one is publishing to?
Q- Can I publish and subscribe using the same client connection?
Q- Are messages stored on the broker?
A- Yes but only temporarily. Once they have been sent to all subscribers they are then discarded. But see next question.
Q- What are retained messages?
A- When you publish a message you can have the broker store the last published message. This message will be the first message that new subscribers see when they subscribe to that topic. MQTT only retains 1 message. See Retained Messages by example
Q- What is a last will message?
A– It is a message sent by a broker when an MQTT client gets disconnected abnormally- See Last Will and Testament by example
Q- What is MQTT-SN?
MQTT-SN stands for MQTT for sensor networks. It uses UDP instead of TCP and isdesigned to work over UDP, ZigBee and other transports. See MQTT-SN working Notes.
Q- How do I delete, clear or remove all retained messages on the Mosquitto broker.
A- If you’re not using the persistent database then easiest way is to stop and restart mosquitto. Otherwise you will need to subscribe to all topics to check and clear the retained messages. You can use my Python script to do this. However this is not recommended on a busy broker.
Q-How do I delete a topic or topic hierarchy?
A- You can’t delete a topic from the broker. Topics are created by the clients. Topics are automatically remove from a broker when no client is subscribed to them or the broker isn’t holding a topic open for a client that has a persistent connection. See Understanding topics and MQTT clean sessions.
Internet of Things (IOT)
Q- What is IIOT?
A- IIOT stands for Industrial Internet of things.
Q- What Other IOT protocols are available besides MQTT?
A- There are 4 main protocols that are being used in IOT applications. See IOT Messaging Protocols-Quick Overview
- What is The Internet?
- What is the Cloud
- How many devices can Use my Internet connection?
- Can I connect to the Internet without having a landline ?
- How do I connect multiple Wi-Fi devices to the Internet when traveling?
- I only Need occasional access to the Internet what should I do?
- Can I connect My TV to the Internet even though it isn’t a smart TV?
- I Have poor Wi-Fi signal in some parts of my House -What Can I do?
- What is BT WiFI and how can I use it?
- Why is the Upload speed different from the Download speed?
- What is the Difference between Streaming and Downloading?
- The Broadband package is advertised as X Mbits/s but I am only getting Y Mbits/s.
- I’m Using BT ADSL will switching to Talktalk ADSL be any faster?
- The broadband offer is for unlimited broadband. Is it really unlimited?
- I’m using my mobile phone to Connect to the Internet over 3G can I share the connection with my Laptop?
- I use public Wi-fi a lot when traveling is it secure? can I make it secure?
- What is a URL?
- Can I use Bluetooth For transferring files
- What is the difference between a Gateway and a router?
- How do I find my IP Address ?
- Why does my IP address start with 169.254.x.x ?
- Where does my IP Address come from?
- How do I access my PC from a remote location?
- What is a VLAN
- What is Zero Configuration Networking?
What is The Internet?
The Internet is a global communications network built around the technology developed in the 1960s by ARPA (later DARPA) for the United states Government and revolves around TCP/IP protocols.
Simply put -It is a very large computer network.
Here is a video that explains the basics of the Internet-
How Many Devices can use My Internet Connection?
Normally there is no real limit imposed by ISPs, but the more devices you have accessing the Internet through a connection the slower the access for each user will be.
Can I connect to the Internet without having a landline ? –
Yes you can use the 3G/4G mobile network especially if you live in a city or town. In rural areas you will need to check your network availability. See 3G,4G & Wi-Fi
What is the Cloud
The cloud is another name for the Internet. Cloud based storage is simply internet storage and cloud computing is using internet based applications.
How do I connect multiple Wi-Fi devices to the Internet when traveling?–
Use a 3G/4G to Wi-FI hub commonly known as Mi-FI (Mobile Wi-Fi)
See 3G,4G & Wi-Fi
I only Need occasional access to the Internet what should I do?
Can I connect My TV to the Internet even though it isn’t a smart TV? – Yes but you will need to use a laptop or an external box. Google, Amazon,Apple and others provide these along with download TV services.
I Have poor Wi-Fi signal in some parts of my House -What Can I do?
You should first try relocating your WI-FI access point. If this is your Internet router (most likely is) then you need to located it near a telephone extension.
What is BT WiFI and how can I use it?
BT WiFI is an example of a community network and it allows you Wi-Fi access to the Internet across the UK through BT Hotspots. See BT Wi-FI overview.
Why is the Upload speed different from the Download speed?
The technology used for broadband is ADSL which allocates more bandwidth for data from the Internet than is allocated to data sent to the Internet.
This is because most users download much more data than they upload.
See Upload vs Download Speeds
What is the Difference between Streaming and Downloading?
If you watch a film or listen to music on the Internet then the film/music can either be downloaded or streamed to your device
Many services like YouTube only support streaming whereas others like The BBC iplayer support both.
Streaming is very much like the old TV or radio network were the show was broadcast, and you had to watch it then.
When you download a film from the internet then a local copy of the film exists on your PC, and you can watch the film at any time. You can also transfer/copy it to other devices.
Video Streaming Vs Downloading Q&A
|Do I Need an Internet connection to stream or download ?||Yes||Yes|
|Do I Need to be connected to the Internet To Play the video ?||Yes But see Note:||No|
|Do I Need a Fast Internet Connection?||Yes (2-5 Mbits/s download speed)||No|
|Can I watch while video is being
streamed or ownloaded?
|Will downloading/streaming use part of my Data Allowance?||Yes||Yes|
|Will downloading or streaming Use
space on my device?
|Yes bur relatively small as video isn’t stored permanently||Yes- Lots of space used -allow 1GB for every hour of video|
|Note: Software Like playlater can be used|
The Broadband Package is advertised as X Mbits/s but I am only getting Y Mbits/s
Broadband providers advertise the fastest download speeds possible over the connection. However you will rarely get the advertised speed because it varies according to your distance from the telephone exchange and other factors- See How fast is my Internet
What is a URL?
URL stands for Uniform resource locator and is used primarily at the moment for accessing web pages/ websites. It is one of two common Internet addresses that you will encounter. See Web and Internet Addresses for beginners.
Q- I’m Using BT ADSL will switching to Talktalk ADSL be any faster?
No : BT is the only UK providers of Telephone connections (except for cable). Therefore all other Broadband providers must use the BT provided telephone lines for the broadband connection. See How to choose an ISP
Q- The broadband offer is for unlimited broadband. Is it really unlimited?
Perhaps – You usually have to read the small print for this as some providers will use traffic management techniques.These have the effect of slowing down your Internet connection, usually at peak time.
Even if they don’t actively do traffic management your connection may become slow due the way they have provisioned their own network.
Q-I use public Wi-fi a lot when traveling is it secure? can I make it secure?
Q- I’m using my mobile phone to Connect to the Internet over 3G can I share the connection with my Laptop?
Yes you can share the connection using a variety of techniques the most common is tethering. You can also purchase mini GSM/Wi-fi hubs which allow you to share the connection with several Wi-Fi equipped devices.
Can I use Bluetooth For transferring files?
Yes you can but it is much slower than Wi-Fi which is why it tends only to be used for connecting peripherals to get ether. See beginners guide to bluetooth.
What’s the difference between TCP and UDP?
A- TCP is a connection orientated protocol like a telephone call whereas UDP is a connection less protocol like email. See TCP vs UDP
What is the difference between a Gateway and a router?
A – A Gateway is a device that translates from one protocol to another, just like a translator would translate from English to French. Common gateways are email to fax, email to sms.
A router connects two networks at the networking level. It will route IP to IP,IPX to IPX but not IP tp IPX as that would be a translation as they are different protocols.
What is the Default Gateway?
When configuring TCP/IP networks you will come across the term default Gateway. It is basically the main way out of your network, and is usually the address of your home router.
How do I find my IP Address ? –
On Windows go to a command line a type
ipconfig or ipconfig/all
on Linux type
See understanding IP addresses for more details
Why Is my IP address start with 169.254.x.x ?
This is because your machine cannot locate a DHCP server and it has assigned its own address. See Troubleshooting Internet connection problems.
Where does my IP Address come from?
On most networks addresses are assigned by a DHCP server. The DHCP server on home networks is generally your router.
How do I access my PC from a remote location?
Normally access to your internal network from across the Internet isn’t possible because it is blocked by the router, which is normally a NAT router.
To allow access you need to open up the router to allow this and this involves a technique called port forwarding. See the port forwarding tutorial
What the Difference between a Socket and A port?
A networking socket is a term used to describe a port + IP address combinations. See TCP/IP Ports and Sockets Explained.
What is DNS ?
DNS is a service that provides name to IP address resolution and is crucial component of the Internet.
See A Beginners guide to DNS
On Home networks Internal name resolution is done without needing DNS see Understanding Name Resolution.
What is the Hosts File?
The host file is used for mapping Names to IP addresses and is available on all systems but it has been replaced by DNS. However it is still usually the first name resolver method -See Understanding and Using the Hosts File
What Is a VLAN?
A VLAN is used to partition a local network into separate segments using software. VLANS are common on corporate networks but not on home networks.
What is Zero Configuration Networking?
It is collection of technologies that allow devices to operate on computer networks without requiring any manual configuration. It relies upon three core technologies:
- Automatic IP address assignment
- Automatic name assignment and name resolution
- Automatic registration and location of network services.