Communications Review and Summary

[From the last episode: we saw how spectrumA range of frequencies. A prism shows a range, or spectrum, of visible light frequencies (yes, light is a wave). This is the literal definition of spectrum. Other uses – like references to the autism spectrum use the word figuratively to indicate a continuous range. In our context, this refers to the range of radio frequencies available for communication. Access to those frequencies is usually regulated by governments since they're viewed as a public asset. is allocated for different uses, and how the IoTThe Internet of Things. A broad term covering many different applications where "things"  are interconnected through the internet. fits in.]

OK, let’s take a breather and review what we’ve looked at since last November. Our focus has been on communications, and:

• We looked at what it means for a machine to send a message.
• We saw how messages can be made up of packets.
• We saw how packets get from here to there.
• We looked at what happens when messages are too big for a packet.
• We then took a quick break to look at a real-world situation that makes us question when machinesIn our context, a machine is anything that isn't human (or living). That includes electronic equipment like computers and phones. should make decisions and when we should, and who should win when they disagree.
• We then saw different ways of getting the message out, starting with the simple from-here-to-there case…
• … the message-to-everywhere case…
• … and sending a message to a select group of multiple recipients. We also looked at publish-and-subscribeA way of sending data to multiple destinations. The destinations subscribe to the data using a broker; whatever is generating the data (possibly a sensor) publishes the data to the broker; the broker either sends to the data to the subscribers or lets the subscribers request data. along with this.
• We then contrasted pub/sub with request/response as an alternative scheme.’
• We saw how cloud serversA computer with a dedicated purpose. Older familiar examples are print servers (a computer that controls local printing) and file servers (a computer used for storing files centrally). More modern examples are web servers (the computers that handle your web requests when you use your browser) or application servers (computers dedicated to handling the computing needs of a specific application). Servers are often powerful, expensive machines since they have to handle a heavy load. can handle huge numbers of requests.
• And we explored a notion that makes sure things don’t go wrong if communication fails and we need to repeat something.
• We saw a couple of different ways in which engineers program devices and how they relate to two different communication protocolsAn agreed way of doing something. Like a convention, except that protocols tend to be related to processes..
• We saw how spectrum gets allocated for wireless communication, and how that affects some of the protocols that IoT – and especially IIoTIndustrial Internet of Things. A broad collection of factory, automotive, agricultural, medical, and other areas where IoT technology is used. – devices may use.

Now that we have some communications concepts down, we’ll look at how we can do things securely – whether communicating or anything else.