Computer Networks: Fundamentals

Life is good in Boston, Massachusetts. You and your friend Joel are living in the North End on 21st Street, where all the houses are lined up across the road. Each house is initially self-sufficient, with years' worth of rations and a sustainable source of energy via solar panels.

But after the fungus outbreak everyone realised that even though each house is self-sufficient , there may be times when some houses have more resources than they need, while others may have a shortage.?You decide to set up a network that connects all the houses on 21st Street.

Just like how each house on 21st Street was self-sufficient with its own resources, standalone applications in the pre-internet era were self-contained and did not rely on an internet connection to function.

Standalone applications, such as?Microsoft Excel?or?Word, were installed and run on a local computer without requiring an internet connection. The application contained all the necessary code and resources to function, such as data storage, processing, and display capabilities.

Users would typically save their files on a local hard drive or a?removable storage device?like a floppy disk or a flash drive. To share a file with others, users would have to physically deliver the storage device containing the file or send it via email, which could be unreliable due to the limitations of the?internet connection?at the time.

With the increasing speed and accessibility of the internet, people have come to realize that it's not necessary to burden their computer's memory with a multitude of software applications. Instead, cloud-based solutions like?Google Spreadsheets?offer a convenient way to store data remotely. It's comparable to sharing a fridge with your neighbor to keep excess food, thus avoiding overloading your own fridge. However, there is always a risk associated with this approach. For instance, there's the possibility of your neighbor accessing, consuming, or selling your ice cream. But we can discuss the topic of data theft on another day.

Now, I will provide you with some fundamentals, and for each fundamental, you have to determine whether you can send a file from your computer to:

• Your neighbor's computer over the network
• A stranger's computer over the internet, i.e., across multiple networks

MAC address: Similar to the houses in the analogy mentioned above, each device, including phones, computers, and even some smartwatches, has a unique MAC address associated with it.

Now, let's pause for a moment and consider whether the MAC address alone is sufficient to send files across:

• To a neighbor's computer - Yes, it's possible. Since there is a limited number of houses/computers on your street/network, you can go around and ask if anyone has the relevant address/MAC address.
• To a stranger's computer - No, it's not feasible. With multiple streets/networks containing a large number of houses/computers, it's not practical to go around asking for addresses/MAC addresses. Doing so may even result in someone calling the police on you.

Router: Since it's difficult and painfully slow to send files across multiple networks, the creators of the internet proposed a unique solution. They suggested that each street/network should be connected via a router/crossroad. The naming of each network would be determined by the router, based on its capacity to handle traffic. However, there is a limit to how many networks can be connected via a single router.

IP Address: IP stands for Internet Protocol. This is the label assigned by the router to each network.

However, even with routers and IP addresses, it is not yet possible to send files across networks, as there are still?technical limitations?that need to be addressed. While it may be relatively easy to navigate across different streets and houses, sending files across multiple networks is still a challenge that needs to be overcome.

Host: Now that each street/network has a name, it's necessary to label every house/computer. Host is basically virtual address of your computer since physical address is your MAC address. Your virtual address will keep changing as your router assigns a new address to every computer connected to it everytime it restarts.

With the router, IP address, and host, you can now easily find a stranger's house and deliver the bag full of vegetables.

Port: Once you arrive at the correct house, you'll have to knock on the door to deliver the bag of vegetables. Similarly, computers have reserved ports such as:

• Port 25: Simple Mail Transfer Protocol (SMTP) used by email servers
• Port 53: DNS protocol
• Port 80: Used for accessing web servers

Congratulations, you have successfully recalled the correct port to knock and have delivered your bag/file!

As we end this edition, we see that networking and file sharing technologies have come a long way since the early days. We'll continue exploring new advancements in the next edition.