CNC - Networks + Distributed & Parallel Computing (Lesson)

Networks + Distributed & Parallel Computing

Computer Networks

So what is a computer network?  A computer network is about sharing information between computers. Computers are grouped to enable the sharing of information between them.  The group size of the network varies depending on the need and the type of sharing required.  Sharing can also be virtually and physically.

Sharing ? Why would I share? My computer needs to be private!  Ah yes, we want the access to information on our computer to be for us only, but the majority of us need to share.  

How would I not share? You would be on your own dedicated computer with your computer having dedicated access to a printer wired or wireless to only your device. No internet! Therefore no email! No sharing! The "dark" ages of the computer works only to get your document done and printed out to take to your teacher at school. Technology has moved a long way to where we are now.

Today on a computer we 

  • share files
  • email
  • watch videos or online video chat with an instructor online to learn course material
  • share printers (you can print at your house and everyone else in the house prints to the same printer)
  • access files through a browser around the world
  • get the latest news on an app
  • download software
  • play interactive and multiplayer games

The above list is not exhaustive, but a good beginning of the sharing between computer systems that happens in our daily lives as we access our computer.  Our home computer communicates to many other computers around the world through a browser and the structure of the internet for the transfer of all of this information.

Types of Networks

Networks types are many and varied depending on the type of sharing that is going to take place and the security that will be in place for the users of the network.  The basic network setups are listed below.

  • Personal Area Network (PAN) - your computer is the key here. Any device that the computer needs would be connected to the computer either wired or wireless, thus dedicated to your computer only.  Your computer is the center of control.
  • Home Area Network (HAN) - connects devices within the home for sharing.  This includes computers, printers, TV's, smartphones, tablets, and other devices. Other devices might include a refrigerator, oven, and your home security system, etc.
  • Local Area Network (LAN) - connects a limited area of space like a small office, a school, or maybe your home.
  • Wide Area Network (WAN) - connects computers over a larger geographic area that encompasses multiple buildings and areas and covers area greater than a mile in radius.
  • Metropolitan Area Network (MAN) - the area of a city is connected together using LAN's and maybe even a WAN.
  • Global Area Network (GAN) - connects computers worldwide.  The internet is a good example.

Now let's see a few specialized area networks.  These use a combination of the LAN's and WAN's to achieve a purpose for a specific area.

  • Campus Network - private or public this is a network of interconnectivity on a college campus, businesses, etc. that have a group of buildings in close proximity for the sharing of information.
  • Enterprise Network - privately connects computers at multiple business sites to share resources.
  • Intranet - a network of computers that is controlled internally for communication within the organization as well as access to any communication outside of the network. 

The Intranet is a unique specialized access network. Communication within the organization is logged and software applications shared. Computers are an intranet system have controlled access to the internet.  Yes you can get to the internet, but accessing a site that might harm the computer with a virus, or provide information not relevant to an age group or to the business environment will be blocked. Messages sent from your browser are checked prior to going out on the internet and incoming items from the internet are checked prior to coming back to your computer. This is a security feature to stop viruses invading the system, once in they could destroy the network or take information that is proprietary or drain the organization's bank account. 

Everyone should have security on their computer to check for material that could have malicious content or links to such, that could harm the computer or a network. If you do not have security software on a home computer you should invest in it. The intranet provides an umbrella of safety for the business or school for their network based on their access rules. Security software on your home computer will assist you in staying safe using the shared resources.

Topography of Computer Connections 

The work topography means the lay of the land.  In our case, the land is our computers. How are they connected together to work with the area networks or to share devices or applications. Let's see some of the various topographies.  

  • Bus Topography - each computer is connected via a straight line cable, like a bus line.  A message from one computer moves along the cable passing other computers connected to the cable until reaching the network.  A break in the cable along the line will disconnect all computers behind the break to the network.  This type of topology is used in computer labs at school to connect to the network. 
  • Mesh Topography - each computer connects to all other computers in the group directly.
  • Ring Topography - computers are connected from one to the next using cable to form a ring of computers. Messages from one computer to another must pass other computers on the way to get to where it needs to go, i.e. one-way traffic.  A break in the cable requires fixing or changing the structure to get messages to the nodes (computers or devices) after the break in the connection.  
  • Star Topography - the central network router is connected independently to each individual computer like the points of a star. The central node routes the computer message to the printer, etc. A break in connection of one computer does not affect the others in the topology layout.  Cabling is normally in use.
  • Hybrid Topography - a combination of any of the other types of topologies.

Interesting tidbit:   Bus and ring topography require each node (computer or device) on the line to check to see if the incoming address is theirs and accept the message.  Star and mesh topographies are direct connect to the other computer.

Distributed & Parallel Computing

Now that we have reviewed network types and topography, let's look more closely at computers sharing information, specifically at Distributed Computing and Parallel Computing. These are specialized networks of computers connected specifically for a task.

Distributed Computing

A distributed system of computing involves the use of email, the internet, intranet, phone communications and more. The system must be scalable to add other devices as they come onto the network. The computers in the distributed system are all using their memory, processing information, and communicating with the other computers on the system over the network to provide the fastest turnaround possible. Hundreds or even thousands of computers work together with their own memory in the distributed computing system.

However, the communication is asynchronous and knowing why a failure occurs is not easy to determine. Did the message get queued, lost due to a system going down, delay due to overload, etc.? So what is returned back on the computer screen of the person who sent the email, may be timeout, retry, etc. that does not explain what happened. We have learned to go on. Try sending the message again and what you wanted appears on the screen. A different path was possibly taken, the computer you needed to get material from just came back online, etc. Alternatively, the problem could have been close to home, the cable was cut up the street from your house. Oops, the bus network failed, and now you are not working again from home until a repair is made. The distributed system is still working for others, but those on your street affected by the cut cable do not have internet access until the cable is fixed. 

Parallel Computing

A parallel computing system breaks large problems down into smaller problems.  A multi-processor computer or multiple computers networked may be in use for the problem, each with a section of the work to solve and return the solution to designated memory space. Memory may be directly shared within a multi-processor computer or a global memory space for asynchronous updates for multiple computers use.

The system time use for this type of computer is the longest time any of the computers takes to solve it's assigned portion of the problem. If the portion taking the longest time is critical to continuing on in the solution all of the other computers wait until the long process is finished for further work on the problem to continue. 

A quick analogy for parallel computing is cooking a recipe. You access the ingredients needed to complete a catering job for a large order of cookies in the bakery shop. You know that you can get started, but the flour will run out. You send one of your workers to the store for more flour since your order did not come in on the truck today. Everyone else starts making the cookies and cooking in the oven. Flour runs out prior to the worker returning with the flour. Those workers mixing cookie dough with flour must stop until the flour arrives. 

OER AND GAVS CREATED MATERIAL