NETWORKING 101

By Justin Pineda

This article is created to serve as an introduction to basic networking concepts. This involves some discussion about the Internet, network devices, how it works and the like. We will also talk about some technical concepts for us to better understand the networking process (i.e. how a data is transmitted over the network).

Introduction

 

In today’s world, the Internet plays a vital role in communication. Everything became easier because of the Internet. Distance is not a barrier anymore. Before the arrival of Internet, the popular mode of communication to far places requires time, like when sending a mail for example. Now, it’s just a click away through e-mail. We can also talk to our friends real-time through Instant Messenger (IM). Now, do you know how data is transmitted to your friend when you chat?

A normal flow of communication contains a sender, a receiver and a channel. This also applies to a network. But of course, aside from the humans, devices also play its role. When you chat for example, the data is translated into a series of numbers which we call binary numbers (1 & 0) to be understood by the computer and to be able to send it to its proper channel. There is a process of converting these messages to binary numbers through layers and network protocols.

Elements of a Network

 

As mentioned, the communication process for computer networking remains the same. What we need to understand now are things that make up the communication for computer networking. There are four elements:

1.                  Rules

Like when sending a snail mail to a friend, there are procedures on how to successfully send it. This includes putting it in an envelope, writing the address both of the sender and receiver of the mail at the back of the envelope and putting stamps. This is same with networking where rules, which are technically termed as protocols, define how the data is sent.

2.                  Message

Message is the actual data itself. It is the file that you have sent through email. It is the video you are waiting to view in You Tube. This is the message in the letter you sent. This is self-explanatory.

3.                  Medium

The medium is the element that says in what way the message is sent. For example in networking, for a typical Local Area Network (LAN), standard workstations are connected through a cable (a straight cable to be exact) while other laptops/net books connect via Wi-Fi (Wireless Fidelity).

4.                  Device

Of course, the device is an essential element as well. Different devices have their own role. Computers are used by the end users and these are connected to a switch and data are transmitted by a router to another.

These elements comprise the network. We will take a look at each element and give more details to each one of them.

Network Architecture

If you are tasked to create a network, what will your basis be? Will you just buy workstations and connect them in a switch? There are concepts you need to consider in order to build a good network. You need to design your network based on the following key factors:

1.                  Fault Tolerance

In creating a network, you shouldn’t think of an ideal scenario where everything is all right. You have to think of possible problems which your network might encounter. For example, you put all your workstations connected in one switch. You find it very easy to do, setup and configure. But what happens if the switch goes down? Then your network will go down as well. Fault tolerance refers to the capability of the network to withstand forms of interruptions of its service. So most cases, there are back up servers, generators and network planned topologies in order to cater this particular concern.

2.                  Scalability

So you have created the fault tolerant network that is good for the users in it. But is your network ready for a dynamic environment? Have you considered that the network may grow and will require more space, bandwidth etc? Scalability refers to the capability of the network to adjust in changes in the components of the network, may it be the number of users or devices.

3.                  Security

When you design your network, considerations must be made in order to group workstations based on security importance. What is security in this context? Security refers to giving access that is only needed by a particular type of user. For example, company reference materials should only be available within the company’s network. External users should not be able to access these files. These particular privileges of access should be determined in the network design. The example I gave is what we call Intranet, which means access only “inside” the local network. You have to consider which part of the network should be given Admin access, User access and Guest access.

4.                  Quality of Service (QoS)

The demands for network bandwidth vary from the type of work that people have. Which is more likely to consume more network bandwidth, the cashier or the web developer? You need to give priority over the ones who need more. In the field like IT Security, Security Analysts like me need more bandwidth because we are all connected to the Internet and all our work relies on having good network connection access.

Network Communication

So let’s say that you try to send an e-mail through http://mail.yahoo.com. The first thing you do is to type the Uniform Resource Locator (URL) of the website which is – http://mail.yahoo.com. The URL is equivalent to an Internet Protocol (IP) address which is represented by numbers. We have URL’s so that we don’t need to remember numerical forms of addresses. Instead, we just type it based on the name that we associate with it like “mail” and “yahoo.” A particular protocol which is the Domain Name System (DNS) resolves the URL to its corresponding IP address. So think of the IP address a Website ID and the URL as the Website name.

The image above shows how the personal workstation travels going to http://mail.yahoo.com with IP address – 203.84.219.114.

I just showed you how data travels to the domain Yahoo. Anyway, when the website appears in a web browser like the Internet Explorer or Mozilla Firefox, the data from the Yahoo site goes to your network and displays it. So from data understandable by the user, it goes through different layers which translate this data understandable by machines that can travel through different media (such as cables, atmosphere etc). A reference model is used for protocol classification per layer. We call it the Open Systems Interconnection (OSI) model. The OSI model has 7 layers which defined to sort of give us an understanding of how data is transmitted and retransmitted.

So going back to the Yahoo mail site, the user interface that we see in the web browser is in the Application Layer of the OSI model. This is the topmost layer of the OSI model. This is quite easy to understand since the Application Layer gives interface of the data to the user. For this example, the protocol used is Hyper Text Transfer Protocol (HTTP). HTTP is a protocol used to be able to browse web pages. There are a lot of Application Layer protocols aside from HTTP.

The next layer is the Presentation Layer. Its main responsibility is to do compression/decompression, coding, conversion and encryption/decryption. For example, when you load an HTTP, when we try to save images, there’s a default “Save As” to type of image which the site dictated what it should be like .jpg, .gif etc. Same is true with video types and media files. Sometimes for proprietary sites they have their own extensions.

After the data is compressed, converted and coded, it checks the status of the data and connection. Did the data go to the correct destination? Is the connection active or not? Is the device idle or has been receiving information?

Let’s now go to the next layer called the Transport Layer. This layer is responsible for determining the kind of services the client/server are running and directing this particular service to the right port. For example, when you visit the site http://mail.yahoo.com, you go to a particular IP address 203.84.219.114. This particular domain might be running different services. Like for example, if you open its site through HTTP, it actually connecting to Yahoo’s domain through port 80. If you are trying to send an e-mail through Yahoo mail, a connection is made through port 25 which is Simple Mail Transfer Protocol (SMTP).

There are two popular protocols under the Transport Layer- User Datagram Protocol (UDP) and the Transmission Control Protocol (TCP). The former is connectionless while the other is connection-based. There are services that are considered very essential to have an established first to make that the communication of data is received successfully. The three way handshake is a process used by TCP to ensure that connection is established before transmitting data. For example, in SMTP, the sure way to send an e-mail is to established a connection between the client and the server. Otherwise, we are not sure whether the data is sent properly or not.

Basically, we learned how services are connected through ports. But before we’re able to send the data to the right service, we have to send the data to the right network. This what makes the IP address necessary. This next protocol is called the Network Protocol. An IP address can be private or public. A private IP is an address given by a router used for local network. These include IP families from 192.168.x.x, 172.x.x.x and 10.x.x.x. Any IP addresses under those mentioned families are considered to be private. Public IP’s are numbers otherwise and doesn’t exceed 255.255.255.255. There are other conditions though. But for simplicity sake, public IP’s are those that host a site for a particular organization.

Each Local Area Network (LAN) has a gateway. When a particular host tries to send a data to another IP, it first checks whether the said destination IP is found within the network. If it finds it, then it is send directly to it. However for most cases, the destination is outside the LAN. Now, a target IP that is not found on the LAN is directly sent to the default gateway. This gateway passes the data to other routes in order to find the right destination. The router has three processes: forward the packet to the next route, deliver the packet to the destination or drop the packet. There are mechanisms through routing protocols used on how to determine best paths for data routing.