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What You Need To Know. In this day and age of high speed Internet access being almost universally available, you tend to hear the term broadband thrown around a lot. Private IP addresses are not, and most are typically hidden behind a device with a public IP address. While a router provides the bandwidth, an access point extends that bandwidth so that the network can support many devices, and those devices can access the network from farther away. Understanding the basics of how networks are put together is an important step in building a wireless network in a community or neighborhood. Find the IP addresses assigned to your computer, and your network. When a computer on an Ethernet network transmits data across an Ethernet network containing PCs connected to a hub, the data is actually sent to every computer on the network.
At one time making sure that a network card matched the network medium was a really big deal, because there were a large number of competing standards in existence. For example, before you built a network and started buying network cards and cabling, you had to decide if you were going to use Ethernet, coaxal Ethernet, Token Ring, Arcnet, or one of the other networking standards of the time.
Each networking technology had its strengths and weaknesses, and it was important to figure out which one was the most appropriate for your organization. Today, most of the networking technologies that I mentioned above are quickly becoming extinct. Pretty much the only type of wired network used by small and medium sized businesses is Ethernet.
You can see an example of an Ethernet network card, shown in Figure A. Figure A: This is what an Ethernet card looks like. Modern Ethernet networks use twisted pair cabling containing eight wires. These wires are arranged in a special order, and an RJ connecter is crimped onto the end of the cable.
Figure B: This is an Ethernet cable with an RJ connector installed. As you can see, computers use network cards to send and receive data. The data is transmitted over Ethernet cables. In this day and age of high speed Internet access being almost universally available, you tend to hear the term broadband thrown around a lot. Broadband is a type of network in which data is sent and received across the same wire. In contrast, Ethernet uses Baseband communications.
Baseband uses separate wires for sending and receiving data. What this means is that if one PC is sending data across a particular wire within the Ethernet cable, then the PC that is receiving the data needs to have the wire redirected to its receiving port.
You can actually network two PCs together in this way. You can create what is known as a cross over cable. A cross over cable is simply a network cable that has the sending and receiving wires reversed at one end, so that two PCs can be linked directly together.
The problem with using a cross over cable to build a network is that the network will be limited to using no more and no less than two PCs. Rather than using a cross over cable, most networks use normal Ethernet cables that do not have the sending and receiving wires reversed at one end. Of course the sending and receiving wires have to be reversed at some point in order for communications to succeed.
This is the job of a hub or a switch. Hubs are starting to become extinct, but I want to talk about them any way because it will make it easier to explain switches later on.
There are different types of hubs, but generally speaking a hub is nothing more than a box with a bunch of RJ ports. Each computer on a network would be connected to a hub via an Ethernet cable. You can see a picture of a hub, shown in Figure C.
Figure C: A hub is a device that acts as a central connection point for computers on a network.
A hub has two different jobs. Its first job is to provide a central point of connection for all of the computers on the network. Every computer plugs into the hub multiple hubs can be daisy chained together if necessary in order to accommodate more computers. Right now you might be wondering how data gets to the correct destination if more than two PCs are connected to a hub. The secret lies in the network card.
When a computer on an Ethernet network transmits data across an Ethernet network containing PCs connected to a hub, the data is actually sent to every computer on the network.
As each computer receives the data, it compares the destination address to its own MAC address. If the addresses match then the computer knows that it is the intended recipient, otherwise it ignores the data. As you can see, when computers are connected via a hub, every packet gets sent to every computer on the network. The problem is that any computer can send a transmission at any given time. Have you ever been on a conference call and accidentally started to talk at the same time as someone else?
This is the same thing that happens on this type of network.
When a PC needs to transmit data, it checks to make sure that no other computers are sending data at the moment. If the line is clear, it transmits the necessary data. If another computer tries to communicate at the same time though, then the packets of data that are traveling across the wire collide and are destroyed this is why this type of network is sometimes referred to as a collision domain.
Both PCs then have to wait for a random amount of time and attempt to retransmit the packet that was destroyed. As the number of PCs on a collision domain increases, so does the number of collisions. As the number of collisions increase, network efficiency is decreased.
This is why switches have almost completely replaced hubs. A switch, such as the one shown in Figure D, performs all of the same basic tasks as a hub. The difference is that when a PC on the network needs to communicate with another PC, the switch uses a set of internal logic circuits to establish a dedicated, logical path between the two PCs.
What this means is that the two PCs are free to communicate with each other, without having to worry about collisions. An example of an IP address is An IP address is similar to a street address.
Parts of the address describe where in the world the building is located, another part narrows it down to a state or city, then the area within that state or city, then the location on the street.
The complete addresses for each of these houses is: There are different classifications, or types of IP addresses. A network can be public, or it can be private. Public IP addresses are accessible anywhere on the Internet. Private IP addresses are not, and most are typically hidden behind a device with a public IP address. Here we can see an example—a street with two buildings with public IP addresses —representing computers with addresses that are visible to the entire Internet.
These buildings might be anywhere in the world, but their addresses are complete, so we know exactly where they are and can send messages to them.
We have a new building on the street. That building has a public IP address, and a private IP address.
There is also a fence that blocks the rest of the Internet from seeing and passing messages to addresses on the street. The postal building controls messages that travel between the Internet and the street, keeping track of messages that leave the street, and directs return messages to the right house.
On the street, it has the address Traditionally, computers are connected to each other using cables—creating a network. The cable used most often is Ethernet, which consists of four pairs of wires inside of a plastic jacket.
It is physically similar to phone cables, but can transport much more data. But cables and computers alone do not make a good network, so one early solution was to use a network hub. The Ethernet cables from the computer connect to the device similar to the hub of a bike wheel—where all of the spokes come together in the center.
An example of how a hub works is shown below. Computer A wants to send a message to computer B. It sends the message through the Ethernet cable to the hub, then the hub repeats the message to all of the connected computers. A network using a hub can slow down if many computers are sending messages, since they may try and send messages at the same time and confuse the hub.
To help with this problem, networks began to use another device called a switch. Instead of repeating all messages that come in, a switch only sends the message to the intended destination. This eliminates the unnecessary repetition of the hub. Using a switch, computer A sends a message to computer B —the other computers do not see the message.
Those computers can send other messages at the same time without interfering. Switches do have a limitation though—they only know about the addresses of equipment that is plugged directly into them. So, you can only send messages to a small number of devices—however many ports the switch has!
If you need to send a message to a computer on another network, it will need to be sent through a router, which we discuss next. Routers do the majority of the hard work on a network - they make the decisions about all the messages that travel on the network, and whether to pass messages to and from outside networks. There are three main functions:. Routers separate networks into sections, or bridge different networks together, as we see in the example above—the private network of They can assign IP addresses.
In the example of They can filter messages or keep users out of private networks. Most routers have a Firewall built in. This is a software function that keeps unwanted messages from reaching the computers on the inside, or private part, of the network. Let us take another look at As it turns out, that postal service building is acting as a Router. In this case, the postal service building is routing messages between the rest of the Internet using its public address and the street with private addresses.
This module is intended to provide some helpful background on networking. We recommend reading the upcoming but not finished!