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Types of Network Topology

November 17th, 2009



Network topology refers to the physical layout of the network i.e. the locations of the computers and how the cable is run between them. To select the right topology for how the network will be used is very important. Each topology has its own strength and weaknesses.

The choice of a topology for installing a computer network depends upon a combination of factors such as, reliability, performance of the system, number of nodes and geographical distribution of the system.

The main 2 types are

Bus Topology & Peer to Peer Topology

Peer to Peer topology consists of Star topology and Ring topology.

Bus Topology

It is often used when network installation is small, simple or temporary. On a typical bus network the cable is just 1 or more wires with no active electronics to amplify the signal or pass it along from computer to computer. This makes the bus a passive topology. When 1 computer send a signal up the wire all the computers receive the information but only one with the address that matches accepts the information, the rest disregard the message.

Advantages:

1) Easy to use and to understand.

2) Requires least amount of cable to connect the computers together. It is therefore less expensive than other cabling arrangements.

3) It is easy to extend a bus; two cables can be joined into 1 longer cable with a BNC, Barrel connector making a longer cable and allowing more computers to join the network.

Disadvantages:

1) Heavy network traffic can slow a bus considerably as only 1 computer can send a message at a time.

2) It is difficult to troubleshoot the bus. A cable break or loose connector causes reflection and stops all the activity.

Star Topology

In this kind of topology all the cables run from the computers to the central location where they are all connected by a device called hub or switch. Each computer on a star network communicates with a central device that resends the message either to each computer or only to the destination computer, e.g. if it is a hub then it will send to all and if it is a switch then it will send to only destination computer.When network expansion is expected and when the greater reliability is needed, star topology is the best.

Advantages:

1) It is easy to modify and add new computers without disturbing the rest of the network.

2) The center of the star network is a good place to diagnose the faults.

3) Single computer failure does not necessarily bring down the whole star network.

Disadvantages:

1) If the central device fails the whole network fails to operate.

2) Star networking is expensive because all network cables must be pulled to one central point, requires more cable than other network topologies.

Ring Topology

In this type each computer is connected to the next computer with the last one connected to the first. Each retransmits what it receives from the previous computer. The message flows around the ring in one direction. The ring network does not subject to signal loss problem as a bus network experiences. There is no termination because there is no end to the ring.

Advantages:

1) Each node has equal access.

2) Capable of high speed data transfer.

Disadvantages:

1) Failure of one computer on the ring can affect the whole network.

2) Difficult to troubleshoot the network.

Topologies remain an essential part of network design speculation. But understanding these can help you to get the deeper knowledge of the elements like hub, switch etc.

By: Deepti Pawar

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Network Redundancy Techniques

November 10th, 2009



When building a network, some considerations must be taken from the point of view ofavailability. In the context of networks, availability means that the network must be operable during the whole day regardless of failures. Thus, some techniques must be taken to make the network available all the time.

In order to develop redundant network one must consider the possible failures that must occur during the network operation. These failures are categorized into two types: link failure and network device failures. In link failures, one cable connecting two computers or two any two devices such as routers or switches can be disconnected and make some of the

network or all of it to be down. On the other end, device failure means that the network device itself is down which could be router, switch, or a hub.

First let us find how to overcome link failures. The solution in link failures is simpler than device failure because all we need to do is to provide multiple links between devices such that when a link is down, other link takes its role. This is simple of course but can lead to problems. This is because when there are more one link connecting the devices the data will find multiple links and the switch will forward the data to multiple links and the receiving end will receive the data more than one time. In addition, looping can occur because the data will be forwarded across the links forever. This will occur because there is more than one path to the destination and because the switch or the hub forwards the data to all ports.

The solution to looping is to use some protocols that block some ports on the switch and open others so that only one path is existed to the destination. This is achieved by what is called spanning tee protocol, which is available on Cisco switches. Notice that the concept of looping and STP are applied only to devices connected through a LAN and not to routers.

Second let us see the other type of failure which is device failure. This type occurs when a network device fails and thus is unable to forward the packets. The failure here can have a big impact on the network if it occurs in the core layer of the network which connects the whole network together. Therefore the solution is suggested to be applied at the core layer where two network devices are connected to the network to forward the data, one is the primary and the other is the secondary If one device fails, the secondary becomes available.

The above technique is configured on the router or the switch depending on what is used. Some protocols are developed to accomplish this function and are available on Cisco devices. When implementing it, one must connect the device at the core which must be redundant to the proper ports of other devices and connect similar device to the rest of the network in the same manner the primary device is connected. If the primary fails, this secondary takes its role.

By: Youssef Edward

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How to Set Up and Install Your Own Home Network

October 22nd, 2009



Setting up a home network doesn’t have to be difficult. It also depends on what time of home network you want to install. Maybe you want to install a wired network or maybe you want to install a wireless network. It depends on the capabilities of the computers within your home as to what route you’re going to take.

The wireless network

The wireless network is probably your easiest network to install. That’s because you don’t have to hide a cord all the way around your home. As a matter of fact, you just need to have a computer that is wireless capable and a router. Seems easy enough, right? Well, it can still be a bit tricky because you have to program that router so that all of your computers can talk to it.

So let’s say that your computer is not wireless capable. What do you do now? Well, you need to get a wireless adapter to plug into the computer or you need to plug it directly into the router with an Ethernet cable. In homes with multiple computers, there is sometimes that one computer that is not wireless capable. If the others are, they can simply talk to the router from wherever they are. If they are not wireless, then Ethernet cables need to be run from those computers to the router. The router is the hub for your network.

Furthermore, you have to set up your Domain Name System so that the router knows what’s going on. You also have to set IPs and your Dynamic Host Configuration Protocol. If you don’t do these things, then your computers are not going to be talking to each other the way you want them to. They have to know who and what they are talking to in order to ensure that permission is granted. You don’t want someone to sit outside of your home on a laptop and pull off of your network. They could gain access to very personal and very sensitive information if you don’t set everything up the way that it needs to be set up. If you’re not sure how to do this, then it is time to seek professional help.

The wired network

This can be a bit more difficult than the wireless network for the simple fact that you have wires you have to hide everywhere. Everything else as far as DNS, IPs, and DHCP applies because someone on the outside could still compromise your network. Again, you don’t want that to happen. What if you have financial information on your computer? Someone could very easily get a hold of credit card and bank account numbers. So again, if you have difficulty with setting up your network, it is a good idea to look into having a professional take care of the job for you.

Once you have your network set up, you’ll be able to share files with the other computers in your home. You can share video files, music files, and so much more. It is a lot of fun to be able to share all of that information. It is almost like having external hard drives all over your home. You’re able to access information beyond your own hard drive and beyond the Internet. Those are the reasons why more and more homes are installing home networks. When something is stored into the “shared” folder on the computer, other computers are able to access it. Permissions can also be set to allow other folders to be accessed from another computer in the home. This is a good way to keep an eye on the kids and see what it is they’re downloading while on the Internet.

By: Anthony Williams Sr.

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