When dealing with networks one has to understand the different types and how they are used along with the advantages and disadvantages of each.
A mesh network allows for redundancy in that if one node goes down all terminals are able to still communicate with
other terminals and networks by taking several possible paths. The mesh network will be more complex and time consuming
to install, but is also the more reliable than other topologies. If each terminal having reliable connectivity is mission
critical, the knowledge is available and cost is not really a factor then a mesh would be the preferred network.
Bus topology is probably the least preferred topology to implement. If one node is removed or non-operational on the bus
then all terminals will not be able to utilize the network. According to Annabel Dodd (2005) “Prior to hubs, each device
in a LAN was wired to another device in a “bus” arrangement.”(p. 26)
Circumstances that may play a factor in this use of this particular topology would be cost savings in regards to cable and
the importance of that particular network to the department’s mission, as well as the network’s size as well as security.
Required speed, number of attachments, cable length, and use play a factor in determining the use of the bus topology.
Bates & Gregory (2000) tell us that bus speed is limited to “10Mbits/s with effective throughput of 3.3-4 Mbits/s” and that
attachments cannot exceed “1024 addressable nodes” and are “limited to cable lengths of 1500 meters.” They continue on to
say that “collisions when the network gets 40% busy, resulting in less throughput.” It seems that the bus topology is also
the least secure in respect to the fact that all transmissions are a broadcast to the entire network.
The star topology is another network architecture. Circumstances to install this type of network would be similar to those of the bus topology. The star topology would be
primarily used with hubs and switches. This topology allows for all terminals to continually communicate on the network
when a terminal is dropped or goes down. This type of topology is important when connectivity of each terminal in the
network is important and is mission critical to operations.
Combinations of all the various topologies will be seen in MAN, WAN, and even some larger LANs. An example would be a
college campus in which each department uses a star topology internally, but meshes with all the other outlying departments.
So in the case of a college campus all departments would still be able to access records from other departments on campus
when one or more departments lose connectivity.
By: Joseph Brochin
Posts Tagged ‘Throughput’
Network Basics
January 30th, 2010Wireless Network Standards – 80211a, 80211b, 80211g, 80211n, 80216
December 28th, 2009
The following describes the current defined wireless protocol standards.
802.11a
This standard was approved in 1999 with the IEEE committee. It specifies a maximum data rate of 54 Mbps using 5.15 GHz – 5.35 GHz and 5.725 GHz – 5.825 GHz unlicensed bands in the United States. The advantage of 802.11a is higher throughput however the cell coverage is smaller and additional access points will be needed. There is much less interference from devices such as cell phones, microwaves and commercial devices using the 2.4 GHz band. There are 23 non-overlapping channels with the current 802.11h specification.
Wireless Network Installation In Larger Up Scale Homes
December 18th, 2009
A regular two story single family homes wireless installation usually only will require one wireless router placed centrally in the home. The newer trend that Schaumuburg Computer Repair faces is the new mega tear down homes that are all brick and have three floors with over 4,000 square feet. The question is how do I give the customer the best wireless coverage for the least price.
Standards Tutorial: 802.11b is old don’t use it. 802.11g runs at a reported 54mbps but actual throughput is 22 mbps, it has greater range than 802.11a. 802.11a is mostly used in areas where there are many wireless access points already such as business offices. Also 802.11a network can have more co-located wireless access points because 802.11a has 8 non-overlapping channels while 802.11g has only 3. 802.11n is only a draft version at this point so do not purchase draft n products. I do recommend purchasing 802.11g wireless access point with MIMO (Multi-in Multi out) technology. These access points are configured with two radios, which allow them to send and receive at the same time.
Phase one: Coverage Area – Defining coverage area for the home is very important because defining areas to blanket can effect the customers cost. We have many customers that do a lot of work in detached garages and basements but many people use wireless in only one room. So the rule of thumb is the more areas the need wireless coverage the higher the price for the customer.
Phase two: Site Survey – Perform a site survey to find out what other wireless networks are in the area. This is very important because in might impact whether you install a 802.11g wireless network or a 802.11a wireless network. If we perform a site survey and find many 802.11g wireless networks on varies channels it might be better to install a 802.11a wireless network which runs on a different frequency. Knowing what channels other networks are running on is very important because each one of your wireless access points will need to run on a different channel. 802.11g standards have only three non-overlapping channels, which are 1,6 and 11 while 802.11a has eight non-overlapping channels. The rule of thumb to follow is that 802.11g is subject to more interference but has greater range than 802.11a.
Phase threee: Distibution system – Now you need to decide how you’re going to distribute your wireless network throughout the home. A wireless access point acts a wireless wire so you will still find a method to get a network connection to that wireless access point. You have three options: running network cables throughout the house (The worst option), setting up power line Ethernet, or setting wireless repeaters or bridges. Running network cables is your last option because it requires drilling and time, which equals more cost. Power line Ethernet is great because it turns your power outlets into network cables. All you have two do is plug in one power line adapter by your internet connected wireless router and then plug in adapters throughout the house where you need wireless access points plugged in. Then your final option is to set up wireless repeaters to which will extend your original signal through out your house.
Phase four: Access point Placement – Your first access points should be in the most central parts of the home with supplemental wireless access points placed in hard to reach areas. Keep the wireless access points away from large metal objects and if the wireless access point can’t be placed in a central location use directional antennas to point the wireless signal internally instead of outside.
Phase five: Wireless access point Configuration – Your site survey will have revealed that 99% of the population purchases a wireless access point from best buy plugs it in and leaves all the defaults. So that means that their SSID is linksys and the wireless router / access point are on channel 6. Our larger home wireless network will need two to three wireless access points so we will configure our first two wireless access points on channels 1 and 11. If a third one is needed then you can use channel 6; just make sure user connections aren’t dropped after the wireless clients are configured. Next you will want to name your wireless network (SSID). Choose a obscure name like house, a color or some thing that can’t link the network with the family. The reason for that many people have their SSID as there last name and the there network key the same or a pet or child’s name. The more hacker knows about the family the easier it will be to hack the network
Phase 6: Security – You will want to use AES encryption with WPA2 handling for the majority of wireless networks. If your clients are going to be gaming over the wireless network you could consider using WEP 128 because on older wireless access points AES encryption is processor intensive. The myth is that wireless encryption can be hacked in five minutes which is true if you have enough network packets to crack. The whole process is collecting the packets then cracking those packets, the collection of those packets could take weeks if not months. Then after the packets are collected the encryption has to be cracked.
By: Eric Meyer
