Carrier Sense Multiple Access

After carefully interviewing the Stake holders of the Leonard Cooper Charter School, several issues were observed. The first noticeable concern was the print server. Their management of print jobs on the print server are called into question because of the many collisions on the print server. They are presently using a half-duplex system for their print jobs. A half-duplex system provides signal communication in both directions, however only one direction at a time. A good example of this technology might be two-way radios. The person listening must wait until the transmitter concludes the signal transmission before responding to the call otherwise a collision will occur and the entire message won’t get received. In a half-duplex Ethernet network, a collision is the result of two devices on the same Ethernet network attempting to transmit data simultaneously. In the event of a network “collision”, both transmitted packets are discarded. Collisions are a normal occurrence on Ethernets. To remedy this problem, an Ethernet standard was put into place called, “Carrier Sense Multiple Access/ Collision Detect (CSMA/CD)” This allows network devices to “take turns” using the signal carrier line.

When a device wants to transmit, it checks the signal level of the line to determine whether someone else is already using it. If it is already in use, the device waits and retries, perhaps in a few seconds. If it isn’t in use, the device transmits. However, two devices can transmit at the same time in which case a collision occurs and both devices detect it. Each device then waits a random amount of time and retries until successful in getting the transmission sent. (Bryant, 2011). Another area of contention is the actual speed of the network. Leonard Cooper is not operating at the optimal speeds necessary to handle daily business. Based on Mr. Fischer’s interview, they are currently working with a 10 megabit connection. It was also discovered that his laptop had a 1 gigabit network card installed. So, the network speed was definitely the problem. In addition, there seems to be some connectivity issues with the backbone of the network. One of the biggest complaints included not being able to use Voice over IP. Therefore, a more suitable media that will increase their network speeds needs to be put into place. A final issue that needs to be addressed is the possibility of adding class room computers to the network. A cost effective, yet scalable solution is substantial. Recommended Solution

The best alleviation for print job collisions is to upgrade from a half-duplex to a full duplex switched environment. Full-duplex is a data communications term that refers to the ability to send and receive data at the same time. Legacy Ethernet is half-duplex, meaning information can move in only one direction at a time. In a totally switched network, nodes only communicate with the switch and never directly with each other. Switched networks also employ either twisted pair or fiber optic cabling, both of which use separate conductors for sending and receiving data. In this type of environment, Ethernet stations can forgo the collision detection process and transmit at will, since they are the only potential devices that can access the medium. This allows end stations to transmit to the switch at the same time that the switch transmits to them, achieving a collision-free environment (Pidgeon, 2011). Therefore, the 24 Port Switch is highly recommended. The solution is to implement 3 print servers each having a 24 port switch connected to it. Having a switch on the server would allow each node to communicate with the switch. The switch communicates with the printer. With proper configuration, this hardware set up will be the resolution to the printer collision issue because the switches would manage the print jobs.

Fortunately, today’s wireless technology is cutting edge therefore remedying the ideal solution for networking the classroom computers. There are a number of benefits involved in adding wireless technology to an existing computer network. To begin with, it’s much more cost effective. There is a lot more money required to have additional cabling installed. With a wireless router, one modem, and a host of wireless antennas strategically located throughout the building, this will enable all computers the needed access to the internet. Depending on the standard that is chosen, wireless can have speed from 11 Mbps to 100 Mbps. The wireless technology that is recommended is the IEEE 802.11n. The 802.11n has more speed and range than the other standards. Wireless networks also offer easy file access regardless of which part of the building you are in. It allows easy transfer of the files between your laptops and desktops. Another reason for wireless is you will always have a connection to the internet. Wireless network technology runs at speeds far greater than broadband internet access. (Garfield, 2006). Based on the many issues discovered in regards to the backbone of the computer network structure, perhaps a more thorough approach is needed. The backbone network is an important architectural element for building enterprise networks.

It provides a path for the exchange of information between different LANs or sub-networks. A backbone can tie together diverse networks in the same building, in different buildings in a campus environment, or over wide areas. Generally, the backbone’s capacity is greater than the networks connected to it. (Sheldon 2001). Although this may not be the most cost effective approach initially, it is the most effective and reliable solution. Therefore, Fiber Optic 1000 Base F is highly recommended. Fiber optic cable has many advantages over copper cable. Fiber transmits data much faster over longer distances than copper. Fiber cable is also smaller diameter and weighs less than its copper counterpart, making it ideal for a variety of cabling solutions.

Fiber optics are immune to RFI (radio frequency interference) and EMI (Electromagnetic Interference) making them ideal for applications where close proximity to electronic devices can cause RFI and EMI disruption. Fiber optic cabling uses less power and provides less signal degradation than copper cables. They are generally non-flammable, virtually unable to be tapped, and are better suited for data and illumination transmission. Because the company needs to have speeds of 1000, 100 networks, a fiber optical cable for the backbone connections would be plausible. The fiber optical can transmit more data because of its design. This standard allows transmission of data at 1 Gbps. (Novison, 2011), this will suffice the required speeds for Voice over IP phones.

References

Bryant, Chris, (2011 January), How Ethernet CSMA/CD Works
Retrieved January 16th 2013, from http://www.mcmcse.com/cisco/guides/csma.shtml Garfield, L, (2006, August), 5 Reasons to Choose Wireless Networking Retrieved January 16th 2013, from
http://ezinearticles.com/?5-Reasons-to-Choose-Wireless-Networking&id=2707
30 Novison, E, (2011). Bandwidth Capacity of Fiber Optic Cable
Retrieved January 16th, 2013 from
http://www.ehow.com/about_6316840_bandwidth-capacity-fiber-optic-cable.html Pidgeon, N, (2011). How Ethernet Works
Retrieved January 16th, 2013 from
http://computer.howstuffworks.com/ethernet15.htm
Sheldon, Tom, (2001, January), Backbone Networks
Retrieved January 16th, 2013 from
http://www.linktionary.com/b/backbone.html