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Collision Avoidance Essay

The importance of protocols in the communication of data packets over networks cannot be under-emphasized. With the advent of increasingly easier forms of communication and technological revolutions happening by the hour, millions and millions of computers are now communicating over networks with one another. Clearly looking at the past decade’s rates of technological growth, it is no surprise that the breakthrough in communication was the creation of the wireless LAN. Without this single invention, the globe would be at least 30% more wired.

In the years to come, this figure could rise and certainly in the long term a solution had to be found to the problems of wired connectivity. Fortunately the solution came even before IP version 6 will be implemented. IP version 6, designed to accommodate more IP addresses than the total number of people on Earth plus their houses plus their dogs and plus a lot of other things. IP version 6 literally gives throwaway IPs and will see millions of computers being added to the global network monthly. There are numerous protocols available for wired and wireless networks.

There are trade-offs between speed, packet loss ratios, costs and distances, however, the bottom line is to meet what matters at the end of the day for that particular type of network (Cottingham, 2005). For example, the network at Cambridge may not be concerned with costs but may focus entirely on speeds and a low packet loss ratio. Thus, it may be having a different protocol than the local cafe whose concern may be costs for their own profitability. The aim of this paper is to discuss the differences between two varieties of the Carrier Sense Multiple Access (CSMA) protocol – Collision Avoidance (CA) and Collision Detection (CD).

The advantages and disadvantages of each will follow after their differences have been explained. Protocol in Focus: Carrier Sense Multiple Access Carrier Sense Multiple Access (CSMA) is a general network data transfer protocol that allows the transfer of packets across a network. Since this is a generic protocol, there are specializations in this protocol which make different types of protocols fitting into wired or wireless networks (Cottingham, 2005). Since CSMA works across the Medium Access Control (MAC) layer and is not a deterministic protocol – rather it is a probabilistic protocol – there are various types of CSMA protocols.

The more important of those are the CSMA/CA and CSMA/CD protocols which work on wireless and wired networks (Ethernet) respectively. CSMA/CA v. CSMA/CD CSMA/CA: This revolutionary transmission protocol used in wireless networks does not offer the capability of “detecting” collisions. A wired medium can easily detect a collision; however, this is not the case in a wireless medium. Thus, the modus operandi of this protocol is to keep waiting for random clock cycles and then begin packet transmission.

However, if there is a collision, it goes unnoticed at the transmission ends (sender and recipient), and thus a collision results in an erroneous packet with no re-transmission of the lost packet (Korkeakoulu, 2009). CSMA/CD: The simplistic model of operation – which has always been the traditional one – is a continuous cycle of waiting for a free wire or medium, transmission of the data packet, immediate suspension of transmission if there is a collision and re-initiation of the transmission after random clock cycles (Korkeakoulu, 2009).

Thus, the basic difference is that CSMA/CA works on wireless networks with no way of detecting collisions in the transmission, while CSMA/CD works on wired networks with collision detection mechanisms and with the possibility of re-transmission of lost packets. Advantages and Disadvantages Obviously, there are trade-offs associated with both CSMA/CA and CSMA/CD protocols. CSMA/CA allows wireless networks and communication possible and if not for this type of MAC protocol, the entire wireless LAN communication systems in the world would be impossible.

At the same time, CSMA/CD offers exceptionally low packet loss ratios providing the highest guarantees of secure and accurate communication. The issues of data security are known to exist in CSMA/CA protocols since the absence of a “wired” medium allows free access to the packets by any recipient (Cottingham, 2005). However, encryption and CSMA/CA security algorithms have reduced risks to lesser odds but still not up to the mark of CSMA/CD. There is an additional delay caused in packet transfers in the CSMA/CA protocol since it is a probabilistic model which will wait a random time before it will transmit a packet.

However, the delay in the CSMA/CD mode is perhaps, on average, greater than the delay in CSMA/CA protocol. This is due to the fact that in a CSMA/CA protocol, there is no re-transmission of a lost data packet. Thus, this essentially results in a serial transfer of packets with small random wait times. Any packets lost result in minute information losses which have been generally tested and found to be suitable even for voice over IP transmissions. However, in the case of CSMA/CD protocol, the re-transmission of the collided packet causes a rather larger delay because the average time to transmit a single packet increases (Korkeakoulu, 2009).

Thus, there is a critical trade-off between accuracy in the transfer of packets in the case of CSMA/CD while at the same time a greater speed in the wireless medium can be achieved using the CSMA/CA protocol. It is therefore very much upon the requirements of a network as to which protocol is chosen for communication and data transfer, however, it should be remembered that each type of protocol has a different set of advantages and disadvantages allowing network specialists the decision to choose their medium to be followed in a network setup.

References Cottingham, D. (2005). Digital Communication II Explanations. Retrieved March 25, 2009, from University of Cambridge: Computer Laboratory Digital Technology Group: http://www. cl. cam. ac. uk/~dnc25/dciiexplanations. html Korkeakoulu, E. (2009). Wireless Personal, Local, Metropolitan, and Wide Area Networks. Retrieved March 25, 2009, from WLAN Part 2: http://www. comlab. hut. fi/studies/3240/luentokalvot/4_wlan2. pdf


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