Ethernet system Essay Example for Free

Ethernet system Essay Robert Metcalfe with his colleagues at the Xerox Palo Alto research Center (PARC) developed the experimental Ethernet system. According to O’Reilly and associates (2000) the main purpose of developing the Ethernet system is to interconnect a personal workstation with graphical user interface called Xerox Alto. The experimental system was used in order to connect Altos and also printers and servers. The systems interface‘s signal clock was patterned in the Alto’s system clock. This resulted to 2. 94 Mbps. data transmission rate on the experimental Ethernet. Ethernet was originally known as Alto Aloha Network. Alto Aloha Network was changed its name to Ethernet by Metcalfe to indicate that the system not only support Alto’s but also other computers. And Metcalfe also point out that the Ethernet has progressed way beyond the Aloha system. He chose the name ether as to describe the essential feature of the system which is the physical medium carries bits to all stations the same way as the aluminiferous ether was once believe to proliferate There are two ways which can be used to allocate the capacity of transmission media: baseband and broadband transmissions. Baseband transmission allocates the entire capacity of the medium to one communication channel. It uses distinct values by measuring the voltage in wire which only carried one signal at a time. In broadband transmission, the system allows two or more communication channels to share the bandwidth of the communication medium. The system uses the technique of dividing the bandwidth into frequency bands which is called frequency division multiplexing (FDM) which works only with analog signals. There is also another technique called time-division multiplexing (TDM) that supports digital signals. Figure 1, show the difference between baseband and broadband transmission mode of operation: Figure 1. Difference in the mode of operation between baseband and broadband Broadband transmission is used in the web hosting companies. This is because of the higher speeds of the broadband. With the use of broadband, people can enjoy the full range of internet services like downloading videos, music, watching movies and plying online games. Transceivers have different speeds which are measured in MHz and also specified in wavelengths. The larger the value of the fiber core of the transceivers, measured in microns, there will be more bandwidth possible but also the distance will be shorter. The 1000 Base-LX is the long wavelength with a signaling speed of 1. 25 ±100 ppm GBd. This transceiver can use both 62. 5 and 50 micron multimode fiber and it also uses single-mode fiber optic cables with distances of 440m, 550m and 5 km. Another transreceiver is the 100 Base-TX which uses 4B5B binary encoding to encode 100 Mbps data stream in a signal of 125 MHz. One pair is used for transmitting data while the other pair is used for receiving the data. Given this, one user can setup a system for full duplex communication given that there are only interfaces in the same collision domain. It is either the two computers are directly connected to each other by crossover cable or a computer directly connected to a switch. Full duplex communication result to doubling the potential throughput but not often reached more than the modest improvement. Based on Sheldon and Big Sur Multimedia (2001), link aggregation is the process of connecting together two or more data channels in order to become a single channel which appears as a single, higher-bandwidth logical link. Also this aggregated links can provide redundancy and fault tolerance if the links follow different physical path. By linking the digital lines, the link aggregation improves the access to public networks. The aggregation is also use in enterprise network to build multigigabit backbone links. It also allows the network’s backbone speed to grow increasingly when the demands on the network increases without replacing everything and buy new and expensive hardware. Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) protocol was intended for local area network (LAN) environments where in all the nodes are positioned few hundred feet from each other. The importance of the protocol is to listen up each node to the channels in a short period of time before it transmits. The main assumption of the protocol is that each node should be able to hear the transmission from every other station. But this assumption is violated in access network and this resulted to several problems. One of the serious problems encountered is the hidden transmitter problem. This occurs when the CSMA/CA cannot function properly due to a wireless node cannot hear one or more of the other nodes. And when this happen, multiple nodes attempt to transmit their data simultaneously over the shared data thus resulting to interference with each other. To address the hidden transmitter problem, the 802. 11 standard uses the protocol request to send/clear to send (RTS/CTS). Before transmitting each packet, each node transmit an RTS packet to other nodes to warn them that it is about to transmit data and after each transmission, it broadcasts CTS packet. This process is time and bandwidth consuming process and it is required for each and every transmission by each and every wireless node. But this process sill does not address the hidden transmitter problem fully because RTS/CTS packets are subjected to repeated collisions. In most applications, the wireless standard 802. 11b operating at 2. 4 ghz is ample enough. This wireless standard is the mostly widely accepted standard among the three wireless standards and also the price of the equipment is the cheapest because of the rising demand for the 802. 11g. Its distance will rely mostly on the communicating devices whether it have line of site or not. And with fewer obstacles among the transmitting and receiving devices, there will be better wireless connection and therefore much better web surfing. The 802. 11b wireless standard is good enough if using wireless route or access point only for internet usage because the connection to internet via broadband modem operates about 2mbps which is very fast. The 802. 11b transfer data at the rate of 11mbps which is sufficient for internet usage. This device saves money on equipment and gives great web surfing services. Another wireless standard being used is the 802. 11g standard. It is replacing the widely accepted standard which is the 802. 11b because both operate on the same frequency and the price drastically goes down on products. This standard is much very similar to 802. 11b because it also usually needs a line of site to achieve optical performance. Both standards, 802. 11b and 802. 11g operate at the same frequency range of 2. 4ghz and are inter-operable with each other. All the devices of 802. 11g can communicate with 802. 11 devices and the main advantage of the 802. 11g devices is that when transferring files betweens computers or networks, it is usually at a greater speed. It is recommended to use 802. 11g when using wireless connection to transfer files (data files, voice, music, and videos) around the home and office. 802. 11g standard also allows manufacturers to developed devices which work at speed of up to 108mbps because it recommended when transferring large data or audio files within LAN. Wi-Fi Protected Access (WPA) is a security technology that is used in wireless network. This was created by an industry trade group called the Wi-Fi Alliance which owns the trademark for the name Wi-Fi and certifies products that bear the name. WPA was created in order to response on the serious weaknesses of the previous system, the Wired Equivalent Privacy (WEP) and also to improve the authentication and encryption features of the WEP. It implements majority of the IEEE 802. 11i and intended to take place the place of WEP. It was designed in order to work with all wireless network interface cards but not with first generation wireless access point. Temporal Key Integrity Protocol (TKIP) is one of the key technologies behind WPA which deals with the encryption weaknesses of the WEP. Also the WAP have built-in authentication which is a key component. The WAP uses the RC4 stream cipher which has a 128-bit key and a 49-bit initialization vector (IV). With the combination of the TKIP and the RC4 stream cipher; this solves the problem of key recovery attacks which was found in WEP. In addition, the WPA provides much improved payload integrity. WPA uses a more secured message authentication code (MAC) but also termed as MIC which stand for message integrity code which is an algorithm â€Å"Michael†. MIC includes a frame counter preventing replay attacks. With the features of the WPA like having increased size of the keys and IV’s, reduced number of packets sent with related keys and adding up of a secured message verification system, it is far more difficult to break in within the system. There is one variation in WPA which is called the WPA pre shared key (WPA-PSK), which is also known as personal mode. This was designed for home and small office usage and networks which can’t afford the cost and complexity of the 802. 1X authentication server. To access the network, the user must enter a pass phrase, with 8 to 63 printable ASCII characters or 64 hexadecimal digits. This can be stored in the user’s computer with discretion under most operating system in order to avoid re-entry and must remain in the Wi-Fi access point. Protected Extensible Authentication Protocol (PEAP) securely transmits authentication information which includes password, over wired and wireless network. It is also an 802. 1x authentication type for wireless LAN’s. The PEAP is created by the Cisco Systems, Microsoft and RSA Security which is base on the Internet Draft submitted to the IETF. (Cisco Systems, 2007) The system uses only server side public key certificates which authenticate clients by creating encrypted SSL/TLS tunnel in between client and authentic server. This protects from casual inspection the resulting exchange of authentication. According to the Cisco Systems Inc. , the following are important benefits of the PEAP web security system: †¢ It relies on the Transport Layer Security (TLS) which allow non-encrypted authentication types (EAP-Generic Token Card and One Time Password (OTP)) support †¢ It uses the server-side Public-Key Infrastructure (PKI) based digital certification authentication †¢ It allows for the authentication to an extended suite of directories which include Lightweight Directory Access Protocol (LDAP), Novell NDS and OTPA databases †¢ It uses the TLS in order to encrypt all the user-sensitive authentication information †¢ It supports the password change at expiration †¢ It does not display the logon username in the EAP identity response †¢ The system is not susceptible to dictionary attacks †¢ It offer dynamic privacy protection while using in combination with Temporal Key Integrity Protocol (TKIP) or the Advanced Encryption Standard (AES) Also the PEAP have enterprise benefit. Based on the Cisco System Inc. , PEAP is based upon the server-side EAP-TLS. This means that organization can avoid the issue associated in the installing of digital certificates on every client machine which is required by the EAP-TLS. This provides the enterprise to choose what method of client authentication depending on their needs. PEAP authentication work in two phases: ? In phase 1, performing the server-side TLS authentication will result to creation of an encrypted tunnel and will achieve server-side authentication. One the process is done the data are encrypted with all the user-sensitive information ? For phase 2 according to the Cisco System Inc. , the client is authenticated by using methods like the EAP-GTC and the Microsoft Challenge Authentication Protocol (MS-CHAP) Public switched telephone network (PSTN) is referred as the public communication providing local, extended and long distance call telephone service. It is composed of telephone exchanges arranged in order to have nationwide telephone communication system. The system is open for those who can afford the service. Packets, pieces of the caller’s conversation are switched and then sent simultaneously to many connections to reach a receiver in the other end. All the phones in PSTN are connected in a way that any phone can call to any other phone due to all the local phone systems are connected to each other. Mitchell (2007) cited that PSTN provides the traditional Plain Old Telephone Service (POTS) to establishments and residences and also some parts of the PSTN are being utilized for DSL, VoIP and other internet-based network. In much relation to internet, this provides much of the internet’s long-distance infrastructure. Internet service providers (ISP) pay the long distance provider for the access to their infrastructure and they share the circuits among users in the process called packet switching. PSTN network link supports 64 kbps and in residences the PSTN phone lines carrying the bandwidth is made up of copper cable. Dial-up modems utilize 56kbps of the bandwidth when they are connected to a phone line. Also the PSTN utilizes the SS7 signaling protocol. SS7 signaling protocol support the exchange of special-purpose messages on public telephone networks. SS7 messages pass over separate channel different from the channel used for voice communication and it is referred as out of band signaling. Wireless local loop is sometimes called radio in the loop (RITL) or fixed –radio access (FRA). It is a system that connects users and subscribers to the public switched telephone network (PSTN) by the use of radio signals as substitute for copper for all part of the connection between subscriber and the switch. This includes cordless access systems; propriety fixed radio access and fixed cellular systems. One of the advantages of the wireless local loop is that it can be deployed in just weeks or months in comparison with copper wire systems which took months and years for the deployments. The instillation of the wireless local loop considerately has much lower construction cost than laying copper lines. The maintenance and operations of the wireless local loop are that easy and the average maintenance time per subscriber is shorter by 3 to 4 times. Signaling is the exchange between information which concerns about the establishment and in the control of a connection and the management of the network. There are many types of signaling: †¢ In-band signaling pertains to the exchange of signaling information within the same channel of the telephone call †¢ Out-of-band signaling is telecommunication signaling meaning exchange of information to control telephone call. It is done over a channel and it separates from channels which is use for telephone call. This signaling is used by Signaling system #7, the signaling standard controlling the world’s phone calls †¢ Line signaling is much concerned in transmitting information on the state of line or channel †¢ Register signaling is focused on the transmittance of information in the calling/ called telephone number †¢ Channels-associated signaling utilizes signaling channels dedicating to a specific bearer channel †¢ Common-channels signaling, utilizes signaling channels which transmit signaling information to multiple bearer channels. †¢ Compelled signaling pertains to the need of the receive signal to be fully acknowledged before the next signal is sent. †¢ Subscriber signaling pertains to the telephone and the telephone exchanges †¢ Trunk signaling pertains to the exchange. References Buis, Paul. (1996, September). Common 100 Mbps Hardware Variations. Ethernet Technology:Underlying Technologies. (Chapter 4). Retrieved September 16,2007 from http://www. cs. bsu. edu/homepages/peb/cs637/ethernet/100mbps. htm Computer Hope. (2007). Ethernet. Retrieved September 16,2007 from http://www. computerhope. com/jargon/e/ethernet. htm ETSTechNEWS. What is the difference between 802. 11g and 802. 11b? Retrieved September 17, 2007 from http://web. monroecc. edu/ETSTechNEWS/80211g Fleishman, Glenn. (2003, November 4). Weakness in Passphrase Choice in WPA Interface. Retrieved September 17,2007 from http://wifinetnews. com/archives/002452. html GNS Wireless LLC. 802. 11a vs. 802. 11b vs. 802. 11g. 2007. Retrieved September 16, 2007 from the http://www. gnswireless. com/AvsBvsG. htm Laverty, Denis. WPA vs. WEP: How your Choice Affects your Wireless Network Security. Retrieved September 16,2007 from http://www. openxtra. co. uk/articles/wpa-vs-wep. php McLauren, Bruce. (1998). Cabling Options. How Gigabit Ethernet works. Retrieved September 15,2007 from http://misnt. indstate. edu/coutinho/ge/WORKS. HTM Mitchell, Bradley. Wireless/networking: â€Å"WPA: Wi-Fi Protected Access. Retrieved September 16,2007 from http://searchnetworking. techtarget. com/sDefinition/0,,sid7_gci214316,00. html Ou, George. (2005,June 2). Understanding the updated WPA and WPA2 standards. Message posted to http://blogs. zdnet. com/Ou/index. php? p=67 Pidgeon,Nick. Introduction to how Ethernet Works. The Ethernet. Retrieved September 16,2007 from http://computer. howstuffworks. com/ethernet. Sheldon, Tom. Link Aggregation. â€Å"The Encyclopedia of Networking and Telecommunications. Retrieve September 16,2007 from http://www. linktionary. com/l/link_aggregation. html Spurgeon, Charles E.. (2000). Why is it called Ethernet?. Ethernet: The Definitive Guide. Retrieved September 16,2007 from http://www. ethermanage. com/ethernet/ethername. html ICT Global. What is Ethernet?. Ethernet FAQ. Retrieved September 16,2007from http://www. ictglobal. com/ICT010/faq1. html Networking Essentials. Band Usage (Baseband or Broadband). Retrieved September 17,2007 from http://www. measureup. com/testobjects/MS_NetEss/5a67289. htm

The Anatomy of Abuse Essay -- essays research papers

The Anatomy of Abuse While this paper cannot be a definitive guide to the nature of the abuser, the victims relationship with the abuser and societies part in encouraging gender bias, I hope it will add to the pool of knowledge. It is my hope that, at least in a small way, this paper will be an aid towards helping us all understand the nature of domestic abuse and those who perpetrate or encourage it. George Rolph. London 2004. The abusers -- Actors in disguise. First and foremost abusers are actors. It makes no difference what gender the abusive personality is, their primary skill is to emulate normal behaviour in order to disguise their own condition. I have spoken to many victims of abuse who say that the person they met and fell in love with â€Å"gradually changed† into a monster. This is often one of the most confusing and distressing aspects of abuse from the victims point of view. It is also a situation that the abuser will exploit with varying degrees of vicious skill. While it is impossible to be specific on these subjects in every case, careful observation and research have uncovered certain general consistencies I want to discuss here. The question is; what is going on in the abusers mind that causes them to suddenly, or gradually, become abusive to their new partner? It appears that the abusive personality has learned, by observation and by mimicry of those around them, how to give every appearance of normality and stability for often quite extended periods of time. This means that they are able to convince new partners that they are really charming, wonderful people who should be trusted and are worthy of love and care. This act is easy to maintain in certain social situations and where the abuser has minimal contact with others in an average day. For example, in a work situation where he/she will be in contact with others for a maximum of eight hours per day. Another social situation may be one of casual friendships made in pubs and clubs. Under these conditions the actor (abuser) need only be convincing as a normal person for a minimum amount of time. This is why many friends of the abuser find it hard to believe that the person they think they know could be capable of such barbarity within a long term relationship. In the case of female abuse rs, this difficulty is compounded by social and political myths that see females only as victi... ... Men and boys are subjected to massive amounts of prejudice in everything from education provision; medical cancer research (breast versus testicular for example); housing provision; Divorce; the right to bring up their children alone; hugely insulting articles; newspaper stories and books; job security issues as a result of so-called â€Å"positive† discrimination; discriminatory advertising on the television; hate speech; political discrimination; legal rights and censorship of the male point of view in the media. If men complain about this they are ridiculed and called whiners sometimes by other so-called men in the media but, most often, by radical feminist media spokesmen. This prejudice has led to an explosion of single mothers and the most confused and damaged generation of children our country has ever known. Will someone please tell me the benefits of this utopian radical feminist, left wing view of modern society? * For a great cautionary tale of statistics and their manipulation go to this page on the Web: http://www.ifeminists.net/introduction/editorials/2004/0324.html Copyright  © George Rolph. April 2004 Founder of No More Silence. Contact: grolph(@)no-more-silence.org

Children Development 3-5 Years

3 – 5 YEARS PHYSICAL DEVELOPMENT Buttons/unbuttons own clothing, cut out simple shapes, draw a person with head, trunk and legs, walk on a line, aim and throw ball, hop on one foot, form letters; write own name, colour in pictures, completes 20-piece jigsaw, skip with a rope, run quickly and able to avoid obstacles, throw large ball to a partner and catch it. Run, jump, begin to climb ladders; can start to ride tricycles; try anything; is very active. INTELLECTUAL DEVELOPMENTUnderstand concepts like grouping and matching, identify parts of a whole, draw, name, and briefly explain pictures, actively seek information. Tell their full name and age, show awareness of past and present, play with words, mimicking and creating sounds, and make rhymes, point to and name many colors, understand order and process, draw a person with detail, learn both by observing and listening to adults' explanations. Begins to notice differences in the way men and women act. Imitate adults. Continue t o learn through senses. Begin to see cause-and-effect relationships.Are curious and inquisitive. LANGUAGE DEVELOPMENT Retell a story (but may confuse facts) Combine thoughts into one sentence Ask â€Å"when? â€Å", â€Å"how? † and â€Å"why? † questions. Use words like â€Å"can,† â€Å"will,† â€Å"shall,† â€Å"should,† and â€Å"might†. Combine thoughts into one sentence. Refer to causality by using â€Å"because† and â€Å"so† Follow three unrelated commands. Understand comparatives like loud, louder, loudest. Understand sequencing of events when clearly explained. Listen to a long story. EMOTIONAL DEVELOPMENT Seem sure of self. May not obey limits, tests rules, and often says no.Need freedom with limits. Self-assured, stable and well-adjusted. Like to be around mother and like to be at home. Like to follow rules. Like being given jobs to do. Can wait for their needs to be met, can feel secure when in a strange p lace away from their main carers, are less rebellious and use language rather then physical outbursts to express themselves. May have imaginary fears and anxieties. Project their own experiences onto dolls and toys. Show awareness of their own feelings and those of others, and talk about feeling. Similar essay: How Different Types of Transitions Can Affect Children

Trial By Fire The Forging Of Modern Physics - 3319 Words

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Of the conflicts that occurred between these great scientists, the two with the most profound impacts were over the founding of calculus and the nature of the fabric of space as it relates to motion. With regards to the debates over credit for calculus, feuding between the two scientists outlined their personalities and methodologies of production, which varied greatly based on attitude and—consequently—actions. Letters between the two, as well as publicly documented debate, not only paint a portrait of the two scientists, but provide insight into their processes of deduction and how theyShow MoreRelatedScientific Management30702 Words   |  123 Pagesworkmen. 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