Information About GSM Vs CDMA Technology

Card Subscriber Identity Module (SIM) phones in the United States and other countries is exclusive use of GSM SIM cards. The removable SIM card allows mobile are activated instantly, allowing mobile data exchange, change and improve, all without the intervention of the owner of the phone. The SIM itself is tied to the network, instead of a regular phone. The phones that are enabled for the card can be used with any GSM carrier.

The CDMA equivalent, a R-UIM card: available only in parts of Asia but remains on the horizon for the U.S. market. CDMA in the U.S. require proprietary devices are attached to some airlines that require it. To upgrade a CDMA phone, the owner must disable the old mobile and then turn on again. The old cell phone will become unusable.

Signal Quality: For the most part, the two networks have a fairly wide coverage in big cities and along major highways. GSM companies, however, have roaming agreements with GSM operators, allowing greater coverage of rural areas in general. CDMA networks can not cover remote rural areas, as well as GSM carriers, but you can make calls using GSM phones with a specific signal for these rural areas, but the charge to the owner will be significantly higher.

International Signal: If you need to make calls to other countries, a GSM operator can offer an international signal, such as GSM networks dominate the global market. If you travel to other countries can use the GSM mobile phone abroad, provided they possess a quad-band phone (850/900/1800/1900 MHz). By purchasing a SIM card with minutes and a local number in the country you are visiting, you can make calls from the SIM card to store international signal rates and pay your phone company back home. CDMA phones and their cards do not have these advantages, however, there are several countries that use CDMA networks. Check with your CDMA provider to find specific requirements.

According CDG.org, CDMA networks support has more than 270 million subscribers worldwide, while GSM.org according to their results have more than 1 billion subscribers. CDMA phones have R-UIM enabled, roaming agreements for this technology from telephony networks tend to improve in the future, the integration of standards over time can make all the differences are clear and convenient for consumers.

The head of the GSM technology in the United States, Cingular Wireless, recently merged with AT & T Wireless and T-Mobile USA. Major CDMA operators are Sprint PCS, Verizon and Virgin Mobile. There are also several smaller cellular companies on both networks.

Rayleigh Scattering Process

Rayleigh scattering is the dominant intrinsic loss mechanism in the low- absorption window between the ultraviolet and infrared absorption tails. It results from in inhomogeneities of a random nature occurring on a small scale compared with the wavelength of the light. These in inhomogeneities manifest themselves as refractive index fluctuations and arise from density and compositional variations which are frozen into the glass lattice on cooling. The compositional variations may be reduced by improved fabrication, but the index fluctuations caused by the freezing in of density in inhomogeneities are fundamental and cannot be avoided. Read More  

Linear Scattering Losses

Linear scattering mechanisms cause the transfer of some or all of the optical power contained within one propagating mode to be transferred linearly into a different mode. This process tends to result in attenuation of the transmitted light as the transfer may be to a leaky or radiation mode which does not continue to propagate within the fiber core, but is radiated from the fiber. It must be noted that as with all linear processes, there is no change of frequency on scattering.

Interrupt Driven I/O in Microprocessor

A disadvantage of conditional programmed I/O is that the microcomputer needs to check the status bit by waiting in a loop. This type of I/O transfer is dependent on the speed of the external device. For a slow device, this waiting may slow down the capability of the microprocessor to process other data. the polled I/O and interrupt I/O techniques are efficient in this type of situation. The external device is connected to a pin called the interrupt (INT) pin on the microprocessor chip. The microcomputer then automatically loads an address into the program counter to branch to a subroutine-like program called the interrupt service routine. This program is written by the user. The external device wants the microcomputer to execute this program to transfer data. the last instruction of the service routine is a RETURN.   

Advantage and Disadvantage of the Caesar Cipher

Most ciphers and especially the early ones had to easy to perform in the field. In particular it was dangerous to have the cryptosystem algorithms written down for the soldiers or spies to follow. Any cipher that was so complicated that its algorithm had to be written out was at risk of being revealed if the interceptor caught a sender with the written instructions. Then the interceptor could readily decode any cipher text messages intercepted. Sidebar 2-2 describes how the British dealt with written codes in world war11. the Caesar cipher is quite simple. During caesar’s lifetime, the simplicity did not dramatically compromise the safety of the encryption, because anything written, even in plaintext, was rather well protected. Its obvious pattern is also the major weakness of the Caesar cipher.   

The Caesar Cipher

The Caesar Cipher has an important place in history. Julius Caesar is said to have been the first to use this schema, in which each letter is translated to a letter a fixed number of places after it in the alphabet. Caesar used a shift of 3, so that plaintext letter pi was enciphered as ciphertext letter ci by the rule

                                                    

                                           Ci=E(pi)=pi+3

A full translation chart of the Caesar Cipher is shown here

Plaintext      A B C D E F G H I J K L M  N O P Q R S T U V W X Y Z

Ciphertext    d  e  f  g  h  i  j  k  l  m  n  o  p  q  r  s  t   u  v  w  x y z  a b c  

 We ca use the encryption process and we get the result as follows;

TREATY IMPOSSIBLE

 It would be encoded as

T  R  E  A  T   Y           I  M  P  O  S  S  I  B  L  E

w  u   h   d   w   b           l   p   s   r   v   v  l   e   o  h  

Encryption Algorithm Process

The cryptosystem involves a set of rules for how to encrypt the plaintext and how to decrypt the cipher text. The encryption and decryption rules, called algorithms, often use a device called a key, denoted by k, so that the resulting ciphertext depends on the original plaintext message, the algorithm, and the key value. We write this dependence as C=E(K, P). Essentially, E is a set of encryption algorithms, and the k selects one specific algorithm from the set.  Sometimes the encryption and decryption keys are the same so P= D(K, E(K,P)).

 This form is called symmetric encryption because D and E are mirror image processes. At other times, encryption and decryption keys come in pairs. Then a decryption key, Kd, inverts the encryption of key Ke, so that P=D(Kd, E(Ke,P)). Encryption algorithms of this form are called asymmetric because converting c back to p involves a series of steps and a key that are different from the steps and key of E. Both a cryptographer and a cryptanalyst attempt to translate coded material back to its original form. Finally cryptology is the research into and study of encryption and decryption.   

Encryption process

Encryption is the formal name for the scrambling process. We take data in their normal unscrambled state called clear text and transform them so that they are unintelligible to the outside observer the transformed data are called enciphered text. Using encryption security professionals can virtually nullify the value of an interception and the possibility of effective modification or fabrication.

 Encryption clearly addresses the need for confidentiality of data. Additionally it can be used to ensure integrity; data that cannot be read generally also cannot easily be changed in a meaningful manner. Although encryption is an important tool in any computer security tool kit, we should not overrate its importance. Encryption does not solve all computer security problems and other tools must complement its use.   

Different Method of Defense

Harm occurs when a threat is realized against vulnerability. To protect against harm then we can neutralize the threat, close the vulnerability or both. The possibility for harm to occur is called risk. We can deal with harm in several ways. We can seek to-

• prevent it, by blocking the attack or closing the vulnerability
• deter it, by making the attack harder but impossible
• deflect it, by making another target more attractive
• detect it, either as it happens or some time after the fact
• recover from its effects

of course, more then one of these can be done at once. So, for example we might try to prevent intrusions. But in case we do not prevent them all. We might install a detection device to warm of an imminent attack. And we should have in place incident response procedures to help in the recovery in case an intrusion does succeed.     

Crackers Descriptions

System crackers often high school or university students attempt to access computing   facilities for which they have not been authorized. Cracking a computer defenses is seen as the ultimate victimless crime. The perception is that nobody is hurt or even endangered by a little stolen machine time. Crackers enjoy the simple challenge of trying to log in, just to see whether it can be done. Most crackers can do their harm without confronting anybody, not even making a sound. An underground network of hackers helps pass along secrets of success as with a jigsaw puzzle, a few isolated pieces joined together may produce a large effect. Read More