Acronym Definition
PUKZ Pack-Up Kits
PUKZ Parti Unitet Kombetars
PUKZ Patriotic Union of Kurdistans
PUKZ Personal Unlocking Keys
PUKZ Pin Unlocking Keys
PUKZ Pop-Up Killers
PUKZ PopUp Killers
PUKZ Potchefstroomkampus
PUKZ Pin Unlocking Keys
A Personal Unblocking Code (PUC) or Personal Unblocking Key (PUK) is used in GSM
mobile phones and some smartcards to unblock a blocked card.
Most mobile telephones offer the feature of personal identification number (PIN)
protection. After switching on the phone, the user, if the PIN security function
is not switched off, is requested to enter a 4-8 digit PIN enabling the phone's
non-emergency calling functions. If the wrong PIN is typed in more than three
times, either the SIM card, the device or both become locked. They can be
reverted to their original unlocked state by entering a PUC, provided by the
service operator through verification. If the wrong PUC is entered ten times in
a row, the device will become permanently blocked and unrecoverable, requiring a
new SIM card. Cellular phone users are therefore advised by most providers to
keep their PUC written down in a safe place separate from the device.
Global System for Mobile communications (GSM: originally from Groupe Spécial
Mobile) is the most popular standard for mobile phones in the world. Its
promoter, the GSM Association, estimates that 82% of the global mobile market
uses the standard . GSM is used by over 2 billion people across more than 212
countries and territories. Its ubiquity makes international roaming very common
between mobile phone operators, enabling subscribers to use their phones in many
parts of the world. GSM differs from its predecessors in that both signaling and
speech channels are digital call quality, and so is considered a second
generation (2G) mobile phone system. This has also meant that data communication
were built into the system using the 3rd Generation Partnership Project (3GPP).
Enlarge picture
The GSM logo is used to identify compatible handsets and equipment
The key advantage of GSM systems to consumers has been better voice quality and
low-cost alternatives to making calls, such as the Short message service (SMS,
also called "text messaging"). The advantage for network operators has been the
ease of deploying equipment from any vendors that implement the standard. Like
other cellular standards, GSM allows network operators to offer roaming services
so that subscribers can use their phones on GSM networks all over the world.
Newer versions of the standard were backward-compatible with the original GSM
phones. For example, Release '97 of the standard added packet data capabilities,
by means of General Packet Radio Service (GPRS). Release '99 introduced higher
speed data transmission using Enhanced Data Rates for GSM Evolution (EDGE).
History
In 1982, the European Conference of Postal and Telecommunications
Administrations (CEPT) created the Groupe Spécial Mobile (GSM) to develop a
standard for a mobile telephone system that could be used across Europe. In
1987, a memorandum of understanding was signed by 13 countries to develop a
common cellular telephone system across Europe.
In 1989, GSM responsibility was transferred to the European Telecommunications
Standards Institute (ETSI) and phase I of the GSM specifications were published
in 1990. The first GSM network was launched in 1991 by Radiolinja in Finland
with joint technical infrastructure maintenance from Ericsson. By the end of
1993, over a million subscribers were using GSM phone networks being operated by
70 carriers across 48 countries.
Technical details
GSM is a cellular network, which means that mobile phones connect to it by
searching for cells in the immediate vicinity. GSM networks operate in four
different frequency ranges. Most GSM networks operate in the 900 MHz or 1800 MHz
bands. Some countries in the Americas (including Canada and the United States)
use the 850 MHz and 1900 MHz bands because the 900 and 1800 MHz frequency bands
were already allocated.
The rarer 400 and 450 MHz frequency bands are assigned in some countries,
notably Scandinavia, where these frequencies were previously used for
first-generation systems.
In the 900 MHz band the uplink frequency band is 890–915 MHz, and the downlink
frequency band is 935–960 MHz. This 25 MHz bandwidth is subdivided into 124
carrier frequency channels, each spaced 200 kHz apart. Time division
multiplexing is used to allow eight full-rate or sixteen half-rate speech
channels per radio frequency channel. There are eight radio timeslots (giving
eight burst periods) grouped into what is called a TDMA frame. Half rate
channels use alternate frames in the same timeslot. The channel data rate is
270.833 kbit/s, and the frame duration is 4.615 ms.
The transmission power in the handset is limited to a maximum of 2 watts in
GSM850/900 and 1 watt in GSM1800/1900.
GSM has used a variety of voice codecs to squeeze 3.1 kHz audio into between 5.6
and 13 kbit/s. Originally, two codecs, named after the types of data channel
they were allocated, were used, called Half Rate (5.6 kbit/s) and Full Rate (13
kbit/s). These used a system based upon linear predictive coding (LPC). In
addition to being efficient with bitrates, these codecs also made it easier to
identify more important parts of the audio, allowing the air interface layer to
prioritize and better protect these parts of the signal.
GSM was further enhanced in 1997 with the Enhanced Full Rate (EFR) codec, a 12.2
kbit/s codec that uses a full rate channel. Finally, with the development of
UMTS, EFR was refactored into a variable-rate codec called AMR-Narrowband, which
is high quality and robust against interference when used on full rate channels,
and less robust but still relatively high quality when used in good radio
conditions on half-rate channels.
There are four different cell sizes in a GSM network—macro, micro, pico and
umbrella cells. The coverage area of each cell varies according to the
implementation environment. Macro cells can be regarded as cells where the base
station antenna is installed on a mast or a building above average roof top
level. Micro cells are cells whose antenna height is under average roof top
level; they are typically used in urban areas. Picocells are small cells whose
coverage diameter is a few dozen meters; they are mainly used indoors. Umbrella
cells are used to cover shadowed regions of smaller cells and fill in gaps in
coverage between those cells.
Cell horizontal radius varies depending on antenna height, antenna gain and
propagation conditions from a couple of hundred meters to several tens of
kilometers. The longest distance the GSM specification supports in practical use
is 35 kilometres (22 mi). There are also several implementations of the concept
of an extended cell, where the cell radius could be double or even more,
depending on the antenna system, the type of terrain and the timing advance.
Indoor coverage is also supported by GSM and may be achieved by using an indoor
picocell base station, or an indoor repeater with distributed indoor antennas
fed through power splitters, to deliver the radio signals from an antenna
outdoors to the separate indoor distributed antenna system. These are typically
deployed when a lot of call capacity is needed indoors, for example in shopping
centers or airports. However, this is not a prerequisite, since indoor coverage
is also provided by in-building penetration of the radio signals from nearby
cells.
The modulation used in GSM is Gaussian minimum-shift keying (GMSK), a kind of
continuous-phase frequency shift keying. In GMSK, the signal to be modulated
onto the carrier is first smoothed with a Gaussian low-pass filter prior to
being fed to a frequency modulator, which greatly reduces the interference to
neighboring channels (adjacent channel interference).
Interference with audio devices
This is a form of RFI, and could be mitigated or eliminated by use of additional
shielding and/or bypass capacitors in these audio devices. However, the
increased cost of doing so is difficult for a designer to justify.
It is a common occurrence for a nearby GSM handset to induce a "dit, dit di-dit,
dit di-dit, dit di-dit" output on PA's, wireless microphones, home stereo
systems, televisions, computers, cordless phones, and personal music devices.
When these audio devices are in the near field of the GSM handset, the radio
signal is strong enough that the solid state amplifiers in the audio chain act
as a detector. The clicking noise itself represents the power bursts that carry
the TDMA signal. These signals have been known to interfere with other
electronic devices, such as car stereos and portable audio players.
Network structure
Enlarge picture
The structure of a GSM network
The network behind the GSM system seen by the customer is large and complicated
in order to provide all of the services which are required. It is divided into a
number of sections and these are each covered in separate articles.
* the Base Station Subsystem (the base stations and their controllers).
* the Network and Switching Subsystem (the part of the network most similar to a
fixed network). This is sometimes also just called the core network.
* the GPRS Core Network (the optional part which allows packet based Internet
connections).
* all of the elements in the system combine to produce many GSM services such as
voice calls and SMS.
Subscriber identity module
M Subscriber Identity Module
Enlarge picture
A SIM for Bell Mobility (Canada)
One of the key features of GSM is the Subscriber Identity Module (SIM), commonly
known as a SIM card. The SIM is a detachable smart card containing the user's
subscription information and phonebook. This allows the user to retain his or
her information after switching handsets. Alternatively, the user can also
change operators while retaining the handset simply by changing the SIM. Some
operators will block this by allowing the phone to use only a single SIM, or
only a SIM issued by them; this practice is known as SIM locking, and is illegal
in some countries.
In Australia, Canada, Europe and the United States many operators lock the
mobiles they sell. This is done because the price of the mobile phone is
typically subsidised with revenue from subscriptions, and operators want to try
to avoid subsidising competitor's mobiles. A subscriber can usually contact the
provider to remove the lock for a fee, utilize private services to remove the
lock, or make use of ample software and websites available on the Internet to
unlock the handset themselves. While most web sites offer the unlocking for a
fee, some do it for free. The locking applies to the handset, identified by its
International Mobile Equipment Identity (IMEI) number, not to the account (which
is identified by the SIM card). It is always possible to switch to another
(non-locked) handset if such a handset is available.
Some providers will unlock the phone for free if the customer has held an
account for a certain time period. Third party unlocking services exist that are
often quicker and lower cost than that of the operator. In most countries,
removing the lock is legal. United States-based AT&T and T-Mobile provide free
unlocking services to their customers after 3 months of subscription.
In countries like Belgium, India, Indonesia and Pakistan, etc., all phones are
sold unlocked. However, in Belgium, it is unlawful for operators there to offer
any form of subsidy on the phone's price. This was also the case in Finland
until April 1 2006, when selling subsidized combinations of handsets and
accounts became legal, though operators have to unlock phones free of charge
after a certain period (at most 24 months).
GSM security
GSM was designed with a moderate level of security. The system was designed to
authenticate the subscriber using a pre-shared key and challenge-response.
Communications between the subscriber and the base station can be encrypted. The
development of UMTS introduces an optional USIM, that uses a longer
authentication key to give greater security, as well as mutually authenticating
the network and the user - whereas GSM only authenticated the user to the
network (and not vice versa). The security model therefore offers
confidentiality and authentication, but limited authorization capabilities, and
no non-repudiation.
GSM uses several cryptographic algorithms for security. The A5/1 and A5/2 stream
ciphers are used for ensuring over-the-air voice privacy. A5/1 was developed
first and is a stronger algorithm used within Europe and the United States; A5/2
is weaker and used in other countries. A large security advantage of GSM over
earlier systems is that the Key, the crypto variable stored on the SIM card that
is the key to any GSM ciphering algorithm, is never sent over the air interface.
Serious weaknesses have been found in both algorithms, and it is possible to
break A5/2 in real-time in a ciphertext-only attack. The system supports
multiple algorithms so operators may replace that cipher with a stronger one.
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RuneScape is set in a medieval fantasy world, similar to "Guild Wars" or "EverQuest",
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RuneScape has often been one of
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RuneScape is a virtual world which
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set in a medieval fantasy world, similar to "Guild Wars" or "EverQuest," where
players control character representations of themselves. As with most MMORPG,
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characters' skills.
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With the rising popularity of
commercial MMORPG games came the desire from ardent players of these games to
run their own servers beside the ones run by the game's creator. Since the
original server software is not usually available, the behavior of the server
has to be re-engineered. This can be done by analyzing the data stream with the
original server, or by disassembling and analyzing the client which is
available.
Ultima Online was one of the first
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very quickly, even during the beta stage of development. The destination to
which the client connects was changeable by simply editing a text file. In beta
stage the client-server data stream was not encrypted yet. The term server
emulator became known through Ultima Online server reimplementation such as UOX,
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its source code was released under the GNU General Public License relatively
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implemented anti-cheating measures, many gamers left and started their own
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Another useful site is
Rune
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A defining moment in internet
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