Call barring is a mobile phone feature that allows the user to set
certain prohibitions on incoming or outgoing calls. This is an
effective means to prevent the phone being used to make expensive
international or premium rate calls, particularly when the phone is
to be used by people other than the subscriber.
Many companies that provide handsets for business use now employ
call barring as a security measure, to control their use and
restrict calls to pre-approved numbers. The user's personal code
must be used to activate this feature.
Keyword(s):
Call return
:
Call return is a network service that allows a user to discover
the number of the last person who called their phone. The service
is activated by dialling a code, e.g. 1471 in the UK or *69 in
the USA, and the number then provided will enable the user to
return the call.
Call return is part of a general phone feature referred to as
Calling Line Identity.
Keyword(s):
Call transfer
:
Call transfer is a mobile phone feature that allows the user to
transfer a caller to another phone number. Either party in a phone
call can dial a number and then exit from the connection, so
leaving the other party ringing the new number.
Keyword(s):
Call waiting
:
Also known as: CW
Call waiting is a phone feature that allows the user to be alerted,
while they are engaged in an active call, that another incoming
caller is trying to contact them.
Depending on the type of mobile phone, the user might be given an
audible 'beeping' warning, or a message on their phone's display
screen. This facility gives the user the option of finishing the
first call before answering the second one, or alternatively the
user could take advantage of call holding to keep the first call
'on hold' while the second caller is dealt with. Other options
might be to reject the waiting call, or to send it to the voice
mail service.
Keyword(s):
Caller group logo
:
Caller group logo is used as a means of identifying either
individual callers, or members of specific caller groups.
Caller group logos usually come preloaded with a mobile phone, and
are saved by the user under caller groups, or individual callers;
they are then displayed whenever that individual user (or a member
of the selected group) calls.
Keyword(s):
Calling Line Identification
Presentation
:
CLIP (Calling Line Identification Presentation) is a supplementary
GSM service used to show the number of a caller. When a call is
initiated, the caller’s MSC provides the destination MSC with the
caller’s identity. The destination MSC then checks to see if the
phone being called has subscribed to CLIP. If it has, then the
caller’s identity is presented. CLIP couples with CLIR to provide
an advanced version of caller line identification in GSM
networks.
The presence of CLIP - and CLI generally - can be very useful for
choosing to forward or even discard calls from certain people or
organisations, as it allows identification of the caller without
answering.
Keyword(s):
Calling Line Identification
Restriction
:
Also known as: CLIR
CLIR (Calling Line Identification Restriction) controls the
presentation of caller identity (via CLIP) in GSM networks. If CLIR
is enabled, the caller’s MSC indicates this restriction to the
destination MSC. The identity is then not forwarded to the
destination mobile station.
There is a GSM override function for the CLIR that is available to
organisations such as the police, and allows the caller ID to be
seen even if they have elected to restrict their identity.
Keyword(s):
CAM
:
computer aided manufacturing
Keyword(s):
Camera Phone
:
Cameraphone (or Camphone) is the name used to describe a device
that combines the features of a mobile phone and a digital camera.
This means that a cameraphone not only functions as a normal mobile
phone, but it is also capable of taking photographs that can then
be transferred over-the-air to other phones. Some cameraphones are
even able to record live video clips, and most 3G phones are
equipped with a camera enabling them to be used for 2-way video
calls.
The usual arrangement is that the camera is completely integrated
within the phone body, although there are several models where the
camera comes as a plug in accessory. As with other digital cameras,
a cameraphone is likely to use either a CCD or CMOS sensor (the two
main types), which converts the light entering the lens into an
electrical signal, and this signal is processed to produce the
photograph. The image may then be viewed on the phone’s screen, or
it can be stored in the phone’s internal memory for later
use.
Cameraphones typically use small lenses with a fixed focus and
aperture, and although these lenses give sharp pictures at a
distance of between a few feet and infinity, they are not suitable
close-ups (with the exception of a couple of phones that have macro
settings). In most cases the lens will be located in a fixed
position on the phone, but some have a moveable lens that can be
rotated by the user.
Most cameraphones provide limited control over the exposure and
other normal camera adjustments, but they do usually offer some
means for the user to edit the photographs taken. Many models are
fitted with a rather weak LED “flash” light, but a few cameraphones
are designed to use a more effective plug in flashgun, which is
often available only as an accessory. A digital zoom control is
provided to magnify parts of the photograph, although this can
worsen the picture quality if over magnified, and due to the way
digital zoom operates it is usually unavailable at the higher
camera resolutions. Cameraphones are now starting to appear with
optical zoom and adjustable lenses, which can only enhance their
functionality.
Taking lots of pictures will put a strain on the phone’s internal
memory, which is of fixed capacity and shared with other phone
features. This problem has been overcome in those phones that have
a memory card slot, since a full card can be easily replaced with
an empty one, and so an unlimited number of pictures can be stored.
As memory cards can be read by other devices, this may prove a
convenient way to transfer picture files, or for printing. Phones
fitted with Bluetooth™, an infrared port or a data cable connector
also offer the user the capability to download their pictures onto
other devices, such as their home PC.
Apart from taking photographs of other people or scenes,
cameraphones also allow a user to take self-portraits. It is
sometimes possible for users to view themselves on the phone’s
display screen, if not, most cameraphones have a small mirror
fitted near their lens, to help aim the shot. A timer is another
universally available feature on cameraphones, which allows a delay
to be set for a shot.
The growth of MMS messaging means that many users now exchange
photographs between compatible MMS phones, although the size of the
MMS file is usually restricted to 100 kB. Some network operators
also allow the user to transfer pictures to a Web-based album, so
that they can be stored online in a virtual photo album, for
sharing with friends and other contacts. Alternatively, the
pictures may be sent as attachments to an e-mail address, if the
phone has an e-mail facility.
The key feature usually quoted for the quality of a cameraphone is
its maximum resolution, a figure given as either a number in pixels
(e.g. 1.3 megapixels) or a standard format (e.g. VGA, or 640 x 480
pixels). The resolution determines the best picture quality that
the camera can capture, and typically a megapixel camera will be
needed to produce acceptable results for standard 6 x 4 inch
photographic prints.
The Sharp Corporation launched the J-SH04 - the world’s first
camera phone - in Japan in November 2000, and this model included a
CMOS image sensor offering a resolution of 110,000 pixels. Today,
all the major mobile phone manufacturers produce cameraphones, and
the latest models are capable of taking photographs of a similar
quality to the average standard digital camera.
Keyword(s):
Carrier Signal
:
Carrier Signal (Carrier Frequency) is a continuous signal of a
single frequency, which is suitable of being modulated with (or
carrying) a second information signal.
This is the normal method of transferring information by wireless
systems, and in telecommunications the carrier frequency is usually
a radio signal of much higher frequency than that contained in the
information signal. Optical fibre communication networks use light
as a communications medium, and the carrier will then be a
laser-generated light beam.
Keyword(s):
CD
:
compact disk
Keyword(s):
CD-ROM,
:
"(Compact Disc Read-Only Memory). Like music CDs, but may contain information in the form of text, graphics, sound and moving video that can be accessed through a computer. A CD-ROM can store as much information as around 450 floppy discs.",
CDR
:
compact disk recordable
Keyword(s):
CDRW
:
compact disk re-writeable
Keyword(s):
Chatting
:
Real time conversations on the Internet, can occur on the world
wide web, Internet relay chat (IRC), through instant messaging,
on-line commercial servers (eg AOL or CompuServe). Can be accessed
through websites. A chat room is an on-line forum where two or more
people can engage in chat (Careaga).
Keyword(s):
Checksum
:
Checksum is a code used to verify data. It is created by
performing a mathematical operation on all the data together, and
will change according to the value of the data.
Checksums are used to make transmitted data is correct. When
sending data, the transmitter calculates the checksum of the data
that is sent, and sends it with the data. The receiver also
calculates the checksum of the data it receives. If the checksums
don't match then the data�must be�different - i.e. it has not
been�correctly transmitted�- and needs to be re-sent.
Keyword(s):
cHTML
:
cHTML (Compact HTML) is effectively a cut down version of the
regular HTML (Hypertext Markup Language) used over the Internet,
which has been adapted for use with small computing devices such as
personal digital assistants (PDAs), mobile phones, and smartphones.
cHTML enables small handheld devices to connect to the World Wide
Web, and to present Internet text content on the mobile device's
display screen.
Because handheld devices have limitations in their display, power
supply, and memory resources, cHTML does not support JPEG images,
tables, image maps, multiple fonts, background colours and images,
frames, style sheets and more than two colours. As pages are
designed to fit the screen, scrolling is also not featured, but
four buttons are used to do all the basic operations. However,
cHTML does support GIF images.
WML (Wireless Markup Language) is a similar markup language used
with the WAP (Wireless Application Protocol). cHTML was originally
developed for use with i-Mode devices by Access Company Ltd., a
Japanese company, and was accepted by the W3C in 1998.
Keyword(s):
Churn
:
Churn is a term referring to customer turnover. The word churn is
used to describe those customers abandoning a service or product,
and it is particularly applied to Internet and cell-phone
subscribers, who tend to often switch providers as a result of
intense competition. Churn rate is calculated as the number of
customers lost over a time period, divided by the average total
number of customers during that period.
For commercial reasons providers will be anxious to understand why
the churn rate is high, and whether it is due to customer
dissatisfaction with the price or type of services offered. Some
providers even offer special deals of free equipment or an initial
charge-free period to attract new customers. Also, to discourage
churn, the customer may be asked to sign a service agreement
containing penalty clauses, to ensure that they stay with the
provider for a minimum period
CIF
:
CIF (Common Intermediate Format) describes a video resolution that
is a quarter of the television drawing area. Whilst this should
strictly mean 352 x 288 pixels for PAL (used primarily in Europe)
and 352 x 240 pixels for NTSC (American) resolutions, the
convention of 352 x 288 pixels tends to be globally adhered to by
mobile phone manufacturers when describing their screens or
cameras.
The acronym CIF was originally brought in to use in the late
eighties to early nineties by video conferencing applications but
is rarely heard these days as the resolution it describes is
relatively small and uncommon, only being used in the context of
VideoCD, and more recently mobile phones and low end digital
cameras. Common Interchange Format is sometimes also known as
D1.
Keyword(s):
Circuit Switching
:
Circuit switching (Line Switching) is a method of transmitting
information (voice, video or other streamed data) between endpoints
within telecommunications systems. Each individual subscriber is
allocated a dedicated channel of constant bandwidth, which must be
maintained open for the duration of their call, even if no actual
conversation is taking place and no data being transferred.
Circuit switched systems were used in the old fixed landline
telephone networks, for point-to-point connections routed directly
between terminals. However, circuit switching may still be the best
option when uninterrupted large file transfers need to be sent, or
for long voice calls and videoconferencing, but it seems to be
mainly suitable for voice traffic. Circuit switching can be
considered as the opposite approach to packet switching, which does
not require a dedicated channel, and makes more efficient use of
the network's resources.