U.S. patent application number 09/827593 was filed with the patent office on 2001-08-16 for method for indicating enciphering of data transmission between a mobile communication network and a mobile station.
Invention is credited to Hamalainen, Jari Pekka, Paajanen, Reijo Uolevi, Rautiola, Markku Matias, Rossi, Markku Juhani.
Application Number | 20010014942 09/827593 |
Document ID | / |
Family ID | 8544551 |
Filed Date | 2001-08-16 |
United States Patent
Application |
20010014942 |
Kind Code |
A1 |
Hamalainen, Jari Pekka ; et
al. |
August 16, 2001 |
Method for indicating enciphering of data transmission between a
mobile communication network and a mobile station
Abstract
The invention relates to a method for indicating enciphering of
data transmission between a mobile communication network and a
mobile station (MS) in the mobile communication network, wherein
signals transferred between a mobile communication network and a
mobile station are monitored, and on the basis of the signal
monitored, the cipher mode is indicated to the user of the mobile
station.
Inventors: |
Hamalainen, Jari Pekka;
(Tampere, FI) ; Paajanen, Reijo Uolevi; (Tampere,
FI) ; Rautiola, Markku Matias; (Tampere, FI) ;
Rossi, Markku Juhani; (Tikkakoski, FI) |
Correspondence
Address: |
PERMAN & GREEN
425 POST ROAD
FAIRFIELD
CT
06430
US
|
Family ID: |
8544551 |
Appl. No.: |
09/827593 |
Filed: |
April 6, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09827593 |
Apr 6, 2001 |
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08763970 |
Dec 10, 1996 |
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6249584 |
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Current U.S.
Class: |
713/151 |
Current CPC
Class: |
H04W 12/02 20130101;
H04W 12/121 20210101; H04L 63/0428 20130101; H04W 12/122 20210101;
H04W 12/033 20210101; H04W 12/037 20210101 |
Class at
Publication: |
713/151 |
International
Class: |
H04L 009/00 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 15, 1995 |
FI |
956036 |
Claims
1. A method for indicating enciphering of data transmission between
a mobile communication network and a mobile station (MS) in the
mobile communication network, characterized in that signals
transferred between a mobile communication network and a mobile
station are monitored, and on the basis of the signal monitored,
the cipher mode is indicated to the user of the mobile station.
2. A method according to claim 1, characterized in that in addition
to indicating the cipher mode, a change in the cipher mode is
indicated to the user of the mobile station.
3. A method according to claim 1 or 2, characterized in that the
data transmission connection between the mobile communication
network and the mobile station (MS) is a radio connection.
4. A method according to any of the claims 1 to 3, characterized in
that the communication network is a digital communication network,
such as a GSM network.
5. A method according to any of the claims 1 to 4, wherein the
mobile station (MS) comprises a display unit (8) and an acoustic
signal forming element (10), known as such, characterized in that
the cipher mode is indicated with the display unit (8) and a change
in the cipher mode is indicated with the acoustic signal forming
element (10).
6. A method according to any of the claims 1 to 4, wherein the
mobile station (MS) comprises a light source (LED), known as such,
characterized in that the cipher mode is indicated with the light
source (LED).
7. A method according to claim 6, characterized in that a change in
the cipher mode is indicated with a flashing light.
8. A method according to any of the claims 1 to 4, characterized in
that the cipher mode is indicated by vibration.
9. A method according to any of the preceding claims, characterized
in that the signal to be monitored is a, control signal.
10. A method according to any of the preceding claims, wherein a
first mobile station (MS1) and a second mobile station (MS2) are in
a data transmission connection with each other through at least one
mobile communication network, characterized in that the cipher mode
between the mobile communication network and the first mobile
station (MS1) is indicated to the user of the second mobile station
(MS2).
11. A method according to any of the preceding claims, wherein the
mobile station is used in connection with a data processor (PC) for
data transmission between a mobile communication network and the
data processor (PC), characterized in that the cipher mode is
indicated on the display unit (12) of the data processor and a
change in the cipher mode is indicated with the acoustic signal
forming element (10) of the data processor.
12. An apparatus for indicating enciphering of data transmission
between a mobile station (MS) and a mobile communication network in
the mobile communication network, characterized in that the
apparatus comprises: means (1) for monitoring signals transferred
between a mobile communication network and a mobile station (MS)
and means (8, 12) for indicating the cipher mode to the user of the
mobile station.
13. An apparatus according to claim 12, characterized in that the
apparatus comprises further means (10, 13) for indicating a change
in the cipher mode.
14. An apparatus according to claim 12 or 13, characterized in that
the means (8, 12) for indicating the cipher mode comprise a display
unit (8) of the mobile station, and the means (10, 13) for
indicating a change in the cipher mode comprise an acoustic signal
forming element (10), such as a sound generator or the like.
15. An apparatus according to any of the claims 12 to 14,
characterized in that the means (10, 13) for indicating a change in
the cipher mode comprise a light source (LED), known as such.
16. An apparatus according to any of the claims 12 to 15,
characterized in that the means (10, 13) for indicating a change in
the cipher mode comprise means for generating vibration.
17. An apparatus according to any of the claims 12 to 16,
characterized in that it is provided in a mobile station (MS).
18. An apparatus according to claim 12 or 13, characterized in that
the means (8, 12) for indicating the cipher mode and the means (10,
13) for indicating a change in the cipher mode are provided in a
data processor (PC) communicating with a mobile station (MS).
Description
[0001] The invention relates to a method and an apparatus for
indicating enciphering of data transmission between a mobile
communication network and a mobile station in the mobile
communication network.
[0002] In mobile networks, at least part of the data transmission
is wireless communication using radio transmitters and receivers.
The radio channel is a physically open resource available to anyone
by means of suitable communication equipment. This involves
security risks, such as eavesdropping or disclosure of privacy of
location. In digital mobile networks, such as GSM networks, digital
data transmission is used which is difficult to eavesdrop. Further,
it is possible to use identification of the caller and enciphering
in data transmission. For preventing eavesdropping in digital
mobile networks, enciphering methods have been developed for
enciphering the speech and data signals modified in digital form.
Moreover, enciphering can be used in the transmission of other
information via the radio channel, such as identification data on
the mobile station (International Mobile Subscriber Identity, IMSI)
and on the location (Location Area Identification, LAI). In the
receiver, the enciphered signal is decoded back to deciphered
speech and data. A so-called encryption key and algorithm are
advantageously known to the respective sending and receiving
devices only, wherein given the effective encryption algorithms
presently in use, decoding a coded signal to intelligible speech
and data as well as into processing signals of the bit stream by
force or illegally, i.e. without the correct encryption key and
algorithm, is practically impossible.
[0003] The most common digital mobile networks are cellular
networks. The base station subsystem (BSS) of the mobile network
comprises base transceiver stations (BTS) and base station
controllers (BSC). The mobile station (MS) communicates via the
radio channel with a base station close to the respective location
of the mobile station. The base station communicates with the base
station controller. Data transmission between the base station and
the base station controller takes place usually via a cable. One
base station controller controls over a group of several base
stations. The base station controller, in turn, communicates with a
mobile services switching centre (MSC). Several mobile services
switching centres, in turn, can communicate with each other as well
as with a landline communication network centre (PSTN, ISDN). The
information to be transmitted is usually divided into frames
containing control information, speech and data converted into
digital form, and error correction information. The frame structure
can have several levels, wherein frames of a higher level are
formed by arranging frames of a lower level. Enciphering can be
used both with control information and with speech and data.
Moreover, enciphering can be realized by using different encryption
keys and algorithms at different frame levels. An example of a
digital data transmission network is the GSM network, the standard
of which contains definitions of the enciphering methods and
algorithms to be used.
[0004] In the GSM network, making a mobile-originated call is
conducted in a way that a GSM mobile station and the GSM system
network give signals, i.e. transmit control and identification
information required for making a call. In response to a request
for a connection, the GSM mo20 bile station is allotted a channel
for signalling, if this is possible within the capacity of the GSM
system network. On this channel, the GSM mobile station requests
speech or data service from the GSM system network. On the side of
the GSM system network, this request is transmitted to a mobile
services switching centre (MSC), where the rights of the GSM
subscriber are checked from a visitor location register (VLR).
[0005] Upon a mobile-terminated call e.g. from a subscription of a
landline telephone network, the operator of the telephone network
transmits e.g. the number of the receiving telephone to the mobile
services switching centre. The mobile services switching centre
finds out the rights of the GSM subscriber from the home location
register (HLR) and from the visitor location register (VLR). After
this, the GSM system network and the GSM mobile station transmit
the control and identification informa35 tion required for making a
call.
[0006] Depending on the implementation and the configuration of the
parameters, the visitor location register VLR can make a request
via the mobile services switching centre to the GSM mobile station
for exchange of identification information and start of
enciphering. This request is made in a so-called cipher mode
command message. It is, however, possible to make a call also
without exchange of identification information and enciphering. In
other words, the call is either enciphered or not enciphered
depending on the network parameters set by the GSM system network
operator.
[0007] In most common mobile communication networks currently
available, however, enciphering is not optional to a user of the
mobile communication network but usually an alternative function
offered by the operator of the mobile network, wherein when current
wireless data transmission equipment is used, the user has no
certainty whether the data transmission is enciphered or not.
Particularly when the mobile station is moving, the mobile station
can be transferred from the area of one base station system to the
area of another base station system, wherein the cipher mode of
data transmission can be changed.
[0008] One purpose of the present invention is to eliminate the
disadvantages described above and to provide a method for
indicating enciphering of data transmission to the user of the
mobile communication network. The invention is based on the idea
that control signals used in data transmission between a mobile
network and a mobile station are monitored and when a control
signal for enciphering is detected, the cipher mode is signalled
with a cipher mode indicator connected to the mobile station. The
method of the invention is characterized in that signals
transferred between a mobile communication network and a mobile
station are monitored, and on the basis of the signal monitored,
the cipher mode is indicated to the user of the mobile station.
[0009] The apparatus according to the invention is characterized in
that the apparatus comprises means for monitoring signals
transferred between a mobile communication network and a mobile
station, and means for indicating the cipher mode to the user of
the mobile station.
[0010] The invention gives significant advantages. Using the method
of the invention, the user of a data transmission device is always
aware of whether the data transmission is enciphered or not.
Further, by using the method of the invention, it is possible to
indicate a possible change in the cipher mode during the data
transmission to the user of the data transmission device.
[0011] In the following, the invention will be described in more
detail with reference to the appended drawings. In the
drawings,
[0012] FIG. 1a shows the call set-up signals during a
mobile-originated call in the GSM mobile communication network,
[0013] FIG. 1b shows the call set-up signals during a
mobile-terminated call in the GSM mobile communication network,
[0014] FIG. 2 is a reduced signal chart on detection of the cipher
mode by the principle of interrupting,
[0015] FIG. 3 is a reduced signal chart on an enquiry about the
cipher mode,
[0016] FIG. 4 is a reduced signal chart on detection of the cipher
mode when enquiries at regular intervals are used,
[0017] FIG. 5 is a reduced block diagram showing the location of
the most essential blocks of a cipher mode indicating device in a
mobile station according to an advantageous embodiment of the
invention,
[0018] FIG. 6 is a reduced block diagram showing the implementation
of a cipher mode indicating device in connection with a mobile
station and a data processor,
[0019] FIG. 7 is a reduced chart on a situation where a data
transmission connection is formed between two mobile stations,
and
[0020] FIG. 8 is a reduced signal chart on an enquiry about the
cipher mode in a situation where a data transmission connection is
formed between two mobile stations.
[0021] FIG. 1a shows call set-up signalling during a
mobile-originated call and FIG. 1b shows call set-up signals during
a mobile-terminated call in the GSM mobile communication network.
During call set-up signalling, enciphering information is exchanged
if the cipher mode is set on. Upon call set-up signalling, the
mobile communication network sends a cipher mode command message
requesting the mobile station MS to start enciphering. When the
mobile station MS receives this message, it sets a cipher
indication data field CIND to show that the cipher mode is on. The
cipher indication data field CIND used can be e.g. a predetermined
binary digit. Thus the value of the binary digit can be either a
logical "0" or a logical "1". For example in logical circuits
having an operating voltage of 3 V, the logical "0" value
corresponds advantageously to a voltage value of approximately 0 V
and the logical "1" value corresponds to a voltage of approximately
3 V, which is known as such. The cipher indication data field CIND
used can be naturally any other data field as well, such as a byte,
wherein advantageously when the value of the byte is zero, the
cipher mode is off and, in a corresponding manner, when the value
of the byte of different from zero, the cipher mode is on. The
contents of the cipher indication data field CIND is cleared upon
starting up the mobile station MS and always after a call has been
ended. When the user starts a new call and the call setup
signalling advances, the value of the cipher indication data field
CIND is changed in connection with the exchange of ciphering
information to be different from zero, i.e. to indicate that the
cipher mode is on.
[0022] Now referring to FIG. 2, when the resource control block 1
of the mobile station MS detects a cipher control signal in the
communication between the mobile station and the base station, the
resource control block sets the value of the cipher indication data
field CIND in a cipher indicator memory block 2 to correspond with
the cipher indication data. The cipher indicator memory block 2
reads the value of the cipher indication data field and detects
that a new value has been set in it, wherein the cipher indicator
memory block 2 makes a request for interruption. A user interface
block 3 detects the request for interruption, wherein it sends an
enquiry on the cipher mode to the cipher indicator memory block 2
which returns the data on the cipher mode to the user interface
block 3. Following this, the user interface block 3 sets the cipher
indicator to the mode corresponding to the ciphering data, for
example with a certain sign on the display of the mobile station.
The change of the cipher mode can also be indicated with an
acoustic signal, wherein the user notices the change in the cipher
mode also when talking to a mobile station. Thus the user does not
need to have visual contact with the display of the mobile station.
The user of the mobile station is informed of the cipher mode at
the beginning of and during the call. This is important
particularly in situations where the cipher mode can be changed
during the call, for example when the mobile station is moving.
[0023] FIG. 3 illustrates a second advantageous embodiment of the
method according to the invention. Here the difference to the
embodiment of FIG. 2 lies primarily in that a change in the cipher
indication data field does not lead to a request for interruption
but the cipher indicator memory block 2 sends the cipher
information to the user interface block 3 whenever the value in the
cipher indicator memory block is changed. In other respects, the
operation of the embodiment shown in FIG. 3 corresponds
substantially to the operation of the embodiment shown in FIG.
2.
[0024] FIG. 4 illustrates a third advantageous embodiment of the
method according to the invention, wherein the user interface block
3 sends cipher mode enquiry messages at regular intervals to the
cipher indicator memory block 2. The cipher indicator memory block
2 sends a response to the enquiry to the user interface block 3
which will transmit the cipher information to the cipher indicator.
In this embodiment, a separate message on the change in the cipher
indication data field is not formed. When using this embodiment,
the interval of sending enquiry messages must be kept sufficiently
short in order to detect a change in the cipher mode sufficiently
quickly. In this embodiment, it is advantageous to form a cipher
mode enquiry message at least in those situations when the mobile
station moves from the area of one base station system to the area
of another base station system.
[0025] During a call, it is possible to transmit so-called short
message services (SMS) to the mobile station. In the transmission
of short messages, the cipher mode may deviate from the cipher mode
of the call in question, wherein the method of the invention can be
used to indicate the cipher mode separately for the call and for
the short message services. Also a change in the cipher mode can be
indicated to the user both for the call and for the short message
services. For indicating the cipher mode and a change in the cipher
mode, signals distinguishable from each other can be used, e.g.
different acoustic signals, wherein the user of the mobile station
is aware of the cipher mode of both the call and the short message
services.
[0026] The method according to the present invention can also be
applied in a way that the existence of enciphering is indicated to
the user already before starting the call. This can be implemented
advantageously by providing the menu structure of the mobile
station with a function whereby the user can ask the mobile
communication network about the cipher mode. When this function is
selected from the menu, the mobile station sends the mobile network
a message inquiring the cipher mode. In practice, this can be
conducted in the GSM mobile network by forcing the mobile station
to a location update procedure. This procedure contains starting of
enciphering if the cipher mode is active in the mobile
communication network. In this way, the mobile station can send to
the mobile communication network an enquiry about the current
cipher mode, which is indicated to the user e.g. by an icon in the
display of the mobile station.
[0027] Problems may result in countries where enciphering is not
allowed to be on during speech because of legislation or for
another reason. However, enciphering can thus be on for signalling,
i.e. the location update procedure shows cipher-on mode although it
is not on for speech. Thus the mobile station can produce an
acoustic signal when it turns on the speech channel and detects a
change in the cipher mode, wherein the user will be informed that
speech is not transferred in enciphered form.
[0028] FIG. 5 is a reduced block diagram showing one embodiment of
the apparatus according to the invention. A functional part of the
central processing unit MCU consists of the resource control block
1 which processes signalling between the mobile communication
network and the mobile station. The resource control block 1 is in
a transmission connection via a first signal bus 4 to a data
transmission bus 5. The data transmission bus 5 is connected with a
memory block MEM by means of a second signal bus 6. Further, the
data transmission bus 5 is connected with a user interface block Ul
via a third signal bus 7. The user interface block Ul includes a
visual display unit 8, a display unit control means 9, an acoustic
signal forming element 10, and a control means 11 for the acoustic
signal forming element. The display unit 8 is preferably the
display of the mobile station, and the acoustic signal forming
element 10 is preferably the sound generator of the mobile station,
or the like.
[0029] Data transmission from the resource control block 1 to the
cipher indication data field CIND is preferably controlled by the
central processing unit MCU, wherein the central processing unit
MCU reads the ciphering information and transmits it to the cipher
indication data field CIND via the first signal bus 4, the
transmission bus 5 and the second signal bus 6. Said buses can
advantageously be arranged by known solutions used in connection
with microcontrollers. Said signal buses can also be placed in the
microcontroller itself, wherein the microcontroller comprises a
central processing unit MCU, a resource control block 1, a cipher
indicator memory block 2 comprising also the cipher indication data
field CIND, as well as said signal buses 4, 6 and data transmission
bus 5.
[0030] The central processing unit MCU has a data transmission
connection also to the user interface block Ul via the first signal
bus 4, the data transmission bus 5 and the third signal bus 7.
Consequently, the central processing unit MCU can advantageously
control also the display unit control means 9 and the control means
11 for the acoustic signal forming element situated in the user
interface block Ul. This control can be arranged in a way that the
central processing unit MCU sets the control line of the display
unit control means 9 (not shown) to a logical "0" value (ca. 0 V)
when the cipher mode is off. The central processing unit MCU sets
the control line of the display unit control means 9 to a logical
"1" value (for example ca. 3 V) when the cipher mode is on.
Acoustic signal formation can be applied in a corresponding manner.
Thus the central processing unit MCU sets the control line of the
control means 11 for the acoustic signal forming element (not
shown) to a logical "0" value, when there are no changes in the
cipher mode. When the cipher mode is changed, the central
processing unit MCU sets said control line for a moment to a
logical "1" value and resets said control line to an "0" value
after a suitable length of time. Thus the length of the acoustic
signal can be influenced by the duration of the "1" value
state.
[0031] Data transmission between different blocks in the apparatus
according to the invention can be arranged using methods known as
such, wherein it is unnecessary to explain it in more detail in
this context.
[0032] The method of the present invention can be advantageously
applied also in mobile stations currently in use in a way that the
functions required in the method are provided in the operational
software of the mobile station. Thus no changes will be required in
the hardware of the mobile station.
[0033] The invention can also be applied in a way that part of the
functions required in the method are provided in the operational
software of the mobile station and part of them are provided in the
software of a data processor which is in transmission connection
with the mobile station. One such embodiment is illustrated as a
reduced block diagram in FIG. 6.
[0034] In this embodiment, the mobile station is also used as a
so-called wireless modem in connection with a data processor, such
as a personal computer, wherein a data transmission connection is
formed from the data processor PC via the mobile communication
network e.g. to another data processor. In this case, it is
advantageous to indicate the cipher mode as a certain sign on the
display 12 of the data processor and possibly also as an acoustic
signal by the acoustic signal forming element 13 of the data
processor. The cipher indicator memory block 2 transmits
information on a change in the cipher indication data field
advantageously to the data processor PC by means of a mobile
station connection element 14 and a PC connection bus 15. The data
processor PC is provided with application software which controls
that the data on the change in the cipher indication data field is
read in the data processor PC from a data processor connection
element 16 and processed preferably in the central processing unit
17 of the data processor. After this the data processor PC sends
out a cipher mode enquiry message which is transmitted back to the
cipher indicator memory block by means of the data processor
connection element 16, the PC connection bus 15 and the mobile
station connection element 14. In response to the enquiry message,
the cipher indicator memory block 2 sends the cipher data to the
data processor PC. From the data processor PC, the cipher data is
read from the data processor connection element 16 and transmitted
to the cipher mode indicator. The cipher mode indicator is
preferably the display unit 12 and possibly also the acoustic
signal forming element 13 of the data processor. Thus the cipher
mode is indicated by a suitable symbol on the display unit 12 of
the data processor. In a corresponding way, a change in the cipher
mode is indicated e.g. as an acoustic signal by the acoustic signal
forming element 13 of the data processor. Also the operation and
structure of the data processor PC are generally known and need not
be explained in more detail in this context.
[0035] Further, the invention can be applied in situations where a
data transmission connection (call) is formed between two mobile
stations. Thus data transmission between the first mobile station
MS1 and a mobile communication network as well as between the
second mobile station MS2 and a mobile communication network takes
place via the radio channel. The mobile stations MS1, MS2 can be
located in areas of different base stations, wherein it is possible
that the cipher mode in communication between the first mobile
station MS1 and the mobile network is different than in
communication between the second mobile station MS2 and the mobile
network. The data transmission connection between the first mobile
station MS1 and the second mobile station MS2 is formed in a way
known as such. After the connection has been made, it is possible
e.g. for the first mobile station MS1 to enquire the cipher mode of
the second mobile station MS2 (FIG. 8). The enquiry can be made for
example as call control signalling, such as in the GSM mobile
network, and also if the ISDN between the mobile services switching
centres MSC is in the user-user information element according to
the GSM Standard 04.08. The resources control block 1 of the first
mobile station MS1 forms a cipher mode enquiry message and
transmits it to the second mobile station. The resource control
block 18 of the second mobile station detects the cipher mode of
the second mobile station and forms a response message where the
cipher mode is transmitted to the resource control block 1 of the
first mobile station. After this, the resource control block 1 of
the first mobile station MS1 sets the cipher indication data field
as disclosed above in this description. The first mobile station
MS1 can also be provided with a second cipher indication data field
for recording cipher data between the second mobile station MS2 and
the mobile communication network. Thus the user of the mobile
station MS1, MS2 can be given the cipher mode separately for
communication between the first mobile station MS1 and the mobile
network and for communication between the second mobile station MS2
and the mobile network. In another alternative, the user of the
mobile station MS1, MS2 is given the cipher mode so that if
communication between both mobile stations MS1, MS2 and the mobile
network is enciphered, the user of the mobile station MS1, MS2 is
informed that the cipher mode is on. In a different case the user
is informed that the cipher mode is off.
[0036] If the cipher mode in the second mobile station MS2 is
changed during a call, it sends a message on the change in the
cipher mode by useruser signalling.
[0037] For enquiring the cipher mode of communication [to and from]
the second mobile station MS2, also other methods can be used, such
as short message services (SMS).
[0038] The ISDN telecommunication network (Integrated Services
Digital Network) provides also an optional user-to-user signalling
service (UUS) which makes communication possible between
telecommunication terminals in a data transmission connection with
each other. Thus, if a data transmission connection is made from a
mobile station MS to a telecommunication terminal of the ISDN type,
the mobile station MS can send the telecommunication terminal an
enquiry about the cipher mode by using the user-to-user signalling
service. If the telecommunication terminal does not recognize the
enquiry message of the mobile station MS, the mobile station MS
will not receive a response to the enquiry, or the response will
consist of an unidentified command or another corresponding
message. In such a case, the mobile station MS can deduce that the
telecommunication terminal is not a mobile station but most
probably a telecommunication terminal connected with a landline
telecommunication network. In this situation, the display unit of
the mobile station MS indicates the user of the mobile station for
example that the cipher mode between the second telecommunication
terminal and the telecommunication network is unknown.
[0039] For indicating the cipher mode and a change in the cipher
mode to the user of the mobile station MS, also other methods,
known as such, can be used. For example, the cipher mode can be
indicated by a light source, such as a light-emitting diode (LED).
Consequently, for example when the cipher mode is on, a control
voltage is supplied to the LED (the LED is emitting) and when the
communication is not enciphered, no control voltage is supplied to
the LED (the LED is unlit). A change in the cipher mode can be
advantageously indicated by flashing the LED. Thus for example when
the communication is not enciphered, the LED is unlit, and when the
communication becomes enciphered, the LED flashes for a moment
after which the LED will emit light continuously as long as the
cipher mode is on. In a corresponding manner, when the
communication becomes unenciphered, the LED will flash for a moment
before it is turned off.
[0040] Further, so-called vibration batteries have been developed
for mobile stations whereby the mobile station can be made to
vibrate in a muffled way. Thus the cipher mode of data transmission
can be indicated also by a vibration battery, wherein for example
upon a change in the cipher mode, a control signal is supplied to
the vibration battery for a moment, which will result in vibration
of the mobile station and detection of the change in the cipher
mode by the user of the mobile station.
[0041] The invention is not limited only to the embodiments
presented above, but it can be modified within the scope of the
appended claims.
* * * * *