FI97184C - Method and apparatus for realizing a subscriber-specific scrambling and descrambling in a subscriber network - Google Patents

Abstract

To provide a simple and flexible equipment for data scrambling in a subscriber network based on a point-to-multipoint system, the scrambling sequences of the subscribers currently corresponding to the time slots of the transmission frame of a signal to be transmitted to subscriber terminals are stored in the central unit of the network, in RAM 61, and the scrambling sequence of a subscriber corresponding to the current time slot of the transmission frame is read to the scrambling means 67 located in the central unit to scramble the subscriber data by the subscriber's own scrambling sequence. The invention also relates to descrambling implemented in similar manner, using descrambling means 65. <IMAGE>

Description

97184

The invention relates to a method for carrying out scrambling in a point-to-multipoint system based on time-division data transmission according to the preamble of appended claim 1. The invention also relates to a method 10 for performing descrambling in such a multipoint system and to an apparatus for performing modification and / or remodeling in such a multipoint system.

The solution according to the invention is particularly suitable for use in combined cable television and telephone networks, PON (Passive Optical Network) networks and in connection with a wireless local loop. Due to the multi-point nature of the connection, these networks must be able to prevent third parties from eavesdropping on calls or from switching to the wrong time slot due to a malfunction of the subscriber unit-20. This could be done by performing speech encryption on each channel with a subscriber-specific encryption key. However, efficient voice encryption is a rather heavy and expensive operation and with normal subscriber connections also an oversized solution. Adequate protection for the transmitted data is provided if the scrambler connected to the normal modem is modified so that the editing sequence provided by the modifier is different for each subscriber.

30 In known modifiers, the modification sequence is formed. typically by means of a feedback shift register • »· Sat. The coupling is used to produce a pseudo-random bit string, which is • summed at the transmitter by modulo-2 summation. The remodeling is performed by the following: · .: 35 devices at the receiver by re-summing 2 97184 of the same pseudo-random bit string to the received data stream by modulo-2 summation.

Such a known method is good for connections between two points, whereby all bits 5 of the data stream pass through the same modifier and remodeler. The subscriber-specific modification of the connection can be done by loading a subscriber-specific seed number into the transfer register, from which sequence generation is started.

However, if it is desired to modify each time slot of the time division signal to a subscriber-specific sequence, a separate modifier is required for each time slot. In this case, for example, a 30-slot system must have 30 parallel modifiers, of which only one is used at a time. If the system is centralized (more space-15 Jia than time slots), the editing sequences must be unique to each subscriber, for example, in a 120-subscriber system, this may be difficult to implement. For this reason, time-lapse data processing has not been used much in known solutions.

20 Another problem with known solutions is the rigidity of the modifiers with respect to the sequence used. If you want to change the sequence, you must change the connection of the editor. Although the coupling can be changed, for example, by means of controllable feedback branches, it should be noted that there are a finite number of shift register couplings producing a meaningful modification sequence. In this case, the only flexible way to change the sequence is to start the sequence to be changed by means of the seed number to be loaded into the transfer register. nip.

• · «30 In known solutions, data editing and .encryption are two completely separate functions. In this way, it has been possible to provide sufficient randomness between the symbols to be transmitted and good protection for the data to be transmitted. However, such wide solutions are quite complex and expensive.

The object of the present invention is therefore to provide a solution which does not have the above-mentioned drawbacks. This is achieved by the methods according to the invention, which are characterized by what is described in the characterizing parts of the appended claim 1 (modification) or 5 (modification). The devices according to the invention, in turn, are characterized by what is described in the characterizing parts of the appended claims 6 and 8.

The idea of the invention is to perform data editing and reworking in the central unit of a multipoint system on a time slot basis with a modifier / remodel based, instead of a fixed connection, on a memory in the central processing unit (RAM) in which sequences are stored on a time slot basis. By reading from the memory in each time slot to the corresponding subscriber modification sequence, a time division signal is obtained from which the recipients can extract only the data of their own time slot in plain language.

The solution according to the invention provides a simple: and flexible device for editing and re-editing data in a multi-point subscriber network. A further advantage of the solution according to the invention is that. that the memory-based modifier / modifier 25 can also be utilized to perform other functions such as encryption, frame structure conversion, or cross-linking.

The solution according to the invention does not make the modifiers of the multipoint system any more complicated than e.g.

• · ·::: 30 standard point-to-point connection modifiers.

:. ·. Using the solution according to the invention, a more advanced encryption is also possible, because the editing sequence can be easily changed even during an ongoing call.

In the following, the invention and its preferred embodiments will be described in more detail with reference to the examples according to the accompanying drawings, in which Figure 1 shows a subscriber network forming a typical environment for the application of the invention, Figure 2a shows in more detail a downlink frame used in the network of Figure 1. structure, Fig. 2b shows 10 bits to be transmitted in downlink TSO time slots of downlink frames, Fig. 3 shows a frame structure used in uplink connections in the network of Fig. 1, Fig. 4 shows a known straightforward way 15 to implement editing and modification in the system of Fig. 1 , which may be centering, Fig. 5 shows a modifier unit implemented according to the principle of the invention, which replaces the central end modifier unit in the apparatus according to Fig. 4, Fig. 6 shows a modifier unit according to the invention, mu equipment for performing thumping and reworking, and Fig. 7 shows a possible memory map of the RAM shown in Fig. 6.

Figure 1 shows a subscriber network implemented with a time division multipoint interface. The network ···· comprises a plurality of subscriber terminals 101 to which a telephone machine or other similar telecommunications terminal 102 of one or more subscribers is connected to each »i · * · * *, and a central processing unit 103 common to all the subscriber terminals. a device that connects subscribers to a Public Switched Telephone Network (PSTN) exchange 104. The interface is one of the standard digital interface methods, such as V2 · / [or V5.1 or V5.2, which (the latter ) also allows 35 centralization (more subscribers than time slots).

li • · 5 97184

The subscriber terminals 101 may be devices placed next to the subscriber, or the subscriber terminal may be formed by a subscriber multiplexer known per se, such as a Nokia ACM2 subscriber multiplexer, to which e.g. a modem establishing RF connection 5 and framing circuits necessary to form a transmission frame from subscriber to exchange are added.

The transmission channel 110 between the subscriber terminal and the central processing unit can be a radio channel, e.g. a coaxial cable of the cable television network 10 or, for example, a passive optical network (PON network). Combinations of these can also be used in such a way that the physical transmission media forming the transmission path are different in different transmission directions. This is a preferred method, e.g. in cases where there is already a fixed one-way distribution network, in which case the uplink can be implemented e.g. by radio.

The copper cable 111 extending from the subscriber terminal to the subscriber device 102 is in practice very short, at most perhaps about 100 m.

Networks such as those described above are also described in FI patent application 932818, to which reference is made for a more detailed description. This application describes in more detail, for example, the structure of the central processing unit 103 and the subscriber terminal 101.

The downlink connection, i.e. the connection from the central unit to the subscriber terminal, can be implemented in a network such as the one described above by modifying the 2048 kbit / s • · · ** '* frame structure as little as possible, but in such a way that the channeling system known per se, «♦ whose frame structure is reserved for each subscriber: 30 its own signaling bits, the message base is switched to. *. icy signaling. The changes affect the structure of time slot zero * · * * 11 / (TS0), and time slot 16 (TS16) is exempted from signaling for other uses. Figures 2a and 2b show the downlink frame structure so that Figure 35 2a shows the actual frame structure and Figure 2b • · 97184 6 time slot zero (TSO) mobile signaling. Reference numeral 201 denotes a frame of a 2048 kbit / s basic channelization system known per se, which is divided into 32 time slots TS0 ... TS31, of which time slots TS1 ... TS15 and 5 time slots TS17 ... TS31 form speech channels in a known manner.

Sixteen consecutive frames F0 ... F15 form a superframe 202 in the system with a length of 2 ms. The superframes of the sixteen frames can still be formed into, for example, a superframe 203 with a length of four superframes, the duration of which is thus 8 ms.

A messaging channel consisting of free bits of odd frames is added to time slot zero (TSO), as shown in Figure 2b. In time slot zero, the bits denoted by S are bits-15 of the signaling message, the bits denoted by KL are frame lock bits, the bits denoted by C are CRC4 bits for monitoring the quality of the connection, the bits denoted by SF are bits, the bits are X, and the bits are does not matter-20. The bits b1 of the odd frames circled in Figure 2b form a superframe lock word according to the recommendations of the CCITT. The following bits (b2), set to one, indicate that the frame in question is missing a frame lock word.

25 signal bits are generated into messages of 40 bits (5 bits in a '' ·· frame, 8 frames in a superframe).

However, since this is not related to the present invention, reference is made in this connection to the above-mentioned FI patent application 932818.

• · ♦: ‘i’: 30 The uplink connection (i.e. the connection from the subscriber terminals to the central unit) is preferably implemented in the network according to Figure i · · 1 using the frame structure shown in Figure 3. The frame consists of one long message transmission / time slot 301 and several shorter subscribers; 35 of the time slots reserved for data transmission (speech or data transmission) 7 97184 302 (i.e. typically K >> M). Each time slot reserved for data transmission comprises an actual subscriber channel 303 with a protection area 304 of a few bits at each end. The advantages offered by such a frame structure in the network according to Figure 1 are described in more detail in the above-mentioned FI patent application 932818.

One subscriber terminal (which may have more than one subscriber) at a time uses the message transmission time slot 301. The burst to be transmitted in the message transmission time slot thus comprises 10 identifiers of the transmitting subscriber terminal. If a collision occurs between two subscriber terminals, the retransmission times are estimated, i.e. after how many frames the transmission is performed again. For signaling, for example, the Slotted Aloha protocol-15a known per se can be used. (The protocol is described in more detail in, e.g., Tanenbaum, AS: Computer Networks, Englewood Cliffs 1989, Prentice Hall, Inc.) For practical hardware implementation, it is preferable to select the same bit rate as the uplink bit rate, i.e., 2,048 kbit / s. . In this case, for example, it is simpler to develop the necessary clock signals. By making, for example, the following selections: - number of data slots N = 54, - length of data slots M = 72 bits, and, 25 - length of message transmission slot K = 208 bits, "V is added to the uplink frame a total of 4096 bits, where *!" The frame duration is (at bit rate). 2 048 kbit / s) 2 ms, • * · · '* which corresponds to the time taken to transmit the downlink superframe.

• | · 30 The present invention performs subscriber point • scrambling and desc- rambling in a time division multipoint system, which • • · », ··. an example of this was given above. Figure 4 shows a conventional and straightforward solution for implementing data-3 5 modification and re-modification in a subscriber network with the basic structure according to Figure • 97184 8 1. A Ti-wide modification sequence is generated in the processing unit 42, the output of which is connected to the first input of the EXCLUSIVE OR gate 45. The signal from the cross-connection unit 41 is in turn connected to the second input of the ABSOLUTE-5 OR gate, which in this example is also a 2 Mbit / s signal containing 30 voice channels (30 TS). In this example, the system is centralized, in which case it may have e.g. The selector control signal-15 slice S_CTRL is selected at the selector output in each case as the output of the modifier whose corresponding subscriber time slot is currently connected to the second input of the ABSOLUTE-OR gate. In this way, the data of each subscriber can be modified with a subscriber-specific modification sequence in the ABSOLUTE-OR-port, the output of which gives the modified data stream SCR_DATA. This data stream is transmitted along the transmission path TP (e.g. radio path) to the receiving subscriber terminals, thus a total of 120. Each subscriber terminal comprises a receiver unit 46 which forms a modified data stream, 25 which is input to the first input of the ABSOLUTE-OR gate 48, and a frame or superframe synchronization signal '*** SYNC which is input to the remodeler 47. · '· * * Tis signal synchronizes the re-editor, which forms a subscriber-specific re-editor sequence, which 3 0 is input to the second input of the ABSOLUTE-OR gate 4 8.

A: Thus, each subscriber is able to re - edit:. only its own data, and cannot receive data belonging to other • wide ·. The output of port 48 provides the original unmodified data stream.

Using the principle of the present invention, the processing unit 42 is replaced by the hardware shown in Fig. 5, comprising a RAM-based processing block 52, a microprocessor 51, which writes data to the RAM and controls it. operation of the device as well as a pointer-5 generator unit 53 which distributes shifts to RAM users. The address generator thus determines, for example, with which modification sequence stored in the RAM the output signal of the modifier block is generated in each case, or because the microprocessor 51 can read the RAM or write 10 therein, e.g. change the sequences in the memory. The address generator receives the overframe synchronization signal MFSYNC and the bit clock CLK, so it knows which time slot is currently in progress for transmission or reception.

Figure 6 shows in more detail the apparatus according to the invention in the central unit of a multipoint system, which implements not only data editing and remodeling, but also buffering and framing. As an example, the solution shown in Figures 1 to 3 is used, in which the upstream and downstream frame structures are as shown. It should be noted, however, that such frame structures are not necessary for the invention, but the frame structure can vary in many ways.

The apparatus consists of one RAM block 61 and 25 connected to its data bus 62a and address bus 62b by silicon "V" and edit and remodel ports 67 and "" 65. The RAM 61 has its own memory area reserved for editing each time slot. and for the modification sequence.

At the beginning of the connection, the sequences of the subscriber operating in time slot 0 0 are stored in RAM. The address generator 53 is practically • · · V · formed by a counter unit and a selector (not shown), which is connected to control the counter unit. Counters • ♦ · · »» «, ···, the counters of the discipline unit count in the down and up bit rates. The selector in each case selects the address indicated by the counter unit on the address bus 62b 35 of the RAM.

10 97184

The counter unit also issues read or write commands on the RAM, i.e. it tells the circuits connected to the RAM block data bus, such as conversion circuits, registers and microprocessor read or write buffers, when they need to read the data on the data block of the RAM block. or write the data in the memory to the data bus. The read and write instructions are decoded directly from the reading given by the counter unit in a manner known per se. The control logic described above operates at a higher clock frequency than the bit clock 10, so that several read and write cycles are available per information bit to be processed.

The microprocessor 51 (only the read and write buffers 68b and 68a of the microprocessor are shown in Fig. 6) can write to the RAM memory via its write buffer 68a just like to its own actual memory. RAM is displayed in its entirety as part of the processor memory space, but is accessed by non-processors.

Thus, in this exemplary case, the downstream (per-subscriber) data stream DATA_A (time slot zero except for the modification described above) is a standard 2 Mbit / s signal that is connected to the first input of the modification port 67. The modification port 67 may be, for example, 25 an ABSOLUTE-OR port in the same manner as shown in the figure. 4. The byte of the slot-specific editing sequence is read from the RAM block • 61 via the parallel / serial conversion circuit 63 to the second input of the editing port 67. This operation is controlled by the counter unit of the address generator, which generates a downlink *.!. · 3 0 by means of its counters stepping in step with the frame structure • · «· the address corresponding to the frame and time slot in question and gives:. ·. instructing the conversion circuit 63 to read the data on the data bus of the RAM block • · · *** · ’, which is a byte of the modification sequence corresponding to the time slot in question. In the modification port 67, the data bits and i 35 modification sequence bits are summed, e.g. Thus, the bit stream to be transmitted per subscriber does not pass through the RAM, but only the bit strings (i.e. the editing sequences) read from the memory 5 are summed into the bit stream.

The remodeling takes place by means of the same RAM block 61. The downlink burst data stream DATA_C is first converted to the parallel format required by the bus in the serial and / or parallel conversion circuit 69, after which the data is stored in the memory 61. This must be done because in the case of the example, the transmissions are bursts and thus deviate from the normal 2 Mbit / s frame structure. Bursts from different subscribers are stored in memory in time slot-specific memory areas (shown in Figure 7). The storage address 15 is obtained on the address bus 62b from a counter of the counter unit that counts the uplink frame in bit rate. The counter unit also issues a write command to the conversion circuit 69. The uplink bit stream stored in the memory is read out of the memory in the order of the normal 2 Mbit / s frame frame-20 field by the slot and frame synchronization pulses obtained from the downlink frame structure. The actual conversion of the frame structure in the uplink takes place when the data stored in the memory is read out from the address 25 provided by the counter unit connected to the address bus.

'* ·. * The read-out data is re-edited in the re-editing unit 65, which in this exemplary case is in parallel form and may thus consist, for example, of the corresponding ABSOLUTE-OR gates, which are a number corresponding to a length of 30 bytes (8). Since this is a single-: port RAM, either a rework sequence is required. for storing a byte or an actual data byte, a register • · · • · * 64 in which the remodeling sequence or data byte is stored until one of these has time to be read out of the memory. From the output of the remodeling unit 65, the 12 ton data is fed to the parallel / serial conversion circuit 66, the output of which provides an uplink standard 2 Mbit / s signal.

Figure 6 also shows the write buffer 68a and the read buffer 68b of the microprocessor 51 5, which allow the microprocessor to access the RAM. When the processor initiates a connection to a subscriber, it writes a subscriber-specific modification sequence to the memory block corresponding to the time slot used by the subscriber. The sequence can be 10 single superframes (16 bytes), but longer sequences can also be used. Since the bit string (editing sequence) to be edited is subscriber-specific, speech encryption can also be performed by selecting different bit strings for different subscribers. If the editing sequence is Aino-15 up to one superframe (16 * 8 bits) and remains unchanged throughout the connection, the encryption is not very good, but changing the sequence during the connection or using a multi-frame bit string can improve the encryption because for example, a periodicity of 2 ms in the available editing sequences can be prevented.

Figure 7 shows a possible memory map of the RAM. The first 512 bytes (addresses 0 ... 511) comprise the editing sequences of time slots TS0 ... TS31. In this case, the sequences are 25 frames long (16 bytes). The next 512 bytes (addresses 512 ... 1023) consist of the remodeling sequences of the time slots TS0 ... TS31. Memory addresses 1024 to 1535, in turn, act as buffer memory locations for uplink execution.

• «I

3 0 conversion of transmitted data from burst format to standard 2 «· ·: Mbit / s frame format.

i. *. The above hardware is capable of performing • · · · editing on a time-by-time basis using a user-selected bit string. Since the bit string can be freely selected, queues can be used which are as easy as possible to form in the subscriber terminal 97184 13. It is also not necessary to perform the modification for all time slots, because a sequence of zeros can be written to the time slot-specific memory area, for example, in which case the time slot in question is in a way left unprocessed.

A cross-connection field can also be made for the data stream stored in the RAM in connection with the frame structure conversion. However, performing this operation requires that the cross-connect information be stored in RAM and that information be taken into account in address generation.

On the subscriber terminal side, a subscriber-specific modifier / modifier known per se is sufficient to carry out the modification / re-modification (in the same way as described above in connection with Fig. 4 for the modifier-15).

Although the invention has been described above with reference to the examples according to the accompanying drawings, it is clear that the invention is not limited thereto, but can be modified within the scope of the inventive idea set forth above and in the appended claims. For example, re-editing can be performed in the central unit even before the frame structure is converted (therefore the transmission frame of the signal from the subscriber terminals to the telephone network mentioned in the appended claims must be understood to include both the subscriber terminals and the central unit and the central unit and the telephone network). In principle, it is also possible to use:. *: * The solution according to the invention only in the other direction of the connection. In principle, what can also be used as memory

• I

3 0 any rewritable and readable memory ·. * * (If only for other memory features: reasonable). The practical implementation will also change e.g.

• · · · for the required conversion circuits, if parallel RAM is not used as in the example above. Modifications can also be made to the network which are not related to the idea according to the invention, e.g. it is in principle possible to integrate the subscriber device and the subscriber terminal into the same housing. In this sense, the reference to separate subscriber equipment and terminals 5 must be understood more broadly.

··· / • ti r • · '«» · • 1 * · · • · · • · · · »11 ·» «» • · · • · ·

Claims (9)

15 (f ;: r t / 'r A method for performing subscriber-specific modification in a subscriber network comprising 5. a plurality of subscriber devices (102), - a plurality of subscriber terminals (101), wherein at least one subscriber device (102) is connected to one subscriber terminal by a transmission link (111), and - a plurality of subscriber terminals 10 ( 103), which connects the subscriber devices to a public telephone network, in which in the subscriber network the data transmission between several subscriber terminals and the central unit takes place in time-division sequential transmission frames via a common transmission path (110) 15, and according to which - the central unit (103) generates a subscriber-specific subscriber data in the editing means (67), characterized in that the editing sequences of the subscribers corresponding to the time slots of the signal transmission frame to be transmitted to the subscriber terminals are stored in the network central unit (103) 20, and e In this transmission frame, the editing sequence of the subscriber corresponding to the time slot in turn is read to the editing elements 25 (67) in the central unit in order to edit the data of the subscriber in question. using an editing sequence. · · · A method according to claim 1, characterized in that the initialization of the editing sequence is always performed at the beginning of the connection. « Method according to Claim 1, characterized in that the length of the superframe is used as the length j, ·, of the editing sequence. m Λ A method according to claim 2, characterized in that a new sequence is stored in the subscriber while the connection is active. 97184 16 A method for performing subscriber-specific modification in a subscriber network comprising - a plurality of subscriber devices (102), - a plurality of subscriber terminals (101), wherein at least one subscriber device (102) is connected to one subscriber terminal by a transmission link (111), and - a central processing unit (103) ), which connects the subscriber equipment to the public switched telephone network (104), 10 in which the communication between a plurality of subscriber terminals and the central unit takes place in time-divided sequential transmission frames via a common transmission path (110), and according to which - the central unit (103) the seasonal sequence is used to re-edit the data of the corresponding subscriber in the re-editing means (65), characterized in that the time of the transmission frame of the signal 20 to be transmitted from the subscriber terminals to the telephone network is stored in the network central unit and that the re-editing sequence of the subscriber corresponding to the time slot in turn in the transmission frame is read to the re-editing elements (65) in the central unit for re-editing the data of that subscriber by means of the subscriber's own re-editing sequence. An apparatus for performing subscriber-specific modification in a subscriber network, comprising - a plurality of subscriber devices (102), 30. a plurality of subscriber terminals (101), wherein at least one subscriber device is connected to the subscriber terminal. / (102) via a transmission link (111), and • · *! * - a central processing unit (103) common to a plurality of subscriber terminals and terminals, which connects the subscriber equipment to a public switched telephone network, in which the communication between a plurality of subscriber terminals and the central unit takes place in successive in transmission frames via a common transmission path (110), the apparatus comprising in the network central unit 5 (103) - means (51) for generating subscriber-specific modification sequences, and - modification means (67) for modifying subscriber data with each corresponding modification sequence, characterized in that the central unit ( 103) further comprises a memory (61) in which there are deposits the transmission sequences of the subscribers corresponding to the time slots of the transmission frame, and means (43, 63) for coupling the editing sequence data of the subscriber corresponding to the respective time slot from the memory 15 to the editing means (67) for editing the data of the subscriber by the subscriber's own editing sequence. Apparatus according to claim 6, characterized in that said memory is RAM (61). An apparatus for performing subscriber-specific modification in a subscriber network, comprising - a plurality of subscriber devices (102), a plurality of subscriber terminals (101), wherein at least one subscriber device 25 (102) is connected to one subscriber terminal by a transmission link (111), and - a central processing unit common to the plurality of subscriber terminals. '· 1' (103), which connects the subscriber equipment to the public telephone network, in which the data transmission between several subscriber terminals and • «· 30 central units takes place in a time-divided manner: in successive transmission frames via a common transmission path (110) • · · [i! .1 in the central processing unit (103) of the network - means (51) for generating subscriber-specific modification sequences, and 97184 18 - modifying means (65) for reproducing the subscriber data by means of each corresponding modification sequence, characterized in that the central processing unit (103) further comprises a memory (61) storing the re-editing sequences of the subscribers corresponding to the time slots of the 5 transmission frames, and means (43, 64) for coupling the re-editing sequence data of the subscriber corresponding to the respective time slot from the memory to the re-editing elements (65) for re-editing the data of the subscriber . Apparatus according to claim 8, characterized in that said memory is RAM (61). • · · • · · · · «1 (1 • • · ♦ • · · · • · 97184 19