FI94694B - A method for transmitting page information in a time division multiplexed basic channelization system - Google Patents

Description

! - 94694

A method for transmitting page information in a time division multiplexed basic channelization system.

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The invention relates to a method for transmitting side information, such as channel-specific signaling, in a time division multiplexed basic channelization system, wherein the page information is transmitted in a predetermined time slot of each frame, and in which more than one channel information is transmitted in at least one time slot of the basic system. The method according to the invention is intended in particular in connection with the European 2048 kbit / s 30-channel basic channelization system, but it is not limited only to this standard.

In the 2048 kbit / s basic channelization system defined in CCITT Recommendation G.704, channel-specific signaling is transmitted in the CAS (Channel Associated Signaling) time slot TS16 by grouping successive frames into 20 larger entities, the so-called as a multiframe containing 16 frames. The time slots TS16 of successive frames included in the superframe are each provided with a signaling channel corresponding to two different speech channels. Thus, 4 bits remain in the slot for both signaling channels. The signaling channels bind the time slots TS16 of the fifteen superframes. The time slot TS16 of the remaining frame 0 includes, among other things, a superframe synchronization signal, as described below.

30 In the basic system described above, a total of 30 voice channels with a capacity of 64 * kbit / s can be transmitted. Today, however, advanced speech coding methods can be used to increase the capacity of a 2048 kbit / s system to 60 or even 120 voice channels. In this case, the speech channel information must be encoded with a transcoder 2 to S4694.

CCITT Recommendation G.761 specifies the 32 kbit / s ADPCM transcoder in detail for fixed slot selection, signaling transmission, and alarm handling.

5 However, this transcoder cannot be connected to the 2048 kbit / s basic system because it uses bits reserved for national use in Recommendation G.704 for the transmission of the alarm. Therefore, the delivery of alarms cannot be guaranteed.

10 On the other hand, although CCITT Recommendations G.726 and G. 727 define 16 kbit / s speech coding, the transcoder that implements it has not yet been defined. One reason for this situation is that the transmission capacity of the time slots TSO and TS16 is not sufficient to transmit the channel-specific sig-15 of the 120 channels in the conventional manner.

Recommendation G.761 also defines alarms, eg forward and reverse AIS (Alarm Indication Signal) alarms. However, the approach defined in the Recommendation is not applicable when using the 16 kbit / s codec 20, as not enough bits are available for alarm transmission. The network operator also uses the free bits of the time slot TSO, which means that they cannot be used for the purpose defined in Recommendation G.761.

It is therefore an object of the present invention to provide a method which does not have the drawbacks described above, but which enables the transmission of side information, in particular signaling and alarms, in a conventional basic channelization system up to a capacity of 120 voice channels. This is achieved by a method according to the invention, characterized in that a "superframe of several superframes" is formed, wherein at least a part of the page information is transmitted in said predetermined time slot, in addition to said page information a superframe sequence number is assigned.

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3 94694 indicates to which channel this page information belongs.

The basic idea according to the invention is to use slower signaling and to utilize the "extra-5" bits remaining in the time slot transmitting the channel-specific page information as "address bits", which indicate which transmission connection is currently being served.

According to a preferred embodiment of the invention, part of the page information is transmitted by changing the sequence of superframe sequence numbers. The idea is thus to utilize a sequence of 10 sequence numbers or a modification thereof to transfer some of the page information. In this way, other page information, e.g. alarms, can be transmitted. It should be noted already at this stage that although the term "superframe" is used in the presentation to clarify the operation of the method to the reader, the operation of the method does not in itself require a single superkeyst in all time slots, but may be different in phase or sequence.

The solution according to the invention is also compatible with 20 n x 2048 kbit / s networks, because the delay deviations occurring in the cross-connect devices (different delay at different time intervals) are eliminated due to the "address bits" used in the solution according to the invention.

A further advantage of the invention is that the bits normally used for network management of the time slot TSO 25, which 1 e.g. are used for other purposes in the above-mentioned Recommendation G.761, are not utilized, but remain in the use of network management.

The invention will now be described in more detail with reference to examples according to the accompanying drawing, in which Fig. 1 shows the formation of superframes from superframes, Fig. 2 shows the transmission of side information in time slot TS16 in successive superframes and superframes, Fig. 3b shows a block diagram of a transmitter part according to the invention. method, and Fig. 4 shows a block diagram of a receiver part in a code cat implementing the method according to the invention.

The following is an example of a 2048 kbit / s 5 basic channelization system in which 120 speech channels are transmitted by means of a 16 kbit / s speech encoder. Thus, each speech channel time slot (time slots TS1 ... TS15 and time slots TS17 ... TS31) contains 4 coded speech channels.

Figure 1 firstly shows one frame 10 of the basic chicken-10 lubrication system, which is divided into 32 time slots TS0 ... TS31. As is known per se, the frame time slot TS16 is used by two signaling channels, leaving 4 bits abcd for each channel. Sixteen consecutive frames F0 ... F15 form a superframe 15 11 in the system, the length of which is 2 ms. Thus, thirty voice channels can be served in a conventional system.

However, in a multiplexer transmitting a conventional telephone service, it is possible to reduce the number of signaling bits actually transmitted per channel to two (hereinafter bits a and b). The other bits (hereinafter bits c and d) are typically connected to a fixed state and thus do not normally need to be transmitted at all.

According to the invention, the superframes 11 of sixteen 25 frames are formed into a superframe structure of four superframes with a duration of 8 ms, and the above-mentioned bits c and d are used so that the transmitter unit always transmits not only the actual signaling bits a and b, but also bits c and d , which indicate the superframe number 30 (1 ... 4) in the superframe. This sequence number indicates. * Which voice channel is currently being served, i.e., the receiver uses "address bits" c and d to update the signaling data of the correct voice channel. Only one of the four speech channels is updated for signaling during superframe 35, so it is only after the superframe that all

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94694 5 voice channel signaling updated once. Thus, in the solution according to the invention, the refresh rate drops from a normal 2 ms rate (superframe rate) to an 8 ms rate. (When using a 32 kbit / s encoder, the refresh rate is 4 ms.) 5 In practice, slowing down the rate to a quarter is not a problem, but even a slower speed is good for normal telephone network signaling.

Figure 2 shows channel-specific signaling for the time slot TS1 by showing the contents of the time slots TS16 of successive frames 10 (there are a total of 64 in the superframe 12) in those frames in which the time slot (TS1) signaling data is transmitted. The third and fourth bits of the time slot TS16 of the second frame F1 of each superframe 11, i.e. the c- and d-bits described above, indicate by means of the sequence number (00, 01, 10 or 11) of the superframe 11 to which the speech channel of the time slot TS1 the respective bits a1 and b1 each belong. Figure 2 further shows the first four bits abcd of the time slot TS16 of the first frame F0 of each superframe, which form the synchronization signal 20 and are all zeros. Respectively, for example, the c and d bits (not shown) following bits a17 and b17 indicate in each case which of the four speech channels of the time slot TS17. bits related. In the time interval TS1, the cd bits form the sequence 00, 01, 10, 11 as described above.

The superframe structure according to the invention may be incoherent, i.e. in each time slot the phase of the "1-4 counter" in question may be different.

According to a preferred embodiment of the invention, cyclically alternating c and d bits are used for the transmission of alarms, so that in the event of an alarm a certain one is exchanged. the normal cd bit sequence is changed to another, e.g. the normal state sequence 00, 01, 10, 11 described above is changed to another. There are six (4! / 4) possible sequences, which are enough to transmit practically all the necessary alarms. Some alarms, e.g., a forwarded 6,9469 4 AIS alarm, may be issued so that the c and d bits become fixed (e.g., 10), i.e., so that the superframe sequence number ceases to rotate from time to time. In this case, of course, the signaling does not work as described above 5, but in an alarm situation it does not matter.

Figures 3 and 4 show an implementation of a codec which implements the method according to the invention. These implementations correspond to the applicant's ADPCM codec 10, which belongs to the product family sold under the name DYNACARD ".

The input of the transmitter section 30 of Fig. 3 has an interface circuit 31 in which data and a clock signal are separated from the incoming PCM signal, which are further transmitted to the respective inputs of the demul-15 duplexer unit 32. The demultiplexer unit separates the signaling bits to be transmitted in time slot TS16, which are passed to the copy unit 35. In addition, data is passed from the demultiplexer unit to the encoder unit 33 and a frame synchronization signal to the encoder control unit 36, which tells the encoder the coding rate used in the system. In copy block 35, the c and d bits of the incoming signal are discarded. The encoded data (speech) and the signaling information from the copying unit, from which the original 25 c and d bits have been removed, are connected to a cross-connect circuit 34, which arranges the time slots again on the outgoing bus TX BUS. The signaling output of the cross-connect circuit has a cd-bit sequencer 38, where new signaling bits c and d are added to the signaling data. The sequencer changes the normal sequence of cd bits 30 (under the control of processor unit 37) to another sequence if an alarm needs to be transmitted. Control for the sequencer comes from the cd-bit sequence generator, which is a counter that steps forward every superframe (and always resets every superke-35 frame). The sequence generator receives an overframe clock from 7,94694 buses.

On the receiver side (Fig. 4), RX-BUS data (speech) and signaling are obtained from the receiver bus to the corresponding inputs of the cross-connect block 41. The cross-connect block 5 arranges the time slots under the control of the processor unit 47 according to the user's choice, and supplies speech data to the decoder unit, signaling bits a and b to the multiplexer unit 43, and bits c and d to the reference block 45. Each received speech channel is ADPCM-decoded What is needed here is channel-specific control information, which is so generalized that it can also be used to decode the time slot internal cross-connection information. This gives the local c and d bits at the same time. Comparison block 45 compares these locally generated c and d bits with the received c and d bits. If these are the same, the comparison block provides the multiplexer with an enable signal to update the signaling memory in the memory of the multiplexer unit 43 for that channel. If the received cd bits and the locally generated cd bits are not the same, the channel signaling unchanged until the comparison shows the CD bits to be the same. The comparison block also infers whether the cd bits have a normal sequence or whether it is an alarm. The processor unit 47 selects the time slot 25 to be examined in each case.

Thus, on the receiving side, it is not necessary to lock in the superframe, but the receiver uses the received signaling bits to update the signaling information of the correct voice channel.

After the side information has been transferred between the transmitter and the receiver part as described above, a conventional PCM signal PCM 1 can be re-constructed at the output of the receiver unit, in which the c and d bits described above are fixed. To this end, the processor unit 47 provides the multip-35 lexer unit 43, at the user's choice, with fixed c-8 94694 and d-bits cdout. However, if some time slots are not decoded in decoder 42, the c and d bits can be switched forward.

The method according to the invention can, of course, also be implemented with very different device structures. However, the additions required for existing devices are minor, mainly limited to devices that provide a free-rotating two-bit overframe counter to the transmitter portion for the signaling bits.

Although the invention has been described above with reference to the example according to the accompanying drawing, it is clear that the invention is not limited thereto, but can be modified in many ways within the scope of the inventive idea set forth above and in the appended claims.

Although the invention has been described above with an example of transmitting 120 voice channel signaling as well as alarms, the invention can be used in other applications as well. For example, instead of voice connections, 16 kbit / s data channels can be transmitted, which involve some other information. The number of chickens-20 can also be e.g. 60, in which case the superframe can be formed from only two superframes. As also stated at the beginning, the actual inventive idea is not limited to the European 2048 kbit / s basic channelization system, but the idea can also be applied to other systems of a similar type.

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Claims (6)

94694 9 A method for transmitting side information, such as channel-specific signaling, in a time division multiplexed basic channelization system, wherein the side information is transmitted in a predetermined time slot (TS16) of each frame, and the method transmits more than one channel in at least one time slot (TS1..TS15, TS17..TS31) of the basic system. information, characterized in that a superframe (12) having a length of a plurality of superframes (11) is formed, wherein at least a part of the page information is transmitted in said predetermined time slot (TS16) so that in addition to said page information a superframe sequence number is transmitted indicating which channel 15 the page information belongs to . A method according to claim 1, characterized in that part of the page information is transmitted by changing the sequence of sequence numbers of the superframe. Method according to Claim 1 or 2, characterized in that the superframe formed is incoherent in such a way that the phase of the superframe is different at different time intervals. Method according to one of Claims 1 to 3, characterized in that the superframe is formed by four superframes. Method according to one of Claims 1 to 3, characterized in that the superframe is formed by two superframes. Method according to one of the preceding claims 2 to 5, characterized in that part of the page information is transmitted by changing the bits (c and d) indicating the sequence number of the superframe (11) to fixed. 94694 10