AU668580B2

AU668580B2 - Method for insertion of auxiliary data into digital frames of plesiochronous or synchronous networks

Info

Publication number: AU668580B2
Application number: AU46072/93A
Authority: AU
Inventors: Christophe Bonnot
Original assignee: Alcatel NV
Current assignee: Alcatel Lucent NV
Priority date: 1992-09-11
Filing date: 1993-09-03
Publication date: 1996-05-09
Anticipated expiration: 2013-09-03
Also published as: AU4607293A; FR2695781A1; FR2695781B1

Description

8; _I P/00/011 28/5/91 Regulation 3.2 668580

AUSTRALIA

Patents Act 1990 9 0 O 0 ii

ORIGINAL

COMPLETE SPECIFICATION STANDARD PATENT a 0 Invention Title: "METHOD FOR INSERTION OF AUXILIARY DATA INTO DIGITAL FRAMES OF PLESIOCHRONOUS OR SYNCHRONOUS NETWORKS" The following statement is a full description of this invention, including the best method of performing it known to us:- L ~1 1 This invention relates to digital data insertion into binary streams, and in particular to an auxiliary data insertion method operating in digital frames of plesiochronous or synchronous radio networks.

It is common knowledge that, when digital data is transmitted via radio link from a transmitter to a receiver, the data to be sent by the radio transmitter user appears in the form of a digital stream. The data is admitted into a frame generator which is present at transmitter level where the digital stream is split into consecutive sub-streams, each of the latter making up a part of the data to be transmitted. Each sub-stream, making up a useful data (item I in figure 1 which illustrates a frame 10 as it appears in the transmission network), has a set length corresponding to a certain number of bytes.

In a plesiochronous radio network, the frame generator places at the start of each frame (10) a frame alignment word, commonly called header and Soa referenced MVT. In a synchronous radio network, the user directly supplies a 1 frame including the header as well as the useful data The function of the 1 header is to synchronise the receiver and the intermediate equipment located between the transmitter and the receiver, with the frames received. The aatf intermediate equipment may consist of repeaters for instance.

Furthermore, at transmitter, receiver and repeater level, there is a check or a. a, a a 20 service data insertion system. This kind of data is commonly called auxiliary data and referenced IA in figure 1. The data is inherent to each radio transmission network. This insertion system positions a certain number of bytes of auxiliary data (IA) after each useful data contained in a frame. The auxiliary data (IA) is made up of service data, parity check bits and error corrector code bits relating to the useful data in the frame In a given channel of the transmission network, type 10 frames follow one another without discontinuity and, all along the transmission sequence, some processing devices carry out insertion operations to insert auxiliary information into the flow of data transmitted. Data retrieval operations may also be carried out in parallel in order to benefit from this additional data forwarded through the channel.

Nevertheless, when the bit rate of the signal to be processed is high, insertion systems are preceded by demultiplexers which divide the incoming itfit, i. 3 digital stream, made up of an uninterrupted series of type-10 frames, into Nstreams of reduced bit rate 1/N. In this case, insertion operations are no longer carried out on the serial message but in parallel on the N streams obtained, hereinafter called parallel digital streams.

Figure 2 represents an auxiliary data insertion/retrieval system existing in each repeater and at transmitter and receiver level.

The incoming digital stream is applied at the input of a demultiplexer (21) via a serial link Demultiplexer (21) divides this incoming stream into N parallel digital streams and supplies them to a header position detection stage Indeed, it is necessary to find out the header position in order to know at which bit of the parallel digital stream the auxiliary data starts. The size of each data (figure 1 MVT, I and IA) is set and known to each insertion/retrieval o, system. Once the header and its position are obtained, the detection stage (22) indicates it, via a link to a device (24) which shifts the parallel digital stream bits, commonly called a barrel shifter. The device (24) shifts the bits of the parallel digital stream in relation with the header position data, such that the t parallel digital streams are at the device output in a set position, independent of the header position. An auxiliary data insertion/retrieval command (INEX) can then be issued; the data retrieved is available over channel (IE) and/or the data a 20 inserted is available over channel The parallel digital streams are then *00 4, ,0 supplied to a multiplexer (26) which supplies over channel (27) a serial stream to o..4 be transmitted to the downstream transmission equipment. Demultiplexer (26) performs the opposite function of demultiplexer (21).

Figures 3A to 3F will provide better understanding of the operation of this .25 auxiliary data insertion/retrieval system, these figures represent respectively a 12-bit frame alignment word (fig. 3A) as it occurs in the incoming digital stream, four possible configurations of parallel digital streams (TR1 to TR4 figs 3B to 3E) following demultiplexing and the four parallel digital streams at the output of the barrel shifter (24).

In these figures, the 12 bits making up the header are itemised bl to bl 2, the last 4 auxiliary data bits of the previous frame are itemised bin.

3 to bin* and the four first useful data bits to be transmitted are itemised bil to b 4 Figure 3B represents one of the possible configurations of parallel digital 1. I.

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4 streams at the output of demultiplexer Several configurations are possible since the demultiplexer is not synchronised at the start of a communication or may not have correctly received the previously transmitted frame (loss of synchronisation due to a change in the header). In this instance, four parallel digital streams (TR1 to TR4) are generated, thus making it possible to process the data at a rate four times smaller than that of the link (incoming digital stream rate). Each bit of the incoming digital stream is directed to one of the N channels forwarding the parallel digital streams from the demultiplexer to the header position detection stage (22).

Header detection position stage (22) contains some means of comparing each word, made up by the series of bits of nth rank in each stream, with a preset word corresponding to the demultiplexing of the reference header entered at the level of each detection stage. Such as word is hereinafter called a Sdemultiplexed word and bears the item number MD1 to MD4. In figure 3B for 15 instance, rank 1 demultiplexed word (MD1) is blb2b3b4, rank 2 demultiplexed word (MD2) is b5b6b7b8, rank 3 demultiplexed word (MD3) is b9blOb11b12, and rank 4 demultiplexed word (MD4) is bibi 2 bi 3 bi 4 In figure 3C, these demultiplexed words are respectively bian*blb2b3, b4b5b6b7, b8b9b10b11 and b12bilbi 2 bi3. The same reasoning applies to demultiplexed words in figures 3D 05 o 20 and 3E. Each possible configuration of a word (MD1 to MD4) is compared with the reference word corresponding to the possible header demultiplexing results.

This is equivalent to checking that sequence bl to b12 is indeed found in the demultiplexed digital stream bits. This identification is equivalent to placing four different masks onto the parallel digital streams and to indicating to the shifter 0 ,'25 (24) which configuration has been recognised. Other operations can be performed on the demultiplexed streams to recognise the header.

Once the sequence has been recognised, detection device (22) indicates, via link to the shifter (24) that the header has been recognised together with the configuration of its bits (configuration shown in one of the figures 3B to 3E). The shifter (24) then shifts the bits of the parallel digital streams such that they appear as in figure,3F configuration. In comparison with figures 3B to 3E configurations, either four, three, two or a single shift are performed in the shifter This provides for a given and fixed bit configuration, irrespective of the configuration of the header bits in the parallel digital streams.

Figure 4 represents a complete demultiplexed frame at the output of shifter Bits bl to b12 having been repositioned in a given configuration, the following bits bil to b 1 i, those making up the useful message I) are also correctly positioned, and the same applies to bits bjal to bian making up the auxiliary data (IA) relating to the useful data It is then easy to retrieve this auxiliary data and/or to insert others at th, level of device Each repeater used in the transmission channel needs to be synchronised on the header transmitted in order to be able to read or write as necessary the auxiliary data forwarded. Hence, if for instance ten repeaters are used between transmitter and receiver, ten successive synchronisation operations are required before the link can be correctly established. This delay varies as a function of the length of the frames transmitted and may lead to an overall synchronisation time unacceptable for the link.

This problem also occurs when the radio network used includes an tee.

emergency channel to which a failing channel is switched. For a channel teat switching operation to occur without error, one has to wait for the emergency channel to be synchronised after the transmission has been set up in parallel, hence this lengthens the duration required for switching and may result in a 1 20 further downgrading of the link.

o An object of the present invention is to provide a method for the insertion of auxiliary data into digital frames which is transparent to the link, i.e. which does not shift the bits of the parallel digital streams.

According to the invention, there is provided a method for insertion of ,'25 auxiliary data into plesiochronous or synchronous frames, each including a start of frame data, a useful data and an auxiliary data, this method being of the type consisting of: demultiplexing an incoming digital stream, made up of at least two consecutive frames, into at least two parallel digital streams; detecting the position of the start of frame data in the parallel digital streams; S inserting auxiliary data into the parallel digital streams; multiplexing the parallel digital streams to obtain a serial frame to be k Y n n n 1 i transmitted, this method being characterised in that auxiliary data insertion is performed as a function of the position of the start of frame data in the parallel digital streams.

Hence, it is no longer necessary to modify the position of the start of frame data bits nor that of the useful data bits to carry out the insertion operations in an identical manner irrespective of the demultiplexing result, and therefore the flow transmitted is no longer subject to phase shift. It follows that the processing devices located downstream are no longer put out of synchronisation.

This method applies preferably to the insertion of auxiliary data in frames of a radio transmission network.

In order that the invention may be readily carried into effect, an embodiment thereof will now be described in relation to the accompanying 1 drawings, on which: 15- Figure 1 represents a frame as occurring in a plesiochronous or hr,; S synchronous transmission network; Figure 2 is a synoptic diagram of a known type of auxiliary data insertion/retrieval system; Figures 3A to 3F respectively represent a 12-bit frame alignment word Qo Ci 20 (fig. 3A) as it occurs in the incoming digital stream, four possible configurations 'rI of the parallel digital streams (figs 3B to 3E) following demultiplexing, and the four parallel digital streams at the output of figure 2 barrel shifter (24) (fig. 3F).

Figure 4 represents a complete demultip!exed frame at the output of figure 2 shifter; 25 Figure 5 is a synoptic diagram of an auxiliary data insertion system, according to a preferred method of implementation of the method of the invention; Figure 6 is a simplified synoptic diagram of the shifter shifting the bits of the data to be inserted; Figure 7A represents the demultiplexed auxiliary information to be inserted, and figures 7B to 7E represent the four possible configurations of the auxiliary data bits at the output of figure 5 shifter.

Figures 1 to 4 were described above in relation with the state of the t B 7 technique.

Figure 5 is a synoptic diagram of an auxiliary data insertion system according to a preferred method of implementation of the method of the invention.

In accordance with the invention, auxiliary data insertion operations are carried out as a function of the position of the header in the parallel digital streams such that the bits of these streams do not require shifting. Therefore, these operations are no longer performed on a given stream configuration independent of the header position.

In figure 5 system, the header position data, supplied by detection stage is applied to a device (50) shifting the bits of data (11) to be inserted in the incoming serial stream. This data (11) is positioned so as to have a configuration 4, complementary to that of the header in the parallel digital streams, to prevent having to shift the bits of these streams. An insertion command (INX) indicates the moment when the auxiliary data bits must be transmitted to an insertion device (51) which replaces the auxiliary data bits contained in the parallel digital i streams with the bits of the auxiliary data (11) to be inserted, corresponding to (IA) in the output frame. Retrieval of auxiliary data bits contained in the parallel digital streams can also be performed, for instance in the same way as used in S 20 the state of the technique.

Figure 6 is a simplified synoptic diagram of the device (50) shifting the bits of the auxiliary data (11) to be inserted.

The first four bits of this auxiliary data are itemised bi to b 4 and each appears on the one hand at an input of a bit time shifter (60 to 63) and on the ',25 other hand at three distinct inputs of demultiplexers (64 to 67). The output of each shifter (60 to 63) is connected to the fourth input of a demultiplexer (64 to 67). The header position indication is coded on two bits and is applied to each demultiplexer via link (23).

The function of such a device is to supply the auxiliary information bits according to four possible configurations. These configurations are represented in figures 7B to 7E, figure 7A representing the demultiplexed auxiliary data to be inserted into the parallel digital streams. There are four possible auxiliary data bit configurations as a function of the header bit configurations, i.e. as a function of

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the header position.

If the header bits are configured as per figure 3B, the auxiliary data bits are configured as per figure 7B. The same applies to configurations 3C, 3D and 3E which are respectively complementary to fig. 7C, 7D and 7E configurations.

The header bits are not shifted and no time shift is applied to the bits in the frame which will subsequently be transmitted.

Figure 8 is an example of confiouration of the parallel digital streams at the output of figure 5 insertion device. In this example, the header bits appear in the parallel digital streams as per figure 3D while the auxiliary data bits are shifted such that they appear as per figure 7D configuration.

It can therefore be seen that auxiliary data insertion occurs in a manner transparent to the network, without generating a bit shift. It follows that the time required for synchronisation of each insertion system is not cumulated. The Ssame applies when a failing channel is switched to an emergency channel.

Furthermore, it is possible to retrieve auxiliary data in the same way as in the proposed system, although retrieval may occur in parallel with a transmission.

The present invention applies in particular to the insertion of auxiliary data in synchronous or plesiochronous radio networks and the number of parallel O 2 I oI 4 o 20 digital streams is at least equal to 2.

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Claims

1. A method for insertion of new auxiliary data into plesiochronous or synchronous frames each including start of frame data, useful data and auxiliary data, said method comprising the steps of: demultiplexing an incoming digital stream made up of at least two consecutive frames, into at least two parallel digital streams; detecting the position of the start of frame data in the parallel digital streams; generating two or more mutually time shifted alternate sets auxiliary data from the new auxiliary data; selecting for each parallel digital stream a corresponding alternate set of auxiliary data which is correctly aligned with the auxiliary data period in relation to the start of frame data; inserting the selected alternate set of auxiliary data in the corresponding parallel digital stream; and multiplexing the parallel digital streams to obtain a serial frame to be transmitted.

2. A method as claimed in claim 1, wherein said method applies to insertion of auxiliary data into the frames of a radio transmission network. S,

3. A method of inserting auxiliary data substantially as herein described with S 20 reference to Figures 5-8 of the accompanying drawings.

4. An insertion arrangement for insertion of new auxiliary data into plesiochronous or synchronous frames each including start of frame data, useful data and auxiliary data, the arrangement including: demultiplexing means to demultiplex an incoming digital stream made up of at least two consecutive frames into at least two parallel streams; start of frame detector means to detect the start of frame data in the parallel digital streams; time shifting means to generate two or more mutually time shifted alternate sets of auxiliary data from the new auxiliary data and to insert each auxiliary data into a corresponding one of the parallel digital streams with which the corresponding alternate set of auxiliary data is aligned in relation to the start of frame data; and L -i tti r I I -e multiplexing means to multiplex the parallel digital streams with the new auxiliary data to obtain a serial frame to be transmitted. An arrangement for inserting auxiliary data substantially as herein described with reference to Figures 5 to 8 of the accompanying drawings DATED THIS TWENTIETH DAY OF FEBRUARY 1996 ALCATEL N.V. I r i rr r I r rr I a" 0>1 I I ABSTRACT A method for insertion of auxiliary data into plesiochronous or synchronous frames each including a start of frame data, a useful data and an auxiliary data, this method being of the type consisting of: demultiplexing an incoming digital stream, made up of at least two consecutive frames, into at least two parallel digital streams; detecting the position of the start of frame data in the parallel digital Sstreams; inserting auxiliary data into the parallel digital streams; i multiplexing the parallel digital streams to obtain a serial frame to be transmitted, I According to the invention auxiliary data insertion is performed as a function of the position of the start of frame data in the parallel digital streams. 'I