EP1226672A1

EP1226672A1 - Method of representing a number of data streams in a common carrying data stream organised in frames and using in a frame descripting index for enabling the contents of a frame to be interpreted

Info

Publication number: EP1226672A1
Application number: EP00973319A
Authority: EP
Inventors: Allan Hansson; Ingmar TÖNNBY; Herbert Sander
Original assignee: Telefonaktiebolaget LM Ericsson AB
Current assignee: Telefonaktiebolaget LM Ericsson AB
Priority date: 1999-10-21
Filing date: 2000-10-19
Publication date: 2002-07-31
Also published as: SE9903808D0; SE9903808L; WO2001030001A1; SE517859C2; AU1184201A

Abstract

The present invention relates to a method of representing a number of carried streams (1a, 1b, and 1c) in a common carrying data stream (1). A so-called carried data stream is a sequence of mutually related stream elements. The carrying data stream (1) is organised in frames (11, 12) and each frame includes stream elements belonging to one or more different carried data streams. Respective frames (11, 12) include a frame descriptive index (111, 112). Mutually sequential frames can be used to transmit mutually different carried data streams and can include different large amounts of data information. Carried stream elements contained in a frame may be allocated spaces of mutually different size and thus include different amounts of data information. The frame descriptive index (111, 112) enables the contents of respective frames to be interpreted.

Description

METHOD OF REPRESENTING A NUMBER OF DATA STREAMS IN A COMMON CARRYING DATA STREAM ORGANISED IN FRAMES AND USING IN A FRAME DESCRIPTING INDEX FOR ENABLING THE CONTENTS OF A FRAME TO BE INTERPRETED Technical field

The present invention relates to a method of representing a number of carried data streams in a common carrying data stream.

A so-called carried data stream is a sequence of mutually related stream elements. The carrying data stream is organised in frames and each frame includes stream elements belonging to one or more different carried data streams.

Description of the background art

It has long been known that multiplexed transmission of digital information can be effected in accordance with different principles. The two general principles most used for the transmission of information according to the above are time division multiplexing (TDM) and data packet handling. In short, time division multiplexing (TDM) involves dividing time into different primary intervals, which can be referred to as time frames. Each time frame includes a number of time slots, which are repetitive individual time intervals of fixed lengths. The length of a primary interval may be 125 μs, for instance.

The number of channels available on a transmission medium that uses time division multiplexing may correspond to the number of time slots present in a time frame. A channel established between a sender and a receiver may also be allocated several time slots within the transmission medium used. The sender knows that data shall be sent within an intended time slot and the receiver knows that data shall be received within the same time slot.

Transmission is synchronous and the bandwidth is dependent on the amount of information that can be transmitted within respective time slots, the number of time slots available to a channel, and the transmission frequency used. Respective multiplexing and demultiplexing principles within TDM can be used hierarchically, meaning that a multiplexed channel can be multiplexed in turn in another channel. When several channels are multiplexed together into one channel, a higher transmission frequency or clock frequency is required. One specific form of TDM is a so-called dynamic transfer mode (DTM) described by Per Lindgren in a paper entitled "A Multichannel Network Architecture Based on Fast Circuit Switching", Department of Teleinformatics, KTH, Stockholm, 1996. Further information on this subject is found in Patent Publications SE-460750, SE-506548, SE-508794 and SE-508889.

Data packet handling involves dividing information to be sent from a sender to a receiver within the data packet. Data packets include a header and a load. The header contains, among other things, address information and information that discloses the size of the packet. The load contains the information to be transmitted. Accordingly, the actual information to be transmitted is designated hereinafter data information, whereas requisite information for addressing, etc., will be designated in some other way.

The time interval between two packets and the size of different packets can vary in data packet handling processes The protocol used on the Internet, Internet Protocol (IP) is one example of protocol that handles data packets. In this case, a packet is sent from a sender on the Internet with a receiver address in the header and an information carrying part that can vary in size from packet to packet. Two mutually sequential packets are handled in the network totally independently of each other and their relative transfer times may vary quite randomly.

However, packets of fixed sizes are normally used, such as in Asynchronous Transfer Mode (ATM). A so-called virtual channel is established through a telecommunications system, where successive packets have a virtual address in the header, thereby enabling all packets to be sent by the same route in accordance with the es- tablished channel and enables a more predictable transmission time to be provided.

A packet of standard size can also be subdivided into a number of smaller parts and therewith enable the space available in the packet to be used more flexibly.

Nodes in a network where packet handling is used multiplex outgoing data packets by placing them in a queue, or line, specified by the destination address of respective packets. A data packet is plucked from the queue and sent to the next node in accordance with available transmission capacity.

Different levels of global or local addressing can be used, and different priority systems can be used in which high priority packets can be allowed to go before packets of lower priority. One characteristic of data packet handling is its unpredictable delay, which can be estimated statistically.

It should also be mentioned that the flow of information varies in time in the case of real time transmissions, such as in the case of speech communication, video conferences, the transmission of information where a receiver wishes to browse through material, for instance. This irregular transmission requirement creates problems in combination with heavy loads.

In the case of TDM, it is necessary to adapt the bandwidth allocated to a channel for real time communication to the greatest transmission requirement, meaning that the allocated bandwidth will not be utilised fully.

A number of different publications exist that describe how different transmission protocols can be used in the transmission of data information.

Patent Publications EP-A1-0 462 349, US-4 661 952, EP-A1-0 510 290, EP-A2-0 428 407, US-A-5 594 734, WO 97/10653, WO 97/36402, WO 97/24846 and WO 97/03526 can be considered to describe the present standpoint of techniques.

Homochronous transmission is a term used in the present description, by which is meant a time preserving transmission, in other words the time relationship between two transmitted signals is retained upon reception of these signals. This means that if given information lies in the time distance between two signals, then this information will be retained upon reception of the signals.

This means that isochronous transmission, where the time interval between two transmitted signals is equal to a unit interval or to a multiple of a unit interval, can be used as means for achieving homochronous transmission.

Summary of the invention

Technical problems

It will be understood that each of the following problems is more pronounced within one of the principles time division multiplexing or data packet handling. For in- stance, one principle is more applicable when certain requirements are placed with respect to the transmission of information, while being less suitable when other requirements are made. The aim of the present invention is to provide a representation that enables a third principle to offer a solution to all of the following problems. When considering the earlier standpoint of techniques as described above, it will be seen that a technical problem resides in the ability to combine a high use ratio with respect to an available bandwidth with guaranteed homochronous transmission when the bandwidth requirement varies in time. In the case of time division multiplexing, a technical problem exists in being able to change dynamically the bandwidth available to an established channel during ongoing communication.

Furthermore, in the case of time division multiplexing a technical problem resides in the ability to provide a wide bandwidth spectrum, such as from 8 kbits to several Gbits, where channels that have totally different bandwidth requirements can be carried by a common transmission medium, and where channels can be allocated dynamically different bandwidths across the whole of this bandwidth spectrum.

In the case of data packet handling, a technical problem resides in the ability to maintain a high use ratio with respect to an available bandwidth and with respect to the transmission of data information, and a low use ratio in respect of the transmission of information relating to addressing and to the format of transmitted information, particularly when using short data packets, such as when transmitting isochronous information with a short delay time requirement.

In the case of time division multiplexing, a problem exists in transmitting a change in the structure of a channel allocation, both with respect to an allocated bandwidth and the insertion of a new channel or the removal of an existing channel, homochronously with the actual change.

In the case of data packet handling, a technical problem exists in guaranteeing homochronous transmission, particularly at high loads. A technical problem also exists in applying data packet handling recursively.

It is impossible to apply time division multiplexing recursively.

It will also be seen that a technical problem resides in providing a method of representing a number of data streams so that when transmitting said streams, there is found a concurrent and common solution to all of the aforesaid problems, i.e. a solution as to how one and the same method can achieve dynamic bandwidth allocation, how this can be achieved over a large bandwidth spectrum, how a high use ratio can be obtained for the transmission of data information, how an homochronous transmission can be achieved, and how recursive multiplexing can be achieved, all with one and the same method. Solution

With the intention of solving one or more of the aforesaid technical problems, the present invention takes as its starting point a representation which is here desig- nated frame multiplexing, implying a number of carried data streams carried in a common carrying data stream, where a so-called carried data stream is a sequence of mutually associated stream elements, where the carrying data stream is organised in frames, and where each frame includes stream elements belonging to one or more different carried data streams. With a starting point from such a method and with the intention of enabling the bandwidth allocated to respective data streams to be adapted dynamically, it is proposed in accordance with the present invention that respective frames include a frame descriptive index, that successive frames can be used to represent mutually different data streams, that mutually successive frames may include different quanti- ties of data information, that carried stream elements contained in a frame can be allocated spaces of mutually different size and thus include different large quantities of data information, and that the frame descriptive index enables the content of a frame to be interpreted.

So that the frame descriptive index will require as little space as possible and therewith enable an allocated bandwidth for data information transmission to be used to the greatest possible extent, it is proposed in accordance with the invention that the frame descriptive index comprises a reference to a position within a frame descriptive table, said position constituting a local description of the frame structure used by a sender and a receiver respectively. In order to enable the content of these dynamically changeable frames to be interpreted, it is proposed in accordance with the invention that the local description of a frame structure discloses the position of respective carried stream elements within a current frame, the size of respective stream elements, and the carried data stream to which respective stream elements belong. According to the invention, the frame descriptive table includes a local description of each available frame structure that can be used for the carrying data stream between the sender and the receiver at a given point in time.

With the intention of providing the sender with the possibility of using dynamically available transmission capacity, it is proposed in accordance with the pres- ent invention that the choice of frame structure is effected dynamically in accordance with the information transmission requirement for respective carried data streams at that moment in time.

This dynamic choice possibility is significant, since, according to the present invention, one and the same data stream can be allocated stream elements in two or more different frame structures.

According to the invention, it may be suitable at times to use an isochronous carrier, such as in the homochronous transmission of a data stream.

This means that the time ratio between two stream elements belonging to a homochronously carried data stream will be retained, since the time ratio between transmitted frames is constant.

With such application, data information belonging to an isochronously carried data stream shall be allocated stream elements within each mutually sequential frame or within frames that include a constant number of intermediate frames. The remaining space within a frame can be divided dynamically between different data streams as earlier described.

When the space for included stream elements differs from the frame capacity, it is proposed in accordance with the present invention that respective frames will include unused regions. With the intention of enabling an inventive method to be applied recursively, it is proposed in accordance with the present invention that a carrying data stream may constitute a first carrying data stream, being one of one or more other carried data streams in a second carrying data stream. This second carrying data stream may also constitute a carried data stream of one or more other carried data streams in a third carrying data stream, and so on.

Advantages

The advantages primarily characteristic of a method according to the present invention reside in the ability to represent a number of carried data streams in a common carrying data stream where the bandwidth for different carried data streams can be adapted dynamically to prevailing transmission requirements, and where only a very small part of the transmission capacity is required to disclose how the received carrying data stream shall be interpreted. This provides a representation that affords dynamic bandwidth allocation over a large bandwidth spectrum with a high use ratio in respect of information transmission, with the possibility of homochronous transmission, and with the possibility of recursive multiplexing, by means of one and the same method. The primary characteristic features of an inventive method are set forth in the characterising clause of the accompanying Claim 1.

Brief description of the drawings

A method that includes features significant of the present invention will now be described in more detail by way of example with reference to the accompanying drawings, in which

Figure 1 is a schematic and highly simplified illustration of the transmission of a number of data streams from a sender to a receiver; Figure 2 illustrates schematically a number of mutually sequential frames; Figure 3 illustrates schematically two frames that have mutually different frame structures; Figure 4 is a schematic illustration of a frame descriptive table; Figure 5 is a schematic illustration of a series of frames of mutually the same size; Figure 6 is a schematic illustration of recursive application of the present invention; Figure 7 is a schematic illustration of further recursive application of the present invention; and Figure 8 is a schematic and highly simplified illustration of one embodiment in which the transmission and the reception of information comprises writing information into and reading information from a memory.

Description of embodiments at present preferred Shown in Figure 1 is a method of representing the transmission of data information from a sender A to a receiver B. The Figure shows that the information is comprised of a plurality of so-called carried data streams, of which some referenced a, b, c, d are shown in the Figure and which are transmitted by means of a common carrying data stream 1 and recreated on the receiving side B as data streams a', b', c\ d\

The present invention requires the carrying data stream 1 to be organised in frames, which are shown schematically in Figure 2 as frames that have the mutually different frame structures 11 , 12, 11 , 15, ..., 1 n. Although these frames are sent sequentially, they are not necessarily sent immediately after one another. The frame reference denotes the structure of the frame. Thus, successive frames may be allocated different structures and the same structure can reoccur for different frames. Figure 3 shows two frames of mutually different structures 11 , 12. A carried data stream a is a sequence of mutually associated stream elements 1a, 2a. A sequence of carried stream elements 1a, 1c, 1d, ..., 1 n from different carried data streams a, c, d, ..., n is organised in the carrying data stream in frames 11 and in positions 11a, 11 b, 11c, ..., 11 n within respective frames, where each frame 11 thus includes stream elements belonging to one or more different carried data streams a, c, d, n.

The following reference signs will be used to describe the present invention, where t? is a digit and x is a letter:

1 : A first carried data stream, x: A carried data stream. 1 n: An nth frame structure that can be used within the first carrying data stream, nx: The nth stream element belonging to the xth carried data stream, for instance 1a is the first stream element belonging to the carried data stream a. 1 nx: The xth position of a stream element within the nth frame structure in the carrying data stream 1. Thus, respective carried stream elements include data information that belongs to a specific carried data stream. For instance, the Figure shows that the carried stream element 1c includes data information belonging to the carried data stream c and that this stream element 1c is allocated a position 11b in the frame structure 11 belonging to the carrying data stream 1.

In the frame structure 12, the carried stream element 1d in position 12a includes data information belonging to the carried data stream d, the stream element 1b in position 12b includes data information belonging to the carried data stream b, the stream element 2a in position 12c includes data information belonging to the carried data stream a, and so on in accordance with the Figure illustration.

Thus, different frame structures 11 , 12 can be used to represent mutually different carried data streams and can also include different amounts of data infor- mation.

Different stream elements included in a frame structure may also be allocated spaces of mutually different size, therewith enabling said stream elements to include mutually different amounts of data information.

Figure 3 shows that the two frame structures 11 , 12 have mutually different sizes and that they carry data streams that are partially different to one another. The

Figure shows that the size of the stream element 1a, 2a for a carried data stream a can vary between different frame structures 11 , 12. This is illustrated in the Figure by virtue of the stream element 2a in position 12c for the carried data stream a being smaller in the frame structure 12 than the corresponding stream element 1 a in posi- tion 11 a for the same carried data stream a in the frame structure 11.

The frame structures 11 , 12 also include a frame descriptive index 111 , 121 that enables interpretation of the contents of a received frame.

As illustrated in Figure 4, the frame descriptive index 111 is comprised of a reference or a pointer 111a to a position FDT1 within a frame descriptive table FDT, which is comprised of a local A, B description of a frame structure that can be used by sender A and receiver B respectively. This local description is comprised of a number of positions FDT1 , FDT2, ..., FDTn in the frame descriptive table, shown in the Figure as columns in the table FDT. The frame descriptive table FDT is stored in a respective memory Am, Bm of the sender A and the receiver B. (Figure 1). The pointer 111a need only comprise an address, or an address reference, to the memory Bm of the receiver B, meaning that the pointer need only take-up a very small space in the frame structure 11.

Respective positions FDT1 in the frame descriptive table FDT include a number of data records FDT1a, FDT1 b, FDT1c, FDT1 n, where one data record is found for each position 11 a, 11 b, 11 c, 11 n in the frame structure 11. These data records FDT1 a, FDT1b, FDT1c, FDT1 n disclose the position of respective stream elements 1a, 1c, 1d, ..., 1 n in the frame, the size of respective stream elements, and the data stream a, c, d, n to which respective stream elements 1 a, 1c, 1d, 1 n belong. A position FDT1 , FDT2, ..., FDTn is found in the frame descriptive table FDT for each frame structure 11 , 12 that can be used in the communication between the sender A and the receiver B at that moment in time.

A further position in the frame descriptive table, FDT7, is shown in Figure 4. This position is exemplified with position number 7 and has been pointed out 171a by the frame descriptive index 171 for the frame structure 17. This position includes data records FDT7a, FDT7b, FDT7c, FDT7d that point to position 17a, 17b, 17c, 17d respectively in the frame structure 17.

Because the data record FDT7b points to the position 17c and the data record FDT7c points to the position 17b, it will be evident that the order of the data rec- ords in the frame descriptive table need not necessarily correspond to the order of the positions pointed out in the frame structure concerned.

The choice of frame structure is made dynamically by the sender A in accordance with the information transmission requirement for respective data streams a, b, c, d at that moment in time, by selecting one of the local available Am frame descrip- tive tables, structuring the frame in accordance with a chosen frame descriptive table and including the corresponding frame descriptive index in the structured frame.

One and the same carried data stream a can be allocated stream elements in two or more different frame structures. In the Figure 3 illustration, the carried data streams a and d are allocated stream elements 1a, 2a and 1d, 2d respectively in both frame structures 11 and 12, whereas the carried data streams b and c are allocated only one stream element 1b and 1c respectively in one of the two frame structures 11 , 12.

According to one preferred embodiment of the invention illustrated in Figure 5, the frame sequence may be isochronous. In other words, mutually sequential frames 11 ', 12', 13' may be transmitted sequentially with a constant time interval t between the frame starts, where the time interval t between transmitted frames can be considered to constitute a primary interval.

The fact that the time ratio between transmitted frames is constant means that the time ratio between two stream elements belonging to a carried data stream will be retained. In turn, this means that a time interval ti between two successive carried stream elements 1 'a, 2'a carried in the positions 11 'a and 13'a belonging to one and the same carried data stream will be retained, therewith enabling homochronous transfer of a carried data stream. It will be understood that when a frame is received on the receiving side B, all stream elements carried in one and the same frame will be received simultaneously and without a relative time difference, meaning that all transmittable time intervals ti for a homochronous data stream are divided discretely in multiples of the primary in- terval f used.

Such an embodiment also enables the transmission of data information belonging to an isochronously carried data stream c, said information constituting a stream element 1 'c, 2'c, 3'c within each transmitted frame, here illustrated by the frame structures 1 1 ', 12', 13', or in frames that include a constant number of interme- diate frames.

The frame structures 1 1 ', 12', 13' may, in other respects, differ between respective frames so that respective frames can transmit stream elements belonging to mutually the same or mutually different carried data streams.

However, this may mean that an empty space will occur between successive frames and, in accordance with the present invention, respective frames can thus include unused regions when the space for included stream elements 1 'a, 1 'b, 1 'c differs from the capacity of a frame structure 1 1 '. The Figure shows an unused region at position 1 1 'd.

Although this unused region is shown to be contained in one part of the frame, there is nothing to prevent said unused region from being divided between two or more different stream elements in the frame.

In respect of a representation of different carried data streams in a common carrying data stream there exist applications where it is desirable to be able handle a carrying data stream as a carried data stream together with one or more other carried data streams such as to apply the method recursively.

Figure 6 is intended to illustrate schematically how this can be achieved by allowing the aforedescribed carrying data stream 1 , which carries the carried data streams a and b in the Figure, to constitute a first carrying data stream which, in turn, constitutes a carried data stream of one or more other carried data streams 2, 3 in a second carrying data stream 4.

There is nothing to prevent one or more of the other carried data streams 2, 3 from constituting a carrying data stream for further carried data streams.

It will be obvious to the person skilled in this art that this can be applied recursively in further levels, so that, for instance, the second carrying data stream 4 can constitute a carried data stream of one or more other carried data streams 5, 6 in a third carrying data stream 7, and so on in accordance with Figure 7.

It is not always possible for the receiver of information to handle the information directly, thereby requiring the information to be buffered upon receipt. Buffering can be achieved by storing the information in some kind of storage medium, such as a buffer memory, from which it can be read at a later time.

This means that information read from the storage medium shall be interpreted according to an available frame descriptive table.

Figure 8 is intended to illustrate that the storage of information can also be effected in accordance with the earlier described representation, where sending of information can be seen as writing information 81 into a storage medium 8 and where the reception of information can be seen as reading information 82 from the storage medium 8.

In this case, the transmission can be considered to take place in time instead of in space, where the sender sends information 81 at a first time point and the receiver receives information 82 at a second time point, which can take place in the same place in space, although not necessarily so. There is nothing to prevent the storage medium 8 from being moved in the space between writing 81 and reading 82 of information. An isochronism can also be obtained with the possibility of an homochronous transmission when the sender 81 , i.e. writing of information into a storage medium 8, takes place isochronously, and when reception 82, i.e. reading of information from the same storage medium, takes place isochronously with the same primary interval as that applied when writing in said information 81. It will be understood that the invention is not restricted to the aforedescribed exemplifying embodiment and that modifications can be made within the scope of the inventive concept illustrated in the accompanying Claims.

Claims

1. A method of representing a number of carried data streams in a common carrying data stream where a so-called carried data stream is a sequence of mutually related stream elements, where said carrying data stream is organised in frames, and where each frame includes stream elements that belong to one or more different carried data streams, characterised in that respective frames include a frame descriptive index; in that mutually sequential frames can be used to represent mutually different carried data streams; in that mutually sequential frames can include different large amounts of data information; in that carried stream elements contained in a frame can be allocated spaces of different sizes and thus include different large amounts of data information; and in that the contents of said frame can be interpreted by virtue of said frame descriptive index.

2. A method according to Claim 1 , characterised in that the frame descriptive index is comprised of a reference to a position in a frame descriptive table; and in that respective positions in said frame descriptive table constitute a local description of a frame structure used by said sender and by said receiver.

3. A method according to Claim 2, characterised in that said local description of a frame structure discloses the position of respective carried stream elements in the frame concerned, the size of respective stream elements, and the carried data stream to which respective stream elements belong.

4. A method according to Claim 3, characterised in that said frame descriptive table includes a local description of each available frame structure that can be used for said carrying data stream between said sender and said receiver at a given point in time.

5. A method according to any one of the preceding Claims, characterised in that frame structure selection is effected dynamically in accordance with the information transmission requirement for respective carried data streams at that moment in time.

6. A method according to any one of the preceding Claims, characterised in that one and the same carried data stream can be allocated stream elements in two or more different frame structures.

7. A method according to any one of the preceding Claims, characterised in that the sequence of frames is isochronous.

8. A method according to Claim 7, characterised in that data information belonging to an isochronously carried data stream is allocated stream elements in each mutually sequential frame or in frames that have a constant number of intermediate frames.

9. A method according to Claim 7 or 8, characterised in that respective frames include unused regions when the space for included stream elements differs from the frame capacity.

10. A method according to any one of the preceding Claims, characterised in that said carrying data stream constitutes a first carrying data stream; in that said first carrying data stream constitutes a carried data stream of one or more other carried data streams in a second carrying data stream; in that said second carrying data stream may constitute a carried data stream of one or more other carried data streams in a third carrying data stream, and so on.

11. A method according to any one of the preceding Claims, characterised in that the transmission of information constitutes writing of said information into a storage medium; and in that the reception of information constitutes reading of information from said storage medium.

12. A method according to Claim 11 , characterised in that a sender of information sends information at a first time point and a receiver of said information receives the information at a second time point, which possibly, but not necessarily, may take place in the same place in the space as the sending of said information.

13. A method according to Claim 11 or 12, characterised in that the information is sent isochronously; and in that the reception of said information takes place isochronously with the same primary interval as that applied when sending said information.