EP0812520A1

EP0812520A1 - Method and device for of voice and data multiplexing

Info

Publication number: EP0812520A1
Application number: EP96944620A
Authority: EP
Inventors: Per Blomquist; Johny Nyman
Original assignee: Telefonaktiebolaget LM Ericsson AB
Current assignee: Telefonaktiebolaget LM Ericsson AB
Priority date: 1995-12-29
Filing date: 1996-12-20
Publication date: 1997-12-17
Also published as: AU1304297A; NO973890L; WO1997024903A1; CN1181868A; NO973890D0; AU711876B2; DE19549126C1

Abstract

A method and device for multiplexing voice and data information onto at least one transmission line of a first type in a communication system, said method comprising the steps of: dividing the transmission line into a plurality of channels, compressing and/or dividing the voice information into one or more streams, each stream transmitting at a rate corresponding to the transmission capacity of one of the divided channels of the transmission line, dividing the data information into one or more streams, each stream transmitting at a rate corresponding to the transmission capacity of one of the divided channels of the transmission line, and dynamically allocating and deallocating the streams of voice and data information to the channels of said transmission line depending on demand.

Description

Method and device for of voice and data multiplexing

The present invention generally relates to the field of information multiplexing in telecommunications. It especially relates to a method of voice and data multiplexing and a voice and data multiplexer in a switch means for multiplexing voice and data information onto transmission lines.

The necessity for transmitting voice signals (e.g. a telephone conversation) and data signals (e.g. relaying computer data from one computer to another) through common telecommunications equipment is becoming ever more important due to the increase in information processing devices having "network capabilities". The common approach is to enable data communication (i.e. the transmission of data as opposed to voice information) through existing classical communication links, i.e. voice (telephone) connections and to use one communication means for both purposes.

This however poses the problem of providing switches that can efficiently handle the different types of information being transmitted. Voice information and data information are different in nature and have different transmission properties. The latter is due to the fact that voice information may generally be compressed and divided into sections of varying importance, i.e. important sections that necessarily need to be received in order to understand the message or recognize the individuality of a voice, and less important sections that influence the sound quality but which may be omitted without making the message impossible to understand. Data information on the other hand is usually such that all parts need to be transmitted, where any loss will result in problems.

The basic problem in this connection is how to transmit the different information on a given set of lines. One possibility is to transmit data information and voice information on separate lines. The other possibility is to let both types of information share one line.

One important aspect in this respect is that there are also different types of lines for transmitting information^" in public world area network (WAN) systems. A first type of line (fixed- cost-type, e.g. leased lines) is charged a fixed rate to thereby be constantly available, but this type is often expensive and especially suffers from the disadvantage of generating costs even when not in use. A second type (cost-on- use type, e.g. ISDN lines) only generates costs depending use, but has the disadvantage that when used, it will eventually exceed the cost of a leased line.

In a switch using different lines for voice and data information, the line of the first type transmits either voice or data information. If voice and data information are transmitted on one line, then the line is divided into channels, and specific channels transmit data information while the remaining channels transmit voice information. Both systems may come into situations where the line of the first type (e.g. a leased line) is not economically used because it still has a free transmission capacity while the line of the second type is already being used. Such a situation can e.g. arise through differing demand for voice and data transmission. If a line having a transmission capacity of 64 kb/s is reserved for voice transmission, but only 32 kb/s are required to meet demand, then half of the capacity can possibly be wasted. The object of the present invention is to provide a method and device for multiplexing voice and data information onto transmission lines of a first type, where the method and device ensure the optimum use of these lines.

This object is solved by a method for multiplexing voice and data information onto at least one transmission line of a first type in a communication system, said method comprising the steps of:

- dividing the transmission line, which has a specifi^'c transmission capacity, into a plurality of channels, each having a specific transmission capacity;

- compressing and/or dividing the voice information into one or more streams, each stream transmitting at a rate corresponding to the transmission capacity of one of the divided channels of the transmission line;

- dividing the data information into one or more streams, each stream transmitting at a rate corresponding to the transmission capacity of one of the divided channels of the transmission line; and

- dynamically allocating and deallocating the streams of voice and data information to the channels of said transmission line depending on demand.

The object is furthermore solved by a switch device for multiplexing voice and data information onto at least one transmission line of a first type, comprising:

first line dividing means for dividing the transmission line, which has a specific transmission capacity, into a plurality of channels, each having a specific transmission capacity; - voice compressing/dividing means for compressing and/or dividing the voice information into one or more streams, each stream transmitting at a rate corresponding to the transmission capacity of one of the divided channels of the transmission line;

- data dividing means for dividing the data information into one or more streams, each stream transmitting at a rate corresponding to the transmission capacity of one of the divided channels of the transmission line; and

- stream allocating means for dynamically allocating and deallocating the streams of voice and data information to the channels of said transmission line depending on demand.

Owing to the dividing of the transmission capacity of the line of the first type into a plurality of channels of smaller transmission capacity and then dynamically allocating voice and data information that has been divided into streams adapted to the channel transmission capacity, it is possible to most efficiently use the line of the first type because the line is thereby flexible in its transmission capacity. Using the inventive method and device, it is possible to first use the channels of the line of the first type before having to resort to other lines, i.e. all channels of the line of the first type can be filled before having to use any other line.

An important aspect of the invention consists in dividing the line of the first type into a plurality of channels, dividing the information into streams, and mutually adapting the channel transmission capacity of the channels on the line of the first type and the transmission rates of the information streams. This makes it possible to avoid any waste of transmission capacity of the line of the first type. According to a prelerred embodiment, the line of the first type having a specific transmission capacity (N kb/s) is divided into a plurality (n) of channels of equal transmission capacity (N/n kb/s) and the streams all have equal rates corresponding to the capacity of the individual channels. Such a division of capacity is the simplest possibility of mutually adapting the transmission capacity of individual channels and individual information streams. Thereby, even if only a certain capacity (e.g. one channel of N/n kb/s) is left on the line of the first type, and there is at the same time a demand for more capacity (e.g. 2N/n kb/s), by dividing the demanded capacity into streams (e.g. 2) of capacity corresponding to the channels of the line of the first type, one stream can be allocated to the remaining channel on the line of the first type, whereas the other stream must be placed on another line (e.g. the line of the second type) . In this way, the line of the first type is used to full capacity. Furthermore, by using dynamic allocation, it is possible to allocate the second stream to a channel on the line of the first type the moment that a channel becomes available, i.e. a channel that was previously occupied becomes available. In this way, the use of the line of the second type is reduced to a minimum and the line of the first type is always used when possible.

Fig. 1 shows one embodiment of the switch device according to the present invention.

Fig. 2 shows the internal structure of the stream allocating means.

Fig. 3 shows a second embodiment of the switch device according to the present invention. Fig. 4 shows a schematic example of a divided transmission line.

Fig. 5 shows a flow chart of the method of multiplexing according to the present invention.

Fig. 5 shows a flow chart for explaining the method of multiplexing according to the present invention. In step Sl the transmission line of the first type is divided into a plurality of channels each having a specified transmission capacity. Then, in step S2, the demand for the transmission of data and voice information is determined. In steps S3 the voice information is divided and/or compressed into streams, whereby the transmission rates of the streams are adapted to the transmission capacity of the channels into which the transmission line was divided. In step S4 the data information is similarly divided into streams with transmission rates corresponding to the transmission capacities of the divided channels. Finally, in step S5, the individual streams are dynamically allocated to the channels.

The reassembly of information (voice and data) at the receiving end is achieved in an analogue manner, i.e. the streams on the individual channels are reassembled (and possibly decompressed) into data or voice information sequences corresponding to those fed to the switching means on the sending side. These are then output by a switching means on the receiving side, as shown schematically in Fig. 3.

According to the invention, the at least one line of the first type is divided into a plurality of channels, where each channel has a specific transmission capacity. As mentioned above, an important point of the invention consists in mutually adapting the channel transmission capacity and the information stream transmission rate. In general, the channels therefore need not have an equal transmission capacity. It is only important that the stream transmission rates and channel transmission capacities are adapted to one another.

This can generally be achieved by keeping track of how the transmission line is divided and at the same time keeping track of how the incoming information is divided into streams. The adaptation then consists in adjusting the transmission rate of a stream to the transmission capacity of an idle channel. An example of this is to divide a transmission line having a transmission capacity of N kb/s into a plurality of channels (e.g. k channels, k being an integer) having transmission capacities of N'nl/p kb/s, N*n2/p kb/s,..., N*nk/p kb/s, respectively, where nl,...,nk and p are integers and nl+n2+...+nk=p. The incoming information (data and voice) is then divided into streams having transmission rates of N*nl/p kb/s, N*n2/p kb/s,..., N*nk/p kb/s, respectively, and the streams are allocated to the corresponding channels having the appropriate transmission capacity.

The choice of a common transmission capacity for all channels (i.e. nl=n2=...nk=l, and k=p) is however preferable and advantageous, because it is the simplest and most effective way of achieving the above mentioned mutual adaptation. The following embodiments will therefore all be described in terms of systems having channels of equal transmission capacity. The present invention is however not restricted thereto, as explained above.

Figure 1 shows one embodiment of the present invention. The figure shows a switch device 1 for switching information between transmission lines 10,20 and 30, 40, respectively. Line 30 is a transmission line for conveying voice information, whereas line 40 is a transmission line for conveying data information. Line 10 is a transmission line of a first type, such as a leased line. The line 10 of the first type is a fixed-cost line, i.e. it is constantly available to one user and the line costs are independent of how much data is transferred through the line. The transmission line of the second type 20 is a cost-on-use line, such as an ISDN line. This means that costs are only generated if the line is used, and these costs depend on how much data is transferred through the line.

It should be noted that the term "transmission line" in this description is meant as referring to any kind of transmission path for communication having a specified transmission rate. The "transmission lines" described in this description can therefore be physical lines, but they are not restricted to being such. All "lines" can e.g. be part of a single optical cable.

It should be noted that Figure 1 only shows 4 lines 10, 20, 30, 40 for the purpose of simplicity. An actual switch system will naturally incorporate a far larger amount of transmission lines, where the four lines 10, 20, 30,40 stand for respective pluralities of lines of the given type.

The lines 10 and 20 have a given transmission capacity N kb/s. A typical transmission capacity is 64 kb/s. The two lines of the first and second type 10, 20 can have different transmission capacities, it is, however, preferable to have lines where the transmission capacity is equal for both lines. Line 10 is connected to a line dividing means 11 for dividing the transmission line 10 into a plurality of channels all having the same transmission capacity. A line having 64 kb/s e.g. be divided into four equal channels having 16 kb/s. This is schematically shown in Fig. 4. The method of dividing the line into different channels can be any known method, such as TDMA (time division multiple access) .

It should be noted that one of the channels created by the division will be reserved for transmitting status information of the connections, such as a D-channel. This is exemplified by the right-most channel in Fig. 4. Data may be transmitted through the ISDN D-channel or via the data path.

The voice line 30 is connected to a voice compressing/dividing means 31. The incoming voice date, e.g. from telephones, can come at different rates, depending on the type of communication apparatus used. The voice compressing/dividing means divides this incoming data into individual data streams. The division is accomplished so that the rate for the individual streams is adapted to the transmission capacity of the channels into which the line dividing means 11 divided transmission line 10. In accordance with the example given above, the voice compressing/dividing means 31 divides the incoming voice information into streams of information having a rate of 16 kb/s. In accordance with the present invention, the device 31 may not only divide the incoming voice information into different streams, it also compress the transmitted voice information. Preferably, the device 31 divides and compresses the incoming voice information. A compression will result in a more efficient use of the subsequent transmission lines.

The data line 40 is connected to a data dividing means 41. The data dividing means 41 divides the incoming data information into individual streams. The individual information streams each have a rate adapted to the transmission capacity of the channels into which the line dividing means 11 divides the transmission line 10. Data is reassembeled at the other end.

It should be noted that the transmission rate of the information streams is adapted to the transmission capacity of the channels. This does not mean that the the transmission rates have to be equal to the transmission capacities, it is however preferable that they are equal.

As both the dividing of transmitted information and the compression of transmitted information are well known in the art, and the precise technique of information dividing and processing is of no relevance to the present invention, a description hereof is omitted.

The switch device 1 furthermore contains a stream allocating means 50. The stream allocating means 50 is connected to the line dividing means 11, the voice compressing/dividing means 31 and the data dividing means 41. The stream allocating means 50 dynamically allocates the streams coming from the devices 31 and 41 to channels on the transmission line 10 or 20. The dynamic allocation is performed on the basis of demand, i.e. only when a demand is indicated for a new connection by an incoming new data stream resulting in transmission queues, does the stream allocating means 50 determine an idle channel and then allocates the new stream to that channel. The process of dynamic allocation is such that the stream allocating means 50 will first determine if idle channels are available on the transmission line 10 of the first type and then allocate the corresponding stream to the idle channel to the transmission line 10 of the first type. Only if no channels are available on the transmission line 10 of the first type, will the stream allocating means 50 allocate an incoming stream to the transmission line 20 of the second type. The above described embodiments thereby guarantee an efficient use of the transmission capacity of the transmission line 10 of the first type.

According to a preferred embodiment, the switch device 1 also comprises a second line dividing means 21 for dividing the line 20 of the second type into a specific number of channels. Preferably, line 20 is also divided into channels each having the same transmission capacity as the channels of line 10 of the first type. This has the advantage that the streams of data information are not only mutually adapted to the channels of the line of the first type, but also to the channels on the line of the second type. The channels of the two types of lines are thereby also adapted to one another. This makes it possible to use the transmission capacities even more efficiently. According to another preferred embodiment of the invention, the stream allocating means 50 will preferably allocate streams corresponding to data information to the transmission line 10 of the first type. This means that the stream allocating means 50 will first determine the demand for communication of data information and then allocate the corresponding streams of data information to idle channels of the transmission line 10 of the first type. Only after that will the newly incoming streams of voice information be allocated to the remaining idle channels of transmission line 10. If the channel capacity of transmission line 10 is not sufficient for the incoming voice information, then the streams of voice information that can not be allocated to channels of transmission line 10 will be allocated to channels of transmission line 20. This corresponds to an overflow function according to which overflowing voice information is channelled through transmission line 20.

Preferably, the allocation means 50 will reallocate streams of voice information assigned to channels on transmission lines 10 to channels on transmission line 20 if the demand for data information channels cannot be met by the idle channels in transmission line 10. This means that voice information streams are removed from channels on transmission line 10 and reallocated to channels on transmission line 20 to thereby make room for the transmission of data information streams on the channels of transmission line 10. According to this embodiment, streams of voice information in an established connection are re-allocated while the connection remains established.

According to a further embodiment of the present invention, the stream allocating means 50 divides the channels of transmission line 10 into a specific number reserved for the transmission of data information and a specific number reserved for the transmission of voice information. The allocation means 50 is able to change the number of channels reserved for data information streams in accordance with the demand for data communication. The allocation means 50 determines the magnitude of demand for data communication, e.g. by counting the number of channels necessary for handling the demanded transmission rate and then comparing this quantity with a predetermined threshold. If the determined demand exceeds the threshold demand, then the number of channels reserved for data information streams in increased. Preferably, the increase will only be performed up to a predetermined maximum number. The increase can be incremental or in one step up to said maximum number.

If the determined magnitude of demand does not exceed^" the given threshold, then it is compared with a second threshold and if it falls under this second threshold, then the number of channels reserved for the transmission of streams of data information is decreased. Preferably, the decrease is only performed down to a predetermined minimum number. The decrease can be incremental or lead down to the predetermined minimum number in one step.

In the above embodiment, an increase in the number of channels reserved for the transmission of data information will preferably lead to a reallocation of voice information streams from channels of transmission line 10 to channels of transmission line 20 to thereby make room for the increase in data information channels. A decrease in the number of channels reserved for transmission of data information will preferably lead to a reallocation of streams of voice information from channels of transmission line 20 to channels of transmission line 10 if channels of transmission line 20 are being used at that time.

The advantage of preferably allocating data information to channels of lines of the first type, consists in the fact that voice information connections (calls) are typically short and have a definite end (on hook) . Data information connections on the other hand are often upheld a long time and thereby unnecessarily occupy dial up lines whose use is charged per minute. Therefore, it is advantageous to preferably allocate data information to lines of the first type and then route overflowing voice calls through a line of the second type.

Figure 2 gives a more detailed description of the stream allocating means 50. A demand determining means 51 is connected to the data dividing means 41 and determines the magnitude of demand by counting the number of streams necessary for handling a demand for data information transmission. The demand determining means 51 supplies the quantity associated with the magnitude of demand, e.g. the number of channels necessary for handling the demanded data information transmission, to a comparison means 53 for comparing the quantity of demand with thresholds read from a memory unit, such as a ROM or RAM. In accordance with the results of the comparisons, a channel number setting means 55 receives a signal from the comparison means 53 to either increase or decrease the number of channels reserved for the transmission of data information, as described above. No signal means that the number of channels remains unchanged. The channel number setting means is connected to a central allocation means 52, which receives the respective data streams from the voice compression dividing means 31 and the data dividing means 41. The central allocation means allocates, deallocates and re-allocates the data streams in accordance with the number set in the channel number setting means 55 and in accordance with an allocation table stored in the memory unit 54. The allocation table associates the respective data streams with corresponding channels on either the first or second transmission line 10, 20. The central allocation means 52 is furthermore connected to a nonvolatile storage means 56, such as an EEPROM, containing the operating program for running the central allocation means. The central allocation means 52 preferably contain a microcomputer (not shown) . In accordance with the stored program, the information streams coming from devices 41 and 31 are allocated by the central allocation means 52 to the respective transmission lines 10 and 20. Fig. 3 shows another preferred embodiment of the invention, where the same reference numerals as in the previous figures refer to the same or equivalent parts. According to this embodiment of the present invention, the switch device 1 is a private branch exchange (PBX) and the voice information line 30 carries telephone calls, while a packet switch (PFA) 2 is provided for supplying the data information to the data line 40. The packet switch 2 contains a CPU 201, which is connected to line 40 for measuring and evaluating the amount of data being transmitted. In this embodiment, the CPU 201 determines if new channels are necessary for transmitting an increased data amount, i.e CPU 201 determines the demand.

Fig. 3 furthermore schematically shows the arrangement at the receiving end of the lines 10 and 20. The receiving side is a mirror image of the sending side, which is illustrated by the dashed lines used for depicting the receiving end.

The CPU 201 is also connected to the stream allocating means 50 via a line 210. It can thereby supply the demand information to the stream allocation means 50. As an alternative, the CPU 201 can also determine the number of necessary channels and then send a corresponding request to the stream allocating means 50. In both cases, the stream allocation means 50, which again preferably contains a microcomputer (not shown) , can process the demand or request information to then accordingly dynamically allocate the new streams to idle channels. In this embodiment, the data transmission demand processing is therefore shared between the switch means 1 (the stream allocation means 50) and the packet switch 2 (CPU 201) .

The method of multiplexing in the above embodiment essentially consists in the PBX 1 dividing the transmission line of the first type into a plurality of channels, each having a specific transmission capacity, where one channel is reserved for data traffic only. The packet switch 2 then determines the data traffic on outgoing line 40 and sends out a request to the PBX

1 for more channels for data information streams when the detected data traffic exceeds a predetermined limit. The PBX 1 receives the request information and at the same time detects if there is a request for a telephone call. Then, on the basis of the demanded transmission of data and voice information, the allocation means 50 dynamically allocates and deallocates streams of data and voice information to the channels.

In further embodiments based on the above embodiment, the allocation of the individual streams to specific channels is conducted as in the previous embodiments, i.e. streams are preferentially allocated to a line of the first type (e.g. leased line) and furthermore the streams relating to data information are preferentially allocated to the line of the first type while overflowing voice streams are routed through another line, e.g. a line of the second type, such as an ISDN line.

Claims

1. A method for multiplexing voice and data information onto at least one transmission line of a first type in a communication system, said method comprising the steps of:

- dividing the transmission line, which has a specific transmission capacity, into a plurality of channels, each having a specific transmission capacity;

2. A method according to claim 1, characterized by dividing said transmission line of the first type into channels all having the same transmission capacity and said streams all having a single transmission rate corresponding to said same transmission capacity.

3. A method according to claim 1, characterized by providing at least one transmission line of a second type and dynamically allocating and deallocating the streams of voice and data information to the channels of said transmission lines of the first and second type depending on demand, such that the streams of information are allocated to idle channels on the line of the first type, and streams are only then allocated to the line of the second type if there are no available channels on the line of the first type.

4. A method according to claim 3, characterized by dividing said transmission line of the second type into a plurality of channels, each channel having the same transmission capacity as the individual channels of said transmission line of the first type.

5. A method according to claim 1, characterized by allocating said streams of data information to said transmission line of the first type with a priority over said streams of voice information.

6. A method according to claim 3, characterized by said transmission line of the first type being a leased line and said transmission line of the second type being an ISDN line.

7. A method according to claim 2, characterized by said transmission line of the first type having a capacity of 64 kb/s and it being divided into 4 channels, each channel having a transmission capacity of 16 kb/s.

8. A method according to claim 1, characterized by

- setting a number indicating how many channels in said transmission line of the first type are to be used for the transmission of streams corresponding to data information;

- increasing said number when the demand for data transmission exceeds a predetermined first threshold; and

- decreasing said number when the demand for data transmission falls below a predetermined second threshold.

9. A method according to claim 8, characterized by said increasing of said number being done up to a predetermined maximum limit, ana saia decreasing of said number being done down to a predetermined minimum limit.

10. A method according to claim 8, characterized by streams corresponding to voice information being reallocated from the transmission line of the first type to the transmission line of the second type when said number is increased.

11. A switch device for multiplexing voice and data information onto at least one transmission line of a first type, comprising:

first line dividing means for dividing the transmission line, which has a specific transmission capacity, into a plurality of channels, each having a specific transmission capacity;

- voice compressing/dividing means for compressing and/or dividing the voice information into one or more streams, each stream transmitting at a rate corresponding to the transmission capacity of one of the divided channels of the transmission line;

12. A switch device according to claim 11, characterized by said first line dividing means dividing said transmission line of the first type into channels all having the same transmission capacity and said data dividing means and said voice compressing/dividing means producing streams all having a single transmission rate corresponding to said same transmission capacity.

13. A switch device according to claim 11, characterized in that a transmission line of a second type is provided and said stream allocating means dynamically allocating and deallocating the streams of voice and data information to the channels of said transmission lines of the first and second type depending on demand, said stream allocating means being arranged for monitoring the channel allocation of the transmission line of the first type and allocating new streams to channels on the transmission line of the first type if there are idle^" channels on the line of the first type, such that the channels of the line of the second type are only used if there are no idle channels available on the line of the first type.

14. A switch device according to claim 13, characterized in that a second line dividing means is arranged to divide said transmission line of the second type into a plurality of channels, each channel having the same transmission capacity as the individual channels of said transmission line of the first type.

15. A switch device according to claim 11, characterized in that said stream allocating means has data priority means for allocating all streams relating to data information to free channels of the transmission line of the first type before allocating streams relating to voice information to free channels of the transmission line of the first type.

16. A switch device according to claim 11, characterized by said transmission line of the first type being a leased line and said transmission line of the second type being an ISDN line.

17. A switch device according to claim 12, characterized by said transmission line of the first type having a capacity of b KD/s ana it oemg aivided into 4 channels, each channel having a transmission capacity of 16 kb/s.

18. A switch device according to claim 11, characterized in that said stream allocating means comprises:

- channel number setting means for setting a number indicating how many channels in said transmission line of the first type are to be allocated to streams corresponding to data information;

- demand determining means for determining the magnitude of demand for the transmission of data information and assigning a quantity to said magnitude of demand;

- comparison means for comparing said quantity with predetermined thresholds;

- wherein said channel number setting means is arranged to increase said number when said quantity exceeds a first threshold and to decrease said number when said quantity falls below a second threshold.

19. A switch device according to claim 18, characterized in that said channel number setting means is arranged to only increase said number up to a predetermined maximum limit, and to only decrease said number down to a predetermined minimum limit.

20. A switch device according to claim 18, characterized in that said stream allocation means is arranged to reallocate streams relating to voice information from the transmission line of the first type to the transmission line of the second type, when said channel number setting means increases said number.

21. A switch device according to claim 11, characterized in that said switch device is contained in a private branch exchange, and in that a packet switch is provided for supplying data information to said private branch exchange.