EP0934639A1

EP0934639A1 - Device and method for receiving data transmitted by means of an asynchronous data transmission technique

Info

Publication number: EP0934639A1
Application number: EP98930730A
Authority: EP
Inventors: Ulf Assmus; Michael Roth
Original assignee: Deutsche Telekom AG
Current assignee: Deutsche Telekom AG
Priority date: 1997-06-06
Filing date: 1998-05-26
Publication date: 1999-08-11
Also published as: US8436938B1; DE19723760A1; WO1998056126A1; DE19723760B4

Abstract

The invention relates to a device for receiving data, especially audio and video data, transmitted by means of an asynchronous data transmission technique, to which device a clock pulse signal is transmitted. The invention provides for a memory device (17) which temporarily stores received data for the period required to compensate for transmission delays (cell delay variations). The invention is characterized in that the clock pulse signal is transmitted to the memory device (17) for reading the data. The invention also relates to a method for transmitting and receiving data signals by means of an asynchronous data transmission technique, whereby the received data signals are temporarily stored and read out at the studio clock rate.

Description

DEVICE AND METHOD FOR RECEIVING DATA TRANSMITTED BY AN ASYNCHRONOUS DATA TRANSMISSION TECHNOLOGY

The invention relates to a device for receiving data transmitted by means of an asynchronous data transmission technology, in particular audio and video data, to which a clock signal is fed, with a memory device. The invention further relates to a method for transmitting and receiving data signals, in particular audio and video data signals, between two studios, each studio having a studio clock.

In this context, a studio is a facility that has means for processing audio and image data signals. Data processing in the studios is taking place increasingly digitally, which requires a joint studio cycle to supply the processing equipment. In the case of data transmission between two studios, for example, there is a need for the studio clocks to be synchronized so that disruptions which occur during the reception and further processing of data as a result of data loss are avoided. A synchronization of the studio clocks is achieved, for example, in that in a so-called master / slave synchronization, a studio provides a clock as the master, which after its transmission is used by the other studio to synchronize its own studio clock. Furthermore, there is a solution such that, for example, a common clock is made available to the studios connected to the network by a common network operator. In both of the aforementioned methods, the useful signal is usually used for the synchronization or transmission of the synchronization signal.

However, these methods have the disadvantage that the signal used for synchronization must be transmitted without interference. However, if the signal shows strong jitter or wandering, this disturbance has an immediate effect on the studio clock derived from it. If data signals are then transmitted to the other studio, which has a jitter-free clock, bit errors and thus strong interference in the analog signal occur. Jitter is understood to mean a phase modulation of the signal clock with a high frequency, while Wander denotes a phase modulation of the signal clock with a very low frequency.

With the increase in digital processing in studios, the data between the studios are also transmitted in digital form, with ATM technology (ATM = Asynchronous Transfer Mode) in particular being used in the future. With this method, a clock recovery on the catch side based on the amount of data received per unit of time. This usually results in a higher-frequency jitter with a very low and therefore not disturbing amplitude and a wander based on the principle of ATM technology with a relatively large amplitude and very low frequency. Due to the low frequency of the wander below the mHz range, the technology used to eliminate jitter in the form of a PLL (phase locked loop) circuit with extreme low-pass behavior is not suitable, since it is one of the changing loads of individual ATM switching nodes ATM data transmission network depends. However, without adequate countermeasures, this wander causes a significant deterioration in the signal, which leads, for example, to audio noises at more or less regularly large intervals in the case of audio signals.

The object of the present invention is therefore to create a device with which error-free reception of data, in particular video and / or audio data, between two with one another _. synchronized studios is possible.

This object is achieved by a device for receiving data transmitted by means of an asynchronous data transmission technique, which has the features of claim 1.

Characterized in that a sufficiently large storage device is implemented in the transmission device, the received data temporarily for a period necessary to compensate for transmission delays and that the studio clock signal for Reading the data is supplied to the storage device, the wander leading to disturbances can be compensated for or the time period between two disturbances generated by wander can be so far apart that the disturbances are not perceived so strongly, especially if they occur at night. In addition, the advantages of ATM technology, such as great flexibility of the data rate, use of a public ATM network, use of dial-up connections, no closed user classes in a special network, no special network technology, can be retained. Another great advantage is that it is possible to create a uniform network which, in addition to audio and video connections, also enables LAN-AN connections (LAN = Local Area Network) and connections between two exchanges for telephone traffic.

Advantageous embodiments of the invention are set out in the subclaims.

The use of ATM technology for the transmission of data is particularly advantageous. Of course, the invention can also be used in PDH networks (PDH = Plesiochronous Digital Hierarchy) or on the components of the SDH hierarchy (SDH = Synchronous Digital Hierarchy, in USA SONET).

The use of a FIFO (FIFO = First In First Out) memory as a memory device is particularly advantageous, the size of the FIFO memory being designed such that data can be stored over a period of preferably n ^* 150 μs. The period results from the number of possible Switching centers within a transmission link, with 100 μs per switching node to be set for an unloaded network and approximately 250 μs for a loaded network.

For the synchronization of two studios, a studio is preferably selected as the master, which transmits a clock signal to the other studio. In larger networks, however, it is advantageous to synchronize the studio clocks in the network by means of a centrally generated normal clock.

If data is transmitted between unsynchronized studios, for example when transmitting across national borders, a means is preferably provided which is designed to adapt the received data stream to the studio clock. For clock adaptation, the means recognizes times at which a falsification of the digital signal after the conversion of the digital signal into the analog signal has no perceptible impairment. In the case of an audio signal, this point in time is recognized, for example, when the state of rest (no signal) is recognized in the signal over several samples. In video applications, the image boundaries are advantageously recognized and then entire images are omitted or read twice.

In a development of the invention, a switchover device is provided which classifies the data received via the network and forwards it to the corresponding receiver. For example, the audio and video data signals represent a class that the studio needs for further processing be fed. Another class is represented, for example, by telephone data signals which are supplied by the switching device to a connected telephone system. Furthermore, computer data belong to a class that is transmitted via a so-called LAN (Local Area Network) network and is supplied to the corresponding network by the switching device. The switching device preferably also works to bundle the different data signals.

The object of the present invention is also achieved by a method which has the features of claim 11.

The fact that the data signals are transmitted by means of an asynchronous data transmission technique and the received data signals are buffered and read out in the studio cycle, faults can be avoided or reduced to such an extent that they are no longer perceived.

Further advantageous embodiments of the method result from the subclaims.

The invention will now be explained in more detail on the basis of exemplary embodiments with reference to the drawing. Show:

Figure 1 is a block diagram of the structure of two studios and their connection;

Figure 2 is a block diagram of the connection of two studios with a normal clock supply, and FIG. 3 shows a block diagram of several studios connected via a common network.

In Figure 1, a device 1 is shown in a schematic representation, which is connected to a substantially similarly constructed further device 3 via a connection 5. Both devices are devices for processing digital data, namely digital audio and video data, which are used in radio and television technology. Such devices 1, 3 are part of digitally working radio and / or television studios. For the sake of simplicity, the two facilities 1, 3 are referred to below as studios. Such a studio has, for example, the task of processing the data of a live broadcast sent by another studio in real time and transmitting it to the viewers via terestrial or wired transmission channels.

For the digital processing of such data, the studio 1 comprises a transmission device 7, which is connected to the transmission link 5 at the receiving end. The transmission device 7 carries out a bundling of different data streams, for example audio and video data streams, for example using the multiplex method, in order to transmit these via a common line of the transmission link 5. The data transmission link is, for example, an STM1 connection with a data transmission rate of 155.52 Mbit / s. Another task of the transmission device 7 is to be seen in the data signals to be transmitted in a form necessary for the transfer. According to the invention, the ATM method (Asynchronous Transfer Mode) is used as the transmission method. Since this method is known per se, its description is omitted.

Furthermore, in the present exemplary embodiment, the transmission device 7 separates the received data stream into an audio data stream and a video data stream, the data packets being unpacked at the same time.

Two devices 9, 11, hereinafter referred to as terminal adapters, are connected to the transmission device 7 via data lines 13. In the present exemplary embodiment, the terminal adapter 9 is assigned to the video data stream, while the terminal adapter 11 is assigned to the audio data stream. The terminal adapters are used to adapt the data coming from the transmission device 7 to the form required within the studio 1, which normally also includes the recovery of the clock used on the transmitter side. The terminal adapters 9 and 11 have to divide the data stream into individual data packets, so-called ATM cells, for transmission in ATM technology, each data packet also containing control information in addition to the actual user data. An ATM cell is usually 53 bytes long.

Such a terminal adapter comprises - as shown schematically in section A of FIG. 1 - a control unit 15 and a storage unit 17. This storage unit comprises at least one as FIFO (First In First Out) memory area 19, to which the data coming from the transmission device 7 are fed. The control unit 15 ensures that the data are read out of the FIFO memory 19 in one cycle, which is provided by a clock source 21 provided within the studio 1. This measure is referred to below as the studio measure. The function of the FIFO memory 19 is therefore to temporarily store a number of data. The size of the FIFO memory depends on the one hand on the data transmission rate and on the other hand on the number of switching centers present in the transmission path. It has been found that the storage capacity could be 300 ATM cells at a transmission rate of 34 Mbit / s and 100 ATM cells at a transmission rate of 8 Mbit / s. This results in a memory size of 13 ATM cells per 1 Mbit / s data transfer rate. The FIFO memory 19 should also be large enough to compensate for time delays caused by transmission technology. Thus, delays referred to as cell delay variation (CDV) occur through switching centers in the transmission link, which cause a delay of 100 μs for an unloaded network node and up to 250 μs for a network node that is loaded (switching center).

The data temporarily stored in the FIFO memory 19 are then read out in the studio cycle and fed to a downstream audio or video coding / decoding device 23 or 25. In the present exemplary embodiment, the audio data are, for example, transmission rate of 2.048 Mbit / s to the audio coding / decoding device 23. The two coding / decoding devices 23, 25 also receive the studio clock from the clock source 21 for further processing of the data. Since the further processing of the corresponding data is not relevant to the present invention, a corresponding description is dispensed with.

It is crucial in the construction of the studio 1 that the studio adapters are fed to the terminal adapters 9, 11 in order to read out the received data from the FIFO memory 19 in the studio admission. According to the invention, clock recovery in the terminal adapter from the received data stream is thus dispensed with.

It is crucial for the error-free processing of the received data that the studio clock used for further processing is synchronous with the clock that is used by the transmitter. In the present exemplary embodiment according to FIG. 1, the transmitter is Studio 3, which corresponds to Studio 1 in terms of its structure. A repeated description of the parts identified by the same reference numerals is therefore omitted.

In the present embodiment, the studio clock 21 of the studio 1 is transmitted to the studio 3 via the transmission path 5 for synchronization. When selecting the transmission channel, care must be taken that the clock signal is transmitted with the highest possible priority and without interference. In Studio 3, this clock signal is transmitted by the supply device 7 the clock generator 21 ^! fed and used there to synchronize the generated studio clock. This type of synchronization is also called master / slave synchronization, with Studio 1 working as a master and Studio 3 as a slave.

The advantage of this type of data transmission is that the advantages of ATM technology, such as great flexibility in data rates, use of a public ATM network, use of dial-up connections, no closed user class in a special network, no special network technologies etc. are retained without to have to accept the inherent disadvantage of wandering (loss of synchronization) in this ATM technology. By means of the FIFO memory 19 with a large amount of memory, disturbances caused by wandering can be avoided or spread over time in such a way that they only occur at night.

Another type of synchronization of two studios 1, 3 is shown in FIG. 2. The two studios 1, 3 themselves correspond to the studios described above, so that there is no further description. The only difference is that both studios do not necessarily have the clock sources 21 to be synchronized. Rather, a clock signal referred to as a normal clock is supplied to them by a central clock generator, for example the network operator 27 (which then synchronizes clock sources 21 that may be used). A further exemplary embodiment is shown in FIG. 3, three studios 1, 3, 29 now being able to be connected to one another via a common ATM network 31. All three studios 1, 3, 29 have an identical structure and correspond to the studio already described with reference to FIG. 1. A description of the parts identified by the same reference symbols is therefore omitted. As explained in connection with FIG. 2, in this exemplary embodiment the clock necessary for synchronization is generated by a central clock generator 27 and made available to each studio 1, 3, 29. There it is used to synchronize the studio clocks.

The ATM network 31 can be, for example, the public ATM network (fixed or dial-up connections). Due to the possibly larger CDV delay in data transmission, the FIFO memory of the terminal adapter must be adapted accordingly.

In addition, it is possible to provide the transmission devices 7 with a switchover unit, which enables the bundling or separation of data of different classes (audio / video data, telephone data, computer data). The ATM network 31 can thus be used for different services.

It is also possible to add a means to the control unit 15 which is designed to adapt the received data stream to the studio clock. For the clock adjustment, the means recognizes times at which a falsification of the digital gnals after the conversion of the digital into the analog signal has no perceptible impairment. In the case of an audio signal, this point in time is recognized, for example, when the state of rest (no signal) is recognized in the signal over several samples. In video applications, the image boundaries are advantageously recognized and entire images are then omitted or read twice. It can also be used to transfer data between a synchronized and an unsynchronized studio.

Claims

1. A device for receiving data transmitted by means of an asynchronous data transmission technology, in particular audio and video data, to which a data-independent clock signal is supplied, with a memory device (17) which temporarily stores the received data over a period of time necessary to compensate for transmission delays (cell delay variation) , characterized in that the clock signal is supplied to the memory device (17) for reading out the data.

2. Device according to claim 1, characterized in that it is designed to receive data transmitted in ATM technology (A-synchronous transfer mode):

3. Device according to claim 1 or 2, characterized in that the memory device (17) is designed as a FIFO memory (19).

, Device according to claim 3, characterized in that the size of the FIFO memory (19) is designed so that received data can be stored over a period of time, preferably from 100 μs to 250 μs per switching center.

5. Device according to one of the preceding claims, characterized in that a clock source (21 ¹ ) providing the clock signal is synchronized with at least one further device (3; master / slave mode).

6. Device according to one of claims 1 to 4, characterized in that the clock source (21) works non-synchronized to the clock source of the sending device, and that means are provided for the clock adaptation of the received data stream to the clock of the clock source (21st ) are designed.

7. The device according to claim 6, characterized in that the means for clock adaptation double or omit certain data signals when reading from the memory unit (17).

8. Device according to one of the preceding claims, characterized in that the clock source (21) is synchronized via an external normal clock.

9. Device according to one of the preceding claims, characterized in that a switching device is provided which classifies the received data into data classes and forwards them to a corresponding device.

10. Method for the transmission and reception of data signals, in particular audio and video data signals between two studios (1,3), each studio having a studio clock, characterized in that the data signals by means of ATM Technology are transferred, and that the received data signals are buffered and read out in the studio clock.

11. The method according to claim 10, characterized in that the studio clocks are synchronized with each other.

12. The method according to claim 9 or 10, characterized in that the received data signals are stored over a period of time which is sufficient to compensate for transmission delays.

13. The method according to any one of claims 10 to 12, characterized in that a normal clock of a network operator is supplied directly or indirectly to synchronize the studio clocks.

14. The method according to any one of claims 10 to 13, characterized in that the clock of a studio is used to synchronize two studios (master / slave mode).

15. The method according to claim 14, characterized in that a normal clock is fed to a studio, which is continued via the connecting line (5) to the other studio.

16. The method according to claim 10, characterized in that with unsynchronized studio clocks a clock adaptation is carried out by a plus / zero / minus stuffing technique.

17. The method according to claim IS, characterized in that when transmitting audio signals these are detected for irrelevant data signals, and irrelevant data signals are continued twice or omitted for clock adaptation.