Multiplex communications – Pathfinding or routing – Switching a message which includes an address header
Reexamination Certificate
1999-08-12
2003-08-12
Ton, Dang (Department: 2661)
Multiplex communications
Pathfinding or routing
Switching a message which includes an address header
C370S470000, C370S471000
Reexamination Certificate
active
06606319
ABSTRACT:
The invention relates to a method for transmitting digital data using the time-division multiplex method, in which the data are transmitted within a sequence of time frames. In each time frame, at least the number of transmitted data bits matches the ISDN Standard.
DESCRIPTION OF THE PRIOR ART
ISDN Standard (Integrated Services Digital Network) is frequently used for transmitting data on two-wire lines, for examples for the telephone, fax and for data transmissions between computers. A disadvantage of the known ISDN Standard is that each line provides only two useful channels, each at 64 kbit/s (kilobits per second). However, the transmission of moving pictures, which may require data rates from several hundred kbit/s up to several Mbit/s, is impossible when transmitting data in accordance with the known ISDN Standard.
On the other hand, transmission standards for high data rates are known, for example the HDSL Standard (High bit rate Digital Subscriber Line), the VDSL Standard (Very high bit rate Digital Subscriber Line) as well as the ADSL Standard (Asymmetric Digital Subscriber Line). The data transmission rate of these Standards is at least fifteen times that of the ISDN Standard.
None of the existing standards solves the problem where it is desired to use: 1) existing terminals, 2) existing two-wire lines, and 3) the proven ISDN concept for higher data transmission, and where one wishes to increase the data transmission rate considerably above the current 128 kbit/s.
SUMMARY OF THE INVENTION
The object of the invention is to specify a simple method for transmitting data which is compatible with the ISDN Standard but which allows higher data rates than this Standard.
This object is achieved by a method having the steps of transmitting data bits within a sequence of time frames matching the ISDN Standard, transmitting overall frames comprised of a plurality of time frames within a time specified by the ISDN Standard for transmitting a time frame, and using a frame identifier (which is contained within at least one overall frame in a sequence of transmitted overall frames) to define an assignment of contained time frames to an overall frame. This object is also achieved by a circuit arrangement for implementing this method, and by other advantageous developments described below.
The invention is based on the knowledge that changes must be carried out in a number of areas in order to increase the data rate of the known ISDN Standard, which was developed for connection-oriented transmissions. However, in order to allow increased data rate transmissions using the ISDN Standard, the basic requirements of the ISDN Standard must not be changed, or they must at least be taken into account when defining an enhanced ISDN. This relates particularly to the number of data bits in a time frame and the time specified by the known ISDN Standard for transmitting the time frames. This time is defined, for example, in Technical Report ETR 080 by the European Telecommunications Standardization Institute for the ISDN Standard with the 2B1Q transmission option (2 Binary, 1 Quaternary) to be 1.5 milliseconds. The same definition is also included in the ITU Recommendation G.961 (International Telecommunication Union).
The invention thus retains the number of data bits per time frame. However, a plurality of time frames, which form an overall frame, are transmitted within the time which is specified by the known ISDN Standard for transmitting an ISDN Standard time frame (1.5 ms). This measure on its own increases the data transmission capacity, corresponding to the number of time frames in an overall frame. If the other features of a time frame which are specified by the known ISDN Standard are also retained, such as the assignment of time slots to useful channels and data channels, then the increased transmission capacity means that more ISDN channels are available on one data line. If, for example, there are two time frames in an overall frame, then four channels at 64 kbit/s each can be used for transmitting useful data.
According to the invention, at least one overall frame in the sequence of transmitted overall frames has a frame identifier. The frame identifier preferably occurs cyclically, for examples in each overall frame or in every tenth overall frame. The frame identifier is used to assign the time frames to their overall frames. The frame identifier makes it possible to determine precisely which time frames in each case belong to one overall frame, and which bits in a time frame are assigned to which channels.
The frame identifier allows a standard concept to be used for processing the overall frames. With one or two time frames per overall frame, differences between the time frames may be unnecessary. But problems in channel assignment arise as the number of time frames per overall frame increases. If the bits or time slots which are assigned to the individual channels in the time frames are arranged differently, which allows an increase in the flexibility of data transmission, then it must be possible to clearly distinguish the time frames from one another. This is precisely what is achieved by the frame identifier.
The requirement for the bits or time slots of a channel to be distributed as uniformly as possible within a time frame, and thus also to be interleaved within the overall frame, also means that the bits which are assigned to the individual channels in the time frames of an overall frame are arranged differently. This interleaving means that in the event of a disturbance or defect, even though a comparably greater number of channels are affected, the number of affected data items per channel is reduced. Error correction can therefore be carried out more easily.
In one exemplary embodiment of the invention, the number of time frames per overall frame is determined in a calibration process, as a function of the transmission quality of the transmission path. This measure allows the maximum permissible transmission capacity to be determined as a function of the quality as well as the length of an already existing line. The transmission then takes place with relatively few errors, since the data transmission capacity and the transmission path are optimally matched to one another. The calibration process is preferably repeated if a predetermined error rate for the transmission of data is exceeded during the transmission. This is the case, for example, if the transmission quality of the line changes over a period of years, possibly as a result of interference being radiated from newly connected lines.
In a further exemplary embodiment of the invention, at least one data item at a specified position in the overall frame and having a specified value, for example) of binary “
0
” is used as the frame identifier. This value differs from a value which is specified for this position in the other time frames of the respective overall frame. In this case, however, it is necessary to ensure that this bit can be evaluated correctly even in the event of transmission errors. The frame identifier must therefore be repeated cyclically at fixed time intervals. If, for example, the bit with the number “
240
” (which is not used in the known ISDN Standard) in every eighth time frame is used as the frame identifier, then this requirement is satisfied.
The frame identifier is expediently determined in combination with the determination of the frame identifiers, which are specified by the known ISDN Standard, in the time frames. Since, as a rule, the time frame identifiers have a number of bits, for example, eighteen, it is simple to determine this identifier. Starting from the time frame, the frame identifier of the overall frame which may be only a single data item, can be determined simply by counting down the data transmitted after the time frame identifier.
In exemplary embodiments of the invention, only data from a connection-oriented transmission can be transmitted. It is also possible to transmit only data from a non-connection-oriented for example for access to the Internet. Simultaneous c
Möhrmann Karl-Heinz
Wildmoser Johann
McCormick Paulding & Huber LLP
Ton Dang
Wilson Robert W.
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