Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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APPARATUS FOR SENDING AND/OR RECEIVING DATA IN AN SDH OR,
RESPECTIVELY, PDH TRANSMISSION SYSTEM
The present invention is directed to an apparatus and a method for sending
and/or receiving data such as, for example, compressed voice data in an SDH
or,
respectively, PDH transmission system.
In the transmission of data such as, for example, compressed voice data in
SDH or, respectively, PDH transmission systems (SDH: synchronous digital
hierarchy,
PDH: plesiochronic digital hierarchy), data incoming on a plurality of
different voice
channels are combined in time-division multiplex and transmitted via a single
channel
such as, for example, a 64 kbit/s channel. An occupancy of the transmission
path that
is higher by the compression factor thus derives. Up to now, static
multiplexing
methods were employed for the combining of the channels such as, for example,
in
mobile radiotelephony. The pre-condition therefor is that all data incoming on
the
various voice channels are compressed to the same rate and that this rate does
not
change during operation. The data on the various data channels arrive
regularly and
are statically multiplexed, i. e. according to a specific, fixed strategy.
This has the disadvantage that a flexible transmission of different data rates
is not possible for the individual voice channels. In static multiplexing,
further, no
reduction of the channel width is possible on the basis of speech pause
suppression.
2 0 The ATM adaptation layer 2 (AAL 2) was defined in the standard ITU-T
L363.2 for the common transmission of a plurality of voice channels via ATM
transmission networks (ATM: asynchronous transfer mode). The AAL2
specification
describes a cell-oriented, two-stage method that is explained with reference
to Figures
4 and 5. In the first stage, voice data supplied on a plurality of voice
channels 1 a, 1 b,
2 5 ... 1 n are arranged in mini-cells 7 of flexible length in a means 2. Such
mini-cells 7a,
7b, .. 7n are shown by way of example in Figure 5. Each mini-cell comprises a
mini-
cell header 8a, 8b, ... 8n at its beginning. The part of the mini-cells 7a,
7b, ... 7n
following the respective mini-cell header contains the respective voice data
9a, 9b, ..
9n of the respective voice channel 1 a, 1 b, ... 1 n.
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2
The mini-cells 7a, 7b, ... 7n are combined into a single data stream in a
means 3, i.e. arranged following one another, as shown in Figure 5. The means
3 thus
implements a static multiplexing of the mini-cells 7a, 7b, ... 7n in order to
merge them
to form a single data or, respectively, mini-cell stream.
In the second stage of the method described in the AAL2 specification, the
data stream is subsequently packed in ATM data packets in a means 4. In other
words, data packets that correspond to the asynchronous transfer mode are
generated
from the data stream in the means 4. An ATM header 10 as well as a start field
11 are
thereby attached to each ATM data packer at its start. The start field 11
contains an
offset field 12 as well as a sequence number 13 and a parity bit 14. The
offset field
12 thereby contains information about the position of the respective mini-
cells 7 in the
ATM data packet. The following ATM data packet similarly contains an ATM
header 15, a start field 16 and a mini-cell 7n. The space that is not required
in this
ATM data packet is filled with stuffing data 17.
In a means 5, the ATM data packets are converted into frame structures,
i.e. into transmission frames, that correspond to the SDH or, respectively,
PDH
transmission system in which the data are to be transmitted. The transmission
can
thereby ensue, for example, via radio or via fixed lines. The transmitted SDH
or,
respectively, PDH transmission frames are received by a reception means that
2 0 comprises the corresponding, inverse devices as the transmission means
shown in
Figure 4. The disadvantage of this method described in the AAL2 specification
is that
the voice data must first be inserted into ATM data packets before they can be
transmitted in the SDH or, respectively, PDH transmission system, as a result
whereof
the available or, respectivEly, possible transmission bandwidth is reduced.
2 5 The document by Johnsson, M. et al., "SUPPORT FOR LOW BITRATE
APPLICATIONS IN ATM NETWORKS", PROCEEDINGS OF IPIP WORKSHOP
ON PERFORMANCE MODELLING AND EVALUATION OF ATM NETWORKS,
3 June 1996, pages 39/1 through 39/14, XP002045906, is concerned with the
problem
of low bitrate data transmission (for example, of voice data) via an ATM
network.
3 0 The data are thereby likewise arranged in mini-~°lls. The mini-
cells are in turn
multiplexed into an ATM cell flow and sent via the ATM network.
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2a
It is thus the object of the present invention is thus to offer an apparatus
for sending data in an SDH or, respectively, PDH transmission system according
to
the preamble of the attached claim 1, a method for sending data in an SDH or,
respectively, PDH transmission system according to the attached claim 6, an
apparatus for receiving data in an SDH or, respectively, PDH transmission
system
according to the preamble of the attached claim 10 and a method for receiving
data
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according to the attached claim 15 that enable an increased transmission
bandwidth in
the transmission of data, for example compressed voice data.
This object is achieved by an apparatus and a method for sending data in an
SDH or, respectively, PDH transmission system comprising the features of the
attached claim 1 or, respectively, the features of the attached claim 6. The
object is
also achieved by an apparatus and a method for the reception of data in an SDH
transmission system comprising the features of the attached claim 10 or,
respectively,
of the attached claim 15.
The apparatus and the method for sending data in an SDH or, respectively,
PDH transmission system according to the present invention are particularly
characterized in that the single data stream composed of the mini-cells is
imaged into
the frame structure of the SDH or, respectively, PDH transmission system in a
direct
way instead of or, respectively, as an alternative to the generation of data
packets
(ATM data packets) corresponding to the asynchronous transfer mode.
Given the apparatus or, respectively, given the method for receiving data in
an SDH or, respectively, PDH transmission system according to the present
invention,
correspondingly, a data stream from which the mini-cells are in turn restored
is
generated in a direct way from the incoming transmission frame corresponding
to the
SDH or, respectively, PDH transmission system instead of or, respectively, as
an
2 0 alternative to the generation of ATM data packets.
The present invention thereby allows a significantly better usage of the
transmission bandwidth in SDH or, respectively, PDH transmission systems, for
example in the transmission of compressed voice data. Further, the present
invention
also allows the employment of dif~'erent compression rates and compression
methods
2 5 within a multiplex bundle and, in particular, the use of a speech pause
suppression
wherein the transmission capacities that are not needed during speech pauses
are filled
up with the voice data of other channels, for example by statistical
multiplexing.
Advantageous developments of the present invention are defined in the
respective subclaims.
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Given the apparatus or, respectively, the method for sending data
according to the present invention, position information with respect to the
position of
the first mini-cell in the transmission frame are thereby advantageously
generated for
each transmission frame generated directly from the data stream. These
position data
are thereby advantageously arranged at the beginning of the respective SDH or,
respectively, PDH transmission frame. It is also advantageous when a
statistical time-
division multiplexing of the data incoming in the plurality of data channels
is
implemented upon generation of the data stream in the apparatus or,
respectively, the
method for sending data. The statistical time-division multiplexing makes its
possible
to multiplex data incoming with different compression rates on the various
voice
channels and produce a single data stream. When the inventive apparatus for
sending
data should also be capable of transmitting data corresponding to the AAL2
specification, then a means for generating ATM data packets from the data
stream and
a means for generating transmission frames corresponding to the SDH or,
respectively,
PDH transmission system from the ATM data packets are to be provided. In this
case,
the inventive apparatus can transmit data corresponding to the AAL2 standard
and
corresponding to the present invention either in parallel fashion or
alternatively. In
particular, the present invention thereby also assures the compatibility of
the apparatus
or, respectively, of the method for sending or, respectively, receiving data
with the
2 0 AAL2 specification and/or with higher layers of standards yet to be
defined. The
present invention thus allows thus utilization of existing AAL2 standards and
of AAL2
standards yet to be defined while avoiding the loss of transmission bandwidth
connected with the use of ATM cells.
In the apparatus or, respectively, the method for receiving data according
2 5 to the present invention, the data stream is advantageously generated on
the basis of
position data with respect to the position of the first mini-cell in the
transmission frame
that are contained in every SDH or, respectively, PDH transmission frame.
Advantageously, the position data are thereby arranged at the beginning of the
respective transmission frame. The distribution of the data contained in mini-
cells in
3 0 the data stream is implemented by demultiplexing the data stream according
to the
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information contained in the mini-cell header. So that the inventive apparatus
for
receiving data can also be employed in a transmission system that is based on
the
AAL2 specification, a means for recovering data packets corresponding tothe
ATM
transmission mode from the SDH or, respectively, PDH transmission frames and a
5 means for generating the data stream from the ATM data packets are also to
be
advantageously provided. The reception of the data according to the AAL2
specification can thereby ensue parallel or alternatively to the inventive
data reception.
The present invention is also directed to a system for the transmission of
data in an SDH or, respectively, PDH transmission system that comprises an
apparatus
for sending data and an apparatus for receiving data according to the present
invention.
The present invention is explained in greater detail below on the basis of
preferred exemplary embodiments with reference to the attached drawings, which
show:
Figure 1 a block diagram of an apparatus for sending data in an SDH or,
respectively, PDH transmission system according to the present invention;
Figure 2 a schematic illustration of the inventively generated mini-cells and
transmission frames when sending data;
Figure 3 a block diagram of an apparatus for receiving data in an SDH or,
2 0 respectively, PDH transmission system according to the present invention;
Figure 4 a block circuit diagram of an apparatus for sending data in an SDH
or,
respectively, PDH transmission system according to the AAL2
specification; and
Figure 5 a schematic illustration of mini-cells and ATM cells generated
according to
2 5 the AAL2 specification.
Figure 1 shows a block circuit diagram of an exemplary embodiment of an
apparatus for sending data in an SDH or, respectively, PDH transmission system
according to the present invention. Voice data supplied in a plurality of
different voice
channels 1 a, 1 b, . .. 1 n are arranged in mini-cells 7a, 7b, ... 7n in a
means 2. The mini-
3 0 cells 7a, 7b, ... 7n have flexible lengths dependent on the respective
voice dataset, as
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schematically shown in Figure 2. The start of each mini-cell 7a, 7b, ... 7n is
formed by
a mini-cell header 8a, 8b, ... 8n that is followed by the respective voice
data 9a, 9b, ...
9n of corresponding length.
The mini-cells 7a, 7b, ... 7n are combined into a single data stream in a
statistical multiplexer 3, whereby the mini-cells that are formed are joined
to one
another dependent on their chronological arrival, as shown in Figure 2.
The transmission means shown in Figure 1 also comprises a transmission
branch according to the AAL2 specification, wherein a means 4 generates ATM
data
packets or, respectively, data packets corresponding to the asynchronous
transfer
mode from the data stream, transmission frames that correspond to the SDH or,
respectively, PDH transmission system being in turn formed therefrom in a
means 5.
Independently thereof or as an alternative thereto, transmission frames that
correspond to the SDH or, respectively, PDH transmission system are
inventively
generated from the data stream in a direct way in a means 6, dependent on the
application. The direct generation of a PDH frame 18 from the data stream is
shown
by way of example in Figure 2. The means 6 thereby inserts a start field 20
that
contains an offset field 21, a sequence number 22 and a parity bit 23 at the
beginning
of the PDH transmission frame 18, i. e. following the frame start 19. The
offset field
21 contains data that identify the position of the first mini-cell 7a in the
PDH frame 18.
2 0 The start field 20 of the PDH frame 18 thereby essentially corresponds to
the staxt field
of the ATM data packets that is schematically shown in Figure 5. Stuffing data
are
provided at the end of the PDH frame 18 in order to fill up the space that is
not
needed.
Figure 3 shows a block circuit diagram of an exemplary embodiment of an
2 5 apparatus for the reception of data in an SDH or, respectively, PDH
transmission
system according to the present invention. The reception means is likewise
designed
for alternative or parallel operation in a transmission system corresponding
to the
AAL2 specification, and its AAL2 reception branch comprises a means 25 at
which
transmission frames that correspond to the SDIT or, respectively, PDH
transmission
3 0 system arrive. These data can be transmitted, for example, either via
mobile
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radiotelephone or via fixed lines. The means 25 generates data packets
corresponding
to the ATM or, respectively, the asynchronous transfer mode from the frames
corresponding to the SDH or, respectively, PDH transmission system. A means 26
generates a data stream composed of mini-cells from the ATM cells. A
demultiplexer
28 distributes the mini-cells contained in the data stream onto the respective
voice
channels 30a, 30b ... 30n, and a means 29 generates to corresponding voice
signals
from the information in the mini-cells. The means 25, 26, 28 and 29 thus meet
the
AAL2 specification.
Inventively, a means 27 is provided wherein the incoming transmission
frames that correspond to the SDH or, respectively, PDH transmission system
are
directly converted into a data stream. Dependent on the requirements, thus,
the means
27 works independently of, alternatively to or parallel to the means 25 and
26. Similar
to the data stream regenerated in the means 26, the data stream directly
generated in
the means 27 is supplied to the demultiplexer 28.
The present invention further comprises a transmission system that contains
an apparatus for sending data according to the exemplary embodiment shown in
Figure
1 as well as a means for receiving data according to the exemplary embodiment
shown
in Figure 3. The SDH or, respectively, PDH transmission system, in accord
wherewith
the data are transmitted, can thereby be a mobile radiotelephone system, a
system with
2 0 fixed lines, etc.
