Layer two compression/decompression in a cellular communications network

The invention relates to the field of the transmission frame data within communications networks, and more particularly the transmission with compression / decompression.

A number of communications networks are provided with compressors / decompressors loaded to compress data contained in frames to be transmitted in order to increase their capacity in terms of links.

In these networks, the compression / decompression is called "layer one (1) "the fact that it applies to the physical layer of all frames to compress, regardless of their type. A compression layer includes detecting redundancies between the data contained in identical portions comprising frames of the stream of frames to be transmitted, said input frame to remove while pointing them so they can be reconstructed during decompression. The stream of frames as well compressed are stored temporarily in queue buffers, to be directed to according to the available transmission capacity.

We remind that the input frame is a frame that feeds compressor. It consists of a plurality of the stream of frames constituting portions of initial frames associated with channels different transmission. For example, in TDMA transmission mode, each input frame is divided into a fixed number of intervals time (or "time slots") each having one byte. This number is equal 32 in the case of E1 type frames, and 24 in the case of type frames T1 in accordance with G.703 / G.704 recommendations of the ITU-T. Usually, the frame frequency is 8 kHz, which allows a frame E1 to convey 31 information channels at 64 kbps (kilobits / s) at a rate of a channel by time interval.

Within a cellular network, the A-bis interface provides coupling between a base station controller (BSC for "Base Station Controller ") and one or more base stations (BTS), using E1 or T1 frame type. The A-bis interface supports two types of flows: flows traffic, speech or data type, and traffic flow. For carry traffic flows, each byte of the E1 or T1 frame is divided either four doublets (two-bit sample called "nibble") of each a traffic channel to 16 kbps (mode called "full rate" or FR) or eight traffic channels in half-speed (mode called "half rate" or HR where each bit corresponds to a voice channel). The signaling flows are as generally carried by two channel bits (16 kbps channels) or 8 bits (64 kbps channels). An initial frame, type E1 or T1, is and a set of transmission channels, size of from 1 bit for the Channels 8 kbps to 8 bits for channels 64 kbps; each channel for conveying the stream of frames, specific to each transmission channel.

Traffic flows are conveyed by TRAU frames (for "Transcoder / Rate Adapter Unit") exchanged between each BTS and center mobile switching PLMN (for "Public Land Mobile Network "), in transiting the transcoder / rate adaptation unit (or TRAU). The latter is in particular for converting the speech data compressed to 13 kbps digitized voice data at 64 kbps to make the speech channels compatible with the switching center mobile. The coupling between the mobile switching center and the TRAU is effected by an interface known as the A, while the coupling between the BSC and the TRAU is by an interface called A-ter.

In what follows, the term "active channel" all established traffic channel, ie for which a call setup procedure was correctly performed through a signaling channel, procedure leading to the establishment of a traffic channel dedicated to that call, maintained until the end of call phase. A traffic channel is used to carry TRAU frames exchanged between a caller and a called throughout the call time, including during the silent phase.

It is also recalled that the TRAU frames can be four types: speech frames (or data transfer) that comprise at least control data and useful data, silence frames which comprise at least control data, SID frames (for "Silence Descriptor") which include at least control data and useful data, and the bad frames (or "Bad frames") which comprise at least control data.

In the following, the case of TRAU frames used to transfer data will be assimilated to the case of TRAU frames used to transport of speech, of the treatment is the same in both cases.

When the decompressor receives the compressed stream of frames, it decompresses successively so as to recompose (or restore) the initial frames of which they are the portions. Such a mode of transmission with compression / decompression can be qualified asynchronous. It introduces indeed transmission delays "end-to-end" for the initial frames (or flow) recomposed (s), which vary depending on the network load. In addition, these periods may vary significantly from canal transmission to another. Moreover, the maximum transmission delay, which can be considered as a parameter guaranteed by the network operator, is high because the processing implemented throughout the chain transmission is not deterministic.

This non-determinism of the time end-to-end, combined with the fact that we must make comfortable margins to guarantee a maximum of transmission, make it almost impossible to use the technique of compression presented above in a voice communications network, such as a GSM network.

The invention therefore aims to improve the situation, including ensure time end-to-end on the chain of transmission, while ensuring an optimal compromise between compression time gain and said end-to-end, and if possible allowing compatibility with operating a compression / decompression layer one.

It proposes to this effect a data compression device input frames consisting of the stream of frames defining portions of TRAU frames and signaling to be transmitted to a network communications and each constituted by at least one header comprising representative monitoring data at least on their type and any useful data, including certain types of data critical and / or non-critical in terms of transmission delay end-to-end.

This compression device is characterized in that it is able to adapt its compression mode depending on the frame type. Such a device thus provides a so-called compression "layer two (2)".

More specifically, the device comprises, firstly, means responsible for analyzing each frame header TRAU or signaling contained in input frames successively received to determine its type, and secondly, compression means responsible for generating periodically (or cyclically) to compressed frames transmit, subdivided into first and second sizes of the sections variables, the first section having compressed critical data synchronously, and the second section having data not critical compressed asynchronously.

In a mode of operation that can be described as "fixed" the sizes of the first and second sections are variable and complementary.

The compression device according to the invention may include other features that can be taken separately or in combination, and especially :<ul><li>the frame types may be selected from i) speech frames comprising including control data and user data reviews, ii) the silence frames comprising at least data of critical control, iii) the SID frames including at least data critical control and non-critical user data, and iv) poor frames including at least critical control data,</li><li>the compression means can be responsible for generating a frame Compressed all N input frames received. They then perform a aggregation of the N input frames into a single compressed frame During a compression cycle, </li><li>the compression means may be adapted to integrate the frame speech in compressed frames, without modification,</li><li>alternatively, when the speech frames include data synchronization, the compression means can be loaded to integrate the speech frames in the compressed frames, having deleted their data synchronization but without changing the control data and useful data,</li><li>the compression means may be designed, once they are possession of the data set for controlling a SID frame or silence, or a bad frame to remove these the redundant information or insignificant to generate a word of relevant information, for example, two bytes,</li><li>the compression means may be responsible for creating frames compressed whose first section includes at least one word of relevant information and / or a speech frame without modification (or alternatively with removal of synchronization data), and a header identifying the start of the compressed frame and information designating each of the input frame received channel which belong the data from which the relevant information or data of the speech frame,</li><li>the compression means may be adapted to extract data Useful contained in the SID frames to store temporarily in a buffer memory, and the frame Signal received, according to their order of arrival, to constitute a "Linking" and then extracting the head of the sequence a portion whose size is selected depending on the variable size during the second section to integrate it into the second section of the frame During compression, accompanied by a header identifying the start of the extracted portion and information designating each frame channel which received input from the user data or data belong signaling that portion web extracted, and finally concatenating the second section to the first section to define a compressed frame to be transmitted, </li><li>the compression means may be adapted sizes respective first and second sections based on traffic within of the network, in terms of speech frames and data transfer.</li></ul>

The invention also provides a pressure relief device of data contained in compressed frames by means of a device compression of the type described above.

This pressure relief device is characterized by the fact that comprises, firstly, detection means responsible for analyzing the compressed frames successively received to separate their first and second sections, a second hand, first means responsible for processing synchronously reconstruct critical data initially contained in the input frames and having been compressed in synchronously, from the first sections received, thirdly, second processing means adapted to reconstruct so asynchronous non-critical data initially contained in the frames input signals and having been compressed asynchronously, from second sections received, and fourthly, the restoration means responsible for rebuilding the input frames from critical data and noncritical replenished.

Preferably, the means for synchronous processing and Asynchronous processing means of such a pressure-relief device operate in parallel.

The invention further provides a compressor / decompressor equipped a compression device and a decompression device type those presented above.

The invention finds a particularly interesting application, although not exclusive in any type of communications networks point point multipoint-to-point or multipoint to multipoint networks such as satellite communications, terrestrial communications networks, such as E1 or T1 networks base and the like, or Basic Ethernet, IP, Frame Relay and ATM, and communications networks ground using a satellite extension (or offset (s) or satellite by wireless means) over part of their bonds, such as cellular network TDMA or CDMA.

Other characteristics and advantages of the invention will appear consideration of the detailed description below and the appended drawings, which :<ul><li>1 illustrates schematically a part of a network of communications satellite extension of the invention,</li><li>Figure 2 schematically illustrates a treatment system frames comprising an exemplary embodiment of a compressor / decompressor according to the invention,</li><li>Figure 3 schematically illustrates an example of E1 input frame,</li><li>Figure 4 schematically illustrates an example of initial frame TRAU,</li><li>5 illustrates schematically an example of a compressed frame according to the invention, and</li><li>Figure 6 schematically illustrates an example of web Non-critical user data stored in a pending buffer Insertion in a second section of a compressed frame type that shown in Figure 5.</li></ul>

The attached drawings may not only serve to complete the invention but also contribute to its definition, if appropriate.

The invention is intended to allow compression / decompression layer two (2) frames of data within a network communications.

In what follows, it is assumed, without limitation, the communications network is a cellular telephony network, such as a GSM (or 2G) or GSM / GPRS (2.5G), satellite extension (Or offset (s) Satellite). However, the invention is not limited to this type of network. As previously indicated, it relates to all network point to point communication, point to multipoint or multipoint multipoint, which are defined in the cable connections to resources fixed or shared transmission or connect resources to radio fixed or shared transmission, including networks of satellite communications, terrestrial communications networks, such as E1 or T1 networks base and the like, or Basic ethernet, IP, Frame Relay and ATM, and communications networks terrestrial radio using a satellite extension (or offset (s) by satellite or terrestrial) over part of their bonds, such as by eg cellular networks TDMA or CDMA.

GSM communications network with satellite extension, type to that illustrated in Figure 1, can, in a very schematic way but nevertheless sufficient for an understanding of the invention be summarized in a classic radio subsystem, called a base station system (BSS "Base Station System"), coupled to a core network or "Core Network", Here materialized, very simplistically, as a center of mobile switching MSC (or "Mobile Switching Centre") itself coupled a PLMN (for "Public Land Mobile Network"). Downtown mobile switching MSC is responsible for conducting all operations necessary for managing communications with terminals EU users.

Conventionally, the BSS comprises at least one central CG traffic management, for example arranged in the form of a "hub" H coupled to a transmitter station / receiver SER by which it will make Li satellite links with a SAT communications relay satellite. In Alternatively, the hub H, which is the clearing with stations ST distant traffic can be separated and / or spaced from the management center CG.

SAT satellite relay is connected by satellite links to ST traffic stations, the BSS, each with a station base called BTS (for "Base Transceiver Station") managing at least one radio cell in which user terminals UE can establish mobile communications. Each base station BTS is coupled to a MT processing system responsible for processing the frames to be transmitted and the received frames and the allocation of resources, and itself coupled a transmitting / receiving station SER 'by which the satellite link takes place Li with the satellite SAT.

We remind that the hub H is connected to different traffic stations ST by satellite links using a shared resource (Lf carrier) in forward mode (that is to say, the hub H to the traffic stations ST) and a set of carriers (Lr) shared by all the mode bonds Return (that is to say, traffic stations ST to the hub H).

The BSS system also comprises at least one controller controller BSC (or Base Station Controller) coupled, on the one hand, to traffic management center CG, specifically its hub H, and the other hand, the MSC mobile switching center. The BSC is primarily responsible for managing the resources of the various stations BTS base that attached to it and the operating functions and maintaining said base stations.

The sharing of transmission resources is controlled by the center CG traffic management. More specifically, the CG traffic management center dynamically allocate satellite resources in the form of frequency transmission (in the operating mode SCPC) or time intervals (Or "time slots") of a time frame (in the operating mode TDMA (time division multiplex)), according to the respective needs of various traffic stations ST it manages. In other words, the center of CG traffic management allocates resources (or transmission channels) of SAT satellite between different satellite links that it manages.

It is considered in the following, without limitation, the network is TDMA.

As indicated above, the coupling between the BSC and the base stations BTS is by the A-bis interface, synchronous, operating with a G.704 type screen (this is called E1 frames, the type illustrated in Figure 3). As illustrated in Figure 1, BSC can also be coupled directly, via offsets A-bis land at the base stations BTS independent satellite links.

The coupling between the BSC and the switching center mobile MSC takes place here via a transcoder / unit rate adaptation (or TRAU for "Transcoder / Rate Adapter Unit"). This last is for converting the speech data compressed to 13 kbps into digitized speech data to 64 kbps in order to make the channel speech compatible with the MSC mobile switching center. It is indeed recalled that the A interface between the MSC and the TRAU transcoder, the transmission of data and signaling in GSM / GPRS networks is carried out in channels at 64 kbps.

As indicated above, the coupling between the center of mobile switching MSC and the TRAU is made by an interface called A, while the coupling between the BSC and the TRAU is effected by a A-ter interface called. In order to ensure a significant area coverage, the MSC mobile switching center may be coupled to several controllers BSC via several interfaces A-ter.

As illustrated in Figure 2, the hub H, as each base station ST, MT includes a frame processing system 1 comprises a modem coupled to a compressor / decompressor 2.

The modem 1 comprises a modulator 3, producing a modulated carrier, for modulating the frames compressed by the compressor / decompressor 2 and originally from the BSC or a BTS, and a set of demodulators each for 4 demodulating the carrier from a remote traffic station ST or BSC in order to restore the compressed frames compressor / decompressor 2 so that decompresses them before transmit to the BSC or the BTS.

Each compressor / decompressor includes a device 2 of 5 compression and decompression device (or expansion) 6. In the practice, each frame processing system MT comprises as many compressors / decompressors that Li 2 satellite links. In fact, every compressor / decompressor 2 is supplied with demodulated frames and compressed by a demodulator 4 and supplies the compressed frames to modulating a modulator 3.

We consider in the following that each compression device 5 receives input frames to compress, type E1 (but it could also include T1 type frames, PDH frame type or frame carried by SDH channels) from the BSC or BTS.

As illustrated in Figure 3, an E1 frame is divided 32 time slots (or time slots) TS0 through TS31 each having a byte, according to G.703 / G.704 recommendations of the ITU-T.

Apart TS0 time slot, each time slot (TS1 to TS31) carries one or more transmission channels to a dedicated communication (link) or transport of signaling. each channel transmission carries a succession of "original frames" which are TRAU frames to transport speech and data transfer, or signaling frames from a BTS or a BSC and to be transmitted to the network or a user terminal UE.

It is recalled that TRAU frame can be of four types different :<ul><li>speech frames (or data transfer) which comprise at least critical control data and useful critical data,</li><li>silence frames which comprise at least control data critics,</li><li>SID frames which have at least critical control data and non-critical user data and</li><li>the improper weft (or bad frames) that include at least critical control data.</li></ul>

An example of a speech type of TRAU frame is illustrated in Figure 4. The synchronization data comprise the first sixteen bit zero (0), and nine of ten bits to one (1), an all of the following sixteen bits. The Control data consists of bits C₁ -C₂₁ and T₁ to T₄. More Specifically, the bits C₁ -C₁₅ constitute the header of the TRAU frame, the bit C₁₆ -C₂₁ constitute a part of the end part of the TRAU frame, and T bit₁ to T₄ (Optional) is another part of the terminal portion the TRAU frame for the time shift (or "time alignment"). All control bits C₁ -C₂₁ characterized the TRAU frame, and including its type among the four types mentioned above. By Moreover, the field for the speech data (or "speech frame data field ") is placed between the header and the end portion. The speech data Here are the useful data.

A TRAU frame thus comprises 320 bits, or 20x16 bits, which correspond to a period of 20 ms (milliseconds) if "full rate" (FR) and "enhanced full rate" (EFR) or 160 bits is 20x8 bits in the case "Half rate" (HR).

In the case of a TRAU frame type silence, the data field speech is invalid. In the case of a TRAU frame type CIS, the speech data field carries the definition of comfort noise.

The case of the TRAU frame type is particularly bad frame. he corresponds to an initial frame received by a BTS with a radio quality insufficient in terms of signal / noise ratio. One of the control bits a Such a frame indicates that poor quality (BFI bit, for "Bad Frame Indication ").

In the example E1 frame illustrated in Figure 3, the shaded parts are reserved for signaling frames, while the unshaded parts are reserved to the floor. In this example, given only as illustration, the time interval TI1 carries a signaling channel at 64 kbps, the time interval IT2 carries a signaling channel at 16 kbps then 3 traffic channels at 16 kbps (or traffic channels 6 to 8 kbps, or even combination of channels to 16 kbps and 8 kbps channels), and the interval IT3 temporal concerns only traffic channels.

A compression device 5 ensures not only the compression frames to be transmitted, but also the adaptation of the blocks of the format data at the interface with the modem 1, which is of type E1, T1, Ethernet, IP or ATM. In addition, a decompression device 6 ensures not only the refund by decompression, the initial frames (that is to say as they were before being compressed in the traffic station ST) but also adaptation to the interface with the modem 1, which is generally the same type as that of the compression part.

As noted above, certain flows, such as those containing speech data, are critical in terms of time transmission end-to-end, and therefore must be treated differently other flows to allow the operator to ensure transmission according within fixed end-to-end and as short as possible.

The invention therefore proposes to address critical flow in a deterministic synchronous processing throughout the chain of transmission (Compression - transmission - decompression), and non-critical flow according asynchronous processing (non deterministic) all along the chain transmission.

The dissociation between streams processed synchronously and asynchronously is established by configuration. More specifically, it is the operator that specifies which channels should be processed synchronously (generally those support voice communications), and which channels are to be treated asynchronously (usually those that support information signaling).

The compression device 5 is thus configured to differentiate the critical flow of non-critical flow and then applying them different treatments (synchronous and asynchronous).

It includes for this purpose an analysis module 7 to analyze the control bits of each TRAU frame received from the BTS or the BSC, to determine the type of the received frame. This analysis module 7 operates by cycle compression. In the example described, the compression cycle covers N = 64 E1 frames, a time of 8 ms, each E1 frame having a duration of 125 microseconds (microseconds). The compression cycle defines the rate at wherein the compressed frames are transmitted from the TC device compression 5 to the decompression device 6 at the other end of the link. The compression cycle also sets the rate at which Input TRAU frames are analyzed.

An initial TRAU frame having a duration of 20 ms, it takes 3 cycles consecutive compression to dispose of all the information it vehicle, including the control bits located at the beginning and end of frame TRAU. Depending on the value of these control bits, the TRAU frame is identified as a speech frame (or data transfer frame) silence frame, SID frame or bad frame. The analysis module 7 can and determining the type of compression to be applied to the frame TRAU received during the three compression cycles considered.

For the signaling channels, the analysis module 7 merely extracting the frames carried by the channel, and storing them in a memory buffer (or buffer) dedicated to the channel considered.

The compression device 5 also comprises a module 8 compression responsible for generating each compression cycle a frame TC compressed, using data extracted by the analysis module 7.

Specifically, when the compressor 8 is warned by the analysis module 7 of the type of TRAU frame, it transmits significant data carried by the TRAU frame:<ul><li>user data and control data for a recognized critical frame as a frame of speech or data transfer,</li><li>control data for a silence frame,</li><li>control data and non-critical user data for one frame recognized as a SID frame,</li><li>control data for a bad frame.</li></ul>

For the signaling channels, the compression module 8 provides the multiplexing of traffic flows with traffic flow.

According to the invention, and as illustrated in Figure 5, each TC frame, compressed by the compression unit 8 comprises first S1 and second S2 sections of varying sizes. The first section S1 includes compressed critical data synchronously, and the second section S2 includes compressed non-critical data so asynchronous.

Preferably, critical data is data (or bits) control (C₁ -C₂₁ and T₁ to T₄) And the speech data, while non-critical data are the comfort noise data (SID frames) and the signaling data (signaling frames).

Compression can be carried out as indicated below.

The compressor 8 is first of all the first S1 sections compressed frames TC, also called frames synchronous. These synchronous frames S1 include, as shown in 5, a header EN1 and a ZIP field and / or a ZD1 field.

The ZIP field is a field dedicated to the said relevant information C contained in the control data₁ -C₂₁ and T₁ to T₄ (25 bits) of SID frames, frames of silence and bad frames. It comprises preferably a word of relevant information (or RI 1-16 for "Reporting Information "), for example, two bytes (16 bits), consisting of removing redundant information contained or insignificant in the 25-bit control data.

The ZD1 field is a field dedicated to data contained speech in the speech frames. It includes for example the entire data contained in the speech frame, ie the synchronization data, the control data and the speech data. But alternatively, it may contain a compressed version of the speech frame, that is to say, only its control data and speech data (bits Synchronization (35-bit) are deleted).

The header field EN1 identifies the beginning of the synchronous frame and thus the beginning of the compressed frame. It also includes the information which designates each of the input frame received channel which owns the data from which the relevant information of word of two bytes (ZIP) or the speech frame data (ZD1). In fact, it includes all the necessary information to the device 6 decompression to restore critical data and therefore the frames which they originate.

Preferably, and as shown, the Zip field is interposed between header EN1 and ZD1 field.

Once the first section consisting S1, the compression module 8 constitutes the second section S2 compressed frames TC, also called asynchronous frame. As illustrated in Figure 5, each frame EN2 asynchronous S2 includes a header and a field ZD2.

The ZD2 field has non-critical data, and more precisely the signaling data and / or the payload of noise comfort SID frames. It may also be at least partially formed of padding data, in the absence of non-critical data transmit or when the number of non-critical data to be transmitted is insufficient.

In fact, these non-critical data is stored temporarily by the compression module 8, as and when they arrive in queues buffers waiting where they are sequences of type shown in Figure 6.

This data is then retrieved by the compression module 8 according to their order of arrival (oldest, that is to say those placed at the head of the sequence being removed first), but above depending on the size available at the time of compression in the second section S2.

The respective sizes of the first S1 and second S2 sections of a compressed frame TC preferably vary independently with a fixed or scalable global value, depending on network load (in terms of number of voice frames to be transmitted).

With fixed transmission resources, the greater the number of frames speech to be transmitted is high, such as during peak hours, plus the size of the first section S1 and the greater the size of the second section S2 is small. Conversely, the less the number of frames of speech to be transmitted is high, such as off-peak, more the size of the second section S2 and the greater the size of the first section S1 is small.

With scalable transmission resources, which is the case with a transmitting device operating in DAMA mode, the two sections may evolve independently one vis-a-vis each other, the transmission device adapting the resources allocated to the load overall constituted by the stream conveyed through the first section S1 and via the second section S2.

The respective sizes of the first S1 and second S2 sections are updated at each compression cycle depending in particular on the traffic load. Thus, each time the compressor 8 knows the amount of non-critical data that it can extract a sequence stored in a buffer for supplying the ZD2 field of the frame asynchronous S2.

When the number of data stored at the head of a chain and belonging to the same frame, for example signaling, is higher than that available (in progress) in the second section S2, only a some of this data is incorporated in the second section S2 and the other part pending its integration in the next compressed frame. We can also consider the number of data stored in a head sequence and belonging to the same frame or lower than available (in progress) in the second section S2. In this case, these data are integrated in the second section S2 by concatenation with a portion (Or all) of the following data in the sequence and belong to another frame.

The header field EN2 identifies the beginning of the asynchronous frame S2. It contains information designating each channel of the input frame received which owns the data from which the data ZD2 contained in the field, as well as the length of said field ZD2. In Indeed, EN2 header field includes all the necessary information decompression device 6 to reconstitute the non-critical data and So the frames from which they arise.

Once the second section S2 is formed, the module 8 compression concatenates the first section S1, which is a compressed frame TC, of ​​the type shown in Figure 5. The device compression 5 can then put the format of the data blocks to the interface with the modem 1, before passing to the modulator 3 concerned.

The delay introduced by the asynchronous compression varies in Depending on the capacity offered by the transmission link at a given moment and of the capacity used by synchronously processed flows, while the delay introduced by synchronous compression is fixed.

The operation of the decompression device 6, according the invention, is roughly reversed from that of the device of compression 5 which has just been described.

More specifically, the decompression device 6 comprises any a first detection unit 9 to analyze the compressed frames TC, it receives (in succession) of the demodulator 4 to which it is coupled to to separate their first S1 and second S2 sections. It detects for that their EN1 respective headers and EN2.

The decompression device 6 also includes a first processing module 10 responsible for reconstructing synchronously, from the first sections S1 received critical data that were initially contained in the input frames and which has been compressed synchronously.

Specifically, the speech frames are reconstructed using payload contained in the ZD1 field (after a possible reintegration synchronization data). They are then transmitted to a frame restoration module 11, the decompression device 6, responsible for returning them to their original location in the E1 input frame, given the information contained in the header EN1.

Silence frames are reconstructed using the words relevant information contained in the ZIP field and restored by the frame restoration module 11 to their original location in the frame E1 input, given the information contained in the header and EN1 the default value of the speech data field.

The reconstruction of SID frames is a little more complex, since it requires a reconstruction performed by a second module 12 treatment of the decompression device 6, dedicated to compressed streams transmitted asynchronously. The processing module 12 stores the content of frames received via the asynchronous transmission channel (Second section S2 of the compressed frame TC) content relating to SID or signaling frames frames. For related content SID frames, the latest content replaces the previous contents; this Content is the useful field D1-D260 of the SID frame, characterizing the comfort noise for the given channel. The second processing module 12 has at least as buffers (or buffers) that channels traffic. To channel D1-D260 received data traffic channel wanted, the second processing module 12 uses the header information EN2 to determine which channel belongs D1-D260 received field, and therefore what buffer (or buffer) data should be stored.

In parallel with this process of storing received data asynchronously, the first processing module 10 reconstructs the body SID frame from the words of relevant information received from synchronous manner, following the same process as the frame silence. The body of the SID frame relates to synchronization bits part, control bits C₁ -C₂₁And time alignment bits T₁ to T₄.

As for speech frames and silence frames, the module Drop frame 11 is responsible for restoring each SID frame to its initial location within the output E1 frame. The returned SID frame by the frame restoration module 11 is formed by the body of the SID frame, reconstructed by the first processing module 10, and by the D1-D260 useful field of the SID frame, buffered by the second module 12 treatment.

For the first silence frame that follows a succession of frames speech, the second processing module 12 may sample the data characterizing the comfort noise in the latest received frame (frame SID) transmitted during the transition from speech mode to silent mode, following the same mode as the speech frames. This ensures a more precise transition of the synchronous transmission mode, which applies to speech frames, the asynchronous transmission mode, which applies to SID frames: comfort noise present in the buffer (or buffer) the channel is considered newer than the one that would have been present without this operation, in this case the noise sampled just before the sequence speech frames. With this operation, the noise present in the memory buffer (or buffer) is just noise sampled at the end of the sequence speech before an asynchronous transmission of data D1-D260 have been performed for this same channel.

It is important to note that the second processing module 12 is also responsible for reconstituting the signaling data which are ZD2 contained in the field. They are then transmitted to the module restitution of frames 11 so that restore them to their original location in the input frame E1, given the information contained in the header IN 2.

Preferably, first 10 and second 12 modules processing work in parallel.

Under offsets by radio or satellite the invention also relates to ensure that the error rate, which is guaranteed for every type of stream meets the constraints of the flow concerned.

As known to those skilled in the art, some modems are arranged to performing encoding of the information contained in the frames pass. This encoding is fixed and independent of the types of transmitted streams. It limits the receiving error rate by inserting data redundancy of the transmitted information. To ensure efficiency Spectral optimal, that is to say maximizing throughput in fixed satellite band, the rate of this encoding is set to a low value, so that the overhead introduced by the redundancy data remains the lowest possible rate for given error. The tolerable error rate an A-bis offset with compression depends on the conveyed stream, for example:<ul><li>error rate generally less than 10^-10 for the header information necessary for the decompression process,</li><li>low error rate also for speech frames of the order of 10^-8,</li><li>low error rate for signaling frames,</li><li>average error rate for the data relating to comfort noise.</li></ul>

To optimize the transmission based on the transmitted flux, the invention offers pre-encoding for making the error rate for every type of flow (or traffic).

To this end, the MT processing system includes an on-encoding module 13, preferably implemented as a compressor / decompressor 2, and charged with pre-encode independently each type of flow, apart from Preferably, the most tolerant flow rate of error, such as flows relating to comfort noise.

This pre-encoding is to introduce redundancy bits for each type of transmitted streams, except for flows requiring quality the lowest transmission (comfort noise in the previous example). The number of redundancy bits depends on the desired quality. Bits redundancy are used in reception to detect and correct errors introduced over the link. Plus the number of redundancy bits, the higher the error rate can be reduced with this principle, link quality data (signal to noise ratio and intermodulation).

pre-encoding the term refers to the introduction of bit Additional redundancy, vis-à-vis those introduced by the device transmission, which makes it also to encoding, the same principle, to reduce the impact of imperfections of the link, however following a use non differentiated between different types of flows routed. The flow separation conducted at the compressor makes it possible to pre-encode each stream based on the criticality of the data conveyed.

For this purpose, the on-encoding module 13 is supplied with frame TC compressed by the compression device 5 and feeds into frames compressed and pre-encoded modulator 3 at which the compressor / decompressor 2 is coupled. The modulator 3 then has only to perform a Classical overall encoding compressed and pre-encoded frames.

In reception, the demodulator 4 performs classically concerned correction of global error on the compressed frame TC received, he previously demodulated, then the on-encoding module 13 applies to compressed frame and a clean demodulated désencodage to each type of flux.

The overall error rate is well suited to each type of feed to data transmission conditions, that is to say for a signal to noise E_b/NOT₀ and given a given intermodulation rate. This increases notably the spectral efficiency of MT treatment system, reducing the redundancy rate applied to the overall flow, the most critical being flow have their own protection.

The compression device 5, and in particular analysis modules 7 and 8 of compression, the decompression device 6, and in particular detection modules 9 and 11 restitution and premier 10 and second 12 processing modules, and the on-encoding module 13 may be made in the form of electronic circuits, software modules (or Computer), or a combination of circuits and software.

The invention combines the benefits of treatment synchronous and asynchronous processing of those. It also allows to have a deterministic delay end-to-end and invariant to the channels the operator considers as critical, and in particular for the transmission of the speech.

In addition, the invention allows for a delay end-to-end short duration, and configurable to compromise with the compression overhead.

In addition, the invention provides a smoothing of asynchronous streams because they are transmitted using the remnants of bandwidth (second sections compressed frames).

Also thanks to the invention, each traffic type can be taken account.

Finally, the invention is compatible with allocation method resources (or transmission channels) of the satellite between different satellite links, called DAMA (for "Demand Assignment Multiple Access") through a total flow rate varying slowly (unlike a traffic burst (or "bursty")).

On this last aspect, the invention takes advantage of the features dynamics of transmitted signals: typically 80% of the traffic is made by voice traffic. Out, speaking slowly changing traffic when new call is established, or when a call ends, or when the word gives way to silence on a given channel, and vice versa. These events occur at a slower pace compared to applications multimedia transmission systems where the data stream are sporadic, especially whenever a user requests a file transfer or accesses a new web page. In addition, for a high number of concurrent calls, which is the case at peak hours, occurs an overall smoothing phenomenon of all traffics speech, around the median value of traffic between 35% and 50% of channels established in accordance with proportion of speaking time vis-à-vis communication period. At the busiest time, and therefore more binding on the transmission device, the relative changes load are reduced by smoothing this phenomenon, so conducive to the operation of compression means associated with a system of DAMA transmission operating in fashion: the reactivity of the system can be relatively slow, traffic moving slowly.

The invention is not limited to the device of embodiments of compression, decompression device, compressor / decompressor and communications network described above, only as examples, but it encompasses all the variants that may be envisaged by art in the scope of the claims below.

Thus, the invention also relates to communications networks other than cellular. The principle of joint transmission synchronous / asynchronous with self-adjustment of transmission resources used for each stream makes it possible to optimize traffic offsets kind speech, data and / or traffic on networks other than cell, depending on the relative criticality of the conveyed flow, and ensuring especially low and deterministic delay for the most flow criticism.