SE523417C2 - A method and apparatus for transmitting data packets in communication networks - Google Patents

Abstract

A method and a transcoder for transcoding data communicated between a sender (100) and a receiver (102). Data units (202, 208) comprising information in a first format (F, IF) are received and coded into new data units (208, 210) in a second format (IF, F'), based on a current coding state (302, 502, 706) extracted from a previous coding of data. A new current coding state is extracted each time a data unit (202, 500, 700) is coded. If a received data unit is in an erroneous sequence order, the current coding state is saved and a new pseudo coding state (DS2', ES2', CS2') is eytracted for codng a next received data unit. Eventually received missing data (F2, S4) is coded into the second format (IF, F') based on the saved coding sate, and may then be used as valid data. In this way, delays are minimised and jitter buffers are not necessary, while still maintaining a high quality.

Description

30 35 523 417 n n u n nn n. n. nn n nn I r I- n nn nu nn n n n nnnn. . -nnnnn nn I ann nn n n O n n n n. »Nn H n 11A its destination to be presented or played to a user at the receiving end. However, due to differences in standards, the sending and receiving equipment is often only equipped to use specific coding schemes that are different from each other, requiring the information encoded by the sender to be recoded somewhere before it reaches the receiving party. This operation is often referred to as "transcoding". In addition, different networks and / or switching nodes along the transmission path can also use formats and coding schemes according to different standards, which results in an additional need for transcoding. Thus, the transmitted data may need to be recoded several times before it reaches the final receiver. For real-time services, and to some extent also media streaming services, it is desirable to minimize delays due to transcoding activities in nodes in the total transmission path. For example, if a delay of more than 200 milliseconds is introduced in a voice call between two parties, the flow of dialogue is significantly disrupted.

Figure 1 illustrates an example of a communication scenario for transmitting data between a sender 100 and a receiver 102. In this simplified example, only asymmetric transmission in one direction at a particular time is considered. For symmetrical transmissions, of course, each party 100 and 102 can act = as both sender and receiver, as for voice calls. The transmitter 100 is connected to an access network 104 which may be a local area network (LAN), a wireless network or the like.

The receiver is likewise connected to another access network 106. Each access network 104, 106 is further connected to respective gateway switches 108, 110 for communication over an intermediate communication system 112, which may include one or more public networks, such as the Internet or the public network. fixed switched telephone network (Public Switched Telephony Network) PSTN. 10 15 20 25 30 35 523 417 1 »v v u.

The sender 100 is equipped to use a first encoding scheme to "encode" data to be sent.The receiver 102, on the other hand, is capable of using a second encoding scheme for decoding received data, the second encoding scheme being different from the first.

In addition, the intermediate communication system 112 may use one or more additional coding schemes in different parts thereof, for transmitting the communicated data. Thus, it is obvious that the communicated data must be recoded each time it enters a new area using a coding scheme that is different from that used before.

Transcoding must, for example, be done between packet-switched networks and circuit-switched networks that use, for example, Time Division Multiplexing TDM. The data is thus transmitted over one or more transcoders (transcoders) to create new data units from the previously received ones, before they are forwarded in the transmission path. The network ports 108, 110, as well as other switching nodes within the intermediate communication system 112 of Figure 1, may typically include such encoders.

In addition, if one or more of the networks 104, 112, 106 use packet-based transmission, there is a potential risk that the data packets will be received by the encoders in the wrong order. In packet-based transmission, each data packet is processed individually and can travel separate transmission paths and / or be exposed to different delays in intermediate nodes. Therefore, a buffer is often provided in encoders and receivers, often referred to as a "jitter buffer", to compensate for packets received with different delays. place in the queue if necessary.Another method is to simply discard packets received in the wrong order, which, however, results in a deterioration in quality.The receiving side of an intermediate node between a 10 15 20 25 30 525 417. in packet area and a TDM area usually includes a jitter buffer.

Techniques for jitter buffering entail the disadvantage that unwanted delay is introduced in the transmission. A clock reference is also required when TDM-based transmission is involved.

Furthermore, the final receiver 102 usually contains a jitter buffer or similar function during decoding, which further contributes to the total waiting time for transmitted data. A transcoding function should not contribute more waiting time than the time required to process the data and to perform the transcoding itself. If, on the other hand, each data packet is recoded sequentially as they arrive, the resulting quality will deteriorate when they arrive in the wrong order. In particular, many coding schemes depend on historical data when a particular piece of data is to be decoded, ie information from previously decoded data is used to decode the next data. All data must therefore be decoded in the same sequence order as those issued by the sending encoder in order to achieve high quality at the receiving end.

It is an object of the present invention to overcome these drawbacks as described above and to achieve high quality of received encoded data when it is decoded at the receiving end, while minimizing transmission delays in intermediate encoders.

DISCLOSURE OF THE INVENTION These and other objects are achieved by a simple solution to minimize delays in encoders eliminating the need for jitter buffers, compensating for data units arriving in an incorrect sequence order by restoring late received data.

A method and a transcoding unit are provided for transcoding communicated data in a transmission path between a sender and a final receiver. Data units comprising coded information in a first format are received and coded to 523 417. 5 u ~. - »o nos- nu one- u. once v o. u new data units in a second format, based on a current coding state obtained from a previous coding of data.

A new current coding state is generated each time a data unit is coded.

When a data unit is received, it is detected if the received data is in an incorrect sequence order. If so, the encoding state generated from the previous encoding of data is saved and a new pseudo-encoding state is generated for encoding a next received data unit. If missing data is finally received, it is encoded to the second format based on the saved encoding state, and the encoded missing data can be used as valid data.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention will now be described in more detail and with reference to the accompanying drawings, in which: Figure 1 is a schematic view of an example of a communication system for transmitting data.

Figure 2 is a schematic view of the data flow in an encoder.

Figure 3 is a logic diagram illustrating decoding of data packets received in the correct order.

Figure 4 is a logic diagram illustrating decoding of data when a data packet arrives in the wrong order.

Figure 5 is a logic diagram illustrating encoding of intermediate data.

Figure 6a is a logic diagram illustrating encoding of data when a data unit is lost.

Figure 6b is a logic diagram illustrating encoding of data when missing data arrives late.

Figure 7 is a logic diagram generally illustrating recoding of data when a data unit arrives in the wrong order. DESCRIPTION OF PREFERRED EMBODIMENTS Figure 1 illustrates an example of a communication system, described above, for transmitting data between a sender 100 and a receiver 102, in which the present invention may be implemented. Of course, the invention can also be used in a wide variety of other types of communication systems.

Figure 2 is a schematic view of the data flow in an example of a transcoding unit 200 for recoding data according to the invention. Data 202 encoded according to a first encoding scheme and having a first format F is received by the recoding unit 200 for recoding the data into a second encoding scheme having a second format F '. The transcoding process in this example is divided into two operations, a decoding operation 204 and an "encoding operation" 206. Between the two operations, the data is in an intermediate decoded format IF 208. However, it is possible within the scope of the invention to transcoding or transcoding the incoming data 202 in the first format F directly to the second format F ', without using any intermediate format.After being encoded to the second format F', the data 210 is passed on to the next node, The recoding unit further comprises a memory 212 for storing coding states, which will be described in more detail below.

The incoming data is usually divided into data units, for example packets or frames, which are encoded according to the first format F. The incoming data can be packet-switched or circuit-switched. Each incoming data unit includes a field or the like with information indicating a sequence order, such as a sequence number or a time stamp, which is read by the receiving transcoding unit 200. Normally, the received data units are sequentially decoded in operation 204 to the next format IF or F ', if the data units 10 15 20 25 30 35 523 417 ø - - fa; I u: us n are received in the correct order as they were originally sent and without any data being lost.

An example of this is illustrated in Figure 3, with further reference to Figure 2, where F1, F2, F3m are data packets 202 of the first format F received in the correct order at the recoding unit 200. The data packets 202 are decoded separately in operation 204 to intermediate data units 300 which has the intermediate format IF. When decoding each data packet 202, information from the previous decoding result is used, which is represented in Figure 3 as a series of current historical decoding states DS 302. A decoding state includes variables or parameters, in addition to the data itself, which are extracted from the performed decoding operation and which reflect certain characteristics of the data.

A received data packet F1 is thus decoded 204 to an intermediate data unit IF1, based on a current decoding state DSO which is derived from the decoding result for a previously decoded data packet, not shown. After the decoding state DSO has been used, a new decoding state DS1 is produced from the most recent decoding of F1.

The next data packet F2 is then decoded 204 to IF2, based on the most recent decoding state DS1, and so on.

In this description, it is generally assumed that all incoming data packets are of the same size, although in reality the packet size may vary.

The decoding procedure illustrated in Figure 3 involves data packets received in the correct sequence order. However, if a data packet is received whose sequence number is higher than the previous sequence number increased by 1, it can be assumed that the missing packet is lost or delayed. The package order can alternatively be indicated by a timestamp or some other order indicating information. If a data packet thus 10 15 20 25 30 F35 523 417 ø. ~ ~ o »o - ~~ un: missing, a fault concealment mechanism can be developed to minimize the resulting quality deterioration at the receiving end. The error-concealing mechanism can derive error-concealing data, based on the previous data packet and the most recent decoding state obtained from the decoding of the previous data packet. Error concealment is a well-known procedure that aims to create the most probable data when no real data is available. Error concealment is usually performed according to a prescribed standard for the data format, or if no standard exists, a single proprietary mechanism can be used.

According to one aspect of the invention, an error concealment mechanism is elicited when data is received in the wrong sequence order, whereby before the error concealment the most recent decoding state is saved for later use if the missing data packet finally appears, but in the wrong order. In that case, the missing data packet is decoded based on the saved decoding state according to the invention.

Figure 4 illustrates an example of a decoding procedure according to the invention when a data packet is received in the wrong sequence order. First, a data packet F1 is decoded to an intermediate data unit IF1, based on the most recent decoding state DSO, as in the previous example in Fig. 3. Then, however, comes a data packet F3 having a sequence number 3 which is higher than the previous sequence number 1 increased by a . When it is detected that the sequence number of the received data packet F3 is incorrect, ie. higher than expected, an error concealing mechanism 400 is developed to derive error concealing data 402 and to generate a new pseudo-decoding state DS2 ', based on the previous decoding state DS1. The pseudo-decoding state DS2 'can be generated in the same way as the other decoding states, since the error concealment is a decoding function in which a decoding state can be generated regardless of whether correct data is available. 10 15 20 25 30 35 523 417 v ~. | now the data packet F3 is then decoded 204 to the intermediate data unit IF3 based on the new pseudo-decoding state DS2 '. Furthermore, the previous decoding state DS1 is stored in the memory 212 in the decoding unit 200. A new decoding state DS3 is also extracted from the decoding 204 of the data packet F3 for later use when a data packet in the next sequence order is decoded, not shown.

In this example, the missing data packet F2 is then received, which can be decoded 204 to the intermediate data unit IF2, based on the saved previous decoding state DS1. The used saved decoding state DS1 can then be removed from the memory 212 in the decoding unit 200.

Finally, the restored intermediate data unit IF2 is inserted in the correct sequence order between IF1 and IF3, which replaces the previously derived erroneous data 402. However, if the missing data packet F2 is not received, for example within a preset time period, the erroneous data 402 may remain valid when the data of the intermediate format 208 is encoded 206 to the second format F 'in the recoding unit 200.

In this way, valid and decoded intermediate data units 300 can be arranged in a correct sequence order before being encoded again into the second format F ', even if one or more data units of the first format F were received in the encoder in an incorrect order. Furthermore, this procedure is performed with a minimum of delay and while maintaining the highest possible quality.

The example described above in Figure 4 was focused on a data packet received outside the sequence. A corresponding procedure can be performed if a plurality of data packets are received outside the sequence, using several saved decoding states. Furthermore, a stored decoding state can be removed from the memory 212 if it has remained unused for a preset period of time. Furthermore, the preset time period for deletion may be configurable or adaptive depending on the characteristics of the data flow, such as the number. . .n data packets in incorrect sequence order that vary over time.

Alternatively, the number of simultaneously saved decoding states may be maximized by a preset threshold value, which may also be configurable or adaptive depending on the characteristics of a data stream. If the number of stored decoding states reaches the preset threshold value, a mechanism can be triggered to remove individual saved decoding states from the memory 212.

After the decoding operation 204, the intermediate data units 300 are arranged into a continuous stream of data 208, which is fed to the decoding operation 206, see Figure 2. The decoding unit 200 then encodes the intermediate data 208 into new data units such as packets, frames or blocks, i.e. data sections of a predetermined size in accordance with the new second coding scheme or format F ', depending on the availability of data. If no intermediate data 208 is currently available, the encoding process can simply wait until it exists. The new data units in the second format F 'are finally transferred to the next node in the transmission path.

Figure 5 illustrates a decoding procedure according to the invention for the intermediate data stream 208 comprising the intermediate data units IF1, IF2, IF3m from the previous decoding operation. First, the intermediate data which can be arranged into new intermediate data segments S1, S2, S3m 500 is received, if necessary, to be encoded to the second format F '. The size of the new intermediate data segments 500, which are indicated by vertical dashed lines in the figure, in this example is different from the size of the intermediate data units 300 coming from the decoding operation 204. Each new intermediate data segment or unit 500 is then encoded 206 into a new data unit 506 in the second format F ', based on a current encoding state ES 502 obtained from a previous encoding operation. An encryption permission 10 15 20 25 30 35 523 417 ~ «u | u ll, v ~ «. . n | | o u includes variables or parameters, in addition to the data itself, derived from the performed encoding operation and which is used to encode data.

An intermediate data segment S1 is thus encoded 206 to a new data unit F'1, based on a last encoding state ESO which is obtained from the previously encoded new data packet, not shown. After using the ESO encryption permission, a new ES1 encryption permission is generated from the most recent encoding of F'1. The next intermediate data segment or unit S2 is then encoded 206 to F'2, based on the last encoding state ES1, and so on.

The intermediate data units 300 can be classified according to properties of their contents so that "good data" has been created directly from utility data in an incoming data packet or unit and erroneously hidden data has been derived from the last decoding state, by using the error concealment mechanism 400 when no incoming data packet or device in a correct sequence order was available. In the example in Figure 5, IF1 and IF2 contain "good data" while IF3 contains "erroneous data", which in the figure is indicated by a slash.

Accordingly, segments S1 and S2 contain only "good data", but segments S3 and S4 contain both "good data" and "erroneous data" as a result of the difference in size between the intermediate data units 300 and the intermediate data segments S00.

According to one aspect of the invention, the intermediate data segments 500 are processed differently depending on the classification of the data. Thus, if a segment 500 contains at least some "good data", the segment is encoded and a new encoding state is generated accordingly.

This year the case for all segments S1 - S4 is shown in Figure 5.

However, if an entire segment contains no "good data", i.e. only "erroneous data", the segment can simply be discarded, and the latest encryption state obtained at least in part from "good data" is saved. 417 12 c ~ ». Now x« »> ~ nonon is illustrated in Figure 6a, where a segment S1 containing" good data "is encoded to a new data unit F'1, whereby a new encoding state ES1 is generated.The new segment S2 indicated by contains "erroneous data" and no "good data", slash in the figure, which is thus discarded 600. A new data unit is thereby considered lost, the latest encryption state ESI is saved for later use in the event that the missing data finally arrives.

Referring to Figure 6b, a segment S1 containing "good data" is encoded to a new data unit F'1, whereby a new encoding state ES1 is generated, just as in the example in Figure 6a. data ", again indicated by a slash in the figure. According to an alternative embodiment, the segment S2 is first encoded to a pseudo-data unit 602, based on the available erroneous data, which is then discarded 600. In this case, a new pseudo-coding state ES2 'can be obtained from the coding of S2, for use in encoding the next segment, not shown, in this example, the missing data finally arrives later in segment S4, which can be encoded into a new valid data unit F'2, based on the previously saved encoding state ESI. that the sequence order of the segments S1 - S4 is selected by the division of the intermediate data stream for illustrative purposes, which should not be confused with the sequence order of the actual data. Thus, in this example, S4 contains data that would have been included in segment S2.

The restored new data unit F'2 can then be transmitted to the next node in the transmission path. It is further possible to transmit F'2 in an incorrect sequence position, in this case after F'3, since the final receiver is often capable of restoring the correct data unit order before decoding.

The procedure described in connection with Figure 6b above can also be performed for a plurality of segments arriving outside the sequence, using a plurality of saved encoding states. In addition, the same mechanisms as described above for saving a plurality of decoding states can generally also be applied to save a plurality of decoding states.

The examples described above include the two separate operations of first decoding received data from a first format to an intermediate format, and then encoding the intermediate data into a second format for transmission.

However, the invention can also be used to encode incoming data in the first format directly to the second format without using an intermediate format.

Figure 7 illustrates the most general case of the invention for a transcoding or transcoding procedure when a data unit is received in the wrong sequence order. In general, F1, F2, F3m denote incoming data units 700 having a first format F. The data units 700 are coded separately in operation 702 into new data units 704, in the figure generally denoted by F'1, F'2, F'3 * having a second format F '. The term "encoding" is used herein to denote either decoding, decoding or decoding. When each incoming data unit 700 is encoded, information from a previous encoding result is used, which is represented in Figure 7 as a series of current historical encoding states CS 706.

A data unit F1 in the first format F is thus encoded 702 into a new data unit F1 in the second format F 'based on a current coding state CSO, whereby a new coding state CS1 is generated. The next received data unit F3 includes a sequence number 3 which is higher than the previous sequence number 1 increased by one. When it is detected that the sequence number of the received data unit F3 is higher than expected, pseudo data 708 is created in the second format F 'based on the current coding state CS1 to produce a new pseudo coding state CS2'. The data unit F3 is then encoded 702 into a new data unit F'3 based on the pseudo-coding state CS2 '. In addition, the previous coding 10 15 20 25 30 523 417 14 o a u | is saved a. u state CS1 in memory 212. A new coding state CS3 is also generated from the coding 702 of data unit F3 to the new data unit F'3.

The missing data unit F2 is next received, which can be coded 702 to a new data unit F'2 based on the saved previous coding state CS1. The used saved coding state C51 can then be removed from the memory 212. Finally, the restored data unit F'2 is used as valid data, and the previously created pseudo data 708 is discarded. However, if the missing data unit F2 is never received within a preset time period, the pseudo data 708 can be used as valid data or discarded, depending on the implementation.

By using the invention as described above, delays in encoders or transcoders are minimized, and the need for jitter buffers is eliminated, while still maintaining high quality of transmitted data. In particular, data units arriving in an incorrect sequence order are compensated for by restoring late incoming data according to the invention.

The invention is primarily intended to be used for transcoding speech, but can also be used for, for example, transcoding faxes, modem data or packet-based video signals.

The inventive method can be implemented in a software code in a computer software product, which is directly loadable into a computer in the recoding unit 200 or stored on a medium that can be used in a computer.

While the invention has been described with reference to particular design examples, the description is intended only to illustrate the inventive concept and should not be construed as limiting the scope of the invention. Various alternatives, modifications and equivalents may be used without departing from the spirit of the invention, which is defined by the appended claims.

Claims (18)

20 25 30 523 4 1 7 NEW PATENT REQUIREMENTS A method of recoding communicated data in a transmission path between a sender (100) and a final receiver (102), comprising the steps of: - A) receiving data units (202,500,700) containing information in a first coding format (F, IF ), - B) to new data units (300,506,704) in a second coding format code (204, 206, 702) the received data units (202,500,700) (IF, F '), based on a current coding state (302,502,706) obtained from a previous coding of data, and - C) generating a new current coding state (302,502,706) each time a data unit (202,500,700) is coded, characterized by the further steps of: - D) detecting if the received data is in an incorrect sequence order, and if so: - E) save the coding state (302,502,706) generated from the previous coding of data and generate a new pseudo-coding state (DS2 ', ES2', CS2 ') for coding a next received data unit (202,500,700), using the saved coding state ds for encoding missing data to the second format, if such missing data is received later. A method according to claim 1, characterized in that upon receipt of missing data (F2, S4) the missing data is coded to the second format (IF, F '), based on the saved coding state (302, wherein the coded missing data ( IF, F'2) 502, 706), is used as valid data. A method according to claim 2, characterized in that the saved coding state (302, 502, 706) is removed after coding the missing data (IF, F'2). 20 25 30 35 .u n .., u n. Un: u A method according to claim 1, characterized in that the saved coding state (302, 502, 706) is deleted if the corresponding missing data is not received within a preset time period. A method according to claim 4, characterized in that the preset time period is based on characteristics of the data flow. characterized by the fact that it saved 502, A method according to claim 1, the coding state (302, 706) is removed if the number of saved coding states reaches a preset threshold value. A method according to claim 6, characterized in that the preset threshold value is based on characteristics of the data flow. A method according to any one of claims 1 to 7, characterized in that the received data units (202,) are decoded in step B), that the coded states are decoding states (302), and that the second format is an intermediate format (IF) . A method according to claim 8, characterized in that the received data units (202) are decoded in step B) into a stream of intermediate data (208) divided into intermediate data segments (soo). A method according to claim 9, characterized in that the intermediate data segments (500) are encoded into new data units (506). A method according to any one of claims 1 to 7, characterized in that the received data units (202) are encoded in step B), that the encoded states are encryption states (502), and that the first format is an intermediate decoded format (IF) . A method according to claim 11, characterized in that the received data units (500) comprise decoded intermediate data (208) which is encoded in step B) into new data units (506). 10 20 25 h. U. n ». . . '_' z _. a ... i .u x .. u: - ~ v v | -. ø u v o n ".. n. n. I n | n...,,,, _ _: z n - u o u n n u u.. -. u .. u n n ... A method according to any one of claims 1 to 12, characterized in that the new pseudo-coding state (DS2 ', ES2 *, CS2') developed in step E) is used for coding a next received data unit (F3, S3). A method according to any one of claims 1 to 13, characterized by reading information indicating a sequence order of (202, in step A) the received data 500, 700, F2, S4). A method according to any one of claims 1 to 14, characterized in that if the received data is in an incorrect sequence order, error-concealing data (402) is derived from the previously received data unit and the current decoding state (302, DS1), wherein the new pseudo-coding state (DS2 ', ES2', CS2 ') is generated in step E) based on the derived error concealing data (402). A transcoding unit (200) located in the transmission path between the sender (100) and the final receiver (102) for performing the method of any of claims 1 - 15. A computer program product directly loadable in a computer in a transcoding unit (200), comprising software coding means for performing the method in any of claims 1 - 15. A computer program product stored in a computer usable medium, comprising lockable software for causing a computer in a transcoding unit (200) to perform the method any of claims 1 - 15.