CN100428733C - Error recovery method and device for IP header compression in mobile communication network - Google Patents

Abstract

The invention discloses an error recovery method for IP header compression in a mobile communication network, which is used to improve the data transmission efficiency between a transmitting unit and a receiving unit. When the receiving unit received the voice data packet, the header decompressor judged whether the increment of its serial number relative to the serial number of the previous voice data packet was less than the aforementioned threshold value, if yes, then it represented that the compressed communication process was normal; if not, The header decompressor then invalidates the session context. The invention also discloses an error recovery device applying the method.

Description

Error recovery method and device for IP header compression in mobile communication network

technical field

The invention relates to a VoIP (Voice Over IP) voice service in a mobile communication network, in particular to a method for improving the compression efficiency of an IP (Internet Protocol) header of a data packet transmitted between a transmitting unit and a receiving unit.

Background technique

VoIP voice service, also known as IP phone, is a communication technology that transmits voice through an IP network, that is, a voice transmission technology based on an IP network. At present, VoIP has been widely used in wired communication systems, providing users with cheap and high-quality voice services.

With the rapid development of mobile communication technology, several mature GSM/CDMA/WCDMA networks have been introduced and established around the world, and the CDMA 1X mobile packet switching network can already provide users with high-speed data services. It is a current hot topic to provide users with high-quality VoIP voice services and other value-added services through mobile packet switching networks.

One of the key technologies for providing high-quality VoIP voice services is IP header compression (IPHC, IPHeaders Compressing) technology, such as the compression technologies defined by compression protocols such as RFC2507 and RFC2508. After using the IP header compression technology RFC2508, the 40-byte IP/UDP/RTP header can be compressed to a minimum of 2 bytes, and when using CheckSum (checksum), the minimum compression is 4 bytes.

The IP header compression technology RFC2508 can refer to Casner, S.and V.Jacobson, "Compressing IP/UDP/RTP Headers for Low-Speed Serial Links", RFC 2508, February 1999.

The IP header compression technology RFC2508 can be applied to fixed communication systems and mobile communication systems. At the transmitting station, the entire header information is compressed by a header compressor, and this compressed header information is transmitted over a wireless communication link; at the receiving station, a header decompressor reconstructs from the received compressed header information The entire header, thereby reducing the amount of wireless communication link resources necessary to transmit the header information.

In the communication process, errors often occur due to various factors. The RFC2508 protocol describes its proposed error recovery mechanism:

Except for the FULL_HEADER package, when the serial number increment of the session environment is not 1, the header decompressor considers the current session environment invalid, and sends a CONTEXT_STATE packet to the header compressor; and, the header decompressor considers that the currently received If the received compressed data packet is invalid, it will be discarded, and the session environment will not be re-established until the FULL_HEADER packet is received.

Although the IP header compression technology RFC2508 can realize effective error recovery to ensure call quality. But when it is applied to the mobile packet switching network, it has some disadvantages.

First of all, when implementing VoIP voice services based on the mobile packet switching network, since the wireless communication link between the mobile terminal (MS) and the base station (BTS) is in the transmission of voice data packets, the probability of losing data packets is relatively high, and the wireless Resources are relatively limited, and the loss of a small amount of data packets will not affect the VoIP voice quality. According to the RFC2508 protocol, when the serial number increment is not 1, the header decompressor invalidates the session environment and sends a CONTEXT_STATE packet to the header compressor; the header compressor receives a CONTEXT_STATE packet and sends a FULL_HEADER frame to re-establish the session environment. This will cause the decompressor to frequently send CONTEXT_STATE data packets, which will occupy too much compressed reverse channel bandwidth and affect the transmission efficiency of the wireless link.

Secondly, the VoIP voice service is a real-time voice media streaming service. During a call, although the loss of individual voice media data packets will not affect the VoIP voice quality, individual voice media data packets are allowed to be discarded. However, according to the RFC2508 protocol, when the serial number jumps, no matter how much it jumps, the header decompressor thinks that the original data packet cannot be completely decompressed, so it is recommended to discard the data packet. From the above analysis, it can be seen that in the transmission of voice data packets in the wireless communication link, the probability of losing data packets is relatively high, which will cause the header decompressor to frequently discard data packets, thereby increasing the possibility of voice quality degradation due to compression.

Contents of the invention

The technical problem solved by the present invention is to provide an error recovery method and device for IP header compression in a mobile communication network, which can effectively improve the transmission efficiency of a wireless link.

For this reason, the technical scheme that the present invention solves technical problem is: provide a kind of error recovery method of IP header compression in the mobile communication network, be used to promote the data transmission efficiency between transmitting unit and receiving unit, comprise steps:

1) Set the incremental threshold value of the serial number of the data packet at the receiving unit;

2) when the receiving unit received the voice data packet, the header decompressor judged whether the increment of its serial number relative to the serial number of the previous voice data packet was less than the aforementioned threshold value, if so, then it represented that the compressed communication process was normal; if If not, go to step 3);

3) The header decompressor invalidates the session context.

Preferably, the step 3) further includes the header decompressor sending the CONTEXT_STATE packet to the header compressor of the transmitting unit.

Preferably, after the step 3), the header compressor further includes receiving the CONTEXT_STATE data packet, and sending the FULL_HEADER frame to the header decompressor.

Preferably, after the step 3), the header compressor is further included to rebuild the session environment.

Preferably, it also includes the step of: when the header decompressor detects that the serial number of the voice data packet jumps, it is judged whether it is the same session environment, if yes, the header decompressor saves the voice data packet that has been correctly decompressed.

Preferably, also include steps:

4) setting a timer in the transmitting unit;

5) When the transmitting unit sends the voice data packet, the header compressor judges whether the time interval between it and the previous voice data packet is less than the value of the timer, if yes, then send after compressing the header; if not, send the following message The first packet rebuilds the session context.

Preferably, in the step 5), the header compressor uses the full header frame format to send the first data packet to be sent subsequently.

The present invention also provides an error recovery device for IP header compression in a mobile communication network, which is used to improve the data transmission efficiency between the transmitting unit and the receiving unit, including a header compressor and a header decompressor; A data packet serial number incremental threshold value setter is used to set a data packet serial number incremental threshold value; when the header decompressor receives a voice data packet, it determines according to the serial number incremental threshold value Whether to invalidate the session context.

Preferably, a timer located in the transmitting unit is also included; when the header compressor sends the voice data packet, it decides whether to rebuild the session environment according to the value of the timer.

Preferably, the timer is integrated in the header compressor or separated from the header compressor. .

Compared with the prior art, the beneficial effects of the present invention are: first, because the present invention sets the serial number increment threshold value, only when the serial number increment is greater than the threshold value, the header decompressor just sets the session environment as invalid and Send a CONTEXT_STATE packet to the compressor. It can effectively reduce the frequency of sending the CONTEXT_STATE data packet by the header decompressor, so as not to occupy too much compressed reverse channel bandwidth, and reduce the impact on the transmission efficiency of the wireless link.

In addition, because in the same session environment, when the serial number jumps, no matter how many jumps, the decompressor will not discard the decompressed data packets, which can protect the integrity of the voice to the greatest extent and reduce the possibility of voice quality degradation due to compression . This is because although some header fields are decompressed incorrectly, the content of the data packet is correct and does not affect routing.

In addition, due to the setting of the timer, after no data packet is sent for a long time, the first data packet to be sent subsequently will be sent using the FULL_HEADER format. This can effectively avoid the desynchronization of the session environment. It is guaranteed that no error packets will occur after a certain period of idle time, which improves the stability of the compression environment between the header compressor and the header decompressor.

Description of drawings

Fig. 1 is the overall architecture diagram of the VoIP voice communication system based on CDMA 1X packet switching network;

Fig. 2 is the flowchart of error recovery method of the present invention;

Fig. 3 is a flow chart of further stabilizing the conversation environment in the error recovery method of the present invention;

Fig. 4 is a schematic diagram of the error recovery device of the present invention.

Detailed ways

In the mobile communication system, the wireless link has the characteristics of high bit error rate, limited bandwidth and long loopback time. The occasional loss of a VoIP voice data packet during transmission has little effect on the voice quality; Characteristics of voice packets. Combined with the characteristics of the wireless link and the characteristics of the VoIP voice service, the present invention effectively optimizes the existing IP header compression protocol. Through optimization to improve compression efficiency, it provides a strong guarantee for VoIP voice quality.

Please refer to Figure 1, which is an overall architecture diagram of a VoIP voice communication system based on a CDMA 1X packet switching network. Wherein, a PPP connection is established between the mobile terminal (MS) 110 and the CDMA 1X packet switching node (PDSN) 120, and they are transmitters and receivers each other, and the session control of the VOIP service is in charge of the VOIP control center 130.

In the VOIP service process of the mobile communication network, the mobile terminal 110 converts the analog voice signal through analog/digital conversion, encodes and compresses it, and then converts the compressed frame into an IP data packet according to a certain packing rule, and transmits it through the packet switching node (PDSN) 120 transmitted to the Internet (Internet), the IP data packet is routed to the packet switching node (not shown) where the called mobile terminal (not shown) is located on the Internet; data decompression and digital/analog conversion are performed at the called mobile terminal to restore Voice, so as to achieve the purpose of voice communication.

When the mobile terminal 110 communicates with the fixed phone 140, when the fixed phone 140 is the calling party, the media gateway 150 is responsible for converting the analog signal into a digital signal and compressing and packaging it into a packet voice signal that can be transmitted on the Internet, and then through the Internet sent to the mobile terminal 110. When the fixed phone 140 is called, the media gateway 150 unpacks, decompresses and decodes the packet data, restores it to an identifiable analog voice signal, and then transmits it to the fixed phone 140 through the public telephone network (PSTN).

In order to save wireless link resources, the IP header compression technology is implemented between the mobile terminal 110 and the CDMA1X packet switching node 120 during the VoIP service process.

It should be noted that, in the embodiment of the present invention, the IP header compression is realized based on the RFC2508 (CompressingIP/UDP/RTPHeaders for Low-Speed Serial Links) protocol, and the optimization of the error recovery process is realized.

The compression goal of IP header compression is to compress the IP/UDP/RTP header of most data packets to 2 bytes without sending UDP checksum, and compress it to 4 bytes with UDP checksum .

The basic idea of the compression technology is: After the serial link is established, during the link maintenance period, since most fields in the IP/UDP/RTP header field remain unchanged, according to this feature, when sending an uncompressed data packet After that, these fields can be deleted from subsequent compressed headers, and the changed fields can be differentially encoded in order to reduce the field length.

Among them, the research on TCP header compression found that half of the bytes of the IP and TCP headers remain unchanged during the entire connection, which is the primary factor among the two elements that reduce the data rate. Therefore, after sending an uncompressed header, these fields can be removed from subsequent compressed headers. The rest of the compression comes from differentially encoding the change field to reduce length, and in the usual case calculating the change based on the packet length to remove the change field entirely. This length is dictated by the link layer protocol.

Some of the same techniques can also be used for the compression of the RTP header. Although there are always a few bytes to change in each packet, the difference from packet to packet is constant, so the quadratic difference is 0. During a session, by maintaining the uncompressed header and primary difference sequence shared by the compressor and decompressor, all that needs to be communicated is an indication that the second difference is zero. In this case, if no loss of information is considered, the decompressor after receiving a compressed packet can reconstruct the original packet header by adding the result of a difference to the saved uncompressed header.

In the RTP header, the SSRC identifier for a given context is constant as part of the context-specific identification. For most packages, only the serial number and timestamp are package-specific. If no packets are lost or out of sequence, the sequence number shall be changed packet by packet by a step value of 1. For audio packets, the timestamp shall increase by the sample period. For video, the timestamp changes on the first packet of each frame and stays the same for the rest of the frame. If each video frame occupies only one packet, and video frames are generated at a constant rate, the change in timestamp from frame to frame is also constant.

Note that whenever this happens, the second difference of the serial number and timestamp fields is 0, so the corresponding field value of the next packet header can be obtained by adding the first difference value of the existing session environment to the field of the previous uncompressed packet header . When the second difference is not 0, the amount of change is usually much smaller than the number of all bits in the field, so the purpose of compression can be achieved by encoding the new first difference and transmitting the code, without transmitting the absolute value.

A state-reliable set of shared information is maintained between the header compressor and header decompressor. For each IP/UDP/RTP data packet flow, a session environment is established according to the combination of the source IP address of the data packet, the destination IP address, the UDP port pair, and the SSRC field of RTP, and is identified by the session environment ID. Usually, each session context is identified by an 8-bit or 16-bit identifier, and the specific range depends on the number of negotiated contexts, so the maximum value is 65536. The session environment contains the following information:

1. Complete IP/UDP/RTP header

2. The primary difference result of the IPV4ID field

3. One-time difference result of RTP timestamp

4. The serial number in the last data packet, to detect the loss of data packets during the communication process.

Certainly, some other information may also be included in the session environment.

In a session environment, the order in which data packets are sent between the header compressor and the header decompressor is identified by a serial number, and whether the data packet is lost during the compressed communication process can be detected through the serial number.

That is, both uncompressed and compressed packets must carry the session context ID and a 4-bit sequence number used to detect loss in packet communication. Each session context has its own sequence number space, so the loss of a single packet will only affect one session context.

A header decompressor can be implemented to use a hash function on these fields to retrieve a stored list of session contexts. Compressed packets carry a small integer called the Session Context Identifier, or CID, to indicate into which session context the packet should be interpreted. The decompressor can use the CID to retrieve it directly from the stored environment list.

In order to realize the compressed communication process smoothly, four types of data packets are defined in the RFC2508 protocol:

FULL_HEADER, uncompressed IP header data packet or full header frame, which carries information such as session environment ID and serial number to establish synchronization between the two parties. The header decompressor establishes the session context after receiving the packet.

COMPRESSED_UDP, compressed IP/UDP header packets, the RTP header is not compressed. Used to deliver IP and UDP headers compressed to 6 bytes or less (typically 2 bytes if UDP checksums are disabled), followed by any subsequent headers (possibly RTP) and data in uncompressed form. This packet type is only used when the constant field of the RTP header is different.

COMPRESSED_RTP, compress IP/UDP/RTP header packets.

CONTEXT_STATE, a special packet sent by the header decompressor to the header compressor to transport session context IDs that have or may have gotten out of sync. The packet is only sent over point-to-point links, so it doesn't need an IP header.

Another package type is also available for this compression scheme:

COMPRESSED_NON_TCP, the compressed IP/UDP packet defined by differential encoding transmission is not required. If it is used for IPv4, in order to carry the IPv4ID field, it uses 1 to 2 bytes more than the COMPRESSED_UDP mentioned above. While IPv6 does not have an ID field, this non-differential compression is more resilient to packet loss.

The present invention recognizes that the VoIP voice communication system based on the mobile packet switching network has the following characteristics:

The packet loss rate of the wireless link between the mobile terminal MS and the base station BTS is relatively high. And wireless resources are very limited.

The VoIP voice service is a real-time voice media streaming service. During a call, the loss of individual voice media data packets will not affect the VoIP voice quality, so it is allowed to discard individual voice media data packets.

During the transmission process, it is necessary to minimize the end-to-end transmission delay and delay jitter of the VoIP voice media data packets.

Please refer to Fig. 2, aiming at the characteristics of the VoIP service based on the mobile packet switching network, the error recovery method proposed by the present invention includes:

First, set the incremental threshold value of the serial number of the data packet. The serial number incremental threshold value is stored in the mobile terminal (MS) and the CDMA 1X packet switching node (PDSN) that are transmitters and receivers each other, and its settings can be upgraded by software or by adding a serial number incremental threshold setter etc. to achieve.

Of course, the serial number increment threshold value can also be stored in the header decompressor, and its value can be set according to service needs.

Second, when the header decompressor receives a packet, it calculates the increment of the sequence number and processes accordingly.

If a FULL_HEADER is received, store the entire header in the session context selected by the context ID. A 4-bit serial number is also present in the environment, enabling synchronization of the header decompressor and header compressor. When using the COMPRESSED_NON_TCP package, the serial number is inserted into the "Data field" of the package. After receiving the COMPRESSED_NON_TCP package, compare the Generation number with the value stored in the environment. If it is different, the environment has expired and needs to be refreshed with the FULL_HEADER package. If they are consistent, the compressed IP and UDP header information, serial number, and RTP header are all stored in the saved environment.

In addition to being set by FULL_HEADER and COMPRESSED_NON_TCP packet data, if the increment of the serial number is less than the threshold value, it means that the compressed communication process is normal, the header decompressor does not invalidate the session environment and does not send the CONTEXT_STATE packet back to the header compressor; otherwise The header decompressor sets the session environment as invalid and sends a CONTEXT_STATE packet to the header compressor, indicating that the session environment has been invalidated. All current packets of an invalid session context MUST be discarded until a FULL_HEADER or COMPRESSED_NON_TCP is received to reestablish a stable state.

In the process of VoIP voice service based on mobile packet switching network, the probability of loss of data packets during the transmission of voice data packets is relatively high, and the loss of a small amount of data packets will not affect the quality of VoIP voice. When the value is 1, the header decompressor invalidates the session context and sends a CONTEXT_STATE packet to the header compressor. The header compressor receives a CONTEXT_STATE packet and sends a FULL_HEADER frame. This will cause the header decompressor to frequently send CONTEXT_STATE data packets, which will occupy too much compressed reverse channel bandwidth and affect the transmission efficiency of the wireless link. Through this optimization, the frequency of sending CONTEXT_STATE data packets by the header decompressor can be effectively reduced.

In addition, when the header decompressor detects that the serial number of the voice data packet jumps, it is judged whether it is the same session environment, and if yes, the header decompressor saves the correctly decompressed voice data packet. The so-called correct decompression means that although some header field decompression errors occur, the content of the data packet is correct.

The RFC2508 protocol considers that the header decompressor cannot fully decompress the original data packet at this time, so it is recommended to discard the data packet. However, after analysis, in the same environment, when the serial number jumps, the ID field of the IP header and the UDP checksum CheckSum field of the data packet decompressed by the header decompressor are inconsistent with the original message. But it does not affect the transmission of the message and the content of the message, so the data packet is not discarded. Such processing can protect the integrity of the voice to the greatest extent and reduce the possibility of voice quality degradation due to compression.

Please refer to FIG. 3 , the error recovery method of the present invention also includes a process of further stabilizing the session environment.

Firstly, a timer is set on the transmitting side; the setting of the timer can be realized by upgrading software or adding hardware.

Certainly, the timer can be integrated in the header compressor or separated from the header compressor; the time length of the timer can be determined according to service requirements, for example, it is defined as 30S.

If there is no data transmission within the time length of the transmitter timer, the first data packet sent subsequently will be sent in the FULL_HEADER format to rebuild the session environment.

A kind of embodiment is: when sending voice data packet, header compressor judges whether its time interval with previous voice data packet is less than the value of timer, if yes, then send after compressing header; If not, then send subsequent The session context is rebuilt when the first packet is sent.

This is because: if there is no data packet sent between the header compressor and the header decompressor for a long time, the subsequent compressed data packets are more likely to cause the session environment to be out of sync, especially in the VoIP voice service. If a data packet in the FULL_HEADER format is sent, a new session environment can be established between the header compressor and the header decompressor. This can effectively avoid the desynchronization of the session environment. It is guaranteed that no error packets will occur after a certain time of idleness, and the stability of the compression environment between the header compressor and the header decompressor is improved.

Please refer to FIG. 4 , corresponding to the aforementioned error recovery method, the present invention provides an embodiment of an error recovery device for IP header compression in a mobile communication network.

The error recovery device includes a header compressor 200, a header decompressor 300, a data packet serial number incremental threshold value setter 400 and a timer 500; In the mobile terminal and the packet switching node of the mobile communication network; the header decompressor 300 is also set in the mobile terminal and the packet switching node of the mobile communication network which are the transmitting party and the receiving party. Wherein, the header compressor 200 and the header decompressor 300 located in the same unit may be integrated or separated.

The data packet serial number incremental threshold value setter 400 is arranged on the receiving side, and is used to set the data packet serial number incremental threshold value; when the header decompressor 300 receives the voice data packet, according to the The sequence number increment threshold determines whether to invalidate the session context.

The timer 500 is set on the transmitting side and is used to preset a certain length of time. When the header compressor 200 sends the voice data packet, it decides whether to rebuild the session environment according to the value of the timer.

It can be understood that the timer 500 is integrated in the header compressor 200 or separated from the header compressor 200 .

To sum up, for the VoIP voice service based on the mobile packet switching network, by adopting the technical solution described in the present invention, the compression efficiency of the RFC2508 compression protocol applied to the VoIP service can be effectively improved. It reduces the end-to-end transmission delay and delay jitter of VoIP voice, and provides an effective guarantee for VoIP voice quality.

The above is only a preferred embodiment of the present invention, it should be pointed out that for those of ordinary skill in the art, without departing from the principle of the present invention, some improvements and modifications can also be made, and these improvements and modifications should also be It is regarded as the protection scope of the present invention.

Claims (10)

1. An error recovery method for IP header compression in a mobile communication network, used to improve the data transmission efficiency between a transmitting unit and a receiving unit, characterized in that, comprising steps: 1) Set the incremental threshold value of the serial number of the data packet at the receiving unit; 2) when the receiving unit received the voice data packet, the header decompressor judged whether the increment of its serial number relative to the serial number of the previous voice data packet was less than the aforementioned threshold value, if so, then it represented that the compressed communication process was normal; if If not, go to step 3); 3) The header decompressor invalidates the session context. 2. The error recovery method according to claim 1, characterized in that: said step 3) further comprises the header decompressor sending the CONTEXT_STATE packet to the header compressor of the transmitting unit. 3. The error recovery method according to claim 2, characterized in that: after the step 3), the header compressor further includes receiving the CONTEXT_STATE data packet, and sending the FULL_HEADER frame to the header decompressor. 4. The error recovery method according to claim 1, characterized in that after the step 3), the header compressor is further included to rebuild the session environment. 5. The error recovery method according to claim 1, further comprising the step of: when the header decompressor detects that the serial number of the voice data packet jumps, it is judged whether it is the same session environment, and if so, then The header decompressor holds voice packets that have been properly decompressed. 6. The error recovery method according to claim 1, further comprising the steps of: 4) setting a timer in the transmitting unit; 5) When the transmitting unit sends the voice data packet, the header compressor judges whether the time interval between it and the previous voice data packet is less than the value of the timer, if yes, then send after compressing the header; if not, send the following message The session context is rebuilt on the first packet. 7. The error recovery method according to claim 6, characterized in that, in the step 5), the header compressor uses the full-header frame format to send the first data packet to be sent subsequently. 8. An error recovery device for IP header compression in a mobile communication network, which is used to improve the data transmission efficiency between the transmitting unit and the receiving unit, including a header compressor and a header decompressor; it is characterized in that: it also includes a device located in the receiving unit The data packet series number incremental threshold value setter is used to set the data packet serial number incremental threshold value; the header decompressor, when receiving the voice data packet, according to the serial number incremental threshold value Determines whether to invalidate the session context. 9. The error recovery device according to claim 8, further comprising a timer located in the transmitting unit; when the header compressor sends the voice data packet, it decides whether to rebuild the session environment according to the value of the timer. 10. The error recovery device according to claim 9, wherein the timer is integrated in the header compressor or separated from the header compressor.

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