EP1532777A1

EP1532777A1 - System for compressing and transmitting multimedia data

Info

Publication number: EP1532777A1
Application number: EP03788154A
Authority: EP
Inventors: So-Young Lee; Seung-June Yi; Young-Dae Lee
Original assignee: LG Electronics Inc
Current assignee: LG Electronics Inc
Priority date: 2002-08-14
Filing date: 2003-08-13
Publication date: 2005-05-25
Also published as: WO2004017577A1; CN1647468B; KR100889864B1; KR20040016063A; CN1647468A; EP1532777A4; AU2003252556A1

Abstract

In a system in which multimedia data is compressed and broadcast or multicast to downlink, UTRAN is quickly transited to a full context formation state or a dynamic context formation state if plural terminals fail to form a full context or a dynamic context. Accordingly, the plural terminals can normally receive a header-compressed MBMS data in a U-mode of an ROHC technique.

Description

METHOD AND SYSTEM FOR COMPRESSING AND TRANSMITTING

MULTIMEDIA DATA

TECHNICAL FIELD

The present invention relates to a data compressing and transmitting method in a wireless mobile communication system, and more particularly to a method and system for compressing and transmitting multimedia data in an UMTS (Universal Mobile Telecommunications System).

BACKGROUND ART

With the remarkable development in a wireless mobile communication, a mobile phone is being more widely used than a wired phone. However, for a service providing a larger amount of data communication than a general voice communication to a mobile phone through a wireless access network, a wireless mobile communication is behind the performance of the existing cable communication system.

A communication system enabling the large amount of data is called IMT-2000, for which techniques development is being promoted in many countries and international cooperation proceeds for its standardization.

A universal mobile telecommunications system (UMTS) is a third generation mobile communication system that has evolved from a standard known as Global System for Mobile communications (GSM). This standard is a European standard which aims to provide an improved mobile communication service based on a GSM core network and wideband code division multiple access (W-CDMA) technology.

In December, 1998, the ETSI of Europe, the ARIB/TTC of Japan, the T1 of the United States, and the TTA of Korea formed a Third Generation Partnership Project (3GPP) for the purpose of creating the specification for standardizing the UMTS.

The work toward standardizing the UMTS performed by the 3GPP has resulted in the formation of five technical specification groups (TSG), each of which is directed to forming network elements having independent operations.

More specifically, each TSG develops, approves and manages a standard specification in a related region. Among them, a radio access network (RAN) group (TSG-RAN) develops a specification for the function, items desired, and interface of a UMTS terrestrial radio access network (UTRAN), which is a new RAN for supporting a W-CDMA access technology in the UMTS.

Figure 1 shows a network structure of a general UMTS.

As shown in Figure 1 , the UMTS is roughly divided into a terminal, a UTRAN and a core network. The UTRAN includes one or more radio network sub-systems (RNS).

Each RNS includes an RNC and one or more Node Bs managed by the RNCs.

The RNC handles allocation and management of a radio resource and serves as an access point with the core network. Node Bs receive information sent by the physical layer of a terminal (e.g., mobile station, user equipment and/or subscriber unit) through an uplink, and transmit data to a terminal through a downlink. Node Bs, thus, operate as access points of the UTRAN for terminal. The core network includes a mobile switching center (MSC) for supporting a circuit switched service, a gateway mobile switching center (GMSC), a serving GPRS support node (SGSN) for supporting a packet switched service, and a gateway GPRS support node (GGSN).

The services provided to the specific terminal is roughly divided into a circuit switched service and a packet switched service. For example, a general voice phone call service belongs to the circuit switched service, while a Web browsing service through an Internet connection is classified as the packet switched service.

In case of supporting the circuit switched service, the RNC is connected to the MSC of the core network, and the MSC is connected to a GMSC (Gateway Mobile Switching Center) managing a connection to other networks.

Meanwhile, in case of the packet switched service, services are provided by a SGSN (Serving GPRS Support Node) and a GGSN (Gateway GPRS Support Node) of the core network.

The SGSN supports a packet communication going toward the RNC, and the GGSN manages connection to other packet switched networks such as the Intemet.

An interface exists between various network components to allow the network components to give and take information to and from each other for a mutual communication. A cable interface between the RNC and the core network is defined as an lu interface.

Connection of the lu interface to the packet switched area is defined as an lu-PS, and connection of the lu interface to the circuit switched area is defined as an lu-CS.

A radio access interface between the terminal and the UTRAN is defined as a Uu interface.

Figure 2 shows a structure of a radio access interface protocol between a terminal and UTRAN on the basis of 3GPP radio access network standard.

The radio access interface protocol is vertically formed of a physical layer, a data link layer and a network layer, and is horizontally divided into a user plane for transmitting data information and a control plane for transmitting a control signal.

The user plane is a region to which traffic information of a user such as voice or an IP packet is transmitted. The control plane is a region to which control information such as an interface of a network or maintenance and management of a call is transmitted. In Figure 2, protocol layers can be divided into a first layer ( L1 ), a second layer (L2), and a third layer (L3) based on three lower layers of an open system interconnection (OSI) standard model well known in a communication system.

The first layer (L1), that is a physical layer, provides an information transfer service to the second layer, an upper layer, by using various radio transfer techniques.

The physical layer is connected to the MAC layer, an upper layer through a transport channel, and data is transferred between the MAC layer and the PHY layer through the transport channel.

L2 layer includes a medium access control (MAC) layer, a radio link control (RLC) layer and a packet data convergence protocol (PDCP) layer.

The MAC layer provides a re-allocation service of the MAC parameter for allocation and re-allocation of radio resources and is connected to the radio link control (RLC) layer through a logical channel.

Various logical channels are provided according to the kind of transmitted information. In general, when information of the control plane is transmitted, a control channel is used, and when information of the user plane is transmitted, a traffic channel is used. The LRC layer supports a reliable data transmission and performs functions of segmentation and reassembly of an RLC service data unit (SDU) received from an upper layer.

The RLC SDU received from the upper layer is controlled in its size to be suitable to a process capacity by the RLC layer, to which header information is added and transferred in a form of protocol data unit (PDU) to the MAC layer. An RLC buffer storing the RLC SDUs or the RLC PDUs received from the upper layer exists in the RLC layer.

The packet data convergence protocol (PDCP) layer is an upper layer of the RLC layer. A data transmitted through a network protocol such as an IPv4(internet Protocol version 4) or an IPv6 (intemet Protocol version 6) can be transmitted effectively on a radio interface with a relatively small band width by virtue of the PDCP layer.

For this purpose, the PDCP layer performs a function of reducing unnecessary control information used in the cable network, which is called a header compression.

As the header compression, header compression techniques called an RFC2507 or an RFC3095 (Robust Header Compression (ROHC) defined by an Internet standardization group called an IETF (Intemet Engineering Task Force).

With such header compression techniques, only information requisite for the header part is transmitted so that less control information can be transmitted and thus the amount of data to be transmitted can be reduced.

The RRC layer positioned in the lowest portion of the third layer is defined only in the control plane and controls the transport channels and the physical channels in relation to the setup, the reconfiguration and the release of the radio bearers (RBs).

A broadcast/multicast control (BMC) layer schedules a cell broadcast (CB) message received from the core network and transmits it to a specific cell, so that every terminal positioned in the cell receives the cell broadcast message. The BMC layer is used to handle only a broadcast function, and the DB message is short message formed of only a character and a numeric and consisting of a maximum 1230 octet between terminals or between a terminal and a system. At the side of UTRAN, information such as a message ID, a serial number or a coding scheme is added to the CB message received from an upper layer and transmitted in a BMC message form to the RLC layer. The BMC message is transmitted to the MAC layer through a CTCH (Common Traffic Channel) logical channel, and at this time, the CTCH logical channel is mapped with a FACH (Forward Access Channel) transport channel, and the FACH transport channel is mapped with a SCCPCH (Secondary Common Control Physical Channel).

The RRC layer positioned in the lowest portion of the third layer (L3). The RRC layer is defined only in the control plane and controls the logical channels, the transport channels, and the physical channels with respect to setup, the reconfiguration, and the release of the RBs. The RB signifies a service provided by the second layer for data transmission between the terminal and UTRAN, and setting-up of the RB means processes of stipulating the characteristics of a protocol layer and a channel required for providing a specific service and setting respective detailed parameters and operation methods.

For reference, the RLC layer can be included in the user plane and the control plane according to a layer connected to the upper layer. When the RLC layer belongs to the control plane, data is received from a radio resource control (RRC) layer. In the other cases, the RLC layer belongs to the user plane.

As shown in Figure 2, in case of the RLC layer and the PDCP layer, a plurality of entities can exist in one layer. This is because, in general, one terminal has a plurality of RBs, and only one RLC entity and only one PDCP entity are used for one RB.

The ROHC (Robust Header Compression) technique that the PDCP layer uses for header compression will now be described. The ROHC technique is generally used to reduce header information of RTP (Real-time transport protocol)/DUP (User Datagram Protocol)/IP (Intemet Protocol) packet.

The RTP/UDP/IP packet refers to a packet with related headers added thereto after the packet transmitted from the upper layer has passed the RTP, the UDP and the IP. The packet includes diverse and much header information required for data to be transmitted to a destination through the

Internet and recovered.

The ROHC technique is based on the fact that each field value of packet headers of consecutive packets belonging to one packet stream is almost fixed. Thus, the ROHC technique does not transfer an overall packet header field but transfer a varied field.

For reference, the overall header size of non-compressed RTP/UDP/IP packet is 40 octet in case of IPv4 (IP version 4) and 60 octet in case of IPv6, and generally, a pure data field of payload has a size of 15-20 octet.

Thus, as for the non-compressed RTP/UDP/IP packet, control information contained in a data has an even greater structure than the data which is to be actually transmitted. This means that its transfer efficiency is very low. Therefore, the header compression technique can considerably reduce the amount of control information, and a header compressed by the ROHC technique usually has a size of about 1 octet to 3 octet.

The ROHC technique is roughly divided into a uni-directional mode (referred to as 'U-mode', hereinafter), a bi-directional optimistic mode (referred to as 'O-mode', hereinafter), and a bi-directional reliable mode (referred to as 'R-mode', hereinafter).

In the U-mode, a uni-directional communication is performed from a sending side to a receiving side. Meanwhile, in the O-mode or R-mode, the sending side transfers a packet on a real time basis, and the receiving side transmits transmission state information to the sending side. Accordingly, the ROHC in the O-mode and the R-mode also controls a reverse transmission of a real time traffic packet upon receiving the ROHC status information (ACK or NACK) from the receiving side, as well as transmission of the header compression packet.

A use purpose of the ROHC status information transferred from the receiving side to the sending side can differ depending on the mode of the ROHC technique.

In the O-mode, the receiving side increases a compression efficiency by mainly transferring NACK related information, and in the R-mode, the receiving side uses a strict logic using the ROHC status information to support more robust header compression.

The U-mode of the ROHC technique will now be described in detail.

A compressor has three states of a full context formation state, a dynamic context formation state and a full context completion state. Different kinds of compressed header packets are transmitted in each state, and operation method differs in each state.

As shown in Figure 3, the full context formation state means a state that a full context should be formed because there is no full context or a full context has been completely damaged so it should be re-constructed.

The dynamic context formation state means a state that a dynamic context portion of the full context is damaged so it should be re-constructed. The full context completion state means a state that a full context is complete without a damage.

Each state is time out at every period and transited to a different state, and each period is different. For example, a transition period from the full context completion state to the full context formation state is even greater than a transition period from the full context completion state to the dynamic context formation state.

A multimedia broadcast/multicast service (MBMS) will now be described.

The MBMS has been proposed to complement the existing cell broadcast service (CBS) provided by the BMC layer which fails to support the multicast function and the size of transmittable short message is limited to a maximum 1230 octet.

As shown in Figure 4, the MBMS is a service for transmitting multimedia data such as audio, video or image data to plural terminals by using a uni-directional point-to-multipoint bearer service. The MBMS supports a broadcast mode and a multicast mode. That is, the MBMS supports an MBMS broadcast service and an MBMS multicast service.

The MBMS broadcast mode is a service for transmitting multimedia data to every user in a broadcast area. One or more broadcast areas may exist in one PLMN, one or more broadcast services can be provided in one broadcast area, and one broadcast service can be provided to several broadcast areas. The broadcast area means a broadcast service available area.

The MBMS multicast mode is a service for transmitting multimedia data only to a specific user group existing in a multicast area. One or more multicast areas can exist in one PLMN, one or more multicast services can be provided in one multicast area, and one multicast service can be provided to several multicast areas. The multicast area means a multicast service available area. As the MBMS transmits a multimedia as a broadcast or a multicast, a packet is considerably large in size, so a header part occupying much portion of the packet is compressed by using the header compression technique in order to heighten a data transmission efficiency. At this time, as the header compression technique for the MBMS service, the ROHC is used. However, MBMS, a uni-directional point-to-multipoint service, is not able to receive ROHC status information and only the U-mode among the three modes of ROHC is available for use.

As shown in Figure 5, regardless of whether a terminal, a receiving side of the MBMS, has successfully received a full header packet and normally formed a full context, or whether a dynamic context has been damaged, the receiving side transmits a corresponding packet to UTRAN, the sending side, in each of three states.

. In other words, in the MBMS, in order to heighten a data transmission efficiency, the header part of multimedia data is compressed into 1 ~2 octet by using ROHC technique, and in this respect, only U-mode of the ROHC technique can be used due to the characteristics of the unidirectional service. However, practically, the U-mode is a method for header compression at a point-to-point link, so that application of the U-mode as it is to the point-to-multipoint link such as the MBMS causes problems.

The problems caused with respect to operation at the point-to- multipoint link of U-mode are as follows.

For example, in case that multimedia data is header-compressed and simultaneously transmitted to several terminals that desire to receive a service by broadcasting and multicasting, UTRAN transmits a full header packet or dynamic context formation packet to the terminals and each terminal forms a full context or a dynamic context according to a type of a received packet. At this time, if each terminal successfully forms a context, it can successfully restore a compressed header packet that is transmitted thereafter. But, if the context formation is failed, it is impossible to restore a compressed header packet transmitted thereafter. That is, terminals can not receive the MBMS service.

Therefore, in the conventional art, if a terminal receives the full header packet or the dynamic context formation packet and fails to form a full context or dynamic context, it should wait until a transition period at which the full context completion state is transited to the dynamic context formation state or the full context completion state is transited to the full context formation state, that is, until time-out, and an operation starts newly in the full context formation state. Thus, the terminal, which has failed to form a context, can not receive the MBMS service for a considerably long period, causing degradation of a usefulness of the service.

As mentioned above, the conventional art has such a problem that when MBMS data with point-to-multipoint characteristics is compressed by using the U-mode of the ROHC at the point-to-point link, if plural terminals fail to form a full context, the header-compressed MBMS data can not be received until UTRAN, the sending side, is transited to the full context formation state, or to the dynamic context formation state in case that the terminals fail to form a dynamic context. The above references are incorporated by reference herein where appropriate for appropriate teachings of additional or alternative details, features and/or technical background.

DISCLOSURE OF THE INVENTION

Therefore, an object of the present invention is to provide a system and method for compressing and transmitting multimedia data in which if plural terminals fail to form a full context, UTRAN, a sending side, is quickly transited to a full context formation state, while if the plural terminals fail to form a dynamic context, UTRAN is quickly transited to a dynamic context formation state, to allow plural terminals to normally receive the header- compressed MBMS data in a U-mode of ROHC technique, thereby heightening a transmission efficiency. To achieve at least the above objects in whole or in parts, there is provided a multimedia data compressing and transmitting system including: UTRAN for compressing MBMS data by using a U-mode of ROHC technique according to a type of a context formation state and transmitting it; and a terminal for forming a corresponding context from a received packet, and transmitting corresponding context-damage information to UTRAN, a sending side, in case of failing to form a context.

UTRAN accumulates the number of full context-damage information and dynamic context-damage information received from the terminal through an RRC layer, and judges whether the number of each accumulated context- damage information is greater than or the same as a pre-set threshold value through comparison by the RRC layer or a header compression handling layer.

If the number of each context-damage information is greater than or the same as the pre-set threshold value, the RRC layer or the header compression handling layer is quickly transited to a previous corresponding context formation state.

If the terminal fails to form a context, an RRC layer of the terminal transmits context-damage information according to a type as an RRC message to the RRC layer of UTRAN. To achieve at least these advantages in whole or in parts, there is further provided a multimedia data compressing and transmitting method including: accumulating the number of context-damage information if a receiving side fails to form a context; and detecting whether the number of accumulated context-damage information is greater than or the same as a threshold value, and quickly transiting to a previous corresponding context formation state if the number of accumulated context-damage information is greater than or the same as the threshold value.

Therefore, in case that MBMS is compressed by using the U-mode of ROHC technique and transmitted, if the terminal, the receiving side, fails to form a full context with a full header packet, that is, the full context is - damaged, the terminal transmits full context-damage information to UTRAN, the sending side, and then, if the number of full context-damage information received from the receiving side is greater than the pre-set threshold value, UTRAN enables a compressor of the header compression handling layer to be transited to the full context formation state to transmit the full header packet, so that the full context can be quickly formed and the terminal can receive the MBMS service.

Meanwhile, if the terminal fails to form a dynamic context with a dynamic context formation packet, that is, the dynamic context is damaged, the terminal transmits dynamic context-damage information to UTRAN, the sending side, and if the number of dynamic context-damage information received from the receiving side is greater than the pre-set threshold value, UTRAN enables the compressor to be transited to the dynamic context formation state to transmit the dynamic context formation packet, so that the dynamic context can be quickly formed and the terminal can receive the MBMS service.

Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objects and advantages of the invention may be realized and attained as particularly pointed out in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in detail with reference to the following drawings in which like reference numerals refer to like elements wherein:

Figure 1 illustrates a network structure of a general UMTS system;

Figure 2 illustrates a structure of a radio access interface protocol between a terminal and UTRAN on the basis of 3GPP radio access network standards; Figure 3 illustrates a state of a compressor of general ROHC U-mode and transition process;

Figure 4 is an exemplary view showing point-to-multipoint characteristics of general MBMS;

Figure 5 is a flow chart of an operation of U-mode of ROHC in accordance with a conventional art;

Figure 6 is a block diagram showing a system for compressing and transmitting MBMS data by using ROHC technique in accordance with a preferred embodiment of the present invention; and Figure 7 is a flow chart of a method for compressing and transmitting

MBMS data by using ROHC technique in accordance with a preferred embodiment of the present invention.

MODES FOR CARRYING OUT THE PREFERRED EMBODIMENTS

Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings.

Figure 6 is a block diagram showing a system for compressing and transmitting MBMS data by using ROHC technique in accordance with a preferred embodiment of the present invention.

As shown in Figure 6, a system for compressing and transmitting MBMS data by using ROHC technique includes: UTRAN 620 for compressing MBMS data by using a U-mode of ROHC technique according to a type of a context formation state and transmitting it; and a terminal 610 for forming a corresponding context from a received packet, and transmitting corresponding context-damage information to UTRAN 620, a sending side, in case of failing to form a context.

UTRAN 620 receives the full context-damage information received from the terminal 610 through an RRC layer 621 and accumulates each number, and the RRC layer 621 or a header compression handling layer 622 judges whether the number of each accumulated context-damage information is greater than or the same as a pre-set threshold value. If the number of context-damage information is greater than or the same as the pre-set threshold value, the header compression handling layer 62 makes a state transition quickly to the previous corresponding context formation state. The threshold value may exist in the RRC layer 621 or in the header compression handling layer of UTRAN. The operation and effect of the present invention will now be described.

In the preferred embodiment of the present invention, the U-mode of ROHC technique, the header compression technique used for UTRAN for an MBMS service, not only transmit a packet for formation of a context but also receive information from the terminal, the receiving side, about whether it has successfully formed a context, for maintaining and managing so that context formation can be successful in the terminal at above a certain rate, thereby heightening a transmission efficiency.

As shown in Figure 6, if a packet received from the header compression handling layer 622 of UTRAN 620 damages a context, a header compression handling layer 612 of the terminal 610 transmits context- damage information to an RRC layer 611 and then the RRC layer 611 transmits context-damage information by using an RRC message. The RRC layer 621 of UTRAN 620 accumulates context-damage information received from the terminal according to types of context formation states.

Thereafter, the RRC layer 621 or the header compression handling layer 622 of UTRAN 620 judges whether the number of context-damage information is greater than or the same as the threshold value. If the number of context-damage information is greater than or the same as the threshold value, the header compression handling layer 622 is transited to the previous full context formation state or to the dynamic context formation state to transmit a packet for formation of a corresponding context.

In short by steps, in a first step, if the terminal 610 fails to form a context, UTRAN 620 accumulates the number of context-damage information received from the receiving side, and in a second step, it is checked whether the number of accumulated context-damage information is greater than or the same as the threshold value, and the state is quickly transited to a corresponding context formation state to transit a compressed header packet. Figure 7 is a flow chart of a method for compressing and transmitting

First, an operation process that UTRAN transmits a full header packet because a full context has not been formed or damaged in an area where one MBMS service is provided, that is, an operation process in a full context formation state of UTRAN, will now be described.

When the sending side is in the full context formation state (step S701), UTRAN initializes a variable (Failure-i) for storing the number of terminals with a damaged full context (step S702) received from terminals and transmits a full header packet to the terminal (step S703).

Next, UTRAN starts transmitting a compressed header packet regardless of whether a full context has been normally formed with the full header packet in the terminal (step S704). If UTRAN receives full context-damage information from the terminal

(steps S708 and S709), it recognizes that a full context has been damaged due to the full header packet in the terminal, increases the number of terminals with the damaged full context, and stores it in the variable (step S710). UTRAN compares the number of accumulated terminals with the damaged full context stored in the variable and the threshold value (N1 _Threshold) (step S711). If the number of accumulated terminals is greater than or the same as the threshold value, it returns to the full context formation state and the full header packet transmission process is repeatedly performed (steps S701 ~ S703).

If, however, the number of terminals with the damaged full context is smaller than the threshold value, the number of accumulated terminals with the damaged full context stored in the variable is maintained as it is, and the compressed header packet transmission process is continuously performed (step S704).

As mentioned above, in the present invention, if the full context is damaged in the terminal, the receiving side, the RRC layer of the terminal transmits the full context-damage information as an RRC message to the RRC layer of UTRAN, the sending side. At this time, UTRAN has the threshold value for the number of terminals with a damaged full context. The threshold value may exist in the RRC layer or the header compression handling layer of UTRAN.

If the threshold value exists in the RRC layer of UTRAN, the RRC layer compares the number of terminals with a damaged full context accumulated by being transmitted from terminals with the threshold value, and if the number of accumulated terminals is greater than the threshold value, the RRC transits the header compression state to the full context formation state to re-transmit the full header packet. Meanwhile, if the threshold value exists in the header compression handling layer of UTRAN, the RRC layer of UTRAN transmits the number of terminals with a damaged full context to the header compression handling layer, so that the header compression handling layer can compare it with the threshold value. If the number of accumulated terminals with a damaged full context is greater than the threshold value, it transits the header compression state to the full context formation state to re-transmit the full header packet.

As stated, in the case that the number of terminals with a damaged full context is greater than or the same as the threshold value so the header compression state is transited to the full context formation state, the number of accumulated terminals with a damaged full context is initialized to 0.

Second, an operation process that UTRAN transmits a dynamic header packet because a dynamic context has not been formed or damaged in an area where one MBMS service is provided, that is, an operation process in a dynamic context formation state of UTRAN, will now be described.

When the sending side is in the dynamic context formation state (step S705), UTRAN initializes a variable (Failurei) for storing the number of terminals with a damaged dynamic context (step S706) and transmits a dynamic header packet to the terminal (step S707).

Next, UTRAN starts transmitting a compressed header packet regardless of whether a dynamic context has been normally formed with the dynamic header packet in the terminal (step S704).

If UTRAN receives dynamic context-damage information from the terminal (steps S708 and S709), it recognizes that a dynamic context has been damaged due to the dynamic header packet in the terminal, increases the number of terminals with the damaged dynamic context, and stores it in the variable (step S712).

UTRAN compares the number of accumulated terminals with the damaged dynamic context stored in the variable and the threshold value (N1 Thres o_ld)- If the number of accumulated terminals is greater than or the same as the threshold value (S713), it returns to the dynamic context formation state and the dynamic header packet transmission process is repeatedly performed (steps S705 ~ S707). If, however, the number of terminals with the damaged dynamic context is smaller than the threshold value, the number of accumulated terminals with the damaged dynamic context stored in the variable is maintained as it is, and the compressed header packet transmission process is continuously performed (step S704). As mentioned above, in the present invention, if the dynamic context is damaged in the terminal, the RRC layer of the terminal informs the RRC layer of UTRAN of the dynamic context damage through an RRC message. At this time, UTRAN has the threshold value for the number of terminals with a damaged dynamic context. The threshold value may exist in the RRC layer or the header compression handling layer of UTRAN.

If the threshold value exists in the RRC layer of UTRAN, the RRC layer compares the number of terminals with a damaged dynamic context accumulated by being transmitted from terminals with the threshold value, and if the number of accumulated terminals is greater than the threshold value, the RRC transits the header compression state to the dynamic context formation state to re-transmit the dynamic header packet.

Meanwhile, if the threshold value exists in the header compression handling layer of UTRAN, the RRC layer of UTRAN transmits the number of terminals with a damaged dynamic context to the header compression handling layer, so that the header compression handling layer can compare it with the threshold value. If the number of accumulated terminals with a damaged dynamic context is greater than the threshold value, it transits the header compression state to the dynamic context formation state to re- transmit the dynamic header packet.

As stated, in the case that the number of terminals with a damaged dynamic context is greater than or the same as the threshold value so the header compression state is transited to the dynamic context formation state, the number of accumulated terminals with a damaged dynamic context is initialized to 0.

Especially, in the operation method of the full context formation state, in the case that the number of accumulated terminals with a damaged full context is greater than or the same as the threshold value so the header compression state is transited to the full context formation state, the number of accumulated terminals with the damaged dynamic context as well as the number of accumulated terminals with the damaged full context is also initialized to 0.

As so far described, the method and system for compressing and transmitting multimedia data of the present invention have the following advantage.

That is, if full context formation is failed in plural terminals, UTRAN, the sending side, quickly is transited to a full context formation state, whereas if a dynamic context formation is failed, UTRAN is quickly transited to a dynamic context formation state, so that the plural terminals can normally receive the header-compressed MBMS data in the U-mode of ROHC technique. Thus, a transmission efficiency can be heightened.

The foregoing embodiments and advantages are merely exemplary and are not to be construed as limiting the present invention. The present teaching can be readily applied to other types of apparatuses. The description of the present invention is intended to be illustrative, and not to limit the scope of the claims. Many alternatives, modifications, and variations will be apparent to those skilled in the art. In the claims, means-plus-function clauses are intended to cover the structure described herein as performing the recited function and not only structural equivalents but also equivalent structures.

Claims

1. A method for compressing and transmitting multimedia data of a wireless system in which multimedia data is compressed by a header compression technique and broadcast or multicast to downlink, wherein transition is made to a full context formation state of a header compression technique on the basis of a full context-damage information received from a terminal, and a full context is successfully formed by a packet received from the terminal at above a certain rate.

2. The method of claim 1 , wherein the transition to the full context formation state comprises: accumulating the number of terminals with a damaged full context on the basis of the full context-damage information terminals transmit when a full context is damaged; and checking whether the number of accumulated terminals with a damaged full context is greater than or the same as a threshold value, and transiting a header compression state to a full context formation state if the number of accumulated terminals with a damaged full context is greater than or the same as a threshold value.

3. The method of claim 1 , wherein if the multimedia data is compressed in the full context formation state, the compressed multimedia data is transmitted in a full header packet form to plural terminal.

4. The method of claim 1 , wherein the compression technique is a U-mode of an ROHC (Robust Header Compression) technique.

5. The method of claim 2, wherein the threshold value is set in a radio resource control (RRC) layer of UTRAN.

6. The method of claim 2, wherein the threshold value is set in a header compression handling layer of UTRAN.

7. The method of claim 2, wherein the number of terminals with a damaged full context is accumulated in the RRC layer of UTRAN, the sending side.

8. The method of claim 3, wherein when a terminal fails to form a context by using the full header packet, it transmits full context-damage information to its RRC layer, and then, the RRC layer of the terminal transmits the full context-damage information to the RRC layer of UTRAN.

9. The method of claim 8, wherein the full context-damage information of the terminal is transmitted to UTRAN by using an RRC message.

10. The method of claim 1 or 5, wherein the comparison between the number of terminals with a damaged full context and the threshold value set in the RRC layer of UTRAN is made at the RRC layer of UTRAN, the sending side.

11 . The method of claim 1 or 6, wherein the comparison between the number of terminals with a damaged full context and the threshold value set in the RRC layer of UTRAN is made at a header compression handling layer of UTRAN.

12. The method of claim 10, wherein if the number of accumulated terminals with a damaged full context is greater than or the same as the threshold value, the RRC layer of UTRAN commands the header compression handling layer of UTRAN to transit to the full context formation state.

13. The method of claim 12, wherein the header compression handling layer of UTRAN transits the header compression state to the full context formation state.

14. The method of claim 11 , wherein if the number of accumulated terminals with a damaged full context is greater than or the same as the threshold value, the header compression handling layer of UTRAN transits the header compression state to the full context formation state.

15. The method of claim 13 or 14, wherein when the header compression state is transited to the full context formation state, the number of accumulated terminals with a damaged full context is initialized to 0.

16. A method for compressing and transmitting multimedia data of a wireless system in which multimedia data is compressed by a header compression technique and broadcast or multicast to downlink, wherein transition is made to a dynamic context formation state of a header compression technique on the basis of a dynamic context-damage information received from a terminal, and a dynamic context is successfully formed by a packet received from the terminal at above a certain rate.

17. The method of claim 16, wherein the transition to the context formation state comprises: accumulating the number of terminals with a damaged dynamic context on the basis of the dynamic context-damage information terminals transmit when a dynamic context is damaged; and checking whether the number of accumulated terminals with a damaged dynamic context is greater than or the same as a threshold value, and transiting a header compression state to a dynamic context formation state if the number of accumulated terminals with a damaged dynamic context is greater than or the same as a threshold value.

18. The method of claim 16, wherein if the data is compressed in the dynamic context formation state, the compressed data is transmitted in a dynamic context formation packet form to plural terminal.

19. The method of claim 16, wherein the compression technique is a U-mode of an ROHC (Robust Header Compression) technique.

20. The method of claim 17, wherein the threshold value is set in a radio resource control (RRC) layer of UTRAN.

21. The method of claim 17, wherein the threshold value is set in a header compression handling layer of UTRAN.

22. The method of claim 17, wherein the number of terminals with a damaged dynamic context is accumulated in the RRC layer of UTRAN, the sending side.

23. The method of claim 18, wherein when a terminal fails to form a context by using the dynamic header packet, it transmits dynamic context-damage information to its RRC layer, and then, the RRC layer of the terminal transmits the dynamic context-damage information to the RRC layer of UTRAN.

24. The method of claim 23, wherein the dynamic context- damage information is transmitted to UTRAN by using an RRC message.

25. The method of claim 16 or 20, wherein the comparison between the number of terminals with a damaged dynamic context and the threshold value set in the RRC layer of UTRAN is made at the RRC layer of UTRAN, the sending side.

26. The method of claim 16 or 21 , wherein the comparison between the number of terminals with a damaged dynamic context and the threshold value set in the RRC layer of UTRAN is made at a header compression handling layer of UTRAN.

27. The method of claim 25, wherein if the number of accumulated terminals with a damaged dynamic context is greater than or the same as the threshold value, the RRC layer of UTRAN commands the header compression handling layer of UTRAN to transit to the dynamic context formation state.

28. The method of claim 27, wherein the header compression handling layer of UTRAN transits the header compression state to the dynamic context formation state.

29. The method of claim 26, wherein if the number of accumulated terminals with a damaged dynamic context is greater than or the same as the threshold value, the header compression handling layer of UTRAN transits the header compression state to the dynamic context formation state.

30. The method of claim 28 or 29, wherein when the header compression state is transited to the dynamic context formation state, the number of accumulated terminals with a damaged dynamic context is initialized to 0.

31. The method of claim 28 or 29, wherein when the header compression state is transited to the dynamic context formation state, the number of accumulated terminals with a damaged full context as well as the number of terminals with a damaged dynamic context is initialized to 0.

32. A multimedia data compressing and transmitting system in which multimedia data is compressed by a header compression technique and broadcast or multicast to downlink, comprising:

UTRAN for compressing MBMS data by using a U-mode of ROHC technique according to a type of a context formation state and transmitting it; and a terminal for forming a corresponding context from a received packet, and transmitting corresponding context-damage information to UTRAN, a sending side, in case of failing to form a context.

33. The system of claim 32, wherein the number of terminals with a damaged full context and the number of terminals with a damaged dynamic context are accumulated through an RRC layer.

34. The system of claim 32, wherein UTRAN sets threshold values in the RRC layer and a header compression handling layer to compare the number of terminals with a damaged full context and the number of terminals with a damaged dynamic context with them.

35. The system of claim 32, wherein when the number of terminals with a damaged context is compared with the threshold value, if the number of terminals with a damaged context is greater than or the same as the pre-set threshold value, UTRAN commends the header compression handling layer to transit the header compression state to a full context formation state or a dynamic context formation state.

36. A multimedia data compression and transmitting method of a wireless system in which multimedia data is transmitted by using a certain compression technique, comprising: transmitting a real time packet from a fixed station to mobile stations; receiving status information on the real time packet from the mobile stations; counting the number of received status information; and transiting the header compression state according to the counting result.

37. The method of claim 36 further comprising: comparing the number of counted status information with a threshold value; and transiting the header compression state to the full context formation state if the count value is greater than or the same as the threshold value.

38. The method of claim 37, wherein the threshold value is transmitted from the RRC layer.

39. The method of claim 36, wherein the compression technique is a U-mode of an ROHC (Robust Header Compression) technique.

40. The method of claim 36, wherein the status information is context-damage information.

41. The method of claim 40, wherein the context-damage information is the full context-damage information or the dynamic context- damage information.

42. The method of claim 36, wherein the header compression state is transited regardless of timeout of a current context state.

43. A multimedia data compression and transmitting method in a wireless system in which multimedia data is compressed by a header compression technique and broadcast or multicast to downlink, wherein a context formation state transition of a header compression technique is determined on the basis of context-damage information received from a terminal.

44. The method of claim 45, wherein the context-damage information is the full context-damage information or the dynamic context- damage information.