HK1084800B - Arrangements and method for controlling transmission of data bits - Google Patents

Description

Apparatus and method for controlling transmission of data bits

Technical Field

The present invention relates to communication systems and methods, and more particularly to controlling transmission of data bits in a bit transfer session.

Background

Communication networks for packet-based delivery of information in the form of data bits are well known to those skilled in the art. The internet is undoubtedly the most widely known data communication network. Various communication protocols have been developed for handling data communications. The transport protocol is used to transfer the data to the correct session. The transmission protocols UDP (user datagram protocol) and TCP (transmission control protocol) are used in the internet. UDP is a connectionless protocol without a flow control mechanism, while TCP is a connection-oriented protocol with a flow control mechanism that provides reliable data transfer between two hosts.

The growing importance of mobile communications has created a need for communicating data over wireless connections. The transfer of data over a wireless link may cause many problems and difficulties not encountered when transferring data over a fixed wired connection. The bandwidth of the air interface is a scarce and limited resource. Therefore, it is of interest to efficiently utilize the available radio resources. The bandwidth available for a radio connection in a mobile communication network may change very rapidly due to changes in the characteristics of the air interface, e.g. due to fading dips or shadows, or due to a redistribution of the bandwidth allocated to the users in a cell. The extremely limited bandwidth over the air interface, as well as the varying bandwidth, can make it difficult to provide an acceptable quality of service (QoS) to end users residing in the mobile system. For example, limited bandwidth may result in long latency, which is annoying to end users.

There are many solutions to how to improve the quality of service for end users residing in mobile systems.

Methods are discussed in g.c ō t é, s.shirani and f.kossenti, "best mode selection and synchronization for robust video communication over error-prone networks" (IEEE Journal on Selected Areas in Communications, vol.18, No.6, 6.2000 months) and in c.hsu, a.orga and m.khansari, "rate control for robust video transmission over error-prone radio channels" (IEEE Journal on Selected Areas in Communications, vol.17, No.5, 5.1999 months) on how channel state information can be used to make a more accurate decision on server control bit rate adjustment.

In "streaming proxy" of g.chenung and t.yoshimura: in the network proxy for media streaming in 3G wireless networks (IEEE Packet Video works 2002), a streaming proxy (SA) between wired and wireless networks is introduced in order to minimize the impact of congestion situations in the wired link under the assumption that the wireless link is almost lossless. The SA sends feedback to the server in time to track the wired link status. Thus, the server may take more appropriate rate exchange decisions.

Schieder et al, "GERAN's resource efficient streaming bearer concept" (WPMC 10 months 2002, Honolulu) discloses a method on how buffer fullness in a client can be used as a trigger for a feedback message to a server. The aim is to efficiently utilize the radio resources in a GSM/EDGE radio access network while providing a good QoS for the end user.

Us patent No. 6151300 describes a method of extending ATM network traffic control to hosts on a LAN communicating over an ATM network. By coordinating the flow control mechanism on the transport layer with the flow control mechanism on the ATM layer, situations that may lead to excessive packet loss and unstable performance can be avoided.

Praadep Sudame b.r.badrinath "support for providing protocol adaptation in a Mobile wireless network" [ Mobile Networks and Applications 0(1999) ], describes an adaptation mechanism that is performed on a Mobile host in response to network environment changes. For example, the adaptation may be a change in TCP initial window size.

In european patent application EP1126716, the concept of utilizing radio network information from a mobile network in order to adjust the application bit rate of a video data service faster and more accurately is introduced.

Many of the prior art solutions described above attempt to solve the QoS optimization problem for end users in mobile networks mainly for UDP based services, such as streaming/video services. For example, in EP1126716, a solution is provided for UDP based services. However, these methods do not solve the optimization problem for applications based on transport protocols with flow control mechanisms, such as TCP.

In addition, many of the above prior art solutions are client-centric, that is, they control the quality of service for the end user using feedback messages from the end user in the mobile system. One drawback of the client-centric solution is that it takes a considerable amount of time before the client does detect a change in the available bandwidth on the connection over the air interface. Since the radio environment is unstable, the client is required to perform filtering or averaging for a long period of time before a reliable feedback message can be sent. Furthermore, feedback messages from the end user must be transmitted over the radio connection to the control system, which adds additional delay to the input data to the control system.

Disclosure of Invention

It is an object of the present invention to provide improved methods and arrangements for controlling the QoS of end users and the use of radio resources for personal to content services in a mobile system.

The above object is achieved by a method according to claim 1, a computer program product according to claim 14, an apparatus according to claim 15 and a system according to claim 28.

A bit transfer session established between a client and an application server in a mobile system via a transport protocol with a flow control mechanism is associated with a plurality of flow control parameters. How to set these flow control parameters is critical for the quality of service of the session and for the utilization of the available radio resources. The present invention utilizes feedback information from the radio resource managing unit to set and update flow control parameters continuously throughout the session. According to the invention, the radio resource managing entity informs the network entity controlling the flow control parameters of the bandwidth allowed for the session over the air interface to the client. Such bandwidth information facilitates optimization of flow control parameters, which allows for enhanced QoS and efficient use of available radio resources.

According to a first aspect of the present invention, there is provided a method of controlling transmission of data bits in a bit transfer session for transmitting data information from an application server to a client, the bit transfer session involving bit transfer via wireless communication by means of a transport protocol with a flow control mechanism. The method comprises the following steps: the network entity receives information from the radio resource managing unit continuously throughout the session about the bandwidth on the wireless link currently allowed for the bit transfer session; and the network entity updating at least one parameter related to a flow control mechanism of the transport protocol in response to said received information in order to control the transmission rate of the session in accordance with the received information.

According to a second aspect of the present invention there is provided an apparatus for controlling transmission of data bits in a bit transfer session for transmitting data information from an application server to a client, the bit transfer session involving bit transfer via wireless communication by means of a transport protocol with a flow control mechanism. The apparatus is comprised in a network entity. The apparatus comprises receiving means for continuously receiving from the radio resource managing unit throughout the session information about the bandwidth on the wireless link currently allowed for the bit transfer session. Furthermore, the device comprises parameter setting means for continuously updating at least one parameter related to a flow control mechanism of the transport protocol in response to the received information throughout the session, in order to control the transmission rate of the session in dependence on the received information.

An advantage of the present invention is that it helps to optimally balance the traffic offered over the air interface by the back-end for person-to-content services over the packet switched domain, resulting in a better utilization of scarce radio resources.

Another advantage of the present invention is that since feedback information for controlling the flow control parameters is constantly provided from the radio resource managing entity located in the radio access network throughout the session, the flow control parameters will be updated according to the current information. This allows for a better parameter setting compared to prior art solutions where the flow control parameters are set only once at the start of a session based on historical data from previous sessions. Since the feedback information used by the present invention is passed from the radio access network to the network entity controlling the flow control parameters, the feedback information is not subject to as much delay as in the client-centric solution described above. The radio access network detects the available bandwidth change of the session faster than the client and does not need to communicate feedback information over the air interface.

The constant monitoring and updating of flow control parameters according to the present invention allows for good QoS throughout the session, not just at the start of the session. In prior art solutions, the parameter settings are not updated during the session, and there is a risk that the QoS may deteriorate during the session if the radio conditions encountered by the session change. Radio conditions may change very quickly and it is therefore more important to update the parameter settings of sessions involving the air interface than to update the parameter settings of sessions based entirely on wired connections.

Another advantage of the present invention is that network feedback is utilized separately for each session, which is used to update the flow control parameters of each session separately. Thus, the parameter settings may be particularly suitable for optimizing QoS for each session. According to some prior art solutions, flow control is handled for a session group. Even though prior art solutions allow few flow control decisions, these solutions may result in poor quality of service for a particular client that locally encounters radio conditions that are much worse than other clients in the same group, compared to the present invention.

Yet another advantage with the present invention is that the fidelity of the transmission rate to the available bit rate over the air interface can be improved. The present invention allows up-conversion and down-conversion of transmission rate according to network feedback information from the radio resource managing unit. The adaptation of the transmission rate according to the invention can be made smoother and more accurate than in prior art solutions. The invention avoids unnecessary application of congestion mechanisms that may lead to a sharp down-conversion of the transmission rate. In general, the present invention reduces extreme decisions based on misinterpretations of network conditions.

Yet another advantage of the present invention is that it can be adapted to all types of applications. The solution according to the invention makes the application network 'agnostic', which means that developers can focus their attention on customizing applications of the mobile environment without having to take into account the transmission medium of the network in particular.

Since the invention allows a faster and more accurate adaptation of the throughput to the currently available bandwidth over the air interface, the risk of overflow in the radio resource managing unit, such as the RNC or BSC, is reduced. Therefore, an additional advantage of the present invention is that the size of the buffer in the radio resource managing unit can be minimized.

Other advantages and objects of embodiments of the present invention will become apparent upon reading the following detailed description in conjunction with the accompanying drawings.

Brief Description of Drawings

Fig. 1 is a schematic block diagram illustrating a communication session between a client and an application server according to the prior art.

Fig. 2 is a schematic block diagram illustrating a communication session between a client and an application server in which the present invention is employed.

Fig. 3 is a diagram illustrating a comparison of the throughput of the sessions shown in fig. 1 and 2.

Fig. 4 is a schematic block diagram illustrating an embodiment of the present invention in a UMTS system.

Fig. 5 is a flow chart illustrating transmission rate adaptation based on network feedback according to the present invention.

Fig. 6 is a block diagram illustrating an alternative embodiment of the present invention in a UMTS system.

Fig. 7 is a combination block and flow diagram illustrating content transformation based on network feedback in accordance with the present invention.

Detailed Description

The present invention now will be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. In the drawings, like numbering represents like elements.

The invention is applicable to personal to content packet switched services in mobile systems, in particular to such services based on transport protocols with flow control mechanisms. Such services include packet communications between the user equipment of the end user and the application server. The mobile system comprises a mobile network, such as a WCDMA, CDMA2000, wireless LAN or GPRS network, in which the user equipment is located. One example of a transport protocol with a flow control mechanism is TCP. The flow control mechanism of TCP includes a number of flow control parameters as is well known to those skilled in the art. Examples of TCP flow control parameters are window size and segment size. The transmission of data bits over a TCP connection may be controlled by changing TCP flow control parameters.

When a communication session is established between a mobile user equipment and an application server, the available bandwidth over the air interface will generally be the limiting factor on the bit rate of the session. Characteristics of the air interface, such as fading dips and shadowing, can have a negative impact on the end user. This is especially true for applications that employ the TCP protocol as the transport bearer. For example, long latency on the air interface may trigger TCP congestion avoidance mechanisms, resulting in less bandwidth used for the session and very poor performance for the end user. On the other hand, if the end user temporarily gets increased bandwidth over the air interface, this will most likely not speed up the TCP connection to the same extent, meaning that scarce radio resources will not be utilized. Since radio resources on the air interface are scarce resources, it is of interest to use them as efficiently as possible, so that a more efficient use of the available radio resources is most likely to improve the quality of service for the end user.

Fig. 1 schematically illustrates a communication session between a client 1 and an application server 2 in a user equipment according to the prior art. Here, the application server 2 is a web server. The session is established over a TCP link 3 between the client 1 and the application server 2. When the client is browsing or downloading information from the application server, the client acknowledges receipt of the data, which thereby indicates the quality of the receipt. The application server uses the information from the acknowledgement to adapt TCP transmission parameters, such as window size or segment size, to the transmission conditions on the TCP link.

A problem with the approach in fig. 1 is that when the transmission link comprises a radio connection, there is a risk that bad radio connection conditions, including multiple retransmissions, are misinterpreted as congestion by the application server 2, thereby triggering the TCP congestion avoidance mechanism. In addition, radio conditions may change very quickly, but feedback in the form of acknowledgements comes later, which further reduces the ability of the server to adequately respond to changed radio transmission conditions. These disadvantages arise because the TCP transmission mechanism is not designed for radio transmission.

Fig. 2 is a schematic block diagram illustrating the basic principles of a communication session employing the present invention. A communication session is established between the client 1 and the application server 2 via the proxy 4 over TCP connections 3a and 3 b. The TCP connection 3b relates to transmission over a radio link in the mobile network 5. According to the invention, the mobile network reports network feedback data to the proxy regarding the quality of service of the radio link transmission. The proxy uses the network feedback data to change the TCP parameter settings of the TCP connection 3b, such as the TCP window size and the segment size. Network feedback may also be used to decide how to acknowledge receipt to the application server over the TCP connection 3 a.

The network feedback data reported to the proxy is information about the bandwidth that the radio resource managing unit of the mobile network has decided to allow the session to be used over the air interface.

Although fig. 2 illustrates the use of the invention for a session established via a proxy and two TCP connections 3a, 3b, the use of a proxy is not essential to the invention. If the session is established directly between the application server and the client without an intermediate proxy, the invention can be implemented such that the network feedback is provided directly to the application server. The application server may then use the network feedback to adequately adjust the TCP parameters of the session.

Fig. 3 is a diagram illustrating a comparison of throughput using the configurations according to fig. 1 and 2, respectively. The rectangular curve 18 illustrates that the radio resource managing unit of the mobile network has decided to allow the bandwidth used by the session over the air interface. Curve 10 illustrates the throughput curve of the prior art arrangement in fig. 1, and the thick curve 11 illustrates the throughput curve of the arrangement according to the invention in fig. 2.

Curve 10 illustrates that the transmission rate first increases exponentially until the maximum available bit rate over the air interface is reached. When this occurs, the client starts reporting "not received", which is interpreted by the application server 2 in fig. 1 as congestion. Thus, the application server employs a congestion avoidance mechanism, thereby greatly reducing the transmission rate. The application server then starts to increase the transmission rate linearly very slowly. This behavior of the application server does not correspond to the actual situation on the radio link.

In contrast, in fig. 2, the proxy 4 (or the server 2 in an embodiment where the network feedback is provided directly to the server) may take more appropriate and faster measures, as it receives the radio link information earlier, which provides a more accurate description of the radio transmission conditions. This is illustrated by the thick curve 11, which illustrates that with the network feedback according to the invention the throughput is increased faster and that the throughput is overall higher, leading to a better quality of service for the end user. With the configuration of fig. 2, an increase in available bandwidth over the air interface will quickly result in greater throughput. By correctly changing the TCP flow control parameters, it is even possible to adjust the transmission rate such that it is stable over a long period of time.

Fig. 4 illustrates an embodiment of the present invention in a UMTS system 20. The system comprises a radio access network 5 comprising a plurality of Base Transceiver Stations (BTS)19 and at least one Radio Network Controller (RNC) 6. The system also comprises a Serving GPRS Support Node (SGSN)9 and a Gateway GPRS Support Node (GGSN)8, which are nodes in a Core Network (CN)12 providing a connection between the radio access network 5 and a Serving Network (SN) 13. The nature and function of the elements in a UMTS system are well known to those skilled in the art and will not be described here.

The service network comprises an application server 2, a proxy 4 and a Service Network Session Database (SNSD) 7. A bit transfer session may be established between an application server 2 in the SN and a client in the User Equipment (UE)1 over a connection 3a, 3b via a proxy 4, a GGSN 8, a CN 12, an SGSN 9 and a radio access network 5. Alternatively, the session may be established between the UE1 and the application server 2 in the foreign network 14 with which the proxy communicates. The connections 3a, 3b may be, for example, TCP connections or connections based on another transport protocol with some kind of flow control mechanism.

As described above, the present invention provides an improved method for controlling the transmission rate of a session, which allows for end-user quality of service optimization. According to the embodiment of the invention in fig. 4, information about the allowed bandwidth on the air interface for the session is sent from the RNC 6 to the SNSD 7 over the connection 15. The SNSD is connected to the proxy 4 and transfers bandwidth information from the RNC to the proxy. The proxy has the ability to optimize the end user's quality of service based on the bandwidth information obtained from the RNC and its own internal algorithms.

The SNSD 7 may be configured to temporarily store bandwidth information from the RNC or forward the information directly to the application server 2 via a proxy. When the UE has activated a Packet Data Protocol (PDP) context, this PDP context contains, among other information, an Access Point Name (APN). The APN provides a logical connection between the UE and the SNSD. For example, the SNSD may store the following information for each UE:

-IP address of UE

-bit rate

Other information, such as the MSISDN of the subscriber, which may be of interest for other purposes than the present invention.

Since the SNSD provides the proxy with the currently allowed bit rate over the air interface, the proxy has the ability to set TCP flow control parameters, such as segment/window size, to adapt to radio resource conditions in an optimal way.

The flow chart of fig. 5 illustrates one example of how the QoS of an end user of a TCP based service, such as downloading or web surfing, may be optimized in accordance with the present invention.

Fig. 5 illustrates a procedure for TCP adaptation, where the TCP link between the UE and the application server is split into two parts, namely TCP connections 3a and 3b, respectively, as shown in fig. 4.

The initial conditions for the example shown in fig. 5 are as follows: the application server sends the payload at a certain bit rate according to the TCP mechanism specified by the IETF, step 31. Due to limitations on the air interface, the proxy is not allowed to forward incoming payloads at the same speed as it arrives. Thus, the proxy temporarily stores the incoming payload in a cache (not shown in the figure) and acknowledges to the application server by sending an Acknowledgement (ACK) as if the payload had been received by the client. This reduces the risk that a TCP congestion control mechanism will be employed. While also minimizing the total download time of the requested object/file.

According to the invention, the following steps are performed in the example of fig. 5:

step 32: the radio resource managing unit, e.g. the RNC, has found that the system has spare capacity and thus informs the SNSD that a particular session can enjoy a new higher bit rate.

Step 33: the agent may periodically check the SNSD for the current allowed transmission bit rate for a given session.

Step 34: in this case, the proxy gets a response from the SNSD indicating that the RNC allows a higher bit rate for a given session.

Step 35: the proxy's internal wireless TCP optimization algorithm adapts to the new conditions. Note that the bit rate coming out of the proxy may be temporarily greater than the input bit rate because the "old" payload is contained in its cache.

Step 36: the end user receives the content at the new bit rate.

Note that this graph shown in fig. 5 is a "snapshot" of the behavior of the network feedback based rate adaptation according to the present invention. The process shown in fig. 5 may be employed multiple times throughout a session as the allowed bit rate for the session on the air interface changes.

Fig. 4 and 5 illustrate an embodiment of the invention in which a proxy is employed and the TCP connection between the client and the application server is divided into two parts: a part between the client and the proxy and a part between the proxy and the application server. As mentioned above, the use of a proxy may be advantageous as it may reduce the risk of using TCP congestion avoidance mechanisms. However, as noted above, the use of an agent is not a requirement of the present invention. According to an alternative embodiment of the invention, the TCP connection 3 is directly from the UE to the application server, as shown in fig. 6. Also, the bandwidth information may go directly from the radio resource managing unit to the application server without using an intermediate database, such as SNSD. If a proxy is used, the proxy may be located in the serving network 13 as shown in fig. 4 or in the core network 12.

According to an alternative embodiment of the invention, the feedback information from the radio resource managing unit is sent to the application server or proxy via the UE 1. A disadvantage of this embodiment compared to the previously described embodiment is that the feedback information is obviously further delayed and also requires additional work by the UE. However, an advantage of looping feedback information via the client is that implementation of such an embodiment may require relatively minor changes in existing protocols.

The transmission rate adaptation based on network feedback from the radio resource managing unit can be supplemented with content switching as an additional measure to provide a good quality of service to the end user. Suppose a user is starting to download a large picture and the cell in which he is located is currently congested. The user may become annoyed by the long wait time for the download, thereby disconnecting the session. An alternative to this could be to speed up the download process by filtering out some information in the picture. The quality of the presentation of the picture is clearly reduced compared to the transmission of the complete information. However, it is convincing that latency has a more severe impact on the overall quality of service experience for the end user than otherwise. Network feedback from the radio resource managing unit helps to correctly determine when to apply the content conversion.

Fig. 7 schematically illustrates the relevant steps involved in content conversion. These steps are as follows:

step 41: the UE1 requests content from an application server 2, which may be e.g. an MMS server. The request is captured directly or indirectly by the agent 4.

Step 42: the agent 4 fetches the content from the application server.

Step 43: before sending the content to the UE1, the proxy 4 searches the SNSD 7 to find the bit rate currently allowable for the UE over the air interface. The IP address associated with the UE may be used to look up session information about the UE in the SNSD.

Step 44: a currently allowable bit rate is received in the proxy.

Step 45: the proxy 4 determines, through some QoS algorithm and the current allowable bit rate as input, that a content transformation is required for the default before passing on to the UE1 in this case. As mentioned above, one example of such a conversion may be a reduction of the information bits of a picture in order to reduce the transmission time.

Step 46: the content is converted and delivered to the UE1 as required.

It may be of interest to use network feedback information from the radio resource managing unit according to the invention for some sessions, but not for others. Therefore, the invention is preferably implemented to inform a resource management entity, e.g. a radio resource management unit, whether a feedback service is required for a session or not. Such notification may be done during i) configuration or ii) session establishment.

The embodiments of the invention described above are implemented in a UMTS system. However, the invention is applicable to many different types of packet-switched networks. For example, the invention may also be implemented in a 2G system, such as a GSM system.

The radio resource managing unit providing network feedback that can be used for transmission rate adaptation according to the present invention is an entity controlling the radio resources on the air interface. In the UMTS system this entity is the RNC, whereas in the GSM system this unit is the BSC. The radio resource managing unit may have other names in other types of networks. It is the radio resource managing unit that is aware of the circumstances regarding the current physical limitations of the air interface, the load information related to different ongoing sessions contending for radio resources in the cell, and other factors that may affect the bandwidth that a particular session may be allowed to use over the air interface. From what it knows, the radio resource managing unit determines the bandwidth, which is passed as network feedback and indicates the bandwidth a given session is allowed to use over the air interface.

There are different implementation alternatives for when the radio resource managing unit sends bandwidth information in the form of network feedback to the application server or proxy. However, it is important for the present invention that the radio resource manager constantly monitors the air interface and reports the current allowed bandwidth throughout the session in order to allow for optimal transmission rate adaptation. By "constantly" is here meant that the radio resource manager reports the allowed bandwidth of the session to the unit that sets the flow control parameters that affect the transmission rate of the session, so that the transmission rate can be adjusted when the radio conditions on the air interface change during the session. This may mean that the radio resource managing unit sends network feedback to the database or parameter setting entity each time the bandwidth that the session is allowed to use over the air interface is changed. Another alternative is that the radio resource managing unit sends information about the currently allowed bandwidth of the session at predetermined intervals, e.g. every 10 seconds. A disadvantage of the latter alternative is that the system may fail to accommodate the change in allowed bandwidth.

The adaptation of the flow control parameters affecting the transmission of bits in the session is performed based on bandwidth information from the radio resource managing unit. For this purpose, it is preferable to use some kind of optimization algorithm, in which the bandwidth information from the radio resource managing unit is a parameter. The choice and nature of the optimization algorithm is beyond the scope of the present invention. The parameter setting entity, such as an application server or proxy, may receive network feedback on the initiative of the radio resource managing unit, or may request this information from an intermediate database, such as the SNSD, or from the radio resource managing unit itself. The parameter setting entity preferably updates the flow control parameters affecting the transmission rate over the air interface immediately upon knowledge of the changed allowable bandwidth.

The adaptation of the flow control parameters according to the invention may result in an up-conversion or a down-conversion of the transmission rate based on the bandwidth information received from the radio resource managing unit. The received bandwidth information enables to provide an appropriate increase or decrease of the transmission rate in view of the available radio resources. By means of the invention the transmission rate can be adjusted more smoothly than by means of many prior art solutions. A smoother reduction of the transmission rate enables in many cases to avoid the application of congestion avoidance mechanisms. As mentioned above, congestion avoidance mechanisms may have an adverse effect on the quality of service. The invention thus allows a more accurate adaptation of the transmission rate to the prevailing radio conditions and a better and more uniform end user quality of service.

The invention allows the minimization of buffer size in a radio resource management unit, such as an RNC or BSC. This is possible because the risk of overflow in the radio resource managing unit is reduced when the transmission rate adapts faster and more accurately to the available bandwidth. For example, assume that the RNC is forced to reduce the available bandwidth from 64Kb/s to 32 Kb/s. Without network feedback, there is a risk that the application server or proxy continues to transmit at 64Kb/s at some time, while the RNC can only provide the air interface at 32 Kb/s. This means that the buffer in the RNC is starting to fill until the application server or proxy adjusts its transmission rate. If the buffer becomes full, the RNC is forced to discard the data, and the discarded data must be retransmitted. With network feedback, the application server or proxy will learn about the reduction in available bandwidth more quickly and will reduce the transmission rate more quickly. Thus, with the network feedback according to the present invention, the RNC needs a smaller buffer.

As described above, the present invention may reduce the risk of using a congestion avoidance mechanism. The congestion avoidance mechanism is a requirement of TCP specified by IETF. However, on a connection within the operator's domain, the operator may choose to disable some of the IETF's requirements on the internet. Thus, when using the present invention, the operator may choose to employ a modified TCP connection between the proxy and the UE, with the congestion avoidance mechanism completely disabled. This allows more liberal setting of parameters for the modified TCP connection.

When implementing the present invention in existing communication systems, existing software and/or hardware will have to be modified, as will be appreciated by those skilled in the art. In most cases, the modification is primarily a software modification. The radio resource managing unit has to be modified so that it can deliver the network feedback according to the invention to another unit, such as the SNSD, a proxy or an application server. In the embodiment shown in fig. 4, one way to convey rate information to the SNSD is to use an established GTP-U tunnel between the RNC and the GGSN. However, this requires additional functionality of the GGSN. Another approach may be to directly inform the RNC about the IP address of the SNSD at i) configuration or ii) session establishment. In this way, the RNC updates the effective bit rate in the SNSD without any inquiry from the intermediate node. Furthermore, according to the present invention, the parameter setting unit that updates the session parameters according to the network feedback must be modified to be able to receive and interpret the network feedback and to be able to adapt the parameters according to the received network feedback. It will be clear to a person skilled in the art how the present invention can be implemented in known hardware and software ways. The network feedback mechanism according to the invention can be implemented using a separate protocol established for this purpose.

In the drawings and specification, there have been disclosed typical preferred embodiments of the invention and, although specific terms are employed, they are used in a generic and descriptive sense only and not for purposes of limitation, the scope of the invention being set forth in the following claims.

Claims (28)

1. A method of controlling transmission of data bits in a bit transfer session for transmitting data information from an application server (2) to a client (1), the bit transfer session involving bit transfer over a wireless communication link by means of a transmission protocol having a flow control mechanism, characterized by the steps of:

-the network entity (2, 4) continuously receiving (32, 34) from the radio resource managing unit (6) throughout the session information about the bandwidth on the wireless link currently allowed to be used by the bit transfer session; and

the network entity updates (35) at least one parameter relating to the flow control mechanism of the transport protocol in response to the received information, so as to control the transmission rate of the session in accordance with the received information.

2. The method of controlling transmission of data bits according to claim 1 characterised in that the network entity (2, 4) receives the information from the radio resource managing unit each time the bandwidth on the radio link that the bit transfer session is allowed to use has changed.

3. The method of controlling transmission of data bits according to claim 1 characterised in that the network entity (2, 4) receives the information from the radio resource managing unit at predetermined intervals.

4. A method of controlling transmission of data bits according to any of claims 1-3 characterised in that the network entity is an application server (2).

5. A method of controlling transmission of data bits according to any of claims 1-3 characterised in that the bit transfer session is established between an application server (2) and a client (1) via a proxy (4) and the network entity is the proxy.

6. The method of controlling transmission of data bits according to claim 5 characterised in that during the bit transfer session, the proxy (4) sends an acknowledgement of the reception of a data packet from an application server (2) to the application server (2) if the information received from the radio resource managing unit (6) indicates that the proxy (4) is not allowed to forward the data packet at the same speed as it arrives.

7. A method of controlling transmission of data bits according to any of claims 1-3 characterised in that the network entity (2, 4) receives the information from a radio resource managing unit (6) via a client (1).

8. A method of controlling transmission of data bits according to any of claims 1-3 characterised in that the transmission protocol is TCP.

9. The method of controlling transmission of data bits according to claim 8 characterised in that said at least one parameter is TCP window size and/or TCP segment size.

10. A method of controlling transmission of data bits according to any of claims 1-3 characterised in that in response to the information received from the radio resource managing unit (6), the network entity (2, 4) also converts the data to be transmitted during the bit transfer session.

11. A method of controlling transmission of data bits according to any of claims 1-3 characterised in that after updating the at least one parameter the bandwidth on the wireless link used by the bit transfer session is increased or decreased.

12. A method of controlling transmission of data bits according to any of the claims 1-3 characterised in that the radio resource managing unit is a radio network controller (6).

13. A method of controlling transmission of data bits according to any of claims 1-3 characterised in that the radio resource managing unit is a base station controller.

14. An arrangement for controlling transmission of data bits in a bit transfer session for transmitting data information from an application server (2) to a client (1), said bit transfer session involving bit transfer over a wireless communication link by means of a transmission protocol with a flow control mechanism, characterized in that the arrangement is comprised in a network entity (2, 4) and in that the arrangement comprises:

-receiving means for continuously receiving from a radio resource managing unit (6) throughout said session information about the bandwidth on the wireless link currently allowed to be used by said bit transfer session; and

parameter setting means for updating at least one parameter related to the flow control mechanism of the transport protocol in response to the received information, so as to control the transmission rate of the session in accordance with the received information.

15. The apparatus for controlling transmission of data bits according to claim 14 characterised in that the receiving means is configured to receive the information from the radio resource managing unit (6) whenever the bandwidth on the radio link that the bit transfer session is allowed to use has changed.

16. The apparatus for controlling transmission of data bits according to claim 14 characterised in that the receiving means is configured to receive the information from the radio resource managing unit (6) at predetermined intervals.

17. An arrangement for controlling transmission of data bits according to any of the claims 14-16 characterised in that the network entity is the application server (2).

18. An arrangement for controlling transmission of data bits according to any of claims 14-16 characterised in that the bit transfer session is established between an application server (2) and a client (1) via a proxy (4) and that the network entity is the proxy (4).

19. The apparatus for controlling transmission of data bits according to claim 18 characterised in that the proxy (4) is configured to send an acknowledgement of the reception of a data packet from an application server (2) to the application server (2) if the information from the radio resource managing unit (6) indicates that the proxy (4) is not allowed to forward the data packet at the same speed as it arrives during the bit transfer session.

20. An arrangement for controlling transmission of data bits according to any of claims 14-16 characterised in that the receiving means is arranged to receive the information from a radio resource managing unit (6) via a client (1).

21. The apparatus to control transmission of data bits according to any of the claims 14-16 characterised in that the transmission protocol is TCP.

22. The apparatus for controlling transmission of data bits according to claim 21 characterised in that said at least one parameter is TCP window size and/or TCP segment size.

23. An arrangement for controlling transmission of data bits according to any of claims 14-16 characterised in that the arrangement further comprises means for converting data to be transmitted during the bit transfer session in response to the information from the radio resource managing unit (6).

24. The apparatus for controlling transmission of data bits according to any of claims 14-16 characterised in that after the parameter setting means updates the at least one parameter the bandwidth over the wireless link used by the bit transfer session is increased or decreased.

25. The apparatus for controlling transmission of data bits according to any of the claims 14-16 characterised in that the radio resource managing unit is a radio network controller (6).

26. The apparatus for controlling transmission of data bits according to any of the claims 14-16 characterised in that the radio resource managing unit is a base station controller.

27. A system for controlling transmission of data bits in a bit transfer session involving bit transfer over a wireless communication link by a transport protocol having a flow control mechanism, the system comprising:

the apparatus of any one of claims 14-16, and

a radio resource management unit (6) configured to constantly send information to receiving means of the device about the bandwidth on the wireless link currently allowed to be used by the bit transfer session throughout the session.

28. The system for controlling transmission of data bits according to claim 27 characterised in that the system further comprises a storage unit (7), the radio resource managing unit (6) is configured to send the information to the device via the storage unit, and the storage unit is configured to forward the information from the radio resource managing unit to the device.