WO2009024188A1

WO2009024188A1 - Data transmission control

Info

Publication number: WO2009024188A1
Application number: PCT/EP2007/058714
Authority: WO
Inventors: Reiner Ludwig; Per Willars
Original assignee: Telefonaktiebolaget Lm Ericsson (Publ)
Priority date: 2007-08-22
Filing date: 2007-08-22
Publication date: 2009-02-26

Abstract

A method of controlling a data transmission over a terminal of a data unit communication network using a transport service offered by said data unit communication network is described. The data transmission comes from a data source (application) associated with said terminal. The data source receives from the data unit communication network one or more indicators comprising first information for determining a value of a first parameter indicating a minimum transmission capacity (e.g. guaranteed bit rate) of said transport service, and second information for determining a value of a second parameter indicating a current transmission capacity (e.g. available bit rate) of said transport service. Then a transmission rate of the data source is adjusted in dependence on at least the second information.

Description

[ Title ]

Data transmission control

[Background of the invention]

The present invention relates to methods and devices for controlling a data transmission over a data unit communication network using a specified transport service offered by the data unit communication network to a terminal.

[Background]

In the field of data unit communications it is known to offer a specified transport service for the transmission of data units over a network. Such a transport service is constituted by associating certain values with service quality parameters of the transport service, e.g. assigning a value to a minimum transmission capacity (sometimes also referred to as a guaranteed bit rate) parameter and assigning a value to a maximum transmission capacity parameter (sometimes also referred to as a maximum bit rate) . A data source associated with a terminal of the network providing the transport service can then be appropriately controlled on the basis of the values assigned to the service quality parameters.

An example of a transport service is a bearer allocated by a communication network for a data transmission of a given terminal of that network. An example of such a network is a mobile telephone network using GPRS, as e.g. can be taken from 3GPP specification TS23.401 describing the so-called evolved 3GPP Packet Switched Domain, which is also referred to as the evolved packet system (EPS) . The evolved 3GPP packet switched domain provides IP connectivity using the evolved universal terrestrial radio access network (E-UTRAN) . Figure 2 schematically shows a system comprising a communication arrangement 20 that contains a data source 201 and a terminal 202 that is part of a network 21, where communication can e.g. be conducted via an access node 210 (e.g. a base station) and a gateway node 211 towards further networks. The communication arrangement 20 can e.g. be a mobile telephone, where the data source 201 can e.g. be an application that generates data (e.g. video telephony) and the terminal 202 is the communication part arranged for executing data transmissions to and from the network 21. In other words, the data source 201 and the terminal 202 can be logically separate parts of a single physical unit, or they can also be physically separate parts.

It is noted that the term "data unit" is used generically in the context of the present specification and claims, and refers to any subdivision of data used for transporting a quantity of data, where such subdivisions carry different names depending on context and protocol, for example frame, packet, segment, protocol data unit, etc.

It is furthermore known that data sources can be rare adaptive, i.e. can adjust their data rate variably. For example, che sending data rate of a data source can be adapted by varying the source encoding rate of a data encoder, such as a speech encoder or video encoder.

In such systems, in which a minimum transmission capacity and a maximum transmission capacity for a transport service are indicated to a data source, there exists the basic problem for the data source to appropriately adjust its data rate, especially when the transport service is being established or modified. Namely, if the maximum transmission capacity assigned to the transport service exceeds the minimum transmission capacity assigned to the transport service, then the data source does not know which value to set for its transmission rate. More specifically, as the area of transmission capacity between the minimum transmission capacity and the maximum transmission capacity is not guaranteed by the network, it is difficult to judge whether or not to set the sending data rate larger than the minimum transmission capacity or guaranteed bit rate of the transport service. In the prior art, the consequence of this insecurity has been to practically set the minimum and maximum transmission capacity to the same value, thereby eliminating the above-mentioned insecurity. On the other hand, this has the disadvantage of not making use of the possibility of assigning a larger maximum than minimum transmission capacity to a transport service, and consequently does not allow for a rate adaptive data source to possibly exploit surplus bandwidth that a network might at least temporarily offer beyond the minimum or guaranteed transmission capacity.

[Object]

The object of the present invention is to provide improved concepts of data unit communication, especially in view of rhe above-mentioned problems .

[Summary of the invention]

The above object is solved by the subject-matter of the independent claims. Advantageous embodiments are described in the dependent claims.

In accordance with one aspect of the invention, a method of controlling a data transmission over a terminal of a data unit communication network using a transport service offered by the data communication network is described, where the data transmission comes from a data source associated with the terminal. According to this method the data source receives from the data unit communication network one or more indicators comprising a first information for determining a value of a first parameter indicating a minimum transmission capacity of the transport service (e.g. a guaranteed bit rate of a bearer) , and a second information for determining a value of a second parameter indicating a current transmission capacity of the transport service . An example of such information would e.g. be an available bit rate of a bearer, i.e. the bit rate that said bearer currently offers at that moment. In accordance with this concept, the data source can then adjust its transmission rate in dependence on at least the second information.

By virtue of the providing of the second information, which enables the data source to determine the value of the current transmission capacity, there exists none of the above- mentxoned insecurity as to how to adjust the momentary sending rate of the data source. It is noted that this advantage can be achieved independent of whether or not an information for determining a value of a parameter indicating the maximum transmission capacity is also provided to the data source, because if the value of the current transmission capacity indicated to the data source exceeds the value of the minimum transmission capacity, then the data source can in any case adjust to the current value, regardless of whether or not a maximum value of the transmission capacity is also indicated.

The concept is particularly well suited for application to data sources that are rate adaptive and send real time traffic. Namely, it is generally considered undesirable for real-time sources to probe for non-guaranteed transmission capacity (e.g. by steadily increasing its data rate until negative feedback sets in) , where an excessive data rate would be signalled by way of data unit dropping. Namely, data unit dropping is undesirable, as it degrades the quality of the real-time transmission. With the concept of the invention, the data source receives information that allows an adjustment to a currently available transmission capacity, thereby avoiding the disadvantages of band-width probing, but at the same time allowing the use of non-guaranteed band- width.

According to another aspect, the invention also extends to a communication arrangement comprising a terminal and a data source, which are arranged co perform the above-described method.

According to a further aspect, the invention relates to a method of controlling a data communication network, especially of controlling a dedicated entity of the network that is responsible for allocation of a transport service, in such a way that it associates with the transport service values for a plurality of transmission capacity parameters that comprise at least the first parameter indicating a minimum transmission capacity and the second parameter indicating a current transmission capacity of the transport service. Then, the above-mentioned first information for determining a value of the first parameter and second information for determining a value of the second parameter is sent to the terminal.

Preferably, the above method is employed in the context of a network that comprises a first entity arranged for handling an access connection between the terminal and an access network of the data communication network, where such an entity can for example be a base station, a base station controller or a radio network controller in the situation in which the terminal is a radio terminal. In this case this first entity can determine the value of the second parameter based on characteristics of the access connection between the terminal and the access network. The data communication network may also comprise a second entity separate from the first entity, which is arranged to send a request to the first entity, where the request specifies values for a plurality of quality of service parameters comprising the first parameter, and where the second entity then receives an acknowledgment in response to the request together with the value of the second parameter that indicates a current transmission capacity. The corresponding information is then provided to the terminal by the second entity. An example of such a second entity is a core network control entity or a gateway entity connecting the data unit transmission network to other networks.

The present invention also extends to such a first entity and second entity.

[Brief description of Figures]

Now detailed examples of the invention will be described with reference to the drawings, in which

Fig. 1 shows a flow chart of a basic embodiment of the invention implemented in connection with a terminal and data source;

Fig. 2 shows a schematic block diagram of a communication arrangement and network;

Fig. 3 shows a schematic block representation of elements involved in a communication and corresponding signalling;

Fig. 4 shows a flowchart of a basic method embodiment implemented in a network entity, and

Fig. 5 shows a flowchart of a further method embodiment of the invention. [Detailed description]

In the following detailed examples of the invention will be described. It is noted that reference will be made to specific technologies and standards, such as GPRS (General Packet Radio Service) or 3GPP TS23.401, but such references only serve to indicate preferred examples but are in no way limiting. Rather, the present invention can be generally applied in the context of any communication system that provides for the use of specified transport services (such as bearers) that are characterised by at least a parameter indicating a minimum transmission capacity and where a data source associated with a terminal can adjust its transmission rate.

A transport service within the meaning of the present specification and claims is a service offered to a terminal for transporting data units. The transport service is characterized by a set of values associated with respective service quality parameters, e.g. values associated with a guaranteed bit rate parameter and a maximum bit rate parameter. The service can comprise many individual parts for transporting data, such as various links and channels. An overall transport service from a terminal to a gateway of a network can comprise a number of sub-services, as e.g. an Evolved Packet System (EPS) bearer can comprise a concatenation of a number of sub-bearers, such as a radio bearer, an Sl bearer and a S5/S8 bearer. An EPS bearer or a radio bearer is an example of a transport service.

The transmission capacity indicates an amount of data that can be sent within a given period of time. It can be expressed in any suitable way, e.g. as a bit rate or byte rate. In the following, the transmission capacity will generally be exemplified as a bit rate. Ir is furthermore noted that within the context of the present specification and claims the term "minimum transmission capacity" or "guaranteed bit rate" does not mean that such a transmission capacity or bit rate is always provided to the terminal. For example, if the terminal is a radio terminal {e.g. part of a mobile phone), then there can be periods of complete communication interruption due to environmental circumstances. Nonetheless, the network will always control its resources in such a way that the minimum or guaranteed bit rate is provided for the transport service to the terminal under all conditions that are under its control, In other words, the '"minimum" or "guaranteed" transmission capacity indicates the assignment of a desired quality for the transport service, i.e. a service quality parameter characterizing the transport service is set to this value, and the network will be controlled to provide this quality to the service if it is in any way possible.

On the other hand, the "maximum transmission capacity" or

"maximum bit rate" is a service quality parameter associated with the transport service by the network that indicates the upper limit that the network will provide for the transport service to the terminal. If the maximum transmission rate is set to a larger value than the minimum transmission rate, then there is no assurance on the part of the network that any value of the transmission rate that exceeds the minimum transmission capacity will be provided. As a consequence, when a data source is informed that the transport service that it uses or is going to use has a value of the maximum transmission capacity that exceeds the value of the minimum transmission capacity, then the data source is not able to properly adjust a sending rate that exceeds the minimum transmission capacity, as the data source does not know whether such a data rate that goes beyond the minimum transmission capacity is actually available at that moment. In accordance with the present invention, a new service quality parameter for transport services offered to terminals is introduced. This new parameter indicates a current transmission capacity of the transport service, i.e. a momentary value of the transmission capacity on the transport service. Such a parameter could e.g. be referred to as an Offered Bit Rate (OBR) . It should be noted that this is value is descriptive of the momentary situation and that it can quickly change.

Figure 1 shows a first example of the invention, namely a method of controlling a data transmission over a terminal of a data communication network using a transport service, such as a bearer, offered by the data communication network to the terminal. The data transmission comes from a data source associated with the terminal, such as the data source 201 associated with the terminal 202 shown in Figure 2. According to the method of Figure 1, the data source receives from the data communication network one or more indicators that comprise first information for determining a value of the first parameter that indicates a minimum transmission capacity of the transport service, and a second information for determining a value of a second parameter indicating the current transmission capacity of the transport service, see step SlO. Then, the transmission rate of the data source is adjusted in dependence on at least the second information, see step SIl.

It is naturally possible that the transmission rate of the data source can also be adjusted in dependence on further information, e.g. values of other service quality parameters than the second parameter. It should also be noted that the network could offer more than one transport service to the terminal, e.g. a plurality of bearers .

The indicators comprising information can be chosen in any suitable and desirable way for conveying the desired information. For example, the values of the first and second parameter can be the Indicators themselves, i.e. control messages are sent to the terminal that comprise the values of the first parameter and the second parameter, and these parameter values are then given to the controller of the data source for adjusting the transmission rate. However, the information can also be conveyed indirectly. For example, it is possible that the parameter values can only assume predefined values, and the indicators sent to the terminal can be simple codes that each identify one of the predetermined values.

As a further example, it Is also noted that the concept of the invention can be applied in a system that is able to on the one hand assign a minimum transmission capacity or guaranteed bit rate to a transport service, and on the other hand can also establish a transport service for which no minimum transmission capacity or guaranteed bit rate is assigned. Such a situation is known from GPRS and described in 3GPP TS23.401, in which so-called GBR bearers (i.e. bearers having a guaranteed bit rate) and non-GBR bearers (i.e. bearers for which no bit rate is guaranteed) are definable. In the context of the present invention, a transport service for which no minimum transmission capacity or guaranteed bit rate is assigned will be understood as a transport service having a minimum transmission capacity of zero. In other words, the network does not guarantee to allocate its resources in such a way that any specific bit rate larger than zero is provided. Nonetheless, the concept of the present invention is also applicable in such a case, as it is still useful for the data source to learn the value of the current transmission capacity, in order to be able to appropriately adjust its transmission rate.

In this case, the indicator that comprises first information for determining a value of the first parameter that indicates the minimum transmission capacity can e.g. be an identification that no minimum transmission capacity is assigned, or can be an indirect indicator such as simply being the lack of an entry in a field of a control unit designed to convey the value of the minimum transmission capacity parameter.

The indicators sent from the data unit communication network to the data source can comprise information relating to values of further service quality parameters, for example the indicators can comprise information for determining a value of a parameter that indicates a maximum transmission capacity of the transport service.

As already mentioned, the indicators and the information can be chosen in any suitable or desirable way. For example, in a system in which the indicators comprise the first information for determining a value of the first parameter that indicates a minimum transmission capacity of the transport service and the third information for determining the value of the third parameter that indicates a maximum transmission capacity of the transport service, the second information can e.g. be arranged to assume two states, a first state that indicates that the value of the second parameter is equal to the value of the first parameter, and a second state indicating that the value of the second parameter is equal to the value of the third parameter. In other words, taking a guaranteed bit rate (GBR) as an example of the first parameter and a maximum bit rate (KSBR) as an example of the third parameter, then the second information can assume a first state such that the offered bit rate (OBR) as an example of the second parameter is equal to GBR and another state according to which OBR is equal to MBR. This solution has the advantage of simplicity, as the information indicating the value of the second parameter can e.g. be coded in a single bit.

The newly introduced second information for determining a value of the second parameter that indicates a current or momentary transmission capacity of the transport service can be received by the terminal and data source during one or more predetermined processes related to the offered transport service. For example, it can be received during the process of establishing the offered transport service and/or during a process of modifying the offered transport service and/or during a process of handing over to the offered transport service.

Preferably, the second information is only received once during the respective process, for adjusting an initial transmission rate. As a consequence, if the second information is sent by the data unit communication network during the establishment of the transport service, then the data source can set its initial data rate in dependence on that information, e.g. equal to the indicated momentary bit rate value. As already mentioned previously, the value of the second parameter indicates a current transmission capacity, and the current transmission capacity can quickly change. As a consequence, it is possible that the data source will change its data rate again after a certain time, depending on control procedures conducted in the data source, and possibly with the help of direct or indirect feedback from the data unit communication network.

It is also possible that the second information is sent by the data communication network and consequently received by the terminal and data source repeatedly during the communication that uses the offered transport service. For example, the second information could be sent at regular intervals, in order to constitute a form of network feedback.

The just described methods of controlling a data transmission are preferably implemented as a control procedure in a communication arrangement that comprises a network terminal and a data source. As already mentioned in connection with Figure 2, such a communication arrangement 20 can be a mobile telephone that comprises a terminal part 202 and a dara source part 201, e.g. an application running on a processor that generates audio and/or video data. It is noted that the above-described methods can also be embodied as a computer program comprising computer program code parts for performing the described methods when executed in a communication device, such as e.g. in a mobile telephone. Furthermore, the invention can also be embodied as a computer program product comprising such a computer program, e.g. as a data carrier containing the computer program.

The invention can also be embodied as such a described communication arrangement 20 for data unit communication over a data unit communication network 21, comprising a terminal 202 and a data source 201 arranged for receiving from the data communication network 21 one or more indicators comprising the first information for determining the value of the first parameter and the second information for determining the value of the second parameter, and where the data source 201 is furthermore arranged to adjust the transmission rate in dependence on at least the second information .

It is noted that the communication arrangement can be a wireless communication device such as a mobile telephone. However, the invention can equally be applied in the context of wire-bound communications. Also, although the communication arrangement can be a single physical unit, such as a mobile telephone, it can also consist of a plurality of physical units.

In correspondence to the methods described in connection with Figure 1, the present invention also relates to a method of controlling a data unit communication network for offering a transport service to a terminal as shown in Figure 4. Namely, in a first step S40 values for a plurality of transmission capacity parameters are associated with the transport service, where the transmission capacity parameters comprise at least the first parameter indicating the minimum transmission capacity of the transport service and the second parameter indicating the current transmission capacity of the transport service. Then, in step S41 the first information for determining the value of the first parameter and the second information for determining the values of the second parameter is sent to the terminal.

The transmission capacity parameters can also comprise further parameters, such as the third parameter that indicates the maximum transmission capacity of the transport service, where an appropriate value is then also sent to the terminal .

The minimum transmission capacity value associated with the transport service can be determined in any suitable or desirable way. For example, this can be done in response to a requested value from the data source associated with the terminal, and/or the value assigned can also depend on subscription related information, and/or operator policy for a specific service. For example, if the provider of the data communication network has different classifications of subscribers, such as subscribers with preferential treatment ("gold subscribers") , then such subscribers with preferential treatment may by default have a larger value assigned to the minimum bit rate for the transport service than less privileged subscribers {e.g. "silver users" or "bronze users") .

The determination of the value for the second parameter that indicates the current transmission capacity can also be done in any suitable or desirable way. For example, transmission capacity data can be collected from various points in the data communication network that are involved in providing the transport service, e.g. from all of the nodes or routers involved in transporting the data units issued by the terminal through the network.

The value of the second parameter can also be determined in any suitable or desirable way. For example, it can be determined on the basis of subscription information relating to a subscriber of the terminal. As an example, in a situation, in which both a minimum and a maximum transmission capacity are assigned to a transport service, subscribers with preferential treatment could receive a setting of the current transmission capacity to the value of the maximum transmission capacity if possible on account of the network load, whereas less privileged subscribers could by default always receive a setting of the value for the current transmission capacity parameter to the value of the minimum bit rate parameter. Alternatively or additionally, the value of the second parameter can also be determined on the basis of network load information. For example, if the network load exceeds a certain limit, then the value of the current transmission capacity parameter could always be set equal to the value of the minimum transmission capacity, whereas otherwise larger values for the value of the current transmission capacity parameter could be allowed. Furthermore, additionally or alternatively, the value of the second parameter can be determined on the basis of communication quality information relating the link between the terminal and the access network of the data unit communication network- For example, the link between terminal 202 and access node 210 can be a wireless link, and the value assigned to the second parameter (i.e. the current transmission capacity parameter) can be made dependent on an indication of the quality of this radio link, e.g. on the channel quality indicators (CQI) provided by the terminal.

The method of Figure 4 can be conducted by one or more entities of the data unit communication network. The term entity refers to one or more nodes that rogether provide a predetermined functionality. According to a preferred embodiment, which is especially preferred in case the terminal is a wireless terminal, the method is conducted such that an entity arranged for handling the access connection between the terminal and the access network of the data communication network determines the value of the second parameter based on the characteristics of the access connection. Namely, in the case of a wireless terminal it can generally be assumed that the wireless link constitutes the bottleneck of the communication, such that the momentary or current transmission capacity that can be assigned to the transport service running over the wireless access connection will be determined by the conditions on that access connection. This entity can e.g. be a base station, a base station controller, a radio access network controller or a similar element, such as an eNB (evolved Node B) known from GPRS. For example, the determination of the value for the second parameter can be done by access node 210 shown in Figure 2 based on the characteristics of the connection to terminal 202.

It is possible that the entire procedure is conducted by such an entity arranged for handling the access connection. According to a further embodiment there is a second entity in the communication network, such as for example the gateway node 211 shown in Figure 2, that sends a request to the first entity where the request specifies values for a plurality of quality of service parameters, among them the first parameter. The first entity then performs a response procedure for determining whether the requested values of the quality of service parameters can be supported, and if the response procedure determines that the values can be supported, responding with an acknowledgment and with the value of the second parameter.

The first entity (the entity arranged for handling the access connection) can be arranged in such a way that it also determines the value of the second parameter based on one or more of the values of the quality of service parameters contained in the request from the second entity. For example, from 3GPP TS 23.401 it is known to associate a so-called label and an Allocation and Retention Priority (ARP) with a bearer. The label is a scalar that is used as a reference to access node-specific parameters that control bearer level packet forwarding treatment and that have been pre-configured by the operator owning the access node. The value of ARP indicates a priority of allocation and retention, i.e. serves as an element in a decision on whether a bearer establishment/modification request can be accepted or needs to be rejected in case of resource limitations. The value of ARP can also be used to decide which bearers to drop during exceptional resource limitation (e.g. at handover) . As a consequence, in accordance with the invention, the entity handling the access connection may also base its determination of the value of the second parameter (the current transmission capacity parameter) on the value of the label and/or the value of the ARP.

In this connection it is pointed out that the assigning of a value to the second parameter that indicates the current transmission capacity does not require the measurement of the actual momentary transmission capacity. Namely, the assigning of a value is a control operation designed to convey information to the data source associated with the terminal, such that the data source will adjust its transmission rate accordingly. The important thing is that the data source receives information that allows it to set its sending rate, e.g. the initial sending rate, such that there is no insecurity in the adjustment procedure, but the value of the parameter can be chosen by the network as is desirable for the network, without having to reflect the actual, physical transmission capacity e.g. available on the link between the terminal and the access node of the network.

The above-described method based on Figure 4 can be embodied as a computer program comprising computer program code parts for performing the appropriate method steps when executed in a network entity, or can also be embodied as a computer program product that comprises such a computer program.

Figure 3 shows a schematic representation of entities involved in an example of the present invention. Elements 30 and 34 represent a data source and data receiver, respectively, that operate at an application or service layer 301. 31 represents a terminal of a data unit communication network that furthermore comprises an access control entity 32, which comprises a controller 321, and a second network entity 33 that is responsible for associating service quality parameters with transport service being offered to the terminal 31, and comprises a controller 331. The elements 31 to 33 are situated at a layer 303 associated with the transport service, e.g. a bearer level situated at the link layer and lower.

An operation of the system shown in Figure 3 will be described in connection with Figure 5. In the described example, entity 33 will be assumed to be a gateway entity and data unit receiver 34 will be associated with a different network than uhe one to which elements 31 to 33 belong. Thus, the communication is carried over gateway 33. In a first step S50 the gateway 33 sends a request comprising a value of a guaranteed bit rate GBR {an example of a minimum transmission capacity) and a value of a maximum bit rate (an example of a maximum transmission capacity) to the radio link control entity 32. In step 351 the controller 321 of radio link control entity 32 determines whether the requested GBR and MBR can be supported. This decision can e.g. depend on the characteristics of the access connection between nerminal 31 and entity 32. If the result of the procedure is that the requested GBR and MBR cannot be supported, then a non- acknowledgment (NACK) is sent in step S52, and the procedure ends, as the desired service quality parameters cannot be associated with the transport service.

On the other hand, if they can be supported, then the controller 321 determines a value for the second parameter (the current transmission capacity parameter) according to one of the above described methods, see step S53, and then sends an acknowledgment of the request together with the determined value of the second parameter to the gateway entity 33 in step S54. In step S55 the controller 331 of gateway entity 33 appropriately sends indicators to the terminal 31, said indicators containing information for determining GBR, MBR and the value OBR of the second parameter. These are then passed to the data source 30 through the network/transport layer 302, such that the data source can appropriately adjust its transmission rate in step S56, as already described previously.

As can be seen from the example of Figures 3 and 5, the present invention can also be embodied as a network entity 33 that comprises a controller 331 for associating with a transport service values for a plurality of transmission capacity parameters that comprise at least the first parameter indicating a minimum transmission capacity of the transport service, and the second parameter that indicates the current transmission capacity of the transport service. Furthermore, the controller is arranged for sending to the terminal 31 first information for determining the value of the first parameter and second information for determining the value of the second parameter.

The invention can also be embodied as a network entity 32 that handles an access connection between the terminal 31 and an access network of the data communication network, which comprises a controller 321 for determining a value of the transmission capacity parameter that indicates a current transmission capacity of the transport service offered to the terminal {i.e. value of the second parameter) based on characteristics of the communication between the terminal 31 and the access network.

Claims

Cla ims

1. A method of controlling a data transmission over a terminal of a data unit communication network using a transport service offered by said data unit communication network, said data transmission coming from a data source associated with said terminal, said method comprising: said data source receiving from said data unit communication network one or more indicators comprising first information for determining a value of a first parameter indicating a minimum transmission capacity of said transport service, and second information for determining a value of a second parameter indicating a current transmission capacity of said transport service, and adjusting a transmission rate of said data source in dependence on at least said second information.

2. The method of claim 1, wherein said indicators furthermore comprise third information for determining a value of a third parameter indicating a. maximum transmission capacity of said transport service.

3. The method of claim 2, wherein said second information can assume two states, a first state indicating that the value of the second parameter is equal to the value of the first parameter, and a second state indicating that the value of the second parameter is equal to the value of the third parameter.

4. The method of one of claims 1 to 3, wherein said second information is received during one or more predetermined processes related to the offered transport service.

5. The method of claim 4, wherein said one or more predetermined processes comprise a process of establishing said offered transport service, a process of modifying said offered transport service and a process of handing over to said offered transport service .

6. The method of claim 4 or 5, wherein said second information is only received once during each of said one or more predetermined processes for adjusting an initial transmission rate.

7. The method of one of claims 1 to 5, wherein the second information is received repeatedly during the communication that uses the offered transport service.

8. A computer program comprising computer program code parts for performing the method of one of claims 1 to 7 when executed in a communication device.

9. A computer program product comprising a computer program according to claim 8.

10. A communication arrangement for data unit communication over a data unit communication network, comprising: a terminal, a data source arranged for receiving from said data unit communication network one or more indicators comprising first information for determining a value of a first parameter indicating a minimum transmission capacity of said transport service, and second information for determining a value of a second parameter indicating a current transmission capacity of said transport service, and said data source furthermore being arranged to adjust a transmission rate in dependence on at least said second information.

11. The communication arrangement of claim 10 _r wherein said data source is furthermore arranged for receiving third information for determining a value of a third parameter indicating a maximum transmission capacity of said transport service.

12. A method of controlling a data unit communication network for offering a transport service to a terminal, comprising: associating with said transport service values for a plurality of transmission capacity parameters, said transmission capacity parameters comprising at least a first parameter indicating a minimum transmission capacity of said transport service, and a second parameter indicating a current transmission capacity of said transport service, and sending to said terminal first information for determining a value of the first parameter, and second information for determining a value of the second parameter.

13. The method of claim 12, further comprising associating with said transport service a value of a third parameter indicating a maximum transmission capacity of said transport service and sending to said terminal third information for determining said value of said third parameter.

14. The method of claim 12 or 13, wherein said value of said second parameter is determined on the basis of one or more of subscription information relating to a subscriber of said terminal, network load information, and communication quality information relating to a link between said terminal and an access network of said data unit communication network.

15. The method of one of claims 12 to 14, wherein said data unit communication network comprises a first entity arranged for handling an access connection between said terminal and an access network of said data unit communication network, where said first entity determines said value of said second parameter based on characteristics of said access connection.

16. The method of claim 15, wherein said data unit communication network comprises a second entity, where said second entity sends a request to said first entity, said request specifying values for a plurality of quality of service parameters comprising said first parameter, said first entity performs a response procedure for determining whether the requested values of said quality of service parameters can be supported, and if said response procedure determines that the values can be supported, responding with an acknowledgement and said value of said second parameter to said second entity.

17. The method of claim 16, wherein said first entity also determines said value of said second parameter based on one or more of said values of said quality of service parameters .

18. A computer program comprising computer program code parts for performing the method of one of claims 12 to 17 when executed in a network entity of a data unit communication network.

19. A computer program product comprising a computer program according to claim 18.

20. A network entity of a data unit communication network for offering a transport service to a terminal, comprising: a controller for associating with said transport service values for a plurality of transmission capacity parameters, said transmission capacity parameters comprising at least a first parameter indicating a minimum transmission capacity of said transport service, and a second parameter indicating a current transmission capacity of said transport service, and said controller furthermore being arranged for sending to said terminal first information for determining a value of the first parameter, and second information for determining a value of the second parameter.

21. The network entity of claim 20, wherein said controller is furthermore arranged to send a request to another entity of said data unit communication network, said request specifying values for a plurality of quality of service parameters comprising said first parameter, and for making the associating of said values for said plurality of transmission capacity parameters with said transport service dependent on whether an acknowledgement is received for said request, and said controller being arranged to receive said value of said second parameter from said another entity.

22. A network entity of a data unit communication network for handling an access connection between a terminal and an access network of said data unit communication network, comprising: a controller for determining a value of a transmission capacity parameter indicating a current transmission capacity of a transport service offered to said terminal based on characteristics of a communication between said terminal and said access network.

23. The network entity of claim 22, wherein said controller is furthermore arranged for receiving from another network entity a request specifying values for a plurality of quality of service parameters comprising another transmission capacity parameter indicating a minimum transmission capacity of said transport service offered to said terminal, said controller being arranged for determining whether the requested values of said quality of service parameters can be supported, and if it is determined that the values can be supported, responding with an acknowledgement and said value of said parameter to said other network entity.