WO2013167647A1

WO2013167647A1 - Mechanism for controlling buffer setting in flow control

Info

Publication number: WO2013167647A1
Application number: PCT/EP2013/059568
Authority: WO
Inventors: Jeroen Wigard; Jani Matt i Johannes MOILANEN; Hans Thomas HÖHNE
Original assignee: Nokia Siemens Networks Oy
Priority date: 2012-05-11
Filing date: 2013-05-08
Publication date: 2013-11-14

Abstract

There is provided a flow control mechanism usable for a multiflow communication. An RNC sends to the Node Bs involved in the multiflow communication a target buffer delay value determined by the RNC. The Node Bs use the target buffer delay value for determining a target buffer size which is signaled to the RNC for flow control purposes.

Description

M ECHANISM FOR CONTROLLING BU FFER SETTING IN FLOW CONTROL

DESCRIPTION

BACKGROU ND OF TH E INVENTION

Field of the invention The present invention relates to a flow control mechanism . Specifically, the present invention is related to an apparatus, a method and a computer program product which provide a mechanism allowing setting, in a flow control procedure, of parameters for a configuration of transmission buffers of a communication element, such as a base station or Node B, in an optimized way, in particular in a multiflow communication mode.

The following meanings for the abbreviations used in this specification apply:

ACK : acknowledgement

BS : base station

DL: downlink

e2e : end-to-end

HARQ : hybrid automatic repeat request

HSDPA: high speed downlink packet access

HS-DSCH : high speed downlink shared channel

LI : layer 1 (physical layer)

LTE : Long Term Evolution

LTE-A: LTE Advanced

MAC : medium access control

MAC-ehs : MAC enhanced high speed

NACK : non-acknowledgement

NB : node B

O&M : operation and maintenance PDCP: packet data convergence protocol

PDU : payload data unit

QoS: quality of service

RLC: radio link control

RNC: radio network controller

RTT: round trip time

SRNC: serving RNC

SN : sequence number

TCP: transmission control protocol

TTI: transmission time interval

Tx: transmission

UE: user equipment

UL: uplink

UTRA : U TS radio access network

In the last years, an increasing extension of communication networks, e.g . of wire based communication networks, such as the Integrated Services Digital Network (ISDN), DSL, or wireless communication networks, such as the cdma2000 (code division multiple access) system, cellular 3rd generation (3G) and fourth generation (4G) communication networks like the Universal Mobile Telecommunications System (UMTS), enhanced communication networks based e.g. on LTE or LTE-A, cellular 2nd generation (2G) communication networks like the Global System for Mobile communications (GSM), the General Packet Radio System (GPRS), the En ha nced Data Rates for Gl oba l Evol ution ( EDG E) , or other wireless communication system, such as the Wireless Local Area Network (WLAN), Bluetooth or Worldwide Interoperability for Microwave Access (WiMAX), took place all over the world . Various organizations, such as the 3rd Generation Partnership Project (3GPP), Telecoms & Internet converged Services & Protocols for Advanced Networks (TISPAN), the International

Telecommunication Union (ITU), 3rd Generation Partnership Project 2 (3GPP2), Internet Engineering Task Force (IETF), the IEEE (Institute of Electrical and Electronics Engineers), the WiMAX Forum and the like are working on standards for telecommunication network and access environments. Generally, for properly establishing and handling a communication connection between terminal devices such as a user equipment (UE) and another communication network element or user equipment, a database, a server, etc . , o n e o r m o re i nte rmed i ate netwo rk el e ments s u ch as communication network control elements, communication network elements such as base transceiver stations, support nodes or service nodes are involved which may belong to different communication network. In a communication system based on e.g . 3GPP specifications, data to be transmitted to a terminal device are sent from a communication network control element, such as an RNC, via a base transceiver station or Node B to a terminal device or UE as a data steam. Specifically, the data are sent from the RNC to the Node B via a specific interface, which is referred to as IuB interface, according to a flow control indicating how fast the data can be transmitted . In the Node B, the data can be stored in a transmission buffer from which the data are forwarded via a suitable communication path to the receiving end (e.g . the UE). For flow control over Iub, flow control signaling is used in which the Node B can request the RNC to send the data and indicate a requested amount of data to be sent, e.g. by sending periodically flow control parameters or "credits" to the RNC by which the Node B indicates how much data it would like to receive from the RNC, i .e. how much data the RNC can send in a particular data flow during a next flow control period or cycle, for example.

Hence, by a corresponding flow control mechanism, the Node B is able to impact how much data it has in its transmission buffers.

That is, in an examplary flow control procedure, the following signaling is exchanged between an RNC and a Node B, for example. First, the RNC can send a capacity req uest, such as a„HS-DSCH Capacity Request" to the Node B. This message which indicates how much data the RNC has in its' buffer for a given user data flow. Then, the Node B sends, for example, a "HS-DSCH Capacity Al l ocation " message (as a response to the Capacity Request or at any time) indicating how much data the RNC can send to the Node B during a given HS-DSCH interval (which is also defined in the Capacity Allocation message by the Node B), Hence, for a flow control procedure, the Node B provides an upper limit for how much data the RNC is allowed to send . That means, while the RNC has the final control over the data flow transmission as such, it is at least implicitly controlled by the

Node B due to the indicated amount of data not to be exceeded (i.e. an upper limit provided by NodeB). Thus, in a typical implementation, the RNC tries to send exactly as much data as was indicated by the credits. Basically, it is desirable to ensure that there is always a sufficient amount of data in the Node B buffers. By means of this, it can be avoided that the buffers run empty, leading to a disturbance or unnecessary interruption of a data flow of which data are still to be scheduled for transmission. On the other hand it is also desirable to keep the size of buffers (i.e. the amount of data buffered therein) as short as possible so as to minimize the amount of data that have to be retransmitted to another Node B, for example in the case that the receiving UE is handed over to the other Node B.

While for users located relatively in the centre of a cell served by a Node B or the like a data flow is usually conducted by the serving Node B alone, the situation for user being located, for example, on a cell edge or in the vicinity of another cell, is different. In case of a cell edge user or the like, it is contemplated to use a multiflow communication mode. For example, according to 3GPP based systems, a so-called HSDPA multiflow transmission ( referred to hereinafter as "multiflow") is implemented which al lows to improve the cell edge users' data rates and robustness, which is achieved by enabling that transmissions are received not only from the (serving) Node B of the present cell, but also from neighboring cells. SUMMARY OF THE INVENTION

It is an object of the invention to provide an improved flow control mechanism. Specifically, the present invention provides an apparatus, a method and a computer program product which provide an improved flow control mechanism allowing setting of parameters for a configuration of transmission buffers of a communication element, such as a base station or Node B, in an optimized way, in particular in a multiflow communication mode. These objects are achieved by the measures defined in the attached claims.

According to an example of an embodiment of the proposed solution, there is provided, for example, an apparatus comprising at least one processor, at least one interface to at least one other network element, and at least one memory for storing instructions to be executed by the processor, wherein the at least one memory and the instructions are configured to, with the at least one processor, cause the apparatus at least to perform : a connection property determination function configured to determine a connection property for a communication using a transmission buffer, a calculation function configured to calculate a target buffer delay value on the basis of the determined connection property, and a control function configured to cause transmission of a control information indicating the calculated target buffer delay value. Furthermore, according to an example of an embodiment of the proposed solution, there is provided, for example, a method comprising determining a connection property for a communication using a transmission buffer, calculating a target buffer delay value on the basis of the determined connection property, and transmitting a control information indicating the calculated target buffer delay value.

According to further refinements, these examples may comprise one or more of the following features:

- a measurement signal may be transmitted via a specified interface towards another network element, a response signal may be received in reply to the measurement signal, wherein the connection property may be determined for a communication via the specified interface on the basis of information of the measurement signal and the response signal, and the target buffer delay value may be calculated on the basis of the determined connection property; - the connection property may be a round trip time of the communication via the specified interface which may be determined on the basis of timing information of the measurement signal and the response signal;

- a multiflow communication may be conducted with at least two other network elements by splitting a data flow into plural independent data streams towards each of the at least two other network elements, wherein a respective measurement signal may be transmitted via the specified interface towards each of the at least two other network elements, a respective response signal may be received in reply to each the respective measurement signals, respective connection property values may be determined for a communication via the specified interface on the basis of information of each of the respective measurement signals and each of the respective response signals, one of the determined connection property values may be used as the connection property value for calculating the target buffer delay value, and the control information indicating the calculated target buffer delay value may be transmitted to each of the at least two other network elements;

- the respective connection property is a respective round trip time of the communication via the specified interface which is determined on the basis of timing information of the respective measurement signal and the respective response signal, wherein the highest one of the determined round trip times is used for calculating the target buffer delay value;

- a ping-type signal may be transmitted as the measurement signal, and an acknowledgement signal may be received in reply to the ping-type signal;

- the measurement signal may be transmitted periodically and/or triggered by a predetermined event;

- the target buffer delay value may be calculated by multiplying the determined round trip time with a predetermined value, wherein the predetermined value may be equal to or greater than 2.5;

- a data rate fluctuation may be determined, it may be monitored whether the data rate fluctuation exceeds a threshold, and, if the data rate fluctuation exceeds the threshold, a value of the target buffer delay value may be increased ; - an indication regarding a buffer underrun state may be received an processed, and if the indication regarding the buffer underrun state is received, a value of the target buffer delay value may be increased ;

- the above processing may be implemented in a communication network control element, such as a radio network control ler of a 3G PP based cellular communication network, and the specified interface may be an interface between the communication network control element and at least one base transceiver network element controlled by the communication network control element.

In addition, according to a further example of an embodiment of the proposed solution, there is provided, for example, an apparatus comprising at least one processor, at least one interface to at least one other network element, and at least one memory for storing instructions to be executed by the processor, wherein the at least one memory and the instructions are configured to, with the at least one processor, cause the apparatus at least to perform : a control information receiving and processing function configured to receive and process a control information indicating a target buffer delay value, a flow control parameter determining function configured to determine a flow control parameter on the basis of the received target buffer delay value, and a flow control function configured to cause transmission of the determined flow control parameter to another network element for setting a data stream to be received via a specified interface. Moreover, according to the further example of an embod iment of the proposed solution, there is provided, for example, a method comprising receiving and processing a control information indicating a target buffer delay value, determining a flow control parameter on the basis of the received target buffer delay value, and transmitting the determined flow control parameter to another network element for setting a data stream to be received via a specified interface.

According to further refinements, these examples may comprise one or more of the following features: - a target buffer size of a transmission buffer may be calculated by multiplying the received target buffer delay value with a data rate of a downlink communication to which the transmission buffer is related, and the flow control parameter may be determined on the basis of the calculated target buffer size;

- a measurement signal may be received via the specified interface, and a response signal in reply to the measurement signal may be prepared and transmitted ;

- a ping-type signal may be received as the measurement signal, and an acknowledgement signal may be prepared and transmitted in reply to the ping-type signal;

- a buffer underrun state may be detected, and a buffer undderun indication may be sent to the communication network control element;

- the above processing may be implemented in a communication element, such as a base transceiver network element of a 3GPP based cellular communication network, and the specified interface may be an interface between the communication element and a communication network control element such as a radio network controller controlling the communication element.

In addition, according to examples of the proposed solution, there is provided, for example, a computer program product for a computer, comprising software code portions for performing the steps of the above defined methods, when said product is run on the computer. The computer program product may comprise a computer-readable medium on which said software code portions are stored . Furthermore, the computer program product may be directly loadable into the internal memory of the computer and/or transmittable via a network by means of at least one of upload, download and push procedures.

By virtue of the proposed solutions, it is possible to provide an improved flow control mechanism in which parameters for a configuration of a transmission buffer of a communication element, such as a base station or Node B, can be set in such a manner that, when communicating, for example, in a multiflow communication mode, problems caused by skew can be avoided and the necessity of retransmissions in a handover scenario can be minimized. In particular, it is possible to set buffer parameters like buffer delay and buffer size in such a manner that the above mentioned advantages can be achieved. Furthermore, it is possible to provide an automated parameter setup procedure minimizing the necessity for an operator to interact. In addition, O&M operation can be simplified since target buffer delay parameter setting is not to be specified individually in an O&M interface. The above and still further objects, features and advantages of the invention will become more apparent upon referring to the description and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 shows a diagram illustrating a communication network configuration where examples of embodiments of the invention are implemented.

Fig. 2 shows a diagram illustrating a dependency of skew to a target buffer delay.

Figs. 3a and 3b show diagrams illustrating an impact of a flow control period to an average goodput in case of different target buffer delays. Fig . 4 shows a flowchart il I ustrating a processing executed in a communication network control element according to examples of embodiments of the invention.

Fig. 5 shows a flowchart illustrating a processing executed in a communication network control element according to further examples of embodiments of the invention. Fig . 6 shows a flowchart illustrating a processing executed in a communication network element according to examples of embodiments of the invention.

Fig . 7 shows a block circuit diagram of a communication network control element including processing portions conducting functions according to examples of embodiments of the invention.

Fig . 8 shows a block circuit diagram of a communication network element including processing portions conducting functions according to examples of embodiments of the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

In the following, examples and embodiments of the present invention are described with reference to the drawings. For illustrating the present invention, the examples and embodiments will be described in connection with a cellular communication network based on a 3GPP based communication system, for example a UMTS based system. However, it is to be noted that the present invention is not limited to an application using such types of communication system, but is also applicable in other types of communication systems and the like.

A basic system architecture of a communication network where examples of embodiments of the invention are applicable may comprise a commonly known architecture of one or more communication systems comprising a wired or wireless access network subsystem and a core network. Such an architecture may comprise one or more access network control elements, radio access network elements, access service network gateways or base transceiver stations, such as a base station ( BS) or N B, which control a coverage area also referred to as a cell and with which one or more communication or terminal devices such as a UE or another device having a similar function, such as a modem chipset, a chip, a module etc., which can also be part of a UE or attached as a separate element to a UE, or the like, are capable to communicate via one or more channels for transmitting several types of data. Furthermore, core network elements such as gateway network elements, policy and charging control network elements, mobility management entities and the like may be comprised .

The general functions and interconnections of the described elements, which also depend on the actual network type, are known to those skilled in the art and described in corresponding specifications, so that a detailed description thereof is omitted herein. However, it is to be noted that several additional network elements and signaling links may be employed for a communication to or from a communication or terminal device like a UE, a communication network element like a base transceiver station or Node B, or a communication network control element like an RNC, besides those described in detail herein below.

Furthermore, the described network elements, such as terminal devices like UEs, communication network elements like Node Bs or communication network control elements like RNCs and the like, as well as corresponding functions as described herein may be implemented by software, e.g . by a computer program product for a computer, and/or by hardware. In any case, for executing their respective functions, correspondingly used devices, nodes or network elements may comprise several means and components (not shown) which are required for control, processing and communication/sig nal ing functional ity. Such means may comprise, for example, one or more processor units including one or more processing portions for executing instructions, programs and for processing data, memory means for storing instructions, programs and data, for serving as a work area of the processor or processing portion and the like (e.g . ROM, RA M , E E PRO M , a n d the l i ke ) , i n p ut mea n s fo r i n p utti n g d ata a n d instructions by software (e.g . floppy disc, CD-ROM, EEPROM, and the like), user interface means for providing monitor and manipulation possibilities to a user (e.g . a screen, a keyboard and the like), interface means for establishing links and/or connections under the control of the processor unit or portion (e.g . wired and wireless interface means, an antenna, etc. ) and the like. It is to be noted that in the present specification processing portions should not be only considered to represent physical portions of one or more processors, but may also be considered as a logical division of the referred processing tasks performed by one or more processors.

According to examples of embodiments of the invention, a flow control mechanism is proposed in which a communication network control element, such as an RNC, provides communication network elements, such as Node

Bs, being controlled by the communication network control element and participating in a (multiflow) communication for delivering a data flow to a terminal device, such as a UE, a target buffer delay value determined by the RNC on the basis of connection property information derived at a connection between the communication network element and the com mun ication network control element. The communication network elements, such as the Node Bs, use the target buffer delay value for determining a target buffer size, which is signaled to the RNC for flow control purposes. With regard to Fig . 1 , a d iagram il lustrating a general configuration of a communication network where examples of embodiments of the invention are implemented . It is to be noted that the configuration shown in Fig . 1 shows only those devices, network elements and parts which are useful for understanding principles underlying the examples of embodiments of the invention . As also known by those skilled in the art there may be several other network elements or devices involved in a communication between the communication devices (UEs) and the network which are omitted here for the sake of simplicity. In Fig . 1 , a communication network configuration is ill ustrated in which examples of embodiments of the invention are implementable. The network according to Fig . 1 is for example based on 3GPP specifications and forms part of an UTRAN. It is to be noted that the general functions of the elements described in connection with Fig . 1 as well as of reference points/interfaces therebetween are known to those skilled in the art so that a detailed description thereof is omitted here for the sake of simplicity.

As shown in Fig . 1 , in the exemplary communication network, a com m u n icatio n netwo rk contro l el ement such as a n RNC ( S RNC ) 1 is provided for controlling plural cells. The RNC provides a connection to the core network of the communication network.

Each cell controlled by the RNC 10 is provided with a corresponding communication network element, such as Node B 20 and 25. The Node Bs 20 and 25 are connected to the RNC 10 via a specific interface which is referred to as the IuB interface, for example.

Furthermore, a terminal device or U E 30 is assumed to be present in the communication network. The U E 30 is configured to communicate with the communication network via at least one Node B by using an interface which is referred to as Uu interface.

It is to be noted that the RNC 10 can control more than the two cells (or Node Bs) shown in Fig . 1. Furthermore, it is possible that more than one U E is Iocated in the communication network.

When the U E 30 is Iocated, for example, at a cell edge between the cell of Node B 20 and Node B 25, a multiflow communication mode, i.e. a so-called inter-site m u ltifl ow mode, can be used to i mprove robustness a nd d ata rates for communications to the U E 30. That is, in the multiflow communication, as indicated in Fig . 1 , a downlink data flow (indicated by arrows from a PDCP layer in the RNC 10) is split into two (or even more) independent data streams at an RLC layer in the RNC 10 wherein each data stream is g uided to a respective one of the Node Bs via MAC layer and LI layer communications, respectively.

In case of a single data flow (i.e. when multiflow is not activated ), the RLC layer relies on one MAC-ehs entity in the Node B 25 that delivers RLC PDUs in seq uence to a Node B (e .g . Node B 20) which forwards the PDUs to the UE 30. In case of a missing PDU, which can be detected for example when the RLC in UE 30 receives a PDU with an SN that is higher than next expected SN, the transmission of an RLC NACK is triggered so as to indicate this to the RNC 10 for causing a retransmission.

However, in case of multiflow communication, as indicated in Fig . 1, there are two independent MAC-ehs entities in Node B 20 and Node B 25, each forwarding a data stream to the UE 30. This structure may cause, for example due to scheduling issues, HARQ retransmission etc., different delays at each MAC-ehs entity. Therefore, RLC PDUs being split from each other and forwarded via the different Node Bs due to the multiflow mode, may arrive out of order to UE's RLC layer. That is, since e.g . a PDU with an unexpected SN is received at the U E (caused by different delays over the respective links to the Node Bs, for example), RLC NACK signaling may be caused which in turn can lead to unnecessary RLC retransmission . This is also referred to as "skew".

In order to minimize the skew problems, it is contemplated that in case either the network or the U E detects a missing PDU , a "skew timer" is started . The request for retransmission is issued only after this skew timer expires. By means of this measure, it is tried to provide the opportunity to receive the missing PDU within the timer period so as to avoid the (possibly) unnecessary retransmission. However, it is to be noted that the e2e performance in the communication may be impacted by the skew timer. The reason is that a delay of (necessary) retransmissions of actually lost RLC PDUs is caused . Such a delay may cause, however, TCP timeouts and corresponding congestion actions.

In order to keep this impact small, the skew timer should be kept small. That means that the skew should be kept as small as possible. In general it can be said that despite the skew timer, from e2e performance point of view, it is desirable to minimize the skew to avoid jitter (which can e.g. lead to TCP slow starts) and keep delays as small as possible. It has been found out that in order to minimize the skew and delays, Node B buffer delays should be kept equal and as small as possible. For example, assuming that a target buffer delay for a data flow in the scenario shown in Fig . 1 is 100ms, and estimated data rates over the links are 500kbps via Node B 20 and 1000kbps via Node B 25. In this case, an luB flow control aims to maintain a target buffer size of SOkbit in the transmission buffer (not shown) of Node B 20 and a target buffer size of lOOkbit in the transmission buffer (not shown) of Node B 25.

Referring to Fig . 2, a diagram is shown illustrating the dependency of a skew size (in TTI) to a target buffer delay (in TTI). It is to be noted that the TTI in case of an HSDPA system is 2ms, for example.

Specifically, the curve indicated by reference sign 51 shows a case where an ideal flow control is assumed, while the curve indicated by reference sign 52 shows a case where a realistic flow control is assumed . As can be seen from the curve 52, the size of skew depends linearly on the Node B target buffer delay. Specifically, the smaller the target delay, the smaller the skew size is.

Figs. 3a and 3b show diagrams illustrating an impact of a flow control period defined by TTI to an average goodput (i.e. the number of useful information bits delivered by the network to a certain destination per unit of time) defined by bytes/TTI in case of different target buffer delays.

Specifically, Fig . 3a shows a case where the target buffer delay is assumed to be 50 TTI (or 100ms in case of HSDPA), and Fig . 3b shows a case where the target buffer delay is assumed to be 100 TTI (or 200ms in case of HSDPA) . It is to be noted that both diagrams according to Figs. 3a and 3b do not consider an IuB delay (to be discussed below) .

As indicated in both Figs. 3a and 3b by means of a double-arrow, a relation between a flow control period and a proper goodput can be derived . The target buffer delay depends on how fast is the flow control. As shown in Figs. 3a and 3b, in case the flow control period is kept < 40% of target buffer delay, the risk that buffers in Node B run occasionally empty due to the variations in the link throughput can be avoided . For example, as shown in Fig . 3a where the target buffer delay is 100ms (50 TTI), the flow control period, i.e. the period where the RNC 10 receives the (next) flow control information from a Node B should be 40ms (or faster). On the other hand, as shown in Fig . 3b where the target buffer delay is 200ms (100 TTI), the flow control period, i.e. the period where the RNC 10 receives the (next) flow control information from a Node B should be 80ms (or faster).

A practical limit for the flow control speed is set by IuB transport delays. However, lub delays can vary per transport link (depending on the transport media and the load) so that it is difficult to consider them. For example, lub delays can differ as much as several 100ms; for example, in case a fiber is used, delays can get as small as 1 ms, whereas there are also cases of delays of 300 ms, for example in case a Node B is located on an island far away of the RNC connected via a slow medium. Therefore, according to examples of embodiments of the invention, it is contemplated to set the target buffer size based on an IuB delay value.

In particular, according to examples of embodiments of the invention, a communication scenario using a multiflow mode is considered where a dynamic target buffer delay optimization is considered .

In a single flow scenario, one possible way for flow control is that a Node B aims to keep the Node B buffer delays at a given target. The target may be an O&M parameter.

According to examples of embodiments of the invention, in order to improve the flow control, a new signaling is provided between a communication network control element, such as the RNC 10, where the control of several cells is bundled, via which the multiflow communication is to be conducted, a nd com m u n ication network elements su ch as the cel l rel ated base transceiver stations or Node Bs ( Node B 20 and Node B 25, for example). By means of the new signaling, on the one side, a connection property such as QoS parameter or a round-trip-time (RTT) for packets sent over the interface between the communication network control element and each communication network element, such as the luB interface is measured, and the measured connection property, such as the RTT, is used to define a suitable Node B target buffer delay. Furthermore, the RNC 10 controls the flow control procedure in the Node Bs 20 and 25 by providing the target buffer delay to the Node Bs 20 and 25 which consider this parameter in the flow control processing .

In other words, according to examples of embodiments of the invention, the RNC 10 measures e.g . the RTT for packets sent over the IuB interface to the Node B (in the example of Fig . 1, to both Node Bs 20 and 25, but according to further examples it is also possible to use more than two Node

Bs in a multiflow communication, or to send measure the RTT to only a single Node B and use the RTT value for a control of the flow control. On the basis of the RTT which is measured by means of a common procedure, the RNC 10 defines the target delay of the Node B's transmission buffer. Then, the RNC 10 sends the target buffer delay to the Node B (20 and 25, for example).

When receiving the target buffer delay from the RNC 10, the Node B 20 (or 25) adapts its flow control on the basis thereof. That is, for the flow control, the Node B 20 calculates the "credits" provided to the RNC 10 (i.e. requests for an amount of data to be received) on the basis of the received target buffer delay.

According to examples of embodiments of the invention, each Node B 20 and 25 calculates a target buffer size of the transmission buffer (which is usable as a value for the "credits") individually, for example by using a bandwidth-delay-product according to the following equation ( 1) : target buffer size = data rate x target buffer delay •( 1) That is, according to examples of embodiments of the invention, the RNC 10 uses a new signaling over IuB interface to take control of the target buffer delay, and enables more dynamic operation. As an example, the RNC 10 uses, as a measuring signal, ping-type messages for measuring the RTT for the IuB links to each Node B, wherein the respective Node B sends e.g . an

ACK message to the ping-type message allowing the determination of the RTT on the RNC 10 side.

Furthermore, according to examples of embodiments of the invention, the processing incl ud ing the RTT measurement and the target buffer delay determination can be executed periodically (i.e. the measurement signal is sent in predetermined intervals) and/or triggered by some event (for example, in a setup phase of a multiflow communication connection).

As indicated above, according to examples of embodiments of the invention, the measured RTT is used to select reasonable Node B target buffer size. In case of multiflow, according to examples of embodiments of the invention, this is based by using or selecting the highest RTT value of all determined RTT values on the plural (two or more) IuB links.

For example, according to an example of embodiments of the invention, it is assumed that the flow control period is roughly equal to RTT. Therefore, a suitable target buffer delay would be approximately 2.5 RTT (or higher in order to define some safety margin). By means of this value, it is possible to meet the goal of having a flow control period of <40% of target buffer delay (as indicated in Fig . 3a, 3b, for example).

Hence, according to examples of embodiments of the invention, the target buffer delay can be set to an optimized value under the control of the RNC 10 w h i ch l ea d s to l owe r s kew i n ca se of m u l ti fl ow a n d l ess R LC retransmissions in case of handovers. Furthermore, since the processing in the RNC does not require an interaction of an operator, a fully automated parameter setup is possible. Alternatively or additionally to the above described examples of embodiments of the invention, according to further examples of embodiments of the invention, the flow control mechanism is modified as follows.

As described above, it is desirable to keep the NodeB buffer size as short as possible. However, it is also desirable to also avoid buffer underrun.

Thus, as a further or alternative connection property used for determining the target buffer delay value besides the connection property based on the lub RTT value, according to the present examples of embodiments of the invention, a fluctuation of a data rate is considered .

The fluctuation of the data rate has an impact on the end-to-end throughput. Thus, in order to take this into account, a measu re of the throughput fluctuation is taken by the communication network control element (the RNC) and used to further refine the target buffer delay.

For example, according to examples of embodiments of the invention, the the fluctuation is estimated in the RNC 10 by monitoring the credits received from the Node Bs (i.e. the requests for data based on a determined buffer size which is dependent on a data rate). The monitoring can be executed for a predetermined time. If it is determined in the monitoring phase by the RNC that there is a fluctuation exceeding, for example, a certain threshold value (i.e. the difference between a maximum and a minimum credit value is greater than a threshold, or the like), the RNC decides to change the target buffer delay value currently set, for example by increasing the current target buffer delay value. By means of this, a larger safety margin is added so as to avoid that a buffer underruns.

According to another examples of embodiments of the invention, as a connection property indication, the RNC 10 receives and processes an indication from the Node Bs indicating a transmission buffer underrun. When receiving this underrun indication, the RNC 10 increases the currently set target buffer delay value. Otherwise, in case such an underrun indication is not received, the set target buffer delay value may be maintained or even decreased .

The above described examples of embodiments of the invention can be combined with each other in a common flow control, for example.

Fig . 4 shows a flowchart illustrating a processing executed in a communication network control element like the RNC 10 of Fig . 1 according to examples of embodiments of the invention in a flow control mechanism as described above.

In step S100, a measurement signal (e.g . the ping-type signal) is transmitted via a specified i nterface (e . g . the Iu B interface) towards another network element, i.e. to one or more (in case of multiflow communication) Node B.

In step S110, a response signal in reply to the measurement signal is received from the one or more (in case of multiflow communication) Node

B, for example in the form of an ACK signal related to the ping-type signal, via the specified interface (IuB interface, for example).

In step S120, a connection property, such as a round trip time of a communication via the specified interface is determined on the basis of timing information (period between sending time and receiving time, or the like) of the measurement signal and the response signal. In case of the multiflow communication, at the same time, one of the determined connection property values, such as the highest RTT is selected (for example, in case RTT to Node B 20 is higher than to Node B 25, the RTT related to Node B 20 is selected).

In step S130, a target buffer delay value is calculated on the basis of the determined (selected) connection property, such as the round trip time. For example, in order to achieve the desired value of > 40%, a calculation of the target buffer delay according to 2.5 x RTT is conducted (also a value greater than 2.5 can be used).

In step S140, control information for the flow control conducted by the Node Bs is prepared and transmitted to each Node B 20 and 25. The control information indicates the calculated target buffer delay value.

Thereafter, the processing is ended .

As ind icated above, the processing according to Fig . 4 can be executed periodically and/or triggered by a predetermined event, e.g . when a multiflow communication is detected to be setup.

Fig . 5 shows a flowchart illustrating a processing executed in a communication network control element like the RNC 10 of Fig . 1 according to further examples of embodiments of the invention in a flow control mechanism as described above. The processing described in Fig . 5 may be combined with the processing of Fig . 4 in a common flow control processing, as described above.

In step S300, a connection property is determined by the RNC 10. For example, according to one example of the embodiment of the invention, a fluctuation of a data rate at the Node B is detected in the RNC by means of monitoring requests/credits received from the Node B for a predetermined time. Alternatively or additionally, according to examples of embodiments of the invention, a buffer state of the Node B is determined from a corresponding indication sent by the Node B, such as a buffer underrun state indication.

In step S310, it is decided whether the determined connection property, e.g . the fluctuation of data rate or an indication of buffer underrun derived from signals received from the Node B, requires a modification of a target buffer delay value. A modification is decided to be required, for example, in case the fluctuation exceeds a predetermined value, or in case a predetermined number (one or more) of buffer underrun indications is received .

It is to be noted that the target buffer delay value to be modified can be the target buffer delay value determined according to the processing of Fig . 4, or set by other means or measures (e.g. an initially set default value, or the like).

If the decision in step S310 is negative, step S330 is executed (described later) . Otherwise, in case the decision in step S310 is positive, step S320 is executed .

In step S320, the current target buffer delay value is modified . For example, the target buffer delay value is increased by a preset amount or by an amount determined on the basis of the connection property (e.g . the higher the fluctuation the higher the increasing amount; or the more buffer underrun indications, the higher the increasing amount).

In step S330, control information for the flow control conducted by the Node Bs is prepared and transmitted to each Node B 20 and 25. The control information indicates the modified (or maintained) target buffer delay value.

Thereafter, the processing is ended .

Fig . 6 shows a flowchart illustrating a processing executed in a communication network element like the Node B 20 or 25 of Fig. 1 according to examples of embodiments of the invention in a flow control mechanism as described above.

In step S200, control information from a communication network control element such as RNC 10 is received and processed so as to derive a target buffer delay value for a transmission buffer of the communication network element (the Node B) used in a DL communication, which is indicated therein. In step S210, a flow control parameter is determined on the basis of the received target buffer delay value. The flow control parameter represents for example the target buffer size of the transmission buffer which is determined by multiplying the target buffer delay value and a data rate towards a receiver of the respective data flow, i.e. a data rate to the UE 30.

In step S220, the determined flow control parameter is sent to the RNC 10 for setting a data stream to be received via a specified interface (IuB interface).

It is to be noted that even not shown in Fig . 5, the Node B 20 or 25 is also configured, according to examples of embodiments of the invention, to assist the RNC 10 in the determination of the connection property such as the RTT according to step SlOO to S120 of Fig . 4. That is, the Node B 20 or

25 is further configured to execute steps for receiving the measurement signal sent in step S110 via the specified interface (IuB interface), and to prepare and transmit the response signal received by the RNC 10 in step S120.

In Fig . 7, a block circuit diagram illustrating a configuration of a communication network control element, such as of RNC 10, is shown, which is configured to implement the flow control processing as described in connection with the examples of embodiments of the invention. It is to be noted that the communication network control element or RNC 10 shown in

Fig . 7 may comprise several further elements or functions besides those described herein below, which are omitted herein for the sake of simplicity as they are not essential for understanding the invention. Furthermore, even though reference is made to an RNC, the communication network control element may be also another device having a similar function, such as a chipset, a chip, a module etc., which can also be part of a control element or RNC or attached as a separate element to an RNC, or the like.

The communication network control element or RNC 10 may comprise a processi ng function or processor 1 1 , such as a CPU or the l ike, wh ich executes instructions given by programs or the like related to the flow control mechanism. The processor 11 may comprise one or more processing portions dedicated to specific processing as described below, or the processing may be run in a single processor. Portions for executing such specific processing may be also provided as discrete elements or within one or more further processors or processing portions, such as in one physical processor like a CPU or in several physical entities, for example. Reference sign 12 denote transceiver or input/output (I/O) units (interfaces) connected to the processor 11. The I/O units 12 may be used for communicating with one or more communication network elements like a

Node B. The I/O unit 12 may be a combined unit comprising communication equipment towards several network elements, or may comprise a distributed structure with a plurality of different interfaces for different network elements. For example, the I/O units 12 comprise the IuB interface as indicated in Fig . 1. Reference sig n 13 denotes a memory usable, for example, for storing data and programs to be executed by the processor 11 and/or as a working storage of the processor 11.

The processor 11 is configured to execute processing related to the above described flow control mechanism. In particular, the processor 11 comprises a sub-portion 110 as a processing portion which is usable for conducting a multiflow communication. Furthermore, the processor 11 comprises a sub- portion 111 usable as a portion for transmitting and receiving a signaling related to the connection property (e.g. RTT) measurement. The portion 111 may be configured to perform processing according to steps S100 and

S110 of Fig . 4, for example. Furthermore, the processor 11 comprises a sub-portion 112 usable as a portion for determining/selecting a connection property value (e.g . highest RTT value, determining that fluctuation exceeds threshold so that modification is required). The portion 112 may be configured to perform processing according to step S120 of Fig . 4 and/or processing according to steps S300 and S310 of Fig . 5, for example. In addition, the processor 11 comprises a sub-portion 113 as a processing portion which is usable for calculating or modifying a target buffer delay. The portion 113 may be configured to perform processing according to step S130 of Fig . 4 and/or processing according to step S320 of Fig . 5, for example. Furthermore, the processor 11 comprises a sub-portion 114 usable as a portion for preparing and transmitting control information related to a flow control in the Node B. The portion 114 may be configured to perform processing according to step S140 of Fig . 4, for example.

In Fig . 8, a block circuit diagram illustrating a configuration of a communication network element, such as of Node B 20 or 25, is shown, which is configured to implement the processing for the flow control as described in connection with the examples of embodiments of the invention.

It is to be noted that the communication network element or Node B 20 shown in Fig . 8may comprise several further elements or functions besides those described herein below, which are omitted herein for the sake of simplicity as they are not essential for understanding the invention. Furthermore, even though reference is made t o a N o d e B , t h e communication network element may be also another base transceiver station of communication device having a similar function, such as a modem chipset, a chip, a module etc., which can also be part of a communication network element or Node B or attached as a separate element to a Node B or the like.

The communication network element or Node B 20 or 25 may comprise a processing function or processor 21, such as a CPU or the like, which executes instructions given by programs or the like related to the flow control mechanism. The processor 21 may comprise one or more processing portions dedicated to specific processing as described below, or the processing may be run in a single processor. Portions for executing such specific processing may be also provided as discrete elements or within one or more further processors or processing portions, such as in one physical processor like a CPU or in several physical entities, for example. Reference sign 22 denote transceiver or input/output (I/O) units (interfaces) connected to the processor 21. The I/O units 22 may be used for communicating with a communication network control element like RNC 10 and one or more terminal devices like UE 30. The I/O unit 22 may be a combined unit comprising communication eq u ipment towards severa l network elements, or may comprise a distributed structure with a plurality of different interfaces for different network elements. For example, the I/O units 22 comprise the IuB interface and the Uu interface as indicated in Fig . 1. Reference sign 23 denotes a memory usable, for example, for storing data and programs to be executed by the processor 21 and/or as a working storage of the processor 21.

The processor 21 is configured to execute processing related to the above described flow control mechanism. In particular, the processor 21 comprises a sub-portion 211 as a processing portion which is usable for receiving and processing control information for deriving a target buffer delay value. The portion 211 may be configured to perform processing according to step S200 of Fig . 5, for example. Furthermore, the processor 21 comprises a sub-portion 212 usable as a portion for determine a flow control parameter, such as a target buffer size. The portion 212 may be configured to perform processing according to step S210 of Fig . 5, for example. In addition, the processor 21 comprises a sub-portion 213 as a processing portion which is usable for transmit the flow control parameter to the RNC 10. The portion

213 may be configured to perform processing according to step S230 of Fig . 4, for example. Furthermore, the processor 21 may comprise a sub-portion

214 usable as a portion for conducting the processing allowing the RNC 10 to determine the RTT by processing the measurement signal transmitted by the RNC 10, and/or the processor 21 may comprise a sub-portion 215 usable as a portion for detecting and sending a buffer underrun indication the RNC 10.

According to further examples of embodiments of the invention, there is provided an apparatus comprising connection property determination means for determining a connection property for a communication using a transmission buffer, calculation means for calculating a target buffer delay value on the basis of the determined connection property, and control means for causing transmission of a control information indicating the calculated target buffer delay value. In addition, according to examples of embodiments of the invention, there is provided an apparatus comprising control information receiving and processing means for receiving and processing a control information indicating a target buffer delay value, flow control parameter determining means for determining a flow control parameter on the basis of the received target buffer delay value, and flow control means for causing transmission of the determined flow control parameter to another network element for setting a data stream to be received via a specified interface. For the purpose of the present invention as described herein above, it should be noted that

- an access technology via which signaling is transferred to and from a network element may be any technology by means of which a network element or sensor node can access another network element or node (e.g . via a base station or general ly an access node) . Any present or futu re technology, such as WLAN (Wireless Local Access Network), WiMAX (Worldwide Interoperability for Microwave Access), LTE, LTE-A, Bluetooth, Infrared, and the like may be used ; although the above technologies are mostly wireless access technologies, e.g . in different radio spectra, access tech nol og y i n the sense of the present i nventio n i m pl ies a lso wi red technologies, e.g . IP based access technologies like cable networks or fixed lines but also circuit switched access technologies; access technologies may be distinguishable in at least two categories or access domains such as packet switched and circuit switched, but the existence of more than two access domains does not impede the invention being applied thereto,

- usable communication networks, stations and transmission nodes may be or comprise any device, apparatus, unit or means by which a station, entity or other user equipment may connect to and/or utilize services offered by the access network; such services include, among others, data and/or (audio-) visual communication, data download etc. ;

- a user equipment or communication network element (station) may be any device, apparatus, unit or means by which a system user or subscriber may experience services from an access network, such as a mobile phone or smart phone, a personal digital assistant PDA, or computer, or a device having a corresponding functionality, such as a modem chipset, a chip, a module etc., which can also be part of a UE or attached as a separate element to a UE, or the like;

- method steps likely to be implemented as software code portions and being run using a processor at a network element or terminal (as examples of devices, apparatuses and/or modules thereof, or as examples of entities including apparatuses and/or modules for it), are software code independent and can be specified using any known or future developed programming language as long as the functionality defined by the method steps is preserved ;

- generally, any method step is suitable to be implemented as software or by hardware without changing the idea of the invention in terms of the functionality implemented ;

- method steps and/or devices, apparatuses, units or means likely to be implemented as hardware components at a terminal or network element, or any module(s) thereof, are hardware independent and can be implemented using any known or future developed hardware technology or any hybrids of these, such as a microprocessor or CPU (Central Processing Unit), MOS (Metal Oxide Semiconductor), CMOS (Complementary MOS), BiMOS (Bipolar MOS), BiCMOS (Bipolar CMOS), ECL (Emitter Coupled Logic), TTL (Transistor-Transistor Log ic), etc. , using for example ASIC (Appl ication

Specific IC (Integrated Circuit)) components, FPGA (Field-programmable Gate Arrays) components, CPLD (Complex Programmable Logic Device) components or DSP (Digital Signal Processor) components; in addition, any method steps and/or devices, units or means likely to be implemented as software com p o n e nts m a y fo r exa m p l e be b ase d o n a n y se cu rity architecture capable e.g . of authentication, authorization, keying and/or traffic protection;

- devices, apparatuses, units or means can be implemented as individual devices, apparatuses, units or means, but this does not exclude that they are implemented in a distributed fashion throughout the system, as long as the functionality of the device, apparatus, unit or means is preserved ; for example, for executing operations and functions according to examples of embodiments of the invention, one or more processors may be used or shared in the processing, or one or more processing sections or processing portions may be used and shared in the processing, wherein one physical processor or more than one physical processor may be used for implementing one or more processing portions dedicated to specific processing as described,

- an apparatus may be represented by a semiconductor chip, a chipset, or a (hardware) module comprising such chip or chipset; this, however, does not exclude the possibility that a functionality of an apparatus or module, instead of being hardware implemented, be implemented as software in a (software) module such as a computer program or a computer program product comprising executable software code portions for execution/being run on a processor;

- a device may be regarded as an apparatus or as an assembly of more than one apparatus, whether functionally in cooperation with each other or functionally independently of each other but in a same device housing, for example.

As described above, there is provided a flow control mechanism usable for a multiflow communication . An RNC sends to the Node Bs involved in the multiflow communication a target buffer delay value determined by the RNC. The Node Bs use the target buffer delay value for determining a target buffer size which is signaled to the RNC for flow control purposes.

Although the present invention has been described herein before with reference to particular embodiments thereof, the present invention is not limited thereto and various modifications can be made thereto.

Claims

1. An apparatus comprising

at least one processor,

at least one interface to at least one other network element, and at least one memory for storing instructions to be executed by the processor, wherein

the at least one memory and the instructions are configured to, with the at least one processor, cause the apparatus at least to perform :

a connection property determination function configured to determine a connection property for a communication using a transmission buffer, a calculation function configured to calculate a target buffer delay value on the basis of the determined connection property, and

a control function config u red to cause transmission of a control information indicating the calculated target buffer delay value.

2. The apparatus according to claim 1, wherein the at least one memory and the instructions are further configured to, with the at least one processor, cause the apparatus at least to perform :

a measurement signal transmission function configured to cause transmission of a measurement signal via a specified interface towards another network element,

a response signal receiving function configured to receive a response signal in reply to the measurement signal,

wherein the connection property determination function is configured to determine a connection property for a communication via the specified interface on the basis of information of the measurement signal and the response signal, and

the calculation function is configured to calculate the target buffer delay value on the basis of the determined connection property.,

3. The apparatus according to claim 2, wherein the at least one memory and the instructions are configured to, with the at least one processor, further cause the apparatus at least to perform : a multiflow communication function configured to conduct a multiflow communication with at least two other network elements by splitting a data flow into plural independent data streams towards each of the at least two other network elements, wherein

the measurement signal transmission function is further configured to cause transmission of a respective measurement signal via the specified interface towards each of the at least two other network elements,

the response signal receiving function is further configured to receive a respective response signal in reply to each the respective measurement signals,

the connection property determination function is configured to determine respective connection property values for a communication via the specified interface on the basis of information of each of the respective measurement signals and each of the respective response signals,

the ca lcu l ation fu nction is fu rther config u red to use one of the determined connection property values as the connection property value for calculating the target buffer delay value, and

the control function is further configured to cause transmission of the control information indicating the calculated target buffer delay value to each of the at least two other network elements.

4. The apparatus according to claim 2, wherein the connection property is a round trip time of the communication via the specified interface which is determined on the basis of timing information of the measurement signal and the response signal.

5. The apparatus according to claim 3, wherein the respective connection property is a respective round trip time of the communication via the specified interface which is determined on the basis of timing information of the respective measurement signal and the respective response signal, wherein the calculation function is further configured to use the highest one of the determined round trip times for calculating the target buffer delay value.

6. The apparatus according to any of claims 2 to 5, wherein the measurement signal transmission function is further configured to cause the transmission of a ping-type signal as the measurement signal, and

the response signal receiving function is further configured to receive an acknowledgement signal in reply to the ping-type signal.

7. The apparatus according to any of claims 2 to 6, wherein

the measurement signal transmission function is further configured to cause the transmission of the measurement signal periodically and/or triggered by a predetermined event.

8. The apparatus according to any of claims 4to 5, wherein

the calculation function is further configured to calculate the target buffer delay value by multiplying the determined round trip time with a predetermined value.

9. The apparatus according to claim 8, wherein the predetermined value is equal to or greater than 2.5.

10. The apparatus according to claim 1, wherein the connection property determination function is further configured

to determine a data rate fluctuation,

to monitor whether the data rate fluctuation exceeds a threshold, and wherein the calculation function is further configured to, if the data rate fluctuation exceeds the threshold, increase a value of the target buffer delay value.

11. The apparatus according to claim 1, wherein the connection property determination function is further configured

to receive and process an ind ication regard ing a buffer underru n state,

and wherein the calculation function is further configured to, if the indication regarding the buffer underrun state is received, increase a value of the target buffer delay value.

12. The apparatus according to any of claims 1 to 12, wherein the apparatus is comprised in a communication network control element, such as a radio network controller of a 3GPP based cellular communication network, and

the specified interface is an interface between the communication network control element and at least one base transceiver network element controlled by the communication network control element.

13. A method comprising

determining a connection property for a communication using a transmission buffer,

calculating a target buffer delay value on the basis of the determined connection property, and

transmitting a control information indicating the calculated target buffer delay value.

14. The method according to claim 13, further comprising :

transmitting a measurement signal via a specified interface towards another network element,

receiving a response signal in reply to the measurement signal, wherein the connection property is determined for a communication via the specified interface on the basis of information of the measurement signal and the response signal, and

the target buffer delay value is calculated on the basis of the determined connection property.

15. The method according to claim 14, further comprising

conducting a multiflow communication with at least two other network elements by splitting a data flow into plural independent data streams towards each of the at least two other network elements, wherein a respective measurement signal is transmitted via the specified interface towards each of the at least two other network elements,

a respective response signal is received in reply to each the respective measurement signals,

respective connection property values are determined for a communication via the specified interface on the basis of information of each of the respective measurement signals and each of the respective response signals,

one of the determined connection property values is used as the connection property value for calculating the target buffer delay value, and the control information indicating the calculated target buffer delay value is transmitted to each of the at least two other network elements.

16. The method according to claim 14, wherein the connection property is a round trip time of the communication via the specified interface which is determined on the basis of timing information of the measurement signal and the response signal.

17. The method according to claim 15, wherein the respective connection property is a respective round trip time of the communication via the specified interface which is determined on the basis of timing information of the respective measurement signal and the respective response signal, wherein the highest one of the determined round trip times is used for calculating the target buffer delay value.

18. The method according to any of claims 14 to 17, wherein

a ping-type signal is transmitted as the measurement signal, and an acknowledgement signal is received in reply to the ping-type signal.

19. The apparatus according to any of claims 14 to 18, wherein

the measurement signal is transmitted periodically and/or triggered by a predetermined event.

20. The method according to any of claims 16 to 17, wherein

the target buffer delay value is calculated by mu lti plyi ng the determined round trip time with a predetermined value.

21. The method according to claim 20, wherein the predetermined value is equal to or greater than 2.5.

22. The method according to claim 13, further comprising determining a data rate fluctuation,

monitoring whether the data rate fluctuation exceeds a threshold, and, if the data rate fluctuation exceeds the threshold, increasing a value of the target buffer delay value.

23. The method according to claim 13, further comprising

receiving and processing an indication regarding a buffer underrun state,

and if the indication regarding the buffer underrun state is received, increasing a value of the target buffer delay value.

24. The method according to any of claims 13 to 23, wherein

the method is implemented in a communication network control element, such as a radio network controller of a 3GPP based cellular communication network, and

25. An apparatus comprising

at least one processor,

a control information receiving and processing function configured to receive and process a control information indicating a target buffer delay value,

a fl ow co ntro l pa ra mete r determ i n i n g fu n cti o n co nfi g u red to determine a flow control parameter on the basis of the received target buffer delay value, and

a flow control function configured to cause transmission of the determined flow control parameter to another network element for setting a data stream to be received via a specified interface.

26. The apparatus according to claim 25, wherein the at least one memory and the instructions are further configured to, with the at least one processor, cause the apparatus at least to perform :

a target buffer size calculation function configured to calculate a target buffer size of a transmission buffer by multiplying the received target buffer delay value with a data rate of a downlink communication to which the transmission buffer is related, wherein

the flow control parameter determining function is further configured to determine the flow control parameter on the basis of the calculated target buffer size.

27. The apparatus according to claim 25 or 26, wherein the at least one memory and the instructions are further configured to, with the at least one processor, cause the apparatus at least to perform :

a measu rement sig nal receiving function config ured to receive a measurement signal via the specified interface, and

a response signal preparing and transmitting function configured to prepare and cause transmission of a response signal in reply to the measurement signal.

28. The apparatus according to claim 27, wherein

the measurement signal receiving function is further configured to receive a ping-type signal as the measurement signal, and

the response signal preparing and transmitting function is further configured to prepare and cause transmission of an acknowledgement signal in reply to the ping-type signal.

29. The apparatus according to claim 25, wherein the at least one memory and the instructions are further configured to, with the at least one processor, cause the apparatus at least to perform :

a buffer underrun state detection device configured to detect a buffer underrun state and to send a buffer undderun indication to the communication network control element.

30. The apparatus according to any of claims 25 to 29, wherein the apparatus is comprised in a communication element, such as a base transceiver network element of a 3GPP based cellular communication network, and

the specified interface is an interface between the communication element and a communication network control element such as a radio network controller controlling the communication element.

31. A method comprising

receiving and processing a control information indicating a target buffer delay value,

determining a flow control parameter on the basis of the received target buffer delay value, and

transmitting the determined flow control parameter to another network element for setting a data stream to be received via a specified interface.

32. The method according to claim 31, further comprising

calculating a target buffer size of a transmission buffer by multiplying the received target buffer delay value with a data rate of a downlink communication to which the transmission buffer is related, and

determining the flow control parameter on the basis of the calculated target buffer size.

33. The method according to claim 31 or 32, further comprising

receiving a measurement signal via the specified interface, and preparing and transmitting a response signal in reply to the measurement signal.

34. The method according to claim 33, wherein

a ping-type signal is received as the measurement signal, and an acknowledgement signal is prepared and transmitted in reply to the ping-type signal.

35. The method according to claim 31, further comprising

detecting a buffer underrun state and send a buffer undderun indication to the communication network control element.

36. The method according to any of claims 31 to 35, wherein

the method is implemented in a communication element, such as a base transceiver network element of a 3GPP based cellular communication network, and

37. A computer program product for a computer, comprising software code portions for performing the steps of any of claims 13 to 24 or 31 to 36 when said product is run on the computer.

38. The computer program product according to claim 37, wherein

the computer program product comprises a computer-readable medium on which said software code portions are stored, and/or

the computer program product is directly loadable into the internal memory of the computer and/or transmittable via a network by means of at least one of upload, download and push procedures.