WO2006086691A2

WO2006086691A2 - A network for providing a streaming service

Info

Publication number: WO2006086691A2
Application number: PCT/US2006/004845
Authority: WO
Inventors: Anthony Richard May; Craig Cameron Watson; Andrew Poh
Original assignee: Motorola, Inc.
Priority date: 2005-02-10
Filing date: 2006-02-10
Publication date: 2006-08-17
Also published as: WO2006086691A3; GB2423219A; GB2423219B; GB0502816D0

Abstract

A communication system (100) comprises a wireless network node (109) and a server (101) which provides a service to an end client in the wireless network node (109). The service may be a streaming audio or video signal. The communication system (100) further comprises a network proxy client (113) to facilitate the service by operating as a proxy client for the server (101) and to communicate with the end client (103) over a wireless communication link (111). The network proxy client (113) may specifically operate as a proxy server for the end client (103). The network proxy client (113) is further arranged to control a characteristic of the server (101) in response to a radio characteristic indication of the wireless link (111). The network proxy client (113) may specifically control the source encoding data rate of the server (101) in response to a throughput indication for the wireless link (111).

Description

A NETWORK PROXY CLIENT, A COMMUNICATION SYSTEM AND A METHOD FOR PROVIDING A SERVICE BETWEEN A SERVER AND AN END

CLIENT

Field of the invention

The invention relates to a network proxy client, a communication system and a method for providing a service between a server and an end client and in particular, but not exclusively, to provision of a streaming service.

Background of the Invention

In the last decade, data communication has become increasingly widespread and in the last few years wireless data communication in domestic and enterprise environments have become increasingly commonplace and an increasing number of wireless communication systems have been designed and deployed. Most such data communication networks comprise both wired and wireless segments. For example, a cellular communication system comprises a wired core network and a radio access network comprising both wired network connections as well as wireless connections to mobile stations over the air interface.

As another example, traditional wired Local Area Networks (LANs) are increasingly being provided with wireless Access Points allowing network nodes to connect through wireless connections. In particular, the use of wireless networking has become prevalent and wireless network standards such as IEEE 801.11b and IEEE 8OLlIg have become commonplace. Many of these wireless networks use the Internet Protocol (IP) for a practical and convenient implementation. In traditional wired (IP) networks there is only a single type of network between a server and a client. This wired network may suffer from network congestion and a number of techniques and algorithms have been developed for an efficient utilization of the network. In particular, multimedia streaming architectures and protocols have been designed to ensure that a multimedia stream is efficiently and reliably transmitted across such a network even as the congestion conditions vary.

However in wireless (IP) networks there are typically two different types of network between the server and the client, namely a wired core network and a wireless edge network. These two network types have substantially different characteristics and properties. For example, the wired core network typically suffers from congestion problems whereas the wireless part of the network typically suffers from packet loss caused by characteristics of the radio channel. However, current solutions do not consider the performance of each network type separately but assume that the end to end link can be treated as a homogeneous network.

Such an approach typically results in suboptimal performance.

For example, the radio propagation conditions for a wireless connection may change very quickly and accordingly the communication characteristics for the transmission of data over this link may also change very quickly. Specifically, the data rate and error rate may change quickly and substantially and the change may further be independent of the general loading of the communication network.

It may e.g. cause problems when the available data rate on a wireless link suddenly drops so that the current data rate provided by the server can no longer be supported. After a delay, due to e.g. network transport delays or averaging delays in the client etc, the server can adjust the data rate of the stream to match the current throughput of the wireless link in response to feedback data from the end client. However, due to the delay, a number of data packets at the higher data rate are already transmitted from the server and these data packets must be buffered until they can be transmitted over the wireless link. Accordingly, an increased buffer size is required. Specifically, the packet buffer of a wireless base station may typically contain a number of packets at the previous higher data rate, and these data packets must be transmitted before the packets of the lower data rate stream can be transmitted. The transmission time of these packets can greatly exceed the presentation time of the packets, causing the client buffer to become depleted, i.e. playout buffer starvation. This can result in the mobile client having to stop playback of the stream and re- buffer data before continuing playback. Thus, a very noticeable disruption to a streaming service may result.

In G Cheung, T Yoshimura, "Streaming Agent: A Network Proxy for Media Streaming in 3G Wireless Networks", International Packet Video Workshop, April 24-26, 2002, Westin Convention Center, Pittsburgh, PA, USA, it has been proposed that a streaming system can be improved if a network proxy agent is added at the junction between the wired and wireless parts of the network. This network proxy agent comprises functionality for acknowledging packets as they arrive.

This approach may allow the server to distinguish between packet losses caused by congestion in the wired network and packet losses in the wireless section thereby allowing for an improved adaptation strategy. However, it does not provide for an optimal performance of the communication system and a further improvement would be advantageous. For example, although improved measurements are provided the system remains inflexible and does not allow for an optimized adaptation to the individual characteristics of the wired and wireless sections of the network. In particular, this may result in the requirement of large buffers in the end client and for the wireless link.

As a specific example, a drop in the data rate of the wireless link may be detected by the server which may accordingly modify a data rate of the transmitted service. However, before the reduced data rate data packets are transmitted over the wireless link, the buffered higher data rate data packets must first be transmitted resulting in a significant delay in the adaptation. This may cause interruptions in the presentation of a streaming signal due to the client buffer emptying as the wireless link cannot keep up with the streaming rate of the buffered higher data rate data packets.

As another example, if the wireless link is temporarily lost, the server will continue to send out data packets until this is detected. This may cause an overflow of the buffer of the transmitter for the wireless link. Eventually, the client in the wireless node will report that data packets have been lost but due to the inherent delay, this may require retransmission of a significant number of packets resulting in an inefficient use of the wired network.

Hence, an improved system for a communication network comprising a non-wireless and a wireless section would be advantageous and in particular a system allowing increased flexibility, reduced buffer levels, more efficient usage of the wired network, fewer service disruptions and/or improved performance would be advantageous.

Summary of the Invention

Accordingly, the Invention seeks to preferably mitigate, alleviate or eliminate one or more of the above mentioned disadvantages singly or in any combination.

According to a first aspect of the invention there is provided a communication system comprising: a wireless network node; a server for providing a service to an end client of the wireless network node; a network proxy client arranged to facilitate the service by operating as a proxy client for the server and to communicate with the end client over a wireless communication link, the network proxy client being arranged to control a characteristic of the server in response to a radio characteristic indication of the wireless link.

The invention may allow an improved performance in a communication network and may in particular allow an improved adaptation to the individual characteristics of the wireless section and the wired section of a communication network. The invention may allow an improved adaptation of server operation to variations in characteristics of the wireless link. This may provide improved performance and may in many embodiments provide reduced buffer size requirements.

The wireless network node is not necessarily a network node which communicates directly over a wireless network but may be a network node which is directly or indirectly coupled to another network node that communicates over the wireless link. Thus, a wireless network node is a network node for which the path between the server and the end client includes at least one wireless link.

The radio characteristic indication may specifically be a parameter or characteristic which is indicative of a throughput rate of the wireless link. Typically, the network proxy client is arranged to control the characteristic of the server by transmitting data, such as control commands or feedback data, to the server. The controlled characteristic may in particular be a characteristic of the data transmissions supporting the service.

According to an optional feature of the invention, the network proxy client is arranged to operate as a server for the end client. This provides increased flexibility and/or improved adaptation to the individual characteristics of the wired and wireless sections. The feature may additionally or alternatively facilitate implementation of the server, the end client and/or the network proxy client. Specifically, the server may interact with the network proxy client without any knowledge of the end client. Alternatively or additionally, the end client may interact with the network proxy client without any knowledge of the server.

According to an optional feature of the invention, the radio characteristic indication comprises a buffer characteristic of a buffer for the wireless link.

The radio characteristic indication may be a buffer loading of a storage means buffering data for transmission over the wireless link. The buffer characteristic may be a particularly suitable indication allowing improved performance. According to an optional feature of the invention, the radio characteristic indication comprises a buffer characteristic of a buffer of the end client.

The radio characteristic indication may be a buffer loading of a presentation buffer of the end client. The presentation buffer may be storage means buffering data for presentation to a user by the end client. The buffer characteristic may be a particularly suitable indication allowing improved performance.

According to an optional feature of the invention, the network proxy client is arranged to modify a data rate of the server in response to the radio characteristic indication. This may provide for an improved performance and may in particular allow for a data rate of the server to be adapted to the characteristics of the wireless link.

According to an optional feature of the invention, the data rate is a source encoding data rate. This may provide particularly suitable performance and may in particular provide an improved quality of a presented signal for the current properties of the wireless link.

According to an optional feature of the invention, the network proxy client is arranged to request retransmission of data packets already transmitted to the proxy client at a different data rate in response to the radio characteristic indication.

Specifically, the invention may in some embodiments allow data already present in a transmission buffer for the wireless link to be retransmitted at a different (source) data rate from the server. The data of the transmission buffer may then be replaced by data at the updated data rate. The feature may allow improved performance and in particular a faster adaptation to varying characteristics of the wireless link. The feature may mitigate or eliminate service disruptions, buffer overflows or underflows and/or may reduce buffer size requirements. According to an optional feature of the invention, the network proxy client is arranged to transmit a time stamp of the earliest data packet of a buffer for the wireless link. This provides for a practical and efficient means of controlling the server and is particularly suitable for indicating data to be retransmitted at a different data rate.

According to an optional feature of the invention, the network proxy client is arranged to pause data from the server in response to the radio characteristic indication. This may allow efficient and low complexity operation in many embodiments and may improve performance and/or mitigate or eliminate service disruptions, buffer overflows or underflows and/or may reduce buffer size requirements.

According to an optional feature of the invention, the network proxy client is arranged to pause data from the server in response to a disruption of the wireless link. This may allow efficient and low complexity operation in many embodiments and may improve performance and/or mitigate or eliminate service disruptions, buffer overflows or underflows and/or may reduce buffer size requirements. Specifically, if the wireless link is disrupted, the server may be paused thereby reducing the buffer requirements of the network.

According to an optional feature of the invention, the network proxy client is arranged to transmit keep-alive messages to the server during a data pause. This may allow for a service to be maintained at a server despite a disruption to a wireless link supporting the service.

According to an optional feature of the invention, the network proxy client is arranged to communicate with the server using a Real Time Control Protocol, RTCP, and the server is arranged to modify the characteristic in response to RTCP data received from the network proxy client.

This may provide for a particularly efficient and low complexity implementation as RTCP is particularly suitable for controlling the server operation. According to an optional feature of the invention, the service is a streaming data service. The invention is particularly suitable for a streaming service such as a streaming video and/or audio service. For example, the server may, in response to signalling from the network proxy client, automatically adjust the operation, such as the source encoding data rate, to match the current characteristics of the wireless link.

According to an optional feature of the invention, the service is a web service and the network proxy client is a web proxy client. The invention may allow an improved web service. The network proxy client may for example reformat HTTP request messages from the end client in response to the radio characteristic indication before forwarding these to the server. As another example, the network proxy client may reformat HTTP request messages to remove images and other bandwidth-intensive graphics from the HTML web pages before delivering them over the wireless link.

According to an optional feature of the invention, the network proxy client is arranged to communicate with the server over a non-wireless communication path. The network proxy client may specifically be located at the transition between a wired core network section and a wireless access network.

The communication system may specifically be a cellular communication system and the network proxy client may be comprised in a base station. The invention may specifically provide an improved cellular communication system and a low complexity implementation.

According to a second aspect of the invention, there is provided a network proxy client for a communication system, the network proxy client being arranged to facilitate a service between a server for providing a service to an end client of a wireless network node by operating as a proxy client for the server and to communicate with the end client over a wireless communication link and the network proxy client further being arranged to control a characteristic of the server in response to a radio characteristic indication of the wireless link. According to a third aspect of the invention, there is provided a method of providing a service between a server and an end client in a wireless node comprising: a network proxy client operating as a proxy client for the server; the network proxy communicating with the end client over a wireless communication link; and the network proxy client controlling a characteristic of the server in response to a radio characteristic indication of the wireless link.

These and other aspects, features and advantages of the invention will be apparent from and elucidated with reference to the embodiment(s) described hereinafter.

Brief Description of the Drawings

Embodiments of the invention will be described, by way of example only, with reference to the drawings, in which

FIG. 1 illustrates an example of a communication system in accordance with some embodiments of the invention;

FIG. 2 illustrates a functional flow of a connection path between a server and an end client in accordance with some embodiments of the invention;

FIG. 3 illustrates a flow chart of an exemplary method of operation for a network proxy client in accordance with some embodiments of the invention;

FIG. 4 illustrates an example of the operation of a typical adaptive streaming system; and

FIG. 5 illustrates an example of the operation of a network proxy client in accordance with some embodiments of the present invention. Detailed Description of Embodiments of the Invention

The following description focuses on embodiments of the invention applicable to a streaming video or audio service in a cellular communication system. However, it will be appreciated that the invention is not limited to this exemplary application.

FIG. 1 illustrates an example of a communication system 100 in accordance with some embodiments of the invention.

The communication system 100 comprises a server 101 which provides a service to and an end client 103. In the described example, the service is a streaming audio or video sequence such as an Internet radio service.

In the system of FIG. 1, the server 101 is coupled to a core network 105. In the example, the communication system is an Internet Protocol (IP) based network wherein the entire system uses the IP protocol and in particular the communication from the server 101 to the end client 103 uses the Internet Protocol. The core network 105 is thus an IP network and it may comprise e.g. elements of the Internet as well as a core network of a cellular communication system such as the Universal Mobile Telecommunication System (UMTS).

The core network 105 is coupled to a base station 107. The base station 107 may specifically be a node B of a UMTS cellular communication system. The base station 107 communicates with a User Equipment (UE) 109 over a wireless link 111 of the air interface of the cellular communication system.

In the example, the UE 109 comprises the end client 103. In other embodiments, the end client 103 may be comprised in other network nodes coupled to the UE 109 for example through a sub-network. In the example, the server 101 thus provides a streaming audio service to the end client 103. The end client 103 and the UE 109 comprise functionality for presenting this to a user. Specifically, the end client 103 comprises functionality for decoding the received signal and for generating an audio signal which is presented through a speaker of the UE 109.

In accordance with the described embodiments of the invention, the communication system furthermore comprises a network proxy client 113 which is arranged to facilitate the service by operating as a proxy client for the server 109. Thus, the server 101 does not directly provide the service to the end client 103 but rather provides the service to the network proxy client 113. The network proxy client 113 communicates with the end client 103 over a wireless communication link thereby providing the service to the end client 103.

In the example of FIG. 1 , the network proxy client 113 is comprised at the boundary between the wired and the wireless sections of the communication system and specifically the network proxy client 113 is located in the base station 107 communicating over the wireless link 111.

The network proxy client 113 is furthermore operable to determine a radio characteristic indication of the wireless link 111. For example, the network proxy client 113 may determine a radio characteristic indication being indicative of the current throughput of the wireless link 111. The network proxy client 113 is furthermore arranged to control a characteristic of the server in response to the radio characteristic indication of the wireless link 111.

The control of the server 101 is specifically achieved by signalling being exchanged between the network proxy client 113 and the server 101. In some embodiments, the network proxy client 113 may transmit specific and explicit commands to the server 101 causing the server 101 to modify its operation. In other embodiments, the server 101 may be capable of modifying the operation in response to non-explicit or nonspecific signalling from the network proxy client 113.

In the described embodiments, the network proxy client 113 is not a transparent proxy but is an individual client. Thus, the network proxy client 113 is not transparent to the server 101. Rather, in some embodiments, the end client 103 may be invisible to the server 101 which operates as if it is providing the service to the network proxy client 113 directly. Thus, the server 101 and/or the end client 103 may only communicate directly with the network proxy client 113 and not with the opposite entity.

FIG. 2 illustrates a functional flow of a connection path between the server 101 and the end client 103 in accordance with some embodiments of the invention. As illustrated, the server 101 communicates with the network proxy client 113 to provide the data supporting the service. The network proxy client 113 then further communicates with the end client 103 to forward the data supporting the service to the end client 103.

It will be appreciated that the network proxy client 113 will not only be able to forward service data but may also forward signalling such as commands between the end client 103 and the server 101. Furthermore, these commands may be modified as appropriate by the network proxy client 113 and new commands may be created by the network proxy client 113 and transmitted to the server 101 or the end client 103.

Specifically, the network proxy client 113 comprises a service proxy client 201 which interfaces with the server 101 and which appears as an end client to the server 101. The connection between the server 101 and the service proxy client 201 is entirely in the wired network section and can thus be optimised for this purpose. For example, the service proxy client 201 may request data from the server to suit the current wired network characteristics and the current buffer loading of the network proxy client 113. Hence, if there is currently no congestion in the wired network and the network proxy client 113 has substantial free buffer capacity, the service proxy client 201 may request additional data from the server 101.

The service proxy server 203 is coupled to the service proxy client 201 and exchanges data service data with this. Furthermore, the service proxy server 203 communicates with the end client 103 over the wireless link 111 and provides the streaming audio data to the end client 103. Specifically, the service proxy server 203 appears as the original server to the end client 103 which need not be aware that the service proxy server 203 is not the originating server. The service proxy server 203 is furthermore arranged to provide data over the wireless link 111 in response to the current characteristics of the wireless link 111. For example, the service proxy server 203 may schedule data using link adaptation wherein data is transmitted at high data rate but only when channel conditions are favourable.

Thus, the arrangement allows for differentiation and separation between the operation for the wired network section and the wireless network section. This allows an improved individual optimisation and adaptation to the individual characteristics of the wired and wireless sections. As these characteristics are typically substantially different a significant benefit may be achieved.

However, although this separation is beneficial, improved performance can be achieved by modifying the operation of the server 101 to suit the characteristics of the wireless link 111. Typically, the wireless link is the most critical part of the path from the server 101 to the end client 103 and is typically the section which varies most and fastest due to the high degree of variation in the propagation conditions for most wireless systems.

Accordingly, the network proxy client 113 is operable to determine a radio characteristic indication and the service proxy client 201 is arranged to transmit messages to the server 101 which cause the server 101 to modify its operation. For example, the network proxy client 113 may determine an average current throughput for the wireless link 111 and the service proxy client 201 may transmit commands to the server 101 causing this to perform a source encoding resulting in the desired average data rate. The service proxy server 203 may however communicate with the end client 103 using e.g. link adaptation and thus an uneven data rate which only on average corresponds to the data rate from the server. Thus, the embodiments may allow for individual adaptation to the individual characteristics while ensuring that the server 101 operates in a suitable way for the entire path. FIG. 3 illustrates a flow chart of an exemplary method of operation for a network proxy client in accordance with some embodiments of the invention. The network proxy client may specifically be the network proxy client 113 of FIG. 1 and 2 and will be described with reference to this.

In the example of FIG. 3, the network proxy client 113 is arranged to adapt the data rate of the transmitted data from the server 101 in response to a radio characteristic indication for the wireless link 111.

The method initiates in step 201 wherein data is received from the server 101. The data is buffered by the network proxy client 113 for transmission over the wireless link 111. Thus, the base station 107 comprises a wireless buffer which buffers the data for transmission over the air interface. In the example, the wireless data buffer is a First-In-First-Out (FIFO) data buffer.

Step 201 is followed by step 203 wherein the network proxy client 113 determines a radio characteristic indication for the wireless link 111. The radio characteristic indication is in the example indicative of the current throughput rate achieved over the wireless link 111.

Specifically, the radio characteristic indication may be a buffer characteristic of the wireless data buffer such as a buffer loading of the wireless data buffer. If the current throughput of the wireless link 111 is less than the data rate of the server 101 the buffer level increases, and if the wireless link 111 is higher than the data rate of the server 101 the buffer level decreases. Accordingly the buffer level provides a good indication of the current throughput of the wireless link 111 and the preferred data rate from the server 101.

In other embodiments, the radio characteristic indication may alternatively or additionally comprise a buffer characteristic of a buffer of the end client 103. For example, the end client 103 may comprise a presentation buffer which buffers data received over the wireless link 111 prior to outputting this to a user. For a given source encoding data rate, data is read from the presentation buffer at a fixed data rate and if the throughout of the wireless link 111 is below that required to support this rate, the loading of the presentation buffer will reduce. Thus, the buffer loading may provide a good indication of the current throughput of the wireless link 111 and the 5 preferred source encoding rate from the server 101. The buffer loading of the presentation buffer may be estimated by the network proxy client 113 from knowledge of a presentation rate and a data rate of transmitted data or may e.g. be reported to the base station 107 by the UE 107.

10 In other embodiments, the radio characteristic indication may alternatively or additionally comprise e.g. direct measurements or characteristics of the wireless link 111 such as an actual throughput rate, error rate, path loss, channel estimate etc. These measures may for example be estimated by the network proxy client 113 in response to feedback from the UE 109.

15

Step 203 is followed by step 205 wherein it is determined if the radio characteristic indication has changed. If not, the method continues in step 207 wherein data is read out from the wireless buffer and transmitted to the end client 103. However, if the radio characteristic indication has changed sufficiently, the method continues in step

20 209.

It will be appreciated that any suitable criterion or algorithm for determining if a sufficient change has occurred may be used including consideration of additional parameters and/or evaluation of the radio characteristic indication over a given time 25 interval (such as averaging). A simple criterion may be to determine that a sufficient change has occurred if the wireless buffer loading is above a first threshold or below a second threshold. Thus, as long as the wireless buffer loading is within a desired interval, no changes are made to the data rate of the server 101.

30 In step 209 the network proxy client 113 signals to the server 101 in order to modify the data rate of the server 101 when providing the service to the end client 103. The signalling may be an explicit message requesting that the server 101 modifies the data rate to a given value or by a given relative value. For example, if the wireless buffer loading increases above a given threshold, the network proxy client 113 may transmit a message to the server 101 requesting that the source encoding rate is 5 reduced to half the current value. In response, the server 101 modifies the source encoding rate (for example by using a different source encoder or by changing the encoding parameters for a multi-rate source encoder). Similarly, if the wireless buffer loading decreases below a given threshold, the network proxy client 113 transmits a message to the server requesting that the source encoding rate is increased to twice the 10 current value. In response, the server 101 modifies the source encoding rate.

Step 209 is followed by step 211 wherein data at the new data rate is received from the server 101.

15 Step 211 is followed by step 207 wherein data is read from the wireless buffer and transmitted to the end client 103.

Hence, as a specific example, the server may comprise a first encoding setting for source encoding an audio signal at 128 kbps and a second encoding setting for source

20 encoding the audio signal at 64 kbps. The network proxy client 113 may control the use of one or the other encoding setting in response to the buffer loading of the wireless buffer. Thus, when the buffer loading increases above the first threshold due to adverse propagation conditions, the network proxy client 113 switches the encoding rate to 64 kbps. When the buffer loading decreases below the second

25 threshold due to improving propagation conditions, the network proxy client 113 switches the encoding rate back to 128 kbps.

This control is managed by the network proxy client 113 without the end client 103 or the server 101 needing to consider that the service is provided over a wireless link 30 111. Indeed the service provided by the server 101 is to a network proxy client 113 which is connected through a wired network and thus data can be readily communicated with typically high certainty, low delay and low variations. Similarly, the end client 103 perceives that it is served by a server, in the form of the network proxy client 113, which is highly adapted to the characteristics of a wireless communication path. This approach may provide numerous advantages.

For example, preferably, the network proxy client 113 requests that data packets that are currently stored in the wireless data buffer are retransmitted from the server before these are transmitted over the wireless link 111. Specifically, when the network proxy client 113 transmits a request for a new data rate in step 209 it further includes a time stamp of the earliest data packet currently in the wireless buffer.

The server 101 then proceeds to encode data at the new data rate from the time indicated by the time stamp and transmits these data packets to the network proxy client 113 in a very short interval. Thus, new data packets comprising source encoded data is transmitted to the network proxy client 113 at a high effective communication data rate. Thus, in a very short time interval, the network proxy client 113 may receive new data packets at a different source encoding rate to replace the ones currently buffered in the wireless buffer.

Accordingly, the current approach allows for a very quick adaptation to the varying conditions of the wireless link 111 without requiring that the wireless FIFO buffer is first emptied by transmission of the buffered data. This may allow a much improved adaptation and may substantially reduce the requirements for the buffer size. It may also allow a significant reduction in disruptions to the data service. For example, it may be avoided that buffered data at a data rate higher than the throughput of the wireless link 111 cause the presentation buffer of the end client 103 to empty before the source encoding data rate reaches the wireless link 111.

In some embodiments, the Real Time Protocol (RTP) and or the User Datagram Protocol (UDP) may be used for the communication between the server 101 and the network proxy client 113. Thus, RTP/UDP/IP may be used to transport the media stream across the network from the server 101 to the network proxy client 113 (and possibly from the network proxy client 113 to the end client 103). In such an embodiment, the network proxy client 113 may provide the RTP timestamp of the oldest RTP packet in the wireless buffer to the server 101 when requesting a data rate change. The server may then provide a higher or lower data rate stream starting immediately after the last packet that was sent over the wireless link 111. All of the RTP packets associated with the media stream at the previous data rate are then replaced by the new RTP packets associated with the media stream at the new data rate. This allows the media stream to adapt very quickly to data rate changes in the wireless network, allowing a smaller buffer and hence better responsiveness in the end client 103, improving the user experience of the multimedia stream.

In some embodiments, the Real Time Streaming Protocol (RTSP) can be used to manage and control the media stream. RTSP is an application-level protocol for control and delivery of data with real-time properties. If the wireless link 111 is temporally lost, then before the wireless buffer overflows, the network proxy client 113 may send an RTSP message to pause the stream from the streaming server. When the wireless link 111 recovers, the network proxy client 113 may re-start the stream. This makes more efficient use of the core network, as packets do not need to be retransmitted. In addition, the network proxy client 113 may send out session keep-alive messages so that the server 101 does not terminate the streaming session. This means that when the wireless link 111 is re-established, the stream can continue without the user having to set up a new streaming session.

In some embodiments, the Real Time Control Protocol (RTCP) may be used between the server 101 and the end client 103. RTCP allows statistics about the media stream to be transmitted from the end client to the server. If the server does not support RTSP requests to change the rate of the encoded stream, then RTCP messages may be used by the network proxy client to modify the rate of the stream being transmitted by the server.

Embodiments of the invention may for example be implemented in future 3^rd

Generation Cellular Communication Systems and may in particular be advantageous in all-IP infrastructure equipment as planned by the 3^rd Generation Partnership Project (3GPP). In current 3GPP GPRS and Release 99 UMTS Terrestrial Radio Access Network (UTRAN) infrastructure equipment, the networks are not all-IP networks. The underlying transport mechanism for GPRS networks is GTP over ATM and SDH. In such networks, the RTP/UDP/IP packets from the streaming server may be 5 multiplexed with other real-time data and encapsulated as GTP packets and AAL5 packets then segmented into lots of ATM packets (also known as ATM cells in ATM terminology). The ATM cells may further be multiplexed with other ATM cells before being routed through the Core Network (CN) to the UTRAN. In current 3GPP UMTS Release 99 and Release 4, AAL2 over ATM are typically used on the User 10 Plane and AAL5 over ATM in the Control Plane. For 3GPP Release 5, 6 and beyond, either AAL2 over ATM or UDP over Data Link is supported.

In order to carry out the steps described in this invention in the RNC or Node B of such a network, the ATM cells may be reassembled back at the network proxy client 15 113 in order to recover the higher layer RTP/UDP/IP packets. Once the RTP packets associated with high data rate packets are replaced with the RTP packets associated with the lower data rate packets, the RTP/UDP/IP packets may be reformatted for transport over the wireless link 111.

20 In the following a specific example of the operation of the network proxy client 113 in controlling the wireless buffer in comparison to a conventional system is described to further clarify some example embodiments of the invention.

In streaming systems it is usual to specify a buffer size based on time, since maximum 5 network delays are specified in time. Hence the size of a buffer in bytes will depend on the bit rate of the stream. In the following figures, this is illustrated by specifying the buffer in terms of numbered bins, each representing a fixed unit of time, and each of which can hold a packet of data at any bit rate. To ease the explanation it is assumed that each bin holds a single packet; in practice they would typically hold 30 multiple packets, of differing sizes that average out to the target bit rate. Each packet is represented by a timestamp, T_n, and a bit rate R_n. The buffers are first in, first out, with data entering from the left and leaving to the right. FIG. 4 illustrates an example of the operation of a typical adaptive streaming system. At time instant t_\ (FIG. 4 illustrates five different time instants indicated by lower case t), the stream has progressed to the point where the end client buffer (e.g. the presentation buffer) is full, and a number of packets have been played out of the buffer. A new packet, T₉, is about to be transmitted over the wireless link 111 just before the average bit rate of the wireless link is halved (e.g. due to a change in wireless propagation conditions). In t₂, the client has played out the next packet of data and another packet, T₁₀, arrives, but because the data rate of the wireless link is halved, it takes twice as long to transmit the T₉ packet. By the time T₉ has been transmitted, another packet, T₁₁, arrives and another packet has been played from the client buffer, as shown for t₃.

At this time it may be identified that there is a problem with the data rate of the wireless link and the server may start transmitting a low data rate stream. In the time it takes to transmit T_1O, two more packets have been played out from the end client buffer and two low bit rate packets have been transmitted from the server, as shown in t₄. t₅ shows the state of the buffers at the time when the end client buffer stops being emptied, i.e. after the last large packet, T₁₁, has been transmitted and two more packets have been played out and transmitted.

FIG. 5 illustrates an example of the operation of a network proxy client 113 in accordance with some embodiments of the present invention.

At t_1; the stream has progressed to the point that the end client buffer is full, and a number of packets have been played out of the buffer. A new packet, T₉, is about to be transmitted over the wireless link just before the average bit rate of the wireless link is halved. At t₂ the client has played out the next packet of data and another packet, T₁₀, arrives, but because the data rate of the wireless link is halved, it takes twice as long to transmit the T₉ packet. By the time T₉ has been transmitted, another packet, T₁₁, arrives and another packet has been played from the client buffer, as shown at t₃. At this time the network proxy client 113 is able to spot that there is a problem with the data rate of the wireless link. Accordingly it may request a low data rate stream, starting from the oldest untransmitted packet in its buffer, which in this case is T₁₀. The server 101 sends the packets that appear before T₁₂, which was the next packet it was due to send, faster than real time in order to maintain the timing of the stream. The network proxy client 113 is then able to replace packets T₁₀, R₁ and T₁₁, R₁ with the new lower rate packets, T_1O, R₂ and T₁₁, R₂, as shown at t₄.

t₅ indicates that packet T_1O is transmitted in the time it takes for packet T₆ to be played out from the end client buffer, meaning that the end client buffer has stopped emptying. In reality the bit rate of the stream will be slightly less than the bit rate of the wireless link 111, and because the server 101 transmitted the extra packets faster than real time, the end client buffer will fill up again.

FIG. 4 and 5 clearly illustrate some benefits of the described embodiment. For the described conditions, the end client buffer in the streaming network proxy client 113 system had a maximum of one empty bin, whereas the server controlled system ended up with three empty bins. Similarly the wireless buffer in the server controlled system required four bins, whereas the streaming network proxy client 113 only required 2 bins, reducing the amount of network memory required. Hence, for a given buffer size, the streaming network proxy client 113 will be able to smooth out larger bit rate changes than a typical server controlled system.

In other embodiments, the network proxy client 113 may be used for other media types. For example, the network proxy client 113 may perform the functionality of a web proxy client. If the wireless channel conditions are poor or the wireless link is temporally lost, then before the wireless buffer overflows, the network proxy client 113 may send out a HTTP request to the web server and temporarily suspend all HTTP requests. This prevents the wireless buffer from overflow and makes more efficient use of the core network as HTTP packets do not need to be retransmitted. The network proxy client 113 may also implement dual TCP/IP stacks. One may be a regular TCP implementation (e.g. TCP Reno) for the wired network for connection to the web server in the core network and the other may e.g. be an optimised TCP implementation for the wireless link 111. The network proxy client 113 may also reformat all HTTP request messages to remove images and other bandwidth-intensive graphics from the HTML web pages before delivering them to the mobile devices.

In some embodiments, the described approach may be used for e.g. IEEE 802.11 wireless LAN networks, where the network proxy client 113 specifically may be located close to the WLAN Access Point (AP). In most current WLAN networks, RTP/UDP/IP packets are segmented into Ethernet frames and transported over the wired network. Accordingly, the RTP/UDP/IP packets may be reassembled from the Ethernet frames at the network proxy client 113.

It will be appreciated that the above description for clarity has described embodiments of the invention with reference to different functional units and processors. However, it will be apparent that any suitable distribution of functionality between different functional units or processors may be used without detracting from the invention. For example, functionality illustrated to be performed by separate processors or controllers may be performed by the same processor or controllers. Hence, references to specific functional units are only to be seen as references to suitable means for providing the described functionality rather than indicative of a strict logical or physical structure or organization.

The invention can be implemented in any suitable form including hardware, software, firmware or any combination of these. The invention may optionally be implemented at least partly as computer software running on one or more data processors and/or digital signal processors. The elements and components of an embodiment of the invention may be physically, functionally and logically implemented in any suitable way. Indeed the functionality may be implemented in a single unit, in a plurality of units or as part of other functional units. As such, the invention may be implemented in a single unit or may be physically and functionally distributed between different units and processors. Although the present invention has been described in connection with some embodiments, it is not intended to be limited to the specific form set forth herein. Rather, the scope of the present invention is limited only by the accompanying claims. Additionally, although a feature may appear to be described in connection with particular embodiments, one skilled in the art would recognize that various features of the described embodiments may be combined in accordance with the invention. In the claims, the term comprising does not exclude the presence of other elements or steps.

Furthermore, although individually listed, a plurality of means, elements or method steps may be implemented by e.g. a single unit or processor. Additionally, although individual features may be included in different claims, these may possibly be advantageously combined, and the inclusion in different claims does not imply that a combination of features is not feasible and/or advantageous. Also the inclusion of a feature in one category of claims does not imply a limitation to this category but rather indicates that the feature is equally applicable to other claim categories as appropriate. Furthermore, the order of features in the claims do not imply any specific order in which the features must be worked and in particular the order of individual steps in a method claim does not imply that the steps must be performed in this order. Rather, the steps may be performed in any suitable order. In addition, singular references do not exclude a plurality. Thus references to "a", "an", "first", "second" etc do not preclude a plurality.

Claims

1. A communication system comprising: a wireless network node; a server for providing a service to an end client of the wireless network node; a network proxy client arranged to facilitate the service by operating as a proxy client for the server and to communicate with the end client over a wireless communication link, the network proxy client being arranged to control a characteristic of the server in response to a radio characteristic indication of the wireless link.

2. The communication system claimed in claim 1 wherein the network proxy client is arranged to operate as a server for the end client.

3. The communication system claimed in any of the previous claims wherein the radio characteristic indication comprises a buffer characteristic of a buffer for the wireless link.

4. The communication system claimed in any of the previous claims wherein the radio characteristic indication comprises a buffer characteristic of a buffer of the end client.

5. The communication system claimed in any of the previous claims wherein the network proxy client is arranged to modify a data rate of the server in response to the radio characteristic indication.

6. The communication system claimed in claim 5 wherein the data rate is a source encoding data rate.

7. The communication system claimed in any of the previous claims wherein the network proxy client is arranged to request retransmission of data packets already transmitted to the proxy client at a different data rate in response to the radio characteristic indication.

8. The communication system claimed in claim 7 wherein the network proxy client is arranged to transmit a time stamp of the earliest data packet of a buffer for the wireless link.

9. The communication system claimed in any of the previous claims wherein the network proxy client is arranged to pause data from the server in response to the radio characteristic indication.

10. The communication system claimed in any of the previous claims wherein the network proxy client is arranged to pause data from the server in response to a disruption of the wireless link.

11. The communication system claimed in claim 10 or 11 wherein the network proxy client is arranged to transmit keep-alive messages to the server during a data pause.

12. The communication system claimed in any of the previous claims wherein the network proxy client is arranged to communicate with the server using a Real Time Control Protocol, RTCP, and the server is arranged to modify the characteristic in response to RTCP data received from the network proxy client.

13. The communication system claimed in any of the previous claims wherein the service is a streaming data service.

14. The communication system claimed in any of the previous claims wherein the service is a web service and the network proxy client is a web proxy client.

15. The communication system claimed in any of the previous claims wherein the network proxy client is arranged to communicate with the server over a non-wireless communication path.

16. The communication system claimed in any of the previous claims wherein the communication system is a cellular communication system.

17. The communication system claimed in claim 16 wherein the network proxy client is comprised in a base station.

18. A network proxy client for a communication system, the network proxy client being arranged to facilitate a service between a server for providing a service to an end client of a wireless network node by operating as a proxy client for the server and to communicate with the end client over a wireless communication link, and the network proxy client further being arranged to control a characteristic of the server in response to a radio characteristic indication of the wireless link.

19. A method of providing a service between a server and an end client in a wireless node comprising: a network proxy client operating as a proxy client for the server; the network proxy client communicating with the end client over a wireless communication link; and the network proxy client controlling a characteristic of the server in response to a radio characteristic indication of the wireless link.