Abstract:
Methods in an access node for establishing digital media streams between a media server and terminals in a customer premises network are provided. The method includes receiving, from the terminal, a request for establishing a first digital media stream by joining an already established digital media stream; determining transmission resources allocated to the customer premises network; comparing a sum of transmission resources required for the first digital media stream and the already established digital media streams between the media server and the customer premises network with the transmission resources allocated to the customer premises network; and establishing a digital substitution media stream replacing the first digital media stream. The digital substitution media stream is adapted to provide the same content as the first media stream but further adapted to require less transmission resources, so that the sum of transmission resources required for the digital substitution media stream and the already established digital media streams does not exceed the transmission resources allocated to the customer premises network. The substitution media stream is established by joining an already established digital media stream that requires less transmission resources.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a 35 U.S.C. §371 national stage application of PCT International Application No. PCT/SE2008/051349, filed on Nov. 26, 2008, the disclosure and contents of which is incorporated by reference herein as if set forth in its entirety. The above-referenced PCT International Application was published in the English language as International Publication No. WO 2010/062227 on Jun. 3, 2010. 
     FIELD 
     The present invention relates to a method and an access node for establishing digital media streams in a communication network. 
     BACKGROUND 
     Multimedia streaming services like IPTV represent a tremendous opportunity for service providers and network operators to deliver a truly personalized service experience to their customers. 
     But, it is also crucial to ensure an adequate Quality of Experience (QoE) for the end-users subscribing to the service. A key aspect of QoE is matching the service offering and the available network resources. In networks without resource control the consequences of a mismatch between service offering and available transmission resources are typically affecting multiple and ongoing services, and is in general a highly undesirable situation for operators. Dynamic resource control is the existing solution to prevent (additional) access to a service that will exceed available transmission resources. A device adapted to dynamically allocate bandwidth between a user and a service provider is disclosed in US patent application US 2007/0002897. Dynamic resource control has however some disadvantages. Rejecting access to a service due to transmission resource limitations does not generate any revenue for the service provider or network operator. Moreover, the reason for the reject is difficult to convey to the end-user. This may in turn generate frustration and complaints. 
     Other related prior art can be found in the international patent application WO2007/139458. This application discloses a method to optimize bandwidth usage at multicast distribution of IPTV. Another prior art is US patent application 2007/0044130. This application discloses a system and a method for facilitating channel change in an IPTV system. The IPTV system comprises a set top box STB and an access network. 
     SUMMARY 
     The present invention relates to the problem of how to avoid the disadvantages mentioned above of rejecting access to a service due to transmission resource limitations. 
     The problem is in the current invention solved by a method of automatically adapting the requested service to the limited transmission resources. The method comprises the steps of first receiving from a terminal in a customer premises network a request for establishing a new digital media stream (as for example an IPTV video stream) from a media server to the terminal. The next step is to determine how much transmission resources are allocated to the customer premises network as such. The allocated transmission resources are compared with the sum of transmission resources required for the new digital media stream and the resources required for all already established digital media streams to terminals in the customer premises network (if any). 
     If the transmission resources required for the new and the already established digital media streams together are greater than the allocated transmission resources, a digital substitution media stream with the same content but requiring less transmission resources is established. A digital media stream demanding less resources can for example be a media stream with less bandwidth and lower transmission quality. Content in this context can for example be an IPTV channel that can be watched simultaneously by a plurality of end-users. 
     At least three options are possible to establish a digital substitution media stream:
         to establish a digital substitution media stream with the same content as the requested new media stream but requiring less transmission resources or   to establish the new requested digital media stream with the requested transmission resources but replacing any of the already established digital media streams with a digital substitution media stream with the same content but requiring less transmission resources or   to establish a digital substitution media stream with the same content as the requested new media stream but requiring less transmission resources and replacing any of the already established media streams with another digital substitution media stream also requiring less transmission resources,
 
so that the total sum of transmission resources required is less or equal to the transmission resources allocated to the customer premises network.
       

     The invention also comprises a method for handling instructions received from a network resource control entity to update data about the transmission resources allocated to the customer premises network. This network resource control entity could for example be a policy server or a network element manager. 
     When receiving the instruction, the data about the transmission resources currently allocated to the customer premises network is determined and compared with the updated data received from the network resource control entity. If more transmission resources are allocated, it is for example possible that an already established digital media stream requiring less transmission resources is substituted with a digital media stream requiring more transmission resources (e.g. having better transmission quality) but still delivering the same content. If less resources are allocated, it is for example necessary that an already established digital media stream is substituted with a digital media stream requiring less transmission resources but still delivering the same content. 
     The current invention also comprises an access node for establishing digital media streams between the media server and the terminals in the customer premises network. The access node comprises a call and admission control unit and at least one resource data base accessible from the call and admission control unit. The resource data base comprises data about the transmission resources allocated to the customer premises network. 
     The call and admission control unit is adapted to receive requests from the terminal to establish a new digital media stream. The call and admission control unit is further adapted to interrogate the resource data base and to compare the transmission resources allocated to the customer premises network with the sum of the transmission resources used for already established digital media streams to the customer premises network and the requested transmission resources for the new requested digital media stream. The call and admission control unit is further adapted to replace any of the requested and the already established digital media streams with at least one substitution digital media stream adapted to have the same content as the requested digital media stream but requiring less transmission resources so that the sum of the transmission resources for the substitution digital media stream and the transmission resources for the remaining already established digital media streams does not exceed the transmission resources allocated to the customer premises network. 
     An advantage with the current invention is that fewer requests for new digital media streams are rejected. More revenue will be generated for the service provider and network operator and more IPTV channels can be watched at each customer premises network. 
     The objective with the current invention is therefore to obviate at least some of the above disadvantages and provide a method and an access node to improve the Quality of Experience. 
     The invention will now be described in more detail and with preferred embodiments and referring to accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram showing an example of an IPTV distribution network. 
         FIG. 2  is a block diagram showing an example of an IPTV distribution network comprising an access node according the current invention. 
         FIG. 3  is a flow chart illustrating how to handle a request to establish a video stream according to the current invention. 
         FIG. 4  is a block diagram showing an example of an IPTV distribution network comprising two video streams established according to a first embodiment of the method in the current invention. 
         FIG. 5  is a block diagram showing an example of an IPTV distribution network comprising two video streams established according to a second embodiment of the method in the current invention. 
         FIG. 6  is a flow chart illustrating how to handle a policy message received from a policy server and how to handle a release of a video stream. 
         FIG. 7  is a block diagram showing a first multicast scenario comprising an access node according the current invention. 
         FIG. 8  is a block diagram showing a second multicast scenario comprising an access node according the current invention. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  is a block diagram illustrating an example of a network for IPTV distribution involving an Access Node  100 . The Access Node  100  is connected to a regional IP network  160  and a number of customer premises networks  170 ,  180 . A customer premises network  170 ,  180  could typically be a home network having a plurality of TV sets and/or computers connected. Each customer premises network  170 , 180  comprises a Customer Premises Equipment  110 , 120  CPE. A CPE is a device interfacing access lines  171 , 181  and can for example be an ADSL modem or a cable modem with router functionality. To each CPE  110 , 120  a number of terminals such as set-top boxes STB  111 , 112 , 122  and personal computers  121  are connected. Each STB  111 , 112 , 122  is connected to a TV set (not shown in  FIG. 1 ). Alternatively, the STB and the TV set are integrated into the same device. For IPTV the content for distribution is stored in a media server, here a Video Server  140 . The Video Server  140  is connected to a core IP network  155  which is separated from the regional IP network  160  by an edge node  130 . The Video Server  140  is in this  FIG. 1  transmitting a high quality digital video stream  141  towards the STBs  112 , 121 . The video stream  141  can be duplicated by a replication unit  104  into a second video stream a so called leaf  141 bis before it reaches any of the STBs  112 , 121 . 
     When using the concept of dynamic resource control, the admission control is implemented in a centralized network resource control entity, here a policy server  150 . When for example an end user to STB  111  requests to establish a high quality video stream (that is, a video stream with high resource demands), a request  151  is sent from the STB  111  to the policy server  150 . The policy server  150  could then admit or deny the request  151  by responding with an answer message  152  depending on available resources in the networks  155 , 160 . Assume in  FIG. 1  that STB  112  is located in a home network  170  and is already receiving a high quality video stream  141 . Another end user having access the home network  170  desires to establish a second high quality video stream with a different content to STB  111 . To achieve this, STB  111  sends a request  151  to establish this second video stream. Due to resource limitations somewhere in the networks  155 , 160 , the policy server  150  rejects the request. This will result in that no second video stream is established at all to STB  111 . 
     However, it could very well be that there are resources available for the STB  111 , but not just enough for carrying a high quality video stream. The current invention uses this fact in order to provide a better Quality of Experience to the end user. This is illustrated in  FIG. 2 . In  FIG. 2 , the access node  100  is equipped with one or several resource databases RDB  101 , 102 . In this embodiment, there is one resource database RDB  101 , 102  for each customer premises network  170 , 180 , but in other embodiments, one common resource data base for all customer premises networks  170 , 180  could be used. By using a local resource database RDB  101 , 102  in the access node  100 , a part of the call/admission control function residing in the policy server  150  is distributed to a call/admission control unit CAC  103  in the access node  100 . The resource databases RDB  101 , 102  comprise data about the transmission resources allocated to each individual customer premises network  170 , 180  respectively. That is, the transmission resources allocated to each customer premises network  170 , 180  corresponds to a common pool of available transmission resources for the corresponding terminals  111 , 112  and  121 , 122  respectively. 
     A request  172  from for example the STB  111  to establish a video stream is received and analyzed by the call/admission control unit CAC  103  in the access node  100 . The procedure to handle this request  172  by the call/admission control unit CAC  103  is further detailed in  FIG. 3 .  FIG. 3  is a flowchart illustrating three embodiments of the method for establishing a video stream according to the current invention. The call/admission control unit CAC  103  in the access node  100  receives in step  301  a request from a STB  111  to establish a high quality video stream (i.e. a video stream with certain requested transmission resources). The call/admission control unit CAC  103  determines the transmission resources allocated to the corresponding customer premises network  170  by interrogating in step  302  the resource database RDB  101 . Having received data about the allocated transmission resources, these resources are compared in step  303  with sum of the resources for the requested video stream and video streams already established (if any) to terminals  111 , 112  in the customer premises network  170 . If, in step  304 , the sum of transmission resources for the requested and all already established video streams together does not exceed the allocated transmission resources, the requested video stream is established in step  315 . If the sum of transmission resources exceeds the allocated resources, different options are available. 
     If in step  305  there are no resources left to even establish a low quality video stream with available coding algorithms, a reject is sent in step  316  to the requesting terminal, in this example STB  111 . 
     If there are resources available and if, in step  306 , there is no video stream already established to any terminal  111 , 112  in the customer premises network  170 , the requested high quality video stream is in step  307  substituted with a low quality video stream providing the same content but requiring less resources so that the allocated resources are not exceed. On the other hand, if, in step  306 , one or more video connections already are established, yet more options are possible to be selected in step  308 . One option is to keep in step  309  the already established video streams unaffected but to substitute the requested video stream in step  310  with a low quality video stream providing the same content so that the sum of transmission resources for the established video streams and the low quality video stream is still below the allocated transmission resources. Another option is to substitute at least one of the already established video streams in step  311  with a corresponding low quality video stream and to establish in step  312  the requested high quality video stream with the requested transmission resources. Yet another option is to substitute at least one of the already established video streams in step  313  with a corresponding low quality video stream and to substitute in step  314  the requested high quality video stream also with a low quality video stream. 
     The result of the first option, that is, if following steps  309  and  310 , is illustrated in  FIG. 4 . In addition to the existing high quality video stream  141 , a low quality video stream  142  is established. The result of the second option, that is, if following steps  311  and  312 , is illustrated in  FIG. 5 . The existing high quality video stream  141 , is substituted by a low quality video stream  143  having the same content and the requested high quality video stream  144  is established. 
     The selection of option can depend on priorities or other parameters stored in the resource databases RDB  101 , 102 . 
     The concept of the current invention is not limited to the establishment of new video streams. Also when already established video streams are released, the call/admission control unit CAC  103  can take actions to distribute the freed transmission resources among the remaining established video streams. This is illustrated by  FIG. 6 . In  FIG. 6  an established video stream is released in step  610 . The resource database RDB  101  is interrogated in step  611 . If, in step  612 , there are enough allocated transmission resources left and if there is one or more low quality video streams established, one or more of these can be substituted in step  613  by a high quality video stream with the same content. Otherwise the already established media streams are kept as they are. Finally, the resource database RDB  101  is updated in step  609 . 
     The video streams are preferably established as multicast connections. With multicast, unnecessary transport of data packets in the networks  155 , 160  is avoided. This is illustrated in  FIG. 7 . For example, if a request for a video stream having the same content is received from two different terminals  112 , 121  it is a waste of transmission resources in the networks  155 , 160  if two individual video streams are established between the video server  140  and each of the terminals  112 , 121 . Instead, one single video stream  145  is established to a node close to both terminals  112 , 121 , in this case the access node  100 . In the access node  100 , the data packets are duplicated by the replication unit  104  into two separate video streams  145 , 145 bis, so called leafs. As receivers of the duplicated videos streams  145 , 145 bis, the terminals  112  and  121  together constitute a so called multicast group  175 . 
     In order to establish multicast connections, the nodes  100 , 130  and other intermediary nodes (like routers etc, not shown in  FIG. 7 ) need to know towards which receivers  111 , 121  the data packets have to be replicated. For this purpose, the IGMP (Internet Group Multicast Protocol) has been developed. IGMP exists in three versions 1 to 3 which are specified in the internet standards RFC1112, RFC2236 and RFC3376 respectively. The IGMP protocol has basically two types of connection control messages, Join and Leave. Join is sent from a terminal that requests to establish a video stream and Leave is sent from the terminal when it wants to release the video stream. 
     In the example in  FIG. 7  it is assumed that STB  112  sends a Join  174  towards the access node  100 . The Join  174  is analyzed by the call/admission control unit CAC  103 . The Join  174  is admitted and as no video stream with the requested content is already established, the Join  174  is sent all the way to the video server  140  and a video stream  145  is established. When another video stream but with the same content is to be established to the desktop computer  121 , the desktop  121  sends a Join  184  to the access node  100 . As the video stream  145  is already established between the video server  140  and the access node  100 , it is enough to add a ‘leaf’  145 bis from the access node  100 . It is assumed that the Join  184  is admitted by the call/admission control unit CAC  103 . Data packets in the video stream  145  are now duplicated by the replication unit  104 . 
     When the video streams  145 ,  145 bis have been established towards the STB  112  and the desktop computer  121 , the access node  100  can periodically send IGMP query messages (not shown in  FIG. 7 ) to check if the STB  112  and the desktop computer  121  are still ‘interested in’ being part of the multicast group  175 . 
       FIG. 8  illustrates a scenario where a request  176  from the STB  111  to establish a high quality video stream with content ‘A’ is received by the call/admission control unit CAC  103 . A high quality video stream  145  (thick line) with some other content ‘B’ is already established between the video server  140  and the other STB  112  in the same customer premises network  170 . In the other customer premises network  180 , a high quality video stream  146  (thick line) with content ‘A’ is established between the video server  140  and the desktop computer  121 . 
     When receiving the request  176 , the call/admission control unit CAC  103  interrogates the resource database RDB  101  and concludes that there are not enough resources allocated to the customer premises network  170  for establishing a high quality video stream with the content ‘A’ to STB  111 . 
     Using the current invention, the request  176  is not rejected. Instead a ‘Join’  177  is sent towards the video server  140  requesting the establishment of a video stream having the same content ‘A’ but with lower transmission quality. A video stream  147  (thin line) with these characteristics is already established to a terminal somewhere else in the network. When the ‘Join’ reaches the edge node  130 , the video stream  147  is replicated in replication unit  134  as video stream  147 bis (thin line) and distributed to the STB  111 . 
     Multicast can be implemented according to different service models. One is Any-Source Multicast (ASM). This is the IP multicast service model defined in RFC 1112. When using Any-Source Multicast (ASM) streams with different quality but having the same content have identical MAC and IP headers. In order to separate the streams so that they are not mixed in the network, they have to be conveyed in Layer  2  tunnels (for example using different Virtual Local Area Networks, VLAN, having different VLAN identities). Join and Leave messages are forwarded to the adequate tunnel if needed. 
     Another model is the Source-Specific Multicast (SSM) model. For SSM, the same principle of using different Layer  2  tunnels can be used. Alternatively, the video streams with same content but different quality are sent from the video server  140  with source specific addresses, removing the need of Layer  2  separation. The access node  100  uses the adequate source addresses when sending Join and Leave messages to establish the video stream. 
     Returning to  FIG. 2 , the call/admission control unit CAC  103  in the access node  100  is also adapted to receive instructions  158 , 158  to update in action  609  the data about the allocations of transmission resources for the customer premises networks  170 , 180 . These instructions  158 , 159  originate from a network resource control entity that can be a Network Element Manager NEM  180  or a Policy Server  190 . This event is illustrated by the flow chart in  FIG. 6 . In  FIG. 6  the call/admission control unit CAC  103  receives in step  601  a policy message  159  from the Policy Server  150 . The call/admission control unit CAC  103  starts to determine the current data about the allocated transmission resources by interrogating the resource database RDB  101  in step  602 . The current data from the resource database RDB  101  is compared with the new data in step  603 . If in step  604  the new data is about an increase of allocated transmission resources, a check is made in step  606  if there are enough transmission resources allocated to let a low quality video stream be substituted with a high quality video stream. If there are enough allocated transmission resources, the low quality video stream is substituted with a high quality video stream in step  608  and the database RDB  101  is updated with the new data in step  609 . If not, none of the established video streams is affected and the resource data base RDB  101  is updated in step  609 . If, on the other hand the new data is about a decrease of the allocated transmission resources, a check is made in step  605  if the allocated transmission resources are decreased to a level where the are not enough resources for the already established video streams. If that is the case, one or more established video streams are substituted by video streams having lower quality in step  607  or are released. The resource database RDB  101  is updated with the new data in step  609 . As an alternative, the update of the resource database RDB  101  can be done already in step  602 . 
     The described embodiments are mainly applied to video streams for IPTV. A person skilled in the art would apply the inventive concept also for the distribution of other media streams as for example audio streams with music, voice, radio channels etc.