Abstract:
The present invention relates transmission network, which involves Passive Optical Network and thereto connected units, e.g. Optical Network Units. It is an object of the present invention to provide a solution to the upstream data packet traffic congestion problem in transmission networks that comprises a PON system. Said problem is solved by providing adapted node devices and methods for such scheduling control that within the prescribed standard requirements, e.g. QoS, for passive optical network systems eliminate the congestion problem.

Description:
TECHNICAL FIELD 
     The present invention relates transmission network, which involves Passive Optical Network and thereto connected units, e.g. Optical Network Units. 
     BACKGROUND 
     In a transmission network comprising a core network, said core network is usually an optical network due to its superior traffic capacity compared to electrical signaling networks. The optical signals may have to be converted, e.g. to electrical signals, when distributed to Network Terminals (NTs) or local distribution networks in the subscriber neighborhood. In an optical fiber telecommunications network, an Optical Network Unit (ONU) is provided for terminating the optical fiber transmission line and for converting between different transmission technologies, such as Passive Optical Network (PON) and another transmission technology. In other words, the object of the ONU is therefore to adapt the data traffic from one transmission technology to another transmission technology in the transition point between the two technologies. 
     According to the present standard specification regarding QoS, high priority packets of the incoming data packet traffic are sent before Low priority. Management traffic always has highest priority and Voice over IP traffic has higher priority than normal Internet traffic. Each ONU is therefore provided with a scheduling mechanism to obtain such a differencing function and performance regarding different classed data packets. The scheduling options in the ONU can be more or less advanced. Schemes like Strict Priority, Weighted Round Robin or Deficit Round Robin may be implemented increasing the complexity of the ONU. The ONU&#39;s advanced scheduling task is regarded as a necessity by network operators for providing and withhold QoS requirements for the PON network, as the incoming data packets often have to be stored according to QoS priority classification before transmitted in the upstream direction towards the OLT. In the point-to-multipoint Passive Optical Network the upstream bandwidth, i.e. the uplink bandwidth, is shared between multiple Optical Network Units (ONUs). The bandwidth is not necessary shared equally between ONUs connected to an upstream located Optical Link Termination (OLT). Even for a single ONU the bandwidth may vary over time. The PON Uplink interface between ONUs and OLT is supposed to be variable in bandwidth, while the interface between the ONU and NT is fixed at e.g. 1 Gbps. Said PON Uplink is controlled and allocated by the OLT independently of the fixed bandwidth and may therefore be shifted over time to a value below that of the fixed bandwidth. If the uplink bandwidth to the OLT is allocated below 1 Gbps, the ONU must involve means for accommodating received data packets. If the ONU is not provided with storing elements or enough buffering capacity, the ONU will start dropping packets when data packet congestion occurs. 
     SUMMARY 
     It is an object of the present invention to provide a solution to the upstream data packet traffic congestion problem in transmission networks that comprises a PON system. 
     Said problem is solved by providing adapted node devices and method for such scheduling control that within the prescribed standard requirements, e.g. QoS, for passive optical network systems eliminate the congestion problem. 
     This object is achieved by the characteristic features of the independent claims. 
     The claimed invention solves the problem by determining a momentary parameter value of at least one scheduling control parameter of a set of different scheduling control parameters. Each determined parameter value is transmitted downstream to at least one node comprising a scheduler, said node whereby the scheduling task for scheduling the upstream data packet communication is moved to said scheduler receiving the determined parameter value. 
     In a first aspect of the invention an Optical Network Unit, ONU, provided for terminating a passive optical network operating according to a PON transmission technology. Said unit is comprising a downlink interface for receiving upstream data packet communication from at least one downstream positioned network operating according to a second transmission technology. Further, the ONU comprises an uplink interface for transmitting upstream data packet communication to at least one upstream positioned PON network node via an optical uplink. Additionally, the ONU comprises converter means for converting data packet communication in a downstream direction from the PON transmission technology to the second transmission technology and converter means for converting data packet communication in an upstream direction from the second transmission technology to the PON technology. In the ONU is provided means for determining a momentary parameter value of at least one scheduling control parameter (P S ) of a set of different scheduling control parameters of the optical uplink and means for transmitting each determined scheduling control parameter value to at least the closest node in the downstream connected network operating according to the second transmission technology, which node comprises a scheduler, wherein each of said scheduling control parameter values is used for adapting the scheduler operation to the latest determined parameter values of the scheduling control parameter and a scheduler for scheduling the data packets upstream in the same order as they were scheduled by said downstream positioned scheduler and received by the downstream interface. 
     In a second aspect of the invention is provided a method for scheduling control of the upstream signal communication through an ONU. The method comprises the following steps of:
         determining a momentary parameter value of at least one scheduling control parameter of a set of different parameters;   transmitting each determined parameter to a downstream positioned node comprising a scheduler   transmitting upstream data packet communication received from said at least one node;   scheduling the data packets upstream in the same order as they were scheduled by the downstream positioned scheduler and received on the downlink interface.       

     In a third aspect of the invention is provided a Network Termination device comprising a scheduler, buffering means and a processing unit. The processing unit is adapted to control a message means for identifying and reading actual scheduling control parameters values received from an upstream positioned Optical Network Unit (ONU) device, and a means for adjusting the scheduling of the scheduler to operate according to the received actual scheduling control parameters values. 
     Different embodiments of the invention are disclosed in the dependent claims. 
     Said determined and transmitted parameter values may be the transmission bandwidth capacity of the optical uplink. 
     The advantages of the invention are reduced complexity in the ONU, thus cost, simpler management and easier software upgrade. 
     Moving the QoS decisions from the ONU thus making it more or less transparent will ensure that the mechanisms in the attached node apply. 
     The ONU continues to schedule the upstream traffic according to the actual uplink bandwidth, however the ONU is relieved from the task of fulfilling precedence requirements. The ONU only needs FIFO scheduling. More advanced scheduling, fulfilling the requirements of underlying equipment, is performed within that equipment. Traffic received from the attached node and network will therefore be in accordance with the uplink bandwidth and no reordering/packet drop is required in the ONU. Specifying the requirements for a passive optical network ONU device is much easier. No considerations need to be taken to ensure the ONU delivers the same QoS mechanisms as the connected device (e.g. IP DSLAM). 
     The management system will not need to keep the QoS mechanisms for the ONU and IP DSLAM synchronized. Only the IP DSLAM will need management to setup/maintain QoS on the passive optical network uplink. 
     Upgrading the QoS mechanisms/features for IP DSLAM/Switch vendors will only mean upgrading the IP DSLAM or switch. Since the ONU only performs FIFO scheduling, the ONU will not need to be upgraded. Time-to-market for additional QoS features could be significantly reduced. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram illustrating a data transmission network according to the invention. 
         FIG. 2  is a block diagram schematically illustrating the scheduling operation between an ONU node and a NT node of a PON system according to prior art when the data rate of the uplink interface and downlink interface is set to the same value. 
         FIG. 3  is a block diagram schematically illustrating the scheduling operation between an ONU node and a NT node of a PON system according to prior art when the data rate of the uplink interface is lower than the data rate of the downlink interface. 
         FIG. 4  is a block diagram schematically illustrating the scheduling operation between an ONU node and a NT node of a PON system according to the present invention. 
         FIG. 5  is a block diagram schematically illustrating an ONU device according to the present invention. 
         FIGS. 6-7  are signaling schemes illustrating a method according to the present invention. 
         FIG. 8  is a block diagram schematically illustrating in more details an ONU device according to the present invention. 
         FIG. 9  is a block diagram schematically illustrating in more details a Network Termination device according to the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of the present invention will now be described with reference to the above listed drawings. The function of the present invention is supported by a number of means, of which some will be described herein in more details, while other means are deliberately not described or illustrated in the drawings as they are considered to be obvious to a person skilled in the art. 
       FIG. 1  is a block diagram illustrating a data transmission network  10  according to the invention. The illustrated data transmission network comprises a Passive Optical Network (PON) and at least two Local Area Networks (LANs). The transition between said networks is indicated in  FIG. 1  by a vertical dashed line. The present invention concerns any PON system, such Gigabit PON, Ethernet PON, etc wherein one or more uplink bandwidth capacity is varied dynamically over time. 
     The PON system is a point-to-multipoint Passive Optical Network system. In the illustrated example, the PON system  10  comprises an Optical Line Termination (OLT)  12 , an optical fibre link  14  to a splitter  16  for splitting traffic from the OLT to all connected Optical Network Unites (ONUs)  20 ′,  20 ″,  20 ′″ and for collecting traffic from said connected Optical Network Units via optical fibre links  18 ′,  18 ″,  18 ′″. 
     Each ONU  20 ′,  20 ″,  20 ′″ connects a Local Area Network (LAN) or a Wide Area Network (WAN) to the PON system. Each LAN is terminated by a Network Termination (NT)  40 ′,  40 ′″ that is connected to a ONU via a link  25 ′,  25 ″,  25 ′″. The NT may be some kind of switch  40 , e.g. Ethernet Switch, Aggregation Ethernet Switch, IP DSLAM (IP DSL Access Multiplier). The switches connects a number of end users (not shown). 
     In the point-to-multipoint Passive Optical Network the upstream bandwidth is shared between multiple ONUs. The bandwidth is not necessary shared equally between ONUs and even for a single ONU the bandwidth may vary over time. 
     In the figure the available uplink bandwidth towards the OLT  12  and the actual amount of traffic sent from each ONU  20  are synchronized by the OLT. No ONU  20  will exceed the bandwidth allocated by the OLT  12 . 
     The problem in a corresponding prior art transmission network system comprising PON technology will now be discussed in more detail with reference to  FIGS. 2 and 3 . 
       FIG. 2  is a block diagram schematically illustrating the scheduling operation between an ONU node and a NT node of a PON system according to prior art when the data rate of the uplink interface and downlink interface is set to the same value, in this case 1 Gbps. The ONU  20  and NT  40  is very schematically illustrated in that a lot of different components is not illustrated in the figures or discussed in the description. Said components have been deliberately omitted as said components do not contribute to the description or the understanding of the problems of interest existing in the prior art network system of the above described kind. 
     With reference to  FIG. 2 , the Network Termination device  40  is provided with a number of data packet queue buffers  47 ,  48 ,  49  and a scheduler  46  for taking QoS decisions regarding when to transmit said data packets upstream in dependency to their individual priority classification. For example, the NT  40  could be an aggregation switch having a number of IP DSLAMs that are connected to its downlink interface  44 . To ensure QoS through-out the LAN both the switch and IP DSLAM will schedule the traffic to ensure that e.g. Management traffic always has highest priority and Voice over IP traffic has higher priority than normal Internet traffic. 
     The NT  40  has also an uplink interface  42  connected to the interface  25  between the NT  40  and the ONU  20 . The ONU  20  for terminating a passive optical network PON comprises an uplink interface  22  for transmitting upstream data packet communication to at least one upstream positioned network node and a downlink interface  24  for receiving upstream data packet communication from at least one downstream positioned transmission network. The uplink interface  22  is connected to a optical fiber link (OL)  18  and the downlink interface  24  is connected to a link or transmission channel  25 . It is up to the ONU to ensure the High priority packets are sent before Low priority depending on the scheduling mechanism. The ONU  20  is therefore provided with a scheduler  26 . The scheduling options in the ONU can be more or less advanced. Schemes like Strict Priority, Weighted Round Robin or Deficit Round Robin may be implemented increasing the complexity of the ONU. The link  25  between the ONU and NT has a fixed data rate/bandwidth, while the uplink  18  may vary in data speed below that of the fixed. If the interface  25  between the ONU and NT is fixed at e.g. 1 Gbps, the ONU must accommodate a rate of received data packets in queue storing elements  27 ,  28 ,  29 , e.g. buffers having enough buffering capacity, while the uplink bandwidth may be allocated below 1 Gbps. The data packets are stored in different queues and buffers depending on their individual QoS classification. An ONU according to prior art will therefore need a complex structure of buffers and queue distribution means to be able to satisfactory fulfill the Quality of Service requirements. 
       FIG. 3  is a block diagram schematically illustrating the scheduling operation between an ONU  20  node and a NT  40  node of a PON system according to prior art when the data rate of the uplink interface is lower than the data rate of the downlink interface. In the figure the ONU will always schedule the upstream traffic according to the actual uplink bandwidth. This will ensure that the queues are serviced according to the scheduling defined by the system or operator. 
     The problem occurs with the aggregation switch where the transmitted traffic towards the ONU is scheduled according to the link speed (between switch and ONU) which could be 1 Gbps, while the PON uplink may be much lower depending on the bandwidth allocation. If the PON uplink of the ONU is less then the downlink the ONU will start buffering packets. If the bandwidth and traffic load remains different long enough, the queue buffers will become full, and excess packets will be dropped. When traffic is dropped by the ONU the scheduling and possible drop decision made by the switch will not be as effective as the ONU will re-schedule and drop traffic according to a different uplink capacity. 
       FIG. 4  is a block diagram schematically illustrating the scheduling operation between an ONU node and a NT node of a PON system according to the present invention, which suggests a solution to the congestion problem in the ONU. Said problem is solved by involving means for determining a momentary parameter value of the transmission bandwidth capacity of the optical uplink (OL U )  18  to the ONU design and transmit said actual bandwidth capacity value P SBWDTH  in a downstream message to at least the closest downstream situated scheduler, i.e. the scheduler  46  of the NT  40 . Said scheduler  46  will adapt its scheduling of the upstream data packet communication to the PON transmission bandwidth capacity. 
     One positive effect by transmitting the actual bandwidth capacity to the closest downstream situated scheduler  46  is that the upstream data packet queues are serviced according to the scheduling defined by the system or operator. The NT scheduler  46  will deliver the same QoS mechanism as the scheduler  26  of the ONU  20 . 
       FIG. 5  is a block diagram schematically illustrating a simplified ONU according to the present invention. The data packet traffic received from the attached node  40  will be in accordance with the uplink bandwidth and no reordering/packet drop is required in the ONU  20 . A less advanced scheduling mechanism  52  is therefore required in the ONU  20 . Only FIFO (First-In-First-Out) scheduling is needed. Further, a less complicated queue buffering system  54  for serving the FIFO scheduling is necessary. 
     The ONU  20  continues to schedule the upstream traffic according to the actual uplink bandwidth, but the scheduling task for scheduling the upstream data packet communication is moved to said PON external scheduler  46  of the NT outside the PON system. 
     The advantages of the invention are reduced complexity in the ONU, thus cost, simpler management and easier software upgrade. 
     Other scheduling control parameters P S  than the actual bandwidth capacity P SBDWTH  may be transmitted from the ONU  20  node to the NT  40  node. One such control parameter could be the ONU buffer queue usage P SBQU . 
     Rapid changes in the PON uplink bandwidth may cause the NT not to adopt the egress traffic towards the ONU at the same rate. Communicating how many buffers are in queue will allow the NT to make calculations and adjust the send rate towards the ONU to ensure the ONU buffer queue is emptied. This will ensure that buffer usage in the ONU is not increasing as this will make the scheduling in the NT ineffective. 
     In more general terms, at least one scheduling control parameter (P S ) of a set of different scheduling control parameters is determined and transmitted said parameter or parameters downstream to a node comprising a PON external scheduler, whereby the scheduling task for scheduling the upstream data packet communication in the PON Uplink is moved to said PON external scheduler which is configured to receive the determined parameter value or values. 
     The signaling or transmission of scheduling control parameters between the ONU and NT will now be describe in more detail with reference to  FIGS. 6 and 7 . 
       FIGS. 6 and 7  are signaling schemes illustrating the protocols used for carrying and transfer the actual scheduling control parameters in the transmission network comprising an ONU in a PON system and a NT node in a network using other transmission technology from the PON system. 
     First, the OLT  12  will generate a message, e.g. GTC protocol, comprising scheduling control parameter values, e.g. allocated bandwidth P SBWDTH  for the PON uplink, to the ONU  20 , which will read the fields of the GTC protocol. 
     As an illustrating example, a Gigabit Passive Optical Network (GPON) will be described. The PCBd (Physical Control Block downstream) fields of a GTC protocol may be used for transporting the parameter values in a GPON system. Every 125 us the OLT will send a GTC downstream frame to the ONU. The GTC frame consists of two blocks: PCBd and Payload. The PCBd fields contain all relevant information for a T-CONT, which is a logical channel in a PON system. The identity of the T-CONT is part of the PCB information. The GTC protocol is used to communicate from OLT to ONU and from ONU to OLT. The GTC frame in downstream direction differs in content from upstream GTC frames. Both types of frames consist of several blocks of information. In the upstream GTC frame one of the block of information is the DBRu (Dynamic Bandwidth Report Upstream) that tells the OLT whether traffic is in queue for this T-CONT. The rate of the upstream GTC (and DBRu information) is dependant on the bandwidth allocated to the T-CONT. The GTC will follow each data packet sent upstream. 
     According to the invention, a message is established by the ONU  20  to be sent between the ONU  20  and the NT  40  allowing the ONU  20  to communicate the P S  values, e.g. bandwidth capacity P SBWDTH  and buffer capacity usage P SBCU , to the NT  40 . When the message is received by the NT  40 , the processing unit of the NT will identify and read the received actual scheduling control parameters values and adjust the scheduling accordingly. 
     The present invention is provided with an additional message protocol which enables the NT  40  to communicate upstream the number of buffers in queue on its side. This information will be processed and used by the ONU  20  in the upstream status reporting with DBRu (Dynamic Bandwidth Report Upstream) messages to the OLT. To fully utilize the capabilities of Dynamic Bandwidth Allocation by the OLT, a message denoted SR DBA (Status Reporting Dynamic Bandwidth Allocation) is used. 
     Alternatively, if NSR (Non-Status Reporting) is used, the buffer queue signaling from NT to ONU is not needed. The message will utilize information from the downstream GTC (GPON Transmission Convergence) frame, where the Upstream Bandwidth Mapping (US BW map) is calculated for the ONU(s) by the OLT. 
       FIG. 7  is illustrating examples of different fields and frames in the messages sent in the two opposite directions between the ONU and NT. 
     As an example, the ONU  20  encapsulates the complete GTC frame in Ethernet frames and sent towards the NT  40 , to minimize the processing overhead of the ONU  20  and make the overall implementation scalable. To minimize configuration in the ONU  20  both the Source MAC Address (SA) and Destination MAC Address (DA) are addresses with the “Universally/Locally Administered address” bit set indicating local addresses, see Table 1: MAC address representation. This will make it possible to implement pattern search and identification in the NT  40 , e.g. normal Switch fabric filtering or Network Processor micro code. 
     
       
         
               
             
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                 MAC address representation 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 
                   
                             
                     
                         
                         
                     
                   
                 
               
               
                   
               
             
          
         
       
     
     The following Internet site (http://standards.ieee.org/regauth/groupmac/tutorial.html) is recommended for studies regarding more information about MAC address representation. 
     A first embodiment of an Optical Network Unit according to the present invention will now be described in more detail with reference to  FIG. 8 . The functionality of the UNO according to the present invention has already been described in the description with reference to  FIGS. 4-7  herein. 
     The Optical Network Unit, ONU,  20  is connected into and is terminating a Passive Optical Network (PON). The ONU comprises a downlink interface  24  for receiving upstream data packet communications WL U  from a downstream positioned network connected to the ONU, and to transmit data packets downstream WL D . The downlink interface  24  is connected to the closest node of said network, and which comprises a Network Termination NT ( 40  in  FIG. 1 ). The NT comprises a scheduler device, as described above. The ONU further comprises an uplink interface  22  for transmitting the received upstream data packet communications (WL U ) via optical uplink OL U  to an upstream positioned network Optical Line Termination in a node. The interface  22  receives downstream data packet communications OL D . 
     Further, the ONU  20  comprises converter means  50  for converting data packet communications in a downstream direction from a PON system using PON transmission technology. Said communications are converted to a second transmission technology used in the downlink network. The converter means  58  for converting data packet communications in an upstream direction from the second transmission technology of the downlink network to the uplink PON network technology is also provided in the ONU  20 . 
     According to the present invention, the ONU  20  is provided with means  62  for determining a momentary parameter value of at least one scheduling control parameter (P S ) of a set of different scheduling control parameters. Said parameter values may either be received directly from the OLT, or the parameter values may be derived from received data values from the OLT. Said parameter values or data values is preferably transferred in a message, such as a suitable protocol. If the network is a Gigabits PON, the message is preferably a GTC (GPON Transmission Convergence) protocol carrying a Upstream Bandwidth map with the actual uplink bandwidth value. It should comprise at least one scheduling control parameter (P S ) of said set of different scheduling control parameters which is related to a corresponding QoS setting of a set of QoS settings defined for an optical uplink (OL U ) provided by a PON to which the ONU  20  is connected. 
     The ONU  20  is further comprising means  64  for transmitting each determined parameter value to a downstream positioned network node comprising a PON external scheduler, said parameter is used for adapting said scheduler to the scheduling control parameter (P S ) of the optical uplink (OL U ) in accordance with the latest determined parameter value. Said means  64  is adapted to insert the determined momentary parameter value of a scheduling control parameter as an message to the downstream positioned NT comprising the PON external scheduler. If the ONU receives a GTC protocol as a message from the OLT, said GTC protocol may be sent as an encapsulated message to the NT. 
     In one alternative embodiment of the invention, said determined and transmitted parameter value is the momentary transmission bandwidth capacity of an optical uplink (OL U ) provided by a PON to which the ONU  20  is connected. 
     A T-CONT (Transmission Container) is a logical channel on the PON fibre. Any one ONU may have several T-CONTs assigned. In stead of having one T-CONT with 10 MBps allocated, the ONU could have 3 T-CONT: One with 512 kbps for Voice traffic, one with 6 MBps for a video channel and the rest for Internet surfing. The uplink transmission capacity may be divided between more than one T-CONT, i.e. multiple T-CONT, which is used for end-user separation or traffic separation (based on traffic type or priority). In this case each T-CONT may be considered a virtual uplink with its own (set of) scheduling parameter(s) that can be individually signaled to downlink positioned scheduler(s). The traffic or related signaling between the ONU and NT(s) may utilize 802.1Q VLAN tagging for separation. This alternative is not excluded from the invention, however, it adds some complexity. 
     Alternatively, the ONU is further comprising means  68  for handling status messages and status reports. Said means  68  for handling transmission status messages and status reports is adapted to receive a buffer queue usage message from the downstream positioned scheduler. It will also comprise means for temporary storing the message content of received messages or protocols. Said means  68  is also adapted to send the buffer queue usage in a suitable message addressed to the OLT. Such a suitable message is the DBRu (Dynamic Bandwidth Report Upstream) protocol. Said means  68  is also performing processing of information in said buffer queue usage messages and determining the parameter content of the DBRu messages. 
     The ONU further comprises a scheduler  52  for scheduling the data packets upstream in the same order as they were scheduled by the scheduler in the Network Termination and received by the downlink interface. 
     The ONU is controlled by a processing unit  60 , which is controlling, e.g. via the indicated control bus  72 , the interfaces  22 ,  24 , converters  50 ,  58 , scheduler  52 , buffering means  54 , downstream devices  70  and Protocol handling means  62 ,  64 ,  66 ,  68  comprised in the ONU. 
     Finally, a Network Termination NT device  40  will be described in more detail with reference to  FIG. 9 . 
     The NT device  40  may be an aggregation Ethernet switch or an access device, for example IP DSLAM or an Ethernet switch. Said switching devices is well-known in prior art and comprises a lot of different components such as uplink interface  42  and downlink interface  44  for receiving and transmitting data packet communications. The downlink interface  44  is adapted to receive upstream data packet traffic  100  Up from connected end-users (not shown) and transmit data packet traffic downstream  100  Do to said end-users. A processing unit CPU  90  is controlling the different means, interfaces  42 ,  44 , scheduler  46 , buffering means  47 - 49  (compare with  FIGS. 2-6 ), switching means  82 ,  84 , etc. The processing unit  90  is controlling said functional entities e.g. via a data bus  92 . 
     The processing unit  90  is adapted to control message means  96  for identifying and reading actual scheduling control parameters P S  values received from an upstream positioned Optical Network Unit device and to control means  94  for adjusting the scheduling of the scheduler  46  to operate according to the received actual scheduling control parameters P S  values. 
     In an alternative embodiment, said Network Termination is also comprising means  98  for determining at least one value of the buffer queue usage, B BCU , of the buffering means. 
     In said alternative embodiment, the message means  96  is adapted for generating outgoing messages involving said buffer queue usage value in a message addressed to said ONU. 
     Thus, the NT device  40  is adapted to support a connected ONU in the PON system. The NT device is provided with a number of means for supporting the communication described above with reference to the signalling scheme in  FIG. 6 . 
     As described in  FIG. 6 , the OLT  12  will generate a message, e.g. GTC protocol, comprising scheduling control parameters, e.g. allocated bandwidth P SBWDTH  for the PON uplink, to the ONU  20 , which will read the fields of the GTC protocol. According to the invention, a message is established by the ONU  20  to be sent between the ONU  20  and the NT  40  allowing the ONU  20  to communicate the P S  values, e.g. bandwidth capacity P BWDTH  and buffer usage P SBQU , to the NT  40 . When the message is received by the NT  40 , the processing unit  90  of the NT  40  will initiate the message means  96  for identifying and reading the received actual scheduling control parameters P S  values. The processor  90  will further activate means  94  for adjusting the scheduling of the scheduler  46  accordingly. 
     Alternatively, the NT  40  is provided with means  98  which checks the buffering means  47 - 49  for continuously or periodically determining a value of the buffer queue usage. Said value is inserted by message means  96  in a suitable message or protocol. The message means  96  is also adapted for generating outgoing messages involving said buffer queue usage value in a message addressed to said ONU. This information will be processed and used by the ONU  20  in the upstream status reporting with DBRu (Dynamic Bandwidth Report Upstream) messages to the OLT. 
     The present invention solves as stated above the congestion problem in the ONU. One advantage is that the traffic received from the attached NT node and network will be in accordance with the uplink bandwidth of the ONU and no reordering/packet drop is required in the ONU. 
     A number of embodiments of the present invention have been described. It will be understood that various modifications may be made without departing from the scope of the invention. Therefore, other implementations are within the scope of the following claims defining the invention. 
     
       
         
               
             
               
               
               
             
           
               
                   
               
               
                 APPENDIX-abbreviations 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 BW 
                 Bandwidth 
               
               
                   
                 DBA 
                 Dynamic Bandwidth Allocation 
               
               
                   
                 DBRu 
                 Dynamic Bandwidth Report Upstream 
               
               
                   
                 DSL 
                 Digital Subscriber Link 
               
               
                   
                 Gbps 
                 Gigabits per second 
               
               
                   
                 GTC 
                 GPON Transmission Convergence 
               
               
                   
                 GPON 
                 Gigabit Passive Optical Network 
               
               
                   
                 IP 
                 Internet Protocol 
               
               
                   
                 IP DSLAM 
                 IP DSL Access Multiplier 
               
               
                   
                 PON 
                 Passive Optical Network 
               
               
                   
                 NSR 
                 Non-status reporting 
               
               
                   
                 NT 
                 Network Termination 
               
               
                   
                 OAM 
                 Operations, Administration and Maintenance 
               
               
                   
                 OLT 
                 Optical Line Termination 
               
               
                   
                 ONU 
                 Optical Network Unit 
               
               
                   
                 PCBd 
                 Physical Control Block Downstream 
               
               
                   
                 QoS 
                 Quality of Service 
               
               
                   
                 SR 
                 Status Reporting 
               
               
                   
                 US 
                 Upstream 
               
               
                   
                 T-CONT 
                 Transmission Container