Patent Publication Number: US-2009238561-A1

Title: Method and apparatus for measuring quality of traffic performance in a passive optical network (PON)

Description:
BACKGROUND OF THE INVENTION 
     Internet Protocol Television (IPTV) delivers video content to viewers using a broadband connection over Internet Protocol (IP). Unlike traditional satellite or cable television, in which all channels are pushed constantly to the consumer&#39;s premises, IPTV delivers only the content that is selected by the consumer. For example, the consumer can request a particular program or channel from a service provider though a graphical interface, and the service provider can then deliver the requested content to the consumer. Content can be distributed on demand, and content providers can tailor the requested content and advertising based on customer preference. 
     In an IPTV network, broadcast television channels are delivered via Internet Protocol (IP) multicasting. Each broadcast television channel is an IP multicast group. The viewer changes the channel by leaving one group and joining a different group. Internet Group Management Protocol (IGMP) is a control mechanism used to control the delivery of multicast traffic to recipients of the traffic. IGMP messages may be used to make upstream equipment stop sending a channel (“leave request”) or begin sending another channel (“join request”). An IGMP host, such as a set-top box (STB), usually sends the IGMP messages to join or leave a multicast group. 
     One method of delivering IPTV content involves the use of a Passive Optical Network (PON), which delivers content over optical fiber networks all, or most of the way, to the consumer. A PON network is configured in a point-to-multipoint fashion and can transport high volumes of upstream and downstream bandwidth. A typical PON network includes an Optical Line Terminal (OLT) at a content provider&#39;s central office and a number of Optical Network Terminals (ONTs) at or near the viewers&#39; locations. 
     SUMMARY OF THE INVENTION 
     One embodiment of the present invention for measuring and reporting performance of communications traffic in a network is a Passive Optical Network (PON) having an Optical Line Terminal (OLT) and multiple Optical Network Terminals (ONTs) downstream of the OLT. The PON network includes passive optical communications paths configured to communicate in a bidirectional manner. The embodiment also includes an aggregator downstream of the multiple ONTs that provides selective access to the communications traffic received by the multiple ONTs, and includes a data collection node coupled to the aggregator that collects information representative of performance of the communications traffic to test traffic communications via the passive optical communications paths in a downstream direction. The data collection node reports the information to a network management node via the OLT to test traffic communications via a communications path to the network management node in an upstream direction. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing will be apparent from the following more particular description of example embodiments of the invention, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating embodiments of the present invention. 
         FIG. 1  is a network diagram illustrating an example Passive Optical Network (PON). 
         FIG. 2  is a network diagram illustrating a network configuration for manually testing traffic performance in a PON network. 
         FIG. 3  is a network diagram illustrating a network configuration for testing traffic performance in a PON network using multiple set-top boxes. 
         FIG. 4  is a network diagram illustrating a network configuration for testing traffic performance in a PON network using a single data collection node. 
         FIG. 5  is a network diagram illustrating a network configuration for testing traffic performance in a PON network using a single data collection node, a content server, and a test management node. 
         FIGS. 6A-6C  are network diagrams illustrating a flow of communications traffic and performance information in a network configuration for testing traffic performance in a PON network using a single data collection node. 
         FIG. 7  is a block diagram illustrating a system for testing traffic performance in a PON network using an aggregator and a single data collection node. 
         FIG. 8  is a flow diagram illustrating testing traffic performance over a PON network using an aggregator and a single data collection node. 
         FIG. 9  is a flow diagram illustrating testing traffic performance in a PON network using a single data collection node. 
         FIG. 10  is a flow diagram illustrating sending and receiving information in a PON network for testing communications traffic performance. 
         FIG. 11  is a flow diagram illustrating testing traffic performance in a PON network according to a selectable timing configuration. 
         FIG. 12  is a flow diagram illustrating further using communications traffic performance information collected by testing traffic performance in a PON network. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A description of example embodiments of the invention follows. 
       FIG. 1  is a network diagram of a Passive Optical Network (PON)  100 . The network includes at least one Optical Line Terminal (OLT)  115   a - 115   n,  a network management node  155  (e.g., Element Management System (EMS)), an Optical Splitter/Combiner (OSC)  125 , and at least one Optical Network Unit (ONU) or Optical Network Terminal (ONT),  135   a - 135   n  (hereinafter both referred to as an ONT), where an ONU generally supports multiple premises and an ONT generally supports a single premises. Data communications  110  may be transmitted between the OLTs  115   a - 115   n  and a wide area network (WAN)  105 . 
     Communication of data transmitted between a given OLT  115   a  and its associated ONTs  135   a - 135   n  may be performed using standard communication protocols known in the art, for example, point-to-multipoint (e.g., broadcast with identifiers of intended recipients) for transmitting downstream data from the OLT  115   a  to the ONTs  135   a - 135   n  and point-to-point for transmitting upstream data from an individual ONT  135   a - 135   n  back to the OLT  115   a  (e.g., time division multiple access (TDMA)). 
     The PON  100  may be deployed for fiber-to-the-premises (FTTP), fiber-to-the-curb (FTTC), fiber-to-the-node (FTTN), and other fiber-to-the-x (FTTX) applications. The optical fiber  127 ,  133  in the PON  100  may operate at bandwidths such as 155 Mb/sec, 622 Mb/sec, 1.25 Gb/sec, and 2.5 Gb/sec, or any other desired bandwidth implementation. The PON  100  may incorporate asynchronous transfer mode (ATM) communications, broadband services such as Ethernet access and video distribution, Ethernet point-to-multipoint topologies, native communications of data and time division multiplex (TDM) formats, and other communications suitable for a PON. Customer premises equipment (e.g., inside homes  140 ) that can receive and provide communications in the PON  100  may include standard telephones (e.g., Public Switched Telephone Network (PSTN) and cellular), Internet Protocol telephones, Ethernet units, video devices, computer terminals, digital subscriber line connections, cable modems, wireless access, as well as any other conventional customer premises equipment. 
     The OLT  115   a  generates or passes through downstream communications  120  to an OSC  125 . After passing through the OSC  125 , the downstream communications  130  are broadcast to the ONTs  135   a - 135   n,  where each ONT  135   a - 135   n  reads data  130  intended for that particular ONT  135   a - 135   n  using, for example, identification information embedded within the communications signal. Data communications  137  may be further transmitted to and from, for example, a user&#39;s home  140  in the form of voice, data, video, and/or telemetry over copper, fiber, or other suitable connection  138  as known to those skilled in the art. The ONTs  135   a - 135   n  transmit upstream communication signals  145  back to the OSC  125  via fiber connections  133 . The OSC  125 , in turn, combines the ONTs  135   a - 135   n  upstream communications signals  145  and transmits the combined signals  150  back to the OLT  115   a  using, for example, a TDM protocol. The OLT  115   a  may further transmit the communication signals  110  to the WAN  105 . 
     Communications between the OLT  115   a  and the ONTs  135   a - 135   n  occur using a downstream wavelength and an upstream wavelength. The downstream communications from the OLT  115   a  to the ONTs  135   a - 135   n  may be provided at, for example, 622 megabytes per second, which may be shared across all ONTs. The upstream communications from the ONTs  135   a - 135   n  to the OLT  115   a  may be provided at, for example, 155 megabytes per second, which may shared among all ONTs  135   a - 135   n  connected to the OSC  125 . 
     Internet Protocol Television (IPTV) traffic may be delivered to viewers over the PON network. To ensure reliable performance, the PON network is typically tested before deploying the network equipment in the field. 
       FIG. 2  is a network diagram illustrating a network configuration for manually testing traffic performance in a PON network  200  having a number of ONTs  235 , which is one method for pre-deployment testing. The method involves the use of a single piece of testing equipment  285  to analyze traffic on the PON network  200 . The equipment  225  is manually cycled through each ONT device  235 , and performance data is gathered for each ONT  235 . The data is later manually correlated together into a summary report. Given a fully loaded PON configuration (e.g., a PON network supporting up to thirty-two ONT units), it is extremely time-consuming and inefficient to manually walk through each ONT device  235  and correlate the gathered data. Additionally, the method does not test communications traffic performance in an upstream direction. 
       FIG. 3  is a network diagram illustrating a network configuration for testing traffic performance in a PON network  300  having a number of ONTs  335  using multiple set-top boxes  345 , which is another approach for measuring IPTV traffic performance. The approach involves building an extensive test bed of expensive equipment that simulates communications traffic (e.g., IPTV traffic) and generates individual performance reports. The individual performance reports are then correlated by software and consolidated into a single report for the entire PON network  300 . Given the high capital outlay required to source the equipment and the labor-intensive configuration required to control the tests, this approach is not cost-effective. As with the method above, this approach also does not test communications traffic performance in an upstream direction. 
       FIG. 4  is a network diagram illustrating a network configuration for testing traffic performance in a PON network  400  using a single data collection node  445 , such as a set-top box, according to an example embodiment of the present invention. The embodiments of the present invention overcome the limitations of the approaches described above. One such embodiment is a method for measuring and reporting communications traffic performance in a Passive Optical Network (PON)  400  having an Optical Line Terminal (OLT)  415  and multiple Optical Network Terminals (ONTs)  435  downstream of the OLT  415 . According to the method, the embodiment transmits communications traffic  470  in a downstream direction via passive optical communications paths in the PON network  400 . At a point downstream of the multiple ONTs  435 , the embodiment aggregates the communications traffic  470  received by the multiple ONTs  435 , selectively accesses the aggregated communications traffic, and collects information representative of performance of the selected communications traffic  472  to test communications traffic via the passive optical communications paths in a downstream direction. Once the performance information  480  is collected, the embodiment reports the information  480  in an upstream direction to a network management node  455 , such as an Element Management System (EMS) or a Network Management System (NMS), via the OLT  415  to test communications traffic via a communications path to the network management node  455  in an upstream direction. 
     Transmitting the communications traffic  470  in the downstream direction may include transmitting communications traffic that is aggregated and selectively accessed according to a selectable timing configuration, and may include transmitting selectable characteristics to the OLT  415  to be distributed to the ONTs  435  along with the communications traffic  470 . Collecting information representative of performance of the selected communications traffic  472  may include displaying the content of the selected communications traffic  472  on customer premises equipment  450 , such as a television or other display unit. Reporting the information  480  upstream to the network management node  455  may include correlating the information  480  with test scenarios effected in the downstream traffic  470 , such as format, delay, content, frame type, and frame size test scenarios. The network management node  455  may store the performance information  480  and may use the stored performance information to test other networks or may sell the stored performance information as part of a deployment service (e.g., simulation results). 
     Advantages provided by the embodiments of the present invention include 1) simplifying the testing process by consolidating all reports in one place (such as the network management node  455 ), 2) enabling more flexible testing, as multiple traffic characteristics can be more easily triggered and measured, and 3) creating value from the testing process by organizing the collected information into traffic models and using the information in conjunction with simulation tools during customer deployment, which may then serve to generate revenue through various professional services. 
     In one example embodiment for testing communications traffic, a PON network  400 , which includes an OLT  415 , an Optical Splitter/Combiner (OSC)  425 , a number of ONTs  435  (for example, thirty two ONTs), an aggregator  440 , such as a layer-2 switch, layer-3 router, or wireless device (hereinafter referred to as a switch), and a data collection node  445 , such as a set-top box (STB), is provided. New equipment may be provided, or an existing ONT farm test bed in a laboratory may be used. According to the example embodiment, the data collection node (e.g., STB)  445  is connected to an aggregate port of the switch  440  and may be connected to a high definition television (HDTV) set  450  as well. Ethernet ports (not shown) of the ONTs  435  (for example, ports 1 through 32) are connected to respective individual ports (not shown) of the switch  440 . 
     In this example embodiment, the STB  445  scans each channel across all ONTs  435  using a Virtual LAN (VLAN) filter. To do so, VLAN group identifiers that map the ONT Ethernet ports are configured, and the VLAN port identifiers are associated with respective individual ports of the switch  440 , which are connected to the respective ONTs  435 . For example, switch ports 1 through 32 may be connected to Ethernet ports 1 through 32 of the respective ONTs  435 . The VLAN port identifiers are also associated with the aggregate port of the switch  440 . 
     Multiple multicast Internet Group Management Protocol (IGMP) addresses are defined and associated with the unique VLAN identifiers, for example, one address for each IPTV stream. The IGMP addresses may be defined by running a script on the STB  445 . Each multicast address and VLAN identifier represents a unique IPTV channel over a particular ONT  435 . 
     To initiate the collection of performance data, the STB  445  sends “join requests” upstream for each ONT  435 . In response, multicast group traffic  470  is sent downstream to the ONTs  435 . Multiple IPTV streams (channel programs) are sent in multicast format via the OLT  415 , such as thirty-two IPTV streams (one for each ONT  435 ). IGMP snooping mechanisms in the ONTs  435  determine which host should receive what multicast stream based on a learned IGMP “join” packet. According to the example embodiment, the VLAN identifier in the switch indicates from which ONT  435  the STB  445  will receive the IPTV stream, and the multicast address determines which channel is to be viewed. 
     The STB  445  cycles through each channel on a periodic basis, for example, every ten seconds. That is, in a PON network having thirty two ONTs, the STB  445  may soak (i.e., measure performance data) on channel  1  over the first ONT  435 - 1  for ten seconds before switching to channel  2  over the second ONT  435 - 2 . The STB  445  may continue to switch from ONT to ONT until performance for all thirty two channels over the thirty two ONTs  435  have been measured. Such periodic cycling may be controlled though the use of a script and may continuously loop though the ONTs  435 . 
     While scanning through each channel from each ONT  435 , the STB  445  records data relating to channel performance. Once the performance data  480  is collected in this example embodiment, the STB  445  reports the traffic performance data  480  for analysis, for example, by sending the performance results  480  via HTTP and threshold crossing alarms via Simple Network Management Protocol (SNMP) of each ONT  435  to a network management node  455 , such as an Element Management System (EMS) or Network Management System (NMS). The management data transport between data collection node  445  and the network management node  455  may be through in-band private VLAN that runs through the OLT&#39;s  415  ONT Management Control Interface (OMCI) channel. 
     After processing and analyzing the data, the network management node  455  generates IPTV performance reports for each channel in an example embodiment. The network management node  455  may store, either internally or externally, the performance information based on various traffic characteristics. This valuable information can be organized in such way that is commercialized and used by customers for network traffic modeling and simulation. 
     The above example embodiment may therefore, by scanning through all thirty-two ONT devices using a single data collection node (e.g., a single STB), provide a realistic and cost effective test environment that reflects IPTV subscriber growth expectation (for example, on thirty-two homes). 
       FIG. 5  is a network diagram illustrating a network configuration for testing traffic performance in a PON network  500  using a single data collection node  545 , such as a set-top box (STB), a content server  510 , and a test management node  560 , according to another example embodiment of the present invention. In such an embodiment, the content server  510  may receive a “join request” message from the data collection node  545 , and may respond by sending multicast IPTV streams  570  to the ONTs  535  via an OLT  515  uplink. Additionally, the example embodiment includes a test management node  560  that, according to various test scenarios, causes the content server  510  to transmit traffic  570  with selectable characteristics to the OLT  515 , which is then distributed to the ONTs  535 . The test management node  560  may run scripts to control the characteristics of the content server&#39;s  510  output for a given test scenario. Such characteristics may include differences in traffic format, delay, content, frame type, and frame size. According to the example embodiment, upon collection of the performance information  580 , the network management node  555  correlates the collected performance information with the test scenarios that were effected in the downstream communications traffic. 
       FIG. 6A-6C  are network diagrams illustrating a flow of communications traffic in a network configuration for testing traffic performance in a PON network  600  using a single data collection node  645 , such as a set-top box (STB), according to another example embodiment of the present invention. 
       FIG. 6A  illustrates the STB (i.e., the data collection node)  645  sending channel “join requests”  665  to a content server via each ONT  635 . The switch  640  forwards each channel “join request”  665  through the respective ONT  635 . Each ONT  635  forwards the channel “join request”  665  to the content server  610  via the OSC  625  and the OLT  615 . 
       FIG. 6B  illustrates the content server  610  sending multicast communication traffic  670 ,  675  corresponding to the “join requests”  665  to the ONTs  635 . At this point, the test management node  660  may launch configuration scripts to control the content server&#39;s  610  output characteristics. Upon receiving the multicast traffic  670 ,  675  at the ONTs  635 , the STB  645  scans each channel associated with each ONT  635  using a VLAN filter, as described above, and records information relating to each channel&#39;s performance. 
       FIG. 6C  illustrates the STB (i.e., the data collection node)  645  sending the collected performance information  680  to a network management node  655 , where the information  680  is processed and analyzed. The network management node  655  generates further information regarding the performance of each channel and stores the generated information for future use. The information may be stored internally or externally and may be organized based on various traffic characteristics. 
       FIG. 7  is a block diagram illustrating a system  700  for testing traffic performance in a PON network using an aggregator  740  and a single data collection node  745 , according to an example embodiment of the present invention. According to this example embodiment, an aggregator  740 , such as a layer-2 switch, layer-3 router, or wireless device, aggregates communication traffic received by multiple ONTs. A data collection node  745 , such as a set-top box (STB), is in communication with the aggregator  740  and selectively accesses the aggregated communications traffic. The data collection node  745  then measures the performance of each selected communications traffic  777 , and records data  780  representative of the measured performance. Once the performance data  780  is collected, the data collection node  745  reports the performance data  780  to a network management node (not shown). 
       FIG. 8  is a flow diagram  800  illustrating testing traffic performance in a PON network using an aggregator and a single data collection node, according to an example embodiment of the present invention. According to the example embodiment, communications traffic that is received at multiple ONTs in a passive optical network is aggregated at a point downstream of the multiple ONTs ( 810 ). The traffic is then selectively accessed ( 815 ) and information representative of performance of the selected communications traffic is collected ( 820 ). The collected information is then reported by transmitting the information in an upstream direction to a network management node ( 825 ). 
       FIG. 9  is a flow diagram  900  illustrating testing of traffic performance in a PON network using a single data collection node, according to an example embodiment of the present invention. According to this example embodiment, communications traffic is first transmitted in a downstream direction to multiple ONTs ( 905 ). Then, similar to the example embodiment of  FIG. 8 , the communications traffic received by the multiple ONTs is aggregated at a point downstream of the multiple ONTs ( 910 ). The aggregated traffic is then selectively accessed ( 915 ) and information representative of performance of the selected communications traffic is collected ( 920 ). The collected information is then reported by transmitting the information in an upstream direction to a network management node ( 925 ). 
       FIG. 10  is a flow diagram  1000  illustrating sending and receiving information in a PON network for testing communications traffic performance, according to an example embodiment of the present invention. According to the example embodiment, communications traffic to be transmitted in a downstream direction to multiple ONTs is initiated by sending “join requests” in an upstream direction via the ONTs to a content server ( 1002 ). Upon receiving the “join requests,” the content server transmits the communications traffic to the multiple ONTs ( 1005 ). As described above, the communications traffic received by the multiple ONTs is aggregated at a point downstream of the multiple ONTs ( 1010 ), selectively accessed ( 1015 ), and information representative of the selected communications traffic&#39;s performance is collected ( 1020 ), which is then transmitted in an upstream direction to a network management node ( 1025 ). 
       FIG. 11  is a flow diagram  1100  illustrating testing of traffic in a PON network according to a selectable timing configuration. According to the example embodiment, once communications traffic is transmitted in a downstream direction to multiple ONTs ( 1105 ) and aggregated at a point downstream of the multiple ONTs ( 1110 ), the aggregated communications traffic is selectively accessed according to a selectable timing configuration. According to the timing configuration, the example embodiment selects communications traffic from a given ONT ( 1112 ), and information representative of performance of a selected communications traffic from the given ONT is collected ( 1117 ). When the information has been collected for a duration specified by the timing configuration, performance information for another selected communications traffic from another ONT is collected, until performance information has been collected for the communications traffic from all of the ONTs ( 1112 ,  1117 ,  1122 ). The collected information is then reported by transmitting the information in an upstream direction to a network management node ( 1125 ). 
       FIG. 12  is a flow diagram  1200  illustrating further using communications traffic performance information collected by testing traffic performance in a PON network, according to an example embodiment of the present invention. According to the example embodiment, once the collected channel performance information is reported to a network management node ( 1205 ,  1210 ,  1215 ,  1220 ,  1225 ), the information may be stored for future use. One example future use is to use the collected information to test traffic performance in other PON networks ( 1230 ). Another example is to sell the collected information as part of a professional service for deployed systems ( 1235 ). 
     While this invention has been particularly shown and described with references to example embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention encompassed by the appended claims. For example, the aggregator may take the form of a layer-2 switch, layer-3 router, or wireless communications device. In embodiments using a wireless device, communications may be transmitted and received using Radio Frequency (RF) communications (e.g., WiFi 802.11 communications). In such embodiments, the wireless device may aggregate the communications traffic at, for example, the data collection node (e.g., STB). Additionally, while the above example embodiments include to a PON network carrying IPTV traffic, embodiments for testing performance of traffic other than IPTV traffic may be implemented. 
     It should be understood that the flow diagrams of  FIGS. 8-12  are examples that can include more or fewer components, be partitioned into subunits, or be implemented in different combinations. Moreover, the flow diagrams may be implemented in hardware, firmware, or software. If implemented in software, the software may be written in any software language suitable for use in networks as illustrated in  FIGS. 4-7 . The software may be embodied on any form of computer readable medium, such as RAM, ROM, or magnetic or optical disk, and loaded and executed by generic or custom processor(s).