Abstract:
The present invention relates to an optical network terminal (ONT), a method for configuring rate limiting attributes of ports, and a method for processing packets. The ONT includes a passive optical network (PON) protocol processing module, and a user network interface (UNI) module, which are connected through an internal interface. The ONT also includes a port rate limiting module connected to a UNI. The port rate limiting module stores rate limiting attributes, and the ONT uses these attributes to control the traffic of the UNI. The port rate limiting attributes are configured for the ONT through an ONT management and control interface (OMCI) message of an optical line terminal (OLT). In this way, when the ONT receives data from the UNI, it can control the traffic of the UNI according to the port rate limiting attributes. The present invention enables the port rate limiting function for the ONT, prevents overflow of the internal receiving buffer of the ONT, and prevents denial of service (DoS) attacks from illegal users.

Description:
RELATED APPLICATIONS 
       [0001]    This application claims a priority from the Chinese Patent Application No. 200610060495.2, filed with the Chinese Patent Office on Apr. 26, 2006 and entitled “Optical Network Terminal, Method for Configuring Rate Limiting Attributes of Ports, and Method for Processing Packets”, the contents of which are incorporated herein by reference in their entirety 
       FIELD OF THE INVENTION 
       [0002]    The present invention relates to the field of passive optical network (PON), and in particular, to an optical network terminal (ONT) in the PON system, a method for configuring rate limiting attributes of ports, and a method for processing packets. 
       BACKGROUND OF THE INVENTION 
       [0003]    At present, the broadband access technology comes in two types: copper wire access technology such as digital subscriber line (xDSL) technology and optical access technology. An access network based on the optical access technology is called an optical access network (OAN). 
         [0004]    The PON technology is an optical access technology for point-to-multipoint transfer.  FIG. 1  shows a PON system. A PON system includes an optical line terminal (OLT), an optical distribution network (ODN), and an optical network unit (ONU). The OLT provides a service node interface (SNI) for the OAN, and is connected to one or more ODNs. An ODN is a passive optical splitting component, which transmits the downstream data of the OLT to each ONU through optical splitting. Likewise, the ODN transmits the upstream data of the ONU to the OLT through convergence. The ONU provides a user network interface (UNI) for the OAN, and is connected to the ODN. If the ONU also provides the user port function, for example, Ethernet user port or plain old telephone service (POTS) user port, the ONU is called an “ONT”. Unless otherwise specified, ONU and ONT are collectively called “ONT” hereinafter. 
         [0005]    In the general PON access technology, the downstream traffic of the OLT is broadcast to each ONT through time division multiplexing (TDM), and each ONT receives the traffic as required; the upstream traffic of the ONT is controlled through the OLT, so that only a specific ONT is allowed to transmit data at a time and the data is transmitted to the OLT through time division multiple access (TDMA). 
         [0006]    The ITU-T has established the broadband passive optical network (BPON) standard and the gigabit passive optical network (GPON) standard. The OLT configuration and ONT management modes are defined in the BPON and GPON standards. The OLT manages the ONT through an ONU management and control interface (OMCI) path. An OMCI is a configuration transmission path defined in the BPON and GPON standards. It is set up by the ONT between the OLT and the ONT when the ONT is registered at the OLT. The OMCI is a master-slave management protocol, in which the OLT is a master device and the ONT is a slave device. Through an OMCI path, the OLT controls multiple ONIs connected under it. 
         [0007]    In the OMCI protocol, the ONT data managed by the OLT is abstracted into an independent management information base (MIB). A basic unit of the MIB is management entity (ME). According to the function configuration of the ONT, multiple MEs of the ONT are controlled by the OLT through an OMCI, as defined by the BPON and GPON standards. Under the control of the OLT, the ONT implements the configuration and management of all the MEs. 
         [0008]    A network device generally has more than one port. A data stream flows in from certain ports, and flows out of other ports after being processed or buffered through a network device. Suppose that the data stream flows in from port A, and flows out of port B. This case may occur: When the rate of the data stream from port A is greater than the rate of the data stream out of port B, the buffer room in the device diminishes gradually. If this case continues for a sufficient time, the buffer inside the device overflows, and the data packets are hence lost. The duration depends on the size of the buffer inside the device, and the ratio of the inbound rate at port A to the outbound rate at port B. The greater the buffer is, the longer time it will take for the buffer to overflow; the greater the ratio of the inbound rate at port A to the outbound rate at port B is, the shorter time it will take for the buffer to overflow. The foregoing case can be prevented by limiting the inbound rate of the data stream at port A. 
         [0009]      FIG. 2  shows how an ONT with n Ethernet ports processes the upstream Ethernet packets to the OLT in a GPON system. The Ethernet packets “E 1 ” and “E 2 ” from a customer premises equipment (CPE)  1  are converged with the Ethernet packet “E 3 ” from a CPE n by a medium access control (MAC) bridge module  21  of the ONT, and sent to a GPON protocol processing module  22  through an internal Ethernet port. The GPON protocol processing module  22  adds the corresponding GPON protocol packet header information Px, Py, and Pz into the packets and then sends the packets to the OLT in the allocated timeslots. When the sum of the rates of data streams received by the MAC bridge module  21  of the ONT from all the UNIs is greater than the total upstream bandwidth of the ONT allocated by the OLT, it is necessary to perform traffic control for the data streams on the ONT to prevent overflow of the internal receiving buffer of the ONT. Moreover, when multiple users share an ONT and each user occupies an Ethernet port of the ONT, if a user supports sending of traffic greater than the traffic of the bandwidth allocated by the OLT to the ONT, congestion will occur in the MAC bridge module  21  of the ONT, and the ONT will discard the packets beyond the allocated bandwidth. Consequently, the denial of service (DoS) attack occurs, and affects normal services of other users. 
         [0010]    A traffic descriptor ME is defined in the BPON and GPON standards. The GPON encapsulation method (GEM) traffic descriptor ME monitors the upstream traffic identified by the GEM Port-ID. This ME is associated with the GEM port network connection termination point (CTP) ME. This ME is described below: 
         [0011]    ME: GEM traffic descriptor. 
         [0012]    Data relationship: This ME is associated with a GEM port network CTP ME. The features of the upstream traffic identified by the GEM Port-ID are expressed by this ME. 
         [0013]    The attributes of this ME are shown in Table 1 
         [0000]    
       
         
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
             
             
               
                   
                 ME ID 
                 This attribute provides a unique ID for each instance 
               
               
                   
                   
                 of the ME. (mandatory, 2 bytes) 
               
               
                   
                 SIR 
                 This attribute represents the sustained information 
               
               
                   
                   
                 rate (SIR), measured in byte/s. (optional, 4 bytes) 
               
               
                   
                 PIR 
                 This attribute represents the peak information rate 
               
               
                   
                   
                 (PIR), measured in byte/s. (optional, 4 bytes) 
               
               
                   
                   
               
             
          
         
       
     
         [0014]    In the GPON standard, the GEM traffic descriptor ME is associated with the GEM port network CTP, both being used to configure and manage the corresponding attributes in the GPON protocol processing module in the ONT. The GEM port network CTP configures and manages a GEM Port. Therefore, when a data stream passes through this GEM port, traffic control will be performed according to the GEM traffic descriptor. 
         [0015]    In the prior art, the traffic control is performed only at the GEM port network CTP. As shown in  FIG. 2 , when the sum of the rates of data received by multiple UNIs is greater than the rate of data transmitted from the MAC bridge module to the GPON protocol processing module through an internal Ethernet port, a traffic conflict occurs on the MAC bridge module. Suppose that the rate of a data stream received by UNI  1  is high but the data significance is low, while the rate of another data stream received by UNI n is low but the data significance is high. The low-significance and high-rate data stream at UNI  1  may lead to loss of the high-significance and low-rate data stream at UNI n. 
       SUMMARY OF THE INVENTION 
       [0016]    An embodiment of the present invention provides an ONT, a method for configuring the rate-limiting attributes of ports, and a method for processing packets to enable the port rate limiting function, to prevent overflow of the internal receiving buffer of the ONT and to prevent denial of service (DoS) attacks from illegal users. 
         [0017]    An ONT provided in an embodiment of the present invention includes: (i) a passive optical network (PON) protocol processing module and a user network interface (UNI) module, both being connected through an internal interface, where the UNI module provides multiple UNIs; and (ii) a port rate limiting module connected to a UNI, where the port rate limiting module stores port rate limiting attributes, and the ONT uses these attributes to control the traffic of the UNI. 
         [0018]    A method for configuring ONT port rate limiting attributes provided in an embodiment of the present invention includes: receiving, by an ONT, an OMCI message from an OLT, where the message carries the port rate limiting attributes for performing traffic control for a UNI; and storing the port rate limiting attributes into a management entity (ME). 
         [0019]    A method for processing packets by an ONT provided in an embodiment of the present invention includes: receiving data from or sending data to a UNI; calculating the rate of the data received from or sent to the UNI; and performing traffic control for the UNI when the rate of the data sent/received at the UNI is greater than the value preset in the port rate limiting attributes for the UNI. 
         [0020]    The ONT in this embodiment of the invention contains a port rate limiting module connected to the UNI, and therefore overflow of the internal receiving buffer of the ONT and DoS attacks from illegal users may be prevented. 
         [0021]    According to the method for configuring port rate limiting attributes of an ONT provided in an embodiment of the present invention, the port rate limiting attributes are configured for the ONT through a configuration terminal, and the ONT stores the port rate limiting attributes into an ME, so that the ONT can implement the port rate limiting function according to the port rate limiting attributes. 
         [0022]    The method for processing packets by an ONT provided in an embodiment of the present invention judges whether the rate of the data transmitted through a UNI is greater than the value set in the port rate limiting attributes of the UNI. If so, traffic control is performed for the UNI to prevent overflow of the internal receiving buffer of the ONT and prevent DoS attacks from illegal users. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0023]      FIG. 1  shows a PON system in the prior art; 
           [0024]      FIG. 2  shows how an ONT with n Ethernet ports processes the upstream Ethernet packets to the OLT in a GPON system in the prior art; 
           [0025]      FIG. 3  to  FIG. 6  show the structure of an ONT according to an embodiment of the present invention; 
           [0026]      FIG. 7  shows how a configuration terminal configures the port rate limiting attributes for a UNI of the ONT through an OLT according to an embodiment of the present invention; 
           [0027]      FIG. 8  is a flowchart of processing upstream packets by an ONT, with port rate limiting attributes configured for a UNI according to an embodiment of the present invention; and 
           [0028]      FIG. 9  is a flowchart of processing downstream packets by an ONT, with port rate limiting attributes configured for a UNI according to an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0029]    The following text describes an ONT, a method for configuring port rate limiting attributes and a method for processing packets according to embodiments of the present invention, supposing that the ONT provides Ethernet user ports in the GPON system. 
         [0030]    For an ONT with Ethernet user ports in the GPON system, the UNI module is a MAC bridge module; the internal interface is an internal Ethernet port; and the PON protocol processing module is a GPON protocol processing module. 
         [0031]      FIG. 3  shows the structure of an ONT according to the first embodiment of the present invention. 
         [0032]    In the first embodiment, an ONT includes: a GPON protocol processing module  30  connected through an internal Ethernet port with a MAC bridge module  31 , and multiple port rate limiting modules  311  inside the MAC bridge module  31 , where the port rate limiting modules  311  are connected in series with the UNIs, that is, data streams need to pass through the port rate limiting modules. In the first embodiment, the MAC bridge module  31  contains multiple port rate limiting modules  311 , and each port rate limiting module is connected to a UNI, that is, the ONT performs the rate limiting function at each UNI in a distributed way. 
         [0033]    Each port rate limiting module  311  stores the port rate limiting attributes. The ONT receives data from a UNI, and calculates the rate of the data received from the UNI. Traffic control is performed for the UNI when the rate of the data received at the UNI is greater than the value preset in the port rate limiting attributes for the UNI. 
         [0034]    In the first embodiment, the upstream data arrives at the MAC bridge module first, and then the data streams undergo rate limiting processing inside the MAC bridge module; the downstream data streams undergo the processing at the port rate limiting module, and then flow out of the MAC bridge module. 
         [0035]      FIG. 4  shows the structure of an ONT according to the second embodiment of the present invention. 
         [0036]    In the second embodiment, an ONT includes: a GPON protocol processing module  30  connected through an internal Ethernet port with a MAC bridge module  41 , and multiple port rate limiting modules  411  outside the MAC bridge module  41 , where the port rate limiting modules  411  are connected in series with the UNIs, that is, data streams need to pass through the port rate limiting modules. In the second embodiment, the ONT contains multiple port rate limiting modules  411 , and each port rate limiting module is connected to a UNI, that is, the ONT performs the rate limiting function at each UNI in a distributed way. 
         [0037]    Each port rate limiting module  411  stores the port rate limiting attributes. The ONT receives data from a UNI, and calculates the rate of the data received from the UNI. Traffic control is performed for the UNI when the rate of the data received at the UNI is greater than the value preset in the port rate limiting attributes for the UNI. 
         [0038]    In the second embodiment, the upstream data undergoes rate limiting processing through the port rate limiting module, and then arrives at the MAC bridge module; the downstream data streams flow out of the MAC bridge module and then undergo the processing at the port rate limiting module. 
         [0039]      FIG. 5  shows the structure of an ONT according to the third embodiment of the present invention. 
         [0040]    In the third embodiment, an ONT includes: a GPON protocol processing module  30  connected through an internal Ethernet port with a MAC bridge module  51 , and multiple port rate limiting modules  511  outside the MAC bridge module  51 , where the port rate limiting modules  511  are connected in parallel with the UNIs, that is, data streams do not pass through the port rate limiting modules, and the UNIs limit the rate of the data streams according to the settings of the port rate limiting modules. In the third embodiment, the ONT contains multiple port rate limiting modules  511 , and each port rate limiting module is connected to a UNI, that is, the ONT performs the rate limiting function at each UNI in a distributed way. 
         [0041]    Each port rate limiting module  511  stores the port rate limiting attributes. The ONT receives data from a UNI, and calculates the rate of the data received from the UNI. Traffic control is performed for the UNI when the rate of the data received at the UNI is greater than the value preset in the port rate limiting attributes for the UNI. 
         [0042]    In the embodiment shown in  FIG. 4 , the port rate limiting modules are connected in series with the UNIs, that is, data streams pass through the port rate limiting modules that perform rate limiting processing directly. 
         [0043]    In the embodiment shown in  FIG. 5 , the port rate limiting modules are connected in parallel with the UNIs, that is, data streams do not pass through the port rate limiting modules, and the port rate limiting modules control the UNIs to limit the rate of data streams. 
         [0044]    In the embodiments shown in  FIG. 3  to  FIG. 5 , each port rate limiting module is connected to a UNI. In other words, the ONT performs the rate limiting function at each UNI in a distributed way. Additionally or alternatively, the rate-limiting function may be implemented at each UNI in a centralized way. 
         [0045]      FIG. 6  shows the structure of an ONT according to the fourth embodiment of the present invention. 
         [0046]    In the fourth embodiment, an ONT includes: a GPON protocol processing module  30  connected through an internal Ethernet port with and a MAC bridge module  61 . The MAC bridge module  61  contains a port rate limiting module  611  which is connected to all UNIs. That is, the ONT performs the rate limiting function at each UNI in a centralized way. 
         [0047]    In the fourth embodiment, the ONT implements the port rate limiting function through a UNI traffic descriptor ME defined in the ME of the OMCI. This ME is described below: 
         [0048]    ME: UNI traffic descriptor 
         [0049]    Data relationship: Each instance of the UNI traffic descriptor ME corresponds to a UNI physical port of an ONT, which is an Ethernet physical port in this embodiment. The ME is managed through a physical path termination point Ethernet UNI. 
         [0050]    The attributes of this ME are shown in Table 2: 
         [0000]    
       
         
               
               
             
           
               
                 TABLE 2 
               
               
                   
               
             
             
               
                 ME ID 
                 This attribute provides a unique ID for each instanceof the ME, 
               
               
                   
                 and this ID is the same as the ID of the UNI physical path 
               
               
                   
                 termination point ME. (read only, set through creation) 
               
               
                   
                 (mandatory, 2 bytes) 
               
               
                 USIR 
                 This attribute represents the upstream sustained information rate 
               
               
                   
                 (USIR), measured in byte/s. (optional, 4 bytes) 
               
               
                 UPIR 
                 This attribute represents the upstream peak information rate 
               
               
                   
                 (PIR), measured in byte/s. (optional, 4 bytes) 
               
               
                 DSIR 
                 This attribute represents the downstream sustained information 
               
               
                   
                 rate (DSIR), measured in byte/s. (optional, 4 bytes) 
               
               
                 DPIR 
                 This attribute represents the downstream peak information rate 
               
               
                   
                 (DPIR), measured in byte/s. (optional, 4 bytes) 
               
               
                   
               
             
          
         
       
     
         [0051]    Port rate limiting attributes may constitute a separate ME (as in the solution mentioned above), or the parameters of the port rate limiting attributes are added to other MEs. The port rate limiting attributes are not limited to the parameters listed above. 
         [0052]    This embodiment of the invention further provides a method for configuring port rate limiting attributes of an ONT, in which the ONT receives an OMCI message from an OLT; the message carries the port rate limiting attributes for traffic control on a UNI; and the ONT stores the port rate limiting attributes in an ME. 
         [0053]    As shown in  FIG. 7 , the method for configuring the port rate limiting attributes of a UNI of the ONT through an OLT according to an embodiment of the present invention includes the following steps: 
         [0054]      71 . The configuration terminal sends a command for configuring port rate limiting attributes to the OLT, in which the configuration parameters of the port rate limiting attributes include an ONT ID, the port number of the UNI that needs configuration of port rate limiting attributes, and rate description parameters of the UNI (including upstream peak rate, and upstream sustained rate); 
         [0055]      72 . The OLT sends an OMCI message to the ONT through an OMCI path, requesting to configure the port rate limiting attributes of the UNI of the ONT. The configuration parameters of the port rate limiting attributes in the OMCI message include an ONT ID, the port number of the UNI that needs configuration of port rate limiting attributes, and rate description parameters of the UNI (including upstream peak rate, upstream sustained rate, downstream peak rate and downstream sustained rate); 
         [0056]      73 . The ONT stores the port rate limiting attributes into the ONI traffic descriptor ME, and returns a configuration response message to the OLT. 
         [0057]    In addition or alternatively, the configuration terminal may send a command for configuring port rate limiting attributes to the ONT through direct control (based on a local serial port) or remote control (based on Telnet or an NMS), and the ONT stores the port rate limiting attributes in the configuration command into the UNI traffic descriptor ME. Moreover, the port rate limiting attributes may also be stored in other MEs. 
         [0058]    In this way, when the ONT receives or sends data through a UNI, traffic control can be performed according to the port rate limiting attributes stored in the ME to limit the port rate. As shown in  FIG. 8 , the method for processing upstream packets by an ONT in an embodiment of the invention includes the following steps: 
         [0059]      81 . The ONT receives data from a UNI; 
         [0060]      82 . The ONT calculates the rate of the data received from the UNI, including the peak rate and the sustained rate. The peak rate refers to a data rate in a short time such as the average rate of packets received within 1 second; the sustained rate refers to the data rate in a relatively long time such as the average rate of packets received within 1 minute or 1 hour; the rate of the received data can be measured through a mean value algorithm or other algorithms; 
         [0061]      83 . The ONT judges whether the rate of the data received from the UNI exceeds the value set in the port rate limiting attributes for the UNI; if not, the process goes to step  85 , or else step  84 ; 
         [0062]      84 . The ONT performs traffic control for the UNI based on the “tail drop” or “random drop” policy, for example, random early detection/weighted random early detection (RED/WRED) algorithm; 
         [0063]      85 . Subsequent processing. 
         [0064]    As shown in  FIG. 9 , the method for processing downstream packets by an ONT in an embodiment of the invention includes the following steps: 
         [0065]      91 . The ONT sends data from a UNI; 
         [0066]      92 . The ONT calculates the rate of the data sent by the UNI, including the peak rate and the sustained rate. The peak rate refers to a data rate in a short time such as the average rate of packets received within 1 second; the sustained rate refers to the data rate in a relatively long time such as the average rate of packets received within 1 minute or 1 hour; the rate of the sent data can be measured through a mean value algorithm or other algorithms. 
         [0067]      93 . The ONT judges whether the rate of the data sent by the UNI exceeds the value set in the port rate limiting attributes for the UNI; if not, the process goes to step  95 , or else step  94 ; 
         [0068]      94 . The ONT performs traffic control for the UNI based on the “tail drop” or “random drop” policy, for example RED/WRED algorithm; 
         [0069]      95 . Subsequent processing. 
         [0070]    In the foregoing embodiments of the invention, an ONT judges whether the rate of the data transmitted through a UNI is greater than the value set in the port rate limiting attributes for the UNI. If so, traffic control is performed for the UNI to prevent overflow of the internal receiving buffer of the ONT and prevent DoS attacks from illegal users. 
         [0071]    One of ordinary skill in the art will understand that all or part of the steps in the preceding embodiments can be completed through a program which instructs related hardware. The program may be stored in a computer-readable storage medium, for example, ROM/RAM, disk and CD. 
         [0072]    Although the invention has been described through some exemplary embodiments, the invention is not limited to such embodiments. It is apparent that those skilled in the art can make various modifications and variations to the invention without departing from the spirit and scope of the invention. The invention is intended to cover the modifications and variations provided that they fall in the scope of protection defined by the following claims or their equivalents.