Patent Publication Number: US-2013232537-A1

Title: Packet filtering at a media converter in a network with optical and coaxial components

Description:
RELATED APPLICATION 
     This application-claims priority to U.S. Provisional Patent Application No. 61/606,440, titled “Packet Filtering at a Media Converter in a Hybrid Fiber-Coaxial Network,” filed Mar. 4, 2012, which is hereby incorporated by reference in its entirety. 
    
    
     TECHNICAL FIELD 
     The present embodiments relate generally to communication systems, and specifically to communication systems with both optical fiber links and coaxial cable (“coax”) links. 
     BACKGROUND OF RELATED ART 
     A network may use both optical fiber and coaxial cable for respective links. For example, the portions of the network that use optical fiber may be implemented using the Ethernet Passive Optical Networks (EPON) protocol, and the EPON protocol may be extended over coaxial cable plants. EPON over coax is called EPOC. The fiber part of the network can potentially support a higher data rate than the coax part of the network. Also, different coax parts of the network (e.g., different cable plants) may have different maximum data rates. Slow coax links thus can limit overall system performance. For example, if the Ethernet Passive Optical Networks protocol is implemented in a network with both fiber (EPON) and coax (EPoC) links, the overall data rate may be limited by the lowest data rate of the worst coax link. 
     Accordingly, there is a need for fiber-to-coax media converters that can accommodate different data rates for different links. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present embodiments are illustrated by way of example and are not intended to be limited by the figures of the accompanying drawings. 
         FIG. 1  is a block diagram of a network with both optical fiber links and coax links in accordance with some embodiments. 
         FIG. 2  illustrates an auto-discovery procedure between an optical link terminal and optical network units. 
         FIG. 3  illustrates an auto-discovery procedure between an optical link terminal and coax network units in accordance with some embodiments. 
         FIG. 4A  is a schematic block diagram of a media converter in a network with both optical fiber links and coax links in accordance with some embodiments. 
         FIG. 4B  is a schematic block diagram of a media converter in a network with both optical fiber links and coax links in accordance with some embodiments. 
         FIG. 5A  is a flowchart illustrating a method of filtering packets in a media converter in accordance with some embodiments. 
         FIG. 5B  is a flowchart illustrating a method of creating and updating a filtering template in accordance with some embodiments. 
     
    
    
     Like reference numerals refer to corresponding parts throughout the figures and specification. 
     DETAILED DESCRIPTION 
     Embodiments are disclosed in which a media converter forward onto a coax medium only a portion of the optical packets that it receives. 
     In some embodiments, a media converter coupled to an optical link terminal and to a plurality of coax network units on a cable plant receives packets from the optical link terminal via an optical link. The packets include first packets addressed to coax network units on the cable plant and second packets addressed to network units outside of the cable plant. The media converter forwards the first packets to the coax network units on the cable plant via one or more coax links, such that the first packets are forwarded to each coax network unit on the cable plant, and discards the second packets. 
     In some embodiments, a media converter includes an optical port to be coupled to an optical link and a coax port to be coupled to a cable plant. The media converter also includes a packet sniffing and filtering module, coupled between the optical port and the coax port, to filter packets received on the optical port. The packet sniffing and filtering module forwards packets addressed to coax network units on the cable plant to the coax port for transmission and discards packets addressed to network units outside of the cable plant. 
     In some embodiments, a non-transitory computer-readable storage medium stores instructions that, when executed by one or more processors in a media converter, cause the media converter to extract identifiers of destination coax network units from packets received on an optical port, compare the extracted identifiers to a filter template storing identifiers of coax network units, forward packets for which the extracted identifiers match an identifier in the filter template, and discard packets for which the extracted identifiers do not match any identifiers in the filter template. 
     In the following description, numerous specific details are set forth such as examples of specific components, circuits, and processes to provide a thorough understanding of the present disclosure. Also, in the following description and for purposes of explanation, specific nomenclature is set forth to provide a thorough understanding of the present embodiments. However, it will be apparent to one skilled in the art that these specific details may not be required to practice the present embodiments. In other instances, well-known circuits and devices are shown in block diagram form to avoid obscuring the present disclosure. The term “coupled” as used herein means connected directly to or connected through one or more intervening components or circuits. Any of the signals provided over various buses described herein may be time-multiplexed with other signals and provided over one or more common buses. Additionally, the interconnection between circuit elements or software blocks may be shown as buses or as single signal lines. Each of the buses may alternatively be a single signal line, and each of the single signal lines may alternatively be buses, and a single line or bus might represent any one or more of a myriad of physical or logical mechanisms for communication between components. The present embodiments are not to be construed as limited to specific examples described herein but rather to include within their scopes all embodiments defined by the appended claims. 
       FIG. 1  is a block diagram of a network  100  that includes both optical fiber links and coax links in accordance with some embodiments. The network  100  includes an optical link terminal (OLT)  110  (which may also be referred to as an optical line terminal) coupled to a plurality of optical network units (ONUs)  120 - 1  and  120 - 2  via respective optical fiber links. The OLT  110  also is coupled to a plurality of media converters  130 - 1  and  130 - 2  via respective optical fiber links. The media converters  130 - 1  and  130 - 2 , which may also be referred to as coax media converters (CMCs) or optical-coax units (OCUs), convert optical signals from the OLT  110  into electrical signals and transmit the electrical signals to coax network units (CNUs) via respective coax links. In the example of  FIG. 1 , a first media converter  130 - 1  transmits converted signals to CNUs  140 - 1  and  140 - 2 , and a second media converter  130 - 2  transmits converted signals to CNUs  140 - 3 ,  140 - 4 , and  140 - 5 . The coax links coupling the first media converter  130 - 1  to CNUs  140 - 1  and  140 - 2  compose a first cable plant  150 - 1 . The coax links coupling the second media converter  130 - 2  to CNUs  140 - 3  through  140 - 5  compose a second cable plant  150 - 2 . In some embodiments, the OLT  110 , ONUs  120 - 1  and  120 - 2 , and media converters  130 - 1  and  130 - 2  are implemented in accordance with the Ethernet Passive Optical Network (EPON) protocol. In some embodiments, the OLT  110  transmits optical signals using time-domain multiplexing (TDM), such that different time slots are used to transmit packets addressed to different network units. 
     In some embodiments, the OLT  110  is located at the network operator&#39;s headend, the ONUs  120  and CNUs  140  are located at the premises of respective users, and the media converters  130  are located at the headends of respective cable plant operators. Alternatively, media converters  130  may be located within cable plants. 
     In some embodiments, each ONU  120  and media converter  130  in the network  100  receives data at the same data rate. The ONUs  120  and media converters  130  each receive all of the packets transmitted by the OLT  110 . For unicast transmissions, each ONU  120  receives every packet transmitted by the OLT  110 , but selects only the packets addressed to it, and discards all packets that are not addressed to it. 
     For unicast transmissions, the media converters  130  also receive every packet transmitted by the OLT  110 , but filter out the packets not addressed to CNUs  140  on their respective cable plants  150 . For example, the media converter  130 - 1  receives every packet transmitted by the OLT  110  but forwards only those packets addressed to the CNUs  140 - 1  and  140 - 2  on the cable plant  150 - 1 . The media converter  130 - 1  forwards each packet addressed to one of the CNUs  140 - 1  and  140 - 2  on the cable plant  150 - 1  to every CNU  140 - 1  and  140 - 2  on the cable plant  150 - 1 . Each CNU  140 - 1  and  140 - 2  selects the packets addressed to it and discards other packets. The media converter  130 - 2  and CNUs  140 - 3  through  140 - 5  function similarly. 
     In some embodiments, the optical fiber links in the network  100  can support higher data rates than the coax links. In one example, the optical links can support data rates of 10 Gbps, while the coax links can support data rates of 1 Gbps. Despite this difference, the OLT  110  transmits at the higher data rate of the optical links (e.g., 10 Gbps). The filtering performed by the media converters  130  prevents the coax links from limiting data rates of the optical links and thus the overall network performance. Because only a portion of the packets transmitted by the OLT  110  are forwarded by the media converters  130 , the coax links can operate at lower data rates than the optical links, which can operate at their maximum potential speed in accordance with some embodiments. By allowing the optical links to operate at full speed, the filtering thus avoids wasting bandwidth. 
     In some embodiments, the data rates of respective coax links vary according to link quality and available bandwidth. Even within a particular cable plant  150 , different CNUs  140  (and thus, different users) may see different channel conditions. The media converters  130 - 1  and  130 - 2  therefore are configurable to transmit coax signals using different modulation and coding schemes (MCSs). For example, different MCSs may be used for different CNUs in a cable plant. (Alternatively, a data rate is chosen such that all CNUs  140  on a cable plant  150  can decode all broadcast packets.) Different multiplexing scheme may be used for different cable links, such as TDM, frequency-division multiplexing (FDM), code-division multiplexing (CDM), and various combinations of such multiplexing schemes. 
     In some embodiments, an MCS is chosen such that when a code word combines packets for different CNUs  140 , all of these CNUs are able to decode the code word. 
     In some embodiments, as mentioned, MCSs are chosen independently for different CNUs  140 , even within the same cable plant  150 . For a respective CNU  140 , an MCS is chosen to provide an adequate data rate (e.g., to maximize the data rate) based on the link quality for the CNU  140 . Also, data rates can be improved or optimized with an appropriate assignment of resources. For example, in a cable plant  150 , two CNUs  140  may see a frequency notch, but at different frequencies. Frequency resources are assigned such that each CNU  140  sees a good channel where its own data is transmitted. 
     Each media converter  130  filters packets (e.g., with corresponding frames, such as Ethernet frames) from the OLT  110  so that only frames addressed to any of the registered CNUs  140  coupled to the converter  130  are forwarded. The media converter  130  builds and manages a filtering template to select the frames to be forwarded. The filtering is based, for example, on the logical link identifier (LLID) encapsulated in the preamble of the frame. 
     To build and manage the filtering template, the media converter may exploit an auto-discovery procedure for network units (e.g., the EPON multi-point control protocol (MPCP), as standardized in the IEEE 802.3 Ethernet standard) in which messages (e.g., MPCP messages) are transmitted between the network units.  FIG. 2  illustrates this auto-discovery procedure as performed for the OLT  110  and ONUs  120 - 1  and  120 - 2 . At the beginning of this procedure, ONU  120 - 1  and ONU  120 - 2  are both unregistered with the OLT  110 . The OLT  110  periodically distributes special GATE messages, called discovery GATE messages, to trigger registration of unregistered network units. At step  1  of the procedure, the OLT  110  distributes one of these discovery GATE messages. At step  2 , unregistered ONUs  120 - 1  and  120 - 2  attempt to register, competing for upstream transmission by replying with a registration request (REGISTER_REQ) message. (The same message can also be issued by an ONU to unregister.) In the example of  FIG. 2 , the ONU  120 - 1  succeeds in transmitting its REGISTER_REQ message to the OLT  110 , but the ONU  120 - 2  fails. When the OLT  110  decodes the REGISTER_REQ message from the ONU  120 - 1 , it replies to the ONU  120 - 1  (at step  3   a ) with a registration (REGISTER) message that assigns a unique LLID to that ONU, and immediately sends a unicast GATE message to the ONU  120 - 1  (at step  3   b ). (The OLT  110  can also instruct the ONU  120 - 1  to unregister.) The ONU  120 - 1  replies at step  4  with a registration acknowledgment (REGISTER_ACK) message to complete registration or with a non-acknowledgment (NACK) message if registration fails. Once the OLT  110  receives REGISTER_ACK, the ONU  120 - 1  is registered with the OLT  110 , but the ONU  120 - 2  remains unregistered. Data transfer now can occur between the OLT  110  and ONU  120 - 1 . The ONU  120 - 2  can attempt to register again in response to a subsequent discovery GATE message. 
     An analogous procedure to that of  FIG. 2  is performed to register CNUs  140 , as illustrated in  FIG. 3  in accordance with some embodiments. In the procedure of  FIG. 3 , the messages are transmitted between the OLT  110  and CNUs  140 - 1  and  140 - 2  through the media converter  130 - 1 . The media converter  130 - 1  monitors the messages, detects the LLIDs, and updates its filter template accordingly. When a CNU  140  registers with the OLT  110 , the media converter  130 - 1  adds the LLID for the CNU  140  to the filter template. If the media converter  130 - 1  subsequently receives a packet specifying that LLID, it forwards the packet. (In some embodiments, an LLID also is added to the list of LLIDs in the filter template in response to upstream transmission of a data packet to the media controller  130 - 1  from a CNU  140  that is not listed in the filter template.) When a CNU  140  unregisters, the media converter  130 - 1  removes the LLID for the CNU  140  from the filter template. If the media converter  130 - 1  subsequently receives a packet specifying that LLID, it discards the packet and does not forward it. The media converter  130 - 1  thereby performs a packet sniffing and filtering process to determine whether to forward or discard packets. 
     The media converter  130 - 1  thus tracks registration and deregistration events, as indicated by corresponding messages (e.g., MPCP messages), for CNUs  140  in its domain (e.g., on its cable plant  150 - 1 ), and updates the filter template accordingly. 
     In some embodiments, to monitor the messages shown in  FIG. 3 , the media converter  130 - 1  reads all frames of 64-byte size and extracts MPCP frames by checking the type. To do this, the media converter  130 - 1  opens the frames. The messages are parsed in the media converter  130 - 1  by filtering on preambles for CNU data. Table 1 illustrates various fields for a frame. The media converter  130 - 1  analyzes respective fields to determine the message type corresponding to the frame. In the example of Table 1, the Length/Type data ( 88 - 08 ) indicates an MPCP message, the opcode (02) indicates a GATE message, and the number of grants/flags (09) indicates a Discovery message. 
     
       
         
           
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
             
            
               
                   
                 Preamble - broadcast 
               
               
                   
                 Destination Address (DA) 
               
               
                   
                 Source Address (SA) 
               
               
                   
                 Length/Type = 88-08 
               
               
                   
                 Opcode = 00-02 
               
               
                   
                 Time Stamp 
               
               
                   
                 Number of grants/flags = 09 
               
               
                   
                 Grant start time 
               
               
                   
                 Grant length 
               
               
                   
                 Sync time 
               
               
                   
                 Pad = 00 
               
               
                   
                 Frame check sequence 
               
               
                   
                   
               
            
           
         
       
     
     For example, if a discovery GATE message is detected in step  1  of  FIG. 3 , the media converter  130  recognizes that a registration process has begun. If a subsequent REGISTER_REQ message is received in step  2  of  FIG. 3 , as identified by its frame size (e.g., 64 bytes), message type (e.g., 88-08) and opcode (e.g., 04), then the media converter  130  stores a record of this message along with the source address of the coax network unit that sent the message. If a REGISTER message is then received in step  3   a  of  FIG. 3  for a CNU  140  with a destination address equal to the source address of the REGISTER_REQ message, the media converter  130  stores the LLID specified in the REGISTER message and associates the LLID with the source address of the REGISTER_REQ message. In some embodiments, the REGISTER message is identified by its frame size (e.g., 64 bytes), message type (e.g., 88-08) and opcode (e.g., 05). Upon receipt of a subsequent REGISTER_ACK message in step  4  of  FIG. 3  (e.g., as identified by a frame size of 64 bytes, a message type of 88-08, an opcode of 06, and a source address equal to the source address of the REGISTER_REQ message), the LLID and associated source address for the newly registered CNU  140  are added to the filter template. 
       FIG. 4A  is a block diagram of a media converter  400  in a network with both optical fiber links and coax links (e.g., the network  100 ,  FIG. 1 ) in accordance with some embodiments. The media converter  400  is an example of a media converter  130  ( FIG. 1 ). An optical port  404  in the converter  400  connects to a fiber link  402 , thereby coupling the converter  400  to an OLT  110  ( FIG. 1 ). The optical port  404  provides optical signals received from the fiber link  402  to an optical-to-electrical converter  406  (e.g., an optical PHY  432 ,  FIG. 4B ), which converts the optical signals to electrical signals. Coupled to the optical-to-electrical converter  406  is a packet sniffer and filter  408  that determines whether to forward or discard respective packets. For example, packets addressed to a CNU  140  on the cable plant of the media converter  400  are forwarded, while packets that are not addressed to a CNU  140  on the cable plant of the media converter  400  are discarded. Packets that the sniffer/filter  408  determines are to be forwarded are provided to one or more coax ports  418  coupled to the sniffer/filter  408 . The one or more coax ports  418  transmit the packets onto respective cable links  420 . Cable links  420  couple the media converter  400  to CNUs  140  on the cable plant of the media converter  400 . 
     The sniffer/filter  408  can be implemented in hardware, software, or a combination of hardware and software. In some embodiments, the sniffer/filter  408  is implemented in a packet parser and filter  436  ( FIG. 4B ). In some embodiments, the sniffer/filter  408  includes a processor  410  coupled to a memory  412 . The memory  412  stores a filter template  414  that includes a table or list of identifiers (e.g., LLIDs) of CNUs (e.g., registered CNUs) on the cable plant of the media converter  400 . The processor  410  extracts the destination addresses of respective packets (e.g., as indicated by respective LLIDs) and compares the destination addresses to the CNU identifiers (e.g., LLIDs) in the filter template  414 . If a respective destination address matches one of the CNU identifiers in the filter template  414 , the corresponding packet is forwarded. If there is no match, the corresponding packet is discarded. The processor  410  also updates the filter template  414 . For example, the processor  410  monitors registration messages (e.g., in accordance with  FIG. 3 ) and adds the LLIDs for newly registered CNUs  140  to the filter template  414 . The processor  410  also deletes LLIDs for deregistered CNUs  140  from the filter template  414 . 
     In some embodiments, the memory  412  includes a non-transitory computer-readable medium (e.g., one or more nonvolatile memory elements, such as EPROM, EEPROM, Flash memory, a hard disk drive, and so on) that stores a packet sniffing and filtering software module  416 . The packet sniffing and filtering software module  416  includes instructions that, when executed by the processor  410 , cause the media converter  400  to perform the packet sniffing and filtering described herein. The module  416  also includes instructions that, when executed by the processor  410 , cause the filtering template  414  to be updated (e.g., as described with regard to  FIG. 3  and Table 1). In some embodiments, the module  416  stores instructions that, when executed by one or more processors (e.g., processor  410 ,  FIG. 4A , and/or message processors  438  and  456 ,  FIG. 4B ), cause the media converter  400  to perform the methods  500  and/or  550  ( FIGS. 5A and 5B ). 
     While the memory  412  is shown as being separate from the processor  410 , all or a portion of the memory  412  may be embedded in the processor  410 . For example, all or a portion of the filter template  414  may be stored in a cache in the processor  410 . 
       FIG. 4B  is a schematic block diagram of an example of a media converter  430  shown in more detail than for the media converter  400  ( FIG. 4A ) in accordance with some embodiments. The media converter  430  is an example of a media converter  130  (e.g., media converter  130 - 1  or  130 - 2 ,  FIG. 1 ). In the downstream direction, packets are received at an optical PHY  432  and provided to a decryptor  434  followed by a packet parser and filter  436 . The optical PHY  432  is an example of the optical-electrical converter  406  ( FIG. 4A ) and the packet parser and filter  436  includes the packet sniffer/filter  408  ( FIG. 4A ) and may include (or be coupled to) all or a portion of the memory  412  (e.g., the filter template  414 ,  FIG. 4A ). 
     The filter portion (e.g., packet sniffer/filter  408 ,  FIG. 4A ) of the packet parser and filter  436  discards packets that are not addressed to CNUs  140  that are coupled to the media converter  430 . The output of the packet parser and filter  436  is split into two streams: one for MPCP packets (e.g., messages such as those shown in  FIG. 3 ) and one for data packets. The MPCP packets are processed by a message processing engine  438 , which monitors downstream messages and in some embodiments maps allocated time slots to coax frequency resources, and are passed into a control queue  440 . The message processing engine  438  is also referred to as a message processor. The data packets are passed into a data queue  442 . A strict priority (SP) scheduler  444  schedules the packets in the control and data queues  440  and  442 , with MPCP packets in the control queue  440  being given priority over data packets in the data queue  442 . A time-stamping element  446  updates timestamps carried in MPCP packets (e.g., replaces the original timestamps with local timestamps) and passes packets into an encryptor  448 . The output of the encryptor  418  is fed into a coax PHY  450 , which transmits the packets downstream. The coax PHY  450  is coupled to or implemented in a coax ports  418  ( FIG. 4A ). 
     In the upstream direction, packets are received at the coax PHY  450  and provided to a decryptor  452 , followed by a packet parser  454 , a message processor  456 , and an upstream queue  458 . The message processor  456  monitors upstream messages (e.g., the upstream messages of  FIG. 3 ) and in some embodiments communicates results of this monitoring to the message processor  438  and/or packet parser and filter  436 . A time-stamping element  460  updates the timestamps carried in MPCP packets (e.g., replaces the original timestamps with local timestamps) and passes packets to an encryptor  462 . The output of the encryptor  462  is fed into the optical PHY  432 , which transmits the packets upstream to the OLT  110  ( FIG. 1 ). 
       FIG. 5A  is a flowchart illustrating a method  500  of filtering packets in a media converter in accordance with some embodiments. The method  500  is performed ( 502 ) by a media converter (e.g., media converter  130 - 1  or  130 - 2 ,  FIG. 1 ) that is coupled to an optical link terminal (e.g., OLT  110 ,  FIG. 1 ) and to a plurality of coax network units (e.g., CNUs  140 - 1  and  140 - 2  or CNUs  140 - 3  through  140 - 5 ,  FIG. 1 ) on a cable plant (e.g., cable plant  150 - 1  or  150 - 2 ,  FIG. 1 ). 
     Packets are received ( 504 ) from the optical link terminal via an optical link. The packets include packets addressed to coax network units on the cable plant and packets addressed to network units outside of the cable plant. The packets are received at a first data rate. 
     For a respective packet received from the optical link terminal, an identifier (e.g., an LLID) of the packet&#39;s destination coax network unit is extracted ( 506 ) and compared ( 508 ) to a filter template (e.g., filter template  414 ,  FIG. 4A ) storing identifiers of coax network units on the cable plant. It is determined ( 510 ) if the extracted identifier matches an identifier in the filter template. 
     If the extracted identifier matches an identifier in the filter template ( 510 —Yes), the packet is forwarded ( 514 ) to the coax network units on the cable plant via one or more coax links. The packet is forwarded to each coax network unit on the cable plant. In some embodiments, the packets are forwarded at a second data rate that is distinct from (e.g., less than) the first data rate. 
     If the extracted identifier does not match an identifier in the filter template ( 510 —No), the packet is discarded ( 512 ) and thus is not forwarded to the coax network units on the cable plant. 
     In some embodiments, the operations  506 - 514  are performed in the packet sniffer/filter  408  ( FIG. 4A ) of the packet parser and filter  436  ( FIG. 4B ). 
       FIG. 5B  is a flowchart illustrating a method  550  of creating and updating a filtering template in accordance with some embodiments. The method  550  is performed ( 552 ) by a media converter (e.g., media converter  130 - 1  or  130 - 2 ,  FIG. 1 ) that is coupled to an optical link terminal (e.g., OLT  110 ,  FIG. 1 ) and to a plurality of coax network units (e.g., CNUs  140 - 1  and  140 - 2  or CNUs  140 - 3  through  140 - 5 ,  FIG. 1 ) on a cable plant (e.g., cable plant  150 - 1  or  150 - 2 ,  FIG. 1 ) and may be performed in conjunction with the method  500  ( FIG. 5A ). 
     The media converter monitors ( 554 ) messages (e.g., MPCP messages) between the optical link terminal and coax network units on the cable plant. This monitoring is performed, for example, by the message processing elements  438  and  456  and/or the packet parser and filter  436  ( FIG. 4B ). It is determined ( 556 ) if the messages register a coax network unit on the cable plant with the optical link terminal. For example, it is determined whether the messages correspond to the messages for the registration process shown in  FIG. 3 . If so ( 556 —Yes), an identifier (e.g., an LLID specified in the REGISTER message of step  3   a ,  FIG. 3 ) of the coax network unit is stored ( 558 ) in a filter template (e.g., filter template  414 ,  FIG. 4A ). Once the identifier has been added to the filter template, packets addressed to the coax network unit will be forwarded (e.g., in accordance with operation  514 ,  FIG. 5A ) instead of being discarded. 
     It is determined ( 560 ) if the messages de-register a coax network unit on the cable plant from the optical link terminal. If so ( 560 —Yes), an identifier of the coax network unit is deleted ( 562 ) from the filter template (e.g., filter template  414 ,  FIG. 4A ). Once the identifier has been deleted from the filter template, packets addressed to the coax network unit will be discarded (e.g., in accordance with operation  512 ,  FIG. 5A ) instead of being forwarded. 
     In some embodiments, an identifier of an unregistered coax network unit also may be added to the filter template if the media converter receives a data packet from the coax network unit. 
     While the methods  500  and  550  include a number of operations that appear to occur in a specific order, it should be apparent that the methods  500  and/or  550  can include more or fewer operations, which can be executed serially or in parallel. An order of two or more operations may be changed and two or more operations may be combined into a single operation. In some embodiments, the operations of both methods  500  and  550  are performed on an ongoing basis. 
     In the foregoing specification, the present embodiments have been described with reference to specific exemplary embodiments thereof. It will, however, be evident that various modifications and changes may be made thereto without departing from the broader spirit and scope of the disclosure as set forth in the appended claims. The specification and drawings are, accordingly, to be regarded in an illustrative sense rather than a restrictive sense.