Abstract:
A system and method provide enhanced link loss forwarding in an Ethernet system to determine link degradation and to selectively block and re-establish transport between a near end device and far end device based on a SONET connection between end devices and link status detection using local packets. When an excessive number of errors are detected in an Ethernet port, a device enters a Links Off mode from a Transport mode where Ethernet ports are turned off at both ends of a circuit associated with the errors. A Block Transport mode is then entered where local packets (e.g., OAM packets) are monitored to evaluate link quality (e.g., SONET bit error rate). Transport mode is re-established when acceptable link quality is achieved for a selected period of time.

Description:
[0001]    This application is a continuation of U.S. patent application Ser. No. 12/551,344, filed Aug. 31, 2009, the entire contents of which are incorporated by reference herein. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present application relates generally to network communication diagnostics and, more particularly, Link Loss Forwarding (LLF) in an Ethernet network. 
       BACKGROUND OF THE INVENTION 
       [0003]    Traditional digital networks have been developed to transfer information such as data among digital computer systems and other digital devices. A variety of types of networks, such as Ethernet, have been developed and implemented using diverse information transfer methodologies. These traditional networks utilize communication ports connected to one another via links in a communication network to send and receive data. However, when one of these links degrades (e.g. the near end transmitting path), the corresponding far end port (e.g. far end receiving port) may continue to receive some data via the corresponding media (e.g., fiber). Accordingly, devices connected to the degraded link operate under a false perception that the link is operating properly. By the time the error is diagnosed, however, substantial data loss may occur. 
         [0004]    Link Loss Forwarding (LLF) exists (e.g. is used in existing Ethernet media converters) that disables a far end signal when a loss of input signal at an end of a circuit occurs. In other words, loss of a valid signal or loss of link is forwarded to the far end. For example, intermediate transport failure such as SONET can cause the link to be dropped. LLF is used to signal a line failure in systems that may not be able to respond to a dropped communication path quickly. After disabling the far end, the system may switch to an alternative path, or a network administrator may then be informed of the disconnection immediately and react as promptly as possible to the situation, in an attempt to minimize losses. 
         [0005]    This LLF technique, however fails to provide adequate tools for determining link degradation or resolution measures for suspected link degradation. For example, if traffic is being carried over aggregated transport (e.g., multiple lines) using Link Access Control Protocol (LACP), one low quality line can result in sufficient retransmission requests to overwhelm the remaining good transport. In other words, the system would be better served if the poor quality line were shut down. 
         [0006]    Current systems lack the ability to determine link degradation that may lead to link failure. Thus, a need exists for enhanced LLF that automatically and proactively determines link degradation. Further, a need exists for enhanced LLF that provides options following a determination of link degradation such as instituting at least a temporary block transport mode and restoring links when a link that indicated excessive errors is working adequately (e.g., at a selected minimal error rate) for a selected period of time. 
       SUMMARY OF THE INVENTION 
       [0007]    Exemplary embodiments of the present invention address at least the above problems and/or disadvantages, and provide at least the advantages described below. 
         [0008]    An illustrative method according to exemplary embodiments of the present invention provides for communicating data in a communication transport system having a communication network, communicating at least one of data packets and local packets between the near end device and the far end device via said communication network; determining a poor quality of said communication network; selecting a links off mode of both the near end device and the far end device to disconnect the near and far end devices from the communication network in response to determining said poor quality of said communication network; operating the near and far end devices in said links off mode for a selected time period; selecting a block transport mode of the near end device and the far end device in response to said selected time period expiring to communicate local packets while inhibiting communication of data packets; determining at least one of a link status, a signal level, and a lack of local packet corruption while operating in said block transport mode; and determining the communication network has been successfully restored based on the at least one of the link status, the signal level, and the lack of local packet corruption. 
         [0009]    Another aspect of the exemplary embodiments of the present invention provides for determining whether the number of successfully communicated local packets is communicated over a selected diagnosis time period. 
         [0010]    Still another aspect of the exemplary embodiment of the present invention provides for selecting a transport mode of the near end device and the far end device for communicating the data packets and the local packets between the near end device and the far end device in response to the number of successfully communicated local packets being communicated within the selected diagnosis time period. 
         [0011]    Yet another aspect of the exemplary embodiment of the present invention provides for detecting at least one corrupted packet communicated between the near end device and the far end device and detecting a transmission signal level of the communication network. 
         [0012]    Another aspect of the exemplary embodiment of the present invention provides for monitoring a timer to determine the selected diagnosis period. 
         [0013]    Yet another aspect of the exemplary embodiment of the present invention provides the selected diagnosis time period being 10 seconds. 
         [0014]    Still another aspect of the exemplary embodiments of the present invention provides for resetting the timer when detecting the at least one corrupt packet within the selected diagnosis time period. 
         [0015]    Finally, another aspect of the exemplary embodiments of the present invention provides for the poor quality of communication network being based on at least one of a selected percentage of corrupted packets received by at least one of the near end device and the far end device, and a selected transmission signal level of the communication network. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]    The above and other exemplary features, aspects and advantages of the present invention will become more apparent from the following detailed description of certain exemplary embodiments thereof when taken in conjunction with the accompanying drawings in which: 
           [0017]      FIG. 1  is a schematic block diagram of a communication transport system including Enhanced Link Loss Forwarding according to exemplary embodiments of the present invention; 
           [0018]      FIG. 2  is a flow diagram of an illustrative method for communicating data in a communication transport system according to exemplary embodiments of the present invention; and 
           [0019]      FIG. 3  is a flow diagram of an illustrative method for communicating data in a communication transport system according to exemplary embodiments of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
       [0020]    Referring to the Figures, wherein like numerals indicate corresponding parts throughout the several views,  FIG. 1  generally shows a communication transport system  10  including a near end device  11  and a far end device  11 ′, each being capable of transporting data bi-directionally and having a synchronous communication network  24  (e.g., OC-48 transport) therebetween. In the illustrative embodiment of the present invention depicted in  FIG. 1 , the far end device  11 ′ is depicted as comprising similar components as the above-described near end device  11 . However, the near end and far end devices  11 ,  11 ′ need not be identical. In addition, although the description of the exemplary embodiment shown in  FIG. 1  may describe data flow being transported from the near end device  11  to the far end device  11 ′, it can be appreciated that data flow may also be transported in an opposite direction i.e., from the far end device  11 ′ to the near end device  11 . 
         [0021]    Each of the near end device  11  and the far end device  11 ′ are connected to a communication network  12  for transporting data bi-directionally. The near end device  11  includes a first near end communication port  14  and a second near end communication port  16 . The first near end communication port  14  electrically and/or optically communicates with the communication network  12  to receive at least one near end data packet  18  and near end local packet  20  and transmits the near end data packet  18  and near end local packet  20  to a first far end communication port  22  via a data transport network  24 . Furthermore, each communication port  14 ,  16 ,  22  and  26  is selectively operable in a first near end enable mode for transmitting and receiving data and a first near end disable mode for being disconnected from the communication network  12 . 
         [0022]    The second near end communication port  16  electrically and/or optically communicates with the communication network  12  to receive at least one near end data packet  18 ′ and near end local packet  20 ′ and transmits the near end data packet  18 ′ and near end local packet  20 ′ to a second far end communication port  26  via the data transport network  24 . As mentioned above, the second near end communication port  16  is selectively operable in a second near end enable mode for transmitting and receiving data and a second near end disable mode for being disconnected from the communication network  12 . Further, although  FIG. 1  shows two communication ports included with each near end device  11  and far end device  11 ′, it can be appreciated that less or additional communication ports  14 ,  16 ,  22 ,  26  may be included. 
         [0023]    The communication transport system  10  further includes a first near end physical interface (PHY) module  28  and a second near end physical interface (PHY) module  30 . The first near end physical interface module  28  has a first PHY input and a first PHY output. The first PHY input is in electrical communication with the first near end communication port  14  for selecting at least one of the enable mode and the disable mode. Similarly, the second near end PHY module  30  has a second PHY input and a second PHY output. The second PHY output is in electrical communication with the second near end communication port  16  for selecting at least one of the enable mode and the disable mode. 
         [0024]    A first link loss forward (LLF) module  32  is in electrical communication with the first near end PHY module  28  for determining whether the first near end communication port  14  is disconnected from the communication network  12 . If the first LLF module  32  detects that the first near end communication port  14  is disconnected from the communication network  12 , the first LLF module  32  generates a first LLF error signal  34 . The communication transport system  10  may include a similar second LLF module  36  in electrical communication with the second near end PHY module  30  for determining whether the second near end communication port  16  is disconnected from the communication network  12 . Upon determining a disconnection, the second LLF module  36  generates a second LLF error signal  38 . 
         [0025]    The communication transport system  10  further includes a multiplexer  40  and demultiplexer  42  for multiplexing and demultiplexing data, respectively. The multiplexer  40  is in electrical communication with the first near end PHY module  28  and the second near end PHY module  30  and the data transport network  24 . The multiplexer  40  delivers data packets  18  from the first near end PHY module  28  to a first far end PHY module  22  and delivers data packets  18  from the second near end PHY module  30  to a second far end PHY module  26 . Moreover, the multiplexer  40  is selectively operable in a mux transport mode for delivering both of the data packets  18  and the local packets  20  and a mux block transport mode for inhibiting delivery of the data packets  18  while receiving and/or communicating the local packets  20 . 
         [0026]    The demultiplexer  42  is in electrical communication with the first near end PHY module  28  and the second near end PHY module  30  for delivering the data packets  18  and the local packets  20  to the first near end communication port  14  via the first near end PHY module  28 . In addition, the demultiplexer  42  delivers the data packets  18  and the local packets  20  to the second near end communication port  16  via the second near end PHY module  30 . Similar to the multiplexer  40 , the demultiplexer  42  is selectively operable in a demux transport mode for receiving both of the data packets  18  and the local packets  20  and a demux block transport mode for inhibiting reception of the data packets  18  while receiving and/or communicating the local packets  20 . Further, the demultiplexer  42  may be in electrical communication with the data transport network  24  for receiving at least one of a far end block transport signal  44 , a far end remote disable signal  46  and a far end link loss forward (LLF) signal  48 . The far end LLF signal, in particular is delivered by demultiplexer  42  to the first near end PHY module  28  for selecting the first near end disable mode and to the second near end PHY module  30  for selecting the second near end disable mode. 
         [0027]    A receiver  50  may further be included in the near end device  11 . The receiver  50  is electrical communication with the demultiplexer  42  and the data transport network  24  for receiving at least one of the far end LLF signal  48  and the far end block transport signal  44  and for detecting a loss of frame (LOF) on the data transport network  24  and for generating a loss of frame (LOF) signal  52  in response to detecting a missing signal input at the receiver  50 . The first near end PHY module  28  and the second near end PHY module  30  may be in electrical communication with the receiver  50  for selecting the first near disable mode and the second near end disable mode, respectively, in response to receiving the LOF signal  52 . 
         [0028]    The near end device  11  features a first enhanced link loss forward module (ELLF)  54  having a first ELLF input in electrical communication with the first PHY output for determining an error on the communication network  12 . The error on the communication network  12  is based on at least one of a percentage of corrupted packets received by at least one of the first near end communication port  14  and the second near end communication port  16  and a transmission signal level of the communication network  12 . 
         [0029]    The first ELLF module  54  has a first ELLF output in electrical communication with the first PHY input of the first near end PHY  28  for generating a first links off signal  56 . The first links off signal  56  initiates the first near end disable mode of the first near end communication port  14 . Further, the first links off signal  56  is multiplexed by the multiplexer  40  and is sent over the data transport network  24  to disable the first far end communication port  22 . In response to receiving the first links off signal  56 , both the first near end communication port  14  and the first far end communication port  22  are disconnected from the communication network  12  for a selected time period in response to determining the error on the communication network  12 . 
         [0030]    The first ELLF module  54  is in further electrical communication with the multiplexer  40  and the demultiplexer  42  for generating a first block transport signal  55  to select the mux block transport mode and the demux block transport mode in response to the selected time period expiring. In addition, the first ELLF module  54  may be in electrical communication with the first LLF module  32  and the multiplexer  40  for detecting a first near end link disconnection between the first near end communication port  14  and the first near end PHY module  28 . In response to detecting the first near end link disconnection, the first ELLF module  54  generates the first links off signal  56  to disable the first near end communication port  14  and the first far end communication port  22 . The error on the communication network  12  is based on at least one of a percentage of corrupted packets  18 ,  20  received by at least one of the first near end communication port  14  and the second near end communication port  16  and a transmission signal level of the communication network  12 . 
         [0031]    A similar second ELLF module  58  is in electrical communication with the second near end PHY module  30  for determining an error on the communication network  12 . In response to determining an error, the second ELLF module  58  generates a second links off signal  60  that disables the second near end communication port  16  and the second far end communication port  26  for a selected time period. As noted above, the error on the communication network  12  is based on at least one of a percentage of corrupted packets  18 ,  20  received by at least one of the first near end communication port  14  and the second near end communication port  16  and a transmission signal level of the communication network  12 . 
         [0032]    As with the first ELLF module  54 , the second ELLF module  58  is in electrical communication with the multiplexer  40  and the demultiplexer  42  for generating a second block transport signal  62 . The second block transport signal  62  selects the mux block transport mode and the demux block transport mode in response to the selected time period expiring. The second ELLF module  58  may be in electrical communication with the second LLF module  36  and the multiplexer  40  for detecting a second near end link disconnection between the second near end communication port  16  and the second near end PHY module  30  and for generating the second links off signal  60  to disable the second near end communication port  16  and the second far end communication port  26  in response to detecting the second near end link disconnection. 
         [0033]    In the illustrative embodiment of the present invention depicted in  FIG. 1 , the far end device  11 ′ is depicted as comprising similar components as the above-described near end device  11 . As stated previously, the near end and far end devices  11 ,  11 ′ need not be identical. 
         [0034]      FIG. 2  is a flow diagram of a method for communicating data using devices in a communication transport system  10  having a communication network  12  connected to a near end device  11  and a far end device  11 ′ according to an exemplary embodiment of present invention. The method starts at step  200 . The near end device  11  and the far end device  11 ′ initially operate in a transport mode for communicating data packets and local packets are communicated between one another end to end via a transport network  24  in step  210 . A quality of the received data is determined in step  220 . If the received data is determined to be corrupt, the method proceeds to step  230 . Otherwise, the method returns to step  200 . In step  230 , both a near end device  11  and a far end device  11 ′ are disabled and are disconnected from the communication network  12  for a selected period of time. In step  240 , the near end ports  14  and/or  16  and the far end ports  22  and/or  26  are reactivated, but packets (e.g., customer packets) are not passed end to end. For example, only local packets are accepted by the ports. The method determines whether the ports  14 ,  16 ,  22 ,  26  included with the communication network  12  are of good quality in step  250 , based on the local packets which can be maintenance packets, for example. It can be appreciated that other types of packets may be received or accepted at the ports in order to determine the quality of the ports  14 ,  16 ,  22 ,  26 . If the received packets remain corrupted or continue to indicate poor link quality, the method returns to step  240 . Otherwise, the near end device  11  and far end device  11 ′ communicate both data packets and local packets and the method returns to step  210  such that the method runs continuously. 
         [0035]      FIG. 3  is an illustrative system and method for providing enhanced LLF in accordance with an exemplary embodiment of the present invention using, by way of an example, the communication transport system  10  in  FIG. 1  comprising a communication network  12  connected a near end device  11  and a far end device  11 ′. The method starts at step  300 . A transport mode is selected in step  310  for initializing a transport mode of a near end device  11  and a far end device  11 ′. In step  320 , the near end device  11  and the far end device  11 ′ communicate data packets and local packets between one another via a transport network  24  in step  310 . In step  330 , the method determines whether data packets are corrupted. For exemplary purposes, the quality of the communication network is based on a percentage of corrupted packets; however, the quality of the communication network  12  may be determined based on detecting at least one corrupted packet received by at least one of the near end device  11  and the far end device  11 ′, a transmission signal level of said communication network  12 , or an attenuated signal level at the first PHY input and/or second PHY input, among other methods. 
         [0036]    If a percentage of corrupted data packets does not exceed a selected threshold value (hereinafter X%), the method returns to step  320 . When a percentage of corrupted data packets exceeds X%, a links off mode of both the near end device  11  and the far end device  11 ′ is selected in step  340 . In response to selecting the links off mode, the Ethernet ports of both the near end device  11  and the far end device  11 ′ are disabled and are disconnected from the communication network  12  in step  350 . Each port will remain disabled for duration T 1 . This time ensures that other devices connected to the communication network  12  will recognize that the port is disabled. When the selected period of time T 1  expires in step  360 , the near and far end devices  11 ,  11 ′ initiate the block transport mode and timer T 2  is initiated in step  370 . In response to initiating the block transport mode, the near and far end Ethernet ports  14  and  22  and/or  16  and  26  are enabled in step  380 ; however, the near and far end devices  11 ,  11 ′ are only partially operational. Specifically, local packets intended for local use are accepted, but data packets such as customer packets are not carried across the transport network  24 . The local packets may include, but are not limited to Operations, Administration and Local (OAM) packets, maintenance packets, and control information, such as Link Access Control Protocol (LACP). 
         [0037]    With reference to  400 ,  420  and  430 , if an error is detected at any of the communication ports  14 ,  16 ,  22 ,  26  during the time T 2 , the timer is reset. Preferably only if there are no packet errors (e.g., or minimal number of packet errors accepted as lack of packet corruption) and minimal or no link status errors during the contiguous time T 2  will the device exit  430  back to  310  where normal transport is resumed; otherwise, the link remains disabled until corrective action is taken (e.g., a cable is repaired or a fiber connection is cleaned). For example, an error free second is determined when, during each second of the diagnosis time period, at least one error free packet is received. Once a selected number (e.g., ten) of error free seconds are detected, the transport mode can be reinstated, resulting in the near and far end ports communicating normally (e.g., transporting customer packets). The enhanced LLF described herein in accordance with exemplary embodiments of the present invention is advantageous because it allows degraded links to be identified or located and proactive measures to be taken (e.g., restorative measures such as repairing a degraded cable or cleaning a degraded fiber connection) before the degradation becomes a link failure with associated link losses. 
         [0038]    The enhanced LLF described herein in accordance with exemplary embodiments of the present invention is also advantageous because it can be compatible with older equipment. For example, the demux block transport mode can be omitted if the near end and far end devices  11  and  11 ′ are both updated to have the enhanced LLF described herein at the same time. By adding the inhibiting of the demux operation, however, the enhanced LLF described herein in accordance with exemplary embodiments of the present invention can be implemented by upgrading only one end (e.g., only one of the near end device or far end device). In such a compatibility mode, the links off state or mode generates the same message as LLF, for example. 
         [0039]    Exemplary embodiments of the present invention can also comprise computer readable codes on a computer readable medium. The computer readable medium can comprise any data storage device that can store data that can be read by a computer system. Examples of a computer readable medium include magnetic storage media (such as, ROM, floppy disks, hard disks, among others), optical recording media (such as, CD-ROMs, or DVDs), and storage mechanisms. It is also envisioned that remote storage or access via the Internet can be utilized as an equivalent to a computer readable medium. The computer readable medium can also be distributed over network coupled computer systems so that the computer readable code is stored and executed in a distributed fashion. Also, functional programs, codes, and code segments for accomplishing exemplary embodiments of the present invention can be construed by programmers of ordinary skill in the art to which the present invention pertains. 
         [0040]    While various embodiments and features of the invention have been disclosed herein, it will be understood by those skilled in the art that various changes and modifications can be made without departing from the scope and spirit of invention as defined in the appended claims.