Patent Publication Number: US-2015063127-A1

Title: Transmission apparatus and transmission method

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2013-177044 filed on Aug. 28, 2013, the entire contents of which are incorporated herein by reference. 
     FIELD 
     Exemplary embodiments of the present disclosure are related to a transmission apparatus and a transmission method. 
     BACKGROUND 
     An IP (Internet Protocol) network such as, for example, Ethernet (registered trademark) accommodates a plurality of transmission apparatuses such as, for example, L 2  switch, and incorporates a maintenance function such as checking of connectability between the transmission apparatuses or specifying of a fault location in the network. The Ethernet OAM (Operation Administration and Management) is known as a technology equipped with the maintenance function. The Ethernet OAM is standardized in, for example, the IEEE (802.1 ag) or ITU-T (Y1731). 
     The Ethernet OAM primarily intends to confirm the connectability between, for example, the transmission apparatuses and incorporates a CC (Continuity Check) function that regularly transmits and receives a CCM (Continuity Check Messages) frame to rapidly detect a fault. For example, an MEP (Maintenance End Point) which indicates a terminal end point of the CCM frame is set in a transmission apparatus and an opposite transmission apparatus. The transmission apparatus regularly transmits the CCM frame to the opposite transmission apparatus. Also, based on the reception result of the CCM frames, the opposite transmission apparatus detects a fault such as, for example, LOC (Loss of Connectivity) which is a fault between the transmission apparatus and the opposite transmission apparatus. 
     The transmission apparatus transmits, for example, a single CCM frame to the opposite transmission apparatus for every one interval. Further, a user changes the transmission interval of the CCM frame appropriately according to the network environment, and sets the changed transmission interval for each of the transmission apparatuses. Also, the opposite transmission apparatus receives a single CCM frame for every one interval.  FIG. 12  is an explanatory view illustrating the state of the CCM frame. 
     For example, as illustrated in (A) of  FIG. 12 , when a CCM frame is received from a transmission apparatus, an opposite transmission apparatus determines that the communication state is in a normal condition. Further, as illustrated in (B) of  FIG. 12 , even when the CCM frame is not received from the transmission apparatus during transmission, the opposite transmission apparatus determines that the state is in the normal condition when a next CCM frame is received within  3 . 5  intervals (three and half intervals). Further, as illustrated in (C) of  FIG. 12 , when the next CCM frame is not received within 3.5 intervals, the opposite transmission apparatus determines that the state is in the LOC at the time when 3.5 intervals elapsed. As a result, the opposite transmission apparatus may recognize the occurrence of a fault between the opposite transmission apparatus and the transmission apparatuses based on the determination result regarding the LOC. 
     See, for example, Japanese Patent Application Laid-Open No. 2011-205301, Japanese Patent Application Laid-Open No. 2009-130474 and Japanese Patent Application Laid-Open No. 2007-251541. 
     SUMMARY 
     Accordingly, it is an object in one aspect of the invention to provide a transmission apparatus including: a transmission unit configured to transmit a control data to an opposite transmission apparatus at a transmission interval; a first determination unit configured to determine a communication quality of a network connected with the opposite transmission apparatus; and an adjustment unit configured to adjust the transmission interval, at which the control data is transmitted, to be longer than a reference transmission interval when the communication quality is equal to or greater than a predetermined value. 
     The object and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the claims. 
     It is to be understood that both the foregoing general descriptions and the following detailed descriptions are exemplary and explanatory and are not restrictive of the invention. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is an explanatory view illustrating an example of a transmission system according to First Embodiment; 
         FIG. 2  is a block diagram illustrating an example of a transmission apparatus; 
         FIG. 3  is an explanatory view illustrating an example of a functional block diagram of a CPU of the transmission apparatus; 
         FIG. 4  is an explanatory view illustrating an example of a transmission interval of a CCM frame of the transmission system; 
         FIG. 5  is a flowchart illustrating an example of processing operations, which is related to a state notification process, of the CPU within the transmission apparatus; 
         FIG. 6  is a flowchart illustrating an example of processing operations of the CPU in the transmission apparatus, which is related to a first transmission interval adjustment process; 
         FIG. 7  is an explanatory view illustrating an occupation ratio of each CCM frame in each user data band; 
         FIG. 8  is an explanatory view illustrating an example of the transmission system according to Second Embodiment; 
         FIG. 9  is an explanatory view illustrating another example of the functional block diagram of a CPU of the transmission apparatus; 
         FIG. 10  is an explanatory view illustrating an example of a specific pattern; 
         FIG. 11  is a flowchart illustrating an example of processing operations of the CPU in the transmission apparatus, which is related to a second transmission interval adjustment process; and 
         FIG. 12  is an explanatory view illustrating a state of CCM frame. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     The transmission interval of the CCM frame is always constant according to user setting irrespective of a line or communication state and thus, an amount of control data, such as a CCM frame, increases, for example, when the transmission interval is set to be shorter. As a result, the user data band used by the user is consumed as the amount of control data increases. 
     Further, for example, the user data band lent to the user is charged except for the control data, and thus, it is important for a communication service provider to reduce the control data to secure the user data band. 
     Hereinafter, referring to accompanying drawings, descriptions will be made in detail on an embodiment of a transmission apparatus and a transmission method that may suppress consumption of the user data band by the control data. Further, disclosed technologies are not limited to the present embodiment. Further, respective embodiments indicated below may be combined appropriately as long as they do not cause any contradiction. 
     First Embodiment  
       FIG. 1  is a block diagram illustrating an example of a transmission system according to First Embodiment. A transmission system  1  illustrated in  FIG. 1  includes a transmission apparatus  2 , an opposite transmission apparatus  100  and a network  3 . An MEP which indicates a terminal end point of a CCM frame is set both in the transmission apparatus  2  and the opposite transmission apparatus  100 . A MEP-A and a MEP-B are set in the transmission apparatus  2  and the opposite transmission apparatus  100 , respectively. Further, for the convenience of explanation, it is assumed that the transmission apparatus  2  includes an adjustment function which automatically adjusts the transmission interval of the CCM frame while the opposite transmission apparatus  100  does not include the adjustment function. 
     The transmission apparatus  2  transmits a user data to the opposite transmission apparatus  100  via the network  3 , and transmits a CCM frame (CCM-A) to the opposite transmission apparatus  100  at a set transmission interval via the network  3 . Also, the opposite transmission apparatus  100  receives the user data from the transmission apparatus  2  via the network  3 , and receives the CCM frame (CCM-A) from the transmission apparatus  2  via the network  3 . 
     Further, the opposite transmission apparatus  100  transmits a user data to the transmission apparatus  2  via the network  3 , and transmits a CCM frame (CCM-B) to the transmission apparatus  2  at a set transmission interval via the network  3 . Also, the transmission apparatus  2  receives the user data from the opposite transmission apparatus  100  via the network  3 , and receives the CCM frame (CCM-B) from the opposite transmission apparatus  100  via the network  3 . 
       FIG. 2  is a block diagram illustrating an example of the transmission apparatus. The transmission apparatus  2  illustrated in  FIG. 2  includes a line card  5 . The line card  5  includes an input interface  11 , an output interface  12 , a ROM (Read Only Memory)  13 , a RAM (Random Access Memory)  14 , a L 2  switch  15  and a CPU (Central Processing Unit)  16 . 
     The input interface  11  is connected to the network  3  through a cable  4  to receive, for example, the CCM frame from other transmission apparatus within the transmission system  1 . The output interface  12  is connected to the network  3  through the cable  4  to transmit, for example, the CCM frame to other transmission apparatus within the transmission system  1 . The L 2  switch  15  is connected with the input interface  11  and the output interface  12  to perform a connection process between channels performed by each of the input interface  11  and the output interface  12 , and at the same time, performs various Layer- 2  level processes. An alarm information table  14 A storing various information such as alarm information is stored in the RAM  14 . Further, the alarm information indicates a fault related to, for example, RDI (Remote Defect Indication) information added to the CCM frame. Further, various programs such as a transmission program is stored in the ROM  13 . 
     The transmission apparatus  2  may appropriately change and set a frame rate, a transmission interval or an interval of the CCM frame depending on, for example, a line state, according to a setting operation from a maintenance console  17  by a maintenance operator. 
     The CPU 16  controls the entire transmission apparatus  2  and reads out the transmission program stored in the ROM  13  to execute a CCM processing function. The CPU  16  includes a reception processing unit  30  and a transmission processing unit  40  as the CCM processing functionalities. The reception processing unit  30  receives the CCM frame from a opposite MEP, for example, a MEP of the opposite transmission apparatus  100 . The transmission processing unit  40  transmits the CCM frame to the opposite MEP. 
       FIG. 3  is an explanatory view illustrating an example of a functional block diagram of the CPU  16  of the transmission apparatus. The reception processing unit  30  illustrated in  FIG. 3  includes a line quality checking unit  31 , a reception unit  32 , an alarm monitoring unit  33 , an alarm unit  34  and a state monitoring unit  35 . 
     The line quality checking unit  31  monitors the degradation state of the line quality in the network  3  based on a frame reception rate or packet loss rate using the FEC (Forward Error Correction). Further, the line quality checking unit  31  determines whether a state of the line abnormality, which will be determined as a LOC before long, exists based on the monitoring result. Further, the line abnormality refers to the line state which is not determined as the LOC at current time but has a likelihood of being determined as the LOC before long. When the line abnormality exists, the line quality checking unit  31  notifies the state monitoring unit  35  of the line abnormality. 
     When the line abnormality does not exist, the reception unit  32  receives the CCM frame from the MEP of the opposite apparatus. When the line abnormality exists, the reception unit  32  discards the CCM frame received from the MEP of the opposite apparatus. Further, the alarm monitoring unit  33  determines whether the LOC exists or not based on the state of the CCM frame received from the MEP of the opposite apparatus. When one or more CCM frame may not be received from the MEP of the opposite apparatus within a predetermined interval, for example, 3.5 intervals (three and half intervals), the alarm monitoring unit  33  determines that the LOC exists. Further, when one or more CCM frame may be received from the MEP of the opposite apparatus within 3.5 intervals, the alarm monitoring unit  33  determines that the LOC does not exist, that is, a normal state. When it is determined that the LOC exists, the alarm monitoring unit  33  stores an alarm information including a determination result of the LOC in the alarm information table  14 A. 
     When it is determined that the LOC exists, the alarm unit  34  sends the alarm information including the determination result of the LOC. The state monitoring unit  35  monitors the state of the network  3  based on the alarm information stored in the alarm information table  14 A. The state monitoring unit  35  notifies the transmission processing unit  40  of the state of the network  3 . Further, when the line abnormality from the line quality checking unit  31  is detected, the state monitoring unit  35  notifies the transmission processing unit  40  of the state of the network  3 . 
     The transmission processing unit  40  includes a generation unit  41 , an adjustment unit  42  and a transmission unit  43 . The generation unit  41  creates a CCM frame. The adjustment unit  42  adjusts the transmission interval of the CCM frame based on the state of the network  3  which corresponds to the monitoring result of the state monitoring unit  35 . Further, in the adjustment unit  42 , the alarm monitoring unit  33  simply needs to transmit at least one CCM frame within  3 . 5  intervals and the transmission interval may be adjusted within a predetermined range.  FIG. 4  is an explanatory view illustrating an example of a transmission interval of a CCM frame within the transmission system  1 . The transmission interval of the CCM frame illustrated in (A) of  FIG. 4  is a reference transmission interval of the transmission apparatus  2  at which one CCM frame is transmitted for every one interval of, for example, CCM-A→CCM-A→ . . . , and is defined as a transmission interval L. The transmission interval of the CCM frame illustrated in (B) of  FIG. 4  is a transmission interval of the transmission apparatus  2  at which one CCM frame is transmitted for every two intervals of, for example, CCM-A→None→CCM-A→None→ . . . , and is defined as a first transmission interval L 1 . The transmission interval of the CCM frame illustrated in (C) of  FIG. 4  is a transmission interval of the transmission apparatus  2  at which one CCM frame is transmitted for every three intervals of, for example, CCM-A→None→None→CCM-A→None→None→CCM-A→ . . . , and is defined as a second transmission interval L 2 . The transmission interval of the CCM frame illustrated in (D) of  FIG. 4  is a reference transmission interval of the opposite transmission apparatus  100  at which one CCM frame is transmitted for every one interval of, for example, CCM-B→CCM-B→ . . . , and is defined as a transmission interval L. 
     The transmission apparatus  2  automatically sets a transmission interval to, for example, the reference transmission interval L, the first transmission interval L 1  or the second transmission interval L 2 , according to the state of the network  3 , for example, according to a communication quality level. In contrast, the opposite transmission apparatus  100  does not include the adjustment function and thus, the transmission interval, for example, the reference transmission interval L is set by the manipulation of the user irrespective of the communication quality of the network  3 . 
     When a communication quality level X of the network  3  is less than the first threshold value X 1  (X&lt;X 1 ), the adjustment unit  42  sets the reference transmission interval L as the transmission interval of the CCM frame. Further, the first threshold value X 1  is equivalent to the communication quality level which indicates, for example, a case where the communication quality of the network  3  is high quality, an error rate is low and further, a non-arrived CCM frame does not exist. Further, when the line abnormality is detected by the line quality checking unit  31 , the adjustment unit  42  sets the reference transmission interval L as the transmission interval of the CCM frame. When the communication quality level X of the network  3  is equal to or greater than the first threshold value X 1  and less than the second threshold value X 2  (X 1 ≦X&lt;X 2 ), the adjustment unit  42  sets the first transmission interval L 1  as the transmission interval of the CCM frame. Further, the second threshold value X 2  is equivalent to a communication quality level having a higher quality than the communication quality level of the first threshold value X 1 . Further, when the communication quality level X of the network  3  is equal to or greater than the second threshold value X 2  (X 2 ≦X), the adjustment unit  42  sets the second transmission interval L 2  as the transmission interval of the CCM frame. The transmission unit  43  transmits the CCM frame to the opposite MEP at the transmission interval set by the adjustment unit  42 . 
     Next, operations of the transmission system  1  of First Embodiment will be described.  FIG. 5  is a flowchart illustrating an example of processing operations of the CPU  16  within the transmission apparatus  2 , which is related to a state notification process,. The state notification process illustrated in  FIG. 5  is a process of determining the state of the network  3  and notifying the adjustment unit  42  of the transmission processing unit  40  of the determination result, which is performed in the reception processing unit  30 . 
     In  FIG. 5 , the line quality checking unit  31  of the reception processing unit  30  checks the line quality and determines whether the line abnormality exists based on the check result (operation S 11 ). Further, the line abnormality refers to the state of the network  3 , for example, the state where signal error is detected and the LOC is determined as being existed. When it is determined that the line abnormality does not exist (“YES” at operation S 11 ), the reception unit  32  of the reception processing unit  30  receives the CCM frame (operation S 12 ). 
     The alarm monitoring unit  33  of the reception processing unit  30  monitors the state of the received CCM frame (operation S 13 ) and determines whether the state of the CCM frame is in a stable condition based on the monitoring result (operation S 14 ). Further, when the CCM frame is received within 3.5 intervals, the alarm monitoring unit  33  determines that the state of the CCM frame is in the stable condition. Further, when the CCM frame is not received within 3.5 intervals, the alarm monitoring unit  33  determines that the state of the CCM frame is not in the stable condition. 
     When it is determined that the state of the CCM frame is not in the stable condition (“NO” at operation S 14 ), the alarm unit  34  of the reception processing unit  30  sends an alarm information which indicates a fault (operation S 15 ). The alarm monitoring unit  33  collects the alarm information (operation S 16 ) and stores the collected alarm information in the alarm information table  14 A (operation S 17 ). 
     The state monitoring unit  35  of the reception processing unit  30  determines a current state of the network  3  based on the alarm information within the alarm information table  14 A (operation S 18 ). The state monitoring unit  35  notifies the adjustment unit  42  within the transmission processing unit  40  of the communication quality level X which is the determination result of the state of the network  3  (operation S 19 ), and ends the processing operations illustrated in  FIG. 5 . 
     When it is determined that the line abnormality exists (“NO” at operation S 11 ), the reception unit  32  discards the CCM frame (operation S 20 ), and proceeds to operation S 13  to monitor the state of the CCM frame. Further, when it is determined that the line abnormality exists, the line quality checking unit  31  notifies the state monitoring unit  35  of the line abnormality. Also, when the line abnormality is detected from the line quality checking unit  31 , the state monitoring unit  35  notifies the transmission processing unit  40  of the state of the network  3  that the line abnormality exists. 
     When it is determined that the state of the CCM frame is in a stable condition (“YES” at operation S 14 ), the alarm monitoring unit  33  proceeds to operation S 16  to collect the alarm information. 
     When it is determined that the state of the CCM frame is not in the stable condition, the reception processing unit  30  for the state notification process illustrated in  FIG. 5  stores the alarm information of the LOC in the alarm information table  14 A and determines the state of the network  3  based on the alarm information within the alarm information table  14 A. The reception processing unit  30  notifies the transmission processing unit  40  of the determination result of the state of the network  3 . As a result, the transmission processing unit  40  may recognize the communication quality level X which is the state of the network  3 . 
       FIG. 6  is a flowchart illustrating an example of processing operations of the CPU  16  in the transmission apparatus  2 , which is related to a first transmission interval adjustment process,. The first transmission interval adjustment process illustrated in  FIG. 6  is a process of setting and changing the transmission interval at the time of transmitting the CCM frame, which is performed in the transmission processing unit  40 . In  FIG. 6 , the generation unit  41  of the transmission processing unit  40  creates a CCM frame (operation S 31 ). The adjustment unit  42  of the transmission processing unit  40  determines whether the communication quality level X of the network  3  is equal to or greater than a first threshold value X 1  (operation S 32 ). 
     When it is determined that the communication quality level X of the network  3  is less than the first threshold value X 1  (“NO” at operation S 32 ), the adjustment unit  42  sets the reference transmission interval L (operation S 33 ). The transmission unit  43  of the transmission processing unit  40  transmits the CCM frame at the set transmission interval (operation S 34 ), and ends the processing operation illustrated in  FIG. 6 . 
     When the communication quality level X is equal to or greater than the first threshold value X 1  (“YES” at operation S 32 ), the adjustment unit  42  determines whether the communication quality level X is equal to or greater than the second threshold value X 2  (operation S 35 ). When it is determined that the communication quality level X is less than the second threshold value X 2  (“NO” at operation S 35 ), the adjustment unit  42  sets the first transmission interval L 1  as the transmission interval of CCM frame (operation S 36 ), and proceeds to operation S 34  to transmit the CCM frame at the set transmission interval. 
     When it is determined that the communication quality level X is equal to or greater than the second threshold value X 2  (“YES” at operation S 35 ), the adjustment unit  42  sets the second transmission interval L 2  as the transmission interval of CCM frame (operation S 37 ), and proceeds to operation S 34  to transmit the CCM frame at the set transmission interval. 
     When it is determined that the communication quality level X is less than the first threshold value X 1 , the transmission processing unit  40  for the first transmission interval adjustment process illustrated in  FIG. 6  sets the reference transmission interval L as the transmission interval for the CCM frame. For example, when the communication quality level X is reduced, the transmission processing unit  40  restores the transmission interval to the reference transmission interval to restore a normal CCM frame monitoring process. 
     When the communication quality level X is equal to or greater than the first threshold value X 1  and less than the second threshold value X 2 , the transmission processing unit  40  sets the first transmission interval L 1  as the transmission interval of CCM frame. As a result, the transmission interval becomes longer and the number of CCM frames becomes less dense compared to a case where the reference transmission interval L is set as the transmission interval and thus, the amount of CCM frames may be suppressed to ½ (one-half). 
     When the communication quality level X is equal to or greater than the second threshold value X 2 , the transmission processing unit  40  sets the second transmission interval L 2  as the transmission interval of CCM frame. As a result, the transmission interval becomes longer and the number of CCM frames becomes less dense compared to a case where the reference transmission interval L is set as the transmission interval and thus, the amount of CCM frames may be suppressed to ⅓ (one-third). 
       FIG. 7  is an explanatory view illustrating an occupation ratio of each CCM frame in each user data band. The table (A) of  FIG. 7  illustrates a ratio of CCM frames in a case where the reference transmission interval L is set as a transmission interval and the table (B) of  FIG. 7  illustrates a ratio of CCM frames in a case where the second transmission interval L 2  is set as a transmission interval. Period value field indicates the length of a single interval. CCM frame rate field indicates the number of frames per second. The CCM frame size field indicates the size per CCM frame. The CCM bit rate field indicates the number of bits of the CCM frame per second. The ratio of the CCM frames for each user&#39;s network speed field indicates an occupation ratio of CCM frame in the user data band at, for example, the user&#39;s network speed of 100 Gbps, 10 Gbps and 1 Gbps. Hereinafter, the 100 Gbps, 10 Gbps and 1 Gbps may be denoted by 100G, 10G and 1G, respectively, by omitting the “bps”. 
     For example, a case is assumed where the reference transmission interval L is set as the transmission interval by noting that the Period value is 3.33 ms, the CCM frame rate is 300 frames/second, the number of VLANs is 8192 and the CCM frame size is 97 bytes. In this case, as illustrated in the table (A) of  FIG. 7 , the ratio of CCM frame to the user data band at 100G is 1.9%, the ratio of CCM frame to the user data band at 10G is 19.1%, and the ratio of CCM frame to the user data band at 1G is 190.7%. In contrast, when the second transmission interval L 2  is set as the transmission interval, the CCM frame ratio is reduced from 1.9% to 0.6% at 100G, from 19.1% to 6.4% at 10G and from 190.7% to 63.6% at 1G. Further, for convenience of explanation, the CCM frame ratio is indicated as 190.7% for a case of 1G but actually, the CCM frame ratio is 100%. 
     For example, a case is assumed where the reference transmission interval L is set as the transmission interval by noting that the Period value is 10 ms, the CCM frame rate is 100 frames/second, the number of VLANs is 8192 and the CCM frame size is 97 bytes. In this case, as illustrated in the table (A) of  FIG. 7 , the CCM frame ratio is 0.6% at 100G, 6.4% at 10G and 63.6% at 1G. In contrast, when the second transmission interval L 2  is set as the transmission interval, the CCM frame ratio is reduced from 0.6% to 0.2% at 100G, from 6.4% to 2.1% at 10G and from 63.6% to 21.2% at 1G. 
     That is, in the transmission apparatus  2 , when the communication quality level X of the network  3  is equal to or greater than the first threshold value X 1 , it is possible to make the transmission interval of the CCM frame longer than the reference transmission interval L using the adjustment function to suppress the amount of the CCM frames for the user data band. 
     When the communication quality level X is less than the first threshold value X 1 , the transmission apparatus  2  of First Embodiment sets the reference transmission interval L as the transmission interval of the CCM frame. As a result, when the communication quality level X is reduced, the transmission apparatus  2  sets the transmission interval to be changed into the reference transmission interval L and thus, the normal CCM frame monitoring process may be restored. 
     When the communication quality level X is equal to or greater than the first threshold value X 1  and less than the second threshold value X 2 , the transmission apparatus  2  sets the first transmission interval L 1  as the transmission interval of CCM frame. As a result, the transmission apparatus  2  transmits the CCM frame to the opposite MEP at the first transmission interval L 1 . Therefore, the occupation ratio of CCM frame in the user data band may be reduced to ½ (one-half) as compared to a case where the reference transmission interval L is set as the transmission interval. Also, utilization efficiency of the user data band may be improved. 
     When the communication quality level X is equal to or greater than the second threshold value X 2 , the transmission apparatus  2  sets the second transmission interval L 2  as the transmission interval of CCM frame. As a result, the transmission apparatus  2  transmits the CCM frame to the opposite MEP at the second transmission interval L 2 . Therefore, the occupation ratio of CCM frame in the user data band may be reduced to ⅓ (one-third) as compared to a case where the reference transmission interval L is set as the transmission interval. Also, utilization efficiency of the user data band may be improved. 
     In the transmission system  1  of First Embodiment, even when the opposite transmission apparatus  100  is not equipped with the adjustment function, the occupation ratio of CCM frame in the user data band at the time when the CCM frame is transmitted from the transmission apparatus  2  to the opposite transmission apparatus  100  may be suppressed. 
     Further, in First Embodiment, a transmission apparatus which is not equipped with the adjustment function is employed as the opposite transmission apparatus  100 , but a transmission apparatus equipped with the adjustment function may be employed as well. Hereinafter, an embodiment in which the transmission apparatus equipped with the adjustment function is employed will be described. 
     Second Embodiment  
       FIG. 8  is a block diagram illustrating an example of a transmission system  1 A according to Second Embodiment. Further, components of the transmission system  1 A that are the same as those of the transmission system  1  of First Embodiment are denoted by the same reference numerals, and descriptions of a redundant configuration and operation thereof will be omitted. The transmission system  1 A illustrated in  FIG. 8  includes a transmission apparatus  2 A, an opposite transmission apparatus  2 B and the network  3 . MEPs indicating a terminal end point of the CCM frame are set in the transmission apparatus  2 A and the opposite transmission apparatus  2 B, respectively. An MEP-A and MEP-C are set in the transmission apparatus  2 A and the opposite transmission apparatus  2 B, respectively. Further, the transmission apparatus  2 A and the opposite transmission apparatus  2 B are equipped with the adjustment function which automatically adjusts the transmission interval of the CCM frame. 
     The transmission apparatus  2 A transmits the user data to the opposite transmission apparatus  2 B via the network  3  and regularly transmits the CCM frame (CCM-A) to the opposite transmission apparatus  2 B via the network  3  at the set transmission interval. Further, the opposite transmission apparatus  2 B receives the user data from the transmission apparatus  2 A via the network  3  and the CCM frame (CCM-A) from the transmission apparatus  2 A via the network  3 . 
     Further, the opposite transmission apparatus  2 B also transmits the user data to the transmission apparatus  2 A via the network  3  and regularly transmits the CCM frame (CCM-C) to the transmission apparatus  2 A via the network  3  at the set transmission interval. The transmission apparatus  2 A receives the data from the opposite transmission apparatus  2 B via the network  3  and the CCM frame (CCM-C) from the opposite transmission apparatus  2 B via the network  3 . 
       FIG. 9  is an explanatory view illustrating an example of a functional block of CPU  16 A of the transmission apparatus  2 A according to Second Embodiment. Further, since the configuration of the opposite transmission apparatus  2 B is the same as that of the transmission apparatus  2 A, the same components are denoted by the same reference numerals, and descriptions of the redundant configuration and operation will be omitted. 
     The CPU 16 A illustrated in  FIG. 9  includes a reception processing unit  30 A, a transmission processing unit  40 A and a test mode management unit  50  as the CCM processing functionalities. The reception processing unit  30 A further includes a recognition unit  36  in addition to the line quality checking unit  31 , the reception unit  32 , the alarm monitoring unit  33 , the alarm unit  34  and the state monitoring unit  35 . The recognition unit  36  recognizes a specific pattern, which notifies changing of transmission interval, from a group of CCM frames sent from the opposite MEP and specifies a transmission interval corresponding to the specific pattern. The alarm monitoring unit  33  determines whether the LOC, which refers to the state of the CCM frame, exists based on the transmission interval specified by the recognition unit  36 . 
     The transmission processing unit  40 A further includes an adjustment unit  42 A in addition to the generation unit  41  and the transmission unit  43 . When the communication quality level X of the network  3  is less than the first threshold value X 1  (X&lt;X 1 ), the adjustment unit  42 A sets the reference transmission interval L as the transmission interval of the CCM frame. In this case, the adjustment unit  42 A transmits a third specific pattern to be described at the time of changing other transmission interval, which is being set, into the reference transmission interval L. 
     When the communication quality level X is equal to or greater than the first threshold value X 1  and less than the second threshold value X 2  (X 1 ≦X&lt;X 2 ), the adjustment unit  42 A sets the first transmission interval L 1  as the transmission interval of CCM frame. In this case, the adjustment unit  42 A transmits a first specific pattern to be described at the time of changing other transmission interval, which is being set, to the first transmission interval L 1 . 
     When the communication quality level X of the network  3  is equal to or greater than the second threshold value X 2  (X 2 ≦X), the adjustment unit  42 A sets the second transmission interval L 2  as the transmission interval of CCM frame. In this case, the adjustment unit  42 A transmits a second specific pattern to be described later at the time of changing other transmission interval, which is being set, to the second transmission interval L 2 . The transmission unit  43  transmits the CCM frame to the opposite MEP at the transmission interval set by the adjustment unit  42 A. 
       FIG. 10  is an explanatory view illustrating an example of a specific pattern. The third specific pattern illustrated in (A) of  FIG. 10  is a CCM frame transmission pattern which notifies the opposite MEP that a transmission interval is changed from other transmission interval, which is being set, to the reference transmission interval L. The third specific pattern is a group of CCM frames that a pattern in which transmittal of one (1) CCM frame every one (1) interval is repeated six (6) times continuously, for example, CCM-A→CCM-A→CCM-A→CCM-A→CCM-A→CCM-A→ . . . , is repeated ten times continuously. The first specific pattern illustrated in (B) of  FIG. 10  is a CCM frame transmission pattern which notifies the opposite MEP that a transmission interval is changed from other transmission interval, which is being set, to the first transmission interval L 1 . The first specific pattern is a group of CCM frames that a pattern of, for example, CCM→None→CCM→CCM→None→CCM→ . . . is repeated ten times continuously. The second specific pattern illustrated in (C) of  FIG. 10  is a CCM frame transmission pattern which notifies the opposite MEP that a transmission interval is changed from other transmission interval, which is being set, to the second transmission interval L 2 . The second specific pattern is a group of CCM frames that a pattern of, for example, CCM→None→None→CCM→None→CCM→ . . . is repeated ten times continuously. 
     When a specific pattern transmitted from the opposite MEP is recognized, the recognition unit  36  of the transmission apparatus  2 A specifies the transmission interval corresponding to the specific pattern. The transmission apparatus  2 A may identify either a case where the transmission interval is made longer and thus the number of times that the CCM frame is transmitted is reduced even when the number of the received CCM frames is small, or a case where the CCM frame is discarded due to degradation of the communication quality. 
     When transmitting the specific pattern to the opposite MEP, the test mode management unit  50  shifts to a test mode different from a mode at the time of the normal CCM frame transmission. The test mode management unit  50  and another test mode management unit  50  within the transmission apparatus  2 B for the opposite MEP notify an initiation of test mode with each other, thereby shifting to the test mode. The transmission unit  43  transmits the specific pattern to the opposite MEP during the test mode. Further, the test mode management unit  50  and another test mode management unit  50  within the transmission apparatus  2 B for the opposite MEP notify a termination of test mode with each other, thereby terminating the test mode. Further, the CCM frame used in the normal CCM monitor processing or the user data are continuously transmitted between the transmission apparatus  2 A and the transmission apparatus  2 B even during the test mode. 
     Next, operations of the transmission system  1 A of Second Embodiment will be described. When the specific pattern transmitted from the opposite MEP is recognized, the recognition unit  36  of the transmission apparatus  2 A specifies the transmission interval of the opposite MEP corresponding to the specific pattern. 
       FIG. 11  is a flowchart illustrating an example of processing operations, which is related to a second transmission interval adjustment process, of the CPU  16 A within the transmission apparatus  2 A. The second transmission interval adjustment process illustrated in  FIG. 11  is a process, which is performed in the transmission processing unit  40 A, of notifying the opposite MEP of the transmission interval when setting the transmission interval at the time of transmitting the CCM frame according to the communication quality and changing the transmission interval. In  FIG. 11 , the generation unit  41  of the transmission processing unit  40 A creates a CCM frame (operation S 41 ). The adjustment unit  42 A of the transmission processing unit  40 A determines whether the communication quality level X is equal to or greater than the first threshold value X 1  (operation S 42 ). 
     When it is determined that the communication quality level X is less than the first threshold value X 1  (“NO” at operation S 42 ), the adjustment unit  42 A sets the reference transmission interval L (operation S 43 ) and determines whether the transmission interval set in the previous time is changed (operation S 44 ). When it is determined that the transmission interval set in the previous time is changed (“YES” at operation S 44 ), the adjustment unit  42 A transmits the third specific pattern, which notifies changing of the set transmission interval into the reference transmission interval L, to the opposite MEP (operation S 45 ). Further, the adjustment unit  42 A is shifted to the test mode by the test mode management unit  50  and transmits the third specific pattern to the opposite MEP during the test mode to end the test mode. Further, when the third specific pattern transmitted from a counter-opposite MEP is detected, an opposite MEP may specify the reference transmission interval L which is set and changed by the counter-opposite MEP. Also, the transmission unit  43  transmits the CCM frame at the set transmission interval (operation S 46 ) and ends the processing operation illustrated in  FIG. 11 . 
     When it is determined that the set transmission interval is not changed (“NO” at operation S 44 ), the adjustment unit  42 A proceeds to operation S 46  to transmit the CCM frame at the set transmission interval. 
     When it is determined that the communication quality level X is equal to or greater than the first threshold value X 1  (“YES” at operation S 42 ), the adjustment unit  42 A determines whether the communication quality level X is equal to or greater than the second threshold value X 2  (operation S 47 ). When it is determined that the communication quality level X is less than the second threshold value X 2  (“NO” at operation S 47 ), the adjustment unit  42 A sets the first transmission interval L 1  (operation S 48 ) and determines whether the transmission interval set in the previous time is changed (operation S 49 ). 
     When it is determined that the transmission interval set in the previous time is changed (“YES” at operation S 49 ), the adjustment unit  42 A transmits the first specific pattern, which notifies changing of the set transmission interval into the first transmission interval L 1 , to the opposite MEP through the transmission unit  43  (operation S 50 ). Further, the adjustment unit  42 A shifts to the test mode in the test mode management unit  50  and transmits the first specific pattern to the opposite MEP during the test mode, and ends the test mode. Further, when the first specific pattern transmitted from the counter-opposite MEP is detected, the opposite MEP may specify the first transmission interval L 1  which is set and changed by the counter-opposite MEP. Also, the adjustment unit  42 A proceeds to operation S 46  to transmit the CCM frame at the set transmission interval. When it is determined that the transmission interval set in the previous time is not changed in the previous time (“NO” at operation S 49 ), the adjustment unit  42 A proceeds to operation S 46  to transmit the CCM frame at the set transmission interval. 
     When it is determined that the communication quality level X is equal to or greater than the second threshold value X 2  (“YES” at operation S 47 ), the adjustment unit  42 A sets the second transmission interval L 2  (operation S 51 ) and determines whether the transmission interval set in the previous time is changed (operation S 52 ). When it is determined that the transmission interval set in the previous time is changed (“YES” at operation S 52 ), the adjustment unit  42 A transmits the second specific pattern, which notifies changing of the set transmission interval into the second transmission interval L 2 , to the opposite MEP (operation S 53 ). Further, the adjustment unit  42 A shifts to the test mode by the test mode management unit  50  and transmits the second specific pattern to the opposite MEP during the test mode, and ends the test mode. Further, when the second specific pattern from the counter-opposite MEP is detected, the opposite MEP may specify the second transmission interval L 2  which is set and changed by the counter-opposite MEP. Also, the adjustment unit  42 A proceeds to operation S 46  to transmit the CCM frame at the set transmission interval. When it is determined that the transmission interval set in the previous time is not changed in the previous time (“NO” at operation S 52 ), the adjustment unit  42 A proceeds to operation S 46  to transmit the CCM frame at the set transmission interval. 
     When the communication quality level X is less than the first threshold value X 1 , the transmission processing unit  40 A for the second transmission interval adjustment process illustrated in  FIG. 11  sets the reference transmission interval L as the transmission interval of the CCM frame. Further, when changing the transmission interval into the reference transmission interval L, the transmission processing unit  40 A notifies the opposite MEP of the third specific pattern, which notifies changing of the reference transmission interval. As a result, the opposite MEP may specify the transmission interval L which is set and changed by the counter-opposite MEP. 
     When the communication quality level X is equal to or greater than the first threshold value X 1  and less than the second threshold value X 2 , the transmission processing unit  40 A sets the first transmission interval L 1  as the transmission interval of the CCM frame. Further, when changing the transmission interval into the first transmission interval L 1 , the transmission processing unit  40 A notifies the opposite MEP of the first specific pattern, which notifies changing of the first transmission interval. As a result, the opposite MEP may specify the first transmission interval L 1  which is set and changed by the counter-opposite MEP. 
     When the communication quality level X is equal to or greater than the second threshold value X 2 , the transmission processing unit  40 A sets the second transmission interval L 2  as the transmission interval of the CCM frame. Further, when changing the transmission interval into the second transmission interval L 2 , the transmission processing unit  40 A notifies the opposite MEP of the second specific pattern, which notifies changing of the second transmission interval X 2 . As a result, the opposite MEP may specify the second transmission interval L 2  which is set and changed by the counter-opposite MEP. 
     The transmission apparatus  2 A and the opposite transmission apparatus  2 B are equipped with the adjustment function in the transmission system  1 A of Second Embodiment. In the transmission system  1 A, the transmission interval of the CCM frame from the transmission apparatus  2 A to the opposite transmission apparatus  2 B and the transmission interval of the CCM frame from the opposite transmission apparatus  2 B to the transmission apparatus  2 A are set to be longer than the reference transmission interval according to the communication quality level. As a result, the number of times that the CCM frame is transmitted from the transmission apparatus  2 A to the opposite transmission apparatus  2 B and the number of times that the CCM frame is transmitted from the opposite transmission apparatus  2 B to the transmission apparatus  2 A may be reduced to significantly suppress the occupation ratio of the CCM frame in the user data band compared to First Embodiment. Also, utilization efficiency of the user data band may be improved. 
     In the embodiments, a threshold value for determination the LOC is set as 3.5 intervals, but the threshold value is not limited to 3.5 intervals and may be appropriately changed. 
     In the embodiments, a transmission interval is set in three stages formed of the reference transmission interval L, the first transmission interval L 1  and the second transmission interval L 2  according to the communication quality level X, but the transmission interval is not limited to the three stages and may be appropriately changed. 
     In the embodiments, the transmission interval is set and changed stepwisely according to the communication quality level, but may also be set and changed continuously according to the communication quality level. Further, a communication quality level for which a communication quality indexes, such as for example, a communication quality, an error rate and a CCM frame reception rate is taken into account is adopted, but the communication quality level is not limited to these communication quality indexes and may be appropriately changed. 
     The transmission apparatus  2  of the embodiments may include a terminal end determination unit which manages the number of MEPs transmitting and receiving the CCM frame within the network  3  to determine whether the number of MEPs exceeds a predetermined number. When the number of MEPs exceeds a predetermined number in the terminal end determination unit, the adjustment unit  24  may set the transmission interval to be longer than the reference transmission interval. When a large number of MEPs exist within the network  3 , the amount of CCM frames also increases to consume the user data band. However, when the number of MEPs exceeds the predetermined number, the transmission apparatus  2  sets the transmission interval to be longer than the reference transmission interval and thus, consumption of the user data band by the CCM frame may be suppressed. 
     Further, when the communication quality level X is equal to or greater than the first threshold value X 1 , the transmission apparatus  2  of the embodiments sets the transmission interval to be longer than the reference transmission interval L. However, the transmission apparatus  2  may determine whether the line abnormality exists continuously for a predetermined period and set the transmission interval to be longer than the reference transmission interval when the line abnormality does not exist continuously for a predetermined period. 
     The line quality checking unit  31  of the embodiments checks the state of the line quality based on, such as, the frame reception rate or the packet loss rate, but may use other index for the line quality to check the state of the line quality without being limited to the frame reception rate and the packet loss rate. 
     Further, the entirety of some of various processing functions performed by each device may be executed on a CPU (or a microcomputer such as, MPU (Micro Processing Unit) or MCU (Micro Controller Unit)). Further, the entirety of some of various processing functions may also be executed on a program analyzed and executed by the CPU (or a microcomputer such as, the MPU or MCU), or hardware configured by a wired logic. 
     All examples and conditional language recited herein are intended for pedagogical purposes to aid the reader in understanding the invention and the concepts contributed by the inventor to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions, nor does the organization of such examples in the specification relate to a showing of the superiority and inferiority of the invention. Although the embodiments of the present invention have been described in detail, it should be understood that the various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention.