Communication system and communication apparatus

A communication system comprising:

• one subscriber accommodation network which includes a first subscriber accommodation device capable of connecting one or more subscriber devices in a time division multiplexing scheme, and a second subscriber accommodation device capable of connecting one or more other subscriber devices in the time division multiplexing scheme, or a plurality of subscriber accommodation networks which include the first or second subscriber accommodation devices individually;
• a first communication network which includes a plurality of subscriber devices, and a first communication device connectable with the plurality of subscriber devices;
• and
• a second communication network which includes the first and second subscriber accommodation devices, and a second communication device that is capable of connecting the first and second subscriber accommodation devices and that has a function of selecting either of subscriber devices connected to the first subscriber accommodation device or subscriber devices connected to the second subscriber accommodation device or subscriber devices connected to the first communication device, to-be-utilized,
• in which the first communication device and the second communication device are connected by a plurality of communication paths through the first communication network, the one or the plurality of subscriber accommodation networks, and the second communication network,
• wherein,
• when both paths of a working system and a protection system have been established, the first communication device simultaneously forwards communication time period measuring frames which includes path identification information and sending timing identification information, to both the paths;
• a first subscriber device which has received the communication time period measuring frame sends a first delay measurement frame to an uplink communication path, in accordance with an assignment of a bandwidth by the first subscriber accommodation device;
• a second subscriber device which has received the communication time period measuring frame sends a second delay measurement frame to an uplink communication path, in accordance with an assignment of a bandwidth by the second subscriber accommodation device;
• the first subscriber accommodation device which has received the first delay measurement frame from the first subscriber device converts the first delay measurement frame from a format for transferring this frame by the subscriber accommodation network, into a packet format for transferring this frame by the second communication network toward the second communication device, and the first subscriber accommodation device transfers the resulting first delay measurement frame to the second communication device;
• the second subscriber accommodation device which has received the second delay measurement frame from the second subscriber device converts the second delay measurement frame from a format for transferring this frame by the subscriber accommodation network, into a packet format for transferring this frame by the second communication network toward the second communication device, and the second subscriber accommodation device transfers the resulting second delay measurement frame to the second communication device;
• the second communication device receives the first delay measurement frame from the first subscriber accommodation device, and records a reception time in a delay database, in association with path identification information and transmission timing identification information which are contained in the first delay measurement frame, while the second communication device receives the second delay measurement frame from the second subscriber accommodation device, and records a reception time in the delay database, in association with path identification information and transmission timing identification information which are contained in the second delay measurement frame;
• the second communication device calculates an arrival time difference between the delay measurement frames from both the paths, on the basis of the reception times of the delay measurement frames having the same transmission timing identification information from both the paths, and records the arrival time difference in the delay database, in association with the path identification information and the transmission timing identification information;
• and
• when the delay measurement frames having the same transmission timing identification information have already been received from a plurality of paths, with reference to the delay database, the second communication device compares the reception times of the delay measurement frames from both the paths, and transmits a delay feedback frame for a revision request containing a correction magnitude based on the arrival time difference, to the first subscriber accommodation device or the second subscriber accommodation device on a side of earlier reception time.

A communication apparatus in a communication system, the communication system comprising:

• one subscriber accommodation network which includes a first subscriber accommodation device capable of connecting one or more subscriber devices in a time division multiplexing scheme, and a second subscriber accommodation device capable of connecting one or more other subscriber devices in the time division multiplexing scheme, or a plurality of subscriber accommodation networks which include the first or second subscriber accommodation devices individually;
• a first communication network which includes a plurality of subscriber devices, and a first communication device connectable with the plurality of subscriber devices;
• and
• a second communication network which includes the first and second subscriber accommodation devices, and a second communication device that is capable of connecting the first and second subscriber accommodation devices and that has a function of selecting either of subscriber devices connected to the first subscriber accommodation device or subscriber devices connected to the second subscriber accommodation device or subscriber devices connected to the first communication device, to-be-utilized,
• in which the first communication device and the second communication device are connected by a plurality of communication paths through the first communication network, the one or the plurality of subscriber accommodation networks, and the second communication network,
• wherein, by the communication apparatus,
• a first delay measurement frame which contains path identification information and sending timing identification information which has been transmitted from an other communication device is received from a path which passes through a first subscriber device and the first subscriber accommodation device, and a reception time thereof is recorded in a delay database, in association with path identification information and transmission timing identification information which are contained in the first delay measurement frame;
• a second delay measurement frame which contains path identification information and sending timing identification information which has been transmitted simultaneously with the first delay measurement frame from the other communication device is received from a path which passes through a second subscriber device and the second subscriber accommodation device, and a reception time thereof is recorded in the delay database, in association with path identification information and transmission timing identification information which are contained in the second delay measurement frame;
• an arrival time difference between the delay measurement frames from both the paths is calculated on the basis of the reception times of the delay measurement frames having the same transmission timing identification information items, from both the paths, and the arrival time difference is recorded in the delay database, in association with the path identification information and the transmission timing identification information;
• and
• when the delay measurement frames having the same transmission timing identification information items have already been received from a plurality of paths, with reference to the delay database, the reception times of the delay measurement frames from both the paths are compared, and a delay feedback frame for a revision request which contains a correction magnitude based on an arrival time difference is transmitted to the first subscriber accommodation device or the second subscriber accommodation device on a side of earlier reception time.