Multiplex communications – Data flow congestion prevention or control – Flow control of data transmission through a network
Reexamination Certificate
1997-08-28
2001-03-06
Nguyen, Chau (Department: 2739)
Multiplex communications
Data flow congestion prevention or control
Flow control of data transmission through a network
C370S395430, C370S410000
Reexamination Certificate
active
06198726
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a plural-line terminating apparatus and a method of OAM processing in this apparatus. More particularly, the invention relates to a plural-line terminating apparatus for accommodating a plurality of lines, converting signals from these plurality of lines to ATM cells and sending the ATM cells to an ATM switch, sending ATM cells from the switch upon converting the cells to line signals, and executing OAM processing of a plurality of lines. The invention further relates to a method of executing this OAM processing.
Asynchronous Transfer Mode (ATM), which is the core of a broadband ISDN, makes it possible to divide a variety of information such as voice, video and data into fixed-length packets, referred to as cells, and to transfer the information over a network at high speed while handling the information in a consolidated manner. Monitoring network failures in the operation of an ATM network is important, and use is made of OAM (Operation, Administration and Maintenance) Fault Management cells (AIS cells, RDI cells, etc.) to monitor connection failure.
FIG. 19
is a diagram for describing the basic mechanism of OAM (Operation, Administration and Maintenance) flow. Shown in
FIG. 19
are an end point
1
on a transmitting side, an end point
2
on a receiving side, and connecting points
3
a,
3
b,
3
c
. . . at which OAM cells can be extracted/inserted. If a defect A has been sensed at a certain connecting point
3
b,
an AIS (Alarm Indication Signal) cell is sent in the downstream direction in order to notify the downstream side of the connection of the defect A. Upon receiving the AIS cell or directly detecting a defect B, the end point
2
downstream of the connection sends back an RDI (Remote Defect Indication) cell to the opposing end point on the upstream side. As a result, the end point
1
upstream of the connection is capable of managing defects on the transmitting and receiving sides in both directions, and the connecting points
3
a~
3
c
are capable of discriminating the occurrence of defects and the locations thereof by monitoring the AIS and RDI cells.
FIGS. 20A and 20B
are formats of OAM cells, in which
FIG. 20A
shows the format (F
4
OAM flow) of an OAM cell for a VP connection and
FIG. 20B
the format (F
5
OAM flow) of an OAM cell for a VC connection.
The F
4
OAM flow implements (1) discrimination and notification of faults in a VP connection (a VP-connection fault management function), and (2) notification of error rate, cell loss rate and cell mixing rate of user information cells (a VP-connection performance management function). The F
5
OAM flow implements a VC-connection fault management function and a VC-connection performance management function in a manner similar to that of the F
4
flow.
The OAM cells of the F
4
and F
5
OAM flows both consist of a 5-octet ATM cell header
100
and a 48-octet ATM cell payload
101
. The ATM cell payload
101
is composed of the following information:
(1) 4-bit OAM cell type
101
a;
(2) 4-bit function type
101
b;
(3) a 45-octet function specific field
101
c,
which specifies fault category and fault location;
(4) a 6-bit reserved field
101
d;
and
(5) a 10-bit ECC field
101
e.
FIG. 21
is a correspondence table of OAM cell type
101
a
vs. function type
101
b.
The following are advised as the OAM cell types:
fault management type (Fault Management) 0001;
performance management type (Performance Management) 0010; and
activation/deactivation management type Activation/Deactivation) 1000.
The fault management type 0001 includes (1) an alarm indication signal (AIS), which is a warning of fault detection, (2) remote defect indication (RDI), (3) continuity check and (4) loopback. The performance management type 0010 includes (1) forward monitoring and (2) backward reporting. The activation/deactivation management type includes (1) performance monitoring and (2) continuity check.
Since an OAM cell (
FIG. 20A
) for a VP connection traverses a path the same as that of a user cell which flows through the VP connection, the OAM cell has a VPI number the same as that of the user cell, and specific VCI values (VCI=3, VCI=4) so that the cell will be identified as an OAM cell. VCI=3 identifies the cell as being a segment OAM cell, and VCI=4 identifies the cell as being an end-to-end OAM cell. A segment OAM cell is a cell inserted/extracted in a segment and is valid only in a segment interval; it is not transmitted outside of a segment interval. An end-to-end OAM cell is a cell valid end to end of a set connection; it is discarded at the end point of a connection.
Since an OAM cell (
FIG. 20B
) for a VC connection traverses a path the same as that of a user cell which flows through the VC connection, the OAM cell has a VPI value and a VCI value the same as those of the user cell, and specific payload type identifiers (PTI=100,PTI=101) so that the cell will be identified as an OAM cell. PTI=100 identifies the cell as being a segment OAM cell, and PTI=101 identifies the cell as being an end-to-end OAM cell.
Thus, in a case where an AIS cell has arrived at a certain ATM connection point, the connection point undergoes a transition to an alarm state at reception of the AIS cell. Restoration to the normal state is made in response to non-reception of the AIS cell for 2.5±0.5 seconds or reception of a user cell (alarm-status recovery cell). Since the function-specific field
101
c
of the Fault Management cell indicates the details of a fault (fault category and location, etc.), as mentioned above, at the time of a failure the maintenance personnel may operate the network by referring to the detailed information that has been recorded in the function-specific field
101
c
of the Fault Management cell.
FIG. 22
is a block diagram illustrating the configuration of an ATM switching system. Shown in
FIG. 22
are subscriber interfaces (or line IFs)
11
11
~
11
1n
,
11
21
~
11
2n
,
11
31
~
11
3n
,
11
41
~
11
4n
connected to corresponding lines (transmission lines), multiplexer/demultiplexers
12
1
~
12
4,
an ATM switch unit
13
, a system controller
14
and a maintenance terminal
15
. The ATM switch unit
13
is connected to the plurality of multiplexer/demultiplexers
12
1
~
12
4,
switches input cells from certain multiplexer/demultiplexers and outputs the cells to prescribed multiplexer/demultiplexers. The multiplexer/demultiplexers
12
1
~
12
4,
which are connected to the pluralities of line interfaces
11
11
~
11
1n
,
11
21
~
11
2n
,
11
31
~
11
3n
,
11
41
~
11
4n
, respectively, multiplex incoming cells from a plurality of line interfaces IF and output the cells to the ATM switch unit
13
. Furthermore, the multiplexer/demultiplexers
12
1
~
12
4
demultiplex and output incoming cells, which arrive from the ATM switch unit
13
, to the pertinent line interfaces.
The line interfaces
11
11
~
11
4n
, which are connected to the corresponding multiplexer/demultiplexers
12
1
~
12
4,
each extract an ATM cell from the payload of a frame signal of a prescribed format (e.g. a SONET frame) that has entered from the line, convert the cell to one having the cell format within the switch and output the cell to the multiplexer/demultiplexer. The cell format within the switch is provided with information TAG for routing purposes. The ATM switch unit switches a cell to a prescribed path by referring to this tag information TAG.
Furthermore, the line interfaces
11
11
~
11
4n
convert the cells of the switch cell format that enter from the multiplexer/demultiplexers
12
1
~
12
4
to cells having the ATM cell format, map each ATM cell to the payload of the SONET frame and send the ATM cell to the line side. The system controller
14
controls the line interfaces
11
11
~
11
4n
, multiplexer/demultiplexers
12
1
~
12
4
and ATM switch unit
13
.
FIG. 23
is a block diagram showing the construction of a line interface. One line interface
11
is provided in correspondence with one set of outgoing/incoming lines and
Hayami Hichiro
Hoshino Tadashi
Fujitsu Limited
Helfgott & Karas P.C.
Hyun Soon-Dong
Nguyen Chau
LandOfFree
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