Path route test apparatus for use in an ATM transmission system

An ATM transmission system transmits cell-formatted data in an asynchronous transfer mode, and aims at conducting an online path route test in the system. If one path route only is established in the system, then one or more valid cell detecting units for detecting, upon receipt of a cell enable signal indicating that a valid cell to pass through the path route has been sent, the arrival of a valid cell are provided at an optional point including an ATM switch in the path route so that the path route can be partially or entirely validity-checked. If plurality of valid path routes are established, the system provides, in addition to the valid cell detecting units, a virtual path identifier and virtual channel identifier comparing unit for comparing values of the VPI and VCI stored therein with values of a VPI and a VCI added to an arriving cell, and a path route validity check unit for partially or entirely validity-checking a path route in the ATM transmission system.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to en ATM (asynchronous transfer mode) 
transmission system for transmitting cell-formatted data in an 
asynchronous transfer mode, and more specifically to an ATM transmission 
system capable of conducting an online path route test to check easily the 
validity of a path route in a system. 
2. Description of the Related Art 
In a transmission system for transmitting data using ATM cells, data are 
contained in an ATM cell having a limed length of 53 bytes. The header of 
the ATM cell is provided with a virtual path identifier (VPI) and a 
virtual channel identifier (VCI) at its initial portion, and applied to a 
switching unit in the transmission system. In the transmission system, the 
data are switched using switching information corresponding to the values 
of the VPI and VCI, and then transmitted to a receiver of the data. 
In conducting a path route test on such an ATM transmission system, there 
has been a problem that it is very difficult to determine externally 
whether or not an ATM cell transmitted from a subscriber is being 
transmitted through a path specified by the software. Another problem with 
the conventional system is that a cell itself or a transmission error can 
be hardly located during the transmission at the debugging of the system. 
SUMMARY OF THE INVENTION 
The present invention aims at conducting an online test on a path route in 
an ATM cell transmission system for asynchronously transmitting cells 
during the actual system operation. 
According to the present invention, a valid cell detector for detecting the 
arrival of a valid cell, a VPI/VCI comparing unit for comparing values of 
VPIs and VCIs as explained later, and a path route validity check unit for 
validity-checking a path route are provided at an input portion and/or an 
output portion of an ATM switch for switching ATM cells, or provided at an 
optional point including the ATM switch in a plurality of path routes, for 
example at an input portion of an interface, multiplexer, demultiplexer, 
etc. Generally, a plurality of valid cell detectors, VPI/VCI comparing 
units, and path route validity check units are provided at a plurality of 
points in the path routes. For example, a path route test can be conducted 
about the validity between an input terminal unit and the input portion of 
the ATM switch, between the input portion of the ATM switch and the output 
portion of the demultiplexer provided at the output portion of the ATM 
switch. 
The valid cell detector receives a cell enable signal indicating that a 
valid cell has been sent and detects the arrival of the valid cell. The 
VPI/VCI comparing unit stores the values of a VPI and VCI added to n call 
to pass through it, compares them with those of the VPI and VCI added to 
the cell that has just arrived, and determines whether or not they match 
respectively. Furthermore, an AND gate as the path route validity check 
unit outputs, for example, "1" as a path route validity check result when 
the valid cell detector detects the arrival of a valid cell and the 
VPI/VCI comparing unit detects coincidences of values of the VPIs and 
VCIs. 
According to the present invention, the ATM transmission system further 
comprises at an optional point in the system a test cell generating device 
for sending a path route test cell in addition to the valid cell detector, 
the VPI/VCI comparing unit, and the path route validity check unit. With 
the configuration, tested is the validity of a path route between the 
position of the test cell generating device and any point in the path 
route using a rest cell. 
If only one path route is established in an ATM transmission system, then 
the path route can be validity-checked by simply detecting the arrival of 
a valid cell at any point in the path route. In this case, the path route 
can be validity-checked by providing a valid cell detector at any point in 
the path route. If a test cell generating device is provided at any point 
in the system, the path route can be validity-checked between the test 
cell generating device and the valid cell detector.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 is the block diagram showing the principle of the present invention. 
It illustrates the principle of a path route test performed by the ATM 
transmission system for transmitting cell-formatted data in an 
asynchronous transmission mode. 
By referring to FIG. 1, explained is an ATM transmission system 1 having a 
plurality of paths established therein. A valid cell detecting unit 2 can 
be, for example, a valid cell detector, and receives a cell enable signal 
indicating that a valid cell has been sent and detects the arrival of the 
valid cell. 
A VPI/VCI comparing unit 3 and a path route validity check unit 4 are 
provided at one or more points in a system together with the valid cell 
detecting unit 2. The VPI/VCI comparing unit 3 stores in, for example, a 
VPI/VCI table a set of a virtual path identifier (VPI) and a virtual 
channel identifier (VCI) added to a cell to be transmitted through the 
points at which these units are provided, and compares using a comparator 
the values of the VPI and VCI with those added to the cell which has just 
arrived and retrieved by, for example, the VPI/VCI monitor. The path route 
validity check unit 4 validity-checks a path route in a system when the 
valid cell detecting unit detects the arrival of a valid cell and the 
VPI/VCI comparing unit 3 detects a coincidental result about the values of 
the VPIs and VCIs. This unit can be, for example, an AND gate. 
If one path only is established in an ATM transmission system, only one set 
of values are determined, thereby requiring no comparison between the 
values, and a path route in the system can be validity-checked by 
providing valid cell detecting units 2 for detecting the arrival of a 
valid cell at one or more points in the ATM transmission system. 
The present invention conducts an online path route test in an ATM 
transmission system. Normally, if a plurality of paths are established in 
an ATM transmission system, then the VPI/VCI comparing unit 3 for 
comparing tile values of VPIs and VCIs and the path route validity check 
unit 4 are provided at any necessary points in the system in addition to 
the valid cell detecting unit 2 for detecting the arrival of a valid cell. 
A path route can be validity-checked to the point where the path route 
validity check unit 4 is positioned if a valid cell detector forming part 
of the valid cell detecting unit 2 receives a cell enable signal and 
detects the arrival of a valid cell, and the values of the VPI and VCI 
stored in the table in the VPI/VCI comparing, unit 3 and added to a cell 
to be transmitted coincide with those added to the cell which has just 
arrived. 
Furthermore, according to the present invention, for example, a test cell 
generating device for sending a path route test cell can be provided at an 
input portion of a transmission system so that a test cell having a value 
of a specific virtual channel identifier (VCI) can be sent and the path 
route can be validity-checked at each point through which the test cell 
passes. Furthermore, a bit stack can be monitored, that is, a fault in a 
bit line can be monitored, by using two test cells in which complements 
are set to each other as a VCI value. 
FIG. 2 is tile block diagram of the general configuration of the ATM 
transmission system. In FIG. 2, for example, data sent by a subscriber 10 
are multiplexed by a multiplexer 12 through a subscriber line equipment 
11, switched in an ATM cell format by a switch unit 13, and sent to a 
receiving subscriber 16 through a demultiplexer 14 and a subscriber line 
equipment 15. 
FIG. 3 is an explanatory view of a cell frame signal indicating the header 
portion of a cell and a cell enable signal indicating a valid or invalid 
cell. In FIG. 3, the dell enable signal indicates "L" for a valid cell, 
and "H" for an invalid cell. 
FIG. 4 is the block diagram showing the configuration of the valid cell 
detector for detecting the arrival of a valid cell. If one path only is 
established in the transmission system shown in FIG. 2, then a cell having 
a virtual path identifier (VPI) and a virtual channel identifier (VCI) 
specified for a line forming part of the path can be transmitted as a 
valid cell. In this case, the arrival of a valid cell can be detected at a 
point in the system through which the cell passes. For example, it can be 
detected in a subscriber line, an input/output portion of a switch unit, 
an output line, etc. 
The valid cell detector shown in FIG. 4 is provided at any point in the 
system, receives an inverse signal of a cell enable signal at a clock 
terminal of a flipflop 19 through an inverter 18, and detects the arrival 
of a valid cell. That is, a cell enable signal is 53 bytes in width (as 
wide as a cell), indicates "H" for a clock input value for a valid cell, 
thereby setting the flipflop 19. 
An LED is provided for each of a plurality of valid cell detectors so that 
the LED can be lighted when a valid cell arrives. An output of the valid 
cell detector can be sent to a software interface unit to send it as one 
piece of status data to the software. With the configuration, an output of 
the valid cell detector can be displayed, and a path route can be 
validity-checked without any additional measuring unit. 
In FIG. 4, when a plurality of valid cells arrive intermittently as shown 
in FIG. 3, FF19 is not reset in a cell unit because the present invention 
determines the penetrability of cells in a system, and only detects the 
arrival of cells. Therefore, for example, the LED of the system remains ON 
until the system is reset. 
In an ATM transmission system, a plurality of paths are normally 
established. In this case, a table for storing virtual path identifiers 
(VPI) and virtual channel identifiers (VCI) added to cells passing through 
any points in the system is provided so that a path route to each point 
can be validity-checked when a valid cell has arrived by comparing the 
contents of the table with the values of the VPI and VCI actually 
transmitted in the ATM cell. 
FIG. 5 is the block diagram showing the configuration of the path route 
test device. In FIG. 5, the path route test device comprises a VPI/VCI 
table 21 for storing the values of VPIs and VCIs added to cells to pass 
through the path route test device, a VPI/VCI monitor 22 for retrieving 
the values of the VPI and VCI from a cell which has arrived, a comparator 
23 for comparing the contents of the VPI/VCI table 21 with the retrieved 
values of a VPI and a VCI, a valid cell detector 24 for detecting the 
arrival of a valid cell, and an AND gate 25 for receiving outputs of the 
comparator 23 and the valid cell detector 24, and outputting a validity 
check result for a path route. The contents of the VPI/VCI table 21 are 
set according to the host-computer not shown in FIG. 5. 
Thus, even when a plurality of paths are established in a system, paths are 
tested one by one, and only one set of values are stored in the VPI/VCI 
table 21 in each test. When another path is tested, a VPI and a VCI are 
set correspondingly. 
In the present invention, for example, an input line of the system has 
abilities of generating a test cell different from a normal 
data-transmission cell, and the system receives a test cell having a 
specific VCI value, thereby performing a test on a path up to any output 
line. The VPI/VCI table 21 in the path route test device provided in an 
optional point in the path stores a set value of a VCI for use in the path 
route validity check. The value of the VCI can be preliminarily set 
corresponding to the system, or can be selected from the values not 
currently used by the software. 
Two values which are complements to each other can be used as values of the 
VCI. For example, the values can be 5555 (HEX) and AAAA. These values are 
valid when each byte, that is, eight bits, is transmitted in parallel, and 
are used in monitoring a fault of a bit stack, that is, a bit line. When a 
bit line is faulty, an output to a specific bit line is constantly fixed 
to "0" or "1" thus realizing a monitoring of a faulty bit, that is, a bit 
stack, using two VCIs which are complements to each other. 
FIG. 6 shows the circuit in which a cell enable signal is generated. The 
circuit is provided in all subscriber line equipments shown in FIG. 2. A 
cell frame signal (CF) is input to a shift register 26 and is output upon 
the fourth output thereof. Data of an input ATM cell is applied to 
flip-flop 27-1 and then sequentially input to flip-flop 27-2 to 27-4. The 
outputs of flip-flops 27-1 to 27-4, i.e. 28-bit data and input to an OR 
circuit 28. With regard to the flip-flop 27-1 only 4 upper bit are used 
because the total of the VPI comprising 12 bits and the VCI comprising 16 
bits is 28 bits. If the OR circuit 28 detects that the value of the 
VPI/VCI in the header of the input ATM cell is all "0", then the cell is 
determined to be invalid. Therefore, when the cell frame signal (CF) and 
data with the value of all "0" are inputted as shown 1 and 2, a cell 
enable signal designating an invalid cell is outputted from a flip-flop 
29. 
FIG. 7 is the block diagram showing the configuration of an embodiment of 
the broadband ISDN system according to the present invention. In FIG. 7, 
the system comprises, for example, a sending terminal adapter (TA1) 30, 
receiving terminal adapters (TA2, TA3) 36 and 44, subscriber line 
interfaces (SINF) 31, 35, and 43, multiplexers/demultiplexers (MDX) 32, 
34, 37, 40, and 42, a broadband remote switch unit (BRSU) 33, fiber loop 
interfaces (FINF) 38, and 39, and a central office switch 41. 
In FIG. 7, the path route test device shown in FIG. 5 is provided at the 
input portion of each device in the system if data are transmitted from 
the terminal adapter (TA1) 30, and a valid cell detector for detecting the 
arrival of a valid cell is provided if one path only is established in the 
system. 
If one path only is established from the terminal adapter 30 to terminal 
adapter 36, then each determination result of VCD at any of a, b, c, k, 
and l should indicate the arrival of a valid cell. Likewise, if one path 
only is established to terminal adapter 44, then VCDs at any of a, b, c, 
d, e, f, g, h, i, and j should indicate the arrival of a valid cell. 
In the former case, if the VCDs at k and l do not detect the arrival of a 
valid cell, then the switch 33 can have an internal fault or exact 
switching information cannot be provided by MDX 32. Then, these two 
factors should be checked. If the detector or the test device is not 
provided, then the only method of specifying a fault is to sequentially 
measuring input/output data of each device using an oscilloscope or a 
logic analyzer. 
Since a terminal adapter is often located apart from a main system, a test 
cell generating device should be provided in the subscriber line interface 
(SINF) or the fiber loop interface (FINF), thus successfully conducting a 
path test within a small area. 
For example, a test can be conducted only for a central office by 
generating a test cell from FINF 38. The central office in this embodiment 
includes FINF 39 through SINF 43. Simultaneously generating test cells by 
both FINF 38 and SINF 43 enables a determination to be made as to whether 
a fault has arisen in the direction from a BRSU to a CO or from a CO to a 
BRSU. A broadband remote station having a BRSU includes SINF 31 through 35 
and FINF 38. 
In an online path test, a path test using a test cell is conducted such 
that an invalid cell is detected where the test cell is generated and the 
invalid cell is replaced with the test cell. 
As described above, the present invention realizes a validity check of a 
path route and a monitor a bit stack through an online operation without a 
measuring unit, and enables a fault to be detected at its earlier stage 
even during a system test, thereby improving the reliability of a system 
and facilitating the maintenance of the system.