JPH10210513A - Private branch of digital exchange with isdn interface - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the private branch of digital exchange with ISDN interfaces by which connection affinity among a caller terminal and a network and a called terminal and the network is contemplated thereby improving the connection performance. SOLUTION: In the case of containing an H0 terminal 4 whose connection capability per call is based on a 64k (the unit in bps is omitted) connection unit, a fact of the 64k connection unit in terms of the connection capability is stored in advance in a storage area of a memory 21 corresponding to the H0 terminal 4. In the case of receiving a 384k setup message from an ISDN public network 1, a plurality of low speed channels are connected to establish the connection of a 384k connection channel by repeating the procedure to send a setup message based on the collation result between the information transmission speed extracted from the received message and the connection unit of a called terminal read from the memory 21 to the terminal of the H0 channel being a called destination and to connect low speed channels for a prescribed number by the processing by a connection control means of a CPU 22.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to an ISDN
(Integrated Services Digital Network), and on the other hand accommodates terminals that meet the ISDN communication protocol and connects with each other
With regard to an in-house digital exchange having N interfaces, in particular, it is possible to improve the connection affinity between a terminal and a network and to connect a call having a channel rate of an integral multiple of 64 kbps with a user / network interface channel type H in the ISDN communication protocol. The present invention relates to an intra-enterprise digital exchange having an ISDN interface.

[0002]

2. Description of the Related Art Conventionally, in an enterprise digital exchange having this kind of ISDN interface, an EPA shown in FIG.
BX (internal enterprise electronic exchange) 100 is an ISDN public network 1, a channel type H0 (a channel speed of 384 kbp).
s) H0 terminal 4, channel type H11 (channel speed 1536 kbps) H11 terminal 5, international standard facsimile type G4 G4 FAX (facsimile machine) 6, telephone terminal 7, and standard telephone 9 Cross-connect between the two.

[0003] The EPABX 100 is an ISDN public network IF (interface) 11 for connecting the ISDN public network 1.
1, an ISDN primary group IF 114 for connecting the H0 terminal 4,
ISDN primary group IF 115, G connecting H11 terminal 5
ISDN basic I connecting 4FAX6 and telephone terminal 7
F116 and a standard telephone IF 119 for connecting the standard telephone 9 are provided.

The EPABX 100 has a TDSW (time division switch) 117. The TDSW 117 is an ISDN.
Public network IF 111, ISDN primary group IF 114, 11
5, ISDN basic IF 116, and standard telephone IF
119 is connected and controlled by a control unit 122 that makes full use of data stored in a memory 121 via a bus.

[0005] In this configuration, for example, a technique aimed at enabling an incoming call to an optimal terminal even if the terminal is not strictly specified by the caller and thereby reducing the burden on the caller has been proposed, for example, It is described in JP-A-6-334756.

In the electronic exchange system described in this publicity bulletin, the called number, transfer mode, and information corresponding to each of the H0 terminal 4, H11 terminal 5, G4 FAX 6, telephone terminal 7, and standard telephone 9 connected to the EPABX 100. Predetermined management information indicating the transfer speed is stored in the circuit switching table and the packet switching table of the memory 121.

For an incoming call from the ISDN public network 1,
In PABX 100, control unit 122 recognizes each of the called number, transfer mode, and information transfer rate indicated in the incoming call by incoming call content identification procedure 123 and is stored in memory 121 as storage means by connection control procedure 124. Incoming call content identification procedure 12 with reference to the
3 selects a terminal corresponding to the called number, transfer mode, and information transfer rate recognized by the terminal 3, and terminates a call to the selected terminal.

[0008]

The above-mentioned conventional ISD
In an in-house digital exchange having N interfaces, the electronic exchange system described in the publication discloses a method of receiving an incoming call from an ISDN line to a plurality of terminals by receiving the call to an optimum terminal based on the called number and the received transmission capability information. I have.

[0009] In this configuration, since the function of receiving a call to the most suitable terminal is prioritized, it cannot be determined how effective the connection procedure between the terminal and the network is. And between the called terminal and the network lacks connection affinity.

In the ISDN interface,
If the connection of one call of the H type (channel type H) having an integral multiple of the channel speed of 64 kbps can be connected only at the channel speed of 64 kbps and this connection is possible between the terminal and the network, this channel Speed 64kb
A procedure that can connect one call of an integral multiple of ps needs to be supported, but if a terminal and a network that do not support this procedure are present in the electronic exchange system, the connection between the calling terminal and the network or There arises a problem that communication cannot be performed between the called terminal and the network due to a different connection procedure.

Specifically, when the channel speed is 384 kbp
When interfacing an ISDN interface having an H0 channel of s with a terminal having six B channels having a communication speed of 384 kbps but a channel speed of 64 kbps, the overall channel speed is the same, Since the individual channel speeds are different, a problem arises in that the communication procedures cannot be performed differently from each other.

An object of the present invention is to solve the above problems,
It is an object of the present invention to provide an intra-enterprise digital exchange having an ISDN interface capable of improving the connection between the calling terminal and the network and between the called terminal and the network and improving the connection.

[0013]

SUMMARY OF THE INVENTION An in-house digital switch with an ISDN interface according to the present invention comprises, on the one hand, an ISD
N (Integrated Services Digital Network) and ISDN on the other hand
In a corporate digital exchange that accommodates terminals that satisfy the communication protocol of the above and connects them to each other, the terminal that has a connection capability of one call in the primary interface of the user / network interface is based on a low-speed connection unit. ,
A memory for storing in advance a low-speed connection unit as a connection capacity in a storage area corresponding to a terminal to be accommodated, an information transfer rate extracted from this message when a message for an incoming call is received from a network, and A predetermined number of steps of matching the connection unit based on the connection capability of the called terminal read from the memory, transmitting a call setup message based on the result of the check to the called terminal, and connecting the low-speed channel,
Connection control means for forming and connecting a high-speed channel by connecting a plurality of low-speed channels.

According to this configuration, a communication channel can be set for a terminal that performs only processing for a low-speed channel type B irrespective of a high-speed channel type H. The connection affinity between the called terminal and the called terminal and the network can be improved, and the connectivity can be improved.

[0015]

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a functional block diagram showing an embodiment of the present invention. The EPABX 10 as an intra-enterprise digital exchange having the ISDN interface shown in FIG. 1 accommodates an ISDN public network 1, an ISDN private line network 2 and an inter-network public interface 3 on one side, and H0 terminals 4 and H on the other side.
Accommodates 11 terminals 5, G4 FAX 6 and telephone terminal 7,
Further, a maintenance console 8 is accommodated and cross-connected between them.

Here, the ISDN public network 1 is based on ITU-T.
TTC of the Telecommunication Standardization Sector of the International Telecommunication Union
(Telegraph and Telephone Technical Committee) Standard: Q931, Q921, I
431, and has an ISDN primary rate and a basic interface.
T standards: ISI1572, Q921, I431, and TTC standards: Q931-a, Q921-a, I431-
It has a multiplexing interface and a primary rate interface conforming to c. Furthermore, the public interface 3 between networks is based on ITU-T and TTC standards: Q703, Q704,
It has a primary rate interface channel type H11 (speed 1544 kbps) and channel type H12 (speed 2048 kbps) conforming to Q731.

On the other hand, the H0 terminal 4 or the H11 terminal 5
Used for TV (television) conference equipment, etc., each having a channel speed of 384 kbps or 1536 kbps, but having a channel speed of 64 kbps.
By having 6 or 24 channels, respectively, and connecting each B channel, 384 kbs or 1
An interface of 536 kbps shall be used.

The difference between the EPABX 10 and the conventional one is that the terminal has a channel speed of 6 as the connection capability of one call.
Even at 4 kbps, connection processing with a high-speed channel can be performed.

As shown in FIG. 1, the EPABX 10 includes an ISDN public network IF11 and an ISDN leased line IF1.
2. ISUP (ISDN user part) inter-network IF 13, IS
TDSW for accommodating, connecting, and cross-connecting the primary primary group IFs 14, 15 and the ISDN basic IF 16,
17, a maintenance console IF 18, a memory 21, and a CPU (central processing unit) 22 as connection control means.

The ISDN public network IF 11 is connected to the physical line IS.
An ISDN public line 1 is connected via a DN line, and an ISDN dedicated line IF 12 is connected via an ISDN line of a physical line or a high-speed digital line based on the TTC standard.
The ISUP inter-network IF 13 connects the inter-network public interface 3 to the TDSW 17 via a physical ISUP inter-network line and the CPU 22 via a bus.
Is exchanging information.

On the other hand, ISDN primary group IF 14 is H0 terminal 4, ISDN primary group IF 15 is H11 terminal 5, and ISDN basic IF 16 is G4 FAX 6 and telephone terminal 7.
Are respectively housed and connected to the TDSW 17 and exchange information with the CPU 22 via the bus. Further, the maintenance console IF 18 accommodates the maintenance console 8 and exchanges information with the CPU 22 via a bus.

The memory 21 has a circuit switching table 210 and a connection capacity execution number storage area 211. In the circuit switching table 210, the accommodation position of the called terminal is indexed from the called terminal information included in the received message. As shown in detail in FIG. 5, the connection capacity execution number storage area 211 stores in advance the connection capacity value of the terminal accommodated corresponding to the accommodation position of each terminal and stores the connection execution number in units of 64 kbps. It is assumed that there is a storage area.

The CPU 22 executes management of event fetching and execution, protocol control, and connection control procedures based on information transmitted and received by connecting to each of the above-described components via a bus, and controls the functional operation of the EPABX 10. .

The ISDN public network IF11, ISDN
Dedicated line IF 12, ISUP inter-network IF, ISDN primary group I
As shown in FIG. 2, each of the interface packages F14 and F15 has a 23B + D channel group and a 24B channel group. The 23B + D group side D channel (control channel: carrying call control information) has a 24B channel group. The side B channel is controlled.

The 1B channel has a transmission rate of 64 kbps, and when dynamically connecting the H-system connection, 6
4 kbps (B channel) line n is connected.
In this case, the interface ID = 0 for the H0 call 2
3B + D or 24B with interface ID = 1
Are connected, and in the case of the H11 call, all 24 B channels having the interface ID = 1 are connected.

Also, as shown in FIG. 3, the H0 terminal 4 has an interface composed of six B channels and has a communication speed of 384 kbps as a whole, but one call communicates with only one B channel, that is, 64 kbps. Cannot be performed.

Next, FIG. 4A shows the EPABX of FIG.
Information elements included in a layer 3 call setup message in a user / network interface conforming to TTC standards Q931 and Q931-a are shown as information transmitted and received by the terminal 10 and the network. The message format includes a call number information element, a message type, channel identifier information, various number information such as a caller number and a called number corresponding to the octet line, and the transmission capability information includes the content. Length, information transfer capability, and information transfer speed, and the information transfer speed further includes 64 kbps, 384 kb.
ps and 1.5 Mbps are included.

FIG. 4B shows information elements included in a level 4 address message in an inter-network interface conforming to the TTC standard Q731 as information transmitted and received by the EPABX 10 of FIG. 1 between networks. The message format includes the point code, line number, message code, connection characteristic display, forward call display, originating user type, call path request, number information, etc., corresponding to the octet line. The information communication path request as a transmission capability includes 64 kbps, 384 kbps,
It is assumed that channel speeds of 1.5 Mbps and 2 Mbps are included.

Next, it is assumed that the connection capacity execution number storage area 211 shown in FIG. 5 has an interface number memory 212 and a connection capacity instruction memory 213.

Interface face number memory 212
Has an interface number area corresponding to the accommodation position information of each interface (IF).
It is assumed that whether or not the terminal and the network accommodated in 10 have the information transfer speed connectable by one call under the control of the layer 3 of the user / network interface.

The connection capacity instruction memory 213 stores a connection capacity value and 64 kb corresponding to the interface number.
It is assumed that each region has a connection execution number in ps units. In the connection capacity value area, “valid for all connection speed capacities”, “only 64 kbps (channel type B) connection is possible”, “384 kbps (channel type H)
It is assumed that codes corresponding to the conditions of “only connection 0) is possible” and “only 1.5 Mbps (channel type H11) can be connected” are registered in advance from the maintenance console 8. Also, it is assumed that a numerical value indicating how many connections in 64 kbps units have been executed is recorded by the CPU 22 in the connection execution number area in 64 kbps units.

Next, FIG. 6 shows an example of a sequence in which the EPABX 10 checks the connection capability of the connection destination.

In the example shown in FIG. 6, the I shown in FIG.
ISDN public network IF11, ISDN leased line IF12, ISUP network I
When a physical line is connected to each of F13, ISDN primary group IFs 14, 15 and ISDN basic IF 16, EP
ABX 10 indicates a data communication band of 384 kbps or more via the package of each ISDN interface.
For example, the TTC is sent to the ISDN public network 1 and the H-system terminal 4.
The connection unit is inquired by the connection capability confirmation instruction of the facility message conforming to the standard I431.

The ISDN public network 1 or the H-system terminal 4 that has received the inquiry returns the information transfer rate that can be connected in one call as a facility message in response information for confirming the connection capability.

If the network or the terminal cannot return the information of the connection capability confirmation, that is, does not have a return procedure, the interface number having the corresponding connection capability in the connection capability value storage area of the connection capability execution number storage area 211 is: The network or terminal is registered in the interface number memory 212 in advance from the maintenance console 8 and can operate.

It is assumed that the connection capability is an information transfer speed that can be connected by one call corresponding to the interface package shown in FIG.

For example, the information that the H0 terminal 4 has a data communication speed of 386 kbps unit, but the connection in one call has only the function of only 64 kbps unit is registered in the memory corresponding to the interface. The registration is performed in the connection capacity value storage area of the connection capacity instruction memory 213 in relation to the interface number memory 212 and the connection capacity instruction memory 213.

Next, referring to FIG. 1 and FIGS. 7 to 9 together, the message sequence of the layer 3 (FIG. 7) which is the procedure of the TTC standard Q931 of the ISDN interface and the operation procedure of the EPABX 10 (FIGS. 8 and 9) ) Will be described.

The H0 terminal 4 shown in FIG.
has a channel speed of 64 kbps, but has six channels of a speed of 64 kbps.
It is assumed that the control terminal has only s units. Procedure A in FIG.
8 is included in FIG. 8, and procedure B is included in FIG.

First, in the EPABX 10, the ISDN public network IF 11 transmits the channel type H from the ISDN public network 1.
A call setup message with a channel speed of 384 kbps is accepted (procedure S1 in FIG. 8), and execution of procedure A in FIG. 7 is started.

In FIG. 8, in the EPABX 10, the call setup message (format of FIG. 4A) accepted by the ISDN public network IF 11 in step S1 is sent to the CPU 22 via the bus. The CPU 22 receives the call setting message and temporarily stores the incoming call event information in the memory 21 by an event fetching process.

Thereafter, the CPU 22 performs a protocol control process on the received information element. In the protocol control process, each information element shown in FIG. 4 is written into the memory 21 for each of the received interface package accommodation positions, and then the CPU 22 enters a connection control procedure process.

The CPU 22 extracts the information transfer speed from the transmission capability information of the information element included in the received call setting message (see FIG. 4) (procedure S2). In the case shown in FIG. 7, 384 kbps is extracted as the information transfer speed (NO in step S3).

The CPU 22 reads the called number information included in the received call setting message and the maintenance console 8 from the memory 21.
Number registered in advance in the circuit switching table 210
The route number information and the accommodation position information of the ISDN primary group IF 14 connecting the H0 terminal 4 are obtained from the signal development information (step S4).

Next, the CPU 22 executes the connection capacity execution area 211 of the memory 21 based on the read accommodation position information.
The interface number is read from the interface number memory 212 (see FIG. 5), and then the connection capability information is derived from the connection capability instruction memory 213 (step S5).

The CPU 22 compares the derived connection capability information with the information transfer speed included in the received call setup message, and starts a connection procedure according to the connection capability of the calling / receiving terminal. In the case of the example shown in FIG.
H0 terminal 4 is 64 kbp for the information transfer rate of bps
Because of the connection capability of only s, the transmission speed does not match and the connection procedure does not match (procedure A6).

Here, the CPU 22 sends the call setting acceptance message by the event sending process to the ISDN public network IF11.
Is returned to the ISDN public network 1 via the ISDN public network 1, while the 384 kbps channel call setup message received from the ISDN public network 1 is converted into a 64 kbps channel call setup message via the ISDN primary group IF 14, 6.
At the beginning of the unit of 4 kbps, the first call shown in FIG. 7, that is, the call setup message which is the connection of the first channel is transmitted to the H0 terminal 4 (procedure S7).

At this time, the CPU 22 stores the transmitted call number information in a storage area of the memory 21 corresponding to the accommodation position of the ISDN primary group IF 14 that has transmitted the event.

When the information transmission speed in step S3 is 64 kbps, a predetermined processing procedure for the B-system channel of channel type B by the basic interface is performed (procedure S11). In addition, the procedure S6 is performed in the
In the case of the channel type H using the normal primary group interface, a predetermined processing procedure for the H-system channel is performed (procedure S12).

Next, the procedure B after the response message of the first connection arrives at the EPABX 10 from the H0 terminal 4 in FIG. 7 will be described with reference to FIG. 9 and FIG.

In the EPABX10, the ISDN primary group IF
14 first receives a response message of the first connection returned from the H0 terminal 4 having a connection unit of 64 kbps (procedure S21), and notifies the CPU 22 that there is an event.

The CPU 22 fetches the event information of the ISDN primary group IF 14 using the event fetching program and stores it in the work area of the memory 21. The CPU 22 operates a protocol control process, reads out the call number stored in the memory 21 from the accommodation position information where the event has occurred, determines the identity of the current event, and in the case of a response message by the same call, The processing shifts to the connection control procedure.

The CPU 22 checks the connection capability preset in the connection capability execution number storage area 211 for the called H0 terminal 4 (procedure S22), and recognizes the connection capability of only 64 kbps (procedure). YES at S23), IS
64 kbps B channel and I of the DN 11
The TDSW 17 connects the SDN primary group IF 14 to the 64 kbps B channel (step S24), and sends a response confirmation message to the H0 terminal 4 via the ISDN primary group IF 14 (step S25).

At this time, the CPU 22 counts the number of times of connection of the B channel in units of 64 kbps (step S26), and stores it in a predetermined area of the connection capacity instruction memory 213 included in the connection capacity execution number storage area 211.

The number of connections in units of 64 kbps is ISD
Before reaching 384 kbps (sixth time) received from the N public network 1 (NO in step S27), the CPU 22 activates an event sending program and sends the call setting message for the next connection in FIG. Since the response message is transmitted to the H0 terminal 4 via the H0 terminal 4 (procedure S28) and the returned response message is received from the H0 terminal 4 (procedure S29), the procedure returns to the step S25, and the response confirmation message of this time is transmitted to the HO terminal 4. .

The above steps S25 to S29 are repeated, and when step S27 is the last connection for the sixth time, the CPU 22 sends the last call setting message to the H0 terminal (step S31). Next, a response message returned from the H0 terminal is received (step S32).

Next, as shown in FIG. 7, the CPU 22 sends a response message to the ISDN public network 1 via the ISDN public network IF 11 to form a communication busy state, and transmits a response confirmation message to the ISDN primary group IF 14 Via the H0 terminal 4. The CPU 22 returns a response confirmation message to the
It is received from the ISDN public network 1 via the SDN public network IF11.

If it is determined in step S23 that the connection capability is the channel type H, the CPU 22 performs a predetermined processing procedure for the H system channel (step S30).

In this way, by connecting the six B channels of the H0 terminal 4 to the ISDN primary rate interface 14, communication between the H0 terminal 4 and the ISDN public network 1 can be performed.

The EPABX 10 that has completed the communication and received the disconnection message from the ISDN public network 1 releases the connection in the above sequence and procedure, performs procedure A in procedure C, procedure B in procedure D, and disconnection message in the call setup message. The response message is replaced with a release message, and the response confirmation message is replaced with a release completion message.

Further, as shown in FIG.
X10 is 384 kbps from inter-network public interface 3
In the above description, the procedures A, B, C, and D correspond to the procedures E, F, G, H,
The 384 kbps call setting message is an address message, the call setting accepting message is an address completion message,
Also, the disconnection message of 384 kbps is read as a release message and executed.

However, the procedure H sends a release completion message from the EPABX 10 to the inter-network public interface 3 and ends the procedure.

In the above description, only the H0 terminal has been described, but other H-system terminals or even higher transmission speeds can be processed in the same manner as long as the channel facilities are prepared. Further, if the communication speed is within the channel speed defined in the ISDN communication protocol, for example, a communication speed that satisfies an integer (n) times 64 kbps, communication can be started using the channel effectively by n 64 kbps unit connections. .

As described above, according to the present invention, regardless of the high-speed channel type H, the low-speed channel type B
A communication channel can be set for a terminal that performs only processing.

[0066]

As described above, according to the present invention, an H-system terminal in which the connection capability for one call in the primary interface among user / network interfaces is based on a low-speed 64 kbps connection unit is accommodated. In the case, the storage area corresponding to the accommodating H-system terminal is provided with a memory for storing in advance that the connection capacity is a low-speed 64 kbps connection unit as a connection capacity, and when the connection control means receives a message for an incoming call from the network, The information transfer rate retrieved from this message is compared with the connection unit based on the connection capability of the called terminal read from the memory, and a call setup message based on the result of the comparison is sent to the H-system terminal of the called party to lower the call setting message. Speed 64kbp
The procedure for connecting the s channel is repeated a predetermined number of times, and by connecting a plurality of low-speed 64 kbps channels, for example, an in-house digital exchange that forms and connects a high-speed 364 kbps channel is obtained.

With this configuration, it is possible to obtain an effect that a communication channel can be set even for a terminal that performs only the processing of the low-speed channel type B irrespective of the high-speed channel type H.

[Brief description of the drawings]

FIG. 1 is a system configuration diagram showing an embodiment of the present invention.

FIG. 2 is a diagram showing a primary group interface package.

FIG. 3 is a diagram showing a connection between an EPABX and an H0 terminal and a flow of data.

FIG. 4 is a layout diagram showing one main element of message information in the ISDN communication protocol.

FIG. 5 is an explanatory diagram of a storage area showing one configuration of a main part in the memory of FIG. 1;

FIG. 6 is a sequence chart showing one mode of sending and receiving a facility message according to the present invention.

FIG. 7 is a sequence chart showing one form of a transmission / reception message from a call setup between a user and a terminal to a line release according to the present invention.

FIG. 8 is a flowchart showing one form of a procedure A in FIG. 5;

FIG. 9 is a flowchart showing one mode of a procedure B in FIG. 5;

FIG. 10 is a sequence chart showing one form of a transmission / reception message from an address message to a line release of the internetwork public interface according to the present invention.

FIG. 11 is a system configuration diagram showing an example of the related art.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ISDN public network 2 ISDN leased line network 3 Public network interface 4 H0 terminal 5 H11 terminal 6 G4 FAX (facsimile machine) 7 Telephone terminal 8 Maintenance console 10 EPABX (internal enterprise automatic exchange) 11 ISDN public network IF (interface) 12 ISDN leased line IF (interface) 13 ISUP (ISDN user unit) inter-network IF (interface) 14, 15 ISDN primary group IF (interface) 16 ISDN basic IF (interface) 17 TDSW (time division switch) 18 Maintenance console IF 21 Memory 22 CPU (central processing unit)

Claims (3)

[Claims] 1. An in-house digital exchange having an ISDN (Integrated Services Digital Network) on the one hand and an ISDN interface on the other hand for accommodating terminals that meet the ISDN communication protocol and interconnecting them with each other. If the connection capability in one call in the group interface accommodates terminals based on low-speed connection units,
A memory for storing in advance a low-speed connection unit as a connection capacity in a storage area corresponding to a terminal to be accommodated, an information transfer rate extracted from this message when a message for an incoming call is received from a network, and A predetermined number of steps of matching the connection unit based on the connection capability of the called terminal read from the memory, transmitting a call setup message based on the result of the check to the called terminal, and connecting the low-speed channel,
Connection control means for forming and connecting a high-speed channel by connecting a plurality of low-speed channels.
In-house digital exchange with SDN interface. 2. The connection capability instruction memory according to claim 1, wherein the memory defines a connection capability value, which is an information transfer rate that can be connected by one call, and the number of connections in the connection unit for each interface number. And an interface number memory for defining the interface number for each accommodation position information for the terminal / network. 3. The channel speed according to claim 1, wherein the connection unit is a channel type B channel speed of 64 kb in a basic interface according to ISDN communication protocol.
In-house digital exchange having an ISDN interface characterized by ps.