CA1078947A - Packet switching system - Google Patents
Packet switching systemInfo
- Publication number
- CA1078947A CA1078947A CA246,310A CA246310A CA1078947A CA 1078947 A CA1078947 A CA 1078947A CA 246310 A CA246310 A CA 246310A CA 1078947 A CA1078947 A CA 1078947A
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- Canada
- Prior art keywords
- terminal
- packet
- frame
- address
- switching
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L9/00—Cryptographic mechanisms or cryptographic arrangements for secret or secure communications; Network security protocols
- H04L9/40—Network security protocols
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- Engineering & Computer Science (AREA)
- Computer Security & Cryptography (AREA)
- Computer Networks & Wireless Communication (AREA)
- Signal Processing (AREA)
- Data Exchanges In Wide-Area Networks (AREA)
Abstract
A PACKET SWITCHING SYSTEM
ABSTRACT OF THE DISCLOSURE
In a packet switching system having at least a character terminal, a receiving terminal, and a subscriber switching station, the character terminal first forwards an information including the address of the receiving station, according to the transmission control procedure of a data transfer phase, and receives the acknowledgement signal according to the transmission control procedure from the subscriber switching station as a response from the receiving terminal. Then, the pair of terminals begins to communicate with each other. Each terminal can have his own transmission control procedure, thus the format of said acknowledgement signal depends upon a terminal.
Thus, the prior connection-establishing procedure requested for a prior character terminal is considerably simplified.
ABSTRACT OF THE DISCLOSURE
In a packet switching system having at least a character terminal, a receiving terminal, and a subscriber switching station, the character terminal first forwards an information including the address of the receiving station, according to the transmission control procedure of a data transfer phase, and receives the acknowledgement signal according to the transmission control procedure from the subscriber switching station as a response from the receiving terminal. Then, the pair of terminals begins to communicate with each other. Each terminal can have his own transmission control procedure, thus the format of said acknowledgement signal depends upon a terminal.
Thus, the prior connection-establishing procedure requested for a prior character terminal is considerably simplified.
Description
107894'7 The present invention relates to a packet exchange system in a data communication system, and in particular re-lates to the system for establishing the address of a receiving terminal in a packet switching network.
In a data communication system, a process of data communication consists of a sequence of phases, for example, the phase of connection o~er a general switch network, the phase of establishment of a data link, the phase of information transfer, the phase of termination, and the phase of clearing of general the switch network, as internationally standardized in the bulletin of the International Organization for Standar- ;
dization, by International Standard ISO 1745-1975 (E).
In data exchange networks, there is an ever increasing demand for higher speed, higher reliability, wider variety of services, and broader service areas. To meet such a demand, at l~ast three switching systems have been known, (a) a circuit switching system, (b) a message switching system or a store-and-forward system, and (c) a packet switching system. me circuit switching system directly connects a pair of subscribers (a calling subscriber and a called subscriber) and is utilized in the world-wide telex system. In the message switching system, a called subscriber is not directly connected to a calling sub-scriber, but a message from a calling subscriber is temporarily stored in a switching station and a stored message is forwarded to a called subscriber. A packet switching system is a combi-nation of a circuit switching system and a message switching system. In a packet switching system, data or information from a subscriber is arranged to form one or more data unit, called "a packet", to be handled by the network. A called subscriber is not connected directly to a calling subscriber, although the former is logically connected to the latter. In a packet .~ ~
~078947 switching system, all data or packets from a calling subscriber and/or a called subscriber are temporarily stored in a switch-ing station and are forwarded to a receiving terminal.
The packet switching network originally used a connection-control system, in which physical data links bet-ween calling terminals and called terminals, such as those in circuit switching networks, are not established, but call-packets and response-packets that do not include information are exchanged between the calling and called terminals, so as to establish logical data links in the switching network through which the information is transmitted. Once the logical data links are established, the information alone can be transmitted and received. The International Telegraph & Telephone Consul-tative Committee's (C. C. I. T. T.) recommendations, X20 and X21, are two international standards concerning a packet switch-ing system.
According to the prior packet switching system in-cluding a character terminal, the logical data link is estab-lished in the following manner. First, a calling terminal originates a call to a subscriber switching station, which re-turns to the calling terminal a permission signal. Then, the calling terminal sends the address information of the called terminal to the switching network~ The format of the address information is that the address information is inserted between a pair of symbols "-" and ~+~O When the address information is correctly received by the called subscriber, an acknowledgement signal (connect-through (CT) signal) is sent to the calling terminal. Then, the calling subscriber begins to send a data, whose format is, for instance that a pair of symbols, STX
(Start of Text) and ETB (End of Transmission Block), sandwiches a data.
Later, another method was contrived for establishing logical data links while disposing information within call-packets and response packets, based on the fact that a connec-tion-establishing phase and information-transferring phase can be simultaneously executed in the packet switching network be-cause the network takes part in the information-transferring phase, too. This method can be easily applied to packet ter-minals, but is difficult to apply to character terminals.
A packet terminal is defined as a terminal which can dissolve and assemble packets, control the sequence of packets, and handle a plurality of logical data links. A character terminal is defined as a terminal which can handle only one logical data link at a time as seen from the network and is used in a conventional circuit switching system or a leased circuit and operates in the conventional transmission control procedure. At the character terminals, the simultaneous execu- `;~
tion of the connection-establishment phase and the data-trans-ferring phase is not contemplated at the same time, since a separate control unit (for instance, a dialing facility) is provided in the character terminal for the connection-establish-ment. Thus, a prior character terminal have the following shortcomings.
(1) Since the control unit for connection-establish-ment is necossary, the terminal is complicated. Said control unit must at least function to send a dial signal inserted between a pair of symbols "-" and "+", and to process a fixed pattern of a permission signal, and a connect-through (CT) signal.
In a data communication system, a process of data communication consists of a sequence of phases, for example, the phase of connection o~er a general switch network, the phase of establishment of a data link, the phase of information transfer, the phase of termination, and the phase of clearing of general the switch network, as internationally standardized in the bulletin of the International Organization for Standar- ;
dization, by International Standard ISO 1745-1975 (E).
In data exchange networks, there is an ever increasing demand for higher speed, higher reliability, wider variety of services, and broader service areas. To meet such a demand, at l~ast three switching systems have been known, (a) a circuit switching system, (b) a message switching system or a store-and-forward system, and (c) a packet switching system. me circuit switching system directly connects a pair of subscribers (a calling subscriber and a called subscriber) and is utilized in the world-wide telex system. In the message switching system, a called subscriber is not directly connected to a calling sub-scriber, but a message from a calling subscriber is temporarily stored in a switching station and a stored message is forwarded to a called subscriber. A packet switching system is a combi-nation of a circuit switching system and a message switching system. In a packet switching system, data or information from a subscriber is arranged to form one or more data unit, called "a packet", to be handled by the network. A called subscriber is not connected directly to a calling subscriber, although the former is logically connected to the latter. In a packet .~ ~
~078947 switching system, all data or packets from a calling subscriber and/or a called subscriber are temporarily stored in a switch-ing station and are forwarded to a receiving terminal.
The packet switching network originally used a connection-control system, in which physical data links bet-ween calling terminals and called terminals, such as those in circuit switching networks, are not established, but call-packets and response-packets that do not include information are exchanged between the calling and called terminals, so as to establish logical data links in the switching network through which the information is transmitted. Once the logical data links are established, the information alone can be transmitted and received. The International Telegraph & Telephone Consul-tative Committee's (C. C. I. T. T.) recommendations, X20 and X21, are two international standards concerning a packet switch-ing system.
According to the prior packet switching system in-cluding a character terminal, the logical data link is estab-lished in the following manner. First, a calling terminal originates a call to a subscriber switching station, which re-turns to the calling terminal a permission signal. Then, the calling terminal sends the address information of the called terminal to the switching network~ The format of the address information is that the address information is inserted between a pair of symbols "-" and ~+~O When the address information is correctly received by the called subscriber, an acknowledgement signal (connect-through (CT) signal) is sent to the calling terminal. Then, the calling subscriber begins to send a data, whose format is, for instance that a pair of symbols, STX
(Start of Text) and ETB (End of Transmission Block), sandwiches a data.
Later, another method was contrived for establishing logical data links while disposing information within call-packets and response packets, based on the fact that a connec-tion-establishing phase and information-transferring phase can be simultaneously executed in the packet switching network be-cause the network takes part in the information-transferring phase, too. This method can be easily applied to packet ter-minals, but is difficult to apply to character terminals.
A packet terminal is defined as a terminal which can dissolve and assemble packets, control the sequence of packets, and handle a plurality of logical data links. A character terminal is defined as a terminal which can handle only one logical data link at a time as seen from the network and is used in a conventional circuit switching system or a leased circuit and operates in the conventional transmission control procedure. At the character terminals, the simultaneous execu- `;~
tion of the connection-establishment phase and the data-trans-ferring phase is not contemplated at the same time, since a separate control unit (for instance, a dialing facility) is provided in the character terminal for the connection-establish-ment. Thus, a prior character terminal have the following shortcomings.
(1) Since the control unit for connection-establish-ment is necossary, the terminal is complicated. Said control unit must at least function to send a dial signal inserted between a pair of symbols "-" and "+", and to process a fixed pattern of a permission signal, and a connect-through (CT) signal.
(2) Call-establishing time is long, because the information-transfer becomes possible only after a calling signal and a selection signal are transmitted and a connect-through (CT) signal is received from the switching network.
i 1078~47
i 1078~47
(3) Due to the last mentioned shortcoming (2), when a short telegram message is transmitted, the connection-establishing process is more prominent than the data-transfer-ring process in the processing at the switching network.
(4) A great deal of signal exchange takes place between a character terminal executing communication and the switching network, so that the operation of the character ter-minal becomes complicated.
It is an object, therefore, of the present invention to overcome the disadvantages and the limitations of a prior packet switching system by providing a new and improved packet switching system.
It is also an object of the present invention to provide a new and improved character terminal and a subscriber exchange for the present packet switching system.
The basic concept of the present invention is that, in a character terminal, a prior means for connection-establish-ment is removed, and the connection-establishment and/or the line-release is performed according to the transmission control procedure of an information transfer phase.
The above and other objects are attained by a packet switching system having at least a character terminal and a subscriber switching station and a receiving terminal, compri-sing the steps of forwarding an information frame including the address of a receiving station according to the transmission control procedure of an information transfer phase from the character terminal to the receiving terminal via the subscriber switching station, forwarding a response packet from the re-ceiving terminal to the switching station, and returning an acknowledgement signal according to the transmission control procedure of an information transmission phase from the sub-scriber switching station to the character terminal when the switching station acknowledges receipt of the response packet from the receiving terminal.
According to a further broad aspect of the present invention, there is provided a method for controlling a packet switching system having at least a character terminal, a sub-scriber switching station and a receiving terminal. The method comprises the steps of forwarding an information frame including the address of a receiving station according to the transmission control procedure of an information transfer phase from the character terminal to the receiving terminal via the subscriber switching station, forwarding a response packet from the receiv-ing terminal to the switching station, and returning an acknow-ledyement signal according to the transmission control procedure of an information transfer phase from the subscriber switching station to the character terminal when the switching station acknowledges receipt of the response packet from the receiving terminal.
According to a further broad aspect of the invention, there is provided a subscriber switching station in a packet switching system, including a line and a terminal. The switch-ing station comprises a frame receiver, an address registration circuit for storing a frame of address information, a packet -transmitter for transmitting a packet to the line from one of the address registration circuit and the frame receiver, a packet receiver for forwarding a packet from the line to the address registration circuit, an acknowledgement transmitter for sending an acknowledgement signal to the terminal, further characterized by comprising a first switching means responsive to the address registration circuit for transferring a signal from the frame receiver to one of the address registration cir-cuit and the packet transmitter and a second switch means res-ponsive to the address registration circuit for switching between ~078947 the frame receiver and the acknowledgement transmitter.
The foregoing and other objects, features and atten-dant advantages of the present invention will be appreciated as the same become better understood by means of the following description and the accompanying drawings wherein:
Fig. 1 is a block diagram, showing the structure of a packet switching network, Fig. 2 shows some examples of a format of a set of frames sent from a character terminal according to the present invention, Fig. 3 is a diagrammatic illustration of an example, in which connection-establishment is executed by using the transmission-control procedure of an information transfer phase, Fig. 4 is a diagrammatic illustration of an example, which is similar to that of Fig. 3, except that the connection-establishment and the information-transfer are simultaneously executed, Fig. 5 is a diagrammatic illustration of an example, which is similar to that of Fig. 4, except that a response signal includes information, Fig. 6 is a diagrammatic illustration of an example, in which operations from the connection-establishment until -~
the connection-release are simultaneously executed, and, Fig. 7 is a block-diagram showing the structure of a character terminal and a subscriber switching station.
Fig. 1 illustrates an example of packet switching net-works, to which the present invention can be applied. The packet switching network consists of subscriber switching stations B (Bl, B2) to which subscriber terminals (character terminals and packet terminals) A (Al, A2) are connected, and relay stations C (Cl, C2, C3) relaying packets, for executing the transfer through the network by selecting an optimal transfer , ~
path for each packet.
There are two types of packet switching networks, namely, packet switching networks in which logical data links are established, and other packet switching networks in which no logical data links are established. An example of the former type packet switching networks with the logical data links will now be described.
It is assumed in this specification that the terminal Al is a character terminal, the terminal A2 is a packet terminal, and the call is originated at the terminal Al.
Fig. 2 shows some examples of the format of a set of frames produced by the character terminal Al.
The information has in the present embodiment a STX symbol (Start of Text), an ETB symbol (End of Transmission Block), and a message frame, between the pair of symbols. The message frame can be (A) a selection frame (SEL) which is the ' address of the called terminal, (B) a data frame (DATA) trans-mitted between a pair of terminals, (C) a release frame (REL) for releasing the line, (D) a selection frame and a data frame, and (E~ a selection frame, a data frame, and a release frame.
Since each character terminal can have his own trans-mission control procedure, the format of a frame depends upon each terminal, and any format except Fig. 2 is of course possible. For instance, a transmission control procedure which has no STX or no ETB is possible. So Fig. 2 is the mere embodiment for the simplicity of the explanation.
Fig. 3 illustrates the manner in which a selection signal is transmitted by applying the transmission-control procedure of an information-transfer phase to a connection-establishing phase, as will be explained below in a step-by-step fashion.
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(1) The character terminal Al initiates a call, as indicated by the arrow (a).
(2) Upon detecting the initiated call (a), the subscriber switching station Bl sends an input~permitting signal (b) to the calling terminaL A .
(3) The thus call-acknowledged character terminal A
sends a selection frame SEL (the address of a called terminal) to the subscriber switching station Bl, which selection frame is in the same frame structure as that of the transmission-control procedure of the information transfer phase. The format of said selection frame is shown in Fig. 2(A).
(4) The subscriber switching station Bl sends the address packet ADR representing the called terminal A2 to that subscriber switching station B2 to which the called terminal A2 is connected, through relay stations Cl and C2.
It is an object, therefore, of the present invention to overcome the disadvantages and the limitations of a prior packet switching system by providing a new and improved packet switching system.
It is also an object of the present invention to provide a new and improved character terminal and a subscriber exchange for the present packet switching system.
The basic concept of the present invention is that, in a character terminal, a prior means for connection-establish-ment is removed, and the connection-establishment and/or the line-release is performed according to the transmission control procedure of an information transfer phase.
The above and other objects are attained by a packet switching system having at least a character terminal and a subscriber switching station and a receiving terminal, compri-sing the steps of forwarding an information frame including the address of a receiving station according to the transmission control procedure of an information transfer phase from the character terminal to the receiving terminal via the subscriber switching station, forwarding a response packet from the re-ceiving terminal to the switching station, and returning an acknowledgement signal according to the transmission control procedure of an information transmission phase from the sub-scriber switching station to the character terminal when the switching station acknowledges receipt of the response packet from the receiving terminal.
According to a further broad aspect of the present invention, there is provided a method for controlling a packet switching system having at least a character terminal, a sub-scriber switching station and a receiving terminal. The method comprises the steps of forwarding an information frame including the address of a receiving station according to the transmission control procedure of an information transfer phase from the character terminal to the receiving terminal via the subscriber switching station, forwarding a response packet from the receiv-ing terminal to the switching station, and returning an acknow-ledyement signal according to the transmission control procedure of an information transfer phase from the subscriber switching station to the character terminal when the switching station acknowledges receipt of the response packet from the receiving terminal.
According to a further broad aspect of the invention, there is provided a subscriber switching station in a packet switching system, including a line and a terminal. The switch-ing station comprises a frame receiver, an address registration circuit for storing a frame of address information, a packet -transmitter for transmitting a packet to the line from one of the address registration circuit and the frame receiver, a packet receiver for forwarding a packet from the line to the address registration circuit, an acknowledgement transmitter for sending an acknowledgement signal to the terminal, further characterized by comprising a first switching means responsive to the address registration circuit for transferring a signal from the frame receiver to one of the address registration cir-cuit and the packet transmitter and a second switch means res-ponsive to the address registration circuit for switching between ~078947 the frame receiver and the acknowledgement transmitter.
The foregoing and other objects, features and atten-dant advantages of the present invention will be appreciated as the same become better understood by means of the following description and the accompanying drawings wherein:
Fig. 1 is a block diagram, showing the structure of a packet switching network, Fig. 2 shows some examples of a format of a set of frames sent from a character terminal according to the present invention, Fig. 3 is a diagrammatic illustration of an example, in which connection-establishment is executed by using the transmission-control procedure of an information transfer phase, Fig. 4 is a diagrammatic illustration of an example, which is similar to that of Fig. 3, except that the connection-establishment and the information-transfer are simultaneously executed, Fig. 5 is a diagrammatic illustration of an example, which is similar to that of Fig. 4, except that a response signal includes information, Fig. 6 is a diagrammatic illustration of an example, in which operations from the connection-establishment until -~
the connection-release are simultaneously executed, and, Fig. 7 is a block-diagram showing the structure of a character terminal and a subscriber switching station.
Fig. 1 illustrates an example of packet switching net-works, to which the present invention can be applied. The packet switching network consists of subscriber switching stations B (Bl, B2) to which subscriber terminals (character terminals and packet terminals) A (Al, A2) are connected, and relay stations C (Cl, C2, C3) relaying packets, for executing the transfer through the network by selecting an optimal transfer , ~
path for each packet.
There are two types of packet switching networks, namely, packet switching networks in which logical data links are established, and other packet switching networks in which no logical data links are established. An example of the former type packet switching networks with the logical data links will now be described.
It is assumed in this specification that the terminal Al is a character terminal, the terminal A2 is a packet terminal, and the call is originated at the terminal Al.
Fig. 2 shows some examples of the format of a set of frames produced by the character terminal Al.
The information has in the present embodiment a STX symbol (Start of Text), an ETB symbol (End of Transmission Block), and a message frame, between the pair of symbols. The message frame can be (A) a selection frame (SEL) which is the ' address of the called terminal, (B) a data frame (DATA) trans-mitted between a pair of terminals, (C) a release frame (REL) for releasing the line, (D) a selection frame and a data frame, and (E~ a selection frame, a data frame, and a release frame.
Since each character terminal can have his own trans-mission control procedure, the format of a frame depends upon each terminal, and any format except Fig. 2 is of course possible. For instance, a transmission control procedure which has no STX or no ETB is possible. So Fig. 2 is the mere embodiment for the simplicity of the explanation.
Fig. 3 illustrates the manner in which a selection signal is transmitted by applying the transmission-control procedure of an information-transfer phase to a connection-establishing phase, as will be explained below in a step-by-step fashion.
~ \
(1) The character terminal Al initiates a call, as indicated by the arrow (a).
(2) Upon detecting the initiated call (a), the subscriber switching station Bl sends an input~permitting signal (b) to the calling terminaL A .
(3) The thus call-acknowledged character terminal A
sends a selection frame SEL (the address of a called terminal) to the subscriber switching station Bl, which selection frame is in the same frame structure as that of the transmission-control procedure of the information transfer phase. The format of said selection frame is shown in Fig. 2(A).
(4) The subscriber switching station Bl sends the address packet ADR representing the called terminal A2 to that subscriber switching station B2 to which the called terminal A2 is connected, through relay stations Cl and C2.
(5) The subscriber switching station B2 caLls up the called terminal A2, and as the terminal A2 responds, a response packet is sent to the Station B2, as indicated by the dotted line, and a response packet (RES) is sent to the subscriber switching station Bl.
(6) The subscriber switching station Bl sends an acknowledging response signal (e.g., ACK) of the transmission-control procedure, as a signal acknowledging the address regis-tration. At this moment, a logical data link is established between the calling terminal and the called terminal, for facilitating the communication therebetween. It is a matter of course that a busy signal instead of an acknowledging res-ponse signal is sent to the character terminal when the called terminal is busy.
Thus, it becomes possible to establish connection by using the transmission-control procedure of the information transfer phase provided in the character terminal. When the _ 9 line is established, the pair of terminals Al and A2 begins to send and receive a data packet or a frame DATA, whose format is shown in Fig. 2(B).
It should be noted that the procedure shown in Fig.
3 is novel and different from a prior packet switching system.
In a prior character terminal of a prior packet switching system, an address signal inserted between a pair of symbols, + and -, is sent from the terminal Al to the subscriber switch-ing station Bl instead of the selection frame (SEL~ of Fig. 3, and the connect-through (CT) signal is returned to the charac-ter terminal. The format or the signal specification of "+", "-" and "CT" is fixed and is determined by the switching net-work, instead of a terminal. According to the present invention, the format and/or the signal specification of the selection frame and an acknowledgement signal which may correspond to the prior +, - and CT depend upon the transmission control proce-dure of each character terminal. While, in a prior character terminal of a prior packet switching system although the ter-minal sends a selection frame SEL, the subscriber switching station Bl returns an acknowledgement signal to the calling terminal Al just after the station Bl receives the selection frame SEL. Said acknowledgement signal just indicates to the terminal Al that the selection frame SEL is received by the station Bl, but it does not indicate that the selection frame SEL is correctly received by the called terminal A2.
Fig. 4 illustrates an example, in which connection-establishment and information-transfer are executed by applying the transmission-control procedure of an information transfer phase to a connection-establishing phase. A call-acknowledged character terminal Al sends a selection unit (the address of a called terminal) and data to be transmitted (SEL + DATA) packed in a single frame as shown in Fig. 2(D) to the subscriber ~078947 switching station Bl, while forming both the selection unit and the data to be transmitted in the same frame structure as that of the transmission-control procedure of an information-transfer phase. The switching network calls up a called terminal A2 through relay stations Cl and C2 and another subscriber switch-ing station B2, so as to receive a response packet (RES). Such a response packet (RES) is sent to the calling terminal's switching station Bl, and the subscriber switching station B
sends an acknowledging response signal (e.g~, an ACK) of the transmission-control procedure of the information transfer phase to the character terminal Al, as a signal acknowledging the address registration. Thus, the connection-establishment and the information-transfer are simultaneously executed by using the transmission-control procedure of the information transfer phase~
Another example, as shown in Fig. 5, is similar to that of Fig. 4, except that the response packet from a called terminal A2 includes data in the form of RES + DATA) so that the data included in the response packet are sent to a charac-ter terminal Al from the subscriber switching station B2 insteadof a mere response packet (RES). In this case, the transmission-control procedure of an information transfer phase is also used, and the connection-establishment and the information-transfer are simultaneously executed, too.
Fig. 6 shows an example, in which the transmission-control procedure of an information transfer phase is applied to a connection-establishing phase, so as to simultaneously execute the connection-establishment, the information transfer, and the connection-release. A character terminal Al, whose call is acknowledged, sends a selection signal (the address of a called terminal), the data to be transmitted, and an indica-tion for releasing toward a subscriber switching s-tation Bl in , ,. .~ ,.
. .~, . ..
1~78947 the single frame structure shown in Fig. 2(E) as that of the transmission-control procedure of an information transfer phase.
Upon detection of the presence of the indication for releasing, the subscriber switching station Bl sends an address informa-tion indicating the called terminal A2 and the indication for releasing toward that subscriber switching station B2 to which the called termianl A2 is connected. At the same time, the switching station Bl sends out an acknowledging response signal of the transmission-control procedure of an information transfer phase toward the character terminal Al and then shifts into a connection-releasing phase. Although the subscriber switching station B2 calls up the called terminal A2 and sends out the data, when the presence of the indication for releasing together with the address and the data is detected, no response packet is returned to the subscriber switching station Bl. Accordingly, the connection-establishment, the information-transfer, and the connection-release are simultaneously executed.
In the preceding examples, only packet terminals are used as the called terminal A2, but similar operations can be performed with called character terminals, too. The case of the character terminals for the called terminals is different from the case of the packet terminals therefor in that there are a call from the subscriber switching station B2 to the character terminal A2 and a response signal thereto.
Fig. 7 shows a block-diagram of the character ter-minal Al and the subscriber switching station Bl.
The character terminal Al sends a calling signal from the call-release unit (CAL/REL) as indicated (a) in Figs. 3 through 6. When the calling signal (a) is received by the call detector (CAL) of the subscriber switching station Bl, station Bl sends an input permitting signal, as indicated (b) in Figs. 3 through 6, to the terminal Al. Upon receipt of the input per-, mitting signal, the terminal Al sends a frame through the frametransmitter (FRM TR) and the modulator-demodulator (MODEM) to the line (LINE). The set of frames is in the format of Fig. 2 and may include a selection frame (SEL), a data frame (DATA), and/or a release frame (REL). The subscriber switching station Bl receives a frame through the frame receiver (FRM REC) and the switch SWl and stores the address information in the frame in the address registration circuit (ADR REG). The switch SWl is in the position "a" in the initial state, and the switch SW2 is in the position "off" in the initial state. When the first frame includes only an address (selection), the address registration circuit (ADR REG) sends the address information to the packet transmitter (PCK TR), which sends, in turn, an address packet (ADR in Fig. 3) to the line (LINE) through the modulator-demodulator (MODEM). The address packet (ADR) is received by the terminal A2 as a ringing packet or a calling packet (CAL). When the first frame includes an address frame and a data frame as shown in Fig. 2(D), the address registra-tion circuit (ADR REG) sends both the address information and the data to the packet transmitter (PCK TR). The address in-formation stored in the address registration circuit (ADR REG) is held until the switching station receives a release frame, and said address information indicates the address of a data packet.
When the switching station Bl receives a response packet (RES) from the called terminal A2 through the subscriber switching station B2 and the relay stations C2 and Cl, the packet receiver (PCK REC) sends the response packet to the ad-dress registration circuit (ADR REG). Then, the address regis-tration circuit (ADR REG) causes the switch SWl to turn to theposition "b" so as to connect the frame receiver (FRM REC) to the packet transmitter (PCK TR), and causes the switch SW2 to 1078~47 turn to the position "on" to connect the frame receiver (FRMREC) to the acknowledgement transmitter (ACK TR3. The switch-ing on condition of the switch SW2 causes the ACK signal trans-mission indication to be sent to the (ACK TR). As a result, - the ACK TR sends the acknowledgement signal to the terminal A, in accordance with the transmission control procedure. The calling terminal Al, upon receipt of the acknowledgement signal through the acknowledgement receiver (ACK REC), begins to trans-mit a data frame by operating the keyboard (KEY). The acknow-ledgement transmitter (ACK TR) functions merely as a paritycheck circuit after the second frame. Upon receipt of the re-lease signal of character terminal Al, the call detector (CAL) sends a signal to address registration circuit (ADR). Upon receipt of said signal from the call detector (CA~), the address registration circuit (ADR) controls the switches SWl and SW2 to turn back to the initial state.
It should be appreciated that the apparatus of Fig. 7 can accept a plurality of character terminals, each of which can have his own transmission control procedure. To meet with the above function, a program control of the subscriber switch-ing station may be preferable.
In Fig. 7, it should be noted that the structure of the character terminal Al may be the same as a conventional terminal used in a leased line, and the presence of the switches SWl and SW2 in the switching station is one of the important features of the present invention.
As is apparent from the foregoing disclosure, the following outstanding effects can be achieved, by using the transmission-control procedure of an information transfer phase provided in a character terminal for executing the connection-establishment or executing the connection-establishment and the information transfe~
,;
(1) The switching function between the conneetion-establishing phase and the information transfer phase can be dispensed with.
(2) Since the control device for connection-establish--ment can be dispensed with, the terminal equipment can be sim-plified.
(3) The waiting time from the call initiation until the data-transmission can be reduced.
(4) The number of signals to be exchanged is small, so that the operations at the terminals and the processing at the switching stations are simplified, so that the processing ability of a switching network can be enhanced.
In addition, if the operation from the connection-establishment to the connection-release are simultaneously ~
executed, the following additional effects can be achieved. -(5) The processing at the switching station can be further simplified, as compared with the case of establishing logieal circuits.
(6) The holding time of a call can be redueed.
From the foregoing, it will now be apparent that a ~-new and improved packet switching system has been found. It should be understood, of course, that the embodiments disclosed are merely illustrative and are not intended to limit the scope of the invention. Reference should, therefore, be made to the appended claims, rather than to the specification as indicating the scope of the invention.
,~ - . .
-, . , . . . ~
Thus, it becomes possible to establish connection by using the transmission-control procedure of the information transfer phase provided in the character terminal. When the _ 9 line is established, the pair of terminals Al and A2 begins to send and receive a data packet or a frame DATA, whose format is shown in Fig. 2(B).
It should be noted that the procedure shown in Fig.
3 is novel and different from a prior packet switching system.
In a prior character terminal of a prior packet switching system, an address signal inserted between a pair of symbols, + and -, is sent from the terminal Al to the subscriber switch-ing station Bl instead of the selection frame (SEL~ of Fig. 3, and the connect-through (CT) signal is returned to the charac-ter terminal. The format or the signal specification of "+", "-" and "CT" is fixed and is determined by the switching net-work, instead of a terminal. According to the present invention, the format and/or the signal specification of the selection frame and an acknowledgement signal which may correspond to the prior +, - and CT depend upon the transmission control proce-dure of each character terminal. While, in a prior character terminal of a prior packet switching system although the ter-minal sends a selection frame SEL, the subscriber switching station Bl returns an acknowledgement signal to the calling terminal Al just after the station Bl receives the selection frame SEL. Said acknowledgement signal just indicates to the terminal Al that the selection frame SEL is received by the station Bl, but it does not indicate that the selection frame SEL is correctly received by the called terminal A2.
Fig. 4 illustrates an example, in which connection-establishment and information-transfer are executed by applying the transmission-control procedure of an information transfer phase to a connection-establishing phase. A call-acknowledged character terminal Al sends a selection unit (the address of a called terminal) and data to be transmitted (SEL + DATA) packed in a single frame as shown in Fig. 2(D) to the subscriber ~078947 switching station Bl, while forming both the selection unit and the data to be transmitted in the same frame structure as that of the transmission-control procedure of an information-transfer phase. The switching network calls up a called terminal A2 through relay stations Cl and C2 and another subscriber switch-ing station B2, so as to receive a response packet (RES). Such a response packet (RES) is sent to the calling terminal's switching station Bl, and the subscriber switching station B
sends an acknowledging response signal (e.g~, an ACK) of the transmission-control procedure of the information transfer phase to the character terminal Al, as a signal acknowledging the address registration. Thus, the connection-establishment and the information-transfer are simultaneously executed by using the transmission-control procedure of the information transfer phase~
Another example, as shown in Fig. 5, is similar to that of Fig. 4, except that the response packet from a called terminal A2 includes data in the form of RES + DATA) so that the data included in the response packet are sent to a charac-ter terminal Al from the subscriber switching station B2 insteadof a mere response packet (RES). In this case, the transmission-control procedure of an information transfer phase is also used, and the connection-establishment and the information-transfer are simultaneously executed, too.
Fig. 6 shows an example, in which the transmission-control procedure of an information transfer phase is applied to a connection-establishing phase, so as to simultaneously execute the connection-establishment, the information transfer, and the connection-release. A character terminal Al, whose call is acknowledged, sends a selection signal (the address of a called terminal), the data to be transmitted, and an indica-tion for releasing toward a subscriber switching s-tation Bl in , ,. .~ ,.
. .~, . ..
1~78947 the single frame structure shown in Fig. 2(E) as that of the transmission-control procedure of an information transfer phase.
Upon detection of the presence of the indication for releasing, the subscriber switching station Bl sends an address informa-tion indicating the called terminal A2 and the indication for releasing toward that subscriber switching station B2 to which the called termianl A2 is connected. At the same time, the switching station Bl sends out an acknowledging response signal of the transmission-control procedure of an information transfer phase toward the character terminal Al and then shifts into a connection-releasing phase. Although the subscriber switching station B2 calls up the called terminal A2 and sends out the data, when the presence of the indication for releasing together with the address and the data is detected, no response packet is returned to the subscriber switching station Bl. Accordingly, the connection-establishment, the information-transfer, and the connection-release are simultaneously executed.
In the preceding examples, only packet terminals are used as the called terminal A2, but similar operations can be performed with called character terminals, too. The case of the character terminals for the called terminals is different from the case of the packet terminals therefor in that there are a call from the subscriber switching station B2 to the character terminal A2 and a response signal thereto.
Fig. 7 shows a block-diagram of the character ter-minal Al and the subscriber switching station Bl.
The character terminal Al sends a calling signal from the call-release unit (CAL/REL) as indicated (a) in Figs. 3 through 6. When the calling signal (a) is received by the call detector (CAL) of the subscriber switching station Bl, station Bl sends an input permitting signal, as indicated (b) in Figs. 3 through 6, to the terminal Al. Upon receipt of the input per-, mitting signal, the terminal Al sends a frame through the frametransmitter (FRM TR) and the modulator-demodulator (MODEM) to the line (LINE). The set of frames is in the format of Fig. 2 and may include a selection frame (SEL), a data frame (DATA), and/or a release frame (REL). The subscriber switching station Bl receives a frame through the frame receiver (FRM REC) and the switch SWl and stores the address information in the frame in the address registration circuit (ADR REG). The switch SWl is in the position "a" in the initial state, and the switch SW2 is in the position "off" in the initial state. When the first frame includes only an address (selection), the address registration circuit (ADR REG) sends the address information to the packet transmitter (PCK TR), which sends, in turn, an address packet (ADR in Fig. 3) to the line (LINE) through the modulator-demodulator (MODEM). The address packet (ADR) is received by the terminal A2 as a ringing packet or a calling packet (CAL). When the first frame includes an address frame and a data frame as shown in Fig. 2(D), the address registra-tion circuit (ADR REG) sends both the address information and the data to the packet transmitter (PCK TR). The address in-formation stored in the address registration circuit (ADR REG) is held until the switching station receives a release frame, and said address information indicates the address of a data packet.
When the switching station Bl receives a response packet (RES) from the called terminal A2 through the subscriber switching station B2 and the relay stations C2 and Cl, the packet receiver (PCK REC) sends the response packet to the ad-dress registration circuit (ADR REG). Then, the address regis-tration circuit (ADR REG) causes the switch SWl to turn to theposition "b" so as to connect the frame receiver (FRM REC) to the packet transmitter (PCK TR), and causes the switch SW2 to 1078~47 turn to the position "on" to connect the frame receiver (FRMREC) to the acknowledgement transmitter (ACK TR3. The switch-ing on condition of the switch SW2 causes the ACK signal trans-mission indication to be sent to the (ACK TR). As a result, - the ACK TR sends the acknowledgement signal to the terminal A, in accordance with the transmission control procedure. The calling terminal Al, upon receipt of the acknowledgement signal through the acknowledgement receiver (ACK REC), begins to trans-mit a data frame by operating the keyboard (KEY). The acknow-ledgement transmitter (ACK TR) functions merely as a paritycheck circuit after the second frame. Upon receipt of the re-lease signal of character terminal Al, the call detector (CAL) sends a signal to address registration circuit (ADR). Upon receipt of said signal from the call detector (CA~), the address registration circuit (ADR) controls the switches SWl and SW2 to turn back to the initial state.
It should be appreciated that the apparatus of Fig. 7 can accept a plurality of character terminals, each of which can have his own transmission control procedure. To meet with the above function, a program control of the subscriber switch-ing station may be preferable.
In Fig. 7, it should be noted that the structure of the character terminal Al may be the same as a conventional terminal used in a leased line, and the presence of the switches SWl and SW2 in the switching station is one of the important features of the present invention.
As is apparent from the foregoing disclosure, the following outstanding effects can be achieved, by using the transmission-control procedure of an information transfer phase provided in a character terminal for executing the connection-establishment or executing the connection-establishment and the information transfe~
,;
(1) The switching function between the conneetion-establishing phase and the information transfer phase can be dispensed with.
(2) Since the control device for connection-establish--ment can be dispensed with, the terminal equipment can be sim-plified.
(3) The waiting time from the call initiation until the data-transmission can be reduced.
(4) The number of signals to be exchanged is small, so that the operations at the terminals and the processing at the switching stations are simplified, so that the processing ability of a switching network can be enhanced.
In addition, if the operation from the connection-establishment to the connection-release are simultaneously ~
executed, the following additional effects can be achieved. -(5) The processing at the switching station can be further simplified, as compared with the case of establishing logieal circuits.
(6) The holding time of a call can be redueed.
From the foregoing, it will now be apparent that a ~-new and improved packet switching system has been found. It should be understood, of course, that the embodiments disclosed are merely illustrative and are not intended to limit the scope of the invention. Reference should, therefore, be made to the appended claims, rather than to the specification as indicating the scope of the invention.
,~ - . .
-, . , . . . ~
Claims (4)
1. A method for controlling a packet switching system having at least a character terminal, a subscriber switching station and a receiving terminal, comprising the steps of for-warding an information frame including the address of a re-ceiving station according to the transmission control pro-cedure of an information transfer phase from the character ter-minal to the receiving terminal via the subscriber switching station, forwarding a response packet from the receiving ter-minal to the switching station, and returning an acknowledgement signal according to the transmission control procedure of an information transfer phase from the subscriber switching station to the character terminal when the switching station acknowledges receipt of the response packet from the receiving terminal.
2. The invention as defined in claim 1, wherein said information frame including the address of a receiving station includes data, too.
3. The invention as defined in claim 2, wherein said information frame further includes the release indication for performing the connection-establishment, the information trans-fer, and the connection release in a single frame.
4. A subscriber switching station in a packet switching system, including a line-and a terminal, said switching station comprising a frame receiver, an address registration circuit for storing a frame of address information, a packet transmitter for transmitting a packet to said line from one of said address registration circuit and said frame receiver, a packet receiver for forwarding a packet from said line to said address regis-tration circuit, an acknowledgement transmitter for sending an acknowledgement signal to said terminal, further characterized by comprising a first switching means responsive to said address registration circuit for transferring a signal from the frame receiver to one of said address registration circuit and said packet transmitter and a second switch means responsive to said address registration circuit for switching between said frame receiver and said acknowledgement transmitter.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP50023868A JPS5199403A (en) | 1975-02-28 | 1975-02-28 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1078947A true CA1078947A (en) | 1980-06-03 |
Family
ID=12122410
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA246,310A Expired CA1078947A (en) | 1975-02-28 | 1976-02-23 | Packet switching system |
Country Status (4)
| Country | Link |
|---|---|
| JP (1) | JPS5199403A (en) |
| CA (1) | CA1078947A (en) |
| FR (1) | FR2302639A1 (en) |
| GB (1) | GB1543832A (en) |
Families Citing this family (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR2448200A1 (en) * | 1979-02-02 | 1980-08-29 | Sitintel Inf Teletransm | Information restoration technique for transmission network - includes storage of identification code for transmitting terminal and latent information indicator |
| US4280217A (en) * | 1979-12-26 | 1981-07-21 | Bell Telephone Laboratories, Incorporated | Time division switching system control arrangement |
| US4322843A (en) * | 1979-12-26 | 1982-03-30 | Bell Telephone Laboratories, Incorporated | Control information communication arrangement for a time division switching system |
-
1975
- 1975-02-28 JP JP50023868A patent/JPS5199403A/ja active Pending
-
1976
- 1976-02-23 CA CA246,310A patent/CA1078947A/en not_active Expired
- 1976-02-24 GB GB7301/76A patent/GB1543832A/en not_active Expired
- 1976-02-27 FR FR7606238A patent/FR2302639A1/en active Granted
Also Published As
| Publication number | Publication date |
|---|---|
| GB1543832A (en) | 1979-04-11 |
| FR2302639A1 (en) | 1976-09-24 |
| JPS5199403A (en) | 1976-09-02 |
| FR2302639B1 (en) | 1981-03-27 |
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