Packet concentrator and packet switching system

Abstract: A method and system are provided for concentrating calls for a packet switching system in a hierarchical communication network. A plurality of terminals (3) communicate with an as­ sociate plurality of packet concentrators (1) that, in turn, communicate with switching equipment (2). The system and method comprise initiating a call at a call terminal (3) to be transferred to the packet concentrator (1) and identifying the call terminal (3) by associating the number of a line (100) connecting the terminal (3) with the concentrator (1) with a logical channel number for communication from the packet con­ centrator (1) to the switching equipment (2). The logic chan­ nel number is recorded in association with the line number at the packet concentrator (1) whereby call communication back to the call terminal (3) can be made on the proper line (100) by relating the line number with the logic channel number of the call and thereby avoiding the need to switch logic channels between the concentrator (1) and the switching equipment (2) to avoid costly call processing at the concentrator (1). Further benefits provided by executing of the general call processing at the switching equipment (2) including tariff control.

Description: Background of the Invention: [Field of the Invention] The present invention relates to a method and an apparatus for concentrating calls in a communication network, particularily in a packet network. [Description of the Prior Art] Typical examples of a multiplexing system for packet switching equipment are described in the CCITT RED BOOK X.25 (a user-network interface) and X.75 (a network-network interface). These examples are also briefly described on pp.100-102 of Packet Switching Technology and Its Application (the Institute of Electronic, Information, and Communication Engineers). For a conventional packet concentrating system, there are known two different concentrating systems as described on pp.88 and 89, and pp.102-105 of the above-mentioned Packet Switching Technology and Its Application . The first concentrating system is shown, for example, in Figure 20 and has a packet multiplexer (PMX) 604 in which data 601-1 to 601-3 is sent from lines connected to a plurality of non-packet mode terminals (NPT) 600-1 to 600-3. The data is packed by the PMX and then sent on the same line 605 with terminal identifications in the labels of the packets 606-1 to 608-n. The second concentrating system is shown, for example, in Figure 21 wherein a packet concentrator 620 (comprised of elements 620-1 to 620-ℓ) and a packet distributor 630 operate so that the output from each concentrator element is provided to the distributor 630 through a number n of output lines (612-1 to 612-n) which is less than a number m of input packet lines (611-1 to 611-m). Here, a logical channel for the terminal data must be set link by link and different logical channels are set between a terminal 610 and the packet concentrator 620 and between the packet concentrator 620 and packet distributor 630. [Problems to be Solved by the Invention] In the first conventional concentrating system mentioned above, input lines connected to the concentrator 604 do not provide any packet multiplexing because they come from only non-packet mode terminals. Therefore, only a single call can be handled per terminal. The lack of efficiency for this system makes it highly undesirable for large or dense data communication systems. In the second conventional concentrator system mentioned above, since an individual call is set link-by-link, it becomes necessary for the concentrator to also switch logical channels. Consequently, the concentrator is required to administrate logical channels, i.e., to have a capability to terminate a control signal and execute call processing. It becomes impossible for any switching equipment which is placed higher than the concentrator to identify the sender of information being transmitted because the logical channel number is changed by the time that switching equipment receives the data signal. The concentrator, besides completing its primary concentrating tasks, is therefore required to also execute extensive controlling processes with regard to the sender such as a tariff control and others. The individual packet switching equipment needs the capability of processing functions to terminate a call control signal as a concentrating node for concentrating multiplexed lines by logical channel numbers. This extensive control processing becomes a substantial problem to be solved with the continued expansion of packet line converging and multiplexing of communication media. The conventional system in which a packet switching equipment is arranged with such a concentrating node is costly, and raises a serious problem in that respect. A need exists for a system that permits the switching equipment to perform the substantive portion of call processing while providing a simpler and less costly concentration of terminal cells. A packet switching system of the type shown in Figure 21 is also disclosed in DE-A-3 210 462. This system uses two different logic channel numbers to identify communication between a terminal and a concentrator on the one hand and between the concentrator and switching equipment on the other hand for each call. The same document also discloses another system, where only one logic channel number is used for the entire communication relating to one call between a terminal and the switching equipment via a concentrator. In this other system, a certain set of logic channel numbers is preallocated to each terminal. When a data packet is to be delivered by a concentrator to a terminal, the logic channel number of the packet is compared with each logic channel number preallocated to each of the terminals connected to said concentrator in order to determine to which terminal the packet has to be transmitted. Brief Summary of the Invention: It is an object of the present invention to provide an efficient method and apparatus of concentrating calls in a hierarchical communication network. This object is solved by the method set forth in claim 1 and the apparatus set forth in claim 10. The subclaims are directed to preferred embodiments of the invention. A packet switching system comprising a concentrator for concentrating multiplexed packet lines without switching logical channels reduces call processing at the concentrator. The concentrator is provided in a packet network in which a switching equipment, a concentrator, and terminals are hierarchically arranged. The concentrator concentrates multiplexed packet lines without switching logical channels. The same logical channel number (LCN) is used between a terminal and a concentrator as well as between a concentrator and the switching equipment in a connection of a call. In order to transmit a down packet from the switching equipment to a concentrator in a line in which an up packet from the terminal having the same LCN as the LCN of said packet is inputted, the concentrator has a means for storing an input line number corresponding to the LCN, and a means for inserting the above-mentioned line number into the data transmitted between the concentrator and the switching equipment as a packet. The switching equipment has a means for charging by each line the number of communication packets counted according to the LCN by use of the line number inserted into the above-mentioned packet. According to another feature, the line number stored in accordance with the LCN in the above-mentioned concentrator is read by each LCN when the down packet from the switching equipment terminates. Thus, the concentrator sends the packet to a terminal line to which said LCN is connected. Also, in a packet communication system including a line number between a switching equipment and a concentrator, the concentrator inserts a line number of the packet received into an up packet, and the switching equipment inserts a line number stored when the up packet is received. Then, the packet is sent by the concentrator to a terminal line to which the terminal of that LCN is connected, while a tariff control can be executed by the switching equipment by the line number. It is a benefit of the present invention that a packet switching system and method can be provided which includes a concentrator which avoids extensive call processing therein for a far less costly system that can readily adapt to the expansion of packet line converging and expansion of communication media. Another benefit is the provision of a packet network which allows a switching equipment placed higher than a concentrator to execute general call processing such as tariff control and other processing steps. Brief Description of the Drawings : Fig. 1 is a schematic diagram illustrating the architecture of a network to which the present invention is applied; Fig. 2 is a diagram showing an example of the structure of a packet concentrator; Figs. 3 and 4 are views each representing the format of a packet being transferred in this network; Figs. 5 to 9 are diagrams showing specific structures of circuits comprising a packet concentrator, and Fig. 5 is a diagram showing the circuitry of a packet switch, Fig. 6 is a diagram showing an up switch of the packet switch circuitry, Fig. 7 is a diagram showing a down switch thereof, and Figs. 8 and 9 are diagrams showing the details of a line interface; Fig. 10 is a view illustrating a shared buffer memory in a packet switch; Figs. 11 to 16 are diagrams showing signal sequences for line number switching in a concentrator; Fig. 17 is a view representing an LCN-to-line number conversion table; Fig. 18 is a schematic diagram showing an example of a packet switching equipment; Fig. 19 is a schematic diagram showing an example of the structure of a line interface in a packet switching equipment; Figs. 20 and 21 are views each representing prior art packet concentrating systems. Detailed Description of the Preferred Embodiment : Referring now to the drawings wherein the showings are for purposes of illustrating preferred embodiments of the invention only and not for purposes of limitation thereto, the FIGURES show a principal embodiment of features of the subject packet switching system. The Embodiment is a system in which a corresponding line for a down signal from a higher packet switching equipment is identified without terminating signals in a packet concentrator, and which has a storing function for an LCN and a line number in a packet concentrator. Description of the architecture (1) The network formation: An embodiment of a packet network comprising the present invention is shown in Fig. 1. The network has a hierarchical structure comprising a plurality of packet concentrators 1 (1-1 to 1-n) for concentrating each of a plurality of packet lines 100 (100-1 to 100-ℓ) from each of a plurality of terminals 3 (3-1 to 3-ℓ) at a packet line 120 (120-1 to 120-n). The packet line 120 is connected to the packet concentrator 1 and packet switching equipment 2 (2A and 2B) which distribute transit packet line 130 (130-1 to 130-m) from switching equipment 2A to the other packet switching equipment 2B. It is a feature of the invention that a logical channel (LCN1) between the packet concentrator 1 and the packet switching equipment 2A is the same as the logical channel between the terminal 3 and the packet concentrator 1, but is different from a logical channel (LCN2) between the packet switching equipment 2A and the packet switching equipment 2B. In other words, an LCN is switched in the packet switching equipment 2, but the LCN is not switched in the packet concentrator 1. As shown in Fig. 2, the packet concentrator 1 comprises a packet switch 11 for concentrating packet lines 100-1 to 100-ℓ connected to packet terminals 3 and line interfaces 12-1 to 12-ℓ for terminating each line, and a line interface 13 connected to the packet line 120 which in turn is connected to the packet switching equipment 2. The packet concentrator 1 according to this embodiment concentrates a plurality of lines (100-1 to 100-ℓ) connected to the terminals 3 on a packet line 120 connected to the higher switching equipment 2A. Fig. 5 is a diagram showing the circuit structure of the packet switch 11, comprising an up switch 106 for processing a packet from the terminal 3 to the switching equipment 2A and a down switch 107 for processing a packet from the switching equipment 2A to the terminal 3. The details of the up switch 106 are shown in Fig. 6, and the details of the down switch 107, in Fig. 7, respectively. The circuit formation of line interfaces 12 and 13 in the concentrator 1 are shown in Figs. 8 and 9. As shown in Fig. 18, the packet switching equipment 2 comprises a packet switch 302 for distributing packets, line interfaces 300 (300-1 to 300-m) for terminating lines 120-1 to 120-n connected to the packet concentrator 1, line interfaces 301 (301-1 to 301-m) that are connected to transit packet lines 130-1 to 130-m, and a CP (Call Processing) module 303 for call processing, maintenance and administration. As noted above, the packet concentrator 1 has a feature that it communicates a packet from the switching equipment to the terminals with the same logical channel number LCN. A function is provided for sending a down packet inputted from the packet switching equipment 2A to the proper inputted line (one of the lines 100) of a terminal 3 by storing a line number corresponding to the LCN. (2) The structure of the packet switch: Each packet switch 11 is based on an ATM (Asynchronous Transfer Mode) switch, a memory switch introduced, for example in a paper IEICE Technical Report SSE88-56 (A study on the ATM switching architecture). As shown in Fig. 5, the entire structure of the packet switch 11 comprises the up switch 106 and the down switch 107. The up switch 106 sends packets received from a plurality of lines 105A (105A-1 to 105A-1) connected to terminals 3, to a line 110A connected to the packet switching equipment, while the down switch 107 sends packets received from a line 110B connected to the packet switching equipment 2A to one of the lines 105B (105B-1 to 105B-ℓ) connected to the terminals. As shown in Fig. 6, the up switch 106 comprises a multiplexer (MUX) 22 for multiplexing a plurality of packet lines 105A-1 to 105A-ℓ, a shared buffer memory (BFM) 21A for temporarily storing packets, an idle address buffer (IABF) 25A which is an FIFO for indicating idle buffer addresses in the BFM, a write address register (WA) 23A for a queuing buffer for an output line (only one line in the up switch), and a read address register (RA) 24A. As shown in Fig. 7, the down switch 107 comprises, in addition to a BFM 21B, an IABF 25B, write address registers (WA) 23B-1 to 23B-ℓ, and read address registers (RA) 24B-1 to 24B-ℓ, a routing detector (RT) 27, a routing filter (RTFLT) 28 for selecting one of the write address registers (WA) 23B-1 to 23B-ℓ, an output control counter (OUTCNT) 29 for specifying output line numbers periodically (1 to ℓ, and an output decoder (OUTDEC) 30 for selecting one of the read address registers (RA) 24B-1 to 24B-ℓ. The shared buffer memory BFM21 (21A and 21B) comprises a next pointer (NP) area 80 and a packet information area 81, as shown in Fig. 10, and each packet is chained at its address by the NP per each output line, respectively. The top address of the chain is set in a read address register RA24 and the last address of the chain is set in a write address register WA23. When packets are received, a hunt idle buffer address is set in the next pointer NP area 80 of the address indicated by the WA23, and when packets are sent, the packet information 81 indicated by RA24 is read. (3) The structure of the line interface: Fig. 8 is a schematic diagram showing the line interface 12 of lines 100 to which terminals 3 are connected. The upward circuit has an optical electrical signal converter (not shown), a serial-parallel converter (not shown), a line terminating equipment 41A for processing packet line synchronization and other normal terminating functions, a traffic counter 45 for counting packet numbers per logical channel number, and a line number inserter 42 for inserting into a packet header a line number assigned for the line interface. The downward circuit has a line number eliminator 43 for eliminating the line number in the packet header, and line terminating equipment 41B the same as the above-mentioned. Fig. 9 is a schematic diagram illustrating the circuit formation of a line interface 13 of the lines 120 connected to the switching equipment 2A. The upward circuit comprises a header separator 47 for separating header information, a line number eliminator 52 for eliminating a line number in a packet header, and a line terminating equipment 50A while the downward circuit comprises a line terminating equipment 50B, an LCN separator 49 for separating an LCN in a packet header, and a line number inserter 51 for inserting a line number in a packet header. Also, in the memory, an LCN-to-line number conversion table 48A is provided, the arrangement of which is shown in Fig. 17. In this table, a line number is written for the LCN in the header information separated by the header separator 47 for the up packet, and a line number is read in accordance with the LCN separated by the LCN separator 49 for the down packet. Description of the Operation In a packet concentrator 1 in which a plurality of input lines 100 are concentrated on an output line 120 without any function of logical channel switching, i.e., the logical channel is the same both for the input and output on a call, a system is thus provided whereby a down packet (the packet being sent to the terminal 3 from the packet switching equipment 2A through the packet concentrator 1) has the same logical channel as an up packet (the packet being sent to the packet switching equipment 2A from the terminal 3 through the packet concentrator 1). How the signal is outputted to the same line from which said up packet is inputted will subsequently be described with reference to Fig. 11 to Fig. 16 which show the signal sequence diagrams. For a particular logical channel number (LCN), three different kinds of LCN's are used from the time a call is originated until it is released. These are a packet LCN for transferring user information; an LCN for a signal control packet for a call setup/release and other normal set up and release functions; and, an LCN for a packet of requirement signal for assignment of a control signal at the time of terminal registration. Fig. 11 is a diagram showing a signal sequence for terminal registration. When a terminal 3 is connected to a network, the terminal 3 sends a packet of requirement signal for LCN assignment for signal control 200 to the concentrator 1 using the LCN 0 for assigning a control LCN predetermined by the packet switching equipment 2A. The composition of a packet in the line 100 between the terminal 3 and the packet concentrator 1 is shown in Fig. 3. The packet is separated for header information and user information, and the header information includes the LCN (LCN 0 ) and the user information includes a signal classification SIG (requirement signal for LCN assignment of control signal). When this packet is inputted to the line interface 12 in Fig. 2, the line interface 12 inserts a line number LN assigned in advance to the packet header information by the line number inserter 42 subsequent to the termination of the inputted signal in the line terminator 41 and the counting of numbers of passing packets by the traffic counter 45, both shown in Fig. 8. The composition format of a packet with an inserted LN is shown in Fig. 4. This packet is sent to the up switch 106 of the packet switch 11 through the line 105A. In the up switch 106 (Fig. 6) of the concentrator packet switch 11, an idle address of the shared buffer memory BFM 21A is taken out of the idle address buffer IABF 25A after the inputted packet is multiplexed by the multiplexer MUX 22. Next, the write address register (WA) 23A is read, and the idle buffer address thus taken out is set up in the next pointer NP 80 (Fig. 10) at an address in the BFM 21A indicated by WA 23A. At the same time, the input packet information is written in the packet area 81 of the idle buffer address, and the WA 23A is renewed with the idle buffer address. Also, during the time of sending the packet, simultaneously with the sending of the packet area information 81 in the BFM 21A indicated by the RA 24A, the NP 80 of the terminating packet is set up in the RA 21A and the address of the packet already sent is inputted in the IABF 25A. The packet is inputted to the line interface 13 in Fig. 2 through the line 110A to take out the LCN and the line number LN of the header information shown in Fig. 4 by the header separator 47 shown in Fig. 9, and to write the line number LN for the LCN on the LCN-to-line number conversion table 48A which comprises data as shown in Fig. 17. In this case, the line number LN is set up in the area for LCN 262 for assigning control signal LCN. The above-mentioned packet is sent to the higher switching equipment 2A through the line number eliminator 52 for eliminating the line number LN in the packet header, the line terminator 50A, and the line 120A. The packet in the line 120A has a format as shown in Fig. 3. When a down packet of an LCN assignment terminating signal 204 having the same LCN is inputted to the line interface 13 shown in Fig. 9 from the switching equipment 2A through the line 120B, the LCN (= LCN 0 ) is taken out by the LCN separator 49. From this LCN, a line number LN for the LCN 0 of the LCN LCN-to-line number conversion table 48A is read, and is inserted into the packet information by the line number inserter 51 and is sent to the line 110B. The packet in the line 110B has a format shown in Fig. 4. When this packet is inputted to the down switch 107 of the packet switch 11 shown in Fig. 7, a routing information reader RT 27 takes out the line number information LN (corresponding to 105B-1 to ℓ) from the packet header information shown in Fig. 4, and reads the WA 23B for the LN by a routing distributor RTFLT 28 in accordance with such information, and then, sets up the idle buffer address taken out from the IABF 25B in the address next pointer (NP) 80 in the BFM 21B indicated by the WA 23B in the same manner as in said up switching operation, while at the same time writing the inputted packet on the packet area 81 of the idle buffer address to renew the address of WA 23B. At the time of sending a packet, the output decoder OUTDEC 30 selects an RA 24B for an output line in accordance with the information whereby an output control counter OUTCNT 29 outputs periodically a 1 to ℓ value as an output line number, and sends a packet in the BFM 21B indicated by this RA 24B to a corresponding output line through a demultiplexer 26. Also, an NP 80 information at the same address as a sending packet is set up in the RA 24B, and the address of the packet already sent is inputted in IABF 25B simultaneously. Therefore, an LCN assignment terminating signal 204 having the LCN for the control signal hunted by the switching equipment 2A shown in Fig. 11 as a parameter can be returned through the concentrator to a terminal 3 from which the assignment requirement is originated. Fig. 12 is a diagram showing a signal sequence for setting the up link to process a call. The terminal 3 sends a requirement signal for link setup (SABME) 210 to the switching equipment 2A through the concentrator 1 by use of the LCN for the control signal assigned as above. The terminating packet at the concentrator 1 is sent to the switching equipment 2A through the line interface 12, the packet switch 11, and the line interface 13 shown in Fig. 2, respectively. At this time, as described previously, the line interface 13 shown in Fig. 2 stores a line number LN in the area for LCN control signal in the LCN-to-line number conversion table 48 shown in Fig. 9. When a link setup terminating signal (UA) 214 is inputted to the concentrator 1 from the switching equipment 2A, the line interface 13 shown in Fig. 2 takes out a line number from the LCN-to-line number conversion table 48, and inserts such number in a packet to be returned through the packet switch 11 to the terminal 3 from which the requirement for the link setup is originated. A phase of call setup shown in Fig. 13 (sending side) and Fig. 14 (terminating side) can also identify, as described above, a line to which said terminal 3 is connected in accordance with a line number LN for the LCNn for the control signal stored in the switching equipment 2A. The information packet which is transferred subsequent to a call setup does not terminate at the switching equipment 2A so that a line number for the information LCN must be stored at the time of the call setup. At the time of a call setup, the switching equipment sends an LCNm for the hunted information to the concentrator 1 as a parameter for a SETUP ACK message 223 shown in Fig. 13 or a SETUP message 231 shown in Fig. 14. The concentrator 1 expands the packet taken out in the LCN separator 49 of the line interface shown in Fig. 9 to cover its signal classification and parameter, and if the signal classifications are SETUP ACK and SETUP, the separator reads a line number from the LCNn for the control signal in the packet header by the LCN-to-line number conversion table 48, and sets up this line number at the address (in the area for the information LCN) of the LCNm in the parameter of the message. In this way, the information packets of LCNm being transferred hereinafter from the switching equipment 2A, for example, the ACK as shown in Fig. 15 and the data shown in Fig. 16, are sent to the line 100 connected to the terminal 3 from which the requirement for connection is originated. As set forth above, in Embodiment 1, the packet concentrator 1 concentrates a plurality of packet lines on a packet line connected to the higher packet switching equipment 2. However, this connection can be arranged in a plurality of parallel connections so as to allow the concentrator to comprise a plurality of equivalent output lines. The subject invention can be summarily characterized in having the following beneficial effects. In the ATM (Asynchronous Transfer Mode) of BISDN (Broadband ISDN), it is assumed that the packet network performs at a high speed of approximately 150 Mbps per line. In a line with 150 Mbps, multimedia such as voice/data/video can be communicated, and as compared with the data network/telephone network currently available, the concentrating ratio becomes extremely high, so that in view of the cost of network, a concentrator is considered more important than a switching equipment itself. The concentrator according to the present invention is simpler than the conventional packet concentrator employed at a concentrating stage because it is a simple concentrator without any of the functions of call processing and it does not terminate a control signal. Therefore, there is no need not only for such hardware as a signal terminator, a processor, and memories for main and auxiliary storages, but also for the associated software for controlling any connection on a call, logical channel number (LCN), tariff and necessary others. As a result, the cost of the entire network can be reduced significantly. The invention has been described with reference to preferred embodiment. Modifications and alterations will occur to others upon the reading and understanding of this specification. It is our intention to include all such modifications and alterations in so far as they come within the scope of the appended claims and the equivalents thereof.

Claims: A method of concentrating calls in a hierarchical communication network wherein a plurality of call terminals communicate packets along a first number of lines (100) to packet concentrators (1) that communicate with a switching equipment (2) along a second number of lines (120), the method comprising the following steps: initiating at a call terminal (3) a call along one of the first number of lines (100) to a packet concentrator (1), associating a line number (LN) of said one line (100) with a logic channel number (LCN) allocated to said initiated call for identification of its packet communication between the call terminal (3) and the switching equipment (2) via said packet concentrator (1), recording said line number (LN) in association with said logic channel number (LCN) at said packet concentrator (1) during setup of said initiated call, and transferring a packet, that is received by the packet concentrator (1) from the switching equipment (2) during packet communication of said call, to said call terminal (3) on said one of the first number of lines (100) by relating the logic channel number (LCN) of the received packet with said recorded line number (LN) without switching logic channel numbers at the packet concentrator (1). A method according to claim 1, wherein said transferring step includes the step of inserting at said packet concentrator (1) the line number (LN) recorded in association with the logic channel number (LCN) of a packet received from the switching equipment (2) into a header of said packet. A method according to claim 1 or 2, wherein the recording step comprises maintaining a conversion table (48A) at the packet concentrator (1) to relate said logic channel number (LCN) to said line number (LN). A method according to any of claims 1 to 3, wherein said line number (LN) is stored at the packet concentrator in association with said logic channel number (LCN) when a control packet which has said logic channel number (LCN) and belongs to a signal (SABME) requesting call initiation is received from the call terminal (3). A method according to any of claims 1 to 4, further comprising the step of tariff control processing at the switching equipment (2) for call communication between the call terminal (3) and the packet concentrator (1). A method according to any of claims 1 to 5, wherein the allocation of said logic channel number (LCN) is requested by said call terminal (3) from said switching equipment (2) through a call set-up signal (SETUP), and said associating step is carried out at the concentrator (1) in response to a control signal (SETUP ACK) delivered from the switching equipment to the call terminal for allocating the logic channel number. A method according to any of claims 1 to 6, further comprising the step of assigning a logic control channel number (LCNn) to said line number in response to a request from the call terminal before the switching equipment codes the call with said logic channel number (LCNm). A method according to claim 7, wherein said switching equipment (2) selects an idle logic channel number to obtain said logic channel number associated with said line number. A method according to any of claims 1 to 8, wherein said call is identified by said logic channel number (LCN) during communication of user information between said call terminal (3) and said concentrator as well as between said concentrator and said switching equipment (2). An apparatus for concentrating calls in a hierarchical communication network while communicating by packet transmission along a first number of lines (100) with a plurality of call terminals (3) and along a second number of lines (120) with switching equipment (2), comprising: means (47) for obtaining a line number (LN) of that one of said first number of lines (100) which has been used by a call terminal (3) to initiate a call and for obtaining a logic channel number (LCN) allocated to said call for identification of the call's packet communication between the call terminal and the switching equipment, means (48A) for recording said line number (LN) in association with said logic channel number (LCN) during set-up of said initiated call, and means (49, 51, 11) for transferring a packet, which is received from the switching equipment (2) during packet communication of said call, to said call terminal (3) on said one of the first number of lines (100) by relating the logic channel number (LCN) of the received packet with the recorded line number (LN) without switching logic channel numbers.

Inventors: KUNIMOTO MASAO, SAKURAI YOSHITO, TAKASE AKIHIKO, TANABE SHIROU, KUNIMOTO, MASAO, SAKURAI, YOSHITO, TAKASE, AKIHIKO, TANABE, SHIROU
Applicants: HITACHI LTD, HITACHI, LTD.
Application year: 1990
Main classification: H04L12
IPC codes: H04L12