GB2335825A

GB2335825A - Establishing packet-switched telephone calls using circuit switched signalling

Info

Publication number: GB2335825A
Application number: GB9905575A
Authority: GB
Inventors: Richard Mcbride
Original assignee: 3Com Technologies Ltd
Current assignee: 3Com Technologies Ltd
Priority date: 1998-03-27
Filing date: 1999-03-12
Publication date: 1999-09-29
Anticipated expiration: 2019-03-12
Also published as: GB9905575D0; GB2335825B

Abstract

A telephone instrument 1,2 comprises means for providing signals for transmission, means for converting signals received by the instrument into output signals, a switching circuit for selectively establishing and terminating a connection between the instrument and a circuit-switched telephone network and for selectively establishing and terminating a connection between the instrument and a packet-switched communication network 4. When calling, the instrument signals over the circuit-switched network for the called instrument's network address on the packet-switched network and establishes a dual connection over the packet-switched network if such a network address is received. When receiving a call, the instrument can terminate the call connection over the circuit-switched network and continue the call by way of the packet-switched network.

Description

2335825 DUAL-CIRCUIT TELEPHONY

Field of the Invention

The present invention relates to telephony and to telephone instruments which have dual circuit capability.

Background to the Invention

Most telephone networks in use at the present time are circuit switched networks, in which telephone subscribers have, at least to a local switchina station, a dedicated line identified by a subscriber's number. Connection to the network is achieved by a switch closing a circuit includine, the subscriber line to the local switching station. Telephone calls may be conveyed from switching station to switching station by a variety of links, but connection is established for the call to the ultimate recipient by means of circuit switching controlled by the generation of pulse trains or tones representing the recipient's telephone number. Although telephone messages, whether voice calls or other types of call, such as facsimile transmissions, may be conveyed between switching. stations by various time division, frequency division or even packetswitched communication links, as far as the end stations, the telephone instruments., are concerned they make connections to an analog circuit-switched network. Owing to the global nature of the existing, circuit-switched networks, their use will obviously continue for many years and telephone instruments are necessarily adapted to establish connections by way of the familiar circuit- switched network.

In recent years there has been increasing use, first in local area networks and then on a wider scale, of packet-switched networks, of which the 'Internet' is the best known. The present invention is based on an appreciation that the usage of packet-switched networks will provide a potential alternative communication link between telephone subscribers.

The present invention envisages a new form of telephone instrument, typically a handset capable of making voice calls, which has a dual circuit capability in that it is capable of establishing, a call -I?connection over the ordinary, circuit-sw,Itched telephone network but may, if desired automatically, transfer the call connection from the circuitswitched telephone network to a packet-switched network.

Summarv of the Invention An instrument according to the invention would normally possess, in common with existing instruments, some means for providing signals for transmission and some means for converting sianals received by the instrument into output signals. The aforementioned means may, in the case of a telephone handset instrument, include the usual microphone and loudspeaker and the usual dialling equipment or tone generation equipment by means of which an intended recipient's number can be transmitted in the format required by, the cl rcult- switched network to the local switchinR station in order to establish a call connection with an intended recipient.

An instrument accordiw to the invention will, however, further comprise not only a switching circuit for selectively establishinR and terminating a connection between the 'instrument and the circuit-switched telephone network but further means for selectively establishing and terminating a connection between the instrument and a packet-switched communication network. The switching circuit for this purpose may include appropriate multiplexing equipment interposed between the call 2eneratin. and receivinc, circuits and the terrrn'nals or connection points for the telephone network and the packet-switched network.

Further, the telephone instrument preferably comprises control means including means operable i W to define or obtain a network address of the instrument in the packet- switched communication network, the control means being operable (1) to control the switching circuit to establish a call connection to another instrument on the telephone network, (n) in response to receipt of an acknowledgement signal including the network address of the other instrument to control the switching circuit to make the call connection to the other instrument by way of the packet- switched network.

1 The instrument may signal information including its network address over the initial call connection. Alternatively, it may obtain its network address only after receipt of the said acknowledament from the other instrument.

The 'instrument may further comprise control means operable on receipt of a call by way of the circuit-switched network to provide an acknowledgement including the network address of the instrument, and on receipt of a subsequent message over the packet-switched network to terminate connection over the circuit-switched network.

Brief Descriwion of the Drawing Figure 1 is a schematic illustration of two telephones having dual connections, Figure 2 Is a schematic drawing of a telephone according to the invention coupled to both a Z Z> public-switched telephone network and a packet-based network, Fi-ure 3 illustrates the operation of call lo ic at a callin. station., and g c Fi-ure 4 illustrates the operation of call logic at a called or receiving station.

w Detailed DescriDtion Figure 1 illustrates broadly the i ended operation of the invention, which assumes the continued int existence of the familiar circuit-switched networks. When therefore a ca ling instrument (hereinafter called 'station') needs to communicate with a second instrument (station) 2, station 1 will initially use a circuit -switched fine 3, since there is a presumption that at least in the foreseeable future the remote station 2 will be connected to the public-switched telephone network. If however the called station 2 is connected to a packet-switched network 4 and the calling station 1 is also connected to the packet-switched network, then the call may be completed over the packet-switched network.

Whether a call should be completed over the packet-switched network 4 may be a matter of selection and programming and may also be dependent upon whether the cost of a call per uni it time is cheaper or more expensive over the packet-switched network 4 than it is over the ordinary telephone line 3 which proceeds through the public-switched telephone network. It will be assumed in the followine that at least the calling instrument or station 1 is configured or programmed to attempt to establish a packet-switched call connection with the remote station 2 if it is feasible to do so.

Ficure 2 Illustrates a callin. station 10 which includes a telephone instrument 1 comprising a w familiar handset 11 and a keypad 12. The instrument 1 is connected to a voice codec 13 which takes analo. si-nals from the handset, dialtizes them and passes the digitized data to a central processing unit (CPU) 14. The CPU may be of the digital signal processor type. It is employed w to process signals both from the handset 1 via the voice codec 13 and also a packet interface 15 and to couple signals from a PSTN interface 16. The packet interface may be any one of a variety of packet interfaces, such as an ASDL inter-face or an Ethernet interface. The packet interface, in this example, transmits Ethernet packets in which the messacre data is constituted by voice data obtained by way of the voice codec 1 3) and CPU 14 from the instrument 1.

F1Rures 3 and 4 illustrate the operation of a station 10 when operating as a calling station and a called or receiving station respectively In the s,,,stem broadly shown in Figure 1. and on the assumption that at least telephone 1 is disposed in a station 10 having a facility for communicating by way of the packet-switched 1 - network 4, the operation is as follows.

User A at station 10 including instrument 1 calls a user B, having telephone 2 by means of obtaining, the keypad information entered by the keypad 12 and calling via the public-switched telephone network, as shown at stages 30 and 3) 1 of Figure 3). If the call did not connect (stage c c 32), a fresh attempt is made to initiate the call (stage 30). In any case, the CPU will collect the digits from the keypad and signal them down the PSTN interface 16 to the public-switched telephone network.

1 1 Once a circuit has been established by way of the public-switched network, users A and B will be able to talk over the circuit as In a standard telephone call. Once the call is established, the originatincr station will attempt to signal the receivin. station to establish whether the receiving station has a packet-switched network that could be used for continuing the call. A basic signalling method that will work on all types of public-switched telephone networks is in-band with the voice signal. One method is to employ DTNE signals to send information from A to B, namely a sequence of tones along with the user's voice data which indicates to the receiving station that the sendincr station 10 is equipped with a secondary packet interface 14. This is shown by stage 3) 3) in Figure -1.

If the receiving station is not equipped with the logic to respond to the DTW tones, the sending station will continue to communicate over the PSTN network, as shown by stages 5 until the call is completed (sta.ge 36). If however the receiving station is equipped with the appropriate loúic, it can respond to the sending station by indicating the network address on the packet network (stage 34). This address might be fixed and unchanging or might be assigned ZY Z> = dynamically in some way. One known method to assign addresses dynamically is to have the station communicate to a centralized entity that will use a protocol to communicate to calling station a free address This communication of the address (however allotted) of the receiving station B is communicated over the packet-switched network to the packet interface 15 and the CPU 14. This is shown by stage 34 in Figure 3.

Once the called station has responded to the calling station with its packet network address the calling station can attempt to obtain a connection over the packet network. Using the packet network address obtained from the called station, the calling station will attempt to connect over the packet network, If the calling station can establish a connection then digitized voice data may be sent from instrument 1 by voice codec 1-31 and CPU 14 over the packet network. Optionally, the called station can verify the quality of the packet link to see whether it is adequate for both voice calls. The quality cheek may determine latency, jitter, reliability or some other attribute of the link.

Thus as shown in Figure 31, there is establishment of the packet connection at stage 37 and the sending of voice data over the packet link (stage 38) until the call is completed.

1 1 With two links established, one over the circuit-switched network and one over the packet-based network., the called station can decide wffich route to choose. A variety of methods may be used to perform the chancyeo,,,er from voice on the public-switched telephone network to voice data on the packet network. For example, the called station may determine when it Is appropriate to switch over from the packet-switched telephone network to the packet network. The called ill analyse the voice information arriving on the packet-switched telephone network station wi 1 1 1 1 1 interface and wait for silence in the voice call. At this point the voice information that is arriving on the packet interface can be sent to the handset without the user being aware of the switch over. At this point the packet-switched telephone network call can be terminated and the remainder of the call connection can continue over the packet network.

Thus, as shown in Flaure 4, the station 4 logic operates as follows.

StaRe 40 indicates the rest state where the station is waiting for a call. Stage 41 indicates the answerinQ of the call o-,.,er the public-switched telephone network. Stage 42 performed in the CPU 14 requires a determination of whether the caller requested the network address of the station If no such request was made, the call over the public-switched telephone network is continued until the call is terminated (stage 43).

If the caller requested the network address for the called instrument, the address is returned (stage 44) over the public-switched telephone network using DTNT tones or other mechanism.

If the call arrived on the packet interface from the calling IP address (stage 43) the call is connected over the packet network (stage 46). The connection quality of the packet is verified (stage 47) and there is a further determination to see whether the quality is acceptable for the packet voice path (stage 48). If the call did not arrive from the packet inter-face from the calling Z LP address or the voice quality is not acceptable for the packet voice path, the call continues over the public-switched telephone network until hang-up. If however the call did arrive on the packet-based network and the voice quality is acceptable for the packet voice path, the called station analyses the public- switched telephone network and packet data for silence (stage 49) and then ternuinates the call over the public- switched telephone network by operation of the CPU u1 the call is complete, when the packet connection dropped (stage 50).

nti 1

Claims

1. A telephone instrument comprising means for providing signals for transmission.

= -5 1 means for converting signals received by the instrument into output signals.

means for selectively establishing and terminating a connection between another telephone instrument by way of a circuit-switched telephone network and for selectively establishing and terminating a connection between the instrument and a packet-switched communication network, and control means operable 1 (1) to signal over the circuit-switched network a request to said another instrument for a network address on the packet-switched network., and Ii) in response to receipt of an acknowledgement signal including a network address for said another instrument to establish a connection to the said other instrument by way of said packetswitched network.

2. A telephone instrument according to claim 1 and operable to signal by way of the call connection by way of the circuit-switched network information including the packet-switched network address of the 'instrument.

3. A telephone instrument according to claim 1 wherein the control means is also operable on receipt of a call by way of the circuit-switched network to provide an acknowledgement. including the network address of the instrument, and on receipt of a consequent message over the packet-switched network to terminate connection to the circuit-switched network and to transfer the call to the packet- switched network connection.

4. A telephone instrument according to claim ') wherein the control means is operable to test 1 the quality, of the call connection over the packet-switched network before terminating, the call connection over the circuit - switched network.

5. A telephone instrument accordine, to claim) wherein the control means is operable to detect temporary silence in the call connection over at least the circuit- switched network before terminatM2 the call connection over the circuit -switched network.

6. A telephone instrument comprising means for providing audio signals for transmission, means for converting signals received by the instrument into output signals.

C> 1 means for selectively establishing and terminating a call connection with another telephone instrument by way of a circuit-switched telephone network and for selectively establishing and terminatincy a connection with a packet-switched communication network.' and c control means operable:

(1) on receipt of a request signal sent over the circuit- switched network for an address of the instrument on the packet-switched network to signal said address over said circuit-switched network, (11) to convey receive call information from said another instrument both by way of said circuitswitched network and said packet-switched network. and (111) selectively to terminate a call connection over the circuit - switched network and to continue the call connection over the packet- switched network.

1