GB2291760A - Ringing signal for a cordless telephone - Google Patents

Abstract

A method for indicating an incoming communication to a handset is provided including sending a ringing signal over the communications resource to the handset after waiting a predetermined time interval wherein the time interval is sufficiently long enough for the handset to be locked on to the communications resource. In this way the first burst of ringing occurs as soon as locking has taken place and a long interval before the first burst is heard is avoided. In an alternative embodiment the time interval is sufficiently long enough for the handset to confirm to the base station that the handset is locked on to the communications resource.

Description

COMMUNICATIONS SYSTEM Field of the Invention This invention relates in general to cordless telephone systems and more particularly to a method of providing an incoming communication indication in a cordless telephone system.

Background to the Invention Cordless telephone systems include Cordless PBX (CPBX) systems or cordless public access systems. Typically such cordless telephone systems include a plurality of cordless (radio) handsets or Cordless Portable Parts (CPPs) and associated Cordless Fixed Parts (CFPs). The Cordless Fixed Parts (CFPs), also known as Radio Fixed Parts (RFPs), are (radio) base stations. The base stations are typically sited in an office environment in the case of Cordless PBXs (CPBXs) or in a public enviroment, in the case of public access systems. Such public access cordless systems are also known as telepoint. Telepoint generically applies to a "one-way" service, providing out-going calls from the cordless handsets, but may also apply to incoming call service in the telepoint environment, which is known as "two-way" telepoint.

The cordless portable parts are essentially low power cordless telephone handsets, and the CFPs or RFPs are the associated base stations, providing connection through a centrally integrated telephone switch to the wired services (e.g. PSTN or ISDN). In general, such telephone switches transmit and switch the voice traffic digitally, and are computer controlled.

It is an essential part of these types of equipment that handsets may not communicate directly with another handset, other than via base stations.

Examples of these types of products include CT2 (second generation cordless telephones) and DECT (Digital European Cordless Telephone).

In both the CPBX and in certain public access environment realisations, the radio base stations are connected digitally to the centralised integrated switch and control, so that the integrated central control has the ability to signal and control the RFPs, and switch voice traffic to the RFPs digitally.

FIG. 1 shows a typical cordless PBX system, including corded telephones 3, base stations 1, cordless handsets 5, and an integrated central controller 7. The corded telephones may be analogue or digital. The handsets 5 communicate over a communications resource 9 such as a radio frequency to a respective base station 1.

FIG. 2 shows an integrated telepoint system having handsets 5 able to communicate over a communications resource 9 to a respective base station 1. The base station 1 is connected to an integrated system controiler 7 which communicates to an ISDN or PSTN.

When an incoming call is to be presented to a handset or set of handsets, it is generally the case that the switch attempts to cause the handset to start ringing or alerting the user as quickly as possible; such "instantaneous" incoming call indication (or ringing) is a strong selling point with some manufacturers of this equipment. In wired PBXs, the ringing signal is applied almost immediately to the analogue or digital telephone instruments 3 connected to the PBX (see FIG 1). Further, it is a feature of many PBXs, that incoming calls from different sources are indicated to the user by applying differing ring cadences to the telephone instrument.

FIG. 3 shows two different ringing cadences 20, 22 as plotted against time in seconds. An incoming call from the PSTN or ISDN (i.e. an "external" call) may have applied ringing cadence of 400ms ringing on, 200ms ringing off, 400ms ringing on, and 2 seconds of ringing off 20. (This specific cadence is the cadence that is normally heard on private telephone lines in the UK) Similarly, a call to one extension on the PBX from another extension on the same PBX (an "internal" call), may have an applied ringing cadence of 1 second ringing on, followed by 3 seconds of ringing off 22. These differing cadences allow the telephone user to distinguish an "internal" call from an "external" call, and thus modify their answering dialogue accordingly.

CT2 equipment has equal access to 40 channels. When a handset (or base) wishes to establish a communications link to base (or handset), the initiating part is mandated to scan the 40 channels and determine from measurement which of the 40 channels is suitable for establishing a link; having chosen a suitable channel, the initiating end begins transmissions on the selected channel. The receiving end is obliged therefore to continually or occasionally scan each of the 40 channels in order to detect a possible call from the initiating end.

In the specific case of CT2 equipment, particularly equipment compliant with the "Common Air Interface" (CAI), (MPT1375 in the UK, or the ETSI interim standard I-ETS 300 131), the CT2 handsets typically run to an internal unsynchronised (with respect to other handsets) 1.4 second cycle. Once during each internal cycle, the handset will scan the 40 channels in order to detect whether or not there is a call from a base that may be trying to contact the handset. In the best case, allowing for a small amount of time required for verification of the calling base, the handset can be contacted within 100ms of the base trying to contact it, and in the worst case, it may take the handset up to 1.5 seconds to detect a calling base.

The signalling provided in the CAI allows a base to call a single handset individually to present an incoming call to the handset, or the base may call up to 32 handsets to present a call to these handsets, by "rollcalling" the handsets in cyclical sequence. In addition, once a handset comes onto the channel being used by the base, it responds to the base each time the handset is roll-called, so that the base can determine which handsets it has called are receiving the incoming call request.

The CAI standard provides a method over a signalling channel to allow the base to instruct the handset when to switch on its internal ringer transducer, and when to switch it off, on a regular basis. This technique allows the base to present ringing cadence to the handset that "cadence follows" the incoming detected ringing voltage (in the case of analogue ringing) so as to allow the user to determine the source of the call; in the case of a digitally controlled radio base station, the central controller could indicate the cadence, and also alter the applied ringing cadence according to the source of the call.

In the cordless technology described above, there is a clear time lag between the base beginning to contact and ring a handset or handsets, and this time lag can be quite extensive. If the method of applying ringing cadence follows that method applied to corded phones, in that ringing is applied immediately, because of the delays that apply to a handset coming on to the channel being used by the base, and thus being able to respond to the ringing commands included in the signals from the base, it is possible that the handset or handsets will miss some or all of the first second of ringing. By the time a second "burst" of ringing is being applied, however, the handset is almost certain to be on the channel, but in some cases, the actual second burst of ringing is the first heard by the user of the handset.

This introduces a perceptible delay of up to 3 seconds before the user is aware of the existence of an incoming call. This problem is shown diagrammatically in FIG. 4. Time line or bar 24 shows that the first burst of ringing is not even received by the handset. In the case of an external call it is not until a full three seconds after the call has been indicated does the handset begin to ring, while in the case of an internal call it is not until after four seconds that the handset begins to ring. A problem exists for the caller who hears the call being indicated but does not realise that the caller's handset is not ringing. Thus, a caller may prematurely hang up or end the communication thinking that no one is answering his call.

It is desirable to have a method of applying ringing instruction to a cordless handset so as to take into account some, or all of the delays that are experienced, and yet attempt to have ringing applied to a handset or handsets as quickly as possible.

Summarv of the Invention According to the present invention, there is a method provided for indicating an incoming communication to a handset including the steps of receiving a call indication for the handset at a base station, sending a ringing signal over the communications resource to the handset after waiting a predetermined time interval wherein the time interval is sufficiently long enough for the handset to be locked on to the communications resource.

In a preferred embodiment the time interval is the minimum amount of time needed for the handset to locked onto the communications resource.

In an alternative embodiment the time interval is sufficiently long enough for the handset to confirm to the base station that the handset is locked on to the communications resource.

Brief Description of the Drawing FIG. 1 shows a prior art cordless PBX system.

FIG. 2 shows a prior art integrated telepoint system.

FIG. 3 shows a timing chart of ringing bursts for two different cadences.

FIG. 4 shows a timing chart for a handset to lock on a channel versus the timing chart of FIG. 3.

FIG. 5 is a flow chart for a method according to an embodiment of the present invention.

FIG. 6 shows a timing chart according to the embodiment of FIG. 5.

FIG. 7 is a flow chart for a method according to an alternative embodiment of the present invention.

FIG. 8 shows a timing chart according to the alternative embodiment of FIG. 7.

Detailed Description of the Preferred Embodiment Referring to FIG. 5, a method is provided for indicating to a handset of an incoming communication according to the present invention. In step 30, an incoming communication is indicated at a respective base station for a particular handset. The base station seizes the communications resource and polls the handset. The base station then delays sending a ringing signal to the respective handset for 1.6 seconds, as in step 32. The time delay may differ in each communications system but should be sufficiently long enough to allow for a handset in the relevant communications system to be able to scan all available communications resources, or channels, and lock onto to any one over which a communication is being attempted with the handset.

Thus, if it takes a handset 1.4 ms to scan all 40 channels as in CT2 equipment and then an extra 200ms for the handset to lock onto to a channel then the base station should not send the ringing signal for 1.6 seconds.

Immediately after the base station sends the ringing signal, as in step 34, the handset receives it and the cadence signalling follows as in step 36.

FIG. 6 shows a resulting timing chart for the method of FIG. 5. The ringing at the handset is delayed 1.6 seconds for all calls after which time the handset has had sufficient time to come onto the relevant channel and does not miss any ringing bursts. Plots 38 and 40 show the ringing cadences for both external and internal calls. Bar 44 shows in a lighter shaded area that it takes a maximum amount of time equal to 1.4 seconds to scan the channels and then a possible 200 ms for the handset to lock on. Thus, after 1.6 seconds the handset should always see the first ringing burst.

An alternative embodiment is shown in FIG. 7. The base station receives an incoming communication for the handset as in step 50. The base station seizes the communications resource and polls the handset. The base station delays sending a ringing signal to the handset until the handset has positively responded to communication over a particular communications resource with the base station or a maximum delay period as in step 52.

This step may include having the handset scan the available communications resources, detect a communication from the base station and then confirm to the base station that the handset is available or locked onto the communications resource. In any event, the base station does not send the ringing signal to the handset until after a communication is received from the handset confirming that the handset is available for communication or after the maximum delay period. After such confirmation or maximum delay period the base station sends the ringing signal to the handset as in step 54. The ringing cadence follows as in step 56.

FIG. 8 shows a resulting timing chart for the method of FIG. 7. The ringing signal is delayed in plots 60 and 62 until immediately after the base station knows that the handset has come onto the proper channel. Bar 64 shows an example of when the handset comes onto the channel after approximately .8 seconds after which the ringing signal is immediately sent to the handset. The handset receives the ringing signal or an incoming communication indication as soon as it is possible for the handset to receive it and can indicate to the user that an incoming communication is being transmitted.

The preferred embodiments have been described with reference to ringing or audible tones but the invention could be applied to other types of call indication such as vibrating indicators.

In both methods the calling party knows when his call is being indicated at the handset.

The method of the present invention applies ringing instruction to a cordless handset so as to take into account some, or all of the delays that may be experienced, and yet attempts to have ringing applied to a handset or handsets as quickly as possible. If instead of applying ringing cadence immediately upon attempting to contact a handset or group of handsets, the base instead delays the application of cadence for between 1 to 2 seconds before starting the first "burst", there is a very good probability that the handset or handsets will be on the channel, and will receive the first applied ringing burst in its entirety.

The alternative embodiment of the invention uses the fact that the base knows when a handset or a complete population of handsets have come onto its calling channel, and then the base station uses this information to determine when to start issuing "ringer on" instructions to the handset or population of handsets, with a back-stop position of delaying the application of ringing for 1 to 2 seconds in the event that a particular handset has not come onto the calling channel (the particular handset could be switched off or out of range, and thus not able to respond). Where the single called handset has responded to the base on the calling channel, the base can begin instructing the handset to start ringing immediately, and where the base determines that a population of handsets it is calling have all come onto the calling channel, the base can begin starting the population of handsets to start ringing.

The present invention provides incoming call indication -to å cordless telephone or set of cordless telephones as quickly as possible, within the constraints of the time delays inherent in the access technology.

Claims (5)

Claims

1. A method for providing an incoming communication indication in a cordless telephone system having a handset, a base station and a communications resource for the handset and base station to communicate over, the method comprising the steps of: receiving a call indication for the handset at the base station; sending a ringing signal over the communications resource to the handset after waiting a predetermined time interval wherein the time interval is sufficiently long enough for the handset to be locked on to the communications resource.

2. The method of claim 1 wherein time interval is the minimum amount of time needed for the handset to locked onto the communications resource.

3. The method of claim 1 wherein the time interval is equal to 1.6 seconds.

4. The method of claim 1 wherein the time interval is sufficiently long enough for the handset to confirm to the base station that the handset is locked on to the communications resource.

5. A method for providing an incoming communication indication in a cordless telephone system substantially as herein described with reference to FIGS. 5 or 7 of the drawing.