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BACKGROUND
1. Field of the Invention
This invention relates generally to the field of Integrated Services
Digital Network (ISDN) Terminals or Terminal Adapters (TA) and more
particularly to an ISDN terminal or terminal adapter which includes a
provision for providing teleconferencing (conference call) by utilizing a
daisy chain switching and summing arrangement at the terminal or terminal
adapter as a conference bridge.
2. Background of the Invention
Conventional teleconference arrangements are based on a centralized
conference bridge architecture. A central processor situate at the hub
location of a star network performs all of the switching and mixing
functions required to conduct a conference. Of course, for such a network
to operate, the central processor must be able to provide such function.
Since this is often out of the control of the end user and often results
in a special charge, this arrangement may be disadvantageous in some
networks.
Another conference arrangement is the so called "hot and holler" circuit.
This arrangement is essentially a private line multi-drop analog circuit
which permits one way voice broadcast. This arrangement has similar
drawbacks.
With the emergence of ISDN, a 2B+D basic rate service (two B Bearer
channels and a packetized D signaling channel) will eventually be widely
available. The present invention provides a flexible and inexpensive
alternative to more conventional techniques which has the advantage of
being controlled by the users terminal or terminal adapter. For purposes
of this document, the term "terminal adapter" is intended to embrace
devices performing conventional terminal or terminal adapter functions as
well as telephone sets, terminals and the like which have the
functionality of a conventional terminal adapter, i.e. 2B+D interface and
multiplexing and the like, built in even though such devices may not
provide some of the functions of a conventional terminal adapter (such as
conversion to RS-232 for connection to non-ISDN type equipment).
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an arrangement for
providing conference calls in an ISDN.
It is another object of the present invention to provide teleconference
capability within an ISDN terminal adapter.
It is an advantage of the present invention that the bridging function is
distributed within the terminal adapters of the network.
It is another advantage that a virtually unlimited number of parties can be
coupled together without concerns about impedance matching and loading.
These and other objects and advantages of the invention will become
apparent to those skilled in the art upon consideration of the following
description of the invention.
In one embodiment of the present invention a device for providing
conference capabilities in an ISDN includes a first receiver for receiving
a first signal representing a first message over a first ISDN B-channel. A
second receiver receives a second signal representing a second message
over a second ISDN B-channel. A receive mixer mixes the first signal with
the second signal to produce a receive mixed signal. A local receiver
receives a local signal representing a local message to be transmitted
over the first and second ISDN B-channel. A first transmit mixer mixes the
first signal with the local signal to produce a first transmit mixed
signal. A first transmitter transmits the first transmit mixed signal over
the second ISDN B-channel. A second transmit mixer mixes the second signal
with the local signal to produce a second transmit mixed signal. A second
transmitter transmits the second transmit mixed signal over the first ISDN
B-channel.
In a method of implementing a conference call in an ISDN terminal adapter
includes the steps of: providing a first terminal adapter with access to
first and second communication channels, the first terminal adapter being
coupled to a first source of information which produces first information;
creating a logical connection to a second terminal adapter over the first
communication channel, the second terminal adapter being coupled to a
second source of information which produces second information; creating a
logical connection to a third terminal adapter over the second logical
channel, the third terminal adapter being coupled to a third source of
information which produces third information; mixing the second
information received over the first communication channel with the first
information; transmitting the mixed second and first information over the
second communication channel; mixing the third information received over
the second communication channel with the first information; transmitting
the mixed third and first information over the first communication
channel; mixing the second and third information received over the first
and second channels respectively together and providing the mixed second
and third information to the first source of information.
In the present invention an ISDN terminal or terminal adapter with
provision for implementing conference calls includes a fist interface for
interfacing with a first B channel. A second interface interfaces with a
second B channel. A third interface interfaces with a terminal. A
conference bridge couples signals from the first B channel with signals
from the second B channel and the terminal to provide an exchange of
signals among at least three parties.
The features of the invention believed to be novel are set forth with
particularity in the appended claims. The invention itself however, both
as to organization and method of operation, together with further objects
and advantages thereof, may be best understood by reference to the
following description taken in conjunction with the accompanying drawing.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a block diagram showing the overall concept of the daisy chain
teleconference arrangement of the present invention.
FIG. 2 shows a more detailed diagram of the daisy chain teleconference
arrangement of FIG. 1.
FIG. 3 shows a detailed block diagram of an ISDN terminal adapter according
to the present invention.
FIG. 4 shows a flow chart of the operation of the conference system of the
present invention.
DETAILED DESCRIPTION OF THE INVENTION
Turning now to FIG. 1, the basic concept of the present invention is
illustrated. In this example, four telephone sets W, X, Y and Z are
coupled together in a teleconference arrangement according to the present
invention via the two logical B channels of the ISDN. In basic rate ISDN,
two B channels (B1 and B2) and a D channel are actually multiplexed
together over a single set of transmission lines. However, the logical
channel connections shown in the drawings are more illustrative of the
daisy chaining of the present invention. For simplicity, the logical B
channels have been illustrated as direct connections between the terminal
adapters, but those skilled in the art will understand how the terminal
adapters actually interface to the ISDN to provide such logical
connections through the network.
In this figure, a telephone set 10 (telephone set W) is connected to a
terminal adapter 12. This terminal adapter 12 is coupled through one of
its logical B channels 14 to a second terminal adapter 16 which is in turn
connected to a second telephone set 18 (telephone set X). During the call
setup, telephone set 18 makes the connection to the next telephone set in
the daisy chain via its second B channel 20 to terminal adapter 22.
Terminal adapter 22 is connected to a third telephone set 24 (telephone
set Y). Thus far, terminal adapter 16 is acting as teleconference bridge
among telephone sets 10, 18 and 24 and adds or mixes the signals from all
three telephone sets appropriately so that each user can hear the other.
To establish the next link in the daisy chain, telephone set 24 places a
call through terminal adapter 22 via its second B channel 26 to terminal
adapter 28 and thus to the fourth telephone set 30 (telephone set Z). This
completes the conference connection among all four telephone sets.
Turning now to FIG. 2, a more detailed drawing of the daisy chain
arrangement of FIG. 1 is shown. In this drawing, the logical B channels
are once again simplified for clarity, but show both inbound and outbound
lines to facilitate discussion of the signal flow. Also, the necessary
switching and normal terminal adapter functions such as transmitter and
receiver, etc. have been omitted for clarity since this figure is intended
to illustrate the summation of the various voice signals. For purposes of
this discussion, the terms summation and mixing and related terms are used
synonymously and interchangably to refer to summation of two or more
signals so that both signals coexist on the same circuit node. This can be
accomplished by analog techniques (e.g. a summing amplifier or audio
mixer) or by digital techniques which are equivalent or by combinations of
the two approaches.
In the preferred embodiment, the mixing or adding function is provided by
using a digital adding circuit. This circuit can be implemented via
dedicated hardware or by a programmed processor. In either event, digital
PCM signals received over the B1 and B2 channels by a terminal adapter are
added sample by sample to produce a binary sum which may then be converted
to analog for transmission to the telephone set for conversion to audio.
In this digital embodiment, as well as some analog embodiments, it will be
appreciated that there may be instances where more than one party is
talking simultaneously for brief periods of time (usually only during
brief interruptions and the like). In this event, it may be possible for
the adders to reach maximum positive or negative output values and
producing clipped speech. Since it is anticipated that these instances
will be brief and a relatively small percentage of the actual conference
time, it is not believed to be a serious problem. This is especially the
case since clipping of the peaks of band limited speech signals often
results in little loss of intelligibility. Several mechanisms can be
devices to partially or fully compensate for this minor problem if
required. For example, dynamic range compression techniques can be used
with expansion being appropriately scaled to prevent clipping. Or, for
example in a 16 bit system, 15 bits of dynamic range can be allocated per
signal to allow the additional bit of range to be used as "headroom" the
summation for times when more than one signal peak occurs simultaneously.
Other compensation methods may occur to those skilled in the art; however,
as stated previously, it is not believed to be a serious enough problem to
warrant concern in most circumstances.
Referring to FIG. 2, the outbound signal from telephone set 10 carries
signal "w" through terminal adapter 12 and out of the outbound path of B2
channel 14 of terminal adapter 12 shown as 34. This "w" signal is received
by terminal adapter 16 via its B1 channel and applied to mixers 36 and 38
therein. The signal "x" from telephone set 18 is applied to mixers 36 and
40 within the terminal adapter 16. Mixer 36 produces the output signal
"w+x" at its output which is directed to an outbound path 44 of B channel
20. Terminal adapter 22 receives the "w+x" signal from path 44 whereupon
it is applied to mixers 48 and 50. The "y" signal from telephone set 24 is
also applied to mixer 48, as well as mixer 52. In mixer 48, the "y" signal
is added to the "w+x" signal to produce a signal "w+x+y" which is shipped
out over an outbound path 56 of B channel 26. This "w+x+y" signal is
received by terminal adapter 28 and passed on to telephone set 30. In this
manner, the signals from each of the other parties W, X and Y are combined
successively in a daisy chain fashion so that they are all received by
telephone set 30.
In a similar manner, the outbound "z" signal from telephone set 30 is
transmitted over path 60 to terminal adapter 22 where it is applied to
mixers 50 and 52. The "z" signal is mixed with the "y" signal in mixer 52
and transmitted to terminal adapter 16 over path 64 as "y+z". In terminal
adapter 16, the "y+z" signal is further mixed with signal "x" at mixer 40
to produce signal "x+y+z". This signal is transmitted over path 66 to
terminal adapter 12 wherein it is delivered to telephone set 10. Thus, the
signals "x", "y" and "z" are combined and provided to telephone set 10.
At telephone set 18, an intermediate telephone set in the daisy chain,
mixer 38 is used to combine signal "w" with signal "y+z" to provide
telephone set 18 with the signals from the other parties to the conference
call. In a similar manner, mixer 50 combines signals "w+x" with signal "z"
to provide telephone set 24 with the signals from the other parties to the
conference call. Thus each four parties, in this example, are provided
with the signals produced by the other three parties.
Terminal adapter 12, which is at the left end of the chain, is shown to
include mixers 70, 72 and 74 which operate in a manner analogous to that
of mixers 36, 38 and 40 respectively of terminal adapter 16. In the
embodiment shown, signal "w" is shown passing through mixer 70 but is
essentially unaffected because, due to internal switching within terminal
adapter 12, there is no signal present at mixer 70 to add to signal "w".
Similarly, no signal is added to signal "x+y+z" in mixer 72 since terminal
adapter 12 is at the end of the chain. Equivalently, the signals could
bypass the respective mixers in terminal adapter 12 without departing from
the invention. Analogous statements apply to terminal adapter 28 with
regard to mixers 80, 82 and 84. The two B channel paths for the second B
channels which are unused (or used for purposes other than teleconference)
are shown coupled to terminal adapters 12 and 28 for completeness.
While the above example shows a four party conference, it is clear that the
number of parties involved is essentially unlimited. Since the signals are
coupled with distributed daisy chain bridges, there are no significant
loading problems or impedance matching issues. It is also noted that the
parties at the end of the chain need not have the present conference
capability and in fact need not even be part of an ISDN per se. They only
need to be able to be called by parties on the ISDN (e.g. a conventional
telephone set may be party to the conference).
During operation, if a party at one of the intermediate nodes leaves the
conference, several possibilities exist. The actual operation of the
terminal adapter depends upon the desired implementation of the present
invention. If an intermediate party leaves the conference, it is evident
that in the absence of some special action, one of two things will happen:
(1) the intermediate TA will have both channels occupied prohibiting the
user from using his telephone, or (2) the conference call will be
segmented into two parts due to the calls being torn down at the TA. In
some circumstances, either of the above actions may be acceptable to the
user. For example, in case 1, if each user has a number of additional
overflow lines which can be used, it may present no particular problem. In
case 2, the conference can be manually reestablished by the parties still
involved in the call by simply having one of the terminated parties
adjacent the intermediate node replace the call to resume the conference.
In this instance, it is desirable for the intermediate TA to notify its
adjacent TA's to establish a reconnection as described below. In small
offices where conferences rarely take place, either of the above
situations may be an acceptable mechanism for providing an economical
access to the present conference capability. This is especially true in
the normal case where a third or fourth party is brought into a conference
only briefly and therefore leaves the conference first.
A more elegant solution to the problem is to provide each TA with the
intelligence to know that a conference is taking place and to remember who
the parties to the conference are. This will permit the conference bridge
to be automatically reestablished by a kind of call transfer or autodial
operation in which the two ends of the bridge are relinked bypassing the
intermediate node. However, it should be noted that the nature of most
conference calls is that there are usually only three to four parties
involved and often a party who leaves the conference is the last party
called (usually someone called in briefly to answer a specific question or
the like). Accordingly, the problem is one which in practice may be
infrequently encountered.
In ISDN networks, 64 Kbps PCM is normally used for voice coding. In such
networks, conversion of PCM to linear may be required prior to summation
for voice conferencing. With subrate multiplexing, the B channels can
carry multiple channels of data across the whole chain in other
embodiments. By using low bit rate compressed voice multiplexed with data,
simultaneous voice and data conferencing is also contemplated.
Turning now to FIG. 3, a block diagram of the terminal adapter of the
present invention is shown. Although the present preferred embodiment is
of a terminal adapter, those skilled in the art will recognize that the
present invention may also be realized within an ISDN telephone or
terminal device. The terminal adapter of FIG. 3 includes a network
interface 80 which provides the interfacing functions necessary to
interface to the S (or T or U) termination definition for the ISDN. The
network interface 80 is coupled to a processor 82 which may be based upon
a microprocessor. Processor 82 provides multiplexing and demultiplexing of
the 2B+D signals as well as interfacing with a control panel 84 for
accepting user commands (e.g. dialing information and conferencing
commands) and a display panel 86 for displaying various information to the
user (e.g. phone number dialed, conference active, display map of the
daisy chain, etc.). Display panel 86 may take various forms including LCD
displays, indicator lights, CRT screens and the like. Also coupled to the
processor 82 is a B1 interface 88 which is coupled to the processor by a
common bus interface 90 and provides an interface to the voice terminal
and provides the summation function as well as analog to digital and
digital to analog conversion. Similarly, a B2 interface 92 is coupled to
the processor vial bus 90 and provides similar functions. Finally, a D
interface 94 is provided for utilization of the ISDN D channel.
Turning now to FIG. 4, operation of the present terminal adapter or
terminal is described beginning at 100. At 102, the originator of a
conference call plans the chain of conference call participants. In the
case of a simple three party conference, this process is obviously quite
simple with complexity increasing with the number of participants.
However, in any case, it is more or less a process of making an ordered
list of participants corresponding to the chain to be built with neighbors
on the list corresponding to neighbors on the chain. At step 104, the
originator calls his neighbors to begin the chain. At step 106, the
originator instructs his neighbors to place calls to their neighbor(s) as
required to construct the chain. If this ends the chain at 108 then the
conference connection has been completed and the conference ensues at 112.
If not, step 106 is repeated with the originator or participants
instructing the new parties to the conference to call the next parties as
required until the chain is complete at 108.
When the end of the conference is reached at 114, all parties simply hang
up at 116 and the process ends at 120. If a party is to leave the
conference chain but the conference is to continue, then a reconfiguration
is required at 122. When this occurs, the affected parties simply hang up
the call and the parties remaining in the conference simply reestablish a
chain configuration by redialing at 124.
While the present invention has been described in conjunction with a voice
application, it will be clear to those skilled in the art that the
invention has other applications including data transmission. In this
case, the mixers must actually accomplish a multiplexing function as
opposed to simple audio mixing or the equivalent. Other applications such
as facsimile, graphics, online computer games and the like are also
possible without departing from the present invention.
Thus it is apparent that in accordance with the present invention an
apparatus that fully satisfies the objectives, aims and advantages is set
forth above. While the invention has been described in conjunction with a
specific embodiment, it is evident that many alternatives, modifications
and variations will become apparent to those skilled in the art in light
of the foregoing description. Accordingly, it is intended that the present
invention embrace all such alternatives, modifications and variations as
fall within the spirit and broad scope of the appended claims.
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