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Description  |
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FIELD OF THE INVENTION
This invention relates generally to video telephony and, more specifically, to bidirectional transmission of voice and picture information among a large number of geographically distributed users.
BACKGROUND OF THE INVENTION
Because two-way video communications can give individuals the ability to communicate graphical information and to see facial expressions and gestures that cannot be conveyed by audio alone, much emphasis has been placed on commercial development
of such systems. Indeed, video telephones that work with analog telephone lines have been demonstrated. However, due to the limited bandwidth of conventional telephone lines, and the consequent limitation on the amount of information that can be
carried therethrough, commercial development has been limited to less-than-full-motion video presented on a small display.
In order to overcome the bandwidth limitation associated with video telephony transmitted over the analog telephone lines, video telephones more recently have been designed to work with digital telephone access lines, such as ISDN. However, at
the present time, digital access facilities to consumer homes are not readily available.
Other systems use optical fiber directly linked to subscriber homes in order to obtain the high bandwidth needed for full motion video. However, these facilities are expensive, and thus are not accessible to the ordinary household. Besides, it
will be decades before most homes are provided with fiber access.
The above-outlined problems are substantially ameliorated by the arrangement disclosed in the co-pending, commonly assigned United States patent application of C. D. Yu entitled "Bidirectional Video Telephony Using Shared Channels on Coaxial
Cable Networks," Ser. No. 787,436, filed Nov. 4, 1991. In a disclosed embodiment of the Yu arrangement, the terminal equipment comprises a standard television set, serving as the audio/video display, and a consumer-type camera or camcorder, serving as
the audio/video source. A coaxial cable network, which is preferably a part of an existing cable television system, provides a local access link for the transmission of the video telephone signals between each originating and destination cable
subscriber location and a respective "head end" located on the cable company premises. A network interface unit, or NIU, at each location provides a control interface between the terminal equipment and the cable television distribution network to deal
with such "housekeeping" chores as allocation of upstream and downstream video telephone channels between the subscriber location and the head end, receiving of "dialing" information from the subscriber, etc. Each of the head ends is connected to a
"point of presence" of a telephone common carrier-illustratively an interexchange carrier such as AT&T-so that a connection between pairs of head ends, and thus between a pair of video telephone locations, can be made via a switched network maintained by
the carrier.
SUMMARY OF THE INVENTION
In accordance with the present invention, the usefulness of a video telephony system which uses cable television distribution networks to connect cable subscriber locations to the telephone network is enhanced by providing the system with the
capability of allowing cable subscriber locations to communicate with non-cable subscriber locations, such as locations that are connected to the switched digital network exclusively via telephone facilities (including locations reached via dialing 800
or 900 numbers of international destinations). The invention thus enables parties who possess a video telephone, but are not served by a video-telephony-capable cable television distribution network, to communicate with parties who are so served but who
do not possess a video telephone. Advantageously, the telephone facilities may include an ISDN connection which supports communications between the point of presence and an ISDN video telephone. However, the invention contemplates that other types of
connections--to which are connected other types of video telephony equipment--may be used including, for example, non-ISDN video telephones which communicate over standard voice channels.
In preferred embodiments, a database containing information about cable subscriber locations is maintained and made available to the switched digital network. When a request to establish a video telephone connection over the switched digital
network is received at the originating point of presence, the database is accessed to determine whether the selected destination location is or is not a cable subscriber location. Note that, in accordance with the invention, that connection request
received at the originating point of presence may have originated either from a cable TV head end or via telephone facilities exclusively. If the selected destination location is, in fact, a cable subscriber location, the connection is established to
the cable television distribution network head end and thence down to the destination location itself. If not, the call is routed via conventional telephone facilities.
The database may also contain information about non-cable subscriber locations, such as the data rate at which video telephone equipment at those locations operate, thereby allowing the system to extend video telephone signals to such locations
at an optimum data rate. If the database does not contain information about a particular cable subscriber location, the equipment thereat is assumed to operate at a predetermined, default rate.
BRIEF DESCRIPTION OF THE DRAWING
Further aspects and features of the invention will become apparent from a consideration of the following detailed description and accompanying drawing, in which
FIG. 1 is a block diagram illustrating a video telephony system embodying the principles of the invention;
FIG. 2 is a block diagram of an analog network interface unit that can be used in the system of FIG. 1;
FIG. 3 is a block diagram of a cable head end used in the system of FIG. 1;
FIG. 4 is a block diagram of a video enhanced services platform (VESP) used in the system of FIG. 1;
FIG. 5 is a block diagram of point of presence (POP) equipment used in the system of FIG. 1;
FIG. 6 is a block diagram of a digital network interface unit that can be used in the system of FIG. 1 instead of the analog network interface unit of FIG. 2;
FIG. 7 shows the inter-relationship between FIG. 3 and FIG. 4;
FIG. 8 is a flowchart setting forth the logical sequence of steps implemented within the system of FIG. 1 to achieve connections between different types of subscriber locations which are served by the system;
FIG. 9 depicts a portion of a database maintained within a video network control point (NCP) that is within the system of FIG. 1; and
FIG. 10 is an enlarged view of one of the subscriber locations in the system of FIG. 1.
DETAILED DESCRIPTION
The block diagram of FIG. 1 shows a video telephony system similar to that disclosed in the above-cited Yu patent application. In particular, an originating cable subscriber location 101 is shown to be able to communicate to a selected
destination cable subscriber location 105 in a video telephone call established via a switched digital telecommunications network 160, the latter being part of an interexchange carrier (IXC) network 150. Cable subscriber locations 101 and 105 are
illustratively private residences, although they need not be. The gateways to network 160 are point of presence (POP) locations 161, 162, which are described in more detail below.
Originating and destination cable subscriber locations 101 and 105 are connected to POPs 161 and 162, respectively, via connections which include respective connections through cable television distribution networks 121 and 126. In particular,
audio and video communication between a network interface unit (NIU) 104 (described in more detail in connection with FIGS. 2 and 6) positioned within originating cable subscriber location 101 and originating head end 122 (located on cable company
premises) uses coaxial cable television distribution network 121, which includes a series of bidirectional (i.e., forward and reverse direction) amplifiers. Such amplifiers are currently available in three bandwidth split categories from sources such as
Scientific Atlanta, Jerrold and Magnavox. Within head end 122, cable head end 124 filters and separates the received signal so that only the portion of RF bandwidth that is dedicated to video telephony is demodulated and applied to a video enhanced
services platform, or VESP, 125 within originating head end 122. The portion of the RF bandwidth that is used for "entertainment channels" received from downstream entertainment channel source 130 is modulated by existing head end equipment and applied
to existing cable system facilities that form no part of the present invention. Cable head end 124 and VESP 125 can be physically located at the same or different locations.
Other cable subscriber locations (not shown) have similar associated connections to head end 122 via coaxial cable television distribution network 121 in a tributary type structure and receive the same signals that are in effect "broadcast" on
coaxial network 121.
Typically, the RF spectrum between 5 MHz and 30 MHz on cable network 121 is reserved for upstream use. Accordingly, four 6 MHz channels can simultaneously carry upstream analog audio and video signals in NTSC format. However, the coaxial
bandwidth can be split in other ways for upstream and downstream use, so that a different number of upstream channels may be available for either upstream video telephone signals or entertainment signals. For example, digital video compression
technology has made possible packing several (e.g., 4) video signals in one 6 MHz bandwidth. Throughout this specification, analog video telephone channels will be assumed to have a 6 MHz or less bandwidth. The capacity of digital channels will be
denoted in terms of kilo bits per second.
In VESP 125, the demodulated audio and video signals are converted to a compressed digital signal, multiplexed with other digital signals, and sent to POP 161 as a 384 Kb/s composite signal via a digital communications channel 131, using an ISDN
primary rate interface (PRI) connection along with other so-called DS1 transmission facilities which are controlled by the D channel of the PRI connection using standard non-facility-associated signaling. (In the drawing, an ISDN connection is shown as
a pair of lines-a solid line representing the B channels and a dotted line representing the D channel.) The composite digital signal is then demultiplexed and one digital signal is transported from POP 161 to POP 162 via the digital switched telephone
network, which may be AT&T's switched 384 Kb/s network.
After the end-to-end link between the originating and destination head ends is established, the digital audio/video signal is transmitted to destination POP 162. The digital signal received in POP 162 is multiplexed with other digital signals
destined for the same destination cable network and the composite signal is transmitted to destination head end 127 via a digital communication channel 136 using an ISDN PRI connection. In a similar fashion to that just described, audio and video
communication between head end 127 and destination location 105 uses the coaxial cable distribution network 126 serving destination location 105, which connects the cable head end 128 within destination head end 127 to a network interface unit 108
positioned within destination location 105. VESP 129 transforms digital signals back to analog audio and video signals, which are then modulated to specific RF carriers allocated for video telephony. Other locations (not shown) are tied into coaxial
cable distribution network 126 in a tributary type structure, so that signals on cable distribution network 126 can represent video telephone information concurrently originating in or destined for several locations, as well as "entertainment channel"
information provided by downstream entertainment channel source 135 and combined in cable head end 128. As with originating head end 122, the cable head end 128 and VESP 129 within destination head end 127 can be physically located at the same or
different locations.
Before proceeding further, it may be observed at this point that, although the establishment of a connection between the originating and destination cable subscriber locations has been described as proceeding step-by-step from the former to the
latter, other techniques for establishing the end-to-end connection may be used. One possibility is to proceed step-by-step in the opposite direction. Another is to establish connectivity from the destination location up to its associated VESP and then
proceeding step-by-step from the originating subscriber location to that VESP.
Within originating cable subscriber location 101 and destination cable subscriber location 105, audio and video signals are originated by cameras 102 and 107, respectively, and received and displayed on conventional television sets 103 and 106,
respectively. These elements are connected to and interact with NIU 104 and 108, respectively, in a manner to be explained more fully below. It will be understood that any audio/video origination source (such as a camcorder or video tape player) can be
used instead of cameras 102 and 107 and that any utilization device (such as a VCR) can be used instead of television sets 103 and 106. Also installed at cable subscriber locations 101 and 105 are conventional voice telephone sets 109 and 119,
respectively, which have standard local loop connections 113 and 118 to nodes within respective local exchange carrier (LEC) networks 140 and 145 (described below) and between which conventional voice communication paths can be established through the
IXC and/or LEC networks.
Switched digital network 160, as shown in FIG. 1, may include a single switch or a plurality of switches, including ISDN-capable switches within POPs 161 and 162 as well as other switches shown as "nodes" 163-165 in FIG. 1. The switches are
interconnected by suitable transmission and signaling facilities, including trunks 192 and including standard common channel signaling, or CCS, facilities 190, that are themselves well known and form no part of the present invention. Suffice it to say
that the digital network is arranged to route calls, which can be digitally encoded to represent audio and video information, as well as associated routing and control signals, to the appropriate destination. For the purposes of controlling network call
flow, carrier 150 includes a number of network control points (NCPs), such as NCPs 184 and 186 discussed in more detail below. The network further includes so-called signal transfer points (STPs) 191 which are interconnected with each other, with the
NCPs, and with the various switching nodes via CCS signaling paths 190 shown as dashed lines.
Also shown in FIG. 1 are local exchange carrier (LEC) networks 140 and 145, which include LEC nodes such as nodes 141 and 146. Nodes 141 and 146 are ISDN-capable digital switches and have trunk connections 151 and 152 to POPs 161 and 162,
respectively. Additionally, signaling lines 142 and 147 connect LEC nodes 141 and 146 to respective STPs 143 and 148. The latter, in turn, are connected to respective STPs 191 within network 160 via signaling lines 144 and 149. Such signaling
interconnections between the LECs and interexchange carriers such as AT&T are not currently ubiquitous, but are required in order to provide ISDN capabilities such as 64 Kb/s transmission. Over time, it is expected that such signaling interconnections
will, indeed, become ubiquitous or at least nearly so.
Also shown in FIG. 1 are originating ISDN subscriber location 110 and destination ISDN subscriber location 115. These, again, are illustratively private residences although they need not be. Subscriber locations 110 and 115 are connected to
POPs 161 and 162 via other than a cable television distribution network--specifically, via respective telephone facilities. In particular, subscriber locations 110 and 115 are connected to LEC nodes 141 and 146, respectively, via ISDN BRI lines 112 and
117. These locations illustratively are outfitted with ISDN video telephones 111 and 116 which communicate video signals using CCITT Recommendations H.221 and H.261. The latter define an international video compression standard for digitization and
compression of video signals at rates which are multiples of 64 Kb/s (i.e., 1.times.64 Kb/s up through 30.times.64 Kb/s). LEC nodes 141 and 146, in turn, respectively connect subscriber locations 110 and 115 to POPs 161 and 162 as already noted.
The overall combination of the IXC and LEC switched facilities--including those which provide both conventional and ISDN-based switched voice, video and other switched communications services--can be viewed as a single switched telecommunications
network.
In accordance with the invention, the system of FIG. 1 is able to effect connections between any pair of subscriber locations, be they cable subscriber locations or ISDN subscriber locations. There are thus four cases to consider, because either
one of the originating and the destination locations can be either a cable subscriber location or an ISDN subscriber location.
We will now consider each of these possibilities in turn.
Looking, first, at the ISDN-to-ISDN case, it will be appreciated that only some of the equipment described hereinabove will, in fact, be involved. Specifically, originating ISDN subscriber location 110 initiates a video telephone call to
destination ISDN subscriber location 115 by dialing the telephone number associated with the latter, i.e., the telephone number assigned to BRI line 117. That telephone number may be thought of as an "address" identifying the destination location.
Since locations 110 and 115 are served by different LECs, the call is routed from LEC node 141 to interexchange carrier 150 and, more particularly, to POP 161 within switched digital network 160. POP 161 recognizes this as a video telephone call by
virtue of unique signaling identifying the call as a video telephone call, that signaling being contained, initially, within the D channel of BRI connection 112 and, thereafter, within CCS messages forwarded to POP 161 from LEC node 141. Upon
recognizing this as a video telephone call, network 160 needs to determine whether the destination location is an ISDN subscriber location or a cable subscriber location. To this end, POP 161 triggers a query to video NCP 184, which includes a database
which lists all of the video telephone cable subscriber locations. Specifically, a message which includes the dialed telephone number is forwarded to NCP 184 requesting a determination as to whether the destination location is or is not registered as a
cable subscriber location. In this example, the destination location is, in fact, an ISDN subscriber location and, as a result, no database entry will be found. In this case, NCP 184--which, as noted above, knows the called telephone number--will
instruct POP 161 to route the call to LEC node 146. From this point forward, the call proceeds like any other ISDN call. Specifically, POP 161 routes the call through network 160 to POP 162 in conventional fashion. The latter, in turn, forwards the
call to LEC node 146 which completes the call to ISDN subscriber location 115.
Inasmuch as this turned out to be an ISDN-to-ISDN call, it will be appreciated that the call could have proceeded without an NCP lookup. That is, the call could, in theory, have been treated as a "standard" ISDN call which could have been
routed, in the first instance, directly to the destination ISDN location. However, since it is not known a priori whether a call coming in to POP 161 is being made to a cable subscriber location or to an ISDN subscriber location, the lookup must be
carried out in order to learn what type of equipment awaits at the destination location.
The second case is the cable-to-cable case (e.g., cable subscriber location 101 originating a call to destination cable subscriber location 105). In particular, the subscriber at originating cable subscriber location 101 initiates a call by
pushing a START button, S, on NIU 104 (or on a remote control device which sends signals to NIU 104) in order to initiate a request signal that is equivalent to an off-hook message used in conventional telephony, that request signal indicating a desire
to originate a video telephone call. This off-hook message is sent to VESP 125 when NIU 104 is polled thereby (by way of cable head end 124). As explained in more detail in conjunction with FIG. 3, VESP 125 includes a processor 360 (preferably a
fault-tolerant mini-computer) and an associated database 361 which contains identity codes for the NIUs that are attached to cable distribution network 121 and which also keeps track of the upstream and downstream channel status on that network,
administers scrambling codes, and performs other "housekeeping" tasks not here relevant.
The NIU constantly receives a signaling message from the VESP indicating the status of the channels over the coaxial cable distribution network 121 through a reserved portion of the bandwidth. Therefore, the NIU always knows if there are free
channels available or not. When the subscriber initiates the call by pushing the START button, if there are no channels available, the NIU gives a busy signal to the subscriber. Otherwise, the NIU sends a message to the VESP to request a channel
through a reserved portion of the bandwidth. If there were contention on this signaling channel, the NIU must re-transmit. (This scheme is similar to the well-known ALOHA system.) After reception of a clear message from the NIU by the VESP, the VESP
transmits a message to the NIU directing it to communicate on a particular pair of channels. After this time, all other signaling is done at the assigned channel. Then, the NIU is directed to transmit a signal representing the video telephone number of
the desired destination location which was supplied by the subscriber via a dialing pad associated with the NIU along with information identifying the originating NIU to processor 360, which packages it into an ISDN-PRI signaling message that is sent to
POP 161.
Pursuant to the invention described in the commonly assigned United States patent application of A. C. Papanicolaou and C. D. Yu entitled "Video Telephony Dialing," filed of even date herewith, the video telephone number for a cable subscriber
location--which, again, may be thought of as an "address" identifying same--is administered to be the same as the standard ten-(i.e., area code plus seven-) digit local exchange carrier telephone number used for regular voice telephone calls directed to
that location. This may be seen from the enlarged view of destination cable subscriber location 105 in FIG. 10 showing that the local exchange carrier telephone number associated with local loop 118 and standard telephone set 119 is the same as the
video telephone number associated with NIU 108. In this case, then, the subscriber at originating cable subscriber location 101 would have entered on the NIU's keypad the ten-digit telephone number associated with telephone set 119 installed at
destination cable subscriber location 105, i.e., the telephone number assigned to local loop connection 118. This is advantageous in that, apart from the fact that a cable-subscriber-originated video call, rather than a conventional voice only call, is
being made, the subscriber at an originating cable location is given the illusion that he/she is initiating a dial-up connection similar to any other dial-up connection that proceeds exclusively through the telephone network, such as a simple voice-only
call. That is, since the video telephone call is initiated to the same telephone number that would have been used if this were a conventional voice call made to the desired destination subscriber location, it appears to the originating subscriber that
all he/she has done is "dial up" the desired destination subscriber from what appears to be nothing more or less than a video-capable "extension" telephone within the originating location. Additionally, subscribers can "give out" a single telephone
number to friends and other potential callers, not having to differentiate between "my voice number" and "my video number" but yet still being able to receive both kinds of calls directed to that same telephone number.
At POP 161, the signaling information associated with the call--including, for example, the called video telephone number--obtained from VESP 125 is used to trigger a query to NCP 184 in the manner described above. Since in this case the called
location is, in fact, a cable subscriber location, NCP 184 accordingly instructs POP 161 to route the call to VESP 129 via switched digital network 160.
The destination NIU 108 receives from cable head end 128 a) upstream and downstream channel assignments and b) appropriate descrambling codes, and it activates a ringer to inform the called subscriber at the location of an incoming video
telephone call. After the called party pushes a START button (equivalent to "off-hook" in telephony), the incoming audio/video signals are fed to television set 106 and camera 107 sends its audio/video signals though the assigned upstream channel to the
calling party's television.
After two-way communication has been established between locations 101 and 105, either location can terminate the call by activating an END button, E, at NIU 104 or 108, or at a remote control device which communicates with the NIUs. The END
signal is transmitted in the upstream data communication channel to the attached head end (122 or 127), and interpreted in a manner equivalent to an on-hook signal in telephony, namely to instruct switched digital network 160 to terminate the video
telephone call and tear down the connection therethrough.
The third case is the cable-to-ISDN case (e.g., cable subscriber location 101 originating a call to destination ISDN location 115). Such a call proceeds identically to the cable-to-cable case up through the query of NCP 184, this being a
consequence of the fact that the equipment at the destination location (cable TV or ISDN) is not known until the database lookup has been effectuated. ISDN subscriber location 115 is not listed in database 184. Moreover, it may be assumed that an ISDN
video telephone at a residence is not one which is capable of operating at 384 Kb/s, which is the rate at which signals are generated by VESP 125. Rather, 128 Kb/s is the most likely case. A video telephone signal at that lower speed must thus be
supplied to destination ISDN location 115.
Typically, however, the node within POP 161 will not be capable of converting the call to a call at a lower speed (although it is possible to enhance the POP 161 and VESP 125 to provide this capability). Accordingly, NCP 184 will return a
message to POP 161 instructing it to clear the call. The POP, in turn, will return a call-clearing message to VESP 125 in standard fashion.
The fact that the call was cleared at POP 161 will be taken by VESP 125 as an indication that the destination location is neither a cable subscriber nor a video telephone that can support a 384 Kb/s signal. As a result, the VESP will a) assume
that the terminal equipment can only support a 128 Kb/s signal, b) will re-digitize the analog signal received from cable head end 124 at the lower rate, and c) will reinitiate a call to POP 161 at that rate. The messaging which accompanies the call
request will be such as to inform POP 161 that no database query is required but that, rather, the call should be immediately routed over switched digital network 160 based on the destination telephone number supplied, thereby re-establishing the call at
the lower rate. From this point, the call proceeds just as in the ISDN-to-ISDN case.
(As is well known, a 128 Kb/s connection is conventionally implemented by establishing two 64 Kb/s connections through the network, those connections being synchronized by the endpoint terminals. For convenience of exposition herein, reference
to a digital connection, or call, should be understood to comprise such a pair of 64 Kb/s calls.)
The fourth case is the ISDN-to-cable case, e.g., ISDN subscriber location 110 originating a call to destination cable location 105. In particular, the call proceeds identically to the ISDN-to-ISDN case up through the query of NCP 184. Here,
destination location 105 is, in fact, listed in the database as a cable subscriber location. Therefore, NCP 184 will return instructions to POP 161 to route the call to destination head end 127 through POP 162. From this point on, the call is like a
cable-to-cable call except that the transmission rate is determined by the rate at which the call was established which, in turn, depends on the capabilities of ISDN originating location 110. VESP 129 is capable of handling calls at various rates and,
in each case, of converting the received video telephone signals to the analog form required by destination cable subscriber location 105.
In the examples given above, it was tacitly assumed that the originating and destination parties are provided with telephone service in different so-called local access and transport areas, or LATAs. If they were in the same LATA, a call from
ISDN location 110 to ISDN location 115 would have been handled without being routed through an interexchange carrier. Since both of those locations are ISDN locations, this is no problem. The call will be treated by the LEC as a standard intra-LATA
ISDN call. A different situation arises, however, if the destination location is a cable subscriber but is still within the same LATA as the originating subscriber. In this case, the LEC will, in the first instance, interpret the call request as being
a request to complete a call to an ISDN subscriber. Since the called subscriber does not have ISDN service, this call will simply fail at the destination LEC node.
One way to resolve this issue is for the LECs to provide connections to the VESPs, thereby in effect replicating, for local calls, the functionality of interexchange carrier 150, as described above. Assuming, however, that the LECs do not offer
this capability, an alternative way of providing service in this case is to provide the ISDN subscriber locations with a mechanism for accessing interexchange carrier 150 directly. One such mechanism is to provide the ISDN subscriber with a telephone
number which can be dialed to initiate an ISDN-to-cable connection.
More particularly, the call--which is assumed in this example to be an 800-type call--would begin from originating ISDN location 110 as a voice call, inasmuch as digital 800 service is not currently offered by interexchange carriers. By virtue
of the number dialed, the call will be routed by LEC network 140 to POP 161 via trunk 151. POP 161, in turn, will request instructions for handling this call from 800 NCP 186. The latter determines from its associated 800 number database that this is,
in fact, a video telephone call and instructs POP 161 to route the call temporarily to voice response unit 166 which may be, for example, a Conversant.RTM. voice response unit available from AT&T. Voice response unit 166 presents audio announcements to
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