Methods and systems for multimedia communications via public telephone networks

Methods and systems for providing multimedia telecommunication services to multimedia workstations communicating with a multimedia central office which includes a digital switch complex coupled to a public digital telephone network, and at least one twisted pair transceiver coupled to at least one twisted pair link in a telephone loop plant. The multimedia central office further includes at least one switch complex operatively associated with the digital switch complex and the at least one twisted pair transceiver. The multimedia central office is capable of transceiving signals with multimedia workstations interfaced to the public digital telephone network, and with multimedia workstations interfaced to the at least one twisted pair link in the telephone loop plant. The signals which are transceived include audio signals, video signals, and digital data signals used in providing the multimedia telecommunication services.

TECHNICAL FIELD 
The present invention relates to methods and systems for providing 
multimedia telecommunications, and more particularly, to methods and 
systems for providing multimedia telecommunications using existing public 
telephone system infrastructure and desktop computers. 
BACKGROUND OF THE INVENTION 
Presently, the cost of both wideband digital transport and interfacing 
equipment is a deterrent to the widespread usage of multimedia services 
for collaboration and other business functions. One component of the cost 
is the tariffs for digital carriers provided by common carriers. Common 
carriers include public telephone networks registered, regulated, and/or 
authorized to provide publicly tariffed telecommunication services. 
Common carriers discount digital bandwidth according to the amount of 
bandwidth on a particular digital carrier. Presently, wide-area 
subscription rates for Fractional T-1 data rates typically break even at 
about half the rate of a full T-1 and rates for eight T-1 carriers 
typically match that of a T-3 carrier providing approximately 30 times the 
bandwidth of a single T-1. 
The reason for this 2:1 to 4:1 discounting is that bulk bandwidth delivery 
and wide-area transport employs less common carrier equipment, management, 
and control than delivery of the same amount of bandwidth in smaller, 
unbundled parcels. For a telecommunications concern outside the common 
carriers, private networks can be made far more cost effective if their 
design leverages these economies of scale in bandwidth purchases from the 
common carriers. 
The transmission of quality audio and video signals to a multimedia 
workstation at a user premises is essential in providing multimedia 
services. In practice, satisfactory quality NTSC//SECAM video and 
medium fidelity audio can be transmitted relatively inexpensively through 
an unshielded twisted pair (UTP) link using analog signals. 
Methods and systems of transmitting continuous motion (25-30 frames/second) 
analog video signals over unshielded twisted pair links range from the 
AT&T Picturephone of the late 1960's to the disclosure in U.S. Pat. No. 
5,283,637 to Goolcharan. However, as the distance of the UTP increases 
beyond an upper limit, typically beyond approximately 2500 feet, crosstalk 
and attenuation increase very rapidly. This effect is more pronounced for 
smaller gauge wires (e.g. 26 gauge) than for larger gauge wires (e.g. 20 
or 19 gauge). 
Typically, an existing public telephone loop plant, i.e. the access portion 
of a public telephone network which connects a user premises with a first 
public telephone building, contains UTP having one or more gauge changes 
at several junctures. Moreover, the length of the UTP between end 
locations is often much larger than the physical distance between the 
locations (a factor of 3.5 is not unusual). At longer UTP loop lengths, 
the multiple junctures and gauge changes combine to create an uneven 
high-frequency response. 
FIG. 1 illustrates the frequency response of a passive UTP metallic loop 
without bridge taps between two buildings, each separated from a public 
telephone central office by approximately 1000 feet. This UTP loop 
involves a 7100 foot wire length with multiple gauge changes. In this 
example, the frequency response exhibits significant peaks and notches 
around 1 MHz. In general, the large notches and peaks which result 
complicate the compensation for the rapid attenuation at high frequencies. 
One approach to this problem is to convert the video to a digital signal 
for transmission over the UTP. Such an approach requires the steps of 
converting the video to a digital form, compressing the digital form of 
the video, and transmitting the compressed digital video over the UTP at 
bit rates whose analog spectra (dictated by pulse shape) is within the 
bounds of the UTP. Standard state-machine pulse coding and pulse 
wave-shaping (such as alternate mark inversion) are typically used to 
reduce the power spectrum only to multiples of the bit rate of 
approximately 1.5 (i.e., 1 Mbps can be transmitted over a 1.5 MHz baseband 
bandwidth). Consequently, even at distances of 2500 feet, digital 
transmissions attain only about 3-4 Mbps. As a result, significant 
compression and cost is required to utilize digital signals for 
transmitting video over the UTP. Although not as costly or confining as 
128-384 kbps Fractional T-carrier channels, deployment of codecs 
compressing two-way, high-quality, full-motion video and audio to 3-4 Mbps 
at each desktop is costly and problematic. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to deliver immediate low-cost, 
wide-area access of multimedia services to multimedia workstations using 
unshielded twisted pair links within an existing telephone loop plant. 
A further object is to reduce the cost of wide-area, wideband digital 
transport in a system for providing multimedia services to multimedia 
workstations utilizing desktop computers. 
In carrying out the above objects, the present invention provides a system 
for providing multimedia telecommunication services to a plurality of 
multimedia workstations. The system comprises a multimedia central office 
which includes a digital switch complex coupled to a public digital 
telephone network, and at least one twisted pair transceiver coupled to at 
least one twisted pair link in a telephone loop plant. The multimedia 
central office further includes at least one switch complex operatively 
associated with the digital switch and the at least one twisted pair 
transceiver. The multimedia central office transceives a first plurality 
of signals with a first at least one of the multimedia workstations 
interfaced to the public digital telephone network, and transceives a 
second plurality of signals with a second at least one of the multimedia 
workstations interfaced to the at least one twisted pair link in the 
telephone loop plant. The first plurality and the second plurality of 
signals each include audio signals, video signals, and digital data 
signals used for providing the multimedia telecommunication services. 
Embodiments of the present invention provide a network approach for 
immediate, low-cost deployment of advanced multimedia telecommunications 
services using current technology. In particular, embodiments of the 
present invention are advantageously capable of utilizing low-cost 
technologies such as analog audio/video hardware, telephone loop twisted 
pair, and existing LAN technologies to provide the multimedia 
telecommunication services. By utilizing the unshielded twisted pair in 
the telephone loop plant, embodiments of the present invention do not 
require the deployment of new ATM and fiber optic systems, which may take 
a number of years before widespread availability and a full, mature 
implementation is attained. Consequently, global infrastructure 
investments in telephone loop plants retain much of their value by being 
capable of providing advanced multimedia telecommunication services. 
Further, embodiments of the present invention are capable of supporting 
advanced multimedia services in a flexible manner so that ATM and fiber 
optic systems may be utilized when economical. 
Embodiments of the present invention are capable of delivering low-cost, 
high-quality video-capable multimedia services including: (i) real-time 
collaboration services, such as desktop teleconferencing, window sharing, 
and full-application sharing; (ii) multimedia messaging services, such as 
multimedia mail and video mail; (iii) access to multimedia information 
repositories, such as on-line catalogs and video news clippings; (iv) 
directory services; and (v) gateways to third-party networks, such as a 
public telephone network and the Internet. 
These and other features, aspects, and advantages of the present invention 
will become better understood with regard to the following description, 
appended claims, and accompanying drawings.

BEST MODE FOR CARRYING OUT THE INVENTION 
A block diagram of an embodiment of a multimedia telecommunication system 
in accordance with the present invention is illustrated in FIG. 2. The 
multimedia telecommunication system is capable of functioning with two 
types of multimedia workstations or equivalent room-based systems. A first 
type of multimedia workstation, indicated by reference numeral 100, is one 
capable of interfacing with a standardized network interface traditionally 
used in a public digital telephone network. Examples of standardized 
network interfacing protocols include, but are not limited to, T-1, T-3, 
ISDN, SONET, X.21, and X.25. A multimedia workstation interface capable of 
connection to a standardized network interface is herein referred to as a 
traditional network interface (TNI). 
A second type of multimedia workstation, indicated by reference numeral 
102, is one having an interface which is not currently supported by the 
public digital telephone network. A multimedia workstation interface 
according to this second type is herein referred to as a nontraditional 
network interface (NTNI). NTNIs are typically designed based upon the 
particular workstation rather than the public digital network. 
The workstations 100 and 102 are illustrated as being located within one of 
a plurality of user premises 104a-104e. Five different types of user 
premises are described for the purpose of illustration. The user premise 
104a includes one or more workstations each having a TNI. The workstations 
in the user premise 104a are directly connected to a local public digital 
network 106 by means of a conventional digital carrier 108. 
The user premise 104b includes one or more workstations, each having a TNI, 
coupled to an internal premise communication system 110. The internal 
premise communication system 110 communicates with the workstations via 
TNI, and provides for sharing of access to the local public digital 
network 106 via TNI. An example is an ISDN PBX or corporate Fractional 
T-carrier cross-connect switch. 
The user premise 104c includes one or more workstations each having an 
NTNI. These workstations communicate with the local public digital network 
106 via a multimedia central office 112 using conventional twisted pair 
114 existing within a telephone loop plant. The multimedia central office 
112 employs the same NTNI as the workstations coupled thereto. The local 
public digital network 106 is coupled to the multimedia central office 112 
by means of a digital carrier 113 which employs a TNI. 
The user premise 104d includes one or more workstations, each having an 
NTNI, coupled to an internal premises communications system 116. The 
internal premises communication system 116 communicates with the 
workstations via an NTNI. Preferably, the internal premises communication 
system is capable of providing both interconnection and resource sharing 
functions, such as the sharing of public network access to the multimedia 
central office 112, using NTNI used to communicate with the workstations. 
An embodiment of such an internal premises communication system is 
described in copending U.S. application Ser. No. 08/131,523. 
The user premise 104e includes one or more workstations, each having NTNI, 
coupled to an internal premises communications system 120. The internal 
premises communications system 120 includes a system for converting NTNI 
signals to TNI signals. As a result, the internal premises communications 
system 120 is coupled to the local public digital network 106 via a TNI 
such as ISDN or a T-carrier. An embodiment of such an internal premises 
communication system is described in copending U.S. application Ser. No. 
08/131,523. 
Other types of premises may be realized based upon a combination of the 
attributes of the abovedescribed premises 104a-104e. For example, for a 
premise with all workstations or rooms using NTNI, some parts of the 
public network access may be done via NTNI and other parts via TNI. 
Moreover, for a premise with some workstations using NTNI and other 
workstations using TNI, some parts of the public network access may be 
provided by a multimedia central office via NTNI and other parts by a 
public local digital network via TNI. Many other combinations are apparent 
to those having ordinary skill in the art. 
The embodiments described thus far illustrate how workstations or rooms may 
access both a multimedia central office and a local public digital network 
regardless of whether NTNI or TNI is used for public network access. This 
results from the use of the digital carrier 113 which links the multimedia 
central office 112 and the local public digital network 106. A number of 
multimedia services can be provided by the multimedia central office 112 
(and other network offices to be described), as is discussed later. 
Access can be provided to a wide area public digital network 122, 
representative of one or more arbitrary public networks, using many 
approaches. In a first approach, the local public digital network 106 is 
linked to the wide area public digital network 122 by means of a digital 
carrier 124. 
In a second approach, the local public digital network is linked to a 
regional hub office 126 by a first digital carrier 130. The regional hub 
office 126 is linked to the wide area public digital network by a second 
digital carrier 132. The regional hub office 126 is capable of providing 
networking, topology, and/or services functions not provided by the direct 
digital carrier link 124. For example, the regional hub office 126 may be 
capable of switching and transmission concentration for the dedicated 
lines used as the digital carriers with the multimedia central offices. 
Further, the regional hub office 126 may be capable of directly providing 
a number of multimedia services. Also, the regional hub office 126 may act 
as a strategic location for geographically-sensitive functions such as 
video messaging storage and conference bridge servers. In addition, 
regional hub offices may be used as gateways to international wide-area 
telecommunications services. 
The use of a regional hub office in a multimedia telecommunications system 
in accordance with the present invention is optional. Practically, the use 
of a regional hub office is dictated by the selected features which are to 
be provided and economics of a particular implementation. 
Selected features and economics of an overall implementation of a 
multimedia telecommunications system may be served by utilizing one or 
more national hub offices 134 linked to the wide area public digital 
network. The national hub offices 134 may provide switching and 
transmission concentration for any dedicated lines used as digital 
carriers with the regional hub offices or the multimedia central offices. 
Further, the national hub offices 134 may directly provide some multimedia 
services, or act as strategic locations for geographically-sensitive 
functions. 
A political nation, i.e. a country, served by embodiments of the multimedia 
telecommunications system may have zero, one, or a plurality of national 
hub offices. A plurality of national hub offices may be redundantly 
employed in a single political nation for the purpose of providing 
improved reliability of service. National offices can also be used to 
provide gateways to international wide-area telecommunication services. 
The use of regional hub offices and national hub offices allows for a 
non-common carrier operator of an embodiment of the present invention to 
implement a multimedia telecommunication system as a private switched 
network formed from dedicated digital carrier services offered by a common 
carrier. More specifically, the non-common carrier operator would 
interconnect the workstations by means of: (i) switched digital carrier 
services connecting the premises to a multimedia central office; (ii) 
dedicated lines among one another in a full or partial mesh topology; and 
(iii) dedicated lines linking multimedia central offices and TNI premises 
with regional hub offices and national hub offices. It is noted that a 
common-carrier operator of an embodiment of the present invention need not 
implement explicit regional or national offices. 
In practice, embodiments of the multimedia telecommunications system 
include one or more multimedia central offices which provide NTNI access 
to nearby users as well as network-based multimedia services and 
reduced-cost transport. Typically, a plurality of multimedia central 
offices are employed, wherein the multimedia central offices are networked 
together by means of a conventional common carrier service, or by 
alternative means such as line-of-site microwave, spread-spectrum radio, 
satellite, or private fibre optic links. In such a network of multimedia 
central offices, there may be further value in including additional nodes 
in the network, namely, one or more of the regional hub offices and the 
national hub offices as described above. 
Alternatively, one or more regional hub offices and national hub offices, 
optionally supplemented by one or more multimedia central offices, may be 
directly accessed by users using TNI digital carriers provided by a common 
carrier. This is beneficial in providing network-based multimedia services 
with a reduced transport cost but without requiring NTNI for access. 
Each of the offices and the networking among them are now described. 
Architectural variations which may be advantageous for using LAN (local 
area network) switching hubs as real-time switches for packetized video 
and audio are presented, followed by network topology aspects. 
FIG. 3 is a block diagram of an embodiment of a multimedia central office 
in accordance with the present invention. The multimedia central office 
includes a digital switch complex 150 capable of performing multiplexing 
and inverse multiplexing functions. Users with TNI which employ switched 
or dedicated digital carriers to access the multimedia central office are 
connected directly to the digital switch complex 150. 
The multimedia central office further includes one or more UTP transceivers 
152, to which users with NTNI are connected via the UTP. The UTP 
transceivers 152 are capable of transceiving audio, video, and digital 
signals communicated between the UTP and the multimedia central office. 
Analog video and audio signals transceived by the UTP transceivers 152 are 
directed to a real-time switch complex 154. The real-time switch complex 
154 may contain, for example, one or more analog switches, DSO 
cross-connects, or switched LAN hubs (used in an effectively collisionless 
mode) therein. Data communication signals, such as Ethernet, in their 
original logical form are processed by the UTP transceivers 152 for 
application to a data hub complex 156. 
In such an arrangement, various options for processing UTP-transceived 
signals are available. For example, a UTP carrying a converted V.35 signal 
or a converted RS-449 signal may be transceived by the UTP transceivers 
152 and connected via the real-time switch complex 154. Here, the UTP 
transceivers 152 may optionally transform the converted signals back into 
the original V.35 or RS-449 format. In a second example, a UTP carrying a 
converted V.35 signal or a converted RS-449 signal may be transceived and 
transformed back into the original V.35 or RS-449 format by the UTP 
transceivers 152 for application to the digital switch complex 150. 
The combination of the digital switch complex 150, the real-time switch 
complex 154, and the data hub complex 156 is used to route multimedia 
communications signals within the multimedia central office. The signal 
routing is used to provide for the interconnection of users attached to 
the multimedia central office, or as reachable through the digital carrier 
113. Interconnection among users terminated on a common multimedia central 
office may be achieved as follows. 
Interconnection of UTP NTNI users employing unlike NTNIs can be provided by 
the data hub complex 156 using service modules 160a-160c, coupled to 
either the real-time switch complex 154 or the digital switch complex 150, 
capable of performing the necessary conversions. In general, the service 
modules 160a-160c can provide any number of functions. For example, the 
service modules may be capable of performing video/audio codec functions, 
such as transforming between analog video/audio and V.35 or RS-449, or 
storage functions as may be used for video mail. 
Interconnection of UTP NTNI users employing converted V.35 or RS-449 
signals with TNI users can be provided by the digital switch complex 150. 
If the UTP transceivers 152 do not provide the transformations needed to 
present V.35 or RS-449 signals to the digital switch 150, then the signal 
is routed through an appropriate service module 160a, as available, via 
the real-time switch 154. Here, the services modules 160a perform the 
transformations between converted V.35 or RS-449 and true V.35 or RS-449. 
If the UTP transceivers 152 do provide the transformation, signals may 
pass directly from the UTP transceivers 152 to the digital switch complex 
150 without the use of service modules. 
The service modules 160a include those capable of performing compression or 
other signal conversion functions required by the service modules 160c. 
These service modules 160a are accessed by the service modules 160c using 
the real-time switch 154. This allows for shared use of a first pool of 
service modules 160a across a second pool of service modules 160c. For 
example, the service modules 160a may include shared video compression 
devices while the service modules 160c may include conference bridges and 
video storage servers. Here, the real-time switch 154 permits sharing of 
the compression devices for conferencing and storage functions. 
In addition, accessing the service modules 160a using the real-time switch 
154 supports implementation of complex feature combinations. For example, 
the service modules 160c may include a pool of K analog multi-point 
conference bridges while the service modules 160a include a pool of 
high-performance video codecs. The pool of video codecs includes M of a 
first type and N of a second type. The real-time switch 154 allows for 
sharing of these codecs across various ports of the conference bridge. 
This allows for support of extensive combinations of compression types and 
conference bridge ports while keeping the values of K, M, and N as small 
as possible. 
The service modules 160b are capable of performing similar functions as the 
service modules 160c, but do not require signal conversion from the 
service modules 160a. 
Embodiments of the multimedia central office may provide data stream 
networking wherein data streams are provided to the users to serve various 
purposes. These purposes include: (i) real-time control signaling for 
connection and services control; (ii) rapid file transfer of image files 
used in snapshot and application-sharing elements of real-time 
collaboration; (iii) real-time drawing and pointing commands used in 
snapshot and application-sharing elements of real-time collaboration; and 
(iv) general LAN interconnection. 
To support data stream networking, the multimedia central office may be 
employed as follows. Any UTP NTNI user data streams which carry data 
communications signals in their original logical form are presented to the 
data hub complex 156 by the UTP transceivers 152. Any UTP NTNI user data 
streams which carry data communications signals converted to V.35, RS-449, 
or a similar interface are presented to data routers 162 with a 
corresponding V.35 interface, an RS-449 interface, or a similar interface 
via the digital switch complex 150. Any UTP NTNI user data streams which 
involve processing or action outside the multimedia central office 
accesses the digital switch complex 150 via the data routers 162 fitted 
with an appropriate interface, such as V.35 or RS-449. Any UTP TNI user 
data streams which involve processing or action within the multimedia 
central office are linked to the data routers 162 (fitted with appropriate 
interfaces) by means of connections within the digital switch complex 150. 
Effectively, these variations act to get all data communications into the 
data hub complex 156 and/or the data routers 162 as necessary. 
The data hub complex 156 is coupled to one or more computers 164. It is 
usually advantageous for the computers 164 to be coupled to other elements 
within the multimedia central office, typically using either a serial or a 
parallel interface. The computers 164 may be employed to perform any of 
the following functions: (i) providing person-based directory services and 
routing services; (ii) providing resource-based directory services; (iii) 
providing resource allocation services; (iv) controlling the connections 
implemented by the digital switch complex 150 and the real-time switch 
complex 154; (v) controlling hardware systems within the service modules 
160a-160c; (vi) implementing any computer-based service feature (such as 
call forwarding, person locator, and application sharing host); and (vii) 
administration, usage, and pre-billing processing functions. 
In addition to providing interconnection of users terminated on the common 
multimedia central office, access may be provided as appropriate to one or 
more other multimedia central offices, a regional hub office, a national 
hub office, a public digital network, or a private network. Here, the 
digital switch complex 150 is coupled to these options via a dedicated or 
switched digital carrier 166. In some circumstances or embodiments, other 
means for communication, such as analog radio or satellite, may be used. 
FIG. 4 is a block diagram of an embodiment of a regional hub office in 
accordance with the present invention. This embodiment of the regional hub 
office may be viewed as a simplified version of the multimedia central 
office in that no UTP or digital carrier user access is supported. 
The regional hub office is connected to one or more multimedia central 
offices via a dedicated or switched digital carrier 200. The regional hub 
office may optionally connect with one or more national hub offices, other 
regional hub offices, or other networks via a dedicated or switched 
digital carrier 202 connected to a wide area public digital network. In 
some circumstances, other means for communication, such as analog radio or 
satellite, may be used. 
Data switching is performed by a data hub complex 204, which accesses the 
digital carriers 200 and 202 by switching within a digital switch complex 
206 and data routers 210 fitted with appropriate interfaces such as V.35 
or RS-449. The data hub complex 204 accesses one or more computers 212 for 
controlling the digital switch complex 206, any real time switch 214, and 
other elements of the regional hub office. The computers 212 control the 
switches 206 and 214, along with other elements of the regional hub 
office, by means of serial and parallel interfaces. The computers 212 may 
further provide the above-described functions for the computers 164 in the 
multimedia central office. 
All through routed connections provided by the regional hub office are 
realized as point-to-point connections within the digital switch complex 
206. For cases where the regional hub office provides other services (such 
as conferencing or video mail), the digital switch complex 206 dynamically 
connects the digital carriers 200 and 202 with service modules 216a-216c. 
The service modules 216a and 216b directly access the digital switch 
complex 206 while service modules 216c require access to service modules 
216a via the real-time switch 214. For example, the service modules 216a 
may include shared video compression devices while the service modules 
216c include conference bridges and video storage servers. Here, the 
real-time switch 214 permits sharing of the compressing devices. Although 
also true for real-time switches in multimedia central offices, it may be 
especially advantageous to implement the real-time switches as a backplane 
hosting service module cards. 
The inclusion of the regional hub office in the multimedia 
telecommunication system may be based upon engineering and economic 
matters, which include: (i) improved utilization of bandwidth facilities 
by concentration of the demand; (ii) improved utilization of services 
resources by concentration of the demand; and (iii) improved reliability 
and rapid failure recovery by utilizing redundant backup systems. An 
improved utilization of many types of service resources and minimization 
of transport costs can result by locating some of the service resources at 
the regional hub offices. 
FIG. 5 is a block diagram of an embodiment of a national hub office in 
accordance with the present invention. The national hub office is 
connected to one or more regional hub offices and/or one or more 
multimedia central offices via a dedicated or switched digital carrier 230 
connected to a wide area public digital network. 
Data switching is performed by a data hub complex 234, which accesses the 
digital carrier 230 by switching within a digital switch complex 236 and 
data routers 240 fitted with an appropriate interface such as V.35 or 
RS-449. The data hub complex 234 accesses one or more computers 242 for 
controlling the digital switch complex 236 and a real time switch 244. The 
computers 242 control the switches 236 and 244, along with other elements 
of the national hub office, by means of serial and parallel interfaces. 
The computers 242 may further provide the above-described functions for 
the computers 164 in the multimedia central office. 
All through routed connections provided by the national hub office are 
realized as point-to-point connections within the digital switch complex 
236. For cases where the national hub office provides other services (such 
as conferencing or video mail), the digital switch complex 236 dynamically 
connects the digital carrier 230 with service modules 246a-246c. The 
service modules 246a and 246b directly access the digital switch complex 
236 while service modules 246c require access to service modules 246a via 
the real-time switch 244. For example, the service modules 246a may 
include shared video compression devices while the service modules 246c 
include conference bridges and video storage servers. Here, the real-time 
switch 244 permits sharing of the compressing devices. 
The inclusion of the national hub office in the multimedia 
telecommunication system may be based upon engineering and economic 
matters, which include: (i) improved utilization of bandwidth facilities 
by concentration of the demand; (ii) improved utilization of services 
resources by concentration of the demand; and (iii) improved reliability 
and rapid failure recovery by utilizing redundant backup systems. In some 
cases, an improved utilization of service resources and minimization of 
transport costs results by locating some of the service resources at the 
national hub offices. 
It is noted that a single, high-quality video stream may be carried by a 
dedicated 5-10 Mbps switched data-LAN channel, such as a switched-Ethernet 
connection. For example, a one-way broadcast-quality JPEG video stream 
requires approximately 7 Mbps of bandwidth, and an uncompressed 16-bit 20 
kHz digital audio requires approximately 600 kbps. In the 1-3 Mbps range, 
MPEG I and II deliver higher compression at good quality, but require 
significantly more expensive encoders. As a result, it is possible to 
carry video and audio in packetized digital form over the UTP using 
conventional LAN protocols. If this approach is taken, some or all of the 
real-time switches can be implemented as high-bandwidth switching hubs. In 
some embodiments, one or more of the following architectural variations 
may be valuable: (i) carrying some or all network and services control 
channels within the real-time video and audio stream; (ii) carrying some 
or all shared image files within the real-time video and audio data 
stream; and (iii) merging of the real-time switches with the data hub 
complexes. 
Embodiments of the multimedia telecommunication system may be realized by a 
variety of different interconnection topologies for the multimedia central 
offices, the regional hub offices, and the national hub offices. The 
principles used in contemporary wide area digital carrier and telephony 
networking, both public and private, may be employed in embodiments having 
more than a small number of multimedia central offices, regional hub 
offices, and/or national hub offices. The incorporation of these 
principals is illustrated by the example topologies which follow. 
In order to simplify the discussion of the topologies, the following 
abstractions are used. All types of user premises are represented 
generically as a user site. All types of access between a user site and 
its serving multimedia central office are represented as a generic user 
access. In the case of digital carriers, this includes both switched and 
dedicated services. The combination of a digital carrier between a 
multimedia central office and a local public digital network, a dedicated 
connection (not switched) provided by the local public digital network, 
and a dedicated services digital carrier to a regional hub office is 
represented as a generic dedicated link. Similarly, the combination of a 
digital carrier between a regional hub office and a wide area public 
digital network, a dedicated connection (not switched) provided by the 
wide area public digital network, and a dedicated services digital carrier 
to a national hub office is represented as a generic dedicated link. Thus, 
generic access involves any type of access used to link a generic user 
site with its serving multimedia central office, while generic dedicated 
links represent any kind of dedicated (not switched) links between pairs 
of offices. 
FIG. 6 is a block diagram of an example topology wherein fully dedicated 
digital carriers are employed between multimedia central offices, regional 
hub offices, and national hub offices. A plurality of user sites 260 are 
each coupled to a corresponding one of a plurality of multimedia central 
offices 262 via a corresponding one of a plurality of generic user access 
links 264. Each of the multimedia central offices 262 is coupled to a 
corresponding one of a plurality of regional hub offices 266 by a 
corresponding one of a plurality of generic dedicated links 270. Each of 
the regional hub offices 266 is coupled to a national office 272 by a 
corresponding one of a plurality of generic dedicated links 274. 
This topology is beneficial in allowing the exploitation of conventional 
bulk pricing of bandwidth, improving the location of shared service 
resources, and providing alternative access means for users which use NTNI 
UTP to communicate with one of the multimedia central offices 262. 
However, this topology does not provide for redundancy for the purpose of 
failure immunity. Further, in order to handle heavy traffic, a brute-force 
approach of increasing the number of trunks in the links 264, 270, and 272 
must be employed with this topology. 
FIG. 7 is a block diagram of another example topology having provisions for 
overflow and failure conditions. As with the topology of FIG. 6, a 
plurality of user sites 280 are each coupled to a corresponding one of a 
plurality of multimedia central offices 282 via a corresponding one of a 
plurality of generic user access links 284. Each of the multimedia central 
offices 282 is coupled to a corresponding one of a plurality of regional 
hub offices 286 by a corresponding one of a plurality of generic dedicated 
links 290. Each of the regional hub offices 286 is coupled to a national 
office 292 by a corresponding one of a plurality of generic dedicated 
links 294. 
Further, a plurality of switched lines are provided by a switched public 
digital network 300 for handling overflow and failure conditions. 
Specifically, the multimedia central offices 282 access the switched 
public digital network via access links 302, the regional hub offices 286 
access the switched public digital network via access links 304, and the 
national office 292 accesses the switched public digital network via 
access links 306. 
Using this topology, a failure or heavy loading of one of the links 290 can 
be recovered by any of the following steps: (i) setting up a connection 
through the switched public digital network 300 using access links 302 and 
304; (ii) setting up a connection with an alternate one of the regional 
hub offices 286 through the switched public digital network 300 using the 
access links 302 and 304; (iii) setting up a connection with one of the 
multimedia central offices 282 through the switched public digital network 
300 using two of the access links 302; or (iv) setting up a connection 
with the national hub office 292 through the switched public digital 
network 300 using the access links 302 and 306. 
Similarly, a failure or heavy loading of one of the links 294 can be 
recovered by any of the following steps: (i) setting up a connection 
through the switched public digital network 300 using access links 304 and 
306; (ii) setting up a connection with one of the multimedia central 
offices 282 through the switched public digital network 300 using the 
access links 302 and 304; or (iii) setting up a connection with one of the 
regional hub offices 286 through the switched public digital network 300 
using two of the access links 304. 
A failure or heavy loading of one of the regional hub offices 286 can be 
recovered by any of the following steps: (i) setting up a connection with 
an alternate one of the regional hub offices 286 through the switched 
public digital network 300 using access links 302 and 304; (ii) setting up 
a connection with the national hub office 292 through the switched public 
digital network 300 using the access links 302 and 306; or (iii) setting 
up a connection with one of the multimedia central offices 282 through the 
switched public digital network 300 using two of the access links 302. 
Similarly, a failure or heavy loading of the national hub office 292 can be 
recovered by any of the following steps: (i) setting up a connection with 
one of the regional hub offices 286 through the switched public digital 
network 300 using access links 302 and 304; or (ii) setting up a 
connection with one of the multimedia central offices 282 through the 
switched public digital network 300 using two of the access links 302. 
One having ordinary skill in the art will recognize that the trade-off in 
cost between switched services, dedicated lines, and minimum cost load 
balancing of the offices 282, 286, and 292 can be exploited in creating a 
specific implementation of the present invention. In particular, 
implementations may be created which stochastically minimize operating 
costs. 
FIG. 8 is a block diagram of an alternative topology which utilizes 
redundant links and offices. The additional links and offices are included 
in this topology in order to obtain higher reliability and trunk 
availability. As with the topology of FIG. 6, a plurality of user sites 
320 are each coupled to a corresponding one of a plurality of multimedia 
central offices 322 via a corresponding one of a plurality of generic user 
access links 324. Each of the multimedia central offices 322 is coupled to 
at least one of a plurality of regional hub offices 326 by a corresponding 
at least one of a plurality of generic dedicated links 330. Each of the 
regional hub offices 326 is coupled to at least one national office 332 by 
a corresponding at least one of a plurality of generic dedicated links 
334. 
FIG. 9 is a block diagram of a topology in which redundant links and 
offices are combined with switched lines. A plurality of user sites 350 
are each coupled to a corresponding one of a plurality of multimedia 
central offices 352 via a corresponding one of a plurality of generic user 
access links 354. Each of the multimedia central offices 352 is coupled to 
at least one of a plurality of regional hub offices 356 by a corresponding 
at least one of a plurality of generic dedicated links 360. Each of the 
regional hub offices 356 is coupled to at least one national office 362 by 
a corresponding at least one of a plurality of generic dedicated links 
364. 
A plurality of switched lines are provided by a switched public digital 
network 370 for handling overflow and failure conditions. Specifically, 
the multimedia central offices 352 access the switched public digital 
network via access links 372, the regional hub offices 356 access the 
switched public digital network via access links 374, and the national 
office 362 accesses the switched public digital network via an access 
links 376. 
The topology of FIG. 9 provides improved immunity to both failure and heavy 
loading in comparison to the topology of FIG. 7 and the topology of FIG. 
8. 
In practice, multimedia services may be provided by various entities using 
embodiments of the present invention. A first approach is for a common 
carrier to provide the multimedia services, either exclusively or in 
partnership with another entity. A common carrier with a UTP loop plant 
can use NTNIs for user access to the multimedia central offices. Within 
the multimedia central offices, each which could be as physically small as 
a large wiring closet in a building, video compression units ("codecs") 
can be included in the service modules for conversion of the NTNI signals 
into streams appropriate for TNI digital carriers. 
TNI digital carrier terminations (i.e., CSU/DSUs), multiplexing, and codec 
equipment can be shared among many users accessing them by means of UTP. 
There are no known tariffed, publicly-offered services of this type. 
UTP transceivers may be used to reconstruct converted LAN signals and 
present them, via a data hub complex and routers, to the digital switch 
complex for transmission on TNI digital carriers. Appropriate UTP 
transceivers, alone or together with conversion systems included in 
service modules, may be used to reconstruct converted V.35, RS-449, or 
other interface signals and present them to the digital switch complex for 
transmission on TNI digital carriers. Dedicated and switched bandwidth can 
be used to link the multimedia central offices to bulk transmission and 
switching facilities. TNI digital carrier terminations (i.e., CSU/DSUs), 
multiplexing, and codec equipment can be shared among many users or leased 
to specific users. 
A common carrier without a UTP loop plant may employ a point-of-presence in 
key buildings and third party operating loops within and/or emanating from 
these buildings. In fact, common carriers with existing points-of-presence 
in key buildings are well suited to utilize embodiments of the invention 
since the UTP loop plant within large buildings is typically conducive to 
the simplest and least costly of the UTP techniques discussed earlier. 
A second approach is for a third party, which purchases bandwidth from a 
common carrier, to provide the multimedia services. For users who use UTP 
with NTNIs for access to a multimedia central office, the bulk-rate 
purchases of dedicated and switched bandwidth help to further lower the 
cost for real-time wide-area video connection services. For users who use 
UTP with NTNIs and are located within a common building or building 
complex, the multimedia central office can be located within the building 
and be connected directly to TNI digital carrier access for the building. 
For users who use UTP with NTNIs and are located within a common 
neighborhood, the multimedia central office may be located within any 
office and may be connected by means of passive UTP loops provided by a 
common carrier. The passive UTP loops are cross connected at the carrier's 
central office or wire center. An example of a common carrier passive UTP 
loop service is Pacific Bell's metallic digital loop tariff 3002. 
For users who use a conventional TNI digital carrier to access a multimedia 
central office, these same bulk-rate purchases of dedicated and switched 
bandwidth may be accessed to provide lower cost connections out of the 
area. Typically, this would entail a bulk-bandwidth purchase and an 
infrastructure investment involved in supporting NTNI UTP users driving 
the availability and lowering the incremental cost for providing real-time 
wide-area video connection services to users using conventional TNI 
digital carriers for access. 
In complex cases where there is partial involvement of common carriers with 
a mix of attributes from each of these cases, one skilled in the art can 
adapt parts from each of these illustrative approaches. 
Abstract pictorials of network connection topologies linking users with 
centralized multi-point conference bridges do not reveal the important 
impact of conference bridge location on transmission costs. As an example, 
if all conference bridges in a nationwide network were located at one site 
serving the entire nation, almost all multi-point conferences would 
involve considerable costly long distance telecommunications. Such an 
approach can be improved upon by migrating some of the conference bridges 
away from a single national center and into regional and neighborhood 
locations. 
In order to illustrate methods of conference bridge allocation, a block 
diagram of a three layer network such as those shown in FIGS. 6-8 is 
considered in FIG. 10. The network comprises a plurality of user sites 
400a-400e, a plurality of multimedia central offices 402, a plurality of 
regional hub offices 404, and a national hub office 406. 
A classification system for multi-point call topologies can be created 
based upon the following designations of components of a multi-point 
conference. Communication between two users connected to the same 
multimedia central office (such as a user at the user site 400a 
communicating with a user at the user site 400b) is designated as a type 
"IN" communication (i.e., within a neighborhood). Communication between 
two users connected to the same regional hub office (such as a user at the 
user site 400a communicating with a user at the user site say 400c) is 
designated as a type "R" communication (i.e., within a region). Finally, 
communication between two users connected to the same national hub office 
(such as a user at the user site 400a communicating with a user at the 
user site 400d) is designated as a type "M" communication (i.e. the 
maximum topological span). 
One user in a multi-point conference is selected as a reference point for 
classifying each of the types of connections in the conference. For a 
K-party conference, there are K-1 such connections which are herein 
referred to as "components". 
Next, a (K-1)-tuple of all connection type designations in the multi-point 
conference call is created. For a 3-party call, there are nine different 
2-tuples: NN, NR, RN, NM, MN, RR, RM, MR, and MM. For a 4-party call, 
there are twenty-seven possibilities: NNN, NNR, NRN, RNN, etc. 
All cases that amount to identical algebraic expressions with respect to 
commutativity of multiplication can be collapsed into a common 
representative form or class. For example, for 3-party calls, although 
there are nine 2-tuples, three are redundant in that they may be written 
in two different ways (e.g., NR=RN, NM=MN, and RM=MR). Thus, there are six 
possibilities for the representational classes: N.sup.2, NR, NM, R.sup.2, 
RM, and MR. For 4-party calls, there are ten possibilities since many of 
the 3-tuples can be written in 3 or 6 ways. These common representative 
forms are used to label the class of each multipoint conference. In 
general, there are K(K-1)/2 possible classes for a K-party conference. The 
number of ways to write a k-tuple is given by the multinomial coefficient 
of the expansion of the algebraic expansion (N+R+M).sup.k. 
For each multi-point conference class, one or more optimal locations for a 
multipoint conference bridge can be identified which minimize the cost 
resulting from long distance transmission. FIGS. 11a-11f illustrate the 
location of a conference bridge CB for the six possible 3-party cases. 
FIGS. 12a-12o illustrate the location of a conference bridge CB for 15 
different 4-party cases. A summary of optimal locations for a centralized 
conference bridge by multi-point conference class is provided in columns 
3-5 of Tables I and II. A few rarely occurring degenerate cases have been 
omitted from FIGS. 11 and 12, and Tables I and II, in order to avoid 
descriptive complexity. 
TABLE I 
______________________________________ 
# 
Codecs 
Ways to N R M # Codecs 
@ R 
Class 
Write optimal? optimal? 
optimal? 
@ N or M 
______________________________________ 
N.sup.2 
1 X 3F 
R.sup.2 
1 X 3 
M.sup.2 
1 X 3 
NR 2 X 2F + 1 
NM 2 X 2F + 1 
RM 2 X 3 
______________________________________ 
TABLE II 
______________________________________ 
# 
Codecs 
Ways to N R M # Codecs 
@ R 
Class 
Write optimal? optimal? 
optimal? 
@ N or M 
______________________________________ 
N.sup.3 
1 X 4F 
R.sup.3 
1 X 4 
M.sup.3 
1 X 4 
N.sup.2 R 
3 X 3F + 1 
N.sup.2 M 
3 X 3F + 1 
R.sup.2 N 
3 X X 2F + 2 4 
R.sup.2 M 
3 X 4 
M.sup.2 N 
3 X X X 2F + 2 4 
M.sup.2 R 
3 X X 4 
NRM 6 X X 2F + 2 4 
______________________________________ 
Columns 6-7 of Tables I and II show how many codecs are needed per 
conference bridge at the indicated location should codecs be required to 
convert signal formats. For example, if the conference bridges use analog 
video and audio, any neighborhood connections which are carried as analog 
video and audio over NTNI UTP can connect directly to a conference bridge 
while all other connections require a codec. For a given neighborhood with 
fraction "F" of such analog NTNI UTP users and fraction "1-F" of users 
requiring a codec to interface to the conference bridge, the number of 
codecs required at that neighborhood statistically behaves as shown in 
column 6. 
For K&gt;3, some classes have more than one optimal choice because several 
choices have identical transmission requirements. For example, in 4-party 
conferences these classes include NRM, NR.sup.2, RM.sup.2, and NM.sup.2 as 
seen in Table II. In these cases, analytic models can be used to compare 
the multiple optimal options for ranges of traffic patterns for more 
efficient use of conference bridge resources for a specified blocking 
factor. Such an analysis will be explored in more detail below, but 
typically the best choice for locating conferencing resources in these 
situations is in the regional hub offices with typical hardware savings 
around 10% over other choices. 
Next, the analytical modeling aspect of the procedure applicable to 
facility sizing will be described. A flow chart of an embodiment of a 
method for optimal allocation to facilities is shown in FIG. 13. As 
indicated by block 420, traffic assumptions are made concerning the 
overall Erlangian traffic and probability distribution of various classes 
of conference calls. These assumptions are used to derive probability 
distributions for each conference class supported by the implementation of 
the invention, as indicated by block 422. In the absence of other 
information, the same probability distribution used for point-to-point 
calls can be used for each communication type to construct the probability 
for each conference class (using standard independence calculations and 
multinomial combinatoric coefficients that correspond to the number of 
ways the class can occur--see column 2 of Tables I and II). 
Using these probability distributions and overall assumptions about traffic 
demand, the pro-rated statistical traffic demand for each conference class 
is calculated, as indicated by block 424. Using optimal location tables 
such as Table I and Table II, each class of conference traffic is directed 
to its optimal location, as indicated by block 426. As indicated by block 
428, the method further includes a step of separately aggregating, for 
each location, the total demand for conference bridges across all 
conference classes. 
As shown in block 430, the method may optionally include overflow 
procedures when appropriate resources are not available (due to loading or 
failure). If these optional features are included, probalistic adjustments 
for overflows across locations may be introduced. As indicated by block 
432, the traffic demand for conference bridges and desired blocking 
performance are applied to the server-variable inverse of the Erlang-B 
formula to determine the required number of conference bridges at each 
location. 
A flow chart of an embodiment of a method of optimal allocation applicable 
to demand-driven resource allocation is shown in FIG. 14. Once a request 
for a conference is received, a step of finding the current location of 
requested participants is performed, as indicated by block 450. 
Preferably, this step is performed by querying various registration 
directory services to obtain the current location of the requested 
participants actively on the system. If some of the requested participants 
are unavailable, appropriate call handling elements are employed. 
As indicated by block 452, the method further includes a step of 
determining the conference class for each of the requested participants 
which are available. A step of finding an optimal conference bridge 
location for the requested participants is performed, as indicated by 
block 454. Preferably, this step produces a prioritized list of best 
conference bridge locations based upon a predetermined look-up table. 
Optionally, the method may further consider other possible participants 
which may be added for inclusion in the creation of the prioritized list 
of best conference bridge locations, as indicated by block 453. 
Next, the method performs steps which attempt to allocate conference 
bridges and communications trunks based upon the prioritized list. 
Starting with the first priority choice, a step of requesting a conference 
bridge in the desired location is performed as indicated by block 458. If 
the request is successful, the necessary trunks are requested in block 
460. If either the requested conference bridge is unavailable or the 
requested trunks are unavailable, the next best choice in the list is 
attempted. 
Embodiments of the above-described allocation methods have several valuable 
impacts: (i) they save considerable transmission costs by providing a 
simple classification scheme for selecting the most optimal conference 
bridge location for each conference call; (ii) they provide a procedure 
for identifying how many conference bridges are required at each network 
office; (iii) an additional 10-20% in conference bridge hardware costs can 
be saved by refining the above procedure to exploit the best allocation 
choices in thus far "don't care where" cases (namely, R.sup.2 N, M.sup.2 
N, M.sup.2 R, and NRM; see Table II); and (iv) they can then be 
incorporated into the actual control algorithms which allocate resources 
when users place conferencing calls. 
Although this aspect of the present invention is targeted at location of 
video conferencing resources, the principles can also apply to 
conventional telephone audio conferencing systems and application sharing 
server systems. 
Next, alternative embodiments of conference bridges for use in the 
multimedia telecommunications system are presented. Preferred embodiments 
of the present invention employ continuous presence conference bridges so 
as to deliver realistic support for multiparty human interaction. The use 
of continuous presence conferencing bridging provides for the distribution 
of conferencing resources among offices and demand-driven allocation 
policies of conferencing resources. This is of value in facilities 
planning and in minimizing transmission costs. Continuous presence 
conference bridges provide an improvement over other available wide-area 
conferencing systems relying on multipoint control units (MCUs), which 
display only one participant's video image at a time. 
The types of continuous presence conference bridging utilized by 
embodiments of the present invention may be categorized as having either a 
centralized or a decentralized geographic spread. Further, the types of 
continuous presence conference bridging may be characterized by the type 
of video mosaic implementation utilized, namely, analog video domain, 
pixel domain, discrete cosine transform (DCT) domain, or variable length 
coding (VLC) domain. 
FIG. 15 is a block diagram of a simplified layered architecture of a 
compression scheme in order to illustrate the aforementioned domains. An 
analog video source 480 provides an analog video signal to an 
analog-to-digital converter 482. The analog-to-digital converter 482 
digitizes the analog video signal to form a digitized video signal. After 
conversion, the digitized video signal is applied to a DCT signal 
processor 484 which provides processing based upon a DCT operation. The 
output of the DCT signal processor 484 is applied to a compressor 486 
which creates a stream of variable length code words. The compressor 486 
may employ one of many compression algorithms known in the art. 
The variable length code words are then passed to a transmitting 
communications subsystem 488 which supplies real-time timing and/or 
file-creation support. A signal transmitted and/or stored by the 
transmitting communications subsystem 488 is received and/or retrieved by 
a receiving communications subsystem 490. The receiving communications 
subsystem 490 acts to recover real-time stream of variable length code 
words. 
The recovered stream of variable length code words is passed to a 
decompressor 492, which employs a decompression algorithm to invert the 
action of the compression algorithm in the compressor 486. The 
decompressor 492 produces a resulting DCT video stream which is applied to 
an inverse DCT signal processor 494. The inverse DCT signal processor 494 
produces a digital video stream which is applied to a digital-to-analog 
converter 496. An analog video stream produced by the digital-to-analog 
converter 496 can be presented to an analog video sink 498 such as a 
display device. 
The signals produced by the analog video source 480 and the 
digital-to-analog converter 496 are regarded as being in an analog video 
domain, since both contain an analog video signal. The signals produced by 
the analog-to-digital converter 482 and the inverse DCT signal processor 
494 are regarded as being in the pixel domain, since both contain a 
digital pixel stream. The signals produced by the DCT signal processor 484 
and the decompressor 492 are regarded as being in the DCT domain, since 
both contain a DCT stream. The signals produced by the compressor 486 and 
the receiver 490 are regarded as being in the VLC domain, since both 
contain a stream of variable length code words. 
Embodiments of the present invention may employ commercially available 
compression schemes which compute a discrete cosine transform to convert 
the image from two-dimensional amplitude distribution to two-dimensional 
frequency distribution. The DCT is the core of many popular deployed and 
commercially available compression schemes, in particular the ITU-TSS 
H.261/H.320 standard supported by many video codec manufacturers. 
With regard to the use of pixel-domain video compositing in the conference 
bridges, embodiments of the present invention may use many different 
approaches. Two specific approaches to pixel-domain video compositing 
include a centralized implementation and a distributed implementation. The 
use of pixel-domain video compositing elements (such as the video mosaic 
units made by Panasonic, For-A, and others) to realize continuous video 
presence in video conferencing is disclosed in U.S. application Ser. No. 
08/131,523 for both centralized and distributed implementations. In 
addition to these approaches, embodiments of the present invention may use 
any of the extensions discussed herein to follow. In particular, the 
distributed implementation of DCT-domain or VLC-domain compositing 
described herein supplements the art of distributed conference bridges as 
described in U.S. application Ser. No. 08/131,523. 
In the pixel-domain, a 2-by-2 mosaic of four full-motion video regions can 
be formed by dropping every other pixel in each image dimension from four 
full-screen pixel streams, and positioning the resulting half-by-half 
sized regions to form a 2-by-2 mosaic. There are many variations of this, 
such as forming 3-by-3 mosaics by dropping every 2 out of 3 pixels in each 
dimension, or forming mixed-region-size mosaics by using different pixel 
dropping rates for the pixel streams emanating from different sources, as 
is obvious to one having ordinary skill in the art. 
In a wide area situation, at least some of the video images will arrive in 
the digital communications signal format. Commercially available video 
mosaic units (such as those made by Panasonic, For-A, and others) provide 
interfaces for signals in the analog video domain, although they 
internally perform the video compositing in the pixel domain. The 
conversions between the analog video domain and the pixel domain are 
performed by separate internal analog-to-digital and digital-to-analog 
converters. The reason for this is that low cost interfaces in the analog 
domain are common and well supported, while low cost interfaces in the 
pixel domain for these types of interconnections are not available or 
defined. 
More preferably, pixel-domain compositing may interface codec systems in 
the pixel domain by means of an appropriate interface. In practice, this 
interface can be engineered to be relatively trivial to implement since 
both commercially available codecs and video mosaic units typically must 
convert to and from the analog domain in a similar fashion. Without a 
coordinated design, the codecs and video mosaic units could well use 
completely different digital representations of the video frame. There are 
cost, complexity, and performance advantages to this approach. 
Switching among a pool of codecs and a pool of video mosaic units can be 
done in a conventional digital backplane. Presently, in the analog video 
domain, this is performed by wideband analog switching matrices, which 
requires additional hardware for cable transceivers, multiple power 
supplies, and low-noise wideband analog backplanes. This redundant 
hardware can be avoided by an appropriate scale server implementation. 
The most likely candidate for the analog video interface signals are 
popular standardized composite signals (NSTC, , and SECAM). Each of 
these introduces image degradation with each pair of digital-to-analog and 
analog-to-digital conversions. This can be somewhat problematic in the 
areas where chroma and luminance frequency bands overlap somewhat and are 
filtered in different ways at each interface. 
As an additional level of improvement, considerable improvements in cost 
and performance can be made by compositing in the DCT domain. This 
technique has been explored by others; see "Video Compositing in the DCT 
Domain", by Chang, Chen, and Messerschmitt, Proceedings of IEEE Workshop 
on Visual Signal Processing and Communications, Rayleigh, N.C., September 
1992. Embodiments of the present invention may employ this approach using 
the methods of Chang, Chen, and Messerschmitt or related methods. 
Effectively, the operations involved in dropping pixels and compositing as 
a mosaic can be represented mathematically as under-sampling and 
translation operations. These under-sampling and translation operations 
have corresponding two-dimensional impulse responses which, when convolved 
in two dimensions with the video stream frames in the pixel domain, create 
the desired video mosaic. When this entire process in transformed into the 
DCT domain, the DCT frames (in the DCT streams within the DCT domain) are 
multiplied in two dimensions with the DCT of the under-sampling and 
translation operations, producing the DCT of the desired mosaic. The 
multiplication is, in general, less complex to implement than the 
convolution. More importantly, the mosaic can be done without use of the 
DCT and the inverse DCT signal processors for video signals arriving at 
the bridge from the wide area. This saves costly hardware, greatly reduces 
codec delay, and is a natural candidate for incorporation into an 
appropriate large-scale server implementation. 
Even further cost savings and performance improvements can be made by 
compositing in the VLC domain. This technique has been explored by others; 
see "Video Bridging Based on H.261 Standard", by Lei, Chen, and Sun, IEEE 
Transactions on Circuits and Systems for Video Technology, Vol. 4, No. 4, 
pp. 425-437, August 1994, for example. Distributed implementations of 
video compositing is also a natural candidate for incorporation into an 
appropriate large-scale server implementation. 
Slight variations allow the aforementioned methods of FIGS. 13 and 14 to be 
applied to optimal allocation of other related resources within the 
multimedia telecommunication system. Specifically, the method may be 
applied to allocate components within service modules such as codecs used 
to provide digital access to analog video domain conference bridges. 
Further, the method may be applied to allocate internal components of a 
conference bridge server, such as the analog-to-digital and the 
digital-to-analog converters used to provide analog access to pixel, DCT, 
or VLC domain conference bridges. 
More specifically, users of the multimedia system may use either analog 
NTNI access or digital access to a multimedia central office. For analog 
video domain conference bridge interfaces, codecs are needed for digital 
access, but are not needed for analog NTNI access. For conference bridge 
interfaces in the pixel domain, the DCT domain, or the VLC domain, 
analog-to-digital and digital-to-analog converters are required to provide 
analog access to pixel, DCT, or VLC domain conference bridges. 
As an example, consider the need for codecs when using analog video domain 
conference bridges. Since the regional hub offices and the national hub 
offices do not have analog NTNI access, the number of codecs needed for 
each conference class (whose optimal location is one of these offices) is 
simply the number of participants in the conference. This is illustrated 
in the column 7 of Table I and Table II. At the multimedia central offices 
and for conference classes where multimedia central offices are the 
optimal conference bridge location, codecs are needed for each outgoing 
trunk in conference classes involving users whose access does not 
terminate on the same multimedia central office. In terms of the 
communication type designations defined earlier, one codec is needed for 
every R or M component of the conference class. 
Further, if the fraction of users terminating on that multimedia central 
office with digital access is denoted by a variable F (which ranges 
between 0 and 1), then the probability a codec is needed is F times the 
number of users terminating on that multimedia central office which are 
participating in the conference. In other words, an additional factor of F 
for the reference user and one each for every N component in the 
conference class is included in the probability that a codec is needed. 
This is illustrated in the column 6 of Table I and Table II. The resulting 
probabilistic (for the multimedia central offices) or deterministic (for 
the regional hub offices and national hub offices) number of codecs needed 
per class can then be used to pro-rate the traffic in the steps indicated 
by blocks 428 and 430 in FIG. 13. Performing the step indicated by block 
432 to the pro-rated traffic gives the number of codecs needed for this 
purpose. 
Since commercially available implementations of pixel-domain video 
compositing elements (such as the video mosaic units made by Panasonic, 
For-A, and others) are single physical hardware units, centralized 
implementations of continuous presence conference bridges would appear to 
be the easiest direct implementation approach to continuous presence video 
compositing. In U.S. application Ser. No. 08/131,523), however, 
distributed implementations of video compositing are shown to be 
advantageous in wide area situations. 
The local video of all participants can be included in the mosaic without 
multiple codec delays (not just those participants who happen to be 
collocated near a centralized conference bridge in a way that no 
round-trip codec delay is incurred for them). 
In many cases, the trunking requirements which result can be considerably 
reduced. For example, with two users in location A and two users in 
location B, the centralized bridge would require 2 trunks if the bridge is 
collocated at a sufficiently near location A or B (and 4 trunks if the 
conference bridge is in a third location), while a distributed bridge 
needs only 1 trunk to give the same results. 
Methods and systems for connecting a workstation or a room to a multimedia 
central office will now be discussed. In general, any means for connecting 
the workstation or room directly with the multimedia central offices via a 
public telephone loop plant UTP are sufficient, as are any means for 
connecting the workstation or room with the multimedia central office 
through an internal premises communications system via the public 
telephone loop plant UTP. Clearly, the longer distances of loop plant UTP 
which can be used, the more valuable reuse of the existing worldwide 
investment in public telephone UTP loop plants. Thus, it is desirable, but 
not essential, to carry audio, video, and data signals through as long a 
length of public telephone loop plant as possible. 
A further discussion of methods and systems for interfacing with NTNI 
workstations and rooms is appropriate. Approaches to computer control 
distribution of analog video and audio within a premises is taught in U.S. 
application Ser. No. 08/131,523, and in U.S. Pat. Nos. 4,686,698, 
4,847,829, and 5,014,267. These approaches rely on the employment of 
on-premises codecs for connecting workstations or rooms to the outside 
world. Embodiments of the present invention avoid the per-premises cost of 
these codecs by use of a public network service providing NTNIs which link 
to publicly shared codecs. Additional cost savings and features are 
realized by designing each resulting element as part of an overall wide 
area collaboration and multimedia networking system. 
In considering how to implement a public network service that avoids the 
cost of these per-premises codecs through use of NTNIs, audio, video, and 
data are delivered by either per-premises trunks or per-workstation/room 
direct lines or per-premises trunks. Preferably, the specifications for 
the audio, video, and data which are delivered are as follows: (i) data 
communications supporting rates between 128 kbps and 10 Mbps; (ii) at 
least 3 MHz, and more preferably, 4-6 MHz analog color video or a 
perceptual near-equivalent; and (iii) at least 5 kHz, and more preferably, 
7-15 kHz analog audio or a perceptual near-equivalent. The alternative of 
"perceptual near-equivalent" is meant to allow for the inclusion of cases 
where signal processing is used in such a way to deliver comparable 
quality with less actual transmission bandwidth. 
Various techniques for delivering these requirements over UTP, focusing on 
the employment of NTNI, but not exclusive thereto, are considered. First, 
the methods by which workstations or rooms 100 connect with public 
networks are explained. 
Referring back to FIG. 2, user premise 104c includes workstations which 
connect to the public network UTP loop plant 114 individually, and user 
premise 104d includes workstations which connect through the internal 
premises communication network 116 with one another and share UTP loops 
within the public network UTP loop plant 118. In each of these cases, the 
workstations do not connect directly with the public network UTP loop 
plant 114 or 118, but rather are linked by connection means to a loop UTP 
transceiver. The connection means may include any of the following: 
(i) UTP transceivers used for premises networking, as described in U.S. 
application Ser. No. 08/131,523; 
(ii) coaxial cable, as described in U.S. Pat. Nos. 4,686,698, 4,847,829, 
and 5,014,267; 
(iii) fiber optic links; or 
(iv) wireless premises radio. 
In cases where a user premise does not provide an internal premises network 
116, the loop UTP transceiver may be physically located in a premises 
wiring closet, or may be collocated with each workstation or room system. 
Alternatively, the connection means may be very short electrical 
connections within a piece of workstation or room equipment so that the 
loop UTP transceiver is actually physically incorporated into the 
workstation or room equipment. 
In cases where a user premise does provide an internal premises network 
116, the loop UTP transceiver is very likely to be physically located in a 
premises wiring closet. In this arrangement, the internal premises network 
116 provides a concentration function to a pool of shared loop UTP 
transceivers. Such an arrangement allows a number of workstations and 
rooms to share a smaller number of UTP trunks and associated transceivers. 
The connection means may include UTP transceivers, coax cable, fiber optic 
links, or wireless premises radio. 
In either of the two aforementioned cases, the part of the loop UTP 
transceiver which interfaces with the public network UTP loop plant 114 or 
118 typically differs from UTP transceivers used for premises networking 
in that it typically provides the following functions: 
(i) lightning protection and other safety isolation functions; 
(ii) additional transmission power and/or receiver sensitivity to 
compensate for the electrical conditions of the public network UTP loop 
plant 114 or 118; 
(iii) additional frequency compensation to compensate for the electrical 
conditions of the public network UTP loop plant 114 or 118; 
(iv) signal processing and transceiving to compensate for the electrical 
conditions of the public network UTP loop plant 114 or 118; and 
(v) response to remotely controlled installation and maintenance functions 
(such as loopback, generation/detection of test signals and automated 
cable compensation adjustments) which in a practical embodiment of the 
invention may be executed from the multimedia central office. 
The loop UTP transceiver employs the public network UTP loop plant 114 or 
118 to reach a matching loop UTP transceiver within the multimedia central 
office. This matching loop UTP transceiver is similar to the loop UTP 
transceiver used on user premises 104c and 104d but may incorporate 
differences in packaging for use in a public utility office. The packaging 
may differ with regard to powering (which may include redundancy 
provisions), the type of input/output connections and/or cabling employed, 
and the physical package format. Further, the matching loop UTP 
transceiver may be capable of: (i) issuing remotely controlled 
installation and maintenance functions (such as loopback, 
generation/detection of test signals, automated cable compensation 
adjustments) which in a practical embodiment of the invention may be 
executed from the multimedia central office; (ii) performing measurements 
of response of loop UTP transceiver to remotely executed installation and 
maintenance functions; or (iii) performing maintenance functions (power 
checks, input/output connection checks) which are relevant. 
A block diagram of a method and system that utilizes inverse multiplexing 
to carry a single bit stream 510 on a plurality of lower-rate digital 
carriers 512 is illustrated in FIG. 16. The bit stream 510 is applied to 
an inverse multiplexer 514 to produce a plurality of lower-rate bit 
streams. The lower-rate bit streams are communicated through a public 
digital network 516 over the plurality of digital carriers 512. The 
lower-rate bit streams are received by an inverse multiplexer 520 which 
reconstructs the original bit stream. Typically, the inverse multiplexing 
is bidirectional. This technique is employed, for example, in video 
teleconferencing where two 56 kbps channels are used to carry a single 112 
kbps stream. 
Due to the limited bandwidth of a public loop plant UTP, particularly at 
longer distances, embodiments of the multimedia telecommunication system 
deliver higher bandwidth signals by "dividing" original signal bandwidth 
across a plurality of public loop plant UTPs. Moreover, both digital and 
analog signals may be carried by the UTP using broadened forms of inverse 
multiplexing. 
The division of a signal across multiple physically separated channels is 
herein referred to as "space division" (in contrast with "time division" 
used in time-division multiplexers). Space division techniques may be 
employed to split a signal across multiple UTPs in order to deliver higher 
bandwidths across longer distances where the transmission properties of 
the UTP may rapidly degrade (e.g. above 1-2 MHz or even lower analog 
frequencies). 
Digital streams can easily be split and reclocked to create multiple 
streams operating at lower clock frequencies and, for the range of 
distances involved, be reassembled into the original digital stream. In 
analog signals the splitting is relatively straightforward, but the 
precision frequency transmitter down-shifting, receiver up-shifting, and 
receiver channel recombining required may be problematic for arbitrary 
high-fidelity analog signals. In the case of NTSC//SECAM analog video 
signals, however, special structural properties of the signal can be 
exploited. 
Methods and systems for splitting a digital stream of a given rate into 
multiple digital streams of lower rates and reconstructing the digital 
stream are well-known in the art. Often, the steps in this process are 
referred to as serial-to-parallel conversion and parallel-to-serial 
conversion. Typically, a public telecommunications network can not provide 
a plurality of channels whose relative transmission delays are within a 
bit-symbol period. Further, in extreme circumstances, differential timing 
jitter among the plurality of channels can also create problems. Modern 
inverse multiplexing equipment provide means at the receiving site for 
measuring the relative transmission delays among the plurality of channels 
and, based on these measurements, inducing compensating delays on all but 
the most delayed channel(s) so as to reconstruct the original relative 
timing used at the transmitting site. 
Embodiments of the present invention may directly employ UTP space division 
(i.e., an adaptation of digital inverse multiplexing) in many ways. For 
digital control/image/data-communications signals, as illustrated in FIG. 
17, inverse multiplexers 530 and 532 are used to transform higher bit rate 
digital signals 534 into a plurality of lower bit-rate signals 536. 
Preferably, each of the lower bit-rate signals 536 has a bit rate higher 
than that for an ISDN basic rate interface. These lower bit-rate digital 
signals are encoded for transmission over a UTP 540 within the public 
telephone UTP loop plant 542 by means of UTP transceivers 544. The UTP 
transceivers 544 include UTP transmitters 544a and UTP receivers 544b. 
Upon receiving the lower bit-rate signals, one of the inverse multiplexers 
530 and 532 reconstructs the original signal. 
For video and audio signals, as illustrated in FIG. 18, digital conversions 
and compression of a signal 560 is performed via a codec 562a. The codec 
562a is capable of producing a digital signal 563 based upon the received 
analog audio or video signal 560. An inverse multiplexer 564a is used to 
create lower bit-rate signals from the digital signal 563. These lower bit 
rate signals are processed by transmitters 566 for transmission over a UTP 
570 to receivers 572. The received signals are presented to an inverse 
multiplexer 564b which produces a reconstruction of the digital signal 
563. The reconstruction is presented to the codec 562b which then creates 
a reconstructed analog signal 574 approximately identical to the original 
signal 560. 
Next, an adapted inverse multiplexer method is presented. Conventional 
inverse multiplexers are designed for use with TNI and the types of 
digital communications channels provided by common carriers. For a UTP 
application, use of TNI often is an added complication as most likely all 
signals will be in an NTNI format. Further, the functions needed to work 
with the types of digital communications channels provided by common 
carriers are excessive for the UTP application. Thus, a preferred 
implementation of the invention utilizes digital inverse multiplexing to 
realize space-division UTP with digital inverse multiplexing methods 
optimized for space-division UTP. 
In a public UTP loop plant, the propagation speed is typically in the 
3.3-6.6.times.10.sup.8 feet/sec range (i.e, between half and full speed of 
light in a vacuum). As a result, the physical length of a baseband bit 
period within the wire is approximately 330-660 feet for a 1 Mbps signal. 
Consequently, there is approximately a 1 bit skew in timing differential 
for each 330-660 feet length difference between any two UTP. Thus, for a 
public UTP loop plant, which by its loop architectural and operational 
policies can assume a maximum differential distance .DELTA.L.sub.max among 
a collection of UTP to be used in a space division transmission system, it 
is possible to bound the maximum bit timing skew at a given bit-rate by 
some related value .DELTA.B.sub.max bits. In practice, because of 
rise-times and fall-times resulting from uncorrected dispersion in the 
wire, the value of .DELTA.B.sub.max may be effectively greater than 
divided by the physical length of a baseband bit period; the exact 
relationship depends on the selected transceiver implementations. 
For a 1 Mbps digital stream and a .DELTA.L.sub.max &lt;200 feet among a 
collection of UTP used in a space division transmission system, bit skew 
correction is not typically necessary. For a 2 Mbps digital stream and a 
.DELTA.L.sub.max &lt;200 feet among the collection of UTP used in a space 
division transmission system, only up to 2 bit periods of skew are 
typically encountered. For a 1 Mbps digital stream and a .DELTA.L.sub.max 
&lt;600 feet among the collection of UTP, only up to 3 bit periods of skew 
are typically encountered. For a 2 Mbps digital stream and a 
.DELTA.L.sub.max &lt;600 feet among the collection of UTP, only up to 6 bit 
periods of skew are typically encountered. 
To implement an adapted inverse multiplexer matched to the needs of UTP 
space division, the following simplified approach can be used. Each 
transmitting digital inverse multiplexer is made capable of transmitting a 
calibrating one-bit transition pattern, upon a command over the UTP loop, 
to provide an auto-calibrating mode. Each receiving digital inverse 
multiplexer applies each of the signals received over the plurality of 
UTPs to one of a plurality of dedicated shift registers. Each of the shift 
registers is clocked by a free-running clock operating at a multiple M of 
the expected operating bit rate of the UTP channel. Typically, the shift 
registers comprise a small number of stages (i.e. M times 
.DELTA.B.sub.max). Typically, M is a small integer such as 2, 3, or 4. 
Since each arriving bit in the received digital signal is effectively 
sampled a multiple number of times, it is possible to more accurately 
isolate the edges and center of the calibrating one-bit transition 
pattern. As a result, bit detection and channel delay can be more 
accurately identified. 
In an auto-calibrating mode, based on the resulting received bit pattern 
distributed within the plurality of shift registers, the shift register 
tap corresponding to the center of the received bit pattern is selected as 
the point to receive the differential-delay-compensated stream for each 
UTP channel when taken out of calibration mode and put into operating 
mode. The transmitter 530 and receiver 532 is then put in the operating 
mode: each differential-delay-compensated UTP channel is connected to 
ports on serial-to-parallel converters at the transmitter 530 and 
parallel-to-serial converters at the receiver 532. 
In addition, it is possible to divide an analog signal of a given bandwidth 
across a plurality of lower bandwidth channels for space division 
transmission. This has been used, for example, for voice-grade telephone 
audio in U.S. Pat. No. 5,136,575 to Kuroda where an audio signal is split 
into two bands and each band is separately transmitted. Using a suitable 
design approach, analog space division can be applied to divide a high 
bandwidth analog signal, such as an NTSC//SECAM video signal, into 
multiple channels for space division transmission over multiple UTPs. 
FIG. 19 is a block diagram of a general frequency-division system for 
splitting an analog signal into a plurality of bands for transmission over 
a plurality of UTP channels, and for reconstructing the signal at a 
receiving end. An analog signal 600 with bandwidth X is presented to a 
bank of N signal filters 602. The signal filters 602 split the analog 
signal 600 into N minimum-overlapping frequency bands and provide a 
separate output for each band. The signal filters 602 may be implemented 
with either digital or analog systems in accordance with quality, cost, 
and manufacturing-scale trade-offs. 
The lowest frequency filter 602a may be low-pass or band-pass; low-pass is 
often an essential choice for a baseband signal that contains DC or very 
low frequency components (such as video luminance signals). The highest 
frequency filter 602b may be high-pass or band-pass; band-pass is often an 
essential choice for high-frequency noise immunity. All other filters are 
band-pass. Ideally, the transition bands for the filters 602 are sharp 
with well-behaved phase and amplitude characteristics. It is typically 
advantageous to use filters whose adjacent bands are such that the 
overlapping transition bands sum to the original signal amplitude and 
phase throughout the transition band. An example of such a filter is the 
Linkwitz-Riley filter often used at audio frequencies in active audio 
crossovers. 
The outputs of the N filters 602 are applied to a corresponding bank of N-1 
or N frequency shifters 604 (or, more generally, N-1 to N remodulators) . 
The lowest frequency band need not be frequency shifted, but could benefit 
from it if the original signal 600 does not have low frequency components. 
In this case, a downshift may be advantageous to lower the bandwidth 
required for UTP transmission of the lowest frequency band. Putting the 
signal on a carrier so as to gain immunity from transmission system 
abnormalities is beneficial, as is done in U.S. Pat. Nos. 3,723,653 and 
3,974,337 to Tatsuawa. Since the frequency shifters may provide such 
immunity from transmission system abnormalities to the other bands, it may 
be advantageous to treat the lowest band in a similar manner. 
If the lowest frequency band is not frequency shifted, frequency shifter 
604a is not included in the bank of frequency shifters. The frequency 
shifters 604 provide frequency down shifting to move the particular band 
served down to near baseband (i.e., having a lowest frequency very near 
zero Hz) for the channel. Each signal emerging from the filters 602 has a 
bandwidth, measured from the zero frequency DC to the highest frequency 
component,, significantly less than the bandwidth X of the original signal 
600. Further, the sum of all the bandwidths from the frequency shifters 
604 (plus any unshifted low frequency band should frequency shifter 604a 
be omitted) preferably sums to only slightly more than the bandwidth X of 
the original signal. The difference between this sum and X corresponds to 
the effective overlap of the N bands. Such overlap is needed to ensure all 
frequency components of the original signal are included in the collection 
of N bands, but otherwise in general cases wastes transmission bandwidth 
and should be minimized. 
The N bands output from the frequency shifters 604 are presented to a bank 
of N UTP transmitters 606 which put the signal out over N pairs of UTP 610 
in a public telephone UTP loop plant 612. Each band is received by a 
corresponding one of a bank of UTP receivers 614. The transceiver outputs 
are then presented to a bank of N-1 to N frequency shifters 616 (or, more 
generally, N-1 to N remodulators). If the frequency shifter 604a is 
omitted, then frequency shifter 616a is omitted as well. Otherwise, all 
frequency shifters in the receiving site undo the frequency shifting 
performed by the transmitting site frequency shifters 604. 
An analog mixer 620 recombines the bands to form an unequalized replica 622 
of the original analog signal 600. The unequalized replica signal 622 can 
be improved by passing it through an optional equalizing filter 624 to 
compensate for phase and amplitude variations encountered where the 
transition regions of consecutive pairs of bands overlap. The output 626 
of the equalizing filter 624 is an improved replica of the original analog 
signal 600. 
Although illustrated in terms of frequency shifting, embodiments of the 
present invention are not limited to this specific form of remodulation. 
Hence, a plurality of remodulators may be substituted for the frequency 
shifters in the above-described embodiments. Further, a remodulator may be 
substituted for a frequency shifter in embodiments described hereinafter. 
An alternative system for implementing space division transmission of 
NTSC//SECAM analog video signals over two UTPs is illustrated in FIG. 
20. This system has the advantages of being relatively inexpensive to 
implement, degrading smoothly as the transmission bandwidth become 
limited, and readily supporting the introduction of audio. 
A composite NTSC//SECAM analog video signal 640 is applied to a low-pass 
filter 642 and a band-pass filter 644. The band-pass filter 644 is tuned 
to pass a chroma carrier signal and sidebands associated therewith 
contained within the video signal 640. The low-pass filter 642 is tuned to 
roll off at a frequency below the chroma carrier signal and the sidebands. 
The output of the low-pass filter 642 provides a luminance component 
contained within the video signal 640 up to the cutoff frequency of the 
low-pass filter 642. 
The pair of separated signals from the output of the filters 642 and 644 is 
similar to the Y-C component format (such as used in SVHS video) with the 
exception that the luminance band need not be as wide (and in most 
practical long distance analog UTP space-division implementations is not 
as wide). If the source happens to already be in Y-C format, rather than a 
composite format, the filters 640 and 642 can be omitted; instead, the Y 
component provides the luminance signal and the C component provides the 
chrominance signal. 
The chrominance signal in a composite NTSC//SECAM analog video signal 
includes an amplitude and phase modulated 3.58 MHz carrier residing above 
the highest luminance frequency. In Y-C component format, the luminance 
signal can overlap into the chroma band which is carried on a physically 
separate circuit. The amplitude and phase modulation is actually 
quadrature amplitude modulation; one component (less sensitive color 
information) has a bandwidth of approximately 0.5 MHz and is transmitted 
double-sideband, the other component (more sensitive color information) 
has a wider bandwidth of approximately 1.8 MHz and is transmitted via a 
lower single-sideband. Since the carrier is at approximately 3.58 MHz, the 
2 MHz-wide chrominance band lies in the contiguous band of 2.1 to 4.15 
MHz. Because of these properties, a simplified approach to chrominance 
signal frequency shifting can be implemented, as described below. 
In a first approach, the carrier is mixed with a sinusoidal reference to 
create a linear offset for each frequency in the chrominance spectrum. In 
an improved approach, conventional chrominance decoders are used to obtain 
and remodulate two raw baseband chrominance components. This approach is 
attractive because integrated circuits exist which perform the functions 
of the filters 642 and 644, and separate the chrominance component. The 
remodulation scheme transmits the two chrominance components in a band 
whose width is less than 2 MHz, for example, the chroma carrier can be put 
at 1 to 1.8 MHz. If the new carrier is less than 1.8 MHz in frequency, the 
wider-bandwidth chrominance component can be filtered to a bandwidth whose 
value is slightly less than this carrier frequency; this introduces only 
slight color distortion. However, by lowering the carrier frequency, 
longer distances of UTP can be supported. Remodulation can be done using 
commercially available composite video signal chip sets, as used in VCRs 
and camcorders, but fed with a lower-than-normal carrier reference 
oscillator frequency. The resulting (or other implementation) chrominance 
frequency shifter 646 operates on the chrominance signal to produce a 
signal whose bandwidth is less than 2 MHz. 
The two space-division signals, at the output of the low-pass filter 642 
and the chrominance frequency shifter 646, split the original 4.1 MHz 
NTSC//SECAM analog video signal 640 into two signals of about half this 
bandwidth. These signals are then presented to UTP transmitters 650 and 
652 for transmission over UTPs 654 and 656 for reception by UTP receivers 
660 and 662. The UTP receiver 660 recovers the baseband luminance signal, 
while UTP receiver 662 recovers the frequency downshifted chrominance 
signal. The frequency downshifted chrominance signal is frequency shifted 
back up to its original format by a frequency shifter 664. 
If the approach described above is used for the downshifting, the received 
signals are again demodulated (preferably using a commercially-available 
integrated circuit with a lower-than-normal carrier reference oscillator 
frequency applied thereto), separated into luminance and both chrominance 
components, and remodulated using a commercially-available integrated 
circuit with a standard carrier reference oscillator frequency applied 
thereto. The resulting implementation of a chrominance carrier frequency 
upshifter 664 creates a replica chroma signal which is combined with the 
luminance signal using an analog mixer 668 to produce a replica video 
signal. Since the luminance band is fully contained within the signal 
produced by the UTP receiver 660, and the chrominance band is fully 
contained within the signal produced by the frequency shifter 664, the 
mixing needs no equalization as there is a guard band between the 
luminance and chrominance bands. 
Although it is not specifically shown in FIG. 20, the arrangement discussed 
thus far can be further enhanced by inclusion of single-sideband FM 
transmission in the baseband path at a carrier frequency only slightly 
higher than the full baseband channel bandwidth. This approach is 
disclosed in U.S. Pat. Nos. 3,723,653 and 3,974,337. As a result, all 
signals in the space division system may be sent by means of FM, giving 
uniform noise and attenuation variation immunity. 
FIG. 21 is a block diagram of a space division transmission system wherein 
an audio signal is introduced. Specifically, a baseband or an FM or PM 
audio signal is inserted into the chrominance UTP signal path in this 
embodiment. This results in the use of two UTPs in each direction, as in 
the NVT and Lightwave products, but with a longer maximum distance 
limitation due to better use of the bandwidth above audio frequencies on 
the second UTP. 
The arrangement of many of the elements illustrated in FIG. 21 is identical 
to the arrangement in FIG. 20, but additional elements have been 
incorporated. An analog audio signal 680 is introduced and, if not already 
assured to be band-limited to 20 kHz, is filtered by an optional low-pass 
filter 682 to some maximum frequency less than 20 kHz. The resulting 
signal is presented to an optional FM or PM modulator 684 and then to a 
mixer 686, or else is applied directly to the mixer 686. The mixer 686 
combines the signal applied thereto with the carrier-downshifted chroma 
signal which has been shifted by the frequency shifter 646 so that the 
pass-bands of the two mixed signals do not overlap. The mixer 686 produces 
a combined signal which is then presented to the UTP transmitter 652. The 
combined signal is transmitted over the associated UTP 656 for reception 
by the associated UTP receiver 662. 
The signal produced by the UTP receiver 662 is applied to a high-pass 
filter 692 (or, alternatively, a bandpass filter) which passes the chroma 
signal. The remaining steps of video processing occur as described in the 
embodiment of FIG. 19. The signal produced by the UTP receiver 662 is also 
presented to a low-pass filter 694 which only passes the audio portion of 
the received signal. If an FM or PM modulator 684 is used on the transmit 
side, the output of the filter is then presented to a corresponding FM or 
PM demodulator 696 which produces a replica audio signal. If no FM or PM 
modulator 684 is used on the transmit side, the output of the filter 694 
directly produces the replica audio signal. 
An alternative method for introducing audio into the arrangement of FIG. 20 
includes a step of inserting normalized PAM (pulse amplitude modulation) 
in the horizontal synchronization pulse stream, and a step of substituting 
the resulting signal for the analog video signal 640. The received replica 
is then passed to a matching audio/video recovery device. Methods for 
transmitting audio by similar means have been used in video transmission 
links for many years; for example, the NICAM system employed by the BBC. 
Transmitting video-band or data signals over UTP lengths longer than 200 to 
400 feet typically require frequency-dependent amplitude and phase 
compensation to correct for the effects of loss and phase-dispersion which 
occur with increasing significance as wire lengths increase. Such 
compensation increases the possible transmission distance, but the 
parameters of the compensation depend on the distance and the gauge of the 
wire. 
In public telephone network loop plants, the UTP running between a user 
premises and central office is typically made up of several smaller 
segments serving only parts of the total path which are linked 
("cross-connected") as needed. As telephone subscribers start and stop 
services, a given segment is cross-connected, released, and 
cross-connected again--possibly to a run with a far different total path. 
In situations with bidirectional transmission, multiple UTPs, and such 
significant volatility in the reuse of segments of UTP runs, manually 
adjusting compensation parameters at the installation of a new service 
subscription can be problematic. A means for automatic adjustment of 
compensation parameters over the full range of UTP distance is a 
significant factor in reducing the deployment cost of the multimedia 
telecommunication system. 
Various circuit techniques, such as employment of emitter follower drive as 
described in U.S. Pat. No. 3,456,206 to Kwartiroff et al., can be used to 
reduce the sensitivity of compensation to variation in the length of the 
UTP. Although these circuit techniques provide a valuable degree of 
distance insensitivity, wider ranges of distances still require adjustable 
compensation. Based on known attributes of UTP as a transmission line, 
self-adapting compensation approaches have been devised in the past, such 
as in U.S. Pat. No. 4,273,963 to Sidel and U.S. Pat. No. 3,568,100 to 
Tarbox. These methods use a fixed-order minimum-phase compensation network 
whose frequency compensation parameters are adjusted by a continuously 
variable element such as a transconductance multiplier or a (variable 
impedance) diode, resulting in a network presenting a complex-valued 
impedance which continuously varies with a continuously reference voltage 
or current. The reference voltage or current is supplied by an amplitude 
detector circuit, and these methods put the detector and compensator in a 
negative-feedback control loop. The Sidel patent also discloses cascading 
multiple stages to compensate for longer distances. However, due to 
loading effects within the lossy character of UTP transmission line that 
vary nonlinearly with distance, adaptive compensation for longer distances 
at video and data LAN bandwidths are problematic in that: (i) losses and 
phase shifts at a given frequency do not increase linearly with distance; 
(ii) the asymptotic 3 dB/octave behavior of the lossy transmission line 
transfer function becomes increasingly difficult to correct with simple 
low-order networks, rather a compensation circuit must begin to alternate 
-6 dB/octave poles and +6 dB/octave zeros with locations in geometric 
progression. 
All of this increasingly becomes a battle of competing losing causes for 
long distances. Increased post-emphasis in the UTP receiver creates noise 
and crosstalk sensitivity while pre-emphasis in the transmitter increases 
noise and crosstalk generation. FCC guidelines (Title 47, Subchapter B, 
Part 68 and Title 47, Subchapter A, Part 15), which must be considered in 
transmitter design, also ultimately bound the potential benefits of 
pre-emphasis in the transmitter. These facts make the space-division 
techniques described previously, which lower the uppermost frequencies 
carried on a given UTP, more attractive for the longest ranges of UTP to 
be employed in the invention. 
To simultaneously maximize the length of UTP of a given gauge and the 
bandwidth which can be transmitted over it with a simple approach, the 
invention may optionally employ a simplified detector and discrete-step 
equalization circuitry. A general block diagram is shown in FIG. 22. A UTP 
receiver or transmitter or transceiver 700 is used to transform signals 
between a signal input 702 or a signal output 704, and a UTP 706. The UTP 
receiver or transmitter or transceiver 700 is responsive to one or more 
frequency compensation circuits 710. A wideband analog switch 712 connects 
the compensation circuits 710 to the UTP receiver/transmitter/transceiver 
700 by a connection 714. The compensation circuits 710 may vary greatly in 
complexity; for example, a compensation circuit 710a might be designed for 
short lengths of UTP, while a compensation circuit 710b might be designed 
for very long lengths of UTP and hence be of increased complexity. 
A selected one of the compensation circuits 710 is determined by logic 
circuitry 716 which acts upon information generated by one or more signal 
detectors 720. The signal detectors 720 examine specific attributes of 
signals presented to them from the UTP receiver or transmitter or 
transceiver 700. In addition, or alternatively, the choice of compensation 
may be made by an external controller. 
The signal detectors 720 and logic circuitry 716 may have various 
implementations. For example, the signal detectors 720 may be designed to 
work with specific signal formats, such as analog video signals or 
raised-cosine bit symbols, and make measurements against known attributes 
of those signals, such as the sync pulses of analog video signals or 
specific transition intervals of raised-cosine bit symbols. The output 
from the signal detectors 720 would then be constantly monitored by the 
logic circuitry 716. As another example, the signal detectors 720 may only 
be monitored by the logic circuitry 716 when certain test signals are 
applied. The resulting selection of one of the compensation circuits 710 
is stored in memory, thus requiring the logic circuitry 716 to include an 
electronic memory. In practice, it is preferred that the memory is 
non-volatile so as to be immune from power glitches. 
The work of Ungerboeck in "Channel Coding with Multilevel/Phase Signals," 
IEEE TRASACTIONS ON INFORMATION THEORY, Vol. 28, No. 1, January 1982, pp. 
44-67, and subsequent developments such as AT&T's CAP (carrierless 
amplitude modulation phase modulation) have given rise to analog 
modulation techniques which can be used to carry relatively high bit-rates 
over relatively limited bandwidth analog lines. Using these techniques, 
5-6 bits per second of digital bandwidth can be carried per Hertz of 
analog bandwidth. This can be scaled to arbitrarily high bandwidth and 
used on any linear analog transmission channel. For example, Silicon 
Design Experts, Inc. recently announced a chip design claiming 155 Mbps 
using 30 MHz of bandwidth on short (&lt;100 meters) lengths of voice grade 
UTP. Embodiments of the present invention can employ these techniques to 
carry digital streams over public loop plant UTP. For example, using 
64-point QAM and Veterbi encoding, reliable 5 Mbps data rates can be 
carried over 1 MHz of bandwidth, the bandwidth being among the worst 
available public loop plant UTP runs. Further, scaled-down versions of 
these techniques have been reported to deliver 1.5 Mbps T-1 service over 
12,000 feet of unconditioned UTP loop plant in a 1989 trial of the 
so-called High-bandwidth Digital Subscriber Line (HDSL). 
Even a modest-scale deployment can cost justify the fabrication of 
integrated circuits which perform the signal processing involved in 
implementing a 64-point QAM/Veterbi encoding chip. When combined with the 
space-division techniques described earlier, 10-20 Mbps digital 
connectivity can be provided for surprisingly little cost using NTNI over 
the public telephone loop plant. Preferably, these more advanced signal 
transmission methods are incorporated to further widen the bit rate 
possible over longer UTP runs. 
The resulting digital channels can be used to expand the bandwidth of NTNI 
UTP channels transmitting digital streams, such as directly-carried data 
signals from LAN ports, digital streams from V.35, RS-449, or similar 
interfaces from codecs, routers, and other wide area networking equipment. 
Public telephone UTP loop plant for digital transmission of digital streams 
at fractional T-1 rates (but not TNI formats) can be utilized in 
accordance with the present invention. Typically, the equipment purchased 
by a business for wide area teleconferencing and data networking is 
designed to interface with one (or more) of the following: 
(i) the voice telephone network interface; 
(ii) non-ISDN switched 56. Kbps service interface (as in AT&T Accunet); 
(iii) ISDN Basic Rate services interface 
(iv) V.35 interfaces to T-carrier interfacing equipment; 
(v) RS-449 interfaces to T-carrier interfacing equipment; or 
(vi) T-carrier interfaces directly. 
Cases (i) to (iii) and (vi) are well served by TNI-based services. Cases 
(iv) and (v) may be more economically served by NTNI using UTP. 
Typically V.35 and RS-449 interfaces are used to carry signals in excess of 
64 kbps to switching and multiplexing equipment which, in turn, is 
interfaced to T-carrier TNI services. V.35 and RS-449 are not directly 
supported by public telephone networks. It is possible, however, to carry 
V.35 and RS-449 streams in near-raw form over UTP to switching and/or 
multiplexer farms within a nearby multimedia central office. The logic and 
conversion circuitry can be implemented in a field programmable logic 
chip. 
FIG. 23 is a block diagram of an interface for carrying either V.35, 
RS-449, or other similar streams in nearly raw form over a UTP. The 
interface comprises one or more data output circuits 740, one or more 
control output circuits 742, one or more control input circuits 744, and 
one or more data input circuits 746. The control circuits 742 and 744 
govern the timing and validity of the signals on the data circuits 740 and 
746. The control circuits 272 and 244 are coupled to a logic circuitry 750 
which uses some of these signals to control a serial-to-parallel converter 
752 and a parallel-to-serial converter 754. The logic circuitry 750 also 
exchanges passed control signals and/or derived control signals with the 
serial-to-parallel converter 752 and the parallel-to-serial converter 754. 
The serial-to-parallel converter 752, parallel-to-serial converter 754, and 
logic circuitry 750 are clocked at a rate which is some multiple of the 
data rate of the V.35, RS-449, or other similar interface. Timing 
information may be provided by a sufficiently fast free-running clock or 
by a frequency-multiplying phase-locked loop (i.e., a phase-locked loop 
with a divide-by-N frequency-dividing counter within its feedback loop) 
which tracks an externally-received timing signal. The serial-to-parallel 
converter 752 and the parallel-to-serial converters 754 also exchange 
information with the UTP receiver and transmitter. 
For a multi-point conference implemented by a distributed conference 
bridge, it is desirable to locate the distributed conference units so as 
to reduce the trunking cost associated therewith. FIG. 24 is a flow chart 
of an embodiment of a method of locating distributed conferencing units 
which provides a minimal trunking cost. 
As indicated by block 800, a step of computing a minimum spanning tree 
across the network topology is performed for the specific collection of 
participants in the conference. The minimum spanning tree may be computed 
by finding a trunk routing for a centralized conference bridge, and 
modifying the results by collapsing any multiple trunk allocations between 
a pair of nodes into a single link therebetween. As indicated by block 
802, a distributed conference bridge unit is located at each node in the 
minimum spanning tree having more than two intersections. As indicated by 
block 804, one trunk is allocated for each link of the minimum spanning 
tree. Preferably, each distributed conference bridge unit performs a 
function dictated by its position in the spanning tree and the overall 
topology of the spanning tree. 
The number of distributed conference bridge units needed at each office may 
be found using a method similar to the method of FIG. 13. Here, the step 
indicated by block 426 is modified so as to assign optimal locations to 
all distributed conference bridge units (by means, for example, of the 
minimum spanning tree method described above) relevant to each conference 
topology class. 
To serve a wide range of multi-point video and audio conferencing needs for 
a large population, it may be advantageous to create a specialized 
conference bridge server having an internal architecture optimized to 
serve a needed collection of features. The features which may be provided 
include: (i) centralized conference bridge units; (ii) distributed 
conference bridge units serving various conference topology classes; (iii) 
allowing varying numbers of participants up to the maximum video mosaic 
and audio mixing capacities; (iv) allowing varying maximum video mosaic 
and audio mixing capacities; (v) allowing varying numbers of participants 
above the mosaic capacity but constrained by some other bound; (vi) one or 
more close-up features; (vii) individual view control features, such as 
private video close-up selection, video mosaic content selection, and 
video or spatial audio layout selection; (vii) one or more compression 
schemes, including H.360 and other algorithms, with one or more parameter 
variations (such as resolution and bit rate); (ix) pixel, DCT, and/or VLC 
domain compositing; and (x) support of multiple input and output streams 
including analog video, switched Ethernet, and JPEG/MPEG. 
An architecture for a conference bridge server may be optimized for the 
specific collection of features to be spanned and overall traffic capacity 
requirements. The potential for optimization results from a flexible 
configuration of smaller element pools which provides for reuse of 
elements. In contrast, a fixed configuration of the smaller elements 
results in inefficient use of much of the hardware. 
An embodiment of a server which provides a collection of the 
above-described features is illustrated in FIG. 25. A plurality of 
incoming video and audio signals from various sources are applied to a 
plurality of input cell groups 810. Each of the input cell groups 810 
contains one or more input cells 812. The input cells 812 are capable of 
accepting different signal formats, and performing initial processing 
steps such as video sampling for compositing. An optional external-input 
switch 814 may be included to connect the incoming signals to the input 
cell groups 810. In cases where the signals come from a single source, 
such as a single office switch, the external-input switch 814 is most 
likely not necessary; its role is to give all inputs equal or near-equal 
access all input cells 812. 
Each of the input cell groups 810 presents a processed signal to a 
corresponding internal-signal switching matrix 816 dedicated to the group. 
Preferably, each internal switching matrix 816 is implemented as a 
card-cage backplane, although this is not required. Each internal-signal 
switching matrix 816 has a corresponding pool of output cells 818 
dedicated thereto. The internal-signal switching matrix 816 directs 
selected signals received from the input cell group 810 to specific inputs 
of the output cells 818. Effectively, each of the output cells 818 has as 
many inputs as the maximum number of participants supported by the 
conference bridge. The output cells 818 assemble video composites and 
perform audio mixing from signal inputs. The output cells 818 also produce 
output signals in the desired output signal format. A group of output 
cells, as well as the internal-signal switch 816, may be implemented 
virtually within a single, high-throughput, dedicated-architecture, 
real-time video image processor. 
Optionally, the output cells 818 are coupled to an external-output 
switching matrix 820 which provides the output signals. One or more 
straight-through links 822 may be connected between the external-input 
switch 814 and the external-output switch 820. The external-output switch 
820 provides equal or near-equal access of the output cells 818 to the 
outputs. In cases where the outputs go to a single sink, such as a single 
office switch, the external-output switch 820 is most likely not 
necessary; in this case the outputs of the output cells 818 can be 
directly presented as the output signals. 
The external-input switch 814, the external output switch 820, the 
internal-signal switches 816, the input cells 812, and the output cells 
818 all may be controlled by a controller 824 in communication therewith. 
It may be advantageous for at least the software of the controller 824 to 
be comprised of two internal subsystems: a first controller subsystem 826 
which governs the assignments of signal routing and parameters of cells, 
and a second controller subsystem 828 which handles variations in these 
assignments and parameters so as to implement service features such as 
individual views. The main reasons for this partition are: (i) the 
assignment controller 826 is best controlled in conjunction with the 
network while the feature controller 828 is best controlled by the users, 
and (ii) the assignment controller 826 may need to first allocate 
resources and control channel handles to activities spawned within the 
feature controller 828. 
The internal-signal switching matrices 816, and optionally, the 
external-input switching matrix 814, and the external-output switching 
matrix 820, may be partitioned into separately controlled audio and video 
layers in order to separately process audio and video signals. When the 
audio and video signals of the external inputs and outputs are 
space-division modulated, the external-input switching matrix 814 and the 
external-output switching matrix 820 are preferably layered. When the 
audio and video signals of the external inputs and outputs are not 
presented in space-division, the input cells 812 and the output cells 818 
may be required to further provide space-division separation and 
integration functions so that internal-signal switching matrices 816 can 
be implemented with space-division separation between the audio and video 
signals. 
To perform a video close-up selection, appropriate audio sources are 
selected by the external-input switch 814 and presented to one of the 
input cells 812 allocated for audio layer processing (herein referred to 
as an audio layer input cell). If the audio and video signals are 
space-division modulated, then the audio layer input cell may only 
comprise a signal buffer amplifier. Outputs of appropriate audio layer 
input cells are selected by the internal-signal switch 816 and presented 
to one of the output cells 818 allocated to provide. Such audio mixing 
functions may include "minus-one" audio mixing as described in U.S. patent 
application Ser. No. 08/131,523. 
If the signals in the video layer are then in a single input format, an 
individual participant can select a video close-up using appropriate 
straight-through links 822 to connect an external video source to the 
appropriate external output. Here, the straight-through links 822 act as 
trunks between the external-input switch 814 and external-output switch 
820. This trunking arrangement cuts down on switch complexity in 
comparison to merging the external-input switch 814 and the 
external-output switch 820 into a single switch, which requires a 
considerably larger switch resulting from many inefficiently used 
cross-points linking the external inputs and the external outputs. The use 
of straight-through links 822 allows a more efficient use of fewer 
cross-points, growing with "close-up" request traffic load rather than 
strictly with the number of inputs and outputs. Note that the appropriate 
controller design and voice detection, voice-activated switching of a full 
close-up can be implemented using these trunks but no input or output 
cell. 
The case of video mosaicing of output cells is described. In one 
embodiment, the output cells 818 perform video compositing based upon a 
fixed compositing configuration. An example of a fixed compositing 
configuration is an N-by-N mosaic of full-motion video images, each image 
at 1/N pixel/unit-length resolution, where N is a fixed value (such as 
N=2). The mosaic area assigned to an image is determined by the 
connections made within the internal-signal switch 816, including any 
voice-detection selection of which participants to display (such as the 
last N that spoke). Consequently, the output cells 818 in such an 
implementation do not require any parameters be passed from the controller 
824. In another embodiment, the output cells 818 allow for more than a 
single choice of N (say {2, 3} or {2, 3, 4}) . In this case, the 
controller 824 passes a value of N to the output cells 818. 
In practice, the mixing of multiple audio streams is less costly than video 
compositing. Consequently, for a large conference of M participants, it is 
economical to mix the audio of all participants but only display the video 
of N (with N&lt;M) of the participants. 
The above-described embodiments allow a participant to privately select a 
composite view based upon an output cell, a close-up, or any video source 
routed to the output cell. For example, all participants could initially 
be provided with a common video mosaic produced by one output cell. If one 
or more participants in a given conference then request a different choice 
(or layout) of video compositing than other participants, additional 
output cells can be dynamically allocated. An output cell can be allocated 
for each participant in the conference, although this may be excessive in 
practice, even for centralized conference bridging. By sharing output 
cells across the total demand for distinctly different composites, the 
total number of output cells 818 and the complexity of the internal-signal 
switches 816 can be significantly reduced. 
The above-described embodiments support both centralized and decentralized 
conference bridging functions. Since each of the output cells 818 performs 
video compositing, parameterized compositing may be performed with 
selected portions of the signal from a given one of the input cells 812. 
The resulting cropping capability, governed by parameters passed to the 
output cell by the controller 824, gives both a compositing and a 
cut-and-paste capability in a single output cell (as required for a 
distributed conference bridge unit). 
Alternative embodiments which support multiple external signal formats 
(such as analog, switched Ethernet, and H.360) and multiple compositing 
approaches may be utilized. Here, signal conversions are done either 
externally to the architecture of FIG. 24, or within the input cells 812 
and the output cells 818 (particularly for close-ups selections). If a 
collection of inhomogeneous signal formats is compatible with a single 
fabric, e.g., the fabric used for the external-input switch 814 and 
external-output switch 820, then the signal conversions may be performed 
within the input cells 472 and output cells 474. This is advantageous for 
many collections of multiple compressed digital signal formats. 
FIG. 26 is a block diagram of an alternative conference bridge server 
capable of handling analog sources, switched LAN sources, and DS0-based 
sources. The analog sources produce analog signals in a format such as 
NTSC, , and/or SECAM with some associated analog audio format. The 
switched LAN sources produce signals having a format such as JPEG, MPEG, 
and/or switched Ethernet with some associated switched-Ethernet-based 
audio format; ATM video and audio may also be handled in this manner. The 
DSO-based sources produce signals having a format such as H.320 and/or 
various video/audio compression algorithms as carried by ISDN and 
Fractional T-carrier. 
The analog signals are applied to an external-input switch 840, the 
switched-LAN signals are applied to an external-input switch 842, and the 
DSO-based signals are applied to an external-input switch 844. Each of the 
external-input switches 840, 842, 844 are matched to the specific format 
of the signals applied thereto. 
The external-input switch 840 is coupled to a plurality of input cells 846 
having an input matched to the analog signal format and an output matched 
to one or more internally-convenient standards. Similarly, the 
external-input switch 842 is coupled to a plurality of input cells 850 
having an input matched to the switched-LAN signal format and an output 
matched to the one or more internally-convenient standards. The 
external-input switch 844 is coupled to a plurality of input cells 852 
having an input matched to the DS0-based signal format and an output 
matched to the one or more internally-convenient standards. 
Internal-signal switching matrices 854, 856, and 860 connect the input 
cells 846, 850, and 852 to selected ones of a plurality of output cells 
862 using the one or more internally-convenient standards. The output 
cells 862 contain a plurality of analog output cells 864, a plurality of 
switched-LAN output cells 866, and a plurality of DS0-based output cells 
870. As illustrated, each of the internal-signal switching matrices 854, 
856, and 860 is dedicated to a corresponding one of the groups of output 
cells 864, 866, and 870. Alternatively, each of the internal-signal 
switching matrices 854, 856, and 860 could be dedicated to a corresponding 
one of the groups of input cells 846, 850, and 852, wherein the output 
cells 862 are connected to each of the internal-signal switching matrices 
854, 856, and 860. 
The analog output cells 864 are coupled to an external-output switch 872 to 
provide analog signals to a plurality of analog sinks connected thereto. 
Similarly, the switched-LAN output cells 866 are coupled to an 
external-output switch 874 to provide switched-LAN signals to a plurality 
of switched-LAN sinks connected thereto. Further, the DSO-based output 
cells 864 are coupled to an external-output switch 876 to provide 
DS0-based signals to a plurality of DS0-based sinks connected thereto. 
Using such an embodiment, any combination of acceptable signal formats 
served by cells in the architecture can be supported in an efficient, 
cost-effective manner. Further, the input cells and the output cells of 
each signal format are utilized quite efficiently; no cells need remain 
non-allocated if there is a participant of that signal format requesting a 
conference. 
The number of cells dedicated to each signal format can be chosen from 
estimated traffic requirements in the same manner described earlier. The 
partitioning of the input cell connections among the dedicated 
internal-signal switching matrices 854, 856, and 860 can also be 
determined by traffic modeling. The following mutually exclusive traffic 
possibilities are common in practice: (i) no known or suspected 
correlations in the request patterns; or (ii) known or suspected 
correlations in the request patterns. In case (ii), some fraction of the 
conferences may use the same signal format, or certain combinations of two 
or more signal formats which are known or suspected to be popular. The 
cited correlations are valuable in accurately sizing the cell requirements 
since batch-arrival effects can significantly increase blocking 
probabilities. 
Window sharing may be incorporated in embodiments of the present invention. 
The utilization of static and dynamic directory services with sufficient 
data networking capacity and performance facilitates the incorporation of 
window sharing. 
Preferably, the network provides directory services to video call and 
conference software. Either dynamic directory services or static directory 
services may be employed. The dynamic directory services are capable of 
capturing locations of active users based on log-in registration made 
available thereto. Further, the dynamic directory services are capable of 
capturing the status of a current user. The status may be indicative of a 
user workstation not responding, a user-invoked automatic call refusal, 
and/or call-forwarding information, for example. The static directory 
services are capable of capturing the capabilities of a workstation or 
other room-based equipment, and particular user preferences supported by 
the network. 
Preferably, the dynamic directory servers are capable of rapid and 
concurrent propagation of data changes among the various directory 
servers. Further, recovery means for unexpected inconsistencies in static 
directories, and means for performing an active backup in case of isolated 
network computing or transmission failures are preferably included. 
By including directory services, window sharing is capable of working 
directly with video call and conference user interfaces. As a result, 
window sharing may be easily invoked one or more times within the duration 
of a video call or conference with minimal user effort. Typically this 
involves default shared windows provided to every participant in the 
conference. Further, window sharing may also be invoked independent of the 
presence or absence of a video call or conference. 
The invocation of a window sharing session or an addition of a later 
participant is performed by a sequence of data communications 
transactions, such as that illustrated by the flow chart in FIG. 27. As 
indicated by block 900, message passing transactions are performed with 
dynamic directory services to determine whether a requested participant is 
logged on, whether the participant is accepting shares, and which machine 
address the participant is using. As indicated by block 902, message 
passing transactions with static directory services are performed to 
determine the capabilities of the participant's machine. As indicated by 
block 904, message passing transactions are performed with each 
participant's machine for such purposes as notification, accept/refuse, 
and priority of image formats available. 
Upon performing the steps in blocks 900, 902, and 904, any sequence of the 
following steps may be performed. Block 906 indicates a step of performing 
a file transfer of window snapshot pix-map files. Block 908 indicates a 
step of message passing of control information. Block 910 indicates a step 
of message passing of near-real-time annotation and telepointing graphics 
events. FIG. 27 shows one example ordering of events; in general the event 
sequence is determined by specific participant use. 
Except for the step in block 906, the required data networking amounts to 
fast message passing of short bursty messages. Because of the number of 
activities in steps 900, 902, and 904 and the real-time responses expected 
in step 908 and 910, it is desirable for the latency for the message 
passing to be low. Bandwidth requirements, however, are modest. In 
contrast, step 906 requires low latency as well as high bandwidth because 
image files are large and in many cases must be transferred losslessly. 
It may be advantageous to include separation of the message passing data 
traffic and image file transfer traffic onto separate data transport 
infrastructures, each fine-tuned to give optimal performance for the type 
of traffic being carried. This prevents one share session's image transfer 
from holding up another session's file transfer in data networking systems 
where file transfers can crowd out message passing. This architectural 
approach has applicability among central, regional, and national network 
offices, and also may be advantageous to extend back to at least some of 
the user sites with premises networks. 
In multi-platform situations, it may also be advantageous to provide 
shared, network-based image format translation pipeline servers to reduce 
latency in image transfer modes of window sharing sessions. In practice, 
considerable latency occurs on user machines in share sessions having 
image file conversions from one of many native image formats to a selected 
exchange format. For example, the native images may include a mix of PC 
Windows, Macintosh, UNIX, and OS/2. This can be particularly problematic 
when less powerful machines are used. A high-power image file conversion 
pipeline server may be employed as a shared network resource to perform 
image file conversions from native formats to a selected exchange format. 
By providing image conversions, better performance can be delivered to 
users with older or low-power machines. 
Embodiments of the present invention further may include application 
sharing. As with window sharing, both static and dynamic directory 
services, and sufficient data networking capacity and performance are 
required for application sharing. In multi-platform situations, it may 
also be advantageous to provide shared, network-based high-powered image 
translation servers to reduce latency in applicable application sharing 
sessions. 
Classes of application sharing, listed in order of increasing complexity, 
include: (i) broadcast of display, common platform; (ii) broadcast of 
display, multiple platforms; (iii) full application sharing, common 
platform; and (iv) full application sharing, multiple platforms. 
Embodiments of the present invention are particularly well-suited for 
classes (i) and (ii). In a broadcast of display, one collaboration 
participant runs an application, but the displayed windows or other 
machine output is effectively multi-cast to all other participants. None 
of the other participants, however, can operate the application. In the 
case of a single common platform, this can be accomplished by 
multi-casting window events, or a periodic or refresh-event driven window 
image capture. If multiple platforms are involved, additional steps of 
window-event translation, image format translation, or other corresponding 
translation, respectively, are performed. In these cases it may be 
advantageous to provide a network-based high-power translation server, 
similar to the image format translator described above. 
There are several commercial and robust experimental full application 
sharing systems which address class (iii). Given adequate interfacing with 
the directory services and adequate data networking capacity and 
performance, these may be readily adapted for use in embodiments of the 
present invention. 
It may be advantageous to provide class (iv) application sharing via a 
network-based high-power translation pipe-line server, similar in concept 
to the image format translator described above. The reasons for this 
include: the software need not be provided on a per-workstation basis; the 
user workstation and/or file server would not be loaded down, which is 
beneficial for older or lower-power machines; support for the platforms 
need not be included in future workstations or file servers; and it is 
immune to volatility in the collection of supported platforms. 
Because of the large user base and relatively small number of servers 
required (compared to one at every workstation, or one or more at every 
user premise), high-performance support of more platforms can be easily 
cost justified. Further, because of the public network aspects of 
embodiments of the present invention, there is considerable motivation for 
platform providers to coordinate their design changes and other updates 
with operators of the present invention. 
The directory services concerns for application sharing track those for 
window sharing. Full application sharing in classes (iii) and (iv) may 
require additional support both within the static directory services and 
within an adaptation of existing or new application sharing software. The 
data networking concerns for application sharing match those for window 
sharing, although events such as window refresh may also create file 
transfers while display updates may only involve small message-passing 
transactions. 
Another feature which can be included in embodiments of the present 
invention is multimedia conferencing recording. A server-based 
implementation for multimedia conference recording in a 
private-network-based system, as described in U.S. application Ser. No. 
08/131,523, may be incorporated into the central, regional, and national 
offices. As a result, multimedia conference recording is provided as a 
network-based service. 
Additionally, it is advantageous to include a storage/usage monitoring 
system suitable for driving billing mechanisms, and a permission system 
for privacy and blocking attempted usage by nonsubscribers, for multimedia 
conferencing recording. These provisions are readily provided by most 
multi-user file systems. For example, secure versions of the UNIX file 
system can readily be integrated with protocols of the billing systems and 
services. 
Wide-area networking may be employed to view, at one location, a conference 
which was recorded earlier at a distant location. The recorded conference 
may be played-back at the network office where it was recorded, and 
transferred in real-time over a wide-area network link using several 
approaches. In a first approach, a digital playback stream is transferred 
directly from a storage medium over wide-area links, and converted to an 
analog format or another format at a network office local to the user 
reviewing the recording. In a second approach, a digital playback stream 
is converted at the network office where it was recorded to a format for 
wide area transmission. In a third approach, a digital playback stream is 
converted, at the network office where it was recorded, to an analog 
format or another format and reconverted to a format for wide area 
transmission. In a fourth approach, a digital playback stream is 
transferred from a storage medium over wide area links at a rate faster 
than required for real-time playback; playback is provided at a network 
office local to the user reviewing the recording. This process can be 
strictly sequential (i.e., transfer first, then playback) or pipelined 
(playback during the transfer phase). 
In other implementations, conference recording files may be transferred and 
played back at a network office local to the user reviewing the 
conference. This can be realized by performing a file transfer either at a 
real-time rate, a rate faster than real-time, or a rate slower than 
real-time. Each of the file-transfer rates have cases where they are 
advantageous. If periods of low real-time traffic tend to be relatively 
short, a faster-than-real-time file transfer may be advantageous, 
particularly if dedicated lines are used. If periods of low real-time 
traffic tend to be relatively long, a slower-than-real-time file transfer 
may be advantageous, particularly if dedicated lines are used. If public 
digital switched services are used for file transfer, the preferred method 
may be any of the above. For the sake of cost-effectiveness, the preferred 
method is dictated by usage charges of the public digital switched 
services. A faster-than-real-time file transfer may be preferred should a 
conference recording need to be transferred for immediate viewing in a 
remote location. 
In some cases, file transfers may be preempted by real-time traffic until 
they become sufficiently "stale" that they are handled with the same 
priority as real-time traffic. A request by the recording creator for 
immediate delivery or a request by a viewer for immediate delivery can be 
used to reduce the time interval designated as stale. 
Another option is to convert the conference recording file to video mail or 
multimedia mail, and utilize an established video mail or multimedia mail 
transport system. Video mail, multimedia mail, and their server-based 
implementation in a private network-based system is described in U.S. 
application Ser. No. 08/131,523. By incorporating the servers described 
therein into the central, regional, and national offices, video mail and 
multimedia mail can be provided as a network-based service. 
Additionally, it is advantageous to include a storage/usage monitoring 
system suitable for driving billing mechanisms, and a permission system 
for privacy and blocking attempted usage by nonsubscribers. These 
provisions are readily provided by most multi-user file systems, for 
example secure versions of the UNIX file system, and can readily be 
integrated with the billing systems and services protocols. 
Wide-area networking may be employed to view, at one location, video mail 
and multimedia mail which was created at a distant location. The mail may 
be played-back at the network office where it was recorded, and 
transferred in real-time over a wide-area network link using the same 
approaches as described for remote playback of a multimedia conference. In 
other implementations, video mail and multimedia mail files may be 
transferred and played back at a network office local to the user 
reviewing the mail. This can be realized by performing a file transfer 
either at a real-time rate, a faster-than-real-time rate, or 
slower-than-real-time rate. Each of the file-transfer rates have cases 
where they are advantageous, similar to the cases as discussed for file 
transfer of multimedia conference recordings. 
Synchronization between video and graphics/video for multimedia services 
may be performed as disclosed in U.S. application Ser. No. 08/131,523. 
Because of the large scale variability of the data networks involved in 
the present invention, there may be cases where computer control of 
real-time events over conventional data LAN and WAN networking does not 
give acceptable results. In these cases it may be advantageous to provide 
an additional data channel in the video synchronization intervals of 
analog video signals delivered to users from the multimedia central 
offices by UTP. Transceivers on each side introduce and recover the 
resulting real-time data channel. At a user terminal, the real-time data 
channel connects with the user workstation by means of a standard serial 
or parallel port interface connector. Software within the user workstation 
directs real-time control signals to the serial or parallel port interface 
connector, and monitors it for received real-time control signals 
affecting graphics on the screen or other computer-controlled events. 
Regardless of whether these techniques are used, it may be advantageous 
within the multimedia central offices, regional hub offices, and national 
offices to use a segregated data network for carrying real-time messages 
as discussed for the window sharing functions. 
The services described above can be used to facilitate a number of valuable 
activities and quasi-vertical industries. In some areas, such as the now 
very popular area of interactive video, the high quality video delivered 
at low cost over existing loop plant UTP via low investments in easily 
reused technology could have a significant impact. 
In general, it may be advantageous for some services to be provided with 
servers not located within a multimedia central office. Such servers may 
be operated as completely separate entities with respect to the multimedia 
telecommunication system. Thus, embodiments of the present invention may 
be utilized by a third-party, high-quality network-based multimedia 
service provider. For such third party cases, it may be advantageous to 
employ high-quality video codecs and greater transmission bandwidth 
between the multimedia central office and a services-providing site so as 
to give the same quality as a service hosted inside the multimedia central 
office. 
There is currently considerable interest in home interactive television. 
Current proposals focus on expensive installations of fiber and coax 
facilities to the home. In comparison, embodiments of the present 
invention provide one-way video/audio delivery to many homes over a 
conventional telephone UTP loop plant. A low-cost interface box can 
connect this to a conventional television set, particularly if the set 
includes conventional baseband video and audio inputs (such as in a VCR). 
The required hardware associated with a complete deployment of an 
embodiment of the present invention costs considerably less than emerging 
ATM switches and other equipment for interactive video. 
At the serving multimedia central office or a third-party service provider 
site connected thereto, digital disk-based broadcast quality video 
servers, such as scaled-up versions of the Parallax DVSS or systems as 
described in U.S. application Ser. No. 08/131,523, can be used to store 
and play video on demand. In the adaptation of such a system, a file 
management hierarchy can be used to stage segments of files so that large 
numbers of homes can watch the same material delivered by the network 
nearly simultaneously, with each free to start, pause, back-up, and skip 
ahead at their leisure. Switching performed at the multimedia central 
office connects individual homes requesting video playback from a 
selection of options to individual playback ports on the large-scale 
digital video/audio storage server previously described. 
Many low-cost alternatives are available for controlling the system. The 
alternatives include: a touch-tone phone; a dedicated control box 
connected to the network by either another UTP link, a conventional public 
analog telephone line (using a modem), or an upstream channel implemented 
on the UTP; and a computer connected to the network by any of the above 
means. A standard consumer-electronics, multi-unit remote control could 
also be used to transmit commands to the dedicated control box. 
In addition, the resulting home interactive video arrangement is upgradable 
to 2-way video/audio (and data) for telecomputing. This creates a cross 
motivation environment where needs or interest in one service of either 
interactive television or telecommuting services can reduce the barrier of 
entry for the other service. Interactive network-based video games 
provided by embodiments of the present invention are also likely to 
generate such cross motivation. 
Embodiments of the present invention can support a home user workstation 
including a conventional low-cost PC, a home TV set, and a small low-cost 
camera/microphone unit such as a conventional camcorder or a unit produced 
by Avistar. If the user's home is served by a first multimedia central 
office in communication with a second multimedia central office which 
serves the user's workplace, successful cold-start telecomputing from the 
home featuring high-quality video teleconferencing and window sharing can 
begin immediately with little financial investment and time investment. 
Video rendering animation and/or visualization computers may be put on the 
public multimedia network by connecting a video rendering output to a 
video networking portion of the system, and connecting a data port on the 
computer to the data networking portion of the system. Audio from the 
computer or an associated computer-driven audio synthesizer can be 
connected to the audio networking portion of the system. 
By putting video rendering animation and/or visualization computers on the 
public multimedia network, animation and visualization servers can be made 
available for business, education, advertising, research, and game usage. 
Putting such machines on the network where they can be used by the masses 
allows important services to be delivered either directly or behind the 
scenes. Games may be of importance as they offer a highly effective format 
for educational software. 
By supplementing a network-based multimedia database (including 
video/audio) with authoring and updating systems, possibly electronically 
linked to third-party video and/or software production houses, multimedia 
advertising incorporating video, audio, images, and animated graphics 
(including valuable telepointers and highlighting overlay annotations) can 
be provided to homes and businesses. By making such services 
directory-based (as in the telephone Yellow Pages) rather than 
intrusion-based (as in television and direct mailing), the advertising is 
less likely to be annoying to some users. 
A network-based multimedia database (including video/audio) can be used to 
provide a video news clipping service and/or a customized electronic 
newspaper service to homes or businesses. Such a service can be directly 
offered or supported by TV broadcast networks and other news services. 
There are many ways that material can be automatically captured from 
existing news media sources. For example, broadcast or cable television 
and radio news can be received and stored in network-based multimedia 
databases. Video news providing conventional close-captioned text streams 
can be fed into systems which recover the text stream as a stream of ASCII 
characters synchronized with the video. The ASCII is used for database 
searches, allowing retrieval of relevant video segments from among 
hundreds or thousand of hours of stored material. News stories can be 
automatically delineated by detecting audio events which identify 
signatures of news story start and end points, and combining this 
information with the recovered ASCII stream. The use of information 
filters can further increase the search value. 
By combining video teleconferencing, network-based animation and 
visualization rendering, simple video-overlay capabilities (such as those 
found in very low cost video boards such as the Video Toaster), and in 
some cases application sharing, it is possible to create an environment 
for producing virtual reality games which can include live video inserts 
of players. Currently, video rendering hardware for this purpose must be 
located at each home. A network-based game service can transcend this 
limitation. 
It is possible to easily add new services as they become available by 
adding new service modules and/or expanding existing ones. Preferably, the 
services architecture employed is structured around the following 
architectural principals: (i) generalized, reusable functions with 
generalized reusable interfaces; (ii) creation of services by linking 
and/or sequential execution of these functions via software descriptions; 
and (iii) allowance for functions to be geographically dispersed yet still 
cooperate to provide executable services. Multimedia network connections 
fit case (i), while call forwarding and distributed conference bridging 
fit cases (ii) and (iii). 
It is most preferred to utilize these principles so that: multimedia 
conferencing, multimedia mail, multimedia conference recording, and 
multimedia databases can all exchange information in a natural way; and 
other services, such as network-based interactive multimedia advertising 
or network-based interactive virtual reality games can interact with, or 
be built from, these services and other services. An approach to this is 
described in U.S. application Ser. No. 08/131,523 and in Ludwig, "A 
Threaded-Flow Approach to Reconfigurable Distributed Systems and Service 
Primitives Architectures," ACM SIGCOM, 1987. The methods described therein 
are also applicable to reconfigurable supercomputer architectures. Hence, 
an embodiment of the present invention may advantageously comprise servers 
implemented as software executing on reconfigurable supercomputers. 
The resulting service primitives approach has many advantages. The approach 
allows rapid deployment of new services around volatile information 
services markets. Also, the approach allows high reuse of components 
across multiple services. By sharing resources across services, a smaller 
number of different types of equipment need be maintained in the network, 
cutting costs in training, spares inventory, parts inventory, manufacturer 
service contracts, and upgrades. Also, failure recovery is more flexible 
and easier to automate. Further, statistical pooling advantages analogous 
to the types of savings realized in the conference bridge server may be 
realized. 
Using a service primitives implementation of the above-described services, 
third-party network-based games may be provided using only a few low-cost 
PCs. The PCs may be fitted with a networking card for connection to the 
data portion, and possibly the video portion, of the network via UTP (LAN 
based WAN connection or via modem). This provides a low-cost approach for 
a third-party to offer games by simply executing simple 
network-controlling scripts. The network-controlling scripts may be used 
to interconnect animation rendering services, teleconferencing services, 
multimedia mail services, video news clipping services, movie segments 
available via interactive television, and advertising services into a 
virtual pop-culture current-events reliving game featuring the live 
participation of the players friends and interesting strangers that match 
the player's interest profile. 
The above-described embodiments of the present invention have many 
advantages. By utilizing existing infrastructure in the public telephone 
system, embodiments of the present invention provide an immediate, 
low-cost approach to deploying advanced multimedia telecommunications 
services using current technology. Further, embodiments of the present 
invention permit infrastructure investments to retain much of their value 
for increased services by including evolutionary features therein. 
Embodiments of the present invention can help reduce the costs of bandwidth 
to the user in several ways. Immediately, embodiments of the present 
invention provide for the utilization of a lower cost NTNI with the UTP 
loop plant and a low cost premises interface equipment (as compared with 
more expensive digital carrier TNI cabling and equipment). 
Further, UTP access demands may be aggregated for transmission via an 
economical digital carrier vehicle (e.g., aggregate multiple fractional 
T-1 demands into T-1 or T-3, aggregate multiple T-1 demands into T-3, 
etc.). In doing so, user premises UTP NTNIs which are matched to the 
multimedia needs of the user may be used without concern for amenability 
to traditional telephony. 
Embodiments of the present invention provide a number of means for lowering 
the cost of network-based versions of multimedia services to levels 
suitable for use in business. The business and societal value of the lower 
costs which result can be of significant value. For example, sufficiently 
lower cost makes multimedia services more attainable, which acts to 
increase usage and participation. This, in turn, increases its value to 
business. Further, by making multimedia services more affordable in 
business, new ways of business can be created. Even as aspects of the 
invention are superseded by advances in the currently cumbersome and 
undeveloped methods of the mainstream, embodiments of the present 
invention can be reused in poorer areas of the world to help develop their 
economies and spheres of influence. 
It is noted that the present invention may be used in a wide variety of 
different constructions encompassing many alternatives, modifications, and 
variations which are apparent to those with ordinary skill in the art. 
Accordingly, the present invention is intended to embrace all such 
alternatives, modifications, and variations as fall within the spirit and 
broad scope of the appended claims.