Note: Descriptions are shown in the official language in which they were submitted.
, . DOCK~T NO. 1973
2 ~ 2
~ AN AUDIOVISUAL TELESERVICES INTh~FACE SUBSYSTEM
"; .
.
~, Technical Field
The present invention relates generally to the technical
field of digital telecommunication and, more par~icularly, to
communicating audiovisual information using digital telecommuni-
cations services such as Integrated services Digital Network
("ISDN") communication.
, s
Background Art
To deal rationally with the complexity of present communi-
cation systems and with the need to make different systems
.. .~
mutually compatible, the International Standards Organization
("ISO'i) developed a model for specifying such systems. Using
this model, called the Open Systems Interconnect t'lOSI") model,
~ a communication system can be broken down into a hierarchial
-~ structure that permits standards to be defined at each level in, the structure. The OSI model provides a hierarchy of seven
different layers that can occur in a communication system. Each
i 20 layer in the OSI model specifies a different ~unction performed
~;~ by the communication system.
~ he lowest layer in the OSI model, called the physical
layer, specifies the physical structure of interfaces in a
particular communication system or network. Thus, a standard for
the physical layer of a communication system specifies such
things as the number of wires, their electrical characteristics,
., .
the characteristics of signals transmitted over the wires,
connectors used for joining two sets of wires into a single
longer set of wires, etc.
~ 30The next higher layer in the OSI model, called the data link
,l la-yer, specifies how data is transmitted error free through the
, communication system. Thus, a standard ~or the second layer in
the OSI model specifies how to detect errors in transmissions
passing over the physical layer, and how to correct any errors
that may occur during transmission.
l The next higher layer in the OSI model, called the network
i! layer, specifies the manner in which connections are formed
JI between various places in the communication system for trans-
",~
. !' i
.
.~
' . ~:
.~
:. " DOCKET NO. 1973
~ 2 ~ 2~2~322
mitting data between them. The standard for the third layer in
the OSI model, thereEore, specifies the signals transmitted over
the data link layer that cause the communication system to
transfer data between two places on the network.
A recommendation by an International Telegraph and Telephone
Consultative Committee ("CCITT") for the ISDN communication
channel specifies the three lowest levels in the OSI model.
Under the CCITT recommendation, a basic ISDN access consists of
two full-duplex 64 kilobits per second ("kbps") digital data
¦ 10 channels, called channel B1 and channel ~2, plus another full-
¦ duplex 16-kbps digital channel, called a D-channel. Under the
~ CCITT recommendation, using time division multiplexing, all three
3 of these digital data channels may be transmitte~ over a single
s pair of twisted wires, or over two pairs of twistsd wires. ISDN
15 basic rake access, as specified by CCITT, was originally intended
~J to provide a basic digital data transmission capability suitable
`, for use by individuals such as in their homes or small business-
l es.
j When ISDN basic rate access was initially specified, each
~ 20 of the B-channels was intended to carry either:
;~ 1. digital data, such as that from a personal computer or
j from a computer terminal;
2. Pulse Code Modulation ("PCM") encoded digital voice
communication; or
~, 25 3. a mixture of lower data rate communications including
digital data and digitized voice that were each
l encoded at a fraction of each B-channel's full 64-kbps
i capacity.
Under the ISDN recommendation, the D-channel serves two purposes.
First, the D-channel carries siqnaling information that controls
the transmission of data over the two B-channels. In addition,
when the D-channel is not carrying signaling information, it may
¦ be used to tran~mit packet-switching or low-speed telemetry. The
com~ined data rate at which digital data may be transmitted over
twisted pairs of wires in accordance with the ISDN recommendation
for basic rate access is 144-kbps, i.e. 128-kbps for the combined
B1 and B2 channels plus 16-kbps for the D-channel.
I
WO93/1~30 ~ 2 ~ 3 ~ /US92/09876
- - 3 -
:
In addition to the ISDN ~asic rate access specifled by CCITT,
that or~anization has also specified a higher performance ISDN
communication channel called primary rate access. Depending upon
the particular geographic region of the world, using time
division multiplexing an ISDN primary rate access has either
twenty-four (24) time-slots or thirty-two (32) time-slots, each
one of which carries the in~ormation of a single ISDN B-channel.
The ISDN primary rate access having 24 time-slots is called a
Tl-connection. The ISDN primary rate access having 32 time-slots
is called a El-connection. One way in which ISDN primary rate
~ access uses these 24 or 32 time-slots is for each o 23 or 30
'~ time-slots to carry independent ~-channels of information with
;l a remaining time-slot carrying a ~-channel of control data.
Moreover, groups of the 23 or 30 time-slots in an ISD~
15 primary rate access may also be used collectively to carry
digital information at higher data rates. For example, using a
connection identified as H0, six (6) time-slots of an ISDN
J primary rate accass may be dedicated to simultaneously carrying
6 ~-channels o~ information. Thus, an ISDN H0-connection carries
20 384-kbps of digital information. In addition to the H0-connec-
tion, CCITT has also specified a service called a Hll-connection
which similarly consists of 24 B~channels. A H1~-connection may
be established o~er an E1-connection or alternatively over a
Tl-connection plus an independent D-channel of control data.
25 Thus, a Hll-connection simultaneously carries 24 B-channels of
in~ormation. CCITT has also specified a service called a
H12-connection in which an El-connection's 32 time-slots
simultaneously carry 30 B-channels of information plus a
D-channel of control data.
Building upon CCITT's ISDN r~:commendation, it has ~lso
j I established a recommendation, H.221, which speoifies data
,~ structures used in transmitting au~iovisual teleservices over
channels having bandwidths from 56 to 1,920 kbps. CClTT's Ho221
Recommendation specifies data structures for communicating
~' 35 audiovisual information over from 1 to 6 B-channels, from 1 to
5 H0-connections, or over either a Hll or a H12-connection.
Using 1 to 6 ~-channels for transmitting audiovisual information
~¦ provides data transmission rates of 6~ ~o 384 kbps in incremenks
..,.
''
" ,' .
::i
,-.1
DOCKET NO. 1973
. ` - 4 - 21~8322
of 64 kbps~ Using 1 to 5 H0-connections provides data transmis-
sion rates of 384 to 1,920 kbps in increments of 38~ kbps. A
, Hll-connection provides a data transmission rate of 1,536 kbps,
', while a H12-connection provides a data transmission rate of 1,920
k~ps
In addition to the H.221 Recommendation, CCITT has also
established a recommendation, H.242, which specifies a pro-tocol
, for establishing audiovisual teleservices. The H.2~2 Recommenda-
ij tion establishes procedures by which two audiovisual terminals
~,10 intercommunicate prior to and during an exchange of audiovisual
information to match their respective capabilities for transmit-
"!, ting and receiving audiovisual information. Included among the
Icapabilities intercommunicated between two such terminals are
their respective audio capabilities, video capabilities, transfer
rate capabilities data capabilities, encryption capabilities, and
bit-rate allocation signal ("BAS") capabilities.
FIG. 1 illustrates the relationship that exists among
B-channels 22 and D-channels 24 of three ISDN basic rate accesses
26 and a layer 28 corresponding to the CCITT H.221 Recommen-
1 20 dation. The B-channels 22 and the D-channels 24 belong to a
layer 30 that implements the CCITT I.400 Recommendation. In the
illustration o~ FIG. 1, an arrow 32 indicates the passage of time
from the beginning of an audiovisual telecommunication until its
end. FIG. 1 also illustrates th~ superposition over each
25 D-channel 24 of a layer 34 that implements a CCI~T Q.921
Recommendation, and a layer 36 that implements a CCITT Q.931
Recommendation. The layers 34 and 36 provide independent call
set-up and tear-down for each o~ the ISDN basic rate accesses 26.
Sets of double~headed arrows 38 extending between each of the
30 B-channels 22 and the H.221 layer 28 indicate bidirectional
~exchang~s of audiovisual information between the two layers 30
'~ !and 28.
yIn addition to exchanges of audiovisual information between
the layers 30 and 28, a set of double-headed arrows 42 indicate
l35 bidirectional exchanging of video data ketween the H.221 layer
!28 and an application layer 44 which may use received video data
to generate a visible image. To provide the application layer
¦44 with video data, the H.221 layer 28 extracts such data from
~i
/i
~ ,
,1 .
~093/l6430 2 ~ 2 8 3 2 ~ PCT/US92/09876
;~ `
5 --
the audiovisual information that it receives from the B-channels
22. Correspondinqly, the H.221 layer 28 embeds video data that
it receives from the application layer 44 into t~e audiovisual
information that it transmits to the B-channels 22. A set of
~,5 double-headed arrows 46 indicate bidirectional exchanging of
audio data between the H. 221 layer 28 and the application layer
,44 which may use the audio da~a to generate an audihle sound.
`!Similar to the processing of audiovisual information and video
data by the H.221 layer 28, the layer 2~ extracts audio data from
the audiovisual info~mation that it receives from the B-channels
22 and passes the audio data to the application layer 44. The
:~,H.221 layer ~8 also embeds audio data received from the applica-
~tion layer 44 into the audiovisual information that it passes to
.,the B-channels 22. Sets of double~headed arrows ~8 and arrows
52 indicate bidirectional exchan~inq respectively of high-speed
data and low-speed data between the H.221 layer 2B and the
~,application layer ~. The ~.221 layer 28 extracts the high-
:~speed, and low-speed data from the audiovisual information that
¦it receives ~rom the B-c~annels 22 and transmits such data to the
application layer 44, and it embeds the high-speed, and low-speed
data that it receives ~rom the application layer 4~ into the
audiovisual information that it transmits to the B-channels 2~.
FIG. 2 illustrates the relationships that exists among the
H.221 layer 28 and twenty-three (23) B channels 22 and a
25 D-channel 24 respe~tively carried by twenty-four (24) time-slots
~ cf an ISDN primary rate access 62. The B-channels 22 and the
'I D-channel 24 of the ISDN primary rate access 62 implement the
¦ I.400 layer 30. In the illustration of FIG. 2, the CCITT Q.921
layer 34 and CCITT Q.931 layer 36 are superimposed over the
l30 time-slot of the ISDN primary rate access 62 which carries the
; !D-channel 241 Similar to FIG. 1, the sets of double-headed
arrows 38 extending between various of the B-channels 22 and the
H.221 la~er 28 indicate bidirectional exchanging of audiovisual
information between the two layers 30 and 280 Two sets of six
35 arrows 38 eac~ in FIG. 2 represent two H0-connections 6~. In the
~¦ illustration of FIG. 2, one of the H0-c~nnections 64 ic made up
'~ of 6 B-channels 22 respectively carried in six i~mediatPly
~ adjacent time-slots. FIG. 2 also illustrates six randomly
J
~'1 ' .
i~ .
J
., .
. .,
. ~ . .
~"! ,
. . .
~W093/1~30 2 ~ 2 ~ 3 2 ~ PCT/US92/09876
- 6 -
`. assigned time-slots carrying the six s-channels 2~ which make up
. the other H0-connection 6~. As indicated by the sets of double-
,
~,`, headed arrows 42, 4~, 48 and 52 in FIG. 2 which are identical to
:~ the sets of double-headed arrows 42, 46, 48 and 52 in FIG. 1,
other than for the rate of data transmission a H.221 layer 28
exchan~ing audiovisual information with one or more
H0-connec~ions 64 provided by an ISDN primary rate access 62 may
~' present an identical interface to the application layer 44 for
. exchanging video, audio, high-speed, and low-speed data as the
10H.221 layer 28 illustrated in FIG. 1 that exchanges audiovisual
in~ormation with three ISDN basic rate accPsses 26.
~:l FIG. 3 illustrates the relationship among the H.221 layer ~8
and the B-channels 22 and the D-channel 24 of a ~ connection
., indicated by the general reference character 72. The
Hll-connection 72 is made up of an ISDN primary rate access 62
, and an ISDN basic rate access 26. Similar to ~he illustrations
-1 of FIGs. 1 and 2, the ISDN primary rate access 62 combined with
.¦ the ISDN basic rate access 26 depicted in FIG. 3 implement t~e
I.400 layer 30 o~ the Hll-connection 72. In accordance with the
20I.400 Recommendation for a H11-connection 72, the D-channel 24
of the ISDN basic rate access 26 carries control information used .;,.
, by the CCITT Q.921 layer 34 and the ~CITT Q.931 layer 36. Thus
;~ in the Hll-connection 72, all twenty-four (24) time-slots of the
:'1 ISDN primary rate access 62 are used as B-channels 22 for
,, ~ , , .
;1 25exchanglng audlovlsual information with the H.221 layer 28 as
,~ indicated by the sets o~ double-headed arrows 38. As indicated
by the sets of double-headed arrows 42, 46, 48 and 52 in FIG. 3
1 which are identical to the sets of double-headed arrows 42, ~6/
~" 48 and 52 in FIGs. 1 and 2, other than for the rate of data
~, 30transmission ~ ~.221 layer 28 exchan~ing audiovisual information
; with twenty-four B-channels 22 pr~idPd by a H11-connection 72
may present an identical interface to the application layer 44
~ for exohanging video, audio, high-speed, and low-speed data as
:ll the H.221 layer 28 respectively illust~ated in FIG. 1 or in FYG.
2.
If two terminals exchan~e audiovisual information using a
connection 72, a ~12-connection, or a single H0-connection
~' 64, then I5DN's operation inherently preserves the inter
,'j'
,
, .
i
!
f:l
:.~Q93/16~30 PCT/US92/09876
2~2~322
, - 7 -
B-channel phase relationship from the transmitting terminal's
~,H.221 layer 28 to the receiving terminal's H.221 layer 28. For
any other form of ISDN transmission permitted under CCITT's H.221
Recommendation, preservation of the phase relationship between
5 B-channels 22 is not assured. Skew can occur between data
received on diff~rent B-channels 22 even if the receiving
terminal connects to a I5DN primary rate access 62 when the
transmitting terminal connects to two or more B-channels 22 of
ISDN basic rate accesses 26, or conversely. That is, if two or
10 more HO-connections 64 or two or more B-channels 22 on an ISDN
basic ra~e accasses 26 are used ~or transmitting or receiving
audiovisual teleservices, data transmitted in-phase need not
arrive in-phase at the receiving terminal. Such skew in received
data may occur whenever audiovis~al teleservices are transmitted
15 over B-channels 22 established by placing different telephone
calls. CCITT's ISDN ~ecommendation permits the inter B-channel
skew between two HO-connections 64 or between two ~-channels 22
~of ISDN basic rate accesses 26 ~o be as great as 1,200 millisec- ;
Jonds. This skew between information carried in B-channels 22 of :~
20 different HO-conne~tions 64 or the differ~nt ~-c~an~els 22 of
fISDN basic rate accesses 26 occurs because H0-connections 64 or ~.-
3B-channelc 22 of ISDN basic rate accesses 26 may be transmitted
between terminals over different paths.
While the CCITT H.221 Recommendation specifies a structure
~125 for digital audiovisual information transmitted over various
differ~nt ISDN accesses or connections, it does not disclose nor
1does it sugqest any digital circuit and/or computer hardware
,~and~or computer software capable of effecting such a communica~
'~tion~ Furt~ermore~ the CCITT H.221 Recon~endation provides no ::
,30 sug~estion of an interface, i.P. data structures and protocols,
for exchanging video, audio, high-speed, and low-speed data
between the ~.221 layer and an application program executed in
~la hos~ c'omputer.
135 Disclosure Q~ Invention ~-
,jAn object of the present invention is to proYide an interface
~ubsystem for exchanging nudiovisual information over digital
.,, ' ~.
: ` ' ` ,
W~ 9~ 30 2 ~ 2 8 3 2 2 PCT/US~2/09876
.. 8 -
3 telecommunications in accordance with CCITT~s ~.221 Recommenda-
:l tion.
, Yet another object of the present invention is to provide a
l cost effective interface subsyste~ capable of exchanging
-' 5 audiovisual information in accordance with CCITT's H.221 Reco-
., mmendation.
A further ohject of the present invention is to provide a
modular interface subsystem that may be programmed to exchange
audiovisual information in accordance with CCI~T~s H~221
' 10 Recommendation.
, A further object of the present invention is to provide an
,.!
~:: inter~ace subsystem for audiovisual teleservices that is program-
;~i, mable ~rom a host digital computer.
.-, A further object of the present invention is to provide a
~' 15 modular interface subsystem capable of exchanging audiovisual
information in accordance with CCITT's H,221 Recommendation
between computers empl~ying the Industry Standard Architecture
~J ("ISA") bus.
,~ A further object of the present invention is to provide data
20 structures and protocols adapted for exchanging messages and/or
data between an audiovisual application being executed within a
computer and an int~rface subsystem tha~ exchanges audiovisual
information with other interface subsystems using digital
~,, telecommunications in accordance with CCITT's H.221 Recommenda-
. 25 tion.
Yet another object of the present invention is to provide an
inte~face subsystem capable of simultaneously exchanging
audiovisual information in accordance with CCITT's H.221
Recommendation with several independent digital telecommunica-
30 tions accesses.
ff .,~ . ~
Briefly in its presently preferred embodiment an interface ~ :
~ubsystem in accordance with the present invention includes an
ISDN ~slc rate interface circuit for exchanging digital
audiovisual information ~ith a first ISDN basic rate access. The
35 interface subsystem in accordance with the present invention also
includes a second I5DN interface circuit for exchanging digital
audiovisual information with at least a secsnd ISDN access. In
,, one ambodiment of the present invention, this second ISD~ access
.'' .~ .
,"~
. "--, . .
. ~ :
.,. ~ .
.4
.: :
~093/16430 2 ~ 2 ~ 3 ~ 2 PCT/~92/09876
:
; may consist of one or more basic rat~ accesses. In an alterna-
; tive embodiment of the present invention, this second ISDN
;, access may be a primary rate access. The interface subsystem
~, also includes a host computer interface circuit for exchanging
., 5 digital audiovisual informatio~ with a host digital computer.
:1 In one embodiment of the present invention, the host computer
interface circuit adapks the interface subsystem for exchanging
digital audiovisual information with a digital Gomputer employing
an ISA bus. A random access memory ("RAM") is also included in
j lO the interface subsystem for storing digital audiovisual informa
.~ tion received by any of the interface circuits.
The interface subsystem further includes a digital signal
processing circuit that is coupled to all the interface circuits
j' and to the RAM for controlling the operation of the interface
. 15 circuits. The digital signal processing circuit exchanges -~ -~ digital audiovisual information with the interface circuits, and
'j processes suc~ data that it receives from the interface circuits.
,1! In processing received digital audiovisual information, the :
¦ digital signal processing circuit synchronizes digital audiovisu~
~ 20 al information received by the interface subsystem from several
, ISDN basic rate accesses, or from a single ISDN primary rate
access. ln processing digital audiovisual information, the
~¦ digital signal processing circuit also multiplexes digitized
video, audio and data signals that are exchanged over the several
¦ 25 ISDN accesses. The digital signal processing circuit also
controls the operation of the interface circuits to respond to
,j initiation of ISDN audiovisual teleservices, and to effect
~ initiation of suc~ services if SQ requested by the host digital
~ computer. In the presently preferred embodiment, the diyital
', 30 signal processing circuit is an integrated circuit digital signal;l ~ prdcessor that receives each successive word of audiovisual
~;., information following its receipt by the ISDN interface circuits,
and tha~ transmits each ~uccessive word of aud ovisual informa-
tion to the ISDN interface circuits for trans~ission to the
~ 35 several I5DN accesses. :
'j ~he ~AM included in the interface su~system contains a
1 plurality of receiving circular buffers that receive a plurality
~i oP ~rares oP audiovisual inrorration. The R~M also contains a
.,
`~093~1~30 ~CT/US9~/09876
212832~
-- 10 --
plurality of sort buffers each addressable location of which
holds an octet, eight bits, of audiovisual informa~ion received
from individual B-e21annels 22. The octets stored in the sort
buffers are scanned to locate a frame alignment signal ("FAS")
specified by CCITT's H.221 Recommen~ation. After the FAS has
been located, the sort buffers receive successive frames of
audiovisual information from individ~al ~-channels 22 wit~ FAS
located in the eighth bit of the first octet through the eighth
bit o~ the eight octet in the sort buffers. Video, audio, high-
speed, and low-speed data are then extracted from successive
frames of audiovisual information in the sort buffers and stored
into individual data buffers located in the RAM of the interface
~subsystem. A set of host computer interface receiving buffers
;~then receive ànd store the video, audio, high-speed, and low-
speed data from which such data may be removed by khe host
`Idigital computer. The interface subsystem also includes a set
of host computer interface transmittinq buffers that receive
video, audio, high-speed, and low-speed data from the host
digital computer for transmission as audiovisual information from
the ISDN interface circuit. The host computer interface
1, . ' .
receiving buffers and transmitting buffers ar~ preferably located ~ -
in shared RAM that is located in the host co~puter interface
circuit.
Vnder particular operating circumstances, the interfa~e
...
subsystem may receive a single stream of audiovisual information
from a plurality of ISDN connections, such as several
H0-connections 64. Under such circumstances, all the video,
audio, high~speed, and low-speed data extracted from the
;1audiovisual information is stored into a single set of host
~omputer interface receivinq buffers. ~nder other operating
, ,circumstances, the interface subsystem may receiYe individual
'.fstreams o~ audiovisual information ~rom a plurality of ISDN
connec~ions, again such as ~everal H0-connections 64. If this
il,second circumstance occurs, the video t audio, high-speed, and
i;'35 low-speed data extracted from the audioYisual information is
stored into several sets of host co~puter interface receiving
buffers. ~his second operating mode of the interface subsystem
~:,
,' .
` ~-```93/1~30 2 ~ 2 8 3 2 2 PCT/VS9~/09~76
1 1 --
permits establish~en~ of con~erence audiovisual teleservices
fully eompatible with CCITT's H.221 Recommendation.
: To effectively and efficiently utilize the various operating
characteristics of the interface subsystem, the interface
: 5 subsystem exchanges messages with the hos~ digital computer for
reporting its status to the host digital computer, and for
,receiving control information from the host digital computer.
.~.For example, the interface subsystem is adapted to receive a
~;:message from the host digital computer for selecting among video, ~ .
.,lO audio, ~igh-speed, and low-speed data for storage into the set
,of host computer interfac~ receiving buffers, or for transmission
flas audiovisual information from the ISDN interface circuit~
jFurthermore, tha interface subsystem sends a message to the host
idigital computer if the set of host computer interface receiving
`j15 buffer~ become full o~ data. Correspondi~gly, the interface
'1.subsystem sends a message to the host digital computer if the set
of host computer interface transmitting buffers lack data.
~An advantage of the present invention is that it adapts a
:,digital computer which employs the ISA bus for receiving and/or
20 transmitting digital audiovisual information in ac~ordance with
CCITT's H.221 Recommendation.
These and other features, objects and advantages will be
understood or apparent to those of ordinary skill in the art from
1the following detailed description of the preferred embodiment
,~25 as illustrated in the various drawinq figures.
Rrief Desçription ~ ~rawin~s
FIG. 1 is a diagram illustrating data transfer relationships
among the B-channels and D-channels of three ISDN basic rate
~30 accesses and a layer representing the CCITT H.221 Recommendation,
Q',',and between the H.221 layer and an application layer;
:lFIG.~2 is a diaqram illustrating data transfer relationships
¦among the B-channels and D channel of an ISDN primary rate ~:
¦accesses and a layer repr~senting the CCITT H.221 Recommendation,
~35 and between the H.221 layer and an application layer; :-
JFIG. 3 is a diagram illustrating data transfer rela~ionships
:~among the B-chann21s and D-channel of a Hll-oonn2ction, made up
~:,of an ISDN primary rate accesses and an ISDN basic rate access,
,.....
,1i
.~ .
., ~
~093/1~30 ~ ~ 2 8 3 ~ ~ PCT/US92/09876
- 12 -
and a layer representing the CCITT H.2~1 Recommendation~ and
between the H.221 layer and an application layer:
,lFIG. 4 is a functional-type block diagram depicting an
Iinterface subsyste~ in accordance with the present invention
including its ISDN basic rate interface circuit, its second
interface circuit, its host computer interface circuit, its RAM,
and its digital signal processing circuit; and
FIG. 5, is a diagram depicting the interrelationship between
FIGs. 5a, 5b and 5c, the combined FIGs. forming a diagram that
depicts data structures which exist in the RAM of the interface
subsystem and in a memory in its host computer i~terface circuit,
and that are used in exchanging audiovisual teleservices data
with the I.400 layer, in processing such data through a H.221
~llayer, and in supplying video, audio, high-speed, and low-speed
115 data to an application layer.
Best Mode f~r_~ryin~ O~ut the Invention
The block diagram of FIG. 4 depicts an interface subsystem
in accordance with the present inviention enclosed within a dashed
line 100. The interface subsystem 100 includes an ISDN basic
rate interface circuit 102 for exchanging audiovisual teles~rvice
signals with an ISDN basic rate access 26 (not illustrated in
I FIG. 4) via a first ISDN basic rate access connector 104. Two
'I pairs of ele~trical leads 106 couple the Eirst ISDN basic rate
access connector 104 to an isolation transformer circui~ 108.
The isolation transformer circuit 108 electrically isolates an
:7 Am79C~2 ISDN Data Controller ("IDC") integrated circuit 1~2, with
which it exchanges audiovisual teleservice si~nals, fr~m signals
present on an ISDN basic rate access 26 (not illustrated in FIG.
4). The IDC 112, which is marketed by Advanced Micro DeYices,
Inc. ("AMD"~, 901 Thompson Place, Sunnyvale, California 94088
3453, is more completely described in an AMD publication entitled
'Communication Products Overview" copyright 1991, AMD publication
:~ no. 15513A. The IDC 112 provides data transmission and reception
'3 35 capability on the two (2) B-channels 22 and the D-channel 24 of
;1 a ~our-wire S/T ISDN basic rate access 26. The IDC 112 also
exchanges audiovisual teleservice signals with an Am82525 Hi~h-
~ Level Serial coDunications Controller Extended ("HSCX")
'I
l `
,!
i3
3
' ' ' .
:!, . ...
~ DOCKET NV. 1973
. ~ .
: ~ - 13 ~ 2 1 2 ~3 2 2
integrated circuit 114. The HSCX 114, also marketed by AMD, is
also more completely described in the AMD "Communication Products
Overview" publication. In receiving or transmitting audiovisual
.-iteleservices via an ISDN basic rate access 26, the IDC 112
~l5 processes inf~rmation exchanged over t~le D-channel 24, while the
i~HSCX 114 processes information exchanged over the two s-channels
.. : 22.
i Both the IDC 112 and the HSCX 114 exchange audiovisual
: .~
:linformation with a digital signal processing circuit 122 via an
110 interface subsystem bus 124. The digital signal processing
circuit 122 is preferably a TMS320C25 Digital Signal Processor
("DSP"~, which is marketed by Texas Instruments Incorporated
("TI"), Post Office Box 809066, Dallas, Texas 75380-9066. The
TMS320C25 is more completely described in a TI publication
entitled "TMS320C2x User's Guide" copyright 1990, TI publication
no. 164907-9721 revision B December 1990. The interface
.:!
subsystem bus 12~ also connects the digital signal processing
~circuit 122 to a memory 126, a programmable array logic ("PAL")
.:lintegrated circuit 128, and to a second ISDN interface circuit
j
130. An ISDN access control and status signal bus 132 couples
the PAL 128 to the IDC 112, to the HSCX 114, and to a second ISDN
.~. interface circuit 130. The PAL 128 adapts various control
~:~signals transmitted by the digital signal processing circuit 122
/~for controlling the operation of the IDC 112, the HSCX 114, and
;25 the second ISDN interface circuit 130; and adapts various status
signals transmitted by the IDC 112, the HSCX 11~, or the second
ISDN interface circuit 130 for receipt by the digital signal
processing circuit 122. The memory 126 preferably includes 320
~ilobytes o~ static RAM and 64 kilobytes of read only memory
~"ROM"). The RO~ of the memory 126 stores only a "boot routine"
~uf~icient to enable loading a computer program executed by the
diglital signal processing circuit 122 into the RA~ of the memory
126, preferably from a host digital computer ~Not illustrated in
FIG. 4)O
Th~ second ISDN interface circuit 130 adapts the inter~ace
subsystem 100 for exchanging audiovisual teleservice signals with
additional ISDN accesses. In the presently preferred embodiment,
the second ISDN interface circuit 130 may be selected to adapt
the inter~ace subsystem 100 for exchanging audiovisual
, I
,:~
:,~
, .. .
J
W093/1~30 ~ 1 2 8 3 2 ~ PCT/US92,09876
-. - 14 -
i teleservice signal either with two additional ISDN basic rate
accesses 26, or, as illustrated in FIG. 4, with a single ISDN
primary rate access 62. To adapt the interface subsystem 100 for
exchanging audiovisual teleservice signals with an ISDN primary
rate access 62, electrical leads 134 connect the second ISDN
; interface circuit 130 to a primary rate access connector 136, and
: the second ISDN interface circuit 130 is selected from one of two
~i different types of Line Card Stiks ("LCS") mar~eted by Dallas
Semiconductor, 4401 South Beltwood Parkway, Dallas, Texas 75244-
10 3292. To adapt the interface subsystam 100 for exchanging
audiovisual teleservice signals with a 1,536 kbps ISDN primary
rate access 62 of the type employed in many countries throughout
the world such as in the United States and Japan, the second ISDN
interface circuit 130 is preferably a DS2283 Enhanced Tl LCS.
To adapt the interface subsystem 100 for exchanging audiovisual
teleservice signals wit~ a 2,048 kbps ISDN primary rate access
62, which is employed in many European countries, t~e second ISDN
;~ inter~ace circuit 130 is preferably a DS2281 CEPT LCS. Both the
.~ ~S2283 LCS and the DS2281 LCS are more completely described in
-~ 20 a Dallas Semiconductor 1992~1993 ~roduct Data BookD To adapt the
~ interface subsystem 100 for exchanging audioYisual teleservice
:i signals with two additional ISDN basic rate accesses 26, the
second ISDN interface circuit 130 incorporates one ~SCX 114, two
IDCs 112, two isolation transformer circuits 108, two dual pairs
o~ electrical leads 106, a~d two ISDN basic rate access connec-
tors 104, that are respectively interconnected with the interface
`~ subsystem bus 124 and with the PAL 128 in substantially the same
~anner as depicted in FIG. 4 and described above.
If the interface subsystem 100 as described above exchanges
audiovisual teleservice signals with a H12-connection, it may
exchange audiovisual information with thirty (30) ~-channels ~2
of the ISDN primary rate access 62 at a comhined data rate of
1,920 Xbps. ~he ~.221 layer 28 of such an interface subsystem
100 may also exchange audi~visual informati~n at a data rate of
~84 ~bps with a H0-connection provided by only ~ix (6) ~-channels
22 of the thirty (30) or twenty-~our (24) B-channels 22 provided
;1 by the ISDN primary rate access 62. Similarly, thP Ho221 layer
. 28 of such an interface subsystem I00 may exchange audiovisual
: -
,
... .
. ~ . .
. '
~ g3/~6430 2 ~2 8 3 ~ 2 PCT/US92/09876
- 15 -
:', information at data rates from 6~ kbps to 3~4 kbps in increments
of 64 kbps with one [1) to six (6) B-channels 22 of the thirty
, (30) or twenty-four (24) B-channels 22 provided by the ISDN
t primary rate access 62. If the interface subsystem 100 described
5 above exchanges audiovisual teleservices with a Hll-connection ..
72 such as that depicted in FIG. 3 rather than a H12-connection,
the only dlfference in the operation of the interface subsystem
100 from that described above for a H12-connection is that the
maximum rate at which ~.221 layer 28 may exchange audiovisual
1 10 informatlon with the ISDN primary rate access 62 reduces from
;3 1,92n kbps to 1,536 kbps. This reduction in the maxim~m data
rate occurs because the ISDN primary rate access 62 of a
~ Hll-connection 72 provides only twenty-four (24) B-channels 22
i rather than the thirty (30) B-channels 22 provided by a
H12-connection.
If the interface subsystem lOo exchanges audiovisual
j teleservice signals with only ~n ISDN primary rate ~ccess 62,
.I then the H.221 layer 28 of such an inter~ace sub~ystem 100 may
. exchange audiovisual information at a data rate of 384 kbps with
a H0-connection provided by only six (6) B-channels 22 of the
thirty ~30) or twenty-four (24) B-channels 2~ provided by the
~i ISDN primary rate access 62. Alternatively, the H.221 layer 28
of such an interface subsystem 100 may exchange audiovisual
information at data rates from 64 kbps to 384 kbps in increments
. 25 o~ 64 kbps with one (1) to six (6) ~-channels 22 of the thirty
(30) or twenty-four (24) B-channels 22 provided by the ~SDN
primary rate access 62. If the interface subsystem 100 exchanges
l~ audio~isual teleser~ice signals with one (1) to three (3) ISDN
¦ basic rate accesses 26, th~ H.221 layer 28 of such an interface
sub~ystem 100 may exchange audiovisual information at data rates
,1 of 64 kbps or 12~ kbps with one (1) or two (2) of t~e ~-channels
¦ 22 provided by only a single ISDN basic rate access 26, ak 64
kbps t~ 256 kbps in increments of 64 kbps usin~ one (1) to four
i, (4) ~-channels 22 ~rovided by two ISDN basic rate accesses 26,
:j 35 ~nd at 64 ~bps to 384 kbps in increment~ of 6~ kbps using one (1)
to six ~6) B-chann~ls 22 provided by three ISDN basic rate
accesses 26.
1 :
~093/1~30 PCT/~S92/09876
2~832~,~
~ - 16 -
. ~ .
A multi-tas~ing computer program stored in the memory 126 and
executed by the di~ital signal process'ng circuit 122 supervises
i the overall operation of the ISDN basic rate interface circuit
i~ 102 and of the second ISDN interface circuit 130 to effect the
exchange of audiovisual information between the various ISDN
~, accesses and the inter~ace subsystem 100. Thus, the computer
:~ program executed by the digital signal processing circuit 122
:i processes digital data received from or transmitted to these ISDN
' accesses appropriateiy in accor~ance with the protocols
established by CCITT's Q.921 Recommendation, its Q.931
~eco~mendation, its ~.~42 Recommendation, and its H.221 Recommen-
dation.
The interface subsysten, bus 124 also con~ects the digital
~.~ signal processing circuit 122 and the memory 126 to interface
'. 15 subsys~em transceivers 142 that are i~cluded in a host computer
interface circuit 1~4. The interPace subsystem transceivers 142
are coupled to a shared RAM 146 which stores 32 kilo-words of
data. The,shared RAM 146 is also coupled to ISA bus transceivers
148 which are coupled to a connector 152 that plugs into the ISA
bus (not illustrated in FIG. 4). An arbitration circuit 154
connects to the interface subsystem transceivers 142, to the ISA
bus transceivers 148, and to the ISA conn~ctor 152. R~sponsive
~¦ to request signals received from the interface subsystem
~ transceivers 142, from the ISA bus transceivers 148, and from the
,' 25 ISA connector 15~, the arbitration circuit 154 assigns control
over the operation of the shared RAM 146 to either the digital
signal processing circuit 122 or to a host computer which
, controls the operation of the ISA bus (not illustrated in FIG,
~ The host co~,puter interface circuit 14~ permits the computer
"i 30 program executed by the digital signal processing circuit 122 and
., I a c~mputer program executed by the host computer to interact with
each other so the host computer can control the overall operation
-' of the interface subsystem 100 while the interface subsystem 100
e~fects the exchanqe of audiovisual inf~rmation with several ISDN
~5 accesses, and the exchange o~ video, audio, high-speed data, and
:~ lo~-speed data with the host computer.
The diagram formed by combining FIGs. 5a, 5b and 5c in ~he
`} manner illustrated in FIG. 5 depicts several different data
i
;71
.`~j
", ;
.~ '
212 8 3 2 ?J PCT/US9~/09876
- 17 -
.~ structures which exist in the RAM included in the memory 126 and
in the shared RAM 146 of the interface subsystem 100. The data
structures depicted in the combined FIGs. 5a, sb and 5c are used
~, in exchan~ing a~diovisual teleservices data with the I.400 layer
30, in processing such data t~rough the H.221 layer 28, and in
supplying video, audio, high-speed, and low-~peed data to the
~¦ application layer 44. ~o provide a comprehensive background of
all information relevant to realizing such audiovisual
teleservices, the applicants incorporate by reference as though
~ 10 fully set forth her~ CCITT's I.400, Q.921, Q.931, H.242 and H.221
-~ Recommendations.
As described in TI's "TMS320C2x User's Guide" publication,
the preferred digital signal processing circuit 122 includes a
serial port together with two memory mapped 16-bit word regi ters
for transmitting data ~rom the serial port and for recei~ing data
¦ wit~ the serial port. These registers are illustrated in the
~:l3 diagram FIG. 5a, and are respectively called data transmit :-
register (nDXR") 202 and data receive register ("DRR") 204. The
DXR 202 holds data khat the digital signal processing circuit 122
transmits automatically from its serial port. The DRR 204 holds
data re~eived automatically ~y the serial por~ through the
l operation of the digital signal processing circuit 122. When the
'~ interface subsys~em 100 exchanges data with an ISDN primary rate
access 62, every 8 to 10 microseconds the digital signal
¦ 25 processing circuit 122 gen~rates an interrupt which requires a
serial port interrupt handling routine, that is included in a
multitasking co~puter program executed by the digital signal
processing circuit 122, to load a 16-bit word into the DXR 202
or transmission from the ~erial port of the digital signal
processing circuit 122, and to fetch a 16-bit word from the DRR
204 that has been received by the serial port of the digital
signal processing circuit 122.
¦ ~or supplying the next l~-bit word to the DX~ ~02 every 8 to
10 microseconds, indicated in FIGu 5a ~y a ~olid arrow 206, the
RAM of the memory 126 contains a pair of linear buffers respec-
~ tively called ~XA 208A and TXB 208B. ~or receiving the next
`i lS bit word from the DRR ~04 every 8 to 10 microseconds,
indicated in FIG. 5a by a solid arr~w 212, the F~ o~ the memory
.
,, , .
~ W093/16430 2 ~ 2 8 3 ~ 2 PCT/~S92/0~876
- 18 -
126 contains another pair of linear buffers respectivelY called
' RXA 214A and RXB 21~B. If the ISDN primary rate access 62 has
: twenty-four ~24) time-slots, then each of the buffers TXA 208A,
TXB 208B, RXA 214A and RXB 214B stores 960 16-bit words of data.
If the ISDN primary rate access 62 has thirty (30) time-slots,
then each of the buffers TXA 208A, TXB 208B, RXA 214A and RXB
1, 214B stores 1280 16-bit words of data.
j As the serial port interrupt handlinq routine responds to
. successive interrupts, it fetches words of data from successivelocations in one of the linear buffers TXA 208A or TXB 208B, and
1 stores words o~ data into successive locations in the correspond-
ing one of the linear buffers RXA 214A or RXB 214B. When the ~ :
serial port interrupt handling routine reaches the ends of the
pair of linear buffers TXA 208A and RXA 214A, or TXB 208B and RXB
¦ 15 214B, it then transfers its operation to the beginning of the
~, other pair of linear buffers. ~ pair of dashed arr~ws 216 and
218 in ~IG~ 5a indicate that while the linear bufPers TXB 208B
'i¦ and RXB 214B are not presently being used to provide data to the
i~ DXR 202 and to receive data from the D~R 204, they will be so
~ 20 used upon exhaustion o~ the linear buffers TXA 208A and RXA 214A.
¦ In this way, th~ serial port interrupt handling routine continu-
ously ping-ponqs bac~ and fort~ between one pair of linear
buf~ers TXA 208A and ~XA 214A, and the ot~er pair of linear
~ buffers TXB 208B and RXB 214B. Each time the serial port
.~ 25 interrupt handling routine 6witches ~etween one pair TXA 208~ and
RXA 214A and the other pair TXB 208B and RXB 214B it generates
.'l an interrupt that activates a foreground routine included in the
multitasXing computer program executed ~y the digital si~nal
processing circuit 122. Upon each activation of the foreground
: 30 routine by an interrupt generated by the ~erial port interrupt
''''! ! handli~g routine, the foreground routine processes the audiovisu-
al information receive~ by the digital signal processing circuit
. 122 th~t the serial port interrupt handling routine has just
. stored eit~er into the ~XA 21~A or into the RXB 21~B, and ~he
.~ 35 foreground routine loads new audiovisual in~ormation eit~er into
:~ the TXA 208A or into the TXB 208B thereby preparing it for
subsequent trans~ission from the digital signal processing
. circuit 122.
~ ..
~, .:.
.
., ,,
.~ :
! ~
.~ :
. . , .
2 ~ 2 8 3 ~ ~ Pcr/US92/09876
~, -- 19 --
~, The audiovisual information present in ~he RXA 214A or the
~ RXB 214B when the serial port interrupt handling routine
:: generates an interrupt must be processed in accordance with in
CCITT's H.221 and H.242 Recommendations to extract the video,
s audio, high-speed, and low-speed data. In particular, the
audiovisual information present in the RXA ~14A or the RXB 214B
~ust be processed within the H.221 layer 28 to recover the FAS
i and the BAS embedded in the audiovisual information. The H.221
layer 28 of a receiving terminal ~ust process the audiovisual
information in the RXA 214A or the RXB 214B to locate and extract
the FAS and the BAS before it can properly extract the video,
audio, high-speed, and low-speed data from received audiovisual
~ information.
~ As set forth more fully in CCITT's H.221 Recommendation, at
the lowest level audiovisual information is organized into groups
called octets each of which ~olds eight (8) bits of digital data.
Eighty (80) octets are then stacked vertically to ~orm a frame
~¦ that is eight (8) bits wide by eighty (80) octets high. When
audiovisual information exchanged over an ISDN B-channel 22 is
¦20 organized in this way, the eighth bit in each octet, which forms
~a vertical column eighty ~80) bits high along the right hand edqe
`~of the frame, is called the Service Channel ("SC"), FAS consists
; of eight (B) consecutive bits in the SC that are located in the
:upper right hand corner of the ~rame in the eighth bit of the
. 25 ~irst octet through the ei~hth bit of the eighth octet. For even
: numbered frames, FAS ~as the bit pattern "xO011011~" For odd
numbered frames, FAS has the bit pattern l'xlxxxxxx." The value,
0 or 17 assigned to the ~irst bit of FAS is used in specifying
a multi~ra~e structure described in greater detail below. The
.,30 values assigned to the third through eight bits of FAS in odd
~ !numbered ~rames carry control, alarm, and error checking informa-
.~tion.
;~Similar to FAS, BAS consists of eight (8) bits located
:limmediately bèlow the FAS in the SC in the eighth bit of the
,35 ninth octet through the eighth ~it of the sixteenth octet. The
¦BAS oP each ~rame carries codewords which specify the protocol
~or exchanging audiovisual information, i.e. that specify a
iterminal's capabilities for transmitting and receiving audiovisu-
,,~
.li. ,
i~
,,
'~'
.,
"~
,~ , .
., , - 2o~28322
al information and how the video, audio, high-speed, and low-
speed data are to be multiplexed into the audiovisual information
exchanged over the ISDN access(es).
For a H12~connection, for a Hll connection 72, and for a
H0-connection 6~, only one B-channel 22, called the I-channel,
~, contains the FAS, the BAS, and any other control data specified
in CCITT's H.221 Recommendation. When exchanging audiovisual
information in accordance with the H.221 Recommendation, all the
remainlng B-channels 22 of such ISDN services carry only
audiovisual information.
In addition to octets and frames, CCIT~'s H.221 Recommenda-
tion specifies a higher level structure called a multiframe that
~¦consists of sixteen (16) immediately successive frames of
audiovisual information. Furthermore, CCITT's H.221 Recommenda-
tion subdivides each multiframe into eiqht (8) 2-frame sub-
multiframes. The first bit of FAS in each frame carries
multiframe information.
,As illustrated in FIG. 5a, while the serial port interrupt
`jhandling routine is using the pair of linear buffers TXA 208A and
RXA 214A ~or responding to serial port interrupts, as illustrated
;¦by the arrows 222A through 222A~ the foreground routine transfers
16-bit words of data that have been previously stored in the RXB
214B into one or more circular buffers 224A through 224AD located
in the RAM o~ the mPmory 126. If the interface subsystem 100
exchanges audiovisual in~ormation with a ISDN primary rate access
62, then each of the circular buffers 224 stores four t4) frames
;lof audiovisual inormation. Dashed lines are used for outlining
khe circular bu~fers 224B through 224AD and for the arrows 222B
through 222AD because circular buffers 224B through 224AD may or
may not be needed for storing data from the RXB 214B or RXA 214A
depending upon the type of ISDN access with which the interface
subsystem 100 exchanges data. Each of the circular buffers 224A
jthrough 224AD stores audiovisual information received over one
si~o~ the B-channeis 22 of the ISDN access(es). Thus, if the
interface subsystem 100 is exchanging in~ormation with a
H12-connection, then all thirty (30) circular buffers 224A
through 224AD are neçded ~or storing audiovisual information
received over that ISDN access. If the interface subsystem 100
"~
J
.
....
i
~`: ` 2~ 283~2
93/1~30 PCT/US92/09876
- 21 -
~ is presently ~xchanging audiovisual information with the
:, Hll-connection 72, then only twenty-four (24~ circular ~uffers
~24A through 224X are needed for stori~g audiovisual information
:' received over that ISDN access. If the interface subsystem 100
is axchanging audiovisual information over a sinqle H0-connection
, 64, then six (6) circular buffers 224A through 224F are needed
for storing audiovisual information. If the interface subsystem
100 is exchanging audiovisual information over one (1) to three
(3) ISDN basic rate accesses 26, then only one (1) to six (6)
circular buffers 224A through 224~ are needed for storing
audiovisual information.
Associated with each of the circular buffers 224A through
224AD is a ~ifteen (15) word long record 232A through 232AD in
a ~-channel directory 234 located in the RAM of the me~ory 126.
.~ 15 The following table describes the location and data stored in the
., various words of each of the thirty (30) records 232A throuqh
-,,
~ 232AD in the ~-channel directory 23~. .
,
' Word
.! 20 No~ Name ~ _ ~esc~iptiQn~
... 1 SLOT specifiPs the number of the particular .~.
ti~e-slot in a ISDN primary rate
access 62 to which this B-channel 22
is assigned. SLOT has a value of 0 to
. 25 23 ~or a H11 connection 72, and o~ 0
to 29 for a H12-connection.
~ 2 START_ADDRESS specifies th~ address o~ the first.: word in the circular buffer 224x as-
~ sociated with ~his r~cord ~32x in the
,~,! 30 B-channel directory 234.
~ 3 END_ADDRESS specifies the address of the last word
:;~ in the circular buf~er 224x associated
with this record 232x in the B channel
directory 234.
j 35 4 WRITE_ADDRESS ~pecifi~s the address of the location
;, in the circular buffer 22~x associated
.. with this record 232x in the B-channel
. direstory 234 to which the next word
~1 .
,;1
'''!¦
/
' , ' ,......... . .
~83~
~93/'~30 PCT/US92/09876
... . .
. - 22 -
from the RXA 214~ or RXB 214B will be
, written.
5 ADDRESSo specifies the address o~ khe byte loca-
tion in the circular bu~er 224x
, 5 associated with this record 232x in
l the B-channel directory 2~4 at which a
-, frame of audiovisual information be-
~ gins.
;! 6 BAS_STAT stores a numerical value which indi-
! 10 cates the present status of this
B channel.
,.1
1 7 FRAM_CNT stores a numerical ~alue us~d for
counting frames and for monitoring ;~
frame alignment.
R BAD_FRM stores a numerical value used for re-
cordi~g bad ~rame alignment and for -~.
re~overing frame alignment.
, 9 MF SY~C stores a history of the first bit in
,~ .
.~ the SC of odd nu~bered frames, i.e. a
j 20 history of the eighth bit in the first
octet of odd number frames. MF SYNC :-
is used in detec~ing multiframe align-
j ment.
lC MF_NUMBER stores a history ~f the first ~it in
the SC of even nu~bered frames, i.e. a
history of the eighth bit in the first
octet of e~en number frames.
MF_NUMBER specifies the number o~ the
current ~rame in a multiframe.
11 MF_CNT stores a numerical value used in
~ counting sub-multiframes in a
,~ multiframe. :~
~, 12 BAD_MF stores a numerical ~alue which indi-
cates that multiframe alignment has
not been ac~ieved.
13 RX_BAS stores the BAS code transmitted from :
another terminal to this terminal. I
d
.
.
21~322.
93/16~30 PCT/~S92/09876
- 23 -
14 TX_FAS stores the frame alignment word used
~`1 in transmitting audiovisual inf~rma-
tion from this terminal.
15 TX_BAS stores the bit-rate allocation signal
~i 5 transmitted from this terminal.
.JAn arrow 242A in FIG. 5a depicts specification by the
START_ADDRESS word of the first record 232A in the ~-channel
,directory 234 of the location of the first word in the circular
:¦ lO buffer 224Ao An arrow 244A depicts ~pecification by the
END_ADDRESS word of the location of the first record 232A in the
:~B-channel directory 234 of the final word in the circular buffer
:224A. An arrow 246A depicts specification by the WRITE_ADDRESS
~1word in the ~irst record 232~ of the B-channel directory 234 of
the location in the circular buffer 224A to which the next word
:~~rom the RXA 214A or RXB 2l4B will be stored. An arrow 248A
depicts specification by the A~DRESS0 word in the ~irst record
~232A o~ the ~-channel directnry 234 of the location in the
,.circular buffer 224A of the first byte in the ~rames 252 of
,~20 audiovisual info~mation for this B-channel 22 ~n each of the
,;~circular buffers 224A through 224AD. FIGs. 5a and 5b include
correcponding arrows ~3~AD, 234AD, 236~D and ~8AD that depict
specification by the last record 23~AD in the 9-c~annel directory
234 o~ the same relationships to the thirtie~h circular buffer
, 25 224AD.
;; Each of the circular buffers 224A through 224AD stores
' audiovisual in~ormation from ~our or more consecutive frames 252,
i.e. l~0 l6~bit words o~ audiovisual information. The dashed
li~es 254 indicate the boundary between contiguous frame size
, I 30 are~s o~ storage in the circular buffers 224A through 224~D.
,ji, However, successive frames 252 of audiovisual information stored
~ in the circular bu~fers 224~ through 224AD are not necessarily,
,~ and in general will not be, aligned with the boundaries indicated
,~ by th2 dashed lines 254. The first and last words in each of the
,,. 35 circular buffers 224A ~hrough 224AD are respectively aligned on
~,' a decimal for~y (40) word ~oundary. Aligning the first and last
words o~ the circular bu~fers 224A through 224AD on 40 word
~i boundaries permits testing address wrap from the end of 2
, .:
~ ,.
: , ::
,
~ .
DOCKET NO . 1973
- - 24 _ 21~8 32 2
. circular buffer 224A through 224AD to its beginning only once at
' the end of each sequence of eighty (80) 16 bit word data
., transfers from the RXA 214A or RXB 214B to the respective
circular buffers 224A through 224AD.
While the circular bu~fers 224A -through 224AD depicted ln
FIG. 5a illustrate the skew that can occur between audiovisual
information transmitted over independent B-channels 22, strictly
:~ speiaking that diagram does not accurately depict receipt by the
H.221 layer 28 in the interfacis subsystem 100 of audiovisual
information from a H12 connection, from a H11-connection 72, from
~ a single H0-connection 64, or from a single B-channel 22 of a
;f ISDN basic rate access 26. As set forth above, the CCITT ISDN
recommendation inherently preserves the inter B-channel phase
relationship for the H12-connection, for the Hll-connection 72
`115 and for the H0-connection 64. That is, there is no sXew such as
,that illustrated in FIG. 5a among the frames 252 of audiovisual
',~information exchanged over the thirty (30) B-channels 22 in a
H12-connection, over the twenty-four (24) B-channels 22 in an
ISDN primary rate access 62, or over the six (6) B-channels 22
in a H0-connection 64. However, as stated above skew of the type
illustrated in FIG. 5a may occur among B channels ~2 of two or
~more H0-connections 64, or among several B-channels 22 of one or
'~more ISDN basic rate accesses 26. When using these latter types
of ISDN services, the interface subsystem 100 of the present
-125 invention may properly align the audiovisual information in the
several B~channels 22 only by locating the FAS embedded in the
,ilaudiovisual information stored in the circular buffers 224A
. '~
,~through 224AD.
',';lIn locating the FAS embedded in the audiovisual information
stored in the circular buffers 224A through 224AD, as indicated
by the arrows 262A through 262AD the computer program executed
f ~by the digital signal processing circuit 122 first moves a forty
(403 word segment ~rom each circular buffer 224A through circular
buffer 224AD ~hat store audiovisual information to sort buffers
264A through 264AD depicted in FIG. 5b that are located in the
~RAM of the memory 126. Even though the preferred digital signal
.. ¦ processing circuit 122 addresses full words of memory, to facili-ltate ~inding the FAS and subsequent processing of the audiovisual
,."/ . .
;.,i :
f~!
. .
i,,
:.~
, .
f
` : 2~2~322
. ~93/1~30 PCT/~S92/09876
- 25 -
:j information, each addressable word of eighty (80) in each of the
sort buffers 264A through 264~D holds only one octet of audlovi-
sual infor~ation. After the computer program has moved the
~, audiovisual information into the sort buffers 26~A through 264AD,
-.~ 5 it then scans only those sort buffers 264A through 264AD which
;i contain I-channel audiovisual information looking for the FAS
which must be present there. After the computer program executed
by the digital signal processing circuit 122 establishes the
location of the beginning of the frame 252 in the I-channel by
~, 10 finding the FAS in the sort buffers 264A through 264AD, it then
1 assigns a value to ADDRESS0 in the appropriate records 232A
~' through 232~D of the B-channel directory ~34 which causes
ADDRESS0 to specify the location of the beginning of the frame
, 252 in tha appropriate circular buffers 224A through 224AD.
After proper values have been assigned to the ADDRESS0 words
', for all circular buffers 224A throu~h 224AD that hoid audiovisual
~;i information, the computer program executed by the digital signal
processing circuit 122 then transfers frames 252 of audiovisual
~ information from the circular buffers 224A through 224AD storing
,j 20 audiovisual information into the sort buffers 264A through 26~AD
with the octets of data organized as described previously. With
. all the frames of audiovisual data thus properly registered into
the sort bu~fers 264A through 264AD, the computer program
¦ executed by the digital signal processing circuit 122 then
~:l25 extracts the BAS from the I-channel's audiovisual information.
At this time the computer program executed by the digital signal
processing circuit 122 also processes the audiovisual information
in accordance with CCITT's ~.221 Recommendation to extract video,
~audio, hi~h-speed, and low-speed data, and as indicated by arrows
"!~ 30 272A through 272AD appropriately 6tores the video data i~o a
received video data buffer 274, as indicated by arrows 276A
through 276AD appropriately stores the audio data into a received
audio dàta bu~fer 278, as indicated by arrows 282A through 282AD
appropriately stores the high-speed data into a received
high-speed data buffer 2B4, and as indicated by arrows 286A
through 286AD appropriately stores the low-speed data into a
received low-speed data buffer 288. The received video data
j buffer 274, ~he received audio data buffer 278, the received
. . .
..
.
,
.
~,
093/16430 2 ~ 2 g 3 2 ~ PCS/US92/09876
- 26 -
high-speed data buffer 284 and the received low-speed data buffer
288 are all located in ~he RAM of the memory 126.
For supplying audiovisual information to the TXA 208A and TXB
208B, the foreground task employs data storage structures in the
, 5 RAM of the memory 126 that are equivalent to those described thus
,~ far for processing received audiovisual informa~ion stored into
::i the RXA 214A and RXB 214B except that it omits the circular
3 buffers 224A through 224AD. Thus, the foreground task in
preparing video, audio, high-speed, and low-speed data for
transfer to the TXA 208A and TXB 208~ by the serial port
' interrupt routine uses duplicates of the received low-speed data
:,- buffer 288, the received high~speed data buffer 284, the received
audio data buff~r 278, the received video data bu~fer 274, and
J~ the sort buffers 264A through 264AD.
~. 15 Referring now to FIGs. 5b and 5c, the shared RAM 146 included
', in the host computer interface circuit 14~ provides st~rage for
'7I various data structures used in exchanging a variety of messages,
I and video, audio, high-speed, and low-speed data between the
¦ interface subsystem 100 and the host digital computer (not illus-
trated in any of the FIGs.). Thus, the shared RAM 146 stores a
pointer structure 302 which holds ad~resses of other structures
used in effecting khe exchange of messages and data. To avoid
~ confusing complexity in FIG. 5c, details of the addresses stored
;:3 in pointer structure 302 have been omitted from that FIG. The
~,.j 25 information stored in the pointer structure 302 functions analo-
gously to the START _ADDRESS, END_ADDRESS, WRITE_ADDRESS and
1 ADDRESS0 stored in each of the records 232A thr~uqh 232AD in the
''.! B-channel directory 234. Information stored in the pointer
~:, structure 302 permits computer programs executed by digital
0 signal processing circuit 122 and by thP host digital computer
, to access the structures present in the shared RAM 1~6 that are
i:' used in e~fecting the exchanges of messages and o~ data. The
computer proqrams executed by the di~ital signal processing
circuit 122 and by the host digital computer may also use
35 i~formati~n stored in the pointer structure 302 ~or monitoring
l the 6tatus of these structures~
J ~he information stored in the pointer structure 302 permits
1 the computer program executed by the digital signal processing
!
.1 .
.~
. . .
`~``093/16430 2 ~ 2 ~ 3 2 ~ PCT/US92,09876
: ~ 27 -
circuit 122 to pl~ce messages for the host digital computer int~
a host computer messaqe queue ~04 located in the shared RAM 146.
The host computer ~essage queue 304 receives messages from the
computer program executed by the diqital signal processing
5circuit 122, as indicated by an arrow 306, from which the
computer program executed by the host di~ital computer fetches
them, as indicated by an arrow 308. Information stored in the
pointer structure 302 also permits the computer program executed
by the digital signal processing circuit 12~ to access messages
I 10 stored in an interface subsystem message queue 312 located in the
i shared RAM 146. The interface subsystem message queue 312
receives messages from the host digital computer, indicated ~y
~ an arrow 314, from which the computer proyram executed by the
:7 digital signal processing circuit 122 fetches them, as indicated
;i 15 by an arrow 316.
:l In addition to the host comp~ter message ~ueue 304 and t~e
-~ interface subsystem message queue 312, the pointer structure 302
also permits computer proyrams executed both by the digital
. signal processing circuit 122 and by the h~st digital computer
29 to exchange vldeo, audio, high-speed, and low speed data stsred
in one or more session blocks 318 located in the shared RAM 146.
i~ One session block 318 is required ~or each individual set of
video, audio, high-speed, and low-speed data that the interface
subsystem 100 exchanges over an individual ISD~ connection, such
. 25 as over an individual H0-connection 64 or an individual B-channel
22. Included in each session block 318 is a session ID 322 that
. uniquely identifies each session and its associated individual
: ISDN connection.
Each ~ession bloc~ 318 also includes a rec~ived video
;~ 30 circular buffer 324. The computer program ~xecuted by the
:~ digital signal processing circuit 1~2 fetches video data from the
received video data buffer 274 and stores it into the received
video circular buffer 3~4 as indicated by an arrow 326. The
computer pro~ram executed by the host di~ital computer fetches
3~ video data ~rom the received video circular bufer 324 as
~, indicated by an arrow 328~ ~he session block 318 also includes
a received audio circular buffer 332. The computer program
executed by the digital signal processing circuit 122 fetches
~ .
:``''1
,,~
,; ;,1
.,~,;
`:
' `-~093/1~30 2 ~ ~ 8 3 2 2 PCT/US92/098~6
- 28 -
. audio data from the received audio data buffer 278 and stores it
int~ the received audio circular buffer 332 as indicated by a~
arrow 334. The computer program executed by ~he host digital
computer fetches audio data from the received audio circular
~, 5 buffer 332 as indicated by an arrow 336. The session block ~18
also includes a received high-speed data ~ircular buffer 342.
The computer program executed by the digital signal processinq
circuit 122 fetches high-speed data from the received high-speed
! data buffer 284 and stores it into the received high-speed data
., lO circular buffer 342 as indicated by an arrow 344. The computer
j!~ program executed by the host digital computer fetches high-speed
;, data from the received high-speed data circular buffer 342 as
,~,t indicated by an arrow 346. The session block 318 also includes
a received low-spead data circular buffer 352. The computer
~15 program executed by the digital signal processing circuit 122
,~fetches low~speed data from the received low-speed data buf fer
,j288 and stores it into the received low-speed data circular
ibuffer 352 as indicated by an arr~w 354. The computer program
.,executed by the host digital computer fetches low-speed data from
~!20 the received low-speed data circular huffer 352 as indicated by
an arrow 356.
'1Each session block 318 also includes a transmitted video
circular buffer 362. The computer program executed by the host
digital computer stores video data to be transmitted from the
interface subsystem lO0 ints the transmitted video circular
buffer 362 as indicated by the arrow 364. ~he computer program
~;1executed by the digital siqnal pro~essing circuit 122 fetches
video data stored in the transmitted video circular buffer 362
,;3and stores it into a transmitted video data buffer (not illus-
,~30 trated in any o~ the FIGs.) as indicated by an arrow 366. The
se~sion block 318 also includes a transmitted audio circular
.buffer 372. The computer program executed by the host digital
computer stores audio data to be transmitted from ~he interface
subsystem lO0 into the transmitted audio circular buffer 372 as
indicated by an arrow 374. The computer progra~ executed by the
.digital signal processing circuit ~22 fetches audio video data
~stored in the transmitted audio circular buffer 372 and stores
!it into a transmitted audio data buffer (not illustrated in any
.~
.
,1 ,~
!
. . .
~ . ,`;............ - - - . . . - ... .. . .
~ 93/1~30 2 1 ~ PCT/US92/09876
29
of the FIGs.) as indicated by an arrow 376. The session block
', 318 also includes a transmitted high-speed data circular buffer
382. The computer program executed by the host digital computer
stores high-speed data to be transmitted from the interface
subsystem 100 into the transmitted high-speed data cir~ular
, buffer 382 as indicated by an arrow 384. The computer program
`-! executed by the digital si~nal processiny circuit 122 fetches
high-speed data stored in the transmitted high-speed data
circular buffer 382 and stores it into a transmitted high-speed
data buffer (not illustrated in any of the FIGs.) as indicated
~, by an arrow 386. The session block 318 also includes a transmit-
,¦ ted low speed data circular buffer 392. The computer program ~;
;J executed by the host digital computer stores low-speed data to
be transmitted from the interface subsystem loo into the
transmitted low-speed data circular buffer 392 as indicated by
, an arrow 394. The computer program executed by the digital
., signal processing circuit 122 fetches low-speed data stored in
the transmitted low-speed data circular buffer 392 and stores it
into a transmitted low-speed data buffer (not illustrated in any
:l 20 of the FIGs.) as indicated by an arrow 3960 ~ ~:
! The presence o~ multiple session bloc~s 318 in the shared RAM :~
l 14~ permits the interface subsyste~ 100 to adapt efficiently and ~:
! flexibly to differing communication environments. For example,
.! .
the interface subsystem 100 may exchange a ~ingle stream of
25 audiovisual information with two H0-connections 64 in order to : :
obtain a data transmission rate of 768 ~bps~ Under such
circumstances the two H0-connections 64 function as a single
connection, and the shared ~AM 146 need only provide a single
~ session block 318 having a single set of circular buffers 324,
:, 30 332, 342, 352, 362, 372, 382, ~nd 392 through which pass all
i ` video, audio, high-speed, and low-speed data.
:,1
Alternatively, the interface subsyst~m 100 may exchange two
~ eparatè streams of audiovisual in~ormation with two `~ :
'~ ~0-connections 64. In this sec~nd ~perating envir~nment the two
¦ 35 H0-conneckions 64 operate as individual ISDN connections, and the
,i
I shared RAM 146 ~ust provide at least two session blocks 318
~ having two individual and independent sets of circular buffers
,~ 324, 332, 342, 352, 362, 372, 382, and 392 through which pass
'
~:i
. . .
. .
~093/16430 2 ~ ~ ~ 3 2 2 PCTIUS92/09876
- 30 -
separate streams of video, audio, high-speed~ and low-speed data.
~his second operating mode for the interface subsystem lOo adapts
it for engaging in conference audiovisual teleservices in which
-'the interface subsystem lOo receives two different telecommunica-
;~5 tions and the H.221 layer 28 preserves the identity of the two
,communications in the video, audio, high-speed, and low-speed
data that it exchanges with the application layer 44. By
preserving the identity of ~he two co~munications in the data
exchanged between the interface subsystem lO0 and the host
.~lO digital computer, the interface subsystem lO0 permits the
computer proyram executed by the host di~ital computer to synthe-
size a composite display perhaps presentin~ one half of the data
`from.each of the individual audiovisual teleservices on one~half
''3~,of a display's screen. Alternatively, the computer program ..
executed by the host digital computer might use the display's
entire screen for one of the audiovisual teleservices while
1presenting the other audiovisual teleservices in a small window
.. 1 located within the larger display.
.~When operating to preserve the identity of two or more
separate communications which the interface subsystem lOo
exchanges with individual ISDN connections, the computer program
executed by the digital signal processing circuit 122 establishes
Ithe identity o~ such communications in transferring the audiovi- :
¦sual information out of the circular buffers 224A through 224AD
:25 storing audiovisual information into the sort buf~ers 264A
:through 264AD. Thus, when the interface subsystem lO0 operates
in this manner the computer program executed by the digital
-lsignal processing circuit 122 distinguishes among idPntifiable
¦groups in the sort ~uff~rs 264A through 264AD that respectively
,~30 store audiovisual information for separate communication~.
:1~To control t~e operation of the interface subsystem lO0 for
1exchanging video, audio, high-speed, and low-speed data with the
.~host digital computer as outlined above, the computer programs
exe~uted by the digital signal processing circuit 122 and the
host digital computer exchange various messages via the host
computer message queue ~04 and the interface subsystem ~essage
queue 312. Listed below are various messages specifically
related to audiovisual teleservice cor~unications tbat the
~ , .
93tl~30 PCT/US92/09876
- 31 212~3322
computer program executed by the digital signal processing
circuit 122 may place into the host computer message queue 304.
NEW_RX_BAS
This message informs the host digital computer that the
s computer program executed by the di~ital signal processing
circuit 122 has identified a new and significant BAS in the
received audiovisual information.
NEW_TX_BAS
This message informs the host digital computer that the
computer program executed by the digi~al signal processing --
, circuit 122 has begun preparing audiovisual information for
l transmission from the interface subsystem 100 in a new and ~-
., significantly different way.RX_PR~MING_~OST :~
This message informs the host digital computer of the l~ss
~, of frame or multiframe synchronization in the received
:' audiovisual information.
.~ TX_FRA~ING_LOST
j This message informs the host digital computer that the
terminal receiving audiovisual in~orm tion transmitted from
the inter~ace subsystem 100 has reported a loss of frame ~r
, multi~rame synchronization.
:j ~I221_SYNC
l This message informs the hos-t digital computer that H.221
frame synchronization has been achieved both by the inter- :~
. face subsystem 100 for receiYed audiovisual in~ormation, and
; by the terminal receiving audiovisual information transmit~
t~d from the interface subsystem 100.
N~W_C~PABILITY
~i 30 This m~ssage informs t~e host digital computer that a
specificatio~ of new capabilities in accordance with CCI~T's
.242 Recommendation has been received in the audiovisual
information.
R~_Q~_FULL
; ' 35 This mes~a~e in~orms the host digital computer that the ~-
il received ~ideo circular bufPer 324, the received audio
~ circular buffer 332, the received high-speed data circular ~ :
~ ~uffer 342, or the received low-speed data circular buffer
,,~ ,
,,,.~ . .
~':
.. , ' ~.
.~ ~
, i . . . . . . . ..
:j
:`'
2 ~ 2 8 3 2 ~ PCT/US92/09876
- 32 -
,, ~
. 1 352 lS full, and that computer program executed by the
, digital signal processing circuit 12~ has begun discarding
received video, audio, high-speed; and/or low-speed data.
TX_QUE_EMPTY
This message informs the host digital computer that the
.j transmitted video circular buffer 362, the ~ransmitted audio
l circular buffer 372, the ~ransmitted high-speed data
J circular buffer 3B2 and/or the transmitted low-speed data
~¦ circular buffer 392 is empty, and unless the computer
~~ 10 pro~ram executed by the digital signal processing circuit
', 122 has been properly prepared for the occurrence of this
'I~ condition by a message from the host digital computer, then
:~ the interface subsystem lOO begins transmitting zeros (O) as
-~ audiovisual information.
Listed below are various messages specifically related to
! audiovisual teleservice communications that the compu~er program
.~, executed by the digital signal processing circuit 122 may
,, retrieve from the inter~ace subsystem message queue 312.
1 20 SET_CAP~BILITIES
. This message instructs the co~puter program executed by the
digital signal processing circuit 122 to transmit a speci-
!' fication of new capabilities in accordance with CCITT's
H.242 Recommendation to the te~minal receiving audiovisual
information from the interface subsystem lOO.
GEq'_C~PABILITIES
This message instructs the computer program executed by the
di~ital signal processing circuit 122 to send a
~ NEW_~APABILITI~S message back to the host computer informing
,l~ 30 it o~ the present capabilities of the other terminal~
`¦ ! I~MEDIATE_BAS
~ This message instrllcts the computer program executed by the
,~ digital signal processing circuit 122 to transmit specified
~;~ BAS codes to the terminal receiving audiovisual information
~rom the interf~ce subsystem lOO, and to tr~nsmit subsequent
audiovisual information in accordance with the specified BAS
codes.
l . ;
.
1 .
.,
,1
.
~,
., .
~ ~ ^q 93/1~30 2 ~ ~ ~ 3 2 2 PCT/US92/09876
- 33 -
,', FRA~_CHANNEL
-~. This message instructs the computer program executed by the
digital siqnal processin~ circuit 122 to initiate framing in
, accordance with CCITT's H.221 Recommendation for a specified
~j 5 session's audiovisual teleservices.
i IMMEDIATE_BAS SWITCH
This message instructs the computer program executed by the
digital signal processing circuit 122 to transmit specified
B~S codes to the terminal receiving audiovisual information
from the interface subsystem 100, to transmit subsequent
~' audiovisual information in accordance with the specified BA5
- codes, and to begin exchanging video, audio, hiyh-speed, and
low-speed data with circular buffers in a different session
. . . . .
block 318.
, 15 EHPTY_BAS_SWITCH
:1 ~his message instructs the computer program executsd by the
digital si~nal processing circuit 122 to transmit speci~ied
~A5 codes to the terminal receiving audiovisual information
~, from the interface subsystem 100, and to beginning trans-
mitting subsequent audiovisual in~ormation in accordance
with the specified ~AS c~des when the transmitted video
circular buffer 362, the transmitted audio circular buffer
372, the transmitted high-speed data circular buffer 382 or
the transmitted low-speed data circular bu~fer 392 becomes
empty.
:~! ME~ORY_CONTROL
This message instructs the computer program executed by the
digital signal processing circuit 1~2 to begin or to
terminate storing data into the received video circular
. 70 bu~fer 324, the received a~dio circular buf~er 332, the
received high-speed data circular buffer 342, or the
received low-spaed data ~ircular buf~er 352, or fetching
datà from the transmitted video circular buffer 362, the
1 transmitted audio circular buffer 372, the transmitted
:3 35 high-speed data circular buffer 382, or the transmitted
low-speed data circular buf~er 39~ as specified in the mes-
sage. By transmitting this message the computer program
executed by the host digital computer selects Among the
:;1
.. ~ ..
.,
t ,; ~ . ~; ... -.. .- . - .
~ 93/1~30 PCT/US92/09876
'' 21?~8322
- 34 -
video, audio, high-speed, and low-speed data for storage
into the circular buffers 324, 332, 342 and 352 ~y ~he
computer prog~am ~xecuted by the digital signal processing
, circuit 122. This message also permits the computer program
;, 5 executed by the host digital computer to selec~ among vide~,
audio, high~speed, and low-speed data for transmission fro~
the circular buffers 362, 372, 382, and 392 by the interface
subsystem 100 .
., .
~ 10 In addition to the various messages listed above that relate
.~ specifically to audiovisual teleservice communications, the
-~ computer programs executed by the digital signal processinq
circuit 122 ~nd by the host digital computer als~ exchange a
variety of messages related to establishing and terminating
~, 15 audiovi~ual teleservices such as placin~ a telephone call,
accepting a telephone call, and responding to various other type
! of telephone system control signals such as dual-ton~
multifrequency ~"DTMF") si~nals.
20 Indu~ial Applica~ility
An inter~ace subsystem 100 havinq circular buffers 224A
through 224AD which provide storage for only one-hundred and
`~ twenty (120) frames 252 of audiovisual information in the RAM of
the memory 126 permits only a limited amount of skew between
25 independent B-channels ~2 that are collectively providing a
J single audiovisual teleservice. ~or example, i~ audiovisual
J information is being exchanged over two HO~connections 64 to
obtain a combined data transmission rate of 76B kbps, then the
', inter~ace subsystem 100 can acco~modate approximately 140
30 milliseconds oP skew between them. Under ~uch circumstances,
storage for ~twenty-four (24) frame~ 252 is assigned to khe
circular bu~fers 224A through 224F for the six (6) B-channels 22
that arrive latest in time. ~he remaininq storage for ninety-six
. (96~ fra~es 252 is assigned to the circular buffsrs 224G through
. ~5 224L for the six ~6) B channels 22 that arrive earliest in time.
I~ the ~kew betw~en two such H0-connections 64 exceeds the
. ~aximum allowed, then one of the two connections ~ust be
terminated and the teleph~ne call replaced until two connec~ions
., .
~ 93/1~30 PCl/US92/09876
~ 35 ~ 3 2 ~
~ are obtained that have an acceptable amount of skew. If it
;~` should be necessary to accommodate a larger amount of skew
betwPen independent B-channels 2~, that can be accomplished
simply by increasing the amount of storage in the RAM of khe
memory 126 available for the circular buffers 224,
The received video circular buffer 324, the recPived audio
l circular buffer 332, the received hiqh-speed data circular buffer
.~ 342, and the received low-speed data circular buffer 352 provide
~ host computer interface receiving buffers for received video,
.1 l0 audio, high-speed, and low-speed data after it has been extracted
from the audiovisual information. Similarly, the transmitted
1 video circular buffer 362, the transmitted audio circular buffer
372, the transmitted high-speed data circular buffer 382 and the
, transmitted low-speed data circular buffer 392 provide host
computer interface transmitting buffers for supplying video,
audio, high-speed, and low-speed data for transmission from the
~ interface subsystem l00 as audiovisual in~ormation. While the
;~ preferred e~bodiment of the interfare subsystem l00 employs
circul~r buffers 324, 332, 342, and 35~, other structures are
;1j 20 known which function equivalently to the circular buffers 324,
~ 332, 342 and 352. In particular, first-in firs~-out structures
j ("FIFOs") are equivalent to and may be used in place of the
`1 combined received video data buffer 274 and received video
:~ .
circular buffer 324, the combined received audio data buffer 278
25 and received audio circular buffer 332, the combined received.
high-speed data buffer 284 and received high-speed data circular
~ buffer 342, and the combined received low-speed data buffer 288
;~ a~d received low-speed data circular buffer 352. Similarly,
~ FI~OS are equivalent to and may be used in place of the combined
::/ 30 transmitted video circular bu~fer 362 and transmitted video data
~3 ! buffer, the combined transmitted audio cir~ular buffer 372 and
transmitted audio data bu~fer, khe co~bined transmitted
high sieed data circular bu~er 382 and ~ransmitted high-speed
audio data b~ffer, and the combined trans~itted low-speed data
circul~r buf~er 392 and transmitted low-speed data buffer.
i While the structure and operation of the interface subsystem
l00 has been explained in the context of exchanyinq audiovisual
¦ teleservices using ISDN communications, the interface subsystem
,,:
;,, .
r ~
r !
, . . .
~093JI~0 PCT/US92/0987
~ 36 2 ~ 8 3 2 2
100 accommodates other digital telecommunication services that
are compatible with CCITT~s ~.221 ~ecommendation such as Tl
Switched 56. The interface subsystem loo may be easily used for
transmitting and/or receiving any type of digital data using ISDN
5 communications. Such use of the interface subsystem 100 may be
! realized without altering the multitasking computer progr~m
executed by the digital signal processing circuit 122. Rather,
, the interface subsystem 100 may be used for transmitting and/Gr
J, receiving any type of digital data through the use of a suita~le
.l 10 application layer computer program executed by the host diqital
computer.
~J Although the present invention has been described in terms
of the presently preferred ~mbodiment, it is to be understood
that such disclosure is purely illustrative and is not to be
,, 15 interpreted as limiting. Conse~uently, without departing from
the spirit and scope of the invention, various alterations,
~, modifications, and/or alternative applications of the invention
will, no doubt, be suggested to those skilled in the art after
~l having read the precedin~ disclosure. Accordingly, it is intended
-~ 20 that the followi~g claims be interpreted as enoompassing all
alterations, modifications, or alternativ2 applications as fall
within the true spirit and scope of the invention.
~'
;
:. .,
,',.
!
,,..~
., .
:
'
,'
~;
`5,
: .
,`~i , . .
