Multiplex communications – Channel assignment techniques – Messages addressed to multiple destinations
Reexamination Certificate
1998-07-02
2001-10-16
Kizou, Hassan (Department: 2662)
Multiplex communications
Channel assignment techniques
Messages addressed to multiple destinations
C370S390000, C379S201060
Reexamination Certificate
active
06304579
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention pertains to communication systems and methods for communicating information from a source terminal to two or more destination terminals via an Integrated Services Digital Network (ISDN) network or other network. In particular, the present invention pertains to establishing over a source sub-link, e.g. an ISDN D channel, a communication link between a source terminal and multiple destination terminals via a modified a 1×N (“one by N”) switch and multiple destination sub-links, such as separate ISDN B channels.
2. Discussion of the Background
Conventional facsimile devices communicate over the Public Switch Telephone Network (PSTN) using analog signals that are transmitted over conventional telephone lines. The source terminal (e.g., a facsimile device, computer with scanner and modem facilities, or another device that transmits and/or receives data) converts digital scanned information into a corresponding analog signal so the same may be sent over the PSTN telephone line, via a telephone switch facility, to the destination terminal. The source terminal receives the analog information and converts the analog information back into digital signals which form the basis of an image to be printed, perhaps on facsimile paper.
The Integrated Services Digital Network (ISDN) is emerging as a next generation worldwide public telecommunications network that will replace existing public switch telephone networks and provide a variety of services that are not offered by the PSTN. ISDN will allow the transmission of various types of data between various types of ISDN terminal equipment (TE).
A portion of the ISDN link between a source terminal and a central office, which has a switch facility, is referred to as a “digital pipe”. A capacity of the pipe is generally discussed in terms of separate channels. In particular, a “basic access” digital pipe includes two B channels (basic channels) that each support 64 kbps signaling, and a D channel at 16 kbps. While the total bit rate of these three channels is 144 kbps, framing, synchronization and other overhead bits bring the total bit rate of a basic access link to 192 kbps. Furthermore, the B channels serve as separate communication channels such that the maximum data capacity, as viewed by the user, is 64 kbps per B channel, and 16 kbps for the D channel, not 192 kbps.
Conventionally, the function served by the ISDN D channel, is twofold. First, the D channel is used to establish and maintain signaling between the (customer provided equipment) CPE and the ISDN switch (operated by the telephone company). Thus, the D channel carries signaling information such as that required for dialing the telephone number of the destination terminal and making the connection between the source terminal and the destination terminal. A more complete description of the D channel as employed in narrowband and broadband ISDN, as well as ISDN terminal equipment, protocols, data rates, etc. is provided in the literature, for example in Stallings, W., “Data and Computer Communications”, 5th Edition, Prentice Hall, 1997, pp 740-769 (hereinafter “Stallings”) the contents of this book being incorporated herein by reference.
Other communication protocols are available as well for routing information from a source terminal to a destination terminal. These protocols include Frame Relay, Switch
56
, asynchronous transfer mode (ATM), asynchronous digital subscriber line (ADSL), and digital subscriber line (DSL), which may serve as links to the source terminal's CPE and the destination terminal. A more complete description of Frame Relay and ATM protocols is provided in Stallings at page “301” to page “359”.
FIG. 1
is a block diagram of a conventional ISDN-based system having a source facsimile
10
at a source facility
1
that communicates via an ISDN switch
22
to a destination facsimile
16
(or other type of destination terminal, such as a computer, ISDN equipped photocopier, etc.) in a destination facility
2
. The destination facsimile
16
may, in turn, send the message to one or more subaddressees (Sub
1
, labeled as
16
S
1
in
FIG. 1
, to SubN, labeled as
16
S
2
in FIG.
1
). The source facsimile
10
communicates via a terminal adapter
10
A, shown as an internal device, although a separate external terminal adapter may be used as well. The terminal adapter
10
A provides a protocol (physical layer and intermediate layer) conversion function for converting signal protocols such as V.35, RS-232, Universal Serial Bus (USB), IEEE 1394 (FireWire), etc. to an ISDN compliant protocol over a 4-wire interface.
The NT1
14
connects the source facilities
1
, via a two-wire line
15
, to a switching module
26
located at the ISDN switch
22
. Alternatively, a second network termination (NT2) may be used at the source facility
1
between NT 1 and the terminal adapter
10
A to provide a switching and concentration function, such as with a digital private branch exchange (PBX). Likewise, the NT1 may be replaced with a NT12 that performs the functions of both the NT 1 and NT2.
At the ISDN switch
22
, the switching module
26
connects to a processor
24
and another switch module
28
via a bus
27
, which allows digital commands and data to be passed between the respective switching modules
26
and
28
, and the processor
24
.
The equipment at the destination facility
2
may or may not be exactly similar to that of the source facilities
1
. In the system shown at
FIG. 1
, the destination facility
2
is used as an example and includes the destination facsimile
16
having a terminal adapter
16
A incorporated therein, which connects to another NT1
20
as shown. The subaddress systems
16
S
1
and
16
S
2
may be similarly configured, and are identified by respective subaddresses included in the message sent by the source facsimile
10
. The NT1
20
connects to the switching module
28
in the ISDN switch
22
, via another two-wire line
17
as shown. Thus the ISDN switch
22
connects to the source terminal
1
by a single communications link (line
15
), and connects to the multiple subaddress systems
16
S
1
and
16
S
2
by another single communications link (line
17
).
ISDN communications is based on a seven layer protocol stack, as explained in reference to FIG. A.5 of Stallings, for example. Control signaling is accomplished between the respective user-network interface and occurs at a third layer of the protocol stack (i.e., the “network”layer) and is named 1.451/Q.931. Thus, establishing and maintaining control signaling for a communication link established between the source facility
1
and the destination ISDN facility
2
and facility
3
is made through the D channel, and in particular, the ISDN network layer, data link layer and physical layer.
As appreciated by the present inventor, a user of the source terminal
1
can communicate to the separate subaddresses
16
S
1
to
16
SN only if the link
17
is operational, and only if the NT1
20
, terminal adapter
16
A and destination facsimile
16
are operating properly, because these items are single points of failure for communicating to the separate subaddresses
16
S
1
to
16
SN. Furthermore, the ISDN switch is not configured to send a message from the source facsimile
1
to multiple destination facilities
2
, which are not connected by a common line
17
. While, the ISDN may establish separate communication links to separate facilities, the establishment of these links is done on a per-request basis by the source facsimile, thereby requiring significant set-up time at the source facsimile
1
, and incurring significant set-up cost.
FIG. 2
is a frame structure
200
of a transmission from the source facilities
1
to the ISDN switch
22
, for an ISDN basic rate access. The frame structure
200
includes 48 bits that are transmitted in 250 &mgr;sec. Components of the frame structure
200
include framing bits, F, dc balancing bits, L, B channel bits for the first B channel (16 per frame), B
1
, B channel
Kizou Hassan
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Pezzlo John
Ricoh & Company, Ltd.
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