Facsimile and static presentation processing – Facsimile – Image transmission accuracy verification
Reexamination Certificate
1999-08-16
2002-12-17
Grant, II, Jerome (Department: 2624)
Facsimile and static presentation processing
Facsimile
Image transmission accuracy verification
C358S406000, C358S435000
Reexamination Certificate
active
06496282
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention pertains to synchronous communication systems and methods for communicating information over an Integrated Services Digital Network (ISDN) network. In particular, the present invention pertains to establishing over an ISDN D channel a synchronous communication link between a source terminal and a destination terminal via an ISDN switch, where the established communications link has communications attributes that are favorable to both the source terminal and the destination terminal.
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 to the destination terminal. In turn, 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 evolving into 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) which 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. However, the B channels serve as separate communication channels such that the maximum data capacity, as view by the user, is 64 kbps per channel, not 192 kbps.
The function served by the D channel, is twofold. First, the D channel is used to establish and maintain signaling between the user's equipment and the ISDNs 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 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 which is incorporated herein by reference.
FIG. 1
shows a conventional ISDN system where a source facsimile
10
at a source facility
1
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 source facsimile
10
communicates via a terminal adapter
10
A, which is 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 protocol 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 source facsimile
10
, terminal adapter
10
A, and network termination (NT
1
)
14
, are included at the users' source facility
1
. The NT
1
14
connects, via a two-wire line
15
, to a switching module
26
located at the ISDN switch
22
. Alternatively, a second network termination (NT
2
) may be used at the source facility
1
between NT
1
and the terminal adapter to provide a switching and concentration function, such as with a digital private branch exchange (PBX). Likewise, the NT
1
may be replaced with a NT
12
that performs the functions of both the NT
1
and NT
2
.
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 processor
24
.
The equipment at the destination facility
2
may or may not be exactly similar to that of the source facilities
1
. It is assumed, however, that the source facsimile
10
and the destination facsimile
16
have no prior knowledge of the other's communication attributes. In the system shown at
FIG. 1
, the destination facility
2
includes the destination facsimile
16
having a terminal adapter
16
A incorporated therein, which connects to another NT
1
20
as shown. The NT
1
20
connects to the switching module
28
in the ISDN switch
22
, via another two-wire line
17
as shown.
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 I.451/Q.931. Thus, establishing and maintaining control signaling for a communication link established between the source facility
1
and a destination ISDN facility
2
through the D channel, and in particular, the ISDN network layer, data link layer and physical layer.
A link access protocol (LAPD) D channel is defined for establishing particular LAPD frames that are exchanged between the subscriber equipment (either at the source facility
1
or at the destination facility
2
) and the ISDN switch
22
. The call control protocol I.451/Q.931 is used on the D channel to establish, maintain and terminate connections on B channels.
FIG. 2
illustrates the signaling sequence between the source facility
1
and the ISDN switch
22
. In order to establish a B channel connection between the source facility
1
and the destination facility
2
, an initial communication link must be established on the D channel between the source facility
1
and the destination facility
2
. To this end, a series of messages is sent back and forth between the source facilities
1
and the ISDN switch
22
. This communication between the source facilities
1
and ISDN switch
22
occurs on a continuing basis on the D channel, while communications are maintained between the source facilities
1
and destination facilities
2
on the B channel. As shown in
FIG. 2
, several different messages are sent between the source facilities
1
and ISDN switch
22
while the D channel is maintained.
The direction of the arrows in
FIG. 2
, indicates a direction of communication between the source facilities
1
and the ISDN switch
22
. The process for establishing a connection is initiated by the source facilities
1
by first sending a setup message. Particular features of the setup message will be discussed with respect to
FIG. 3
, however the purpose of the setup message is to provide general information regarding the request to connect to the ISDN switch
22
. Next, the ISDN switch
22
responds with a call proceeding message that indicates that call establishment has been initiated. Subsequently, the ISDN switch
22
, sends a connect message that indicates call acceptance by the source facilities
1
. The source facilities
1
then sends a connect acknowledge signal that indicates the user has been awarded the call. When the user wishes to disconnect a call, the user sends a disconnect message via the source facilities
1
to the ISDN switch
22
, requesting for connection clearing. In response, a release message is sent from the I
Grant II Jerome
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Ricoh & Company, Ltd.
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