Multiplex communications – Pathfinding or routing – Switching a message which includes an address header
Reexamination Certificate
1998-08-06
2002-12-17
Nguyen, Chau (Department: 2663)
Multiplex communications
Pathfinding or routing
Switching a message which includes an address header
C370S468000, C370S524000
Reexamination Certificate
active
06496504
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention pertains to communication systems and methods for communicating information over digital networks, such as an Integrated Services Digital Network (ISDN). In particular, the present invention pertains to establishing over an ISDN D channel one or more data rate selectable communication links between a source terminal and one or more destination terminals via a modified ISDN switch. The modified ISDN switch handles the aggregate bandwidth of two ISDN B channels as a common resource that is available for subdivision and allocation to one or more links to the one or more destination terminals. The aggregation of the two ISDN B channels, as well as the subdivision of the bandwidth afforded thereby, is performed without requiring the source and destination terminals to perform bonding or multilink protocol processes.
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 portions of the existing PSTN and provide a variety of services not offered by the PSTN. ISDN will allow for 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 digital 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 view by the user, is 64 kbps per B channel, and 16 kbps for the D channel, not 192 kbps.
Conventional facsimile devices, such as G3 devices, send signals at rates not exceeding 64 kbps, because only one of the two B channels is used. Because facsimile data is arranged in a predetermined format, sending data over two separate B channels would be a sizable task because conventional ISDN switches handle the B channels separately, and thus may send data of one of the B channels over a completely different route than that of the other B channel. As a consequence, the different communication paths impose different communication delays on the respective B channels.
Other devices such as video teleconference facilities, assume the processing burden of “bonding”, or employing multilink point-to-point (multilink PPP) protocols, so as to increase data rates approaching 128 kbps. The bonding approach imposes a burden on the customer premise equipment (CPE) of dialing the ISDN switch and establishing the subsequent calls needed to achieve the desired data rate. Thus, two separate links are established. In particular, by assuming the burden of maintaining two separate communication connections with the ISDN switch, the CPE can give the appearance to a user that a 128 kbps channel is available to the user. However, the bonding approach is cumbersome in that the ISDN switch assumes each of the B channels may be handled independently, and therefore impart different delays into the separate B channels. As a consequence, the CPE must compensate for the delays between the respective B channels, and piece together the received and transmitted information so as to avoid synchronization problems.
Multilink PPP schemes attack the same problem from a different approach, although also placing a similar processing and data management burden on the CPE. The multilink PPP schemes use a conventional ISDN switch and attempts to make the ISDN switch oblivious to the operation of combining B channels to provide an effective data rate approaching 128 kbps. The multilink protocol involves dividing the user's source data into specific fragments, including overhead information in the respective packets, so that the packets may be sent over all available channels, and later recombined in a contiguous fashion. As with bonding, multilink PPP places a computational and management burden on the CPE, rather than at the ISDN switch.
As recognized by the present inventor, a limitation with conventional ISDN networks and the source and destination terminals that operate therewith, is that the B channels are identified as static, fixed-bandwidth channels that may not be fully utilized by either the source or destination terminals. Moreover, while each B channel is allocated 64 kbps, a source or destination terminal may or may not be able to support the data rate, and thus may use the channel at lower data rates. However, the capacity for the channel remains at 64 kbps, and thus unless the source and destination terminals actually use a full 64 kbps signaling scheme, a portion of the available bandwidth (related to signaling speed) is wasted.
In light of this limitation, the present inventor identified that the “subchannelization” of one or more ISDN B channels is not performed with conventional systems, but would be beneficial if the subchannelization allowed the “wasted” portion of the bandwidth to be used for other communication tasks. Moreover, if a modified ISDN switch were available that could receive a message, or messages, from the source terminal, and route the message, or messages, as subchannel messages to one or more destination terminals at a user-selectable subchannel bandwidth (i.e., data rate), significantly greater flexibility in terms of end-user communication speed, accessibility, and user-friendly operation could be achieved.
Conventionally, the function served by the ISDN D channel, is twofold. First, the D channel is used to establish and maintain signaling between the 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”, 5
th
Edition, Prentice Hall, 1997, pages 740-769 (hereinafter “Stallings”), the contents of this book being incorporated herein by reference.
FIG. 1
is a block diagram of a conventional ISDN system
100
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 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. In the source facility
1
, the bonding or multilink
Lee Andrew
Nguyen Chau
Ricoh & Company, Ltd.
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