Multiplex communications – Pathfinding or routing – Combined circuit switching and packet switching
Reexamination Certificate
1998-01-22
2001-02-27
Chin, Wellington (Department: 2664)
Multiplex communications
Pathfinding or routing
Combined circuit switching and packet switching
C370S392000, C358S438000
Reexamination Certificate
active
06195348
ABSTRACT:
TECHNICAL FIELD
This invention relates to data transmission, and more particularly to an improved facsimile protocol which permits facsimile machines, typically designed for use with circuit switched telephone connections, to operate more effectively when connected through packet switched data networks such as the Internet.
DESCRIPTION OF THE PRIOR ART
Facsimile machines have become standard in every office environment, with most offices having a plurality of such machines. Facsimile machines operate by encoding an image on a paper into a series of tones that are then transmitted over the telephone network. Standard facsimile protocols for effectuating communications between facsimile machines have been defined, and most facsimile machines operate using one or more such protocols.
When the protocols used by most facsimile machines were defined many years ago, virtually the only technique utilized for interconnecting facsimile machines was a circuit switched telephone connection. Such a circuit switched telephone connection establishes a dedicated circuit between a sending and a receiving facsimile machine. The protocols previously defined for facsimile machines therefore presuppose the existence of such a dedicated telephone circuit.
Recently, the Internet and other smaller packet data networks have become ubiquitous. With personal computers on virtually every desktop, communication of voice, data and images over data networks, and particularly the Internet, has become the norm rather than the exception. Additionally, many people have found it more convenient to send and receive faxes electronically, directly from their personal computers, rather than printing them out and feeding paper through a scanning fax machine. Most of these computers are connected to a data network such as the Internet. Accordingly, facsimile technology has evolved to the point where many facsimile transmissions are achieved over a packet data network rather than a dedicated circuit switched connection, and where one or both of the fax machines involved in the transmission is actually a computer.
A typical arrangement for sending facsimile images over the Internet is shown in FIG.
1
and comprises a sending facsimile machine
104
connected to a local server
102
. The local server
102
is utilized to establish a connection with a remote server
103
over the Internet
101
using standard network protocols such as TCP\IP. The remote server
103
is connected to the remote (receiving) facsimile machine
105
, intended to receive the facsimile image.
In operation, a telephone call is made from the sending facsimile machine
104
to the local server
102
and the facsimile image transmitted over such telephone connection in accordance with standard and conventional techniques. Indeed, the local facsimile machine
104
can not distinguish between the local server
102
and a conventional facsimile machine.
After receiving the information at local server
102
, the image is transmitted through Internet
101
and stored at remote server
103
. Subsequent to the termination of the data connection, the facsimile image is then sent to receiving facsimile machine
105
using a conventional facsimile protocol and telephone call as is well known in the art.
One problem is that the main advantage of facsimile, substantially instantaneous conveyance of a document from one place to another, is lost. Specifically, when a sender completes feeding the document through a sending facsimile machine, he can not be sure that the document has been received at the other end. The document may be stored for a substantial amount of time in the network, or may even get corrupted by the network, yet the user sending the document would not be aware of this for a substantial amount of time.
Utilizing public data networks with unpredictable delay characteristics to send and receive faxes in realtime has been heretofore impossible due to a set of problems not present in conventional facsimile systems which utilize circuit switched connections. One such problem created by the utilization of the data network
101
is the fact that packets of information experience varying delays as they are transmitted over the network. The varying delays introduce timing problems which may cause the transmission to not stay within the bounds defined by the facsimile standards. For example, there may be a large burst of data getting through the network very quickly followed by a large amount of time with no data at all. A typical fax machine will not be able to handle the large burst, and may also time out during the interval when there is no data at all. Thus, facsimile transmissions utilizing data networks are typically not accomplished in realtime.
It would be desirable to be able to have the facsimile transmitted in real time over the data network, and to thus have the data network transparent with respect to the facsimile. However, because of the variable delays, the facsimile image must be buffered.
Another problem introduced when one attempts to transmit facsimile images over data network in realtime is that caused by fill bits. Specifically, referring to
FIG. 1
, many of the bits transmitted from the sending facsimile
104
to the local server
102
are not representative of image data (i.e., image data bits) but instead are inserted into the data stream in order to maintain a substantially constant output bit rate from facsimile machine
104
during times that the facsimile machine
104
is performing tasks such as advancing the paper. Thus, the bit stream arriving at local server
102
comprises both data bits that actually represent the image to be transmitted as well as so-called fill bits, which are inserted only to keep the timing correct.
Prior to the local server transmitting the image to remote server
103
, the fill bits are stripped and the data compressed. When the remote server
103
receives the data, there is no way to reconstruct the original bit stream since the fill bits have been lost. Accordingly, there is no known way to keep the average rate at which image data bits arrive into the system at local server
102
approximately the same as the rate at which data bits leave the system from remote server
103
. This means that data may be transmitted from remote server
103
to receiving facsimile machine
105
much faster or slower than it is being sent from sending facsimile machine
104
to local server
102
. Consequently, receiving facsimile machine
105
may experience data arriving too fast or too slow, and the image will not be correctly conveyed. The foregoing is still another reason that facsimile images transmitted over data networks are typically not accomplished in realtime.
In view of the above, there exists a need in the art for a facsimile system which can deliver images in substantially real time, while at the same time, operate over a data network such as the Internet.
SUMMARY OF THE INVENTION
The above and other problems of the prior art are overcome and a technical advance is achieved in accordance with the present invention which relates to an improved method and apparatus for transmitting facsimile images and the like over a data network. In accordance with the teachings of the present invention, a local server receives a facsimile image and converts it into a sequence of packets. Each packet is “tagged” with a value indicative of how long it actually took to receive the data bits representing the image information. The fill bits are then stripped and the data bits and the tag are transmitted over the Internet as a set of packets.
If a sequence of 100 bits arrived at a local server, which sequence included 80 image data bits and 20 fill bits, and such packet took 100 milliseconds to receive, the system would send the 80 bits only along with a tag indicating that those 80 image data bits took 100 milliseconds to receive at the local server.
At the remote server, the tags are read, thereby notifying the remote server of the average amount of time it is taking for the image data bits to be received by t
Chin Wellington
Dialogic Corporation
Duong Frank
Kaplan & Gilman, L.L.P.
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