Computers are commonly used in the workplace for data processing and storage. Access to computer information is a key element in the successful use of computers. Communication between computers has become a critical aspect of access to the computer information. A local area network (LAN) allows several computers to be coupled together to enhance their computing capability. One computer can access information stored in another computer through the LAN. When information is exchanged between two computers, the information must be in a format that the computers can recognize and process. Information is often exchanged in a standard format such as ASCII, for example. However, an ASCII format exchange may require that the information be converted from its original format to ASCII format. The computer transferring information has no way of determining the data processing capabilities of the receiving computer and, therefore, must convert the information to ASCII on the assumption that ASCII is a "universal" format that all computers can recognize.
One form of computer is a facsimile (FAX) machine. A FAX machine may comprise an interface board within a computer, or may be a stand-alone device employing well-known computer technology. FAX machines are used to transfer information from one location to another. FAX machines of older design had little or no computing power and were limited to scanning a page and transmitting a digitized version of the page to a receiving FAX machine that reproduced the page. Modern FAX machines are essentially a form of computer and often have storage capability allowing the FAX machine to scan a document and store the digitized version of the machine for transmission at a later time, such as when telephone rates decrease at night. The receiving FAX machine can store received messages that are confidential and print them out only when the proper identification code is entered.
To minimize transmission time, FAX machines use data compression techniques well known in the art. An international standard for facsimile transmission has been established by the International Telegraph and Telephone Consultative Committee (CCITT) and published as Terminal Equipment and Protocols for Telematic Services (1989). References to CCITT standards are made throughout this disclosure. These standards are well known to those skilled in the art and will not be discussed in detail. To conform to the CCITT standard, all FAX machines have Modified Huffman (MH) encoding capability to compress that digitized data for transmission. Newer FAX machines may also employ MR or MMR encoding techniques to compress the data to a greater extent. The MH and MR data encoding are known as CCITT recommendation T.4 1-dimensional and 2-dimensional encoding, respectively, while the MMR is known as CCITT recommendation T.6 2-dimensional encoding. These data encoding techniques are well known and will not be discussed herein. It is to be understood that reference to a particular encoding capability infers that the particular FAX machine also has the ability to decode that particular data format. For example, a reference to a FAX machine with MMR encoding capability almost always means that the same FAX machine can decode MMR encoded data.
The standardized facsimile data encoding capabilities of a receiving FAX machine are automatically transmitted during what may be termed as the negotiation phase of a facsimile telephone call. The various phases of a facsimile transmission, shown in FIG. 1, are described in the CCITT standards.
Phase A, shown in FIG. 1, is the call establishment phase in which the telephonic communication is established between a calling station and a called station. The calling station is the station initiating the facsimile telephone call and the called station is the station receiving the facsimile telephone call. As is well known, both the calling station and the called station are able to transmit or receive facsimile messages.
Phase B is a pre-message procedure phase or negotiation phase for identifying and selecting facsimile data encoding capabilities between the calling station and the called station. In phase B, the receiving FAX machine transmits a digital identification signal (DIS) data frame that describes the particular data encoding formats that are recognizable to the receiving FAX machine. The individual data bits of the DIS data frame identify the particular facsimile data processing modes of the receiving FAX machine. The DIS data frame is defined by the CCITT standard and cannot be used for other purposes. As previously discussed, the capabilities include data encoding such as MH, MR, and MMR. The MH, MR, and MMR data encoding capabilities are defined within recommendation T.4 and recommendation T.6 of the CCITT standard. In addition to the identification of data encoding capabilities, the DIS data frame is used to provide information about the basic data processing capabilities of the receiving FAX machine. This may include limited information such as resolution (e.g., pixels per inch), paper sizes, and the like. These standardized facsimile data processing capabilities or modes are referred to herein as "CCITT encoding formats." The transmitting FAX machine responds with a confirming signal and selects a mutually compatible CCITT encoding format that allows the most efficient data transfer. The transmitting FAX machine encodes the data according to the selected CCITT encoding format and transmits it to the receiving FAX machine.
Phase C is the actual message transfer phase and comprises two simultaneous phases. Phase C1 is the "In-message" procedure phase, which controls the transfer of data between the transmitting FAX machine and the receiving FAX machine. This includes synchronization, error detection and correction, and line supervision. Phase C2 is the actual data transmission phase in which data is transferred by the transmitting FAX machine to the receiving FAX machine under control of the C1 phase. For simplicity, these simultaneous phases will be referred to as phase C.
Phase D is the post-message procedure phase in which information is transferred regarding the end of message signaling, confirmation signaling and end of facsimile signaling. Phase E is the call release phase in which the telephonic communication between the calling station and the called station is terminated.
The CCITT encoding formats permit basic facsimile communication. However, as with computers coupled together by a LAN, FAX machines may have data processing capabilities that can produce more efficient transmission than merely data encoding using one of the limited CCITT encoding formats. Some FAX machines are actually incorporated into computers by way of a FAX interface board. These computers may have great data processing capability, but the data processing capability cannot be called into play when transmitting or receiving a facsimile because one FAX machine does not know what data processing capabilities the other FAX machine possesses.
Therefore, it can be appreciated that there is a significant need for a system and method for communicating information about data processing capabilities between computers.