Multiplex communications – Wide area network – Packet switching
Patent
1986-01-29
1988-04-05
Olms, Douglas W.
Multiplex communications
Wide area network
Packet switching
370100, H04J 326
Patent
active
047363703
DESCRIPTION:
BRIEF SUMMARY
CROSS REFERENCES TO RELATED APPLICATIONS
This application is related to U.S. application having Ser. No. 758,787.
FIELD OF THE INVENTION
1. Background of the Invention
The present invention relates to a data transmission system, and particularly relates to a transmitting data processing system for transmitting data with a preamble pattern along a transmission line.
2. Description of the Related Art
In a data transmission system such as a local area network (LAN), a plurality of nodes are located along a transmission line as shown in FIG. 1. In FIG. 1, reference numeral 101 is a transmission line and reference symbols N.sub.1, N.sub.2, N.sub.3, - - - , and N.sub.n are the nodes. A preamble pattern is added at the head or beginning of a frame (packet) of data to allow extracting a clock signal from it to relay the data through the nodes. The "Node" herein means an apparatus having the function of relaying the data to next node. The preamble pattern is defined in an IEEE Standard (draft) 802.3.
According to the IEEE Standard 802.3, the frame consists of eight fields: a field for a preamble pattern, a field for a start field delimiter (SFD), a field for a destination address, a field for a source address, a field for indicating the length of the following field, a field of logical link control (LLC) data, and others. The fields are timely arranged in the order of the above description. The preamble pattern is always positioned at the head or beginning of the frame combined with the SFD pattern. The preamble pattern consists of seven octets (56 bits) each looking like "10101010", and the SFD pattern consists of one octet (8 bits) looking like "10101011" in which the last two bits "11" indicated that the preamble pattern is finished and other data will follow after the two bits "11". Accordingly, in this disclosure, the frame will be divided into two fields for simplicity: a field for a preamble pattern consisting of eight octets (64 bits), in which each of the first seven octets is bits like 10101010 and the last octet is bits like 10101011, and a field for transmitting data which includes the address, the data to be sent, and others.
When a node receives a frame, a clock signal is extracted from the preamble pattern of the frame; the clock signal is used for reforming or recreating the received frame in the node and transmitting the reformed frame to another node. Because of the preamble pattern's character, a beginning part of the preamble pattern is dissipated during the period in which the clock signal is extracted from the preamble pattern; therefore, a minimum bit length is necessary for the preamble pattern as the IEEE standard specifies, and if the number of nodes increases, the bit-length of the preamble pattern must be more than 64 bits in an initial state. If the above was not considered, many parts of the preamble pattern would be dissipated, or lost so that the clock signal could not be extracted or even a part of the transmitting data would be dissipated at the nodes near the end of the transmission line.
Recently, the LAN system has been used in a wide area, so that the transmission line is lengthened and the number of nodes increases; accordingly, the preamble pattern must have a long bit length to maintain the IEEE standard at the nodes near the end of the transmission line, which causes a further problem in that the data transmission efficiency will be decreased because each frame has a long preamble pattern on average. If the dissipated or lost part is restored at each node, the problem can be solved and the serviceable or usable area of the data transmission system can be extended.
The dissipation of the beginning part of the preamble pattern is shown in FIG. 2. FIG. 2(a) shows a frame F.sub.1 which comes from node N.sub.1 and is received at node N.sub.2, assume that the frame F.sub.1 includes a standard preamble pattern hereinafter. FIG. 2(b) shows a frame F.sub.2 sent from node N.sub.2 to node N.sub.3. The frame F.sub.1 is composed of a preamble pattern C.sub.1 and transmitting data A,
REFERENCES:
patent: 4099024 (1978-04-01), Boggs et al.
patent: 4593154 (1986-06-01), Takeda et al.
patent: 4596013 (1986-06-01), Tashiro et al.
Pittroff et al., "Don't Forget the Physical Layer", New Electronic, vol. 17, No. 7, Apr. 1984, pp. 37, 39-41.
Hirome Masashi
Shikata Kiyotaka
Fujitsu Limited
Olms Douglas W.
LandOfFree
Transmitting data processing system does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Transmitting data processing system, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Transmitting data processing system will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2238554