Multiplex communications – Channel assignment techniques – Polling
Patent
1997-11-17
2000-03-28
Nguyen, Chau
Multiplex communications
Channel assignment techniques
Polling
370461, H04L 12403, H04L 1243
Patent
active
060440856
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to data bus systems and, in particular, to a ring bus data transfer system. Data transfer systems, such as digital video signal processing systems, process data at high data rates and require correspondingly high bandwidth bus systems for data transfer. For example, digital video data in MPEG format exhibits data rates of 4 to 8 Mbits per second. A bus system based on packetized data may provide sufficient bandwidth. However, hardware and software for implementing packetized systems may be costly, making it impractical for consumer electronic equipment. In addition, a packet bus may require excessive "overhead" such as packet processing delays that preclude providing the high data rates required for MPEG data transfer.
A high data rate data transfer bus which may be constructed at a relatively low cost, and which does not require a high overhead, is desirable for interconnecting consumer electronic equipment.
In accordance with one aspect of the invention, a data transfer bus termed the BeeBus (BBUS) transfers data in bus cycles, each including at least one bit of a control channel. The BBUS is a high data rate bus system which may be used for transfer of digital video data. More specifically, the BBUS system is a time division multiplexed (TDM) bus with a total capacity of 88 Mbits/sec. that is designed to transfer data transparently from a source node to a destination node on the bus. The BBUS operates by serially transmitting nine-bit words from node to node on the ring. Synchronization is maintained among the nodes by transmitting bus cycles of 88 nine-bit words, with the initial word of each bus cycle being a bus cycle synchronization word. Because it may be desired to connect to consumer electronic equipment which has been designed to attach to a prior art consumer electronic bus, called the CEBUS, the BBUS system includes a CEBUS-compatible control channel. One bit of the bus cycle synchronization word carries the data for the CEBUS-compatible control channel The BBUS is designed to carry eight data channels, which can be grouped into blocks to provide the necessary capacity for any combination of number of channels and channel capacity as long as the total number of channels is eight or less, and the total assigned capacity is 88 Mbs or less.
The CEBUS-compatible control bus included in the BBUS system has a message structure that does not involve arbitration on transmission. Each device has a preassigned control channel slot with a capacity well in excess of 10 kbs. Each device has the channel capability to receive messages from 31 other devices simultaneously. However, it is envisioned that the receiving device will process only one message at a time. Thus arbitration will be done by the receiving device, not the transmitting device. The receiving device will process messages in a round robin fashion, one message at a time. Because the message length is about 32 bytes, all control channel messages will be sent with this fixed length, and all messages will start with the same control cycle time slot. This slot is the basic operating system sync. It occurs every 32 control device slots x 32 message slots which is approximately 8 ms. as explained below. Thus a control channel message can be sent every 8 ms. (Sixteen device to device messages could be sent simultaneously.) This compares to about 25 ms. for a CEBUS control message.
As described above, the BBUS transfers information on the CEBUS-compatible control channel one bit per bus cycle (consisting of 88 nine-bit words). This requires message rejection by the receiving device, and can cause possible grid lock and multiple message transmission. A control channel transmission method which obviates these problems is desirable.
In accordance with another aspect of the present invention, each node in such a data transfer system competes for access to the control channel according to the following method. First, an encoded preamble is generated, having a number of successive states, each state being one of a superior and
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Emanuel Peter M
Lee Chiho Andrew
Nguyen Chau
Shoneman David T.
Thomson Consumer Electronics
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