Multiplex communications – Communication techniques for information carried in plural... – Combining or distributing information via frequency channels
Reexamination Certificate
1999-08-27
2004-02-17
Pham, Chi (Department: 2667)
Multiplex communications
Communication techniques for information carried in plural...
Combining or distributing information via frequency channels
C370S206000, C370S483000, C375S146000, C375S147000, C375S152000, C375S329000, C375S334000
Reexamination Certificate
active
06693917
ABSTRACT:
FIELD OF USE
The invention is useful for transmitting digital data such as management and control data out of band on a subchannel carrier transmitted on the same media as high speed data on a network or digital telephone line without interference therewith. The subchannel carrier uses a portion of the bandwidth that is not heavily populated by high energy frequency components of the high speed data traffic.
BACKGROUND OF THE INVENTION
In many large computer systems such as are found in banks, at credit card transaction processing centers; etc., huge amounts of data must be moved and stored. Typically, very large disk arrays are used to store the data and these disk arrays are connected to file servers. These type systems require of the server/disk connection high reliability, high speed, large throughput and large bandwidth since huge amounts of information are being processed and a system shutdown or slowdown adversely impacts customers (and possibly safety in the case of large air traffic control computer systems). Because these systems can be spread out over several buildings or even if all the servers and disk arrays are within the same building, the easiest way to interconnect all the servers and disk drives for maximum redundancy is through a local area network usually with a hub having drop lines connected to all servers, disk drives and other units. Because disks fail frequently and must be replaced by redundant disks, there is a large amount of management and control traffic that must go back and forth over the server/disk array connections and through the hub to the management and control process. This management and control traffic is necessary to determine which disks are on-line, where those disks are on the network, operational disk status, how many fans are still running (because when a fan fails, the disk it cools will probably be next), what servers are still operational, network fault status, network traffic conditions and statistics, etc.
Most if not all such digital data transmission systems require the bidirectional transmission of digital management and control data between nodes to collect data regarding the performance of the system and manage the various nodes, bridges etc. in the system. The out of band management and control data will be hereafter referred to as subchannel data.
There are many ways of modulating subchannel data onto a high speed digital signal, many of which are taught in a prior co-pending application of the assignee of the present application, which is hereby incorporated by reference. However, many of these prior art methodologies will only work in some systems and not in others. For example, modulating the subchannel data onto the clock by phase or frequency modulation will cause too much jitter in some systems, and also requires access to the high speed transmitter and receiver clock generation and clock recovery circuts. This is not possible in all cases, so a methodology that does not requires such access is preferred. The embodiments disclosed herein do not require such access. Amplitude modulation of the data with the subchannel modulation will not work in systems where digital buffers stand between the subchannel transmitter and the transmission media such as occurs where the high speed data media is fiber and a digital electronic-to-light media driver transducer is used to convert the digital high speed data to light signals.
Out of band management topologies get management data to and from the hub easily enough on separate network segments, which has its own set of problems described below. However, getting management and control data to and from the disk arrays in-band is more difficult. The management and control data sits in registers on a board in the disk array. In order to get this low speed, low priority data onto the high speed data path, special circuitry must be built in each disk array which interfaces these registers to the high speed data path. This circuitry functions to collect and format the management and control data into the type of data packets used in the high speed data path and to transmit these packets with the correct communication protocol to the hub. Since the management and control data does not consume an entire packet of the size used to send data on the high speed data path, some packet Space is empty and wasted. The need for this special circuitry to put the management and control data in the high speed data path makes the disk arrays more expensive and complex and placing management and control data in the high speed data packets wastes network throughput.
Some disk arrays store the management and control data on a separate disk drive which can be polled. However, this approach does not solve the problem of the need for special circuitry to get the management and control data into packets in the high speed data path and the resulting extra complexity and wasted throughput. It only allows time shifting thereby enabling transmission of the management and control data when network traffic volume is low and the throughput loss is not as significant. This time shifting is implemented by providing more storage capacity for the management and control data than is provided in the registers of the other prior art type disk arrays described above.
In some networks, management traffic is transmitted in-band by placing the management and control packets inside empty data packets and shipping these partially filled packets over the existing network connections between the server, hub and disk drives. This causes loss in throughput since the data packets are large and the management data does not fill the data packets entirely. This leads to wasted bandwidth. Further, arbitration by the management process to have one or more packets awarded to it for management traffic and to have access to the network so that transmissions to all servers and disk drive arrays of management messages consumes processing resources and network throughput unnecessarily.
One proposal has been made in the prior art to interleave special management and control packets in with the packet stream on the high speed data path to alleviate the above mentioned problem. However, this makes the design of the integrated circuits that implement the processing on the various network protocol layers more complex and difficult. So far this approach has been a commercial failure.
Another approach that has been tried in the prior art for transmission of management and control packets is to provide an entirely separate network for the management and control data such that each server and disk array is connected to the out of band management and control process running on a separate diagnostic processor by its own network segment. This substantially increases the wiring and connection cost of the system, especially in distributed systems, as every server and disk array must have an additional network segment connected thereto. In addition, each server and disk array uses a card slot for the management and control network card which adds to the expense, complexity and failure point count of each of these units.
A multiplexing approach that has been used in the prior art to send multiple television signals over the same media is represented by U.S. Pat. No. 3,623,105. This patent teaches receiving multiple video signals and translating each one to a different channel or subband and adding all the subband signals together to form a composite signal. The composite signal is then applied to the frequency control input of a VCO having a nominal frequency of 750 mHz. The output of the VCO is applied to one input of a pulse width modulator the other input of which receives an 18 gHz carrier. The pulse width modulator serves to key the 18 gHz carrier in accordance with the period of the signal from the VCO so that what is transmitted is a train of 18 gHz waves the width of each wave or “pulse” being set by the instantaneous period of the signal output from the VCO.
Another approach to implement a subchannel or auxiliary channel over a digital communic
Farzaneh Farivar
Feldman Richard Karl
Kauffman Michael Timothy
Broadcom Corporation
Hoang Thai
Pham Chi
Squire, Sanders & Demspey L.L.P.
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