System for communicating a software-generated pulse waveform between two servers in a network

A system for monitoring a status condition of a first server in a server network with a second server in the network, comprising:

• a device, coupled to the first and second servers;
• a pulse transmitter module in the first server, for successively transmitting first and second command signals to said device wherein the first command signal places said device in a first status condition and the second command signal places the device in a second status condition;
• a pulse receiver module in the second server, for monitoring a status condition of said device, wherein a change in the status condition of the device indicates that the first server is operational;
• wherein:
• said device is a SCSI device;
• said first command is a SCSI Reserve Unit command;
• said first status condition is a reserved status;
• said second command is a SCSI Release Unit command;
• and said second status condition is a released status.

A system for assigning control over a network resource between a first server and a second server in the network, comprising:

• a SCSI device coupled to the first and second servers;
• a pulse transmitter module, in the first server, for transmitting SCSI Reserve and Release commands from the server to a SCSI device;
• a pulse receiver module, in the second server, for monitoring a released/reserved status of the SCSI device, wherein a change in the released/reserved status of the SCSI device indicates that the first server remains operational and a constant reserved status of the SCSI device indicates that the first server has failed;
• and
• a Network Directory Database, coupled to the first and second servers, for designating a host server and a backup server for each device in the network, wherein the Network Directory Database designates the second server as the host server of said device if it is determined that the first server has failed.

A system for synchronizing a first operation carried out by a first server with a second operation carried out by a second server, comprising:

• a device coupled to the first and second servers;
• a pulse transmitter module, in the first server, for transmitting a software-generated pulse waveform, having a first frequency, from the first server to said device, wherein said pulse transmitter module comprises a synchronization module for transmitting a synchronization signal to said device by changing the frequency of said pulse waveform to a second frequency and changing the frequency of said pulse waveform back to the first frequency;
• a pulse receiver module, in the second server, for receiving said pulse waveform by monitoring a status condition of said device, wherein said pulse receiver module comprises a frequency detector module for detecting the synchronization signal by detecting a first change in frequency of said pulse waveform from the first frequency to the second frequency and for detecting a second change in frequency from the second frequency back to the first frequency;
• and
• wherein said pulse transmitter module and said pulse receiver module each further include a timing module for setting a reference point in time at a beginning of a first cycle of said pulse waveform after it has returned to the first frequency.

A system for synchronizing a first operation carried out by a first server with a second operation carried out by a second server, comprising:

• a device coupled to the first and second servers;
• a pulse transmitter module, in the first server, for transmitting a software-generated pulse waveform from the first server to a device coupled to the first server, wherein said pulse waveform is uniform such that a first period of time corresponding to a logic level high of said pulse waveform is equal to a second period of time corresponding to a logic level low of said pulse waveform, and wherein said logic level high of said pulse waveform sets a status condition of said device to a first state and said logic level low of said pulse waveform sets the status condition of said device to a second state;
• a pulse receiver module, in the second server, for receiving the software-generated pulse waveform with the second server by sampling the status condition of said device;
• a synchronization module, in the first server, for transmitting a synchronization signal from the first server to said device by frequency modulating the software-generated pulse waveform so as to vary at least one of the first and second periods;
• a detection module, in the second server, for receiving the synchronization signal with the second server by detecting a change in frequency of said pulse waveform;
• and
• wherein, when said pulse transmitter module resumes transmission of the uniform pulse waveform to said device, the detection module detects a second change in frequency and marks a beginning of a first cycle of the uniform pulse waveform, after the synchronization signal, as a reference point in time, and the first server also marks the beginning of the first cycle of the uniform pulse waveform as a reference point in time.

A system for synchronizing a first operation performed by a first server with a second operation performed by a second server, comprising:

• a pulse transmitter program, in the first server, for successively transmitting SCSI Reserve and Release commands from the first server to a SCSI device so as to place the SCSI device in successive states of reserved and released status, wherein the states of the SCSI device serve as a basis for a software-generated pulse waveform;
• a pulse receiver program, in the second server, for sampling the software-generated pulse waveform at a predetermined sampling rate;
• wherein said pulse receiver program detects when said pulse waveform has changed from a first frequency to a second frequency and back to the first frequency;
• and
• wherein the first and second server each record a beginning of a first cycle of said pulse waveform after it has changed from the second frequency back to the first frequency as a common reference point in time.

A system for providing communications between a first server and a second server, comprising:

• a first device coupled to the first and second servers;
• a first pulse transmitter module, in the first server, for transmitting a first software-generated pulse waveform from the first server to the first device, wherein the first pulse waveform changes a status condition of the first device between a first state and a second state;
• a first pulse receiver module, in the second device, for receiving the first software-generated pulse waveform with the second server by sampling the status condition of the first device;
• a first modulation module, in the first server, for frequency modulating the first pulse waveform so as to encode a message into the first pulse waveform;
• and
• a first reading module, in to the second server, for reading the message by sampling the status condition of the first device at a predetermined first sampling rate.

A system for monitoring a status condition of a first server with a second server in a server network, comprising:

• means for transmitting a software-generated pulse waveform from the first server to a device coupled to the first server, wherein the software-generated pulse waveform comprises a first command corresponding to a logic level low and a second command corresponding to a logic level high;
• means for setting said device to a first state during logic level lows of said pulse waveform and to a second state during logic level highs of said pulse waveform;
• and
• means for receiving the software-generated pulse waveform with the second server by determining when said device is in the first state and when it is in the second state.

A system for assigning control over a network resource between a first server and a second server in the network, comprising:

• means for transmitting SCSI Reserve and Release commands from the first server to a SCSI device, coupled to the first server;
• means for monitoring a released/reserved status of the SCSI device with the second server;
• means for determining if the first server is operational;
• and
• means for assigning control over the SCSI device to the second server if it is determined that the first server has failed.

A system for synchronizing a first operation carried out by a first server with a second operation carried out by a second server, comprising:

• means for transmitting a software-generated pulse waveform, having a first frequency, from the first server to a device coupled to the first server;
• means for receiving said pulse waveform with the second server by monitoring a status condition of said device;
• means for transmitting a synchronization signal to said device by changing the frequency of said pulse waveform to a second frequency;
• means for detecting the synchronization signal by detecting a change in frequency of said pulse waveform;
• means for changing the frequency of said pulse waveform back to the first frequency;
• means for detecting a change in frequency from the second frequency back to the first frequency;
• and
• means for setting a reference point in time at a beginning of a first cycle of said pulse waveform after it has returned to the first frequency.

A system for synchronizing a first operation carried out by a first server with a second operation carried out by a second server, comprising:

• means for transmitting a software-generated pulse waveform from the first server to a device coupled to the first server, wherein said pulse waveform is uniform such that a first period of time corresponding to a logic level high of said pulse waveform is equal to a second period of time corresponding to a logic level low of said pulse waveform, and wherein said logic level high of said pulse waveform sets a status condition of said device to a first state and said logic level low of said pulse waveform sets the status condition of said device to a second state;
• means for receiving the software-generated pulse waveform with the second server by sampling the status condition of said device;
• means for transmitting a synchronization signal from the first server to said device by frequency modulating the software-generated pulse waveform so as to vary at least one of the first and second periods;
• means for receiving the synchronization signal with the second server by detecting a change in frequency of said pulse waveform;
• and
• means for resuming transmission of the uniform pulse waveform to said device, wherein the second server detects a second change in frequency and marks a beginning of a first cycle of the uniform pulse waveform, after the synchronization signal, as a reference point in time, and the first server also marks the beginning of the first cycle of the uniform pulse waveform as a reference point in time.

A system for synchronizing a first operation performed by a first server with a second operation performed by a second server, comprising:

• means for executing a pulse transmitter program in the first server, said program successively transmitting SCSI Reserve and Release commands from the first server to a SCSI device so as to place the SCSI device in successive states of reserved and released status, wherein the states of the SCSI device serve as a basis for a software-generated pulse waveform;
• means for executing a pulse receiver program in the second server, said program sampling the software-generated pulse waveform at a predetermined sampling rate;
• means for determining when said pulse waveform has changed from a first frequency to a second frequency;
• and
• means for determining when said pulse waveform has changed from the second frequency back to the first frequency, wherein the first and second server each record a beginning of a first cycle of said pulse waveform after it has changed from the second frequency back to the first frequency as a common reference point in time.

A system for providing communications between a first server and a second server, comprising:

• means for transmitting a first software-generated pulse waveform from the first server to a first device coupled to the first server, wherein the first pulse waveform changes a status condition of the first device between a first state and a second state;
• means for receiving the first software-generated pulse waveform with the second server by sampling the status condition of the first device;
• means for frequency modulating the first pulse waveform so as to encode a message into said pulse waveform;
• and
• means for reading the message with the second server by sampling the status condition of the first device at a predetermined first sampling rate.