Patent Grant
8738792
This invention relates in general to time synchronization within and across a network of processing units, and more particularly, to server time protocol messages and methods that facilitate servers in a timing network synchronizing, for example, to a same root primary reference time.
For performance and data integrity reasons, computing systems that access shared data, such as SYSPLEX offered by International Business Machines Corporation, Armonk, N.Y., must be able to maintain time of day (TOD) clock synchronization to an accuracy that is better than best case communication time between the systems. Currently, in one example, to meet the synchronization requirements, a timer, such as the IBM® 9037 SYSPLEX timer, is used. This timer requires expensive dedicated timing links and a separate external box.
Other networks, such as the Network Timing Protocol (NTP), provide time synchronization, but do not meet the accuracy requirements of high-end systems. NTP requires that each server has access to an external time source that provides accuracy to a microsecond level in order to ensure all servers synchronize to the same reference time. This is a problem for those systems that do not have a capability to attach to external time servers that provide this level of accuracy. Further, a requirement of GPS receivers or similar attachment on each system may be considered infeasible for maintenance, security and reliability reasons.
The shortcomings of the prior art are overcome and additional advantages are provided through the provision of a method of exchanging messages for facilitating synchronization of processing units of a timing network. The method includes: generating an exchange time parameters (XTP) message command at a first processing unit, the XTP message command including a message command transmit timestamp field set by the first processing unit and a message command receive timestamp field which is unset by the first processing unit; transmitting the XTP message command to a second processing unit; setting the message command receive timestamp field in the XTP message command with the time that the XTP message command is received at the second processing unit; and generating an XTP message response at the second processing unit, the XTP message response including the message command transmit timestamp set by the first processing unit and the message command receive timestamp set by the second processing unit obtained from the XTP message command.
System and computer program products corresponding to the above-summarized methods are also described and claimed herein.
Additional features and advantages are realized through the techniques of the present invention. Other embodiments and aspects of the invention are described in detail herein and are considered a part of the claimed invention.
The subject matter which is regarded as the invention is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other objects, features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which:
In accordance with an aspect of the present invention, server time protocol (STP) messages and processing methods employing the same are provided for, for example, transferring timing information between two servers in a timing network to facilitate synchronization thereof. Exchange time parameters (XTP) messages and STP control (STC) messages are described.
Although various networks can be configured to include a stratum-1 server, one such network is a Coordinated Timing Network (CTN). In a Coordinated Timing Network, multiple distinct computing systems maintain time synchronization to form the Coordinated Timing Network. Systems in the Coordinated Timing Network employ a message based protocol, referred to as a Server Time Protocol (STP), to pass timekeeping information between the systems over existing, high-speed data links. This enables the time of day (TOD) clocks at each system to be synchronized to the accuracy required in today's high-end computing systems. Since the protocol makes use of technology within a computing system, synchronization accuracy scales as technology improves. A computing system that provides an STP facility is referred to as a time server or server herein.
A server defined in a CTN as a primary time server provides primary reference time for the CTN. The server in a CTN that determines CST (an estimate of the time-of-day (TOD) clock for the CTN) based on information from another server in the CTN is referred to as the secondary time server. The primary time server may obtain its time from an external time source, which provides the means to synchronize the time of day clocks in a CTN to a defined time standard.
Servers in a CTN that are in the synchronized state are assigned a value, referred to as a stratum level, that specifies the number of servers between it and a primary time server. A primary time server operates at a stratum level of 1; secondary time servers operate at a stratum level of 2 or above, which increases as the number of servers in the timing path to the stratum-1 increases. In general, the quality of timekeeping information decreases as the stratum level increases. The server that is unsynchronized is assigned a stratum level of 0.
The STP facility provides the procedures required to transmit, receive and process STP messages. STP messages are transmitted over one or more physical data links between servers. The data link that has been established between two servers is referred to as an STP path. The STP facility provides the facilities to establish and maintain STP paths.
STP messages include a message command and a message response. Two types of STP messages are supported. The exchange time parameters (XTP) message and the STP control (STC) message. The XTP message is used to exchange the timekeeping information used to determine CST for the CTN. STP control messages are used to set and modify various CTN parameters required by servers in the CTN.
A CTN can operate, for instance, as one of two types of configurations: either as a mixed CTN configuration or as an STP-only CTN configuration. In a mixed CTN configuration, the servers are configured to be part of both an STP network and an External Time Reference (ETR) network. In a mixed CTN configuration, the servers in the CTN are configured with the same, non-null ETR network ID and a timer (e.g., 9037 SYSPLEX timer) provides the primary time reference for the CTN. At least one server in the CTN is to step to timing signals provided by the SYSPLEX timer before synchronization can occur within the CTN. Servers not stepping to the sysplex timer are secondary time servers and achieve synchronization by exchanging STP signals as described further below.
As one example, each server stepping to the timing signals of the SYSPLEX timer receives the time protocol parameters and propagates the information to secondary time servers in the CTN, using, for instance, a CTN parameter update procedure. An example of this procedure is described in U.S. Ser. No. 11/468,352, entitled “Coordinated Timing Network Configuration Parameter Update Procedure”, Carlson et al., filed Aug. 30, 2006, which is hereby incorporated herein by reference in its entirety.
One example of a mixed CTN configuration 100 is described with reference to
Each local area network is coupled to a console 120 used in providing time synchronization within the network. Further, local area network 104 and local area network 110 are coupled to one another via a wide area network 112.
Servers A and B are coupled to an external time reference network 114, and Servers B and C are configured to be part of an STP network 116. Server B is at a stratum-1 level and Server C is at a stratum-2 level. STP links 118 are used to couple the STP facility of Server B with the STP facility of Server C.
In an STP-only CTN, the servers in the CTN are configured to be part of an STP network and none are configured to be part of an ETR network. One example of an STP-only network 150 is described with reference to
Further, LAN 156 is coupled to a console 170 and LAN 160 is coupled to a console 172. Console 170 is further coupled to an external time source (ETS) 174, such as a dial out to a telephone time service (e.g., ACTS: NIST Automated Computer Time Service). In this network, there is no ETR network. Server B has a stratum level of 1, and Servers A and C have a stratum level of 2.
The server that is to act as the active stratum-1 server in the network, such as an STP-only network, is specified as part of a stratum-1 configuration defined for the network. The stratum-1 configuration is maintained at each server of the network and provides information relating to the configuration of the network, including, for instance, the type of configuration defined for the network. The network can be configured as one of various types, including, for instance:
In one example, the stratum-1 configuration information is maintained in a control block, referred to as a stratum-1 configuration information block (SCIB), that is stored on or accessible to each server of the network. The SCIB is used to identify the stratum-1 configuration for a network.
One embodiment of a stratum-1 configuration information block 200 is described with reference to
In addition to the above control block, another control block, referred to as the new stratum-1 configuration information block (NSCIB), may be used to specify a new stratum-1 configuration for the CTN. Additionally, it may be used to specify an update to the CTN ID that is to occur concurrently with the stratum-1 configuration change.
In one example, the NSCIB at a server is meaningful when the server is configured to be part of an STP-only CTN configuration or if the STP-migration bit in the NSCIB is equal to one.
One embodiment of a new stratum-1 configuration information block 300 is described with reference to
If the new stratum-1 configuration information block is not to be used to specify an update to the CTN ID, then the block may not include the CTN ID change bit or the new CTN ID, as an example. Further details on coordinated timing networks and on defining a stratum-1 configuration for a timing network are described in the following co-filed applications: S. Carlson et al., “Facilitating Synchronization of Servers in a Coordinated Timing Network”, Ser. No. 60/887,584, filed Jan. 31, 2007; and S. Carlson, “Defining a Stratum-1 Configuration in a Coordinated Timing Network”, Ser. No. 60/887,562, filed Jan. 31, 2007, both of which are hereby incorporated herein by reference in their entirety.
As noted initially, in one aspect, provided herein are exchange time parameters (XTP) command and response messages, as well as server time protocol control (STC) messages for a server time protocol facility, such as described above. Again, server time protocol (STP) messages are transmitted over STP paths between two servers in the form of a message command and a message response. A message command is sent from a server to an attached server; and an STP message response is sent from a server to an attached server in response to a message command received from the attached server. The message response is sent to the attached server on the link from which the message command was received. As used herein, a server sending a message command is referred to as the message originator, while a server receiving a message command is referred to as the message recipient. A message command contains a message command code that indicates the type of message being transmitted. For example, the STP message command codes may support:
The message response contains a response code that describes the result of the attempt to execute the message command. General responses are defined below. Not all responses apply to all message commands. Additional command-dependent responses may be defined for individual commands. When multiple response conditions can be detected concurrently, the lowest numbered response code may be reported.
Command Codes:
The exchange time parameters (XTP) message is used to exchange timestamps, time keeping information and CTN-parameter information between two directly attached servers. The information in the message response is used by the message originator to calculate the round-trip delay, offset, and dispersion values that are used by STP clock filtering and selection algorithms to select a clock source. It is also used to set CTN time keeping parameters and ensure synchronization of the attached servers.
The STP facility at the server maintains a history of the timestamp and time keeping information received in XTP message responses in an XTP-trace array. The number of samples maintained in the array can vary. XTP-transmit procedures are used to transmit XTP message commands, and XTP-receive procedures are used to receive XTP messages, as described further below.
XTP Message Command
As shown by the example of
Continuing with
The message recipient checks for STP path error, and if detected, invokes error-recovery procedures. Otherwise, the recipient server stores the incoming-message-command-timestamp data from the message command into the timestamp data for the recipient server, and performs an XTP-message-response transmit procedure to generate and send a message response 440 (
XTP Message Response
Returning to
The format used for an XTP-message response by a primary-time server is dependent on whether a CTN-parameter update is in progress. If an update is in progress, then the primary-time server uses the format that contains the parameter being updated. When a CTN-parameter update is not in progress, the format-0 XTP-message response may be used for all responses. The format used for an XTP-message response by a secondary-time server is dependent on whether the server has a clock source. When the server has a clock source, it uses the same format as that provided in the last valid response from the clock source. When the server does not have a clock source, it uses the format-0 response.
Message Command Transmit
The XTP-message-command-transmit procedure is used to transmit the exchange time parameters (XTP) message command to a specified, attached server. The STP path that is used to transmit the message is determined using, for example, a model-dependent STP-path-selection procedure.
Initiative to issue an XTP-message command is established when the message-interval timer for an attached server expires. The message-interval parameter for the attached server specifies the rate at which XTP-message commands are sent to the attached server.
The XTP-message-command-transmit procedure builds the message header, sets the message command code equal to the XTP-command code and builds the remainder of the XTP-message command. Immediately prior to sending the message, the message-command-transmit timestamp in the message command is set equal to the current TOD clock and the command is transmitted over the selected STP path. If an STP-message-undeliverable condition is detected, an invalid entry is added to the XTP-trace array.
Message Response Transmit
The message-response transmit procedure is used to transmit an XTP message response following receipt of an XTP-message command. The procedure builds the message-response header, sets the message-response code and builds the remainder of the XTP-message response. Immediately prior to sending the message, the message-response-transmit timestamp in the message response is set equal to the current time of day value and the response is transmitted on the STP path over which the message command was received.
XTP Receive Procedures
XTP-receive procedures are used to receive an XTP-message command or an XTP-message response.
Message Response Received
The procedure initially checks for an STP-path error 1110, and if an error is detected, an error-recovery procedure 1120 is invoked. If no STP-path error is detected, then the STP-message response is added to the XTP trace array and the entry code is set 1130.
The entry code is set to a first value 1140 to indicate the timestamp data is invalid if any of the following conditions are true:
If the entry code is not set to the first value, then the entry code is set to a second value 1150 to indicate that the timestamp data is valid, but the entry should not be used to determine a usable clock source if any of the following conditions are true:
If the entry code is not set to the first value or second value, then the entry code is set to a third value 1160 (
If the server is in the synchronized state, then the data in the format-dependent data field of the most recent valid time-keeping message response is checked for updates and, if detected, the data is used to update the server's CTN parameters 1170.
Message Command Received
The XTP-message-command-receive procedure is invoked each time an XTP-message command is received on an STP path.
STC Control Messages
An STP control (STC) message command is used to request CTN-parameter updates, to establish and remove STP paths, and to read configuration information from attached servers. The operation-code field in the message command specifies the operation to be performed.
As noted above, STC operations are specified by the operation code transmitted in each STC control message. The following types of operations are supported as described below: Update Request Operations; Read Operations; and Notification Operations.
Update Request Operations
An update request STP control message is sent by a secondary STP server to notify the active-stratum-1 server of a CTN-parameter update request. If the secondary-time server is directly attached to an active-stratum-1 server, then the secondary-time server sends the message to the active-stratum-1 server. If the secondary-time server is not directly attached to an active-stratum-1 server, then the secondary-time server sends the message to all attached servers that have a lower stratum level.
A secondary-time server has initiative to send an update-request message upon receipt of a console command request to update a CTN parameter or upon receipt of an update-request operation from another secondary-time server. When a secondary-time server receives an update-request message, it sends the update-request parameter in the message to all attached servers with a lower stratum level using a new update-request message.
Upon receiving an update-request operation, the active-stratum-1 server performs the CTN-parameter update procedure.
Request Stratum-1 Configuration Change
The request-stratum-1 configuration change operation is issued by a secondary-time server to request a change to the stratum-1 configuration for the CTN. The operation is issued by a secondary-time server after it has accepted a console command to modify the stratum-1 configuration for the CTN. A secondary-time server accepts the modify-stratum-1 configuration command only when the new stratum-1 configuration specifies the secondary-time server as the new active-stratum-1 server. The operation-dependent area of the message command is illustrated in
The operation-dependent area of the message response does not contain meaningful data.
Read Operations
Read commands are used to obtain CTN parameters and configuration information from attached servers. The data that may be obtained from an attached server includes: Node Attachment State; and CTN Parameters.
Read Node Attachment State
The read-node-attachment state command returns the attachment state for the node descriptor provided in the operation-dependent area. Valid responses for this operation may again include:
When the response code is a particular value, the operation-dependent area of the message response may contain an attachment state bit.
The read-CTN-parameters operation reads CTN parameters from the attached server. The CTN parameters that are to be returned are specified in the message command operation-dependent area. The message command operation-dependent area may include:
Valid response codes for the operations may be as follows:
When a particular response code is returned, the operation-dependent area of the message response block has (in one embodiment) the format illustrated in
New Stratum-1 Configuration Information Data Area:
TCPIB Data Area:
Current Stratum-1 Configuration Information Data Area:
Notification operations are used to establish or remove an STP path and for communication between the alternate-stratum-1 server and the arbiter during a stratum-1 takeover.
Establish STP Path
The establish-STP-path (ESP) operation is performed as part of the STP-path initialization procedure to establish a path between two servers. The operation is used to exchange and validate certain parameters associated with each of the attached servers. The message command operation-dependent area has, for example, the format illustrated in
The ESP message response block does not have any operation-dependent data. The following responses are valid for the operation:
The remove-STP-path operation removes an established STP path to an attached server. The sending server sets the path link state to uninitialized as a result of the operation. The message command and message response do not include any operation-dependent data. Valid responses for the operation include:
The sending server sets the path state to uninitialized, and the reason to indicate initialization-not-complete as a result of the operation, regardless of the response.
Set Arbiter Takeover Mode
The set-arbiter-takeover mode operation is issued to the arbiter server by the alternate-stratum-1 server to put the arbiter into takeover mode. The receiving server returns the arbiter takeover-state flag in the response block.
The message command operation-dependent data area has the format illustrated in
The reset-arbiter takeover mode operation is issued to the arbiter server by the alternate-stratum-1 server to take the arbiter out of takeover mode. The message command operation-dependent area does not include any data. Valid responses for the operation include:
The arbiter-takeover-state-active operation is issued to the alternate-stratum-1 server by the arbiter to notify the alternate-stratum-1 server that the arbiter has entered the takeover-active state. The message command operation-dependent area does not include any information. Valid responses for the operation include:
In one embodiment, one or more aspects of the present invention can be executed in a processing environment that is based on one architecture, which may be referred to as a native architecture, but emulates another architecture, which may be referred to as a guest architecture. As examples, the native architecture is the Power4 or PowerPC® architecture offered by International Business Machines Corporation, Armonk, N.Y., or an Intel® architecture offered by Intel Corporation; and the guest architecture is the z/Architecture® also offered by International Business Machines Corporation, Armonk, N.Y. Aspects of the z/Architecture® are described in “z/Architecture Principles of Operation,” IBM Publication No. SA22-7832-04, September 2005, which is hereby incorporated herein by reference in its entirety. In such an environment instructions and/or logic, which is specified in the z/Architecture® and designed to execute on a z/Architecture® machine, is emulated to execute on an architecture other than the z/Architecture®. One example of this processing environment is described with reference to
Referring to
Native central processing unit 1802 includes one or more native registers 1810, such as one or more general purpose registers and/or one or more special purpose registers, used during processing within the environment. These registers include information that represent the state of the environment at any particular point in time.
Moreover, native central processing unit 1802 executes instructions and code that are stored in memory 1804. In one particular example, the central processing unit executes emulator code 1812 stored in memory 1804. This code enables the processing environment configured in one architecture to emulate another architecture. For instance, emulator code 1812 allows machines based on architectures other than the z/Architecture, such as Power PC® processors, pSeries® servers, xSeries® servers, HP Superdome® servers, or others to emulate the z/Architecture® and to execute software and instructions developed based on the z/Architecture®.
Further details relating to emulator code 1812 are described with reference to
Emulator code 1812 further includes an instruction translation routine 1904 to determine the type of guest instruction that has been obtained and to provide one or more native instructions 1909 that correspond to the guest instruction. In one example, the providing includes creating during, for instance, a translation process, a native stream of instructions for a given guest instruction. This includes identifying the function and creating the equivalent native instructions. In a further example, the providing of the native instructions includes selecting a code segment in the emulator that is associated with the guest instruction. For instance, each guest instruction has an associated code segment in the emulator, which includes a sequence of one or more native instructions, and that code segment is selected to be executed.
Emulator code 1812 further includes an emulation control routine 1906 to cause the native instructions to be executed. Emulation control routine 1906 may cause native CPU 1802 to execute a routine of native instructions that emulate one or more previously obtained guest instructions and, at the conclusion of such execution, to return control to the instruction fetch routine to emulate the obtaining of the next guest instruction or group of guest instructions. Execution of the native instructions 1909 may include loading data into a register from memory 1804; storing data back to memory from a register; or performing some type of arithmetic or logical operation, as determined by the translation routine. Each routine is, for instance, implemented in software, which is stored in memory and executed by the native central processing unit 1802. In other examples, one or more of the routines or operations are implemented in firmware, hardware, software or some combination thereof. The registers of the emulated guest processor may be emulated using the registers 1810 of the native CPU or by using locations in memory 1804. In embodiments, the guest instructions 1902, native instructions 1909, and emulation code 1812 may reside in the same memory or may be dispersed among different memory devices.
In yet a further embodiment, a data processing system suitable for storing and/or executing program code is usable that includes at least one processor coupled directly or indirectly to memory elements through a system bus. The memory elements include, for instance, local memory employed during actual execution of the program code, bulk storage, and cache memory which provide temporary storage of at least some program code in order to reduce the number of times code must be retrieved from bulk storage during execution.
Input/Output or I/O devices (including, but not limited to, keyboards, displays, pointing devices, DASD, tape, CDs, DVDs, thumb drives and other memory media, etc.) can be coupled to the system either directly or through intervening I/O controllers. Network adapters may also be coupled to the system to enable the data processing system to become coupled to other data processing systems or remote printers or storage devices through intervening private or public networks. Modems, cable modems, and Ethernet cards are just a few of the available types of network adapters.
One or more aspects of the present invention can be included in an article of manufacture (e.g., one or more computer program products) having, for instance, computer usable media. The media has therein, for instance, computer readable program code means or logic (e.g., instructions, code, commands, etc.) to provide and facilitate the capabilities of the present invention. The article of manufacture can be included as a part of a system (e.g., computer system) or sold separately.
One example of an article of manufacture or a computer program product incorporating one or more aspects of the present invention is described with reference to
A sequence of program instructions or a logical assembly of one or more interrelated modules defined by one or more computer readable program code means or logic direct the performance of one or more aspects of the present invention.
Described herein are capabilities that facilitate the maintaining of time synchronization by multiple distinct computing systems to form a Coordinated Timing Network. Servers in the timing network make use of the Server Time Protocol to pass timekeeping information over existing high speed data links between systems that provide the capability for the time of day clocks at each system to be synchronized to the accuracy required in today's high end computing systems. The use of STP over high-speed, low latency links provides the capability to synchronize all systems in the CTN to the accuracy of, for instance, a few microseconds when based on a reference time provided by a single server.
STP provides the capability to set and maintain timekeeping information within the CTN, such as time zone, daylight savings time offset, and a leap seconds offset. The information may be updated within the CTN in a scheduled and coherent fashion, such that all changes occur at the same time at all servers in the CTN. This prevents potential system exposures and disruptions that occur when these parameters are updated in a haphazard fashion, creating time setting discrepancies between computers.
CTN parameters may be set and read by an operator via the STP console interface. CTN parameters include server connectivity, local time information, such as time zone and daylight savings time, and the leap seconds required to compute the UTC. The console itself is any element that provides an operator interface to display and set CTN parameters, and that has the capability to communicate with the STP facility.
Although one or more examples have been provided herein, these are only examples. Many variations are possible without departing from the spirit of the present invention. For instance, processing environments other than the examples provided herein may include and/or benefit from one or more aspects of the present invention. As an example. Further, the environment need not be based on the z/Architecture®, but instead can be based on other architectures offered by, for instance, IBM®, Intel®, Sun Microsystems, as well as others. Yet further, the environment can include multiple processors, be partitioned, and/or be coupled to other systems, as examples.
Moreover, although various control blocks have been described, each of these control blocks can include additional, less and/or different information. The location within the control block and the size of each field within the control block can vary for different embodiments.
As used herein, the term “obtaining” includes, but is not limited to, fetching, receiving, having, providing, being provided, creating, developing, etc.
Additional information regarding timing networks is provided in the following patent applications, each of which is hereby incorporated herein by reference in its entirety: U.S. Provisional Ser. No. 60/887,584 entitled “Facilitating Synchronization Of Servers In A Coordinated Timing Network”, filed Jan. 31, 2007; U.S. Ser. No. 11/876,152 entitled “Facilitating Synchronization Of Servers In A Coordinated Timing Network”, filed Oct. 22, 2007; U.S. Ser. No. 11/876,199 entitled “Definition Of A Primary Active Server In A Coordinated Timing Network”, filed Oct. 22, 2007; U.S. Provisional Ser. No. 60/887,562 entitled “Defining A Stratum-1 Configuration In A Coordinated Timing Network”, filed Jan. 31, 2007; U.S. Ser. No. 11,876,240 entitled “Employing Configuration Information To Determine The Role Of A Server In A Coordinated Timing Network”, filed Oct. 22, 2007; U.S. Provisional Ser. No. 60/887,576 entitled “Method And System For Establishing A Logical Path Between Servers In A Coordinated Timing Network”, filed Jan. 31, 2007; U.S. Ser. No. 11,876,272 entitled “Establishing A Logical Path Between Servers In A Coordinated Timing Network”, filed Oct. 22, 2007; U.S. Provisional Ser. No. 60/887,586 entitled “Facilitating Recovery In A Coordinated Timing Network”, filed Jan. 31, 2007; U.S. Ser. No. 11/876,323 entitled “Facilitating Recovery In A Coordinated Timing Network, And Methods Therefor”, filed Oct. 22, 2007; U.S. Provisional Ser. No. 60/887,544 entitled “Channel Subsystem Server Time Protocol Commands”, filed Jan. 31, 2007; U.S. Ser. No. 11/876,796 entitled Channel Subsystem Server Time Protocol Commands and System Therefor”, filed Oct. 23, 2007; U.S. Provisional Ser. No. 60/887,512 entitled “Server Time Protocol Messages And Methods”, filed Jan. 31, 2007; U.S. Ser. No. 11/940,558 entitled “Server Time Protocol Control Messages and Methods”, filed herewith; U.S. Ser. No. 11/468,352, entitled “Coordinated Timing Network Configuration Parameter Update Procedure,” filed Aug. 30, 2006; U.S. Ser. No. 11/460,025, entitled “Directly Obtaining By Application Programs Information Usable In Determining Clock Accuracy,” filed Jul. 26, 2006; U.S. Ser. No. 11/223,886, entitled “System And Method For TOD-Clock Steering;” U.S. Ser. No. 11/532,168, entitled “Synchronization Signal For TOD-Clock Steering Adjustment;” U.S. Ser. No. 11/468,501, entitled “Managing Data Access Via A Loop Only If Changed Locking Facility;” U.S. Ser. No. 11/223,878, entitled Clock Filter Dispersion;” U.S. Ser. No. 11/223,876, entitled “Method And System For Clock Skew And Offset Estimation;” U.S. Ser. No. 11/223,577, entitled “Use Of T4 Timestamps To Calculate Clock Offset And Skew;” and U.S. Ser. No. 11/223,642 entitled “System And Method For Calibrating A TOD Clock.”
The capabilities of one or more aspects of the present invention can be implemented in software, firmware, hardware, or some combination thereof. At least one program storage device readable by a machine embodying at least one program of instructions executable by the machine to perform the capabilities of the present invention can be provided.
The flow diagrams depicted herein are just examples. There may be many variations to these diagrams or the steps (or operations) described therein without departing from the spirit of the invention. For instance, the steps may be performed in a differing order, or steps may be added, deleted, or modified. All of these variations are considered a part of the claimed invention.
Although embodiments have been depicted and described in detail herein, it will be apparent to those skilled in the relevant art that various modifications, additions, substitutions and the like can be made without departing from the spirit of the invention, and these are, therefore, considered to be within the scope of the invention as defined in the claims.
This application claims priority to U.S. Provisional Application No. 60/887,512, entitled “Server Time Protocol Messages and Methods”, filed Jan. 31, 2007, which is hereby incorporated herein by reference in its entirety.
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