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Topic: Logical clocks

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	LogicalTime - PineWiki
		Lamport's clock has the advantage of requiring no changes in the behavior of the underlying protocol, but has the disadvantage that clocks are entirely under the control of the logical-clock protocol and may as a result make huge jumps when a message is received.
		Because the protocol can't change the clock values on its own, when a message is received with a timestamp later than the current clock value, its delivery is delayed until the clock exceeds the message timestamp, at which point the receive event is assigned the extended clock value of the time of delivery.
		If some process's clock is too far off, it will have trouble getting its messages delivered quickly (if its clock is ahead) or receiving messages (if its clock is behind)—the net effect is to add a round-trip delay to that process equal to the difference between its clock and the clock of its interlocutor.
	pine.cs.yale.edu /pinewiki/LogicalTime (1623 words)

	RFC 1059 (rfc1059) - Network Time Protocol (version 1) specification and i
		Stratum (sys.stratum, peer.stratum, pkt.stratum) This is an integer indicating the stratum of the logical clock.
		Logical Clocks In order to implement a logical clock, the host must be equipped with a hardware clock consisting of an oscillator and interface and capable of the required precision and stability.
		The logical clock is implemented using a 48-bit Clock Register, which increments at 1000-Hz (at the decimal point), a 32-bit Clock-Adjust Register, which is used to slew the Clock Register in response to offset corrections, and a Drift-Compensation Register, which is used to trim the oscillator frequency.
	www.faqs.org /rfcs/rfc1059.html (14249 words)

	CS333 Lab A-2: Logical Clocks
		However, if the clocks at the sender and the receiver are sufficiently skewed, a clock-based trace of the events might report that the receive occurred before the send.
		Logical clocks do not "tick" like real time clocks, but instead keep track of the order of events that occur at each process, and ensure that events are assigned consistent logical times according to the following happens before relation.
		Whenever a process receives a message (receive event), it first compares its own logical clock time to the logical time sent with the message, and sets its own logical clock to be the maximum of the two times.
	www.cs.wustl.edu /~kjg/cs333/logicaltime.html (1170 words)

	Mandragor & Apinc - Free Documentation Base
		Synchronizing Network Clocks The algorithms described in the previous section are designed to achieve a high degree of accuracy and stability of the logical clocks in each participating host.
		Note the different nomenclature: The term "reference clock" applies to the physical clock itself, while the term "reference host" applies to the logical clock of the host to which it is connected.
		The clock is read via a 1200-bps asynchronous line, which introduces an additional delay of about 7 ms between the on-time transition of the first character and the interrupt at the middle of the first stop bit.
	docs.mandragor.org /files/RFCs/9xx/957 (8717 words)

	RFC 957 (rfc957) - Experiments in network clock synchronization
		Such clocks are readily available in several models ranging in accuracies of a few hundred milliseconds to less than a RFC 957 September 1985 Experiments in Network Clock Synchronization millisecond and are typically synchronized to special ground-based or satellite-based radio broadcasts.
		In typical clock interface designs such as the DEC KMV11-A RFC 957 September 1985 Experiments in Network Clock Synchronization the Counter Register is implemented in the interface as a buffered counter driven by a crystal oscillator.
		RFC 957 September 1985 Experiments in Network Clock Synchronization Given the considerations above, it would seem feasable for hosts to synchronize logical clocks to a particular power grid, but only if corrections were transmitted often enough to maintain the required accuracy and these corrections were delivered to the hosts essentially at the same time.
	www.faqs.org /rfcs/rfc957.html (8733 words)

	[No title]
		For this purpose each virtual clock residing in a physical host is assumed to run in synchronism with zero offset relative to the logical clock of that host.
		An uncorrected logical clock based on this equipment could be expected to maintain time to within a millisecond for at least eight minutes and to within three minutes in a year.
		Once each second the period of the logical clock is increased by a quantity equal to 1/1024 of this variable and the variable is decreased by the same quantity.
	www.isi.edu /in-notes/ien/ien173.txt (3141 words)

	[No title]
		"logical clocks" can be used so that distributed processes agree on the order of events (not absolute time), i.e.
		Lamport's logical clocks are used for timestamping messages so that processes can agree on the order that messages are sent among them.
		All processes agree that a message with a smaller timestamp was sent out "earlier" than a message with a larger timestamp, although in real absolute time terms that may not be true due to clock skew between the times processes update their logical clocks from the timestamps of incoming messages.
	www.mcs.drexel.edu /~shartley/MCS721/Lectures/11.sync (992 words)

	RFC957
		RFC 957 September 1985 Experiments in Network Clock Synchronization millisecond and are typically synchronized to special ground-based or satellite-based radio broadcasts.
		RFC 957 September 1985 Experiments in Network Clock Synchronization the Counter Register is implemented in the interface as a buffered counter driven by a crystal oscillator.
		RFC 957 September 1985 Experiments in Network Clock Synchronization Note that the standard deviations and extrema are higher than in the previous experiments, but the mean offset is about the same.
	www.unix.org.ua /rfc/rfc0957.html (8626 words)

	CIS 307: Clocks
		All logical clocks, whether scalar or vector, suffer of a basic problem: though they represent that an even occurred (or not) before another, they do not represent before by how much, that is, there is no measure of elapsed time.
		Another problem of logical clocks, even vector clocks, is that they cannot account for information exchanged outside of the computer systems, say because user A at system 1 receives output from the system and says that information to user B at system 2.
		The are an unlimited number of uses for synchronized physical clocks and for logical clocks.
	www.cis.temple.edu /~ingargio/cis307/readings/logicalClock.html (1653 words)

	[No title] (Site not responding. Last check: 2007-11-04)
		This kind of diagram was examplified in slide 12 The next two slides are about the many possible execution, or "traces", that may be observed for a distributed algorithm.
		A first possibility is offered by "logical clocks", then "vector clocks" improve on the same principle.
		You are proposed to experiment with Lamport's logical clock.
	www-inf.int-evry.fr /~meunier/DistrAlgos/lab5-6.htm (956 words)

	[No title]
		ANSWER : Yes, need to ensure that there is one clock tick between every two local events (e.g., two message transmissions) ---------------------------------------------------------------------------- ---------------------------------------------------------------------------- Topic: Logical clocks Problem: How do we maintain a global view of the order of events in the system that is consistent with the happens-before relationship?
		Logical time algorighm: Each node Ni maintains a local logical timestamp Ci.
		Property P2 is satisfied by (2)+(3) ---------------------------------------------------------------------------- ---------------------------------------------------------------------------- Topic: Example logical clocks Insert example timelines involving multiple nodes sending messages between one another.
	www.cs.utah.edu /classes/cs7460/lectures/lecture6.txt (378 words)

	Logical Clocks
		Implement a Logical Clock: Write a Java application that implements the logical clock algorithm described above.
		Build a simple visualization of the distributed system, where each process is displayed in a different color depending on its state.
		Time, clocks, and the ordering of events in a distributed system.
	www.cs.wustl.edu /cs/cs/archive/CS333_SP99/logicaltime.html (1128 words)

	Logical clock - Wikipedia, the free encyclopedia
		A logical clock is a mechanism for capturing chronological and causal relationships in a distributed system.
		As physical clocks cannot be perfectly synchronized, event timestamps derived from readings of physical clocks cannot in general be used to find out the order in which events happened.
		Lamport logical clocks, which is a monotonically increasing software counters
	en.wikipedia.org /wiki/Logical_clocks (118 words)

	COP 5611 L03
		We can extend the partial ordering of the happened-before relation to a total ordering on ervents, by using the logical clocks and resolving any ties by an arbitrary rule based on the processor/process ID.
		That is, the ordering we get from Lamport's clocks is not enough to guarantee that if two events precede one another in the ordering relation they are also causally related.
		The following Vector Clock scheme is intended to improve on this.
	www.cs.fsu.edu /~xyuan/cop5611/lecture5.html (652 words)

	[No title] (Site not responding. Last check: 2007-11-04)
		How close the clocks can be resynchronized depends upon how far apart they are allowed to drift (synchronization interval R).
		Instead of sending numbers, the processes send their clocks; instead of taking a majority, they use the median value.
		We compute CORR based on the midpoint of local time for all processors in the system, barring those where faults are likely to occur.
	www.utdallas.edu /~ilyen/course/advos.new/proj.05s/slides/C.ppt (830 words)

	Antique Clock - Ian Coote MBHI, clockmaker and repairer - sales and services (Site not responding. Last check: 2007-11-04)
		I hope there will be something of interest to professional horologists, interested amateurs and potential buyers.
		I have been repairing antique clocks and barometers for over 20 years, but I also buy and sell antique clocks, watches and barometers.
		I also sell new Branson Ultrasonic tanks for clock repairers.
	www.coote.demon.co.uk (169 words)

	[No title]
		The software clock Ci can be used to timestamp any event at pi.
		Enable clients to resynchronize sufficiently frequently to offset the rates of drift found in most computers.
		Whenever a message is sent between processes, the event of sending the message occurred before the event of receiving the message.
	www.daimi.au.dk /~jones/dDist2004aften/slides/DS10.ppt (886 words)

	[No title]
		0 typically, d = 1 R2: each message contains the clock value of its sender at sending time.
		When the receiving process receives a message, it set the maximum of received clock value or its own clock value as its new clock value, executes R1 and proceeds to deliver the message.
		Scalar clocks are consistent (show it) but not necessarily strongly consistent.
	www.ics.uci.edu /~rgupta/ics212/ics212/w2002/Source/clock-time.ppt (148 words)

	[No title]
		Extending logical timestamps for complete knowledge of causalityêîäï ”ððHð$ð( ð ðHðr ðH Sð¬4¿ÿð°ÐðÃ ð ðr ðH Sð6¿ÿðð°Ð`ðÃ ð ðH ðH ð0“”Þ½h¿ÿ ?ð ÿÿÿÌ33ÌÌÌÿ²²²rÃ ÈõíõÉCè,é(àà ò®/È 0ÒÕä·DTimes New Roman4Ñ´ÕÕì 0´ÕWo 0·DWingdingsRoman4Ñ´ÕÕì 0´ÕWo 0 ·DSymbolgsRoman4Ñ´ÕÕì 0´ÕWo 0¤ `ÿÿÿÿ¥ .© @£nÿý?" dd@ÿÿïÿÿÿÿÿÿ @@``ðð¨L9 cð$¿Àÿñÿ@ñ÷ðóÐ7ºuìÊ;2NÍÉÊ;úgþý4CdCdì 0¨Õ¬ÿÿÿÔþÿÿpûppû@
		ó¨ Observation about Logical Clocks àFor any two distinct events a and b, either ts.a
		Extending logical timestamps for complete knowledge of causalityêîäï ”ððð<ð$ð( ð ð<ðr ð< Sð¸v¿ÿð°ÐðÃ ð ðr ð< Sð`w¿ÿðð°Ð`ðÃ ð ðH ð< ð0“”Þ½h¿ÿ ?ð ÿÿÿÌ33ÌÌÌÿ²²²r{ø±$õíWø&C
	www.cse.msu.edu /~cse812/fall03/Slides/lc.ppt (418 words)

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