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Berkeley Algorithm
The Berkeley algorithm is a method of clock synchronisation in distributed computing which assumes no machine has an accurate time source. It was developed by Gusella and Zatti at the University of California, Berkeley in 1989. Like Cristian's algorithm, it is intended for use within intranets. The algorithm Unlike Cristian's algorithm, the server process in the Berkeley algorithm, called the ''leader'', periodically polls other ''follower'' processes. Generally speaking, the algorithm is: # A ''leader'' is chosen via an leader election, election process such as Chang and Roberts algorithm. # The ''leader'' polls the ''followers'' who reply with their time in a similar way to Cristian's algorithm. # The ''leader'' observes the round-trip time (RTT) of the messages and estimates the time of each ''follower'' and its own. # The ''leader'' then averages the clock times, ignoring any values it receives far outside the values of the others. # Instead of sending the updated current tim ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Clock Synchronisation
Clock synchronization is a topic in computer science and engineering that aims to coordinate otherwise independent clocks. Even when initially set accurately, real clocks will differ after some amount of time due to clock drift, caused by clocks counting time at slightly different rates. There are several problems that occur as a result of clock rate differences and several solutions, some being more acceptable than others in certain contexts. Terminology In serial communication, clock synchronization can refer to clock recovery which achieves frequency synchronization, as opposed to full phase synchronization. Such clock synchronization is used in synchronization in telecommunications and automatic baud rate detection. Plesiochronous or isochronous operation refers to a system with frequency synchronization and loose constraints on phase synchronization. Synchronous operation implies a tighter synchronization based on time perhaps in addition to frequency. Problems As a result ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Distributed Computing
A distributed system is a system whose components are located on different computer network, networked computers, which communicate and coordinate their actions by message passing, passing messages to one another from any system. Distributed computing is a field of computer science that studies distributed systems. The components of a distributed system interact with one another in order to achieve a common goal. Three significant challenges of distributed systems are: maintaining concurrency of components, overcoming the clock synchronization, lack of a global clock, and managing the independent failure of components. When a component of one system fails, the entire system does not fail. Examples of distributed systems vary from service-oriented architecture, SOA-based systems to massively multiplayer online games to peer-to-peer, peer-to-peer applications. A computer program that runs within a distributed system is called a distributed program, and ''distributed programming' ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cristian's Algorithm
Cristian's algorithm (introduced by Flaviu Cristian in 1989) is a method for clock synchronization which can be used in many fields of distributive computer science but is primarily used in low-latency intranets. Cristian observed that this simple algorithm is probabilistic, in that it only achieves synchronization if the round-trip time (RTT) of the request is short compared to required accuracy. It also suffers in implementations using a single server, making it unsuitable for many distributive applications where redundancy may be crucial. Description Cristian's algorithm works between a process ''P'', and a time server ''S'' connected to a time reference source. Put simply: # ''P'' requests the time from ''S'' at time . # After receiving the request from ''P'', ''S'' prepares a response and appends the time from its own clock. # ''P'' receives the response at time then sets its time to be , where . If the RTT is actually split equally between request and response, the sync ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Intranets
An intranet is a computer network for sharing information, easier communication, collaboration tools, operational systems, and other computing services within an organization, usually to the exclusion of access by outsiders. The term is used in contrast to public networks, such as the Internet, but uses the same technology based on the Internet protocol suite. An organization-wide intranet can constitute an important focal point of internal communication and collaboration, and provide a single starting point to access internal and external resources. In its simplest form, an intranet is established with the technologies for local area networks (LANs) and wide area networks (WANs). Many modern intranets have search engines, user profiles, blogs, mobile apps with notifications, and events planning within their infrastructure. An intranet is sometimes contrasted to an extranet. While an intranet is generally restricted to employees of the organization, extranets may also be accessed ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Leader Election
In distributed computing, leader election is the process of designating a single process as the organizer of some task distributed among several computers (nodes). Before the task has begun, all network nodes are either unaware which node will serve as the "leader" (or coordinator) of the task, or unable to communicate with the current coordinator. After a leader election algorithm has been run, however, each node throughout the network recognizes a particular, unique node as the task leader. The network nodes communicate among themselves in order to decide which of them will get into the "leader" state. For that, they need some method in order to break the symmetry among them. For example, if each node has unique and comparable identities, then the nodes can compare their identities, and decide that the node with the highest identity is the leader. The definition of this problem is often attributed to LeLann, who formalized it as a method to create a new token in a token ring n ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Chang And Roberts Algorithm
The Chang and Roberts algorithm is a ring-based coordinator election algorithm, employed in distributed computing. The algorithm The algorithm assumes that each process has a Unique Identification (UID) and that the processes can arrange themselves in a unidirectional ring with a communication channel going from each process to the clockwise neighbour. The two part algorithm can be described as follows: # Initially each process in the ring is marked as ''non-participant''. # A process that notices a lack of leader starts an election. It creates an ''election message'' containing its UID. It then sends this message clockwise to its neighbour. # Every time a process sends or forwards an ''election message'', the process also marks itself as a participant. # When a process receives an ''election message'' it compares the UID in the message with its own UID. ## If the UID in the election message is larger, the process unconditionally forwards the ''election message'' in a clockw ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Round-trip Time
In telecommunications, round-trip delay (RTD) or round-trip time (RTT) is the amount of time it takes for a signal to be sent ''plus'' the amount of time it takes for acknowledgement of that signal having been received. This time delay includes propagation times for the paths between the two communication endpoints. In the context of computer networks, the signal is typically a data packet. RTT is also known as ping time, and can be determined with the ping command. End-to-end delay is the length of time it takes for a signal to travel in one direction and is often approximated as half the RTT. Protocol design Round-trip delay and bandwidth are independent of each other. As the available bandwidth of networks increases, the round trip time does not similarly decrease, as it depends primarily on constant factors such as physical distance and the speed of signal propagation. Networks with both high bandwidth and a high RTT (and thus high bandwidth-delay product) can have very larg ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Make (software)
In software development, Make is a build automation tool that automatically builds executable programs and libraries from source code by reading files called ''Makefiles'' which specify how to derive the target program. Though integrated development environments and language-specific compiler features can also be used to manage a build process, Make remains widely used, especially in Unix and Unix-like operating systems. Besides building programs, Make can be used to manage any project where some files must be updated automatically from others whenever the others change. Origin There are now a number of dependency-tracking build utilities, but Make is one of the most widespread, primarily due to its inclusion in Unix, starting with the PWB/UNIX 1.0, which featured a variety of tools targeting software development tasks. It was originally created by Stuart Feldman in April 1976 at Bell Labs. Feldman received the 2003 ACM Software System Award for the authoring of this widesprea ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
