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Scalability Gateway Protocol Internal BGP scalabilityAn autonomous system with internal BGP (iBGP) must have all of its iBGP peers connect to each other in a full mesh (where everyone speaks to everyone directly). This full-mesh configuration requires that each router maintain a session to every other router. In large networks, this number of sessions may degrade performance of routers, due to either a lack of memory, or too much CPU process requirements. Gateway Protocol Internal BGP scalabilityRoute reflectors and confederations both reduce the number of iBGP peers to each router and thus reduce processing overhead. Route reflectors are a pure performance-enhancing technique, while confederations also can be used to implement more fine-grained policy. Gateway Protocol Internal BGP scalabilityRoute reflectors reduce the number of connections required in an AS. A single router (or two for redundancy) can be made a route reflector: other routers in the AS need only be configured as peers to them. Gateway Protocol Internal BGP scalabilityConfederations are sets of autonomous systems. In common practice, only one of the confederation AS numbers is seen by the Internet as a whole. Confederations are used in very large networks where a large AS can be configured to encompass smaller more manageable internal ASs. Gateway Protocol Internal BGP scalabilityConfederations can be used in conjunction with route reflectors. Both confederations and route reflectors can be subject to persistent oscillation unless specific design rules, affecting both BGP and the interior routing protocol, are followed. Gateway Protocol Internal BGP scalabilityHowever, these alternatives can introduce problems of their own, including the following: Gateway Protocol Internal BGP scalabilityroute oscillation Gateway Protocol Internal BGP scalabilityAdditionally, route reflectors and BGP confederations were not designed to ease BGP router configuration. Nevertheless, these are common tools for experienced BGP network architects. These tools may be combined, for example, as a hierarchy of route reflectors. analogous meaning is implied when the word is used in an economic context, where scalability of a company implies that the underlying business model offers the potential for economic growth within the company., as a property of systems, is generally difficult to define and in any particular case it is necessary to define the specific requirements for scalability on those dimensions that are deemed important. It is a highly significant issue in electronics systems, databases, routers, and networking. A system whose performance improves after adding hardware, proportionally to the capacity added, is said to be a scalable system. refers to the ability of a site to increase in size as demand warrants. concept of scalability is desirable in technology as well as business settings. The base concept is consistent the ability for a business or technology to accept increased volume without impacting the contribution margin (= revenue variable costs). For example, a given piece of equipment may have capacity from 11000 users, and beyond 1000 users, additional equipment is needed or performance will decline (variable costs will increase and reduce contribution margin). MeasuresScalability can be measured in various dimensions, such as: MeasuresAdministrative scalability: The ability for an increasing number of organizations or users to easily share a single distributed system. MeasuresFunctional scalability: The ability to enhance the system by adding new functionality at minimal effort. MeasuresGeographic scalability: The ability to maintain performance, usefulness, or usability regardless of expansion from concentration in a local area to a more distributed geographic pattern. MeasuresLoad scalability: The ability for a distributed system to easily expand and contract its resource pool to accommodate heavier or lighter loads or number of inputs. Alternatively, the ease with which a system or component can be modified, added, or removed, to accommodate changing load. ExamplesA routing protocol is considered scalable with respect to network size, if the size of the necessary routing table on each node grows as O(log N), where N is the number of nodes in the network. ExamplesA scalable online transaction processing system or database management system is one that can be upgraded to process more transactions by adding new processors, devices and storage, and which can be upgraded easily and transparently without shutting it down. ExamplesSome early peer-to-peer (P2P) implementations of Gnutella had scaling issues ExamplesThe distributed nature of the Domain Name System allows it to work efficiently even when all hosts on the worldwide Internet are served, so it is said to "scale well". Horizontal and vertical scalingMethods of adding more resources for a particular application fall into two broad categories: horizontal and vertical scaling. Horizontal and vertical scalingTo scale horizontally (or scale out) means to add more nodes to a system, such as adding a new computer to a distributed software application Horizontal and vertical scalingTo scale vertically (or scale up) means to add resources to a single node in a system, typically involving the addition of CPUs or memory to a single computer Horizontal and vertical scalingThere are tradeoffs between the two models Database scalabilityA number of different approaches enable databases to grow to very large size while supporting an ever-increasing rate of transactions per second. Not to be discounted, of course, is the rapid pace of hardware advances in both the speed and capacity of mass storage devices, as well as similar advances in CPU and networking speed. Beyond that, a variety of architectures are employed in the implementation of very large-scale databases. Database scalabilityOne technique supported by most of the major database management system (DBMS) products is the partitioning of large tables, based on ranges of values in a key field Database scalabilityOracle RAC uses a different model to achieve scalability, based on a "shared-everything" architecture that relies upon high-speed connections between servers. Database scalabilityIn any case, whether or not adhering to traditional relational concepts, there appears to be no limit in sight to database scalability. Design for scalabilityIt is often advised to focus system design on hardware scalability rather than on capacity Weak versus strong scalingIn the context of high performance computing there are two common notions of scalability. Weak versus strong scalingThe first is strong scaling, which is defined as how the solution time varies with the number of processors for a fixed total problem size. Weak versus strong scalingThe second is weak scaling, which is defined as how the solution time varies with the number of processors for a fixed problem size per processor. Terminal Server Project - ScalabilityInitially, the MILLE-Xterm project, funded by Canadian public agencies and school districts in the province of Quebec, created a version of LTSP integrating four subprojects: a portal (based on uportal), an open-source middleware stack, a CD with free software for Windows/Mac and, finally, MILLE-Xterm itself. The MILLE-Xterm project's goal was to provide a scalable infrastructure for massive X-Terminal deployment. Terminal

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