IBM mainframe computers, a Coupling Facility or CF is a piece of computer hardware which allows multiple processors to access the same data.
A Parallel Sysplex relies on one or more Coupling Facilities (CFs). A coupling facility is a mainframe processor, with memory and special channels (CF Links), and a specialised operating system called Coupling Facility Control Code (CFCC). It has no I/O devices, other than the CF links. The information in the CF resides entirely in memory as CFCC is not a virtual memory operating system. A CF typically has a large memory - of the order of several gigabytes. In principle any IBM mainframe can serve as a coupling facility. The CF runs no application software.
Supported by CFs, a Sysplex cluster scales very well up to several hundreds of CPUs (in up to 32 members, each with up to 64 CPUs) running transaction and data base applications. Using the CF links, data can be directly exchanged between the CF memory and the memory of the attached systems, using a direct memory access like mechanism, without interrupting a running program. Systems in a Sysplex cluster store CF information in local memory in an area called a bit vector. This enables them to locally query critical state information of other systems in the Sysplex without the need for issuing requests to the CF. The System z Architecture includes 18 special machine instructions and additional hardware features supporting CF operation.
Sunday, March 1, 2009
File sharing applications
One of the most interesting debates over decentralized computing involves Napster, a music file sharing application, which granted users access to an enormous database of files. Record companies brought legal action against Napster, blaming the system for lost record sales. Napster was found in violation of copyright laws by distributing pirated software, and was shut down.
After the fall of Napster, there was a demand for a file sharing system that would be less vulnerable to litigation. Gnutella, a decentralized system, was developed. This system allowed files to be queried and shared between users, without a central directory, and therefore shielded the network from law.
After the fall of Napster, there was a demand for a file sharing system that would be less vulnerable to litigation. Gnutella, a decentralized system, was developed. This system allowed files to be queried and shared between users, without a central directory, and therefore shielded the network from law.
Peer-to-Peer
Based on a “grid model” a peer-to-peer system, or P2P system, is a collection of applications run on several local computers, which connect remotely to each other to complete a function or a task. There is no main operating system to which satellite systems are subordinate. This approach to software development (and distribution) affords developers great savings, as they don’t have to create a central control point.
Decentralized computing
Decentralized computing is a trend in modern day business environments. This is the opposite of centralized computing, which was prevalent during the early days of computers. Decentralized computing is the allocation of resources, both hardware and software, to each individual workstation, or office location. In contrast, centralized computing exists when the majority of functions are carried out, or obtained from a remote centralized location.
A decentralized computer system has many benefits over a conventional centralized network. Desktop computers have advanced so rapidly, that their potential performance far exceeds the requirements of most business applications. This results in most desktop computers remaining idle (in relation to their full potential). A decentralized system can utilize the potential of these systems to maximize efficiency. However, it is debatable whether these networks increase overall effectiveness.
All computers have to be updated individually with new software, unlike a centralised computer system. Decentralised systems still enable file sharing and all computers can share peripherals such as printers and scanners as well as modems, allowing all the computers in the network to connect to the internet.
A collection of decentralized computers systems are components of a larger computer network, held together by local stations of equal importance and capability. These systems are capable of running independently of each other.
A decentralized computer system has many benefits over a conventional centralized network. Desktop computers have advanced so rapidly, that their potential performance far exceeds the requirements of most business applications. This results in most desktop computers remaining idle (in relation to their full potential). A decentralized system can utilize the potential of these systems to maximize efficiency. However, it is debatable whether these networks increase overall effectiveness.
All computers have to be updated individually with new software, unlike a centralised computer system. Decentralised systems still enable file sharing and all computers can share peripherals such as printers and scanners as well as modems, allowing all the computers in the network to connect to the internet.
A collection of decentralized computers systems are components of a larger computer network, held together by local stations of equal importance and capability. These systems are capable of running independently of each other.
Network tomography
Network tomography is the study of a network's internal characteristics using information derived from end point data. The word tomography is used to link the field, in concept, to other processes that infer the internal characteristics of an object from external observation, as is done in magnetic resonance imaging or positron emission tomography. The field is a recent development in electrical engineering and computer science, founded in 1996.[1] Network tomography advocates that it is possible to map the path data takes through the Internet by examining information from "edge nodes," the computers where data is originated and requested from.
The field is useful for engineers attempting to develop more efficient computer networks. Data derived from network tomography studies can be used to increase quality of service by limiting link packet loss and increasing routing optimization.
The field is useful for engineers attempting to develop more efficient computer networks. Data derived from network tomography studies can be used to increase quality of service by limiting link packet loss and increasing routing optimization.
Bridges
A network bridge connects multiple network segments at the data link layer (layer 2) of the OSI model. Bridges do not promiscuously copy traffic to all ports, as hubs do, but learn which MAC addresses are reachable through specific ports. Once the bridge associates a port and an address, it will send traffic for that address only to that port. Bridges do send broadcasts to all ports except the one on which the broadcast was received.
Bridges learn the association of ports and addresses by examining the source address of frames that it sees on various ports. Once a frame arrives through a port, its source address is stored and the bridge assumes that MAC address is associated with that port. The first time that a previously unknown destination address is seen, the bridge will forward the frame to all ports other than the one on which the frame arrived.
Bridges come in three basic types:
1. Local bridges: Directly connect local area networks (LANs) 2. Remote bridges: Can be used to create a wide area network (WAN) link between LANs. Remote bridges, where the connecting link is slower than the end networks, largely have been replaced by routers. 3. Wireless bridges: Can be used to join LANs or connect remote stations to LANs.
Bridges learn the association of ports and addresses by examining the source address of frames that it sees on various ports. Once a frame arrives through a port, its source address is stored and the bridge assumes that MAC address is associated with that port. The first time that a previously unknown destination address is seen, the bridge will forward the frame to all ports other than the one on which the frame arrived.
Bridges come in three basic types:
1. Local bridges: Directly connect local area networks (LANs) 2. Remote bridges: Can be used to create a wide area network (WAN) link between LANs. Remote bridges, where the connecting link is slower than the end networks, largely have been replaced by routers. 3. Wireless bridges: Can be used to join LANs or connect remote stations to LANs.
Thursday, May 1, 2008
Computer networking
Computer networking is the engineering discipline concerned with communication between computer systems or devices. Networking, routers, routing protocols, and networking over the public Internet have their specifications defined in documents called RFCs.[1] Computer networking is sometimes considered a sub-discipline of telecommunications, computer science, information technology and/or computer engineering. Computer networks rely heavily upon the theoretical and practical application of these scientific and engineering disciplines.
A computer network is any set of computers or devices connected to each other with the ability to exchange data.[2] Examples of networks are:
* local area network (LAN), which is usually a small network constrained to a small geographic area.
* wide area network (WAN) that is usually a larger network that covers a large geographic area.
* wireless LANs and WANs (WLAN & WWAN) is the wireless equivalent of the LAN and WAN
All networks are interconnected to allow communication with a variety of different kinds of media, including twisted-pair copper wire cable, coaxial cable, optical fiber, and various wireless technologies.[3] The devices can be separated by a few meters (e.g. via Bluetooth) or nearly unlimited distances (e.g. via the interconnections of the Internet[4]).
A computer network is any set of computers or devices connected to each other with the ability to exchange data.[2] Examples of networks are:
* local area network (LAN), which is usually a small network constrained to a small geographic area.
* wide area network (WAN) that is usually a larger network that covers a large geographic area.
* wireless LANs and WANs (WLAN & WWAN) is the wireless equivalent of the LAN and WAN
All networks are interconnected to allow communication with a variety of different kinds of media, including twisted-pair copper wire cable, coaxial cable, optical fiber, and various wireless technologies.[3] The devices can be separated by a few meters (e.g. via Bluetooth) or nearly unlimited distances (e.g. via the interconnections of the Internet[4]).
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