Powered By Blogger

Minggu, 21 November 2010

Apa Yang di maksud Distribute System ?

Distributed computing is a field of computer science that studies distributed systems. A distributed system consists of multiple autonomous computers that communicate through a computer network. The computers interact with each other in order to achieve a common goal. A computer program that runs in a distributed system is called a distributed program, and distributed programming is the process of writing such programs.[1]

Distributed computing also refers to the use of distributed systems to solve computational problems. In distributed computing, a problem is divided into many tasks, each of which is solved by one computer.

The word distributed in terms such as "distributed system", "distributed programming", and "distributed algorithm" originally referred to computer networks where individual computers were physically distributed within some geographical area.[3] The terms are nowadays used in a much wider sense, even referring to autonomous processes that run on the same physical computer and interact with each other by message passing.[4]

While there is no single definition of a distributed system,[5] the following defining properties are commonly used:

* There are several autonomous computational entities, each of which has its own local memory.[6]
* The entities communicate with each other by message passing.[7]

In this article, the computational entities are called computers or nodes.

A distributed system may have a common goal, such as solving a large computational problem.[8] Alternatively, each computer may have its own user with individual needs, and the purpose of the distributed system is to coordinate the use of shared resources or provide communication services to the users.[9]

Other typical properties of distributed systems include the following:

* The system has to tolerate failures in individual computers.[10]
* The structure of the system (network topology, network latency, number of computers) is not known in advance, the system may consist of different kinds of computers and network links, and the system may change during the execution of a distributed program.[11]
* Each computer has only a limited, incomplete view of the system. Each computer may know only one part of the input.[12]

(a)–(b) A distributed system.
(c) A parallel system.
[edit] Parallel or distributed computing?

The terms "concurrent computing", "parallel computing", and "distributed computing" have a lot of overlap, and no clear distinction exists between them.[13] The same system may be characterised both as "parallel" and "distributed"; the processors in a typical distributed system run concurrently in parallel.[14] Parallel computing may be seen as a particular tightly-coupled form of distributed computing,[15] and distributed computing may be seen as a loosely-coupled form of parallel computing.[5] Nevertheless, it is possible to roughly classify concurrent systems as "parallel" or "distributed" using the following criteria:

* In parallel computing, all processors have access to a shared memory. Shared memory can be used to exchange information between processors.[16]
* In distributed computing, each processor has its own private memory (distributed memory). Information is exchanged by passing messages between the processors.[17]

The figure on the right illustrates the difference between distributed and parallel systems. Figure (a) is a schematic view of a typical distributed system; as usual, the system is represented as a graph in which each node (vertex) is a computer and each edge (line between two nodes) is a communication link. Figure (b) shows the same distributed system in more detail: each computer has its own local memory, and information can be exchanged only by passing messages from one node to another by using the available communication links. Figure (c) shows a parallel system in which each processor has a direct access to a shared memory.

The situation is further complicated by the traditional uses of the terms parallel and distributed algorithm that do not quite match the above definitions of parallel and distributed systems; see the section Theoretical foundations below for more detailed discussion. Nevertheless, as a rule of thumb, high-performance parallel computation in a shared-memory multiprocessor uses parallel algorithms while the coordination of a large-scale distributed system uses distributed algorithms.
[edit] History

The use of concurrent processes that communicate by message-passing has its roots in operating system architectures studied in the 1960s.[18] The first widespread distributed systems were local-area networks such as Ethernet that was invented in the 1970s.[19]

ARPANET, the predecessor of the Internet, was introduced in the late 1960s, and ARPANET e-mail was invented in the early 1970s. E-mail became the most successful application of ARPANET,[20] and it is probably the earliest example of a large-scale distributed application. In addition to ARPANET and its successor Internet, other early worldwide computer networks included Usenet and FidoNet from 1980s, both of which were used to support distributed discussion systems.

The study of distributed computing became its own branch of computer science in the late 1970s and early 1980s. The first conference in the field, Symposium on Principles of Distributed Computing (PODC), dates back to 1982, and its European counterpart International Symposium on Distributed Computing (DISC) was first held in 1985.
[edit] Applications

There are two main reasons for using distributed systems and distributed computing. First, the very nature of the application may require the use of a communication network that connects several computers. For example, data is produced in one physical location and it is needed in another location.

Second, there are many cases in which the use of a single computer would be possible in principle, but the use of a distributed system is beneficial for practical reasons. For example, it may be more cost-efficient to obtain the desired level of performance by using a cluster of several low-end computers, in comparison with a single high-end computer. A distributed system can be more reliable than a non-distributed system, as there is no single point of failure. Moreover, a distributed system may be easier to expand and manage than a monolithic uniprocessor system.[21]

Examples of distributed systems and applications of distributed computing include the following:[22]

* Telecommunication networks:
o Telephone networks and cellular networks.
o Computer networks such as the Internet.
o Wireless sensor networks.
o Routing algorithms.
* Network applications:
o World wide web and peer-to-peer networks.
o Massively multiplayer online games and virtual reality communities.
o Distributed databases and distributed database management systems.
o Network file systems.
o Distributed information processing systems such as banking systems and airline reservation systems.
* Real-time process control:
o Aircraft control systems.
o Industrial control systems.
* Parallel computation:
o Scientific computing, including cluster computing and grid computing and various volunteer computing projects; see the list of distributed computing projects.
o Distributed rendering in computer graphics.

[edit] Theoretical foundations
Main article: Distributed algorithm
[edit] Models

Many tasks that we would like to automate by using a computer are of question–answer type: we would like to ask a question and the computer should produce an answer. In theoretical computer science, such tasks are called computational problems. Formally, a computational problem consists of instances together with a solution for each instance. Instances are questions that we can ask, and solutions are desired answers to these questions.

Theoretical computer science seeks to understand which computational problems can be solved by using a computer (computability theory) and how efficiently (computational complexity theory). Traditionally, it is said that a problem can be solved by using a computer if we can design an algorithm that produces a correct solution for any given instance. Such an algorithm can be implemented as a computer program that runs on a general-purpose computer: the program reads a problem instance from input, performs some computation, and produces the solution as output. Formalisms such as random access machines or universal Turing machines can be used as abstract models of a sequential general-purpose computer executing such an algorithm.

The field of concurrent and distributed computing studies similar questions in the case of either multiple computers, or a computer that executes a network of interacting processes: which computational problems can be solved in such a network and how efficiently? However, it is not at all obvious what is meant by “solving a problem” in the case of a concurrent or distributed system: for example, what is the task of the algorithm designer, and what is the concurrent or distributed equivalent of a sequential general-purpose computer?

The discussion below focusses on the case of multiple computers, although many of the issues are the same for concurrent processes running on a single computer.

Three viewpoints are commonly used:

Parallel algorithms in shared-memory model

* All computers have access to a shared memory. The algorithm designer chooses the program executed by each computer.
* One theoretical model is the parallel random access machines (PRAM) that are used.[23] However, the classical PRAM model assumes synchronous access to the shared memory.
* A model that is closer to the behavior of real-world multiprocessor machines and takes into account the use of machine instructions, such as Compare-and-swap (CAS), is that of asynchronous shared memory. There is a wide body of work on this model, a summary of which can be found in the literature.[24][25]

Parallel algorithms in message-passing model

* The algorithm designer chooses the structure of the network, as well as the program executed by each computer.
* Models such as Boolean circuits and sorting networks are used.[26] A Boolean circuit can be seen as a computer network: each gate is a computer that runs an extremely simple computer program. Similarly, a sorting network can be seen as a computer network: each comparator is a computer.

Distributed algorithms in message-passing model

* The algorithm designer only chooses the computer program. All computers run the same program. The system must work correctly regardless of the structure of the network.
* A commonly used model is a graph with one finite-state machine per node.

In the case of distributed algorithms, computational problems are typically related to graphs. Often the graph that describes the structure of the computer network is the problem instance. This is illustrated in the following example.
[edit] An example

Consider the computational problem of finding a coloring of a given graph G. Different fields might take the following approaches:

Centralized algorithms

* The graph G is encoded as a string, and the string is given as input to a computer. The computer program finds a coloring of the graph, encodes the coloring as a string, and outputs the result.

Parallel algorithms

* Again, the graph G is encoded as a string. However, multiple computers can access the same string in parallel. Each computer might focus on one part of the graph and produce a colouring for that part.
* The main focus is on high-performance computation that exploits the processing power of multiple computers in parallel.

Distributed algorithms

* The graph G is the structure of the computer network. There is one computer for each node of G and one communication link for each edge of G. Initially, each computer only knows about its immediate neighbours in the graph G; the computers must exchange messages with each other to discover more about the structure of G. Each computer must produce its own colour as output.
* The main focus is on coordinating the operation of an arbitrary distributed system.

While the field of parallel algorithms has a different focus than the field of distributed algorithms, there is a lot of interaction between the two fields. For example, the Cole–Vishkin algorithm for graph colouring[27] was originally presented as a parallel algorithm, but the same technique can also be used directly as a distributed algorithm.

Moreover, a parallel algorithm can be implemented either in a parallel system (using shared memory) or in a distributed system (using message passing).[28] The traditional boundary between parallel and distributed algorithms (choose a suitable network vs. run in any given network) does not lie in the same place as the boundary between parallel and distributed systems (shared memory vs. message passing).
[edit] Complexity measures

In parallel algorithms, yet another resource in addition to time and space is the number of computers. Indeed, often there is a trade-off between the running time and the number of computers: the problem can be solved faster if there are more computers running in parallel (see speedup). If a decision problem can be solved in polylogarithmic time by using a polynomial number of processors, then the problem is said to be in the class NC.[29] The class NC can be defined equally well by using the PRAM formalism or Boolean circuits – PRAM machines can simulate Boolean circuits efficiently and vice versa.[30]

In the analysis of distributed algorithms, more attention is usually paid on communication operations than computational steps. Perhaps the simplest model of distributed computing is a synchronous system where all nodes operate in a lockstep fashion. During each communication round, all nodes in parallel (1) receive the latest messages from their neighbours, (2) perform arbitrary local computation, and (3) send new messages to their neighbours. In such systems, a central complexity measure is the number of synchronous communication rounds required to complete the task.[31]

This complexity measure is closely related to the diameter of the network. Let D be the diameter of the network. On the one hand, any computable problem can be solved trivially in a synchronous distributed system in approximately 2D communication rounds: simply gather all information in one location (D rounds), solve the problem, and inform each node about the solution (D rounds).

On the other hand, if the running time of the algorithm is much smaller than D communication rounds, then the nodes in the network must produce their output without having the possibility to obtain information about distant parts of the network. In other words, the nodes must make globally consistent decisions based on information that is available in their local neighbourhood. Many distributed algorithms are known with the running time much smaller than D rounds, and understanding which problems can be solved by such algorithms is one of the central research questions of the field.[32]

Other commonly used measures are the total number of bits transmitted in the network (cf. communication complexity).
[edit] Other problems

Traditional computational problems take the perspective that we ask a question, a computer (or a distributed system) processes the question for a while, and then produces an answer and stops. However, there are also problems where we do not want the system to ever stop. Examples of such problems include the dining philosophers problem and other similar mutual exclusion problems. In these problems, the distributed system is supposed to continuously coordinate the use of shared resources so that no conflicts or deadlocks occur.

There are also fundamental challenges that are unique to distributed computing. The first example is challenges that are related to fault-tolerance. Examples of related problems include consensus problems,[33] Byzantine fault tolerance,[34] and self-stabilisation.[35]

A lot of research is also focused on understanding the asynchronous nature of distributed systems:

* Synchronizers can be used to run synchronous algorithms in asynchronous systems.[36]
* Logical clocks provide a causal happened-before ordering of events.[37]
* Clock synchronization algorithms provide globally consistent physical time stamps.[38]

Properties of distributed systems

So far the focus has been on designing a distributed system that solves a given problem. A complementary research problem is studying the properties of a given distributed system.

The halting problem is an analogous example from the field of centralised computation: we are given a computer program and the task is to decide whether it halts or runs forever. The halting problem is undecidable in the general case, and naturally understanding the behaviour of a computer network is at least as hard as understanding the behaviour of one computer.

However, there are many interesting special cases that are decidable. In particular, it is possible to reason about the behaviour of a network of finite-state machines. One example is telling whether a given network of interacting (asynchronous and non-deterministic) finite-state machines can reach a deadlock. This problem is PSPACE-complete,[39] i.e., it is decidable, but it is not likely that there is an efficient (centralised, parallel or distributed) algorithm that solves the problem in the case of large networks.
[edit] Architectures

Various hardware and software architectures are used for distributed computing. At a lower level, it is necessary to interconnect multiple CPUs with some sort of network, regardless of whether that network is printed onto a circuit board or made up of loosely-coupled devices and cables. At a higher level, it is necessary to interconnect processes running on those CPUs with some sort of communication system.

Distributed programming typically falls into one of several basic architectures or categories: client–server, 3-tier architecture, n-tier architecture, distributed objects, loose coupling, or tight coupling.

* Client–server: Smart client code contacts the server for data then formats and displays it to the user. Input at the client is committed back to the server when it represents a permanent change.
* 3-tier architecture: Three tier systems move the client intelligence to a middle tier so that stateless clients can be used. This simplifies application deployment. Most web applications are 3-Tier.
* n-tier architecture: n-tier refers typically to web applications which further forward their requests to other enterprise services. This type of application is the one most responsible for the success of application servers.
* Tightly coupled (clustered): refers typically to a cluster of machines that closely work together, running a shared process in parallel. The task is subdivided in parts that are made individually by each one and then put back together to make the final result.
* Peer-to-peer: an architecture where there is no special machine or machines that provide a service or manage the network resources. Instead all responsibilities are uniformly divided among all machines, known as peers. Peers can serve both as clients and servers.
* Space based: refers to an infrastructure that creates the illusion (virtualization) of one single address-space. Data are transparently replicated according to application needs. Decoupling in time, space and reference is achieved.

Another basic aspect of distributed computing architecture is the method of communicating and coordinating work among concurrent processes. Through various message passing protocols, processes may communicate directly with one another, typically in a master/slave relationship. Alternatively, a "database-centric" architecture can enable distributed computing to be done without any form of direct inter-process communication, by utilizing a shared database.

Wikipedia , 22 November 2010 , 5:42 AM

Apa Yang di maksud Intranet ?

Sebuah intranet adalah sebuah jaringan privat (private network) yang menggunakan protokol-protokol Internet (TCP/IP), untuk membagi informasi rahasia perusahaan atau operasi dalam perusahaan tersebut kepada karyawannya. Kadang-kadang, istilah intranet hanya merujuk kepada layanan yang terlihat, yakni situs web internal perusahaan. Untuk membangun sebuah intranet, maka sebuah jaringan haruslah memiliki beberapa komponen yang membangun Internet, yakni protokol Internet (Protokol TCP/IP, alamat IP, dan protokol lainnya), klien dan juga server. Protokol HTTP dan beberapa protokol Internet lainnya (FTP, POP3, atau SMTP) umumnya merupakan komponen protokol yang sering digunakan.

Umumnya, sebuah intranet dapat dipahami sebagai sebuah "versi pribadi dari jaringan Internet", atau sebagai sebuah versi dari Internet yang dimiliki oleh sebuah organisasi.

Wikipedia , 22 November 2010 , 5:28 AM

Apa Yang di maksud Internet Working ?

Internetworking adalah praktek menghubungkan jaringan komputer dengan jaringan lain melalui penggunaan gateway yang menyediakan metode umum dari routing informasi paket antara jaringan. The resulting system of interconnected networks is called an internetwork , or simply an internet . Sistem yang dihasilkan dari jaringan interkoneksi disebut internetwork, atau hanya internet.

The most notable example of internetworking is the Internet , a network of networks based on many underlying hardware technologies, but unified by an internetworking protocol standard, the Internet Protocol Suite , often also referred to as TCP/IP . Yang penting Contoh yang paling dari internetworking adalah Internet , jaringan dari jaringan berdasarkan banyak teknologi perangkat keras yang mendasarinya, tetapi disatukan oleh standar protokol internetworking, dari Internet Protocol Suite , sering juga disebut sebagai TCP / IP .
Internetworking dimulai sebagai sebuah cara untuk terhubung jenis teknologi jaringan yang berbeda, tetapi menjadi luas melalui kebutuhan berkembang untuk menghubungkan dua atau lebih jaringan area lokal melalui beberapa jenis wide area network . The original term for an internetwork was catenet . Istilah asli untuk internetwork adalah catenet .

The definition of an internetwork today includes the connection of other types of computer networks such as personal area networks . Definisi hari ini internetwork termasuk koneksi jenis lain dari jaringan komputer seperti jaringan wilayah pribadi .

The network elements used to connect individual networks in the ARPANET , the predecessor of the Internet, were originally called gateways , but the term has been deprecated in this context, because of possible confusion with functionally different devices. elemen-elemen jaringan yang digunakan untuk menghubungkan jaringan individu dalam ARPANET , pendahulu dari Internet, awalnya disebut gateway , tetapi jangka waktu telah usang dalam konteks ini, karena kebingungan mungkin dengan berbagai perangkat fungsional. Today the interconnecting gateways are called Internet routers . Hari ini gateway interkoneksi disebut Internet router .

Another type of interconnection of networks often occurs within enterprises at the Link Layer of the networking model, ie at the hardware-centric layer below the level of the TCP/IP logical interfaces. Tipe lain dari interkoneksi jaringan sering terjadi di dalam perusahaan di Link Layer dari model jaringan, yaitu pada lapisan-sentris hardware di bawah tingkat TCP / IP interface logis. Such interconnection is accomplished with network bridges and network switches . interkoneksi tersebut dicapai dengan bridge jaringan dan switch jaringan . This is sometimes incorrectly termed internetworking, but the resulting system is simply a larger, single subnetwork , and no internetworking protocol , such as Internet Protocol , is required to traverse these devices. Ini kadang-kadang salah disebut internetworking, namun sistem yang dihasilkan hanya yang lebih besar, satu subnetwork , dan tidak ada internetworking protokol , seperti Internet Protocol , diperlukan untuk melintasi perangkat ini. However, a single computer network may be converted into an internetwork by dividing the network into segments and logically dividing the segment traffic with routers. Namun, jaringan komputer dapat dikonversikan menjadi sebuah internetwork dengan membagi jaringan menjadi segmen dan logis membagi lalu lintas segmen dengan router.

The Internet Protocol is designed to provide an unreliable (not guaranteed) packet service across the network. Protokol Internet dirancang untuk memberikan diandalkan (tidak dijamin) paket layanan di seluruh jaringan. The architecture avoids intermediate network elements maintaining any state of the network. Arsitektur menghindari elemen-elemen jaringan antara mempertahankan setiap keadaan jaringan. Instead, this function is assigned to the endpoints of each communication session. Sebaliknya, fungsi ini ditugaskan untuk titik akhir setiap sesi komunikasi. To transfer data reliably, applications must utilize an appropriate Transport Layer protocol, such as Transmission Control Protocol (TCP), which provides a reliable stream . Untuk mentransfer data andal, aplikasi harus menggunakan yang sesuai Transport Layer protokol, seperti Transmission Control Protocol (TCP), yang memberikan aliran yang dapat diandalkan . Some applications use a simpler, connection-less transport protocol, User Datagram Protocol (UDP), for tasks which do not require reliable delivery of data or that require real-time service, such as video streaming . [ 1 ] Beberapa aplikasi menggunakan koneksi sederhana,-protokol transport kurang, User Datagram Protocol (UDP), untuk tugas-tugas yang tidak memerlukan pengiriman yang dapat diandalkan data atau yang membutuhkan waktu pelayanan yang nyata, seperti video streaming . [1]
[ edit ] Networking models [ sunting ] model Jaringan

Two architectural models are commonly used to describe the protocols and methods used in internetworking. Dua model arsitektur yang umum digunakan untuk menggambarkan protokol dan metode yang digunakan dalam internetworking.

The Open System Interconnection (OSI) reference model was developed under the auspices of the International Organization for Standardization (ISO) and provides a rigorous description for layering protocol functions from the underlying hardware to the software interface concepts in user applications. The Interkoneksi Sistem Terbuka (OSI) reference model dikembangkan di bawah naungan Organisasi Internasional untuk Standarisasi (ISO) dan memberikan gambaran yang ketat untuk melapis fungsi protokol dari perangkat keras yang mendasari untuk konsep antarmuka perangkat lunak dalam aplikasi pengguna. Internetworking is implemented in the Network Layer (Layer 3) of the model. Internetworking diimplementasikan di Network Layer (Layer 3) dari model.

The Internet Protocol Suite , also called the TCP/IP model of the Internet was not designed to conform to the OSI model and does not refer to it in any of the normative specifications in Requests for Comment and Internet standards . The Internet Protocol Suite , juga disebut TCP / IP model Internet tidak dirancang agar sesuai dengan model OSI dan tidak merujuk ke dalam salah satu spesifikasi normatif dalam Permintaan untuk Komentar dan standar Internet . Despite similar appearance as a layered model, it uses a much less rigorous, loosely defined architecture that concerns itself only with the aspects of logical networking. Meskipun penampilannya serupa sebagai model layered, ia menggunakan arsitektur, apalagi yang didefinisikan secara longgar ketat bahwa kekhawatiran itu sendiri hanya dengan aspek jaringan logis. It does not discuss hardware-specific low-level interfaces, and assumes availability of a Link Layer interface to the local network link to which the host is connected. Ini tidak membahas hardware khusus-tingkat interface rendah, dan mengasumsikan ketersediaan Link Layer antarmuka ke link jaringan lokal yang host dihubungkan. Internetworking is facilitated by the protocols of its Internet Layer . Internetworking difasilitasi oleh protokol yang Internet Layer .

Wikipedia , 22 November 2010 , 5:13 AM

Apa Yang di maksud Jaringan Komputer ??

Jaringan komputer adalah sebuah sistem yang terdiri atas komputer, software dan perangkat jaringan lainnya yang bekerja bersama-sama untuk mencapai suatu tujuan yang sama. Tujuan dari jaringan komputer adalah:

* Membagi sumber daya: contohnya berbagi pemakaian printer, CPU, memori, harddisk
* Komunikasi: contohnya surat elektronik, instant messaging, chatting
* Akses informasi: contohnya web browsing

Agar dapat mencapai tujuan yang sama, setiap bagian dari jaringan komputer meminta dan memberikan layanan (service). Pihak yang meminta/menerima layanan disebut klien (client) dan yang memberikan/mengirim layanan disebut pelayan (server). Arsitektur ini disebut dengan sistem client-server, dan digunakan pada hampir seluruh aplikasi jaringan komputer.

Berdasarkan skala :

* Local Area Network (LAN): suatu jaringan komputer yang menghubungkan suatu komputer dengan komputer lain dengan jarak yang terbatas.
* Metropolitant Area Network (MAN): prinsip sama dengan LAN, hanya saja jaraknya lebih luas, yaitu 10-50 km.
* Wide Area Network (WAN): jaraknya antar kota, negara, dan benua. ini sama dengan internet.

Berdasarkan fungsi : Pada dasarnya setiap jaringan komputer ada yang berfungsi sebagai client dan juga server. Tetapi ada jaringan yang memiliki komputer yang khusus didedikasikan sebagai server sedangkan yang lain sebagai client. Ada juga yang tidak memiliki komputer yang khusus berfungsi sebagai server saja. Karena itu berdasarkan fungsinya maka ada dua jenis jaringan komputer:

* Client-server

Yaitu jaringan komputer dengan komputer yang didedikasikan khusus sebagai server. Sebuah service/layanan bisa diberikan oleh sebuah komputer atau lebih. Contohnya adalah sebuah domain seperti www.detik.com yang dilayani oleh banyak komputer web server. Atau bisa juga banyak service/layanan yang diberikan oleh satu komputer. Contohnya adalah server jtk.polban.ac.id yang merupakan satu komputer dengan multi service yaitu mail server, web server, file server, database server dan lainnya.

* Peer-to-peer

Yaitu jaringan komputer dimana setiap host dapat menjadi server dan juga menjadi client secara bersamaan. Contohnya dalam file sharing antar komputer di Jaringan Windows Network Neighbourhood ada 5 komputer (kita beri nama A,B,C,D dan E) yang memberi hak akses terhadap file yang dimilikinya. Pada satu saat A mengakses file share dari B bernama data_nilai.xls dan juga memberi akses file soal_uas.doc kepada C. Saat A mengakses file dari B maka A berfungsi sebagai client dan saat A memberi akses file kepada C maka A berfungsi sebagai server. Kedua fungsi itu dilakukan oleh A secara bersamaan maka jaringan seperti ini dinamakan peer to peer.

Berdasarkan topologi jaringan, jaringan komputer dapat dibedakan atas:

* Topologi bus
* Topologi bintang
* Topologi cincin
* Topologi mesh
* Topologi pohon
* Topologi linier

Berdasarkan kriterianya, jaringan komputer dibedakan menjadi 4 yaitu:

1. Berdasarkan distribusi sumber informasi/data
* Jaringan terpusat

Jaringan ini terdiri dari komputer klient dan server yang mana komputer klient yang berfungsi sebagai perantara untuk mengakses sumber informasi/data yang berasal dari satu komputer server

* Jaringan terdistribusi

Merupakan perpaduan beberapa jaringan terpusat sehingga terdapat beberapa komputer server yang saling berhubungan dengan klient membentuk sistem jaringan tertentu.

2. Berdasarkan jangkauan geografis dibedakan menjadi:
* Jaringan LAN

merupakan jaringan yang menghubungkan 2 komputer atau lebih dalam cakupan seperti laboratorium, kantor, serta dalam 1 warnet.

* Jaringan MAN

Merupakan jaringan yang mencakup satu kota besar beserta daerah setempat. Contohnya jaringan telepon lokal, sistem telepon seluler, serta jaringan relay beberapa ISP internet.

* Jaringan WAN

Merupakan jaringan dengan cakupan seluruh dunia. Contohnya jaringan PT Telkom, PT. Indosat, serta jaringan GSM Seluler seperti Satelindo, Telkomsel, dan masih banyak lagi.

3. Berdasarkan peranan dan hubungan tiap komputer dalam memproses data.
* Jaringan Client-Server

Pada jaringan ini terdapat 1 atau beberapa komputer server dan komputer client. Komputer yang akan menjadi komputer server maupun menjadi komputer client dan diubah-ubah melalui software jaringan pada protokolnya. Komputer client sebagai perantara untuk dapat mengakses data pada komputer server sedangkan komputer server menyediakan informasi yang diperlukan oleh komputer client.

* Jaringan Peer-to-peer

Pada jaringan ini tidak ada komputer client maupun komputer server karena semua komputer dapat melakukan pengiriman maupun penerimaan informasi sehingga semua komputer berfungsi sebagai client sekaligus sebagai server.

4. Berdasarkan media transmisi data
* Jaringan Berkabel (Wired Network)

Pada jaringan ini, untuk menghubungkan satu komputer dengan komputer lain diperlukan penghubung berupa kabel jaringan. Kabel jaringan berfungsi dalam mengirim informasi dalam bentuk sinyal listrik antar komputer jaringan.

* Jaringan Nirkabel(WI-FI)

Merupakan jaringan dengan medium berupa gelombang elektromagnetik. Pada jaringan ini tidak diperlukan kabel untuk menghubungkan antar komputer karena menggunakan gelombang elektromagnetik yang akan mengirimkan sinyal informasi antar komputer jaringan.

Wikipedia , 22 November 2010 , 5:06 AM

Apa Yang di maksud Peer to Peer ??


P2P merupakan singkatan dari Peer-to-Peer (bahasa Inggris) atau teknologi dari “ujung” ke “ujung” pertama kali di luncurkan dan dipopulerkan oleh aplikasi-aplikasi “berbagi-berkas” (file sharing) seperti Napster dan KaZaA. Pada konteks ini teknologi P2P memungkinkan para pengguna untuk berbagi, mencari dan mengunduh berkas.

Sistem P2P yang sebenarnya adalah suatu sistem yang tidak hanya menghubungkan “ujung” satu dengan lainnya, namun ujung-ujung ini saling berhubungan secara dinamis dan berpartisipasi dalam mengarahkan lalu lintas komunikasi informasi-, pemrosesan-, dan penugasan pembagian bandwidth yang intensif, dimana bila sistem ini tidak ada, tugas-tugas ini biasanya diemban oleh server pusat.

Aplikasi P2P yang sebenarnya memerlukan satuan tim-tim kecil dengan ide cemerlang untuk mengembangkan perangkat lunak dan bisnis-bisnis yang mungkin dilakukan oleh perangkat tersebut – dan mungkin saja bisa membuat perusahaan besar yang sudah ada gulung tikar. P2P yang sebenarnya, bila diaplikasikan pada pasar yang sudah matang dan stabil adalah teknologi yang "mengganggu".

Ide mengenai konsep ini muncul kira-kira pada akhir dekade 1980-an, ketika jaringan komputer dan tentunya juga komputer telah mulai masuk ke dalam salah satu barang wajib dalam perusahaan, baik itu perusahaan kecil maupun besar. Tetapi, arsitektur ini berkembang dalam jaringan yang terlalu kecil untuk memiliki sebuah server yang terdedikasi, sehingga setiap komputer klien pun menyediakan layanan untuk berbagi data untuk melakukan kolaborasi antara pengguna.

Jaringan peer-to-peer pun mulai banyak digemari ketika Microsoft merilis sistem operasi Windows for Workgroups, meski sebelumnya sistem operasi MS-DOS (atau IBM PC-DOS) dengan perangkat MS-NET (atau PC-NET) juga dapat digunakan untuk tujuan ini. Karakteristik kunci jaringan tersebut adalah dalam jaringan ini tidak terdapat sebuah server pusat yang mengatur klien-klien, karena memang setiap komputer bertindak sebagai server untuk komputer klien lainnya. Sistem keamanan yang ditawarkan oleh metode ini terbilang lebih rendah dibandingkan dengan metode klien/server dan manajemen terhadapnya pun menjadi relatif lebih rumit.

Konsep ini pun kemudian berevolusi pada beberapa tahun terakhir, khususnya ketika jaringan Internet menjadi jaringan yang sangat besar. Hal ini mulai muncul kira-kira pada akhir dekade 1990-an, di saat banyak pengguna Internet mengunduh banyak berkas musik mp3 dengan menggunakan metode peer-to-peer dengan menggunakan program Napster yang menuai kritik pedas dari industri musik, seperti halnya Metallica dan banyak lainnya. Napster, pada saat dituntut oleh para pekerja industri musik, dikatakan memiliki anggota lebih dari 20 juta pengguna di seluruh dunia. Selanjutnya beberapa aplikasi juga dibuat dengan menggunakan konsep ini: eDonkey, Kazaa, BitTorrent, dan masih banyak lainnya. Meski banyak aplikasi peer-to-peer ini digunakan oleh pengguna rumahan, ternyata sistem ini juga diminati oleh banyak perusahaan juga.
Daftar isi

Penggunaan istilah P2P digunakan luas dan seringkali disalah gunakan. Perusahaan-perusahaan baik besar maupun kecil saling mengaku menjadi “spesialis” dan perusahaan lainnya mencoba untuk menghasilkan uang dengan mengaku menggunakan teknologi P2P selama perusahaannya menggunakan komunikasi langsung antar pengguna atau antar “ujung”. Dalam hal ini istilah P2P benar-benar disalah gunakan.

Wikipedia , 22 November 2010 , 4:57 AM