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Basic Concepts in Network

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Contents

Articles

Network Architecture   1

Network architecture 1

Peer-to-peer 4

Client € server model 11

Network Topologies   14

Network topology 14

ReferencesArticle Sources and Contributors 22

Image Sources, Licenses and Contributors 23

Article Licenses

License 24

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1

Network Architecture

Network architectureNetwork architecture is the design of a communications network. It is a framework for the specification of a

network's physical components and their functional organization and configuration, its operational principles and

procedures, as well as data formats used in its operation.

In telecommunication, the specification of a network architecture may also include a detailed description of products

and services delivered via a communications network, as well as detailed rate and billing structures under which

services are compensated.

The network architecture of the Internet is predominantly expressed by its use of the Internet Protocol Suite, rather

than a specific model for interconnecting networks or nodes in the network, or the usage of specific types of 

hardware links.

OSI Network Model

The Open Systems Interconnection model (OSI model) is a product of the Open Systems Interconnection effort at

the International Organization for Standardization. It is a way of sub-dividing a communications system into smaller

parts called layers. A layer is a collection of similar functions that provide services to the layer above it and receives

services from the layer below it. On each layer, an instance provides services to the instances at the layer above and

requests service from the layer below.

Physical LayerThe Physical Layer defines the electrical and physical specifications for devices. In particular, it defines the

relationship between a device and a transmission medium, such as a copper or optical cable. This includes the layout

of pins, voltages, cable specifications, hubs, repeaters, network adapters, host bus adapters (HBA used in storage

area networks) and more. Its main task is the transmission of a stream of bits over a communication channel.

Data Linking Layer

The Data Link Layer provides the functional and procedural means to transfer data between network entities and to

detect and possibly  correct errors that may occur in the Physical Layer. Originally, this layer was intended for

point-to-point and point-to-multipoint media, characteristic of wide area media in the telephone system. Local area

network architecture, which included broadcast-capable multiaccess media, was developed independently of the ISO

work in IEEE Project 802. IEEE work assumed sublayering and management functions not required for WAN use.

In modern practice, only error detection, not flow control using sliding window, is present in data link protocols such

as Point-to-Point Protocol (PPP), and, on local area networks, the IEEE 802.2 LLC layer is not used for most

protocols on the Ethernet, and on other local area networks, its flow control and acknowledgment mechanisms are

rarely used. Sliding-window flow control and acknowledgment is used at the Transport Layer by protocols such as

TCP, but is still used in niches where X.25 offers performance advantages. Simply, its main job is to create and

recognize the frame boundary. This can be done by attaching special bit patterns to the beginning and the end of the

frame. The input data is broken up into frames.

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Network architecture 2

Network Layer

The Network Layer provides the functional and procedural means of transferring variable length data sequences

from a source host on one network to a destination host on a different network, while maintaining the quality of 

service requested by the Transport Layer (in contrast to the data link layer which connects hosts within the same

network). The Network Layer performs network routing functions, and might also perform fragmentation and

reassembly, and report delivery errors. Routers operate at this layer €sending data throughout the extended network and making the Internet possible. This is a logical addressing scheme • values are chosen by the network engineer.

The addressing scheme is not hierarchical. It controls the operation of the subnet and determine the routing strategies

between IMP and insures that all the packs are correctly received at the destination in the proper order.

Transport Layer

The Transport Layer provides transparent transfer of data between end users, providing reliable data transfer services

to the upper layers. The Transport Layer controls the reliability of a given link through flow control,

segmentation/desegmentation, and error control. Some protocols are state and connection oriented. This means that

the Transport Layer can keep track of the segments and retransmit those that fail. The Transport layer also provides

the acknowledgement of the successful data transmission and sends the next data if no errors occurred. Some

Transport Layer protocols, for example TCP, but not UDP, support virtual circuits provide connection oriented

communication over an underlying packet oriented datagram network .Where it assures the delivery of packets in the

order in which they were sent and assure that they are free of errors .The datagram transportation deliver the packets

randomly and broadcast it to multiple nodes. Notes: The transport layer multiplexes several streams on to 1 physical

channel.The transport headers tells which message belongs to which connnection.

The Session Layer

This Layer provide a user interface to the network where the user negotiate to establish a connection ,the user must

provide the remote address in with he want to contact. The operation of setting up a session between 2 process is

called "Binding" in some protocols it is merged with the transport layer.

Presentation Layer

The Presentation Layer establishes context between Application Layer entities, in which the higher-layer entities

may use different syntax and semantics if the presentation service provides a mapping between them. If a mapping is

available, presentation service data units are encapsulated into session protocol data units, and passed down the

stack.This layer provides independence from data representation (e.g., encryption) by translating between application

and network formats. The presentation layer transforms data into the form that the application accepts. This layer

formats and encrypts data to be sent across a network. It is sometimes called the syntax layer.[citation needed]The

original presentation structure used the basic encoding rules of Abstract Syntax Notation One (ASN.1), withcapabilities such as converting an EBCDIC-coded text file to an ASCII-coded file, or serialization of objects and

other data structures from and to XML.

Application Layer

The Application Layer is the OSI layer closest to the end user, which means that both the OSI application layer and

the user interact directly with the software application. This layer interacts with software applications that implement

a communicating component. Such application programs fall outside the scope of the OSI model. Application layer

functions typically include identifying communication partners, determining resource availability, and synchronizing

communication. When identifying communication partners, the application layer determines the identity and

availability of communication partners for an application with data to transmit.

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Network architecture 3

Distributed computing

In distinct usage in distributed computing, the term network architecture often describes the structure and

classification of a distributed application architecture, as the participating nodes in a distributed application are often

referred to as a network . For example, the applications architecture of the public switched telephone network (PSTN)

has been termed the Advanced Intelligent Network. There are any number of specific classifications but all lie on a

continuum between the dumb network (e.g., Internet) and the intelligent computer network (e.g., the telephonenetwork). Other networks contain various elements of these two classical types to make them suitable for various

types of applications. Recently the context aware network, which is a synthesis of two, has gained much interest with

its ability to combine the best elements of both.

A popular example of such usage of the term in distributed applications, as well as PVCs (permanent virtual

circuits), is the organization of nodes in peer-to-peer (P2P) services and networks. P2P networks usually implement

overlay networks running over an underlying physical or logical network. These overlay network may implement

certain organizational structures of the nodes according to several distinct models, the network architecture of the

system.

Network architecture is a broad plan that specifies everything necessary for two application programs on different

networks on an Internet to be able to work together effectively.

References

€ This article incorporates public domain material from the General Services Administration document

"Federal Standard 1037C"[1]

(in support of MIL-STD-188).

References

[1] http:/   /  www. its. bldrdoc. gov/  fs-1037/  fs-1037c. htm

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Peer-to-peer 4

Peer-to-peer

A peer-to-peer system of nodes without central

infrastructure.

Centralized server-based service model.

Peer-to-peer (P2P) computing or networking is a distributed

application architecture that partitions tasks or workloads between

peers. Peers are equally privileged, equipotent participants in the

application. They are said to form a peer-to-peer network of nodes.

Peers make a portion of their resources, such as processing power,

disk storage or network bandwidth, directly available to other

network participants, without the need for central coordination by

servers or stable hosts.[1]

Peers are both suppliers and consumers

of resources, in contrast to the traditional client • server model

where only servers supply (send), and clients consume (receive).

The peer-to-peer application structure was popularized by file

sharing systems like Napster. The concept has inspired new

structures and philosophies in many areas of human interaction.

Peer-to-peer networking is not restricted to technology, but covers

also social processes with a peer-to-peer dynamic. In such context,

social peer-to-peer processes are currently emerging throughout

society.

Architecture of P2P systems

Peer-to-peer systems often implement an abstract overlay network,

built at Application Layer, on top of the native or physical network 

topology. Such overlays are used for indexing and peer discovery

and make the P2P system independent from the physical network 

topology. Content is typically exchanged directly over the

underlying Internet Protocol (IP) network. Anonymous

peer-to-peer systems are an exception, and implement extra

routing layers to obscure the identity of the source or destination

of queries.

In structured peer-to-peer networks, peers (and, sometimes,

resources) are organized following specific criteria and algorithms, which lead to overlays with specific topologies

and properties. They typically use distributed hash table-based (DHT) indexing, such as in the Chord system(MIT).

[2]

Unstructured peer-to-peer networks do not provide any algorithm for organization or optimization of network 

connections.. In particular, three models of unstructured architecture can be distinguished:

€ In pure peer-to-peer systems the entire network consists solely of equipotent peers. There is only one routing

layer, as there are no preferred nodes with any special infrastructure function.

€  Hybrid peer-to-peer systems allow such infrastructure nodes to exist, often called supernodes.[3]

€ In centralized peer-to-peer systems, a central server is used for indexing functions and to bootstrap the entire

system. Although this has similarities with a structured architecture, the connections between peers are not

determined by any algorithm.

The first prominent and popular peer-to-peer file sharing system, Napster, was an example of the centralized

model.[4]

  Freenet and early implementations of the gnutella protocol, on the other hand, are examples of the

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Peer-to-peer 5

decentralized model. Modern gnutella implementations, Gnutella2, as well as the now deprecated Kazaa network are

examples of the hybrid model.

P2P networks are typically used for connecting nodes via largely ad hoc connections. Data, including digital formats

such as audio files, and real time data such as telephony traffic, is passed using P2P technology.

A pure P2P network does not have the notion of clients or servers but only equal  peer nodes that simultaneously

function as both "clients" and "servers" to the other nodes on the network. This model of network arrangementdiffers from the client • server model where communication is usually to and from a central server. A typical example

of a file transfer that does not use the P2P model is the File Transfer Protocol (FTP) service in which the client and

server programs are distinct: the clients initiate the transfer, and the servers satisfy these requests.

The P2P overlay network consists of all the participating peers as network nodes. There are links between any two

nodes that know each other: i.e. if a participating peer knows the location of another peer in the P2P network, then

there is a directed edge from the former node to the latter in the overlay network. Based on how the nodes in the

overlay network are linked to each other, we can classify the P2P networks as unstructured or structured.

Structured systems

Structured P2P networks employ a globally consistent protocol to ensure that any node can efficiently route a search

to some peer that has the desired file, even if the file is extremely rare. Such a guarantee necessitates a more

structured pattern of overlay links. By far the most common type of structured P2P network is the distributed hash

table (DHT), in which a variant of consistent hashing is used to assign ownership of each file to a particular peer, in

a way analogous to a traditional hash table's assignment of each key to a particular array slot.

Distributed hash tables

Distributed hash tables

Distributed hash tables (DHTs) are a class

of decentralized distributed systems that

provide a lookup service similar to a hashtable: (key, value) pairs are stored in the

DHT, and any participating node can

efficiently retrieve the value associated with

a given key. Responsibility for maintaining

the mapping from keys to values is

distributed among the nodes, in such a way

that a change in the set of participants

causes a minimal amount of disruption. This allows DHTs to scale to extremely large numbers of nodes and to

handle continual node arrivals, departures, and failures.

DHTs form an infrastructure that can be used to build peer-to-peer networks. Notable distributed networks that use

DHTs include BitTorrent's distributed tracker, the Kad network, the Storm botnet, YaCy, and the Coral Content

Distribution Network.

Some prominent research projects include the Chord project, the PAST storage utility, the P-Grid, a self-organized

and emerging overlay network and the CoopNet content distribution system (see below for external links related to

these projects).

DHT-based networks have been widely utilized for accomplishing efficient resource discovery[5]

 [6]

for grid

computing systems, as it aids in resource management and scheduling of applications. Resource discovery activity

involves searching for the appropriate resource types that match the user‚s application requirements. Recent advances

in the domain of decentralized resource discovery have been based on extending the existing DHTs with thecapability of multi-dimensional data organization and query routing. Majority of the efforts have looked at

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Peer-to-peer 6

embedding spatial database indices such as the Space Filling Curves (SFCs) including the Hilbert curves, Z-curves,

k-d tree, MX-CIF Quad tree and R*-tree for managing, routing, and indexing of complex Grid resource query

objects over DHT networks. Spatial indices are well suited for handling the complexity of Grid resource queries.

Although some spatial indices can have issues as regards to routing load-balance in case of a skewed data set, all the

spatial indices are more scalable in terms of the number of hops traversed and messages generated while searching

and routing Grid resource queries.

Unstructured systems

An unstructured P2P network is formed when the overlay links are established arbitrarily. Such networks can be

easily constructed as a new peer that wants to join the network can copy existing links of another node and then form

its own links over time. In an unstructured P2P network, if a peer wants to find a desired piece of data in the

network, the query has to be flooded through the network to find as many peers as possible that share the data. The

main disadvantage with such networks is that the queries may not always be resolved. Popular content is likely to be

available at several peers and any peer searching for it is likely to find the same thing. But if a peer is looking for

rare data shared by only a few other peers, then it is highly unlikely that search will be successful. Since there is no

correlation between a peer and the content managed by it, there is no guarantee that flooding will find a peer that hasthe desired data. Flooding also causes a high amount of signaling traffic in the network and hence such networks

typically have very poor search efficiency. Many of the popular P2P networks are unstructured.

In  pure P2P networks: Peers act as equals, merging the roles of clients and server. In such networks, there is no

central server managing the network, neither is there a central router. Some examples of pure P2P Application Layer

networks designed for peer-to-peer file sharing are gnutella (pre v0.4) and Freenet.

There also exist hybrid P2P systems, which distribute their clients into two groups: client nodes and overlay nodes.

Typically, each client is able to act according to the momentary need of the network and can become part of the

respective overlay network used to coordinate the P2P structure. This division between normal and 'better' nodes is

done in order to address the scaling problems on early pure P2P networks. As examples for such networks can be

named modern implementations of gnutella (after v0.4) and Gnutella2.

Another type of hybrid P2P network are networks using on the one hand central server(s) or bootstrapping

mechanisms, on the other hand P2P for their data transfers. These networks are in general called 'centralized

networks' because of their lack of ability to work without their central server(s). An example for such a network is

the eDonkey network (often also called eD2k ).

Indexing and resource discovery

Older peer-to-peer networks duplicate resources across each node in the network configured to carry that type of 

information. This allows local searching, but requires much traffic.

Modern networks use central coordinating servers and directed search requests. Central servers are typically used for

listing potential peers (Tor), coordinating their activities (Folding@home), and searching (Napster, eMule).

Decentralized searching was first done by flooding search requests out across peers. More efficient directed search

strategies, including supernodes and distributed hash tables, are now used.

Many P2P systems use stronger peers (super-peers, super-nodes) as servers and client-peers are connected in a

star-like fashion to a single super-peer.

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Peer-to-peer 7

Peer-to-peer-like systems

In modern definitions of peer-to-peer technology, the term implies the general architectural concepts outlined in this

article. However, the basic concept of peer-to-peer computing was envisioned in earlier software systems and

networking discussions, reaching back to principles stated in the first Request for Comments, RFC 1.[7]

A distributed messaging system that is often likened as an early peer-to-peer architecture is the USENET network 

news system that is in principle a client • server model from the user or client perspective, when they read or post

news articles. However, news servers communicate with one another as peers to propagate Usenet news articles over

the entire group of network servers. The same consideration applies to SMTP email in the sense that the core email

relaying network of Mail transfer agents has a peer-to-peer character, while the periphery of e-mail clients and their

direct connections is strictly a client • server relationship. Tim Berners-Lee's vision for the World Wide Web, as

evidenced by his WorldWideWeb editor/browser, was close to a peer-to-peer design in that it assumed each user of 

the web would be an active editor and contributor creating and linking content to form an interlinked web of links.

This contrasts to the broadcasting-like structure of the web as it has developed over the years.

Advantages and weaknessesIn P2P networks, clients provide resources, which may include bandwidth, storage space, and computing power. As

nodes arrive and demand on the system increases, the total capacity of the system also increases. In contrast, in a

typical client • server architecture, clients share only their demands with the system, but not their resources. In this

case, as more clients join the system, fewer resources are available to serve each client.

The decentralized nature of P2P networks also increases robustness because it removes the single point of failure that

can be inherent in a client-server based system.[8]

As with most network systems, unsecure and unsigned codes may allow remote access to files on a victim's

computer or even compromise the entire network. In the past this has happened for example to the FastTrack 

network when anti P2P companies managed to introduce faked chunks into downloads and downloaded files (mostly

MP3 files) were unusable afterwards or even contained malicious code. Consequently, the P2P networks of today

have seen an enormous increase of their security and file verification mechanisms. Modern hashing, chunk 

verification and different encryption methods have made most networks resistant to almost any type of attack, even

when major parts of the respective network have been replaced by faked or nonfunctional hosts.

Internet service providers (ISPs) have been known to throttle P2P file-sharing traffic due to the high-bandwidth

usage.[9]

Compared to Web browsing, e-mail or many other uses of the internet, where data is only transferred in

short intervals and relative small quantities, P2P file-sharing often consists of relatively heavy bandwidth usage due

to ongoing file transfers and swarm/network coordination packets. As a reaction to this bandwidth throttling several

P2P applications started implementing protocol obfuscation, such as the BitTorrent protocol encryption. Techniques

for achieving "protocol obfuscation" involves removing otherwise easily identifiable properties of protocols, such asdeterministic byte sequences and packet sizes, by making the data look as if it were random.

[10]

A possible solution to this is called P2P caching, where a ISP stores the part of files most accessed by P2P clients in

order to save access to the Internet.

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Peer-to-peer 8

Social and economic impact

The concept of P2P is increasingly evolving to an expanded usage as the relational dynamic active in distributed

networks, i.e., not just computer to computer, but human to human. Yochai Benkler has coined the term

commons-based peer production to denote collaborative projects such as free and open source software and

Wikipedia. Associated with peer production are the concepts of:

€ peer governance (referring to the manner in which peer production projects are managed)

€ peer property (referring to the new type of licenses which recognize individual authorship but not exclusive

property rights, such as the GNU General Public License and the Creative Commons licenses)

€ peer distribution (or the manner in which products, particularly peer-produced products, are distributed)

Some researchers have explored the benefits of enabling virtual communities to self-organize and introduce

incentives for resource sharing and cooperation, arguing that the social aspect missing from today's peer-to-peer

systems should be seen both as a goal and a means for self-organized virtual communities to be built and fostered.[11]

Ongoing research efforts for designing effective incentive mechanisms in P2P systems, based on principles from

game theory are beginning to take on a more psychological and information-processing direction.

Applications

There are numerous applications of peer-to-peer networks. The most commonly known is for content distribution

Content delivery

€ Many file sharing networks, such as gnutella, G2 and the eDonkey network popularized peer-to-peer

technologies. From 2004 on, such networks form the largest contributor of network traffic on the Internet.

€ Peer-to-peer content delivery networks (P2P-CDN) (Giraffic, Kontiki, Ignite, RedSwoosh).

€ Peer-to-peer content services, e.g. caches for improved performance such as Correli Caches[12]

€ Software publication and distribution (Linux, several games); via file sharing networks.

€ Streaming media. P2PTV and PDTP. Applications include TVUPlayer, Joost, CoolStreaming, Cybersky-TV,

PPLive, LiveStation, Giraffic and Didiom.

€ Spotify uses a peer-to-peer network along with streaming servers to stream music to its desktop music player.

€ Peercasting for multicasting streams. See PeerCast, IceShare, FreeCast, Rawflow

€ Pennsylvania State University, MIT and Simon Fraser University are carrying on a project called LionShare

designed for facilitating file sharing among educational institutions globally.

€ Osiris (Serverless Portal System) allows its users to create anonymous and autonomous web portals distributed

via P2P network.

Exchange of physical goods, services,or space

€ Peer-to-peer renting web platforms enable people to find and reserve goods, services, or space on the virtual

platform, but carry out the actual P2P transaction in the physical world (for example: emailing a local footwear

vendor to reserve for you that comfy pair of slippers which you've always had your eyes on, or contacting a

neighbor who has listed their weedwacker for rent).

Networking

€ Domain Name System, for Internet information retrieval. See Comparison of DNS server software

€ cloud computing

€ Dalesa a peer-to-peer web cache for LANs (based on IP multicasting).

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Peer-to-peer 9

Science

€ In bioinformatics, drug candidate identification. The first such program was begun in 2001 the Centre for

Computational Drug Discovery at the University of Oxford in cooperation with the National Foundation for

Cancer Research. There are now several similar programs running under the United Devices Cancer Research

Project.

€ The sciencenet P2P search engine.€ BOINC

Search

€ YaCy, a free distributed search engine, built on principles of peer-to-peer networks.

Communications networks

€ Skype, one of the most widely used internet phone applications is using P2P technology.

€ VoIP (using application layer protocols such as SIP)

€ Instant messaging and online chat

€ Completely decentralized networks of peers: Usenet (1979) and WWIVnet (1987).

General

€ Research like the Chord project, the PAST storage utility, the P-Grid, and the CoopNet content distribution

system.

€ JXTA, for Peer applications. See Collanos Workplace (Teamwork software), Sixearch

Miscellaneous

€ The U.S. Department of Defense has started research on P2P networks as part of its modern network warfare

strategy.[13] In May, 2003 Dr. Tether. Director of Defense Advanced Research Project Agency testified that U.S.

Military is using P2P networks.

€ Kato et al.‚s studies indicate over 200 companies with approximately $400 million USD are investing in P2P

network. Besides File Sharing, companies are also interested in Distributing Computing, Content Distribution.

€ Wireless community network, Netsukuku

€ An earlier generation of peer-to-peer systems were called "metacomputing" or were classed as "middleware".

These include: Legion, Globus

€ Bitcoin is a peer-to-peer based digital currency.

Historical perspective

Tim Berners-Lee's vision for the World Wide Web was close to a P2P network in that it assumed each user of the

web would be an active editor and contributor, creating and linking content to form an interlinked "web" of links.

This contrasts to the current broadcasting-like structure of the web.

Some networks and channels such as Napster, OpenNAP and IRC serving channels use a client • server structure for

some tasks (e.g., searching) and a P2P structure for others. Networks such as gnutella or Freenet use a P2P structure

for nearly all tasks, with the exception of finding peers to connect to when first setting up.

P2P architecture embodies one of the key technical concepts of the Internet, described in the first Internet Request

for Comments, RFC 1, "Host Software" dated April 7, 1969. More recently, the concept has achieved recognition in

the general public in the context of the absence of central indexing servers in architectures used for exchanging

multimedia files.

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Peer-to-peer 10

Network neutrality controversy

Peer-to-peer applications present one of the core issues in the network neutrality controversy. In October 2007,

Comcast, one of the largest broadband Internet providers in the USA, started blocking P2P applications such as

BitTorrent. Their rationale was that P2P is mostly used to share illegal content, and their infrastructure is not

designed for continuous, high-bandwidth traffic. Critics point out that P2P networking has legitimate uses, and that

this is another way that large providers are trying to control use and content on the Internet, and direct peopletowards a client-server-based application architecture. The client-server model provides financial barriers-to-entry to

small publishers and individuals, and is quite inefficient for sharing large files.

References

[1] R‚diger Schollmeier, A Definition of Peer-to-Peer Networking for the Classification of Peer-to-Peer Architectures and Applications,

Proceedings of the First International Conference on Peer-to-Peer Computing, IEEE (2002).

[2] Kelaskar, M.; Matossian, V.; Mehra, P.; Paul, D.; Parashar, M. (2002), A Study of Discovery Mechanisms for Peer-to-Peer Application (http:/ 

 /  portal. acm.org/  citation. cfm?id=873218),

[3] Beverly Yang and Hector Garcia-Molina, Designing a super-peer network , Proceedings of the 19th International Conference on Data

Engineering (2003).

[4] Napster - the first prominent example of a centralized P2P system (http:/   /  www8. cs. umu.  se/  ~bergner/  thesis/  html/  node30.  html)

[5] Ranjan, Rajiv; Harwood, Aaron; Buyya, Rajkumar (1 December 2006), A Study on Peer-to-Peer Based Discovery of Grid Resource

 Information (http:/   /  www. cs. mu. oz. au/  ~rranjan/  pgrid. pdf),

[6] Ranjan, Rajiv; Chan, Lipo; Harwood, Aaron; Karunasekera, Shanika; Buyya, Rajkumar. "Decentralised Resource Discovery Service for

Large Scale Federated Grids" (http:/   /  gridbus. org/  papers/  DecentralisedDiscoveryGridFed-eScience2007. pdf) (PDF). .

[7] RFC 1, Host Software, S. Crocker, IETF Working Group (April 7, 1969)

[8] Lua, Eng Keong; Crowcroft, Jon; Pias, Marcelo; Sharma, Ravi; Lim, Steven (2005). "A survey and comparison of peer-to-peer overlay

network schemes" (http:/   /  academic. research. microsoft. com/  Publication/  2633870/ 

a-survey-and-comparison-of-peer-to-peer-overlay-network-schemes). .

[9] Janko Roettgers, 5 Ways to Test Whether your ISP throttles P2P, http:/   /  newteevee. com/  2008/  04/  02/ 

5-ways-to-test-if-your-isp-throttles-p2p/ 

[10] Hjelmvik, Erik; John, Wolfgang (2010-07-27). "Breaking and Improving Protocol Obfuscation" (http:/   /  www. iis. se/  docs/ 

hjelmvik_breaking.pdf). .

[11] Antoniadis, P. & Le Grand, B. (2007). Incentives for resource sharing in self-organized communities: From economics to social psychology.

Digital Information Management, 2007. ICDIM '07

[12] Gareth Tyson, Andreas Mauthe, Sebastian Kaune, Mu Mu and Thomas Plagemann. Corelli: A Dynamic Replication Service for Supporting

Latency-Dependent Content in Community Networks. In Proc. 16th ACM/SPIE Multimedia Computing and Networking Conference

(MMCN), San Jose, CA (2009). (http:/   /  www. dcs. kcl. ac. uk/  staff/  tysong/  files/  MMCN09.  pdf)

[13] "Walker, Leslie. Uncle Sam Wants Napster! The Washington Post, November 8, 2001" (http:/   /  www. washingtonpost. com/  ac2/ 

wp-dyn?pagename=article& node=washtech/  techthursday/  columns/  dotcom& contentId=A59099-2001Nov7). 2001-11-08. . Retrieved

2010-05-22.

External links

€ Glossary (http:/   /  www. p2pna. com/  glossary. html) of P2P terminology€ Foundation of Peer-to-Peer Computing (http:/   /  www. sciencedirect.com/  science/  issue/ 

5624-2008-999689997-678759), Special Issue, Elsevier Journal of Computer Communication, (Ed) Javed I. Khan

and Adam Wierzbicki, Volume 31, Issue 2, February 2008

€ Ross J. Anderson. The eternity service (http:/   /  www. cl. cam. ac.uk/  users/  rja14/  eternity/  eternity. html). In

 Pragocrypt 1996 , 1996.

€ Marling Engle & J. I. Khan. Vulnerabilities of P2P systems and a critical look at their solutions (http:/   /  www.

medianet.kent. edu/  techreports/  TR2006-11-01-p2pvuln-EK. pdf), May 2006

€ Stephanos Androutsellis-Theotokis and Diomidis Spinellis. A survey of peer-to-peer content distribution

technologies (http:/   /  www. spinellis. gr/  pubs/   jrnl/  2004-ACMCS-p2p/  html/  AS04. html). ACM Computing

Surveys, 36(4):335 • 371, December 2004.

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Peer-to-peer 11

€ Biddle, Peter, Paul England, Marcus Peinado, and Bryan Willman, The Darknet and the Future of Content

Distribution (http:/   /  crypto. stanford. edu/  DRM2002/  darknet5. doc). In 2002 ACM Workshop on Digital Rights

 Management , November 2002.

€ John F. Buford, Heather Yu, Eng Keong Lua P2P Networking and Applications (http:/   /  www. p2pna. com).

ISBN 30-12374-214-5, Morgan Kaufmann, December 2008

€ Djamal-Eddine Meddour, Mubashar Mushtaq, and Toufik Ahmed, ƒ Open Issues in P2P Multimedia Streaming

(http:/   /  multicomm. polito. it/  proc_multicomm06_8.pdf)„, in the proceedings of the 1st Multimedia

Communications Workshop MULTICOMM 2006 held in conjunction with IEEE ICC 2006 pp 43 • 48, June 2006,

Istanbul, Turkey.

€ Detlef Schoder and Kai Fischbach, Core Concepts in Peer-to-Peer (P2P) Networking (http:/   /  www. econbiz. de/ 

archiv1/  2008/  42151_concepts_peer-to-peer_networking. pdf). In: Subramanian, R.; Goodman, B. (eds.): P2P

Computing: The Evolution of a Disruptive Technology, Idea Group Inc, Hershey. 2005

€ Ralf Steinmetz, Klaus Wehrle (Eds). Peer-to-Peer Systems and Applications (http:/   /  www. peer-to-peer.info/  ).

ISBN 3-540-29192-X, Lecture Notes in Computer Science, Volume 3485, September 2005.

€ Ramesh Subramanian and Brian Goodman (eds), Peer-to-Peer Computing: Evolution of a Disruptive Technology

(http:/  

 /  

www.igi-pub. 

com/  

books/  

details. 

asp?ID=4635), ISBN 1-59140-429-0, Idea Group Inc., Hershey, PA,USA, 2005.

€ Shuman Ghosemajumder. Advanced Peer-Based Technology Business Models (http:/   /  shumans. com/ 

p2p-business-models. pdf). MIT Sloan School of Management, 2002.

€ Silverthorne, Sean. Music Downloads: Pirates- or Customers? (http:/   /  hbswk. hbs. edu/  item.  jhtml?id=4206&

t=innovation). Harvard Business School Working Knowledge, 2004.

Client €server model

The client €

server model of computing is a distributed application that partitions tasks or workloads between theproviders of a resource or service, called servers, and service requesters, called clients.

[1]Often clients and servers

communicate over a computer network on separate hardware, but both client and server may reside in the same

system. A server machine is a host that is running one or more server programs which share their resources with

clients. A client does not share any of its resources, but requests a server's content or service function. Clients

therefore initiate communication sessions with servers which await incoming requests.

Description

Schematic clients-server interaction.

The client € server characteristic describes the relationship of 

cooperating programs in an application. The server component

provides a function or service to one or many clients, which initiate

requests for such services.

 Functions such as email exchange, web access and database access, are

built on the client • server model. Users accessing banking services

from their computer use a web browser client to send a request to a

web server at a bank. That program may in turn forward the request to its own database client program that sends a

request to a database server at another bank computer to retrieve the account information. The balance is returned to

the bank database client, which in turn serves it back to the web browser client displaying the results to the user. The

client • server model has become one of the central ideas of network computing. Many business applications being

written today use the client • server model. So do the Internet's main application protocols, such as HTTP, SMTP,Telnet, and DNS.

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Clientserver model 12

The interaction between client and server is often described using sequence diagrams. Sequence diagrams are

standardized in the Unified Modeling Language.

Specific types of clients include web browsers, email clients, and online chat clients.

Specific types of servers include web servers, ftp servers, application servers, database servers, name servers, mail

servers, file servers, print servers, and terminal servers. Most web services are also types of servers.

Comparison to peer-to-peer architecture

A client-server network involves multiple clients connecting to a single, central server. The file server on a

client-server network is a high capacity, high speed computer with a large hard disk capacity.

By contrast, peer-to-peer networks involve two or more computers pooling individual resources such as disk drives,

CD-ROMs and printers[2]

. These shared resources are available to every computer in the network, while each two of 

them communicate in a session. Each computer acts as both the client and the server which means all the computers

on the network are equals, that is where the term peer-to-peer comes from. The advantage of peer-to-peer networking

is the easier control concept not requiring any additional coordination entity and not delaying transfers by routing via

server entities. However, the collision of session may be larger than with routing via server nodes.In the peer to peer network, software applications can be installed on the single computer and shared by every

computer in the network. They are also cheaper to set up because most desktop operating systems have the software

required for the network installed by default. On the other hand, the client-server model works with any size or

physical layout of LAN and doesn't tend to slow down with a heavy use.[3]

.

Peer-to-peer networks are typically less secure than a client-server networks because security is handled by the

individual computers, not controlled and supervised on the network as a whole. The resources of the computers in

the network can become congested as they have to support not only the workstation user, but also the requests from

network users. It may be difficult to provide systemwide services when the client operating system typically used in

this type of network is incapable of hosting the service.

Client-server networks with their additional capacities have a higher initial setup cost for networking than peer to

peer networks. The long-term aspect of administering a client-server network with applications largely server-hosted

surely saves administering effort compared to administering the application settings per each client. In addition the

concentration of functions in performant servers allows for lower grade performance qualification of the clients.

It is possible to set up a server on a modern desktop computer, but it is recommended to consider investment in

enterprise-wide server facilities with standardised choice of hardware and software and with a systematic and

remotely operable administering strategy. It is easier to configure and manage the server hardware and software

compared to the distributed administering requirements with a flock of computers[4]

 [5]

.

ChallengesGenerally a server may be challenged beyond its capabilities. Then a single server may cause a bottleneck or

constraints problem. However, servers may be cloned and networked to fulfill all known capacity and performance

requirements. Limitations include network load, network address volume, and transaction recovery time.

Aspects of comparison for other architectural concepts today include cloud computing as well. Possible design

decision considerations might be:

€ As soon as the total number of simultaneous client requests to a given server increases, the server can become

overloaded. Contrast that to a P2P network, where its aggregated bandwidth actually increases as nodes are

added, since the P2P network's overall bandwidth can be roughly computed as the sum of the bandwidths of every

node in that network. However, this simple model ends with the bandwidth of the network: Then congestioncomes on the network and not with the peers.

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Clientserver model 13

€ Any single entity paradigm lacks the robustness of a redundant configuration. Under client • server, should a

critical server fail, clients‚ requests cannot be fulfilled by this very entity, but may be taken by another server, as

long as required data is accessible. In P2P networks, resources are usually distributed among many nodes which

generate as many locations to fail. If dynamic re-routing is established, even if one or more nodes depart and

abandon a downloading file, for example, the remaining nodes should still have the data needed to complete the

download.

€ Mainframe networks use dumb terminals. All processing is completed on few central computers. This is a method

of running a network with different limitations compared to fully fashioned clients.

€ Using intelligent client terminals increases the maintenance and repair effort. Lesser complete netbook clients

allow for reduction of hardware entities that have limited life cycles.

References

[1] "Distributed Application Architecture" (http:/   /   java. sun.  com/  developer/  Books/   jdbc/  ch07. pdf). Sun Microsystem. . Retrieved 2009-06-16.

[2] Understanding peer-to-peer networking (http:/   /  www. isafe. org/  imgs/  pdf/  education/  P2PNetworking. pdf)

[3] [Peer-to-Peer Networking and Applications]

[4] Book: Computers are your future[5] Peer to Peer vs. Client/Server Networks

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14

Network Topologies

Network topology

Diagram of different network topologies.

Network topology is the layout pattern of 

interconnections of the various elements

(links, nodes, etc.) of a computer[1]

 [2]

or

biological network.[3]

Network topologies

may be physical or logical. Physical

topology refers to the physical design of a

network including the devices, location and

cable installation. Logical topology refers to

how data is actually transferred in a network 

as opposed to its physical design. In general

physical topology relates to a core network 

whereas logical topology relates to basic

network.

Topology can be understood as the shape or structure of a network. This shape does not necessarily correspond to the

actual physical design of the devices on the computer network. The computers on a home network can be arranged in

a circle but it does not necessarily mean that it represents a ring topology.

Any particular network topology is determined only by the graphical mapping of the configuration of physical and/or

logical connections between nodes. The study of network topology uses graph theory. Distances between nodes,physical interconnections, transmission rates, and/or signal types may differ in two networks and yet their topologies

may be identical.

A local area network (LAN) is one example of a network that exhibits both a physical topology and a logical

topology. Any given node in the LAN has one or more links to one or more nodes in the network and the mapping of 

these links and nodes in a graph results in a geometric shape that may be used to describe the physical topology of 

the network. Likewise, the mapping of the data flow between the nodes in the network determines the logical

topology of the network. The physical and logical topologies may or may not be identical in any particular network.

Topology classification

There are two basic categories of network topologies:[4]

€ Physical topologies

€ Logical topologies

The shape of the cabling layout used to link devices is called the physical topology of the network. This refers to the

layout of cabling, the locations of nodes, and the interconnections between the nodes and the cabling.[1]

The physical

topology of a network is determined by the capabilities of the network access devices and media, the level of control

or fault tolerance desired, and the cost associated with cabling or telecommunications circuits.

The logical topology, in contrast, is the way that the signals act on the network media, or the way that the data passes

through the network from one device to the next without regard to the physical interconnection of the devices. A

network's logical topology is not necessarily the same as its physical topology. For example, the original twisted pair

Ethernet using repeater hubs was a logical bus topology with a physical star topology layout. Token Ring is a logical

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Network topology 15

ring topology, but is wired a physical star from the Media Access Unit.

The logical classification of network topologies generally follows the same classifications as those in the physical

classifications of network topologies but describes the path that the data takes between nodes being used as opposed

to the actual  physical connections between nodes. The logical topologies are generally determined by network 

protocols as opposed to being determined by the physical layout of cables, wires, and network devices or by the flow

of the electrical signals, although in many cases the paths that the electrical signals take between nodes may closelymatch the logical flow of data, hence the convention of using the terms logical topology and signal topology

interchangeably.

Logical topologies are often closely associated with Media Access Control methods and protocols. Logical

topologies are able to be dynamically reconfigured by special types of equipment such as routers and switches.

The study of network topology recognizes seven basic topologies:[5]

€ Point-to-point

€ Bus

€ Star

€ Ring

€ Mesh

€ Tree

€ Hybrid

€ Daisy chain

Point-to-point

The simplest topology is a permanent link between two endpoints. Switched point-to-point topologies are the basic

model of conventional telephony. The value of a permanent point-to-point network is unimpeded communications

between the two endpoints. The value of an on-demand point-to-point connection is proportional to the number of 

potential pairs of subscribers, and has been expressed as Metcalfe's Law.Permanent (dedicated)

Easiest to understand, of the variations of point-to-point topology, is a point-to-point communications

channel that appears, to the user, to be permanently associated with the two endpoints. A children's tin

can telephone is one example of a physical dedicated channel.

Within many switched telecommunications systems, it is possible to establish a permanent circuit. One

example might be a telephone in the lobby of a public building, which is programmed to ring only the

number of a telephone dispatcher. "Nailing down" a switched connection saves the cost of running a

physical circuit between the two points. The resources in such a connection can be released when no

longer needed, for example, a television circuit from a parade route back to the studio.

Switched:

Using circuit-switching or packet-switching technologies, a point-to-point circuit can be set up

dynamically, and dropped when no longer needed. This is the basic mode of conventional telephony.

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Network topology 16

Bus

Bus network topology

In local area networks where bus topology is used, each node is

connected to a single cable. Each computer or server is

connected to the single bus cable. A signal from the source

travels in both directions to all machines connected on the bus

cable until it finds the intended recipient. If the machine address

does not match the intended address for the data, the machine

ignores the data. Alternatively, if the data matches the machine

address, the data is accepted. Since the bus topology consists of 

only one wire, it is rather inexpensive to implement when

compared to other topologies. However, the low cost of implementing the technology is offset by the high cost

of managing the network. Additionally, since only one cable is utilized, it can be the single point of failure. If 

the network cable breaks, the entire network will be down.

Linear bus

The type of network topology in which all of the nodes of the network are connected to a commontransmission medium which has exactly two endpoints (this is the 'bus', which is also commonly referred

to as the backbone, or trunk) • all data that is transmitted between nodes in the network is transmitted

over this common transmission medium and is able to be received by all nodes in the network 

simultaneously.[1]

Note: The two endpoints of the common transmission medium are normally terminated with a device

called a terminator that exhibits the characteristic impedance of the transmission medium and which

dissipates or absorbs the energy that remains in the signal to prevent the signal from being reflected or

propagated back onto the transmission medium in the opposite direction, which would cause

interference with and degradation of the signals on the transmission medium.

Distributed bus

The type of network topology in which all of the nodes of the network are connected to a common

transmission medium which has more than two endpoints that are created by adding branches to the

main section of the transmission medium • the physical distributed bus topology functions in exactly the

same fashion as the physical linear bus topology (i.e., all nodes share a common transmission medium).

Notes:

1. All of the endpoints of the common transmission medium are normally terminated.

2. The linear bus topology is sometimes considered to be a special case of the distributed bus topology • i.e.,

a distributed bus with no branching segments.

3. The physical distributed bus topology is sometimes incorrectly referred to as a physical tree topology • 

however, although the physical distributed bus topology resembles the physical tree topology, it differs

from the physical tree topology in that there is no central node to which any other nodes are connected,

since this hierarchical functionality is replaced by the common bus.

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Network topology 17

Star

Star network topology

In local area networks with a star topology, each network host is

connected to a central hub with a point-to-point connection. All

traffic that traverses the network passes through the central hub.

The hub acts as a signal repeater. The star topology is considered

the easiest topology to design and implement. An advantage of 

the star topology is the simplicity of adding additional nodes.

The primary disadvantage of the star topology is that the hub

represents a single point of failure.

Notes

1. A point-to-point link (described above) is sometimes

categorized as a special instance of the physical star

topology • therefore, the simplest type of network that is

based upon the physical star topology would consist of one

node with a single point-to-point link to a second node, the choice of which node is the 'hub' and whichnode is the 'spoke' being arbitrary.

[1]

2. After the special case of the point-to-point link, as in note (1) above, the next simplest type of network that

is based upon the physical star topology would consist of one central node • the 'hub' • with two separate

point-to-point links to two peripheral nodes • the 'spokes'.

3. Although most networks that are based upon the physical star topology are commonly implemented using a

special device such as a hub or switch as the central node (i.e., the 'hub' of the star), it is also possible to

implement a network that is based upon the physical star topology using a computer or even a simple

common connection point as the 'hub' or central node.

4. Star networks may also be described as either broadcast multi-access or nonbroadcast multi-access

(NBMA), depending on whether the technology of the network either automatically propagates a signal atthe hub to all spokes, or only addresses individual spokes with each communication.

Extended star

A type of network topology in which a network that is based upon the physical star topology has one or

more repeaters between the central node (the 'hub' of the star) and the peripheral or 'spoke' nodes, the

repeaters being used to extend the maximum transmission distance of the point-to-point links between

the central node and the peripheral nodes beyond that which is supported by the transmitter power of the

central node or beyond that which is supported by the standard upon which the physical layer of the

physical star network is based.

If the repeaters in a network that is based upon the physical extended star topology are replaced withhubs or switches, then a hybrid network topology is created that is referred to as a physical hierarchical

star topology, although some texts make no distinction between the two topologies.

Distributed Star

A type of network topology that is composed of individual networks that are based upon the physical

star topology connected together in a linear fashion • i.e., 'daisy-chained' • with no central or top level

connection point (e.g., two or more 'stacked' hubs, along with their associated star connected nodes or

'spokes').

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Network topology 18

Ring

Ring network topology

A network topology that is set up in a circular fashion in which

data travels around the ring in one direction and each device on

the right acts as a repeater to keep the signal strong as it travels.

Each device incorporates a receiver for the incoming signal and

a transmitter to send the data on to the next device in the ring.

The network is dependent on the ability of the signal to travel

around the ring.[4]

Mesh

The value of fully meshed networks is proportional to the exponent of 

the number of subscribers, assuming that communicating groups of any

two endpoints, up to and including all the endpoints, is approximated

by Reed's Law.

Fully connected

Fully connected mesh topology

The number of connections in a full mesh = n(n - 1) / 2.

Note: The physical fully connected mesh topology is

generally too costly and complex for practical networks,

although the topology is used when there are only a small

number of nodes to be interconnected.

Partially connected

Partially connected mesh topology

The type of network topology in which some of the nodes

of the network are connected to more than one other node

in the network with a point-to-point link • this makes it

possible to take advantage of some of the redundancy that

is provided by a physical fully connected mesh topology

without the expense and complexity required for aconnection between every node in the network.

Note: In most practical networks that are based upon the

partially connected mesh topology, all of the data that is

transmitted between nodes in the network takes the

shortest path between nodes, except in the case of a failure

or break in one of the links, in which case the data takes an alternative path to the destination. This

requires that the nodes of the network possess some type of logical 'routing' algorithm to determine the

correct path to use at any particular time.

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Network topology 19

Tree

Tree network topology

The type of network topology in which a central 'root' node (the top

level of the hierarchy) is connected to one or more other nodes that are

one level lower in the hierarchy (i.e., the second level) with a

point-to-point link between each of the second level nodes and the top

level central 'root' node, while each of the second level nodes that are

connected to the top level central 'root' node will also have one or more

other nodes that are one level lower in the hierarchy (i.e., the third

level) connected to it, also with a point-to-point link, the top level

central 'root' node being the only node that has no other node above it

in the hierarchy (The hierarchy of the tree is symmetrical.) Each node

in the network having a specific fixed number, of nodes connected to it at the next lower level in the hierarchy, the

number, being referred to as the 'branching factor' of the hierarchical tree.This tree has individual peripheral nodes.

1. A network that is based upon the physical hierarchical topology must have at least three levels in the hierarchy

of the tree, since a network with a central 'root' node and only one hierarchical level below it would exhibit the

physical topology of a star.

2. A network that is based upon the physical hierarchical topology and with a branching factor of 1 would be

classified as a physical linear topology.

3. The branching factor, f, is independent of the total number of nodes in the network and, therefore, if the nodes

in the network require ports for connection to other nodes the total number of ports per node may be kept low

even though the total number of nodes is large • this makes the effect of the cost of adding ports to each node

totally dependent upon the branching factor and may therefore be kept as low as required without any effect

upon the total number of nodes that are possible.

4. The total number of point-to-point links in a network that is based upon the physical hierarchical topology will

be one less than the total number of nodes in the network.

5. If the nodes in a network that is based upon the physical hierarchical topology are required to perform any

processing upon the data that is transmitted between nodes in the network, the nodes that are at higher levels in

the hierarchy will be required to perform more processing operations on behalf of other nodes than the nodes

that are lower in the hierarchy. Such a type of network topology is very useful and highly recommended.

definition : A tree topology connects multiple star topologies together onto a common single cable.

Hybrid

Hybrid networks use a combination of any two or more topologies in such a way that the resulting network does not

exhibit one of the standard topologies (e.g., bus, star, ring, etc.). For example, a tree network connected to a tree

network is still a tree network topology. A hybrid topology is always produced when two different basic network 

topologies are connected. Two common examples for Hybrid network are: star ring network and star bus network 

€ A Star ring network consists of two or more star topologies connected using a multistation access unit (MAU) as

a centralized hub.

€ A Star Bus network consists of two or more star topologies connected using a bus trunk (the bus trunk serves as

the network's backbone).

While grid networks have found popularity in high-performance computing applications, some systems have used

genetic algorithms to design custom networks that have the fewest possible hops in between different nodes. Some

of the resulting layouts are nearly incomprehensible, although they function quite well.

A Snowflake topology is really a "Star of Stars" network, so it exhibits characteristics of a hybrid network topologybut is not composed of two different basic network topologies being connected together.

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Network topology 20

Daisy chain

Except for star-based networks, the easiest way to add more computers into a network is by daisy-chaining, or

connecting each computer in series to the next. If a message is intended for a computer partway down the line, each

system bounces it along in sequence until it reaches the destination. A daisy-chained network can take two basic

forms: linear and ring.

€ A linear topology puts a two-way link between one computer and the next. However, this was expensive in the

early days of computing, since each computer (except for the ones at each end) required two receivers and two

transmitters.

€ By connecting the computers at each end, a ring topology can be formed. An advantage of the ring is that the

number of transmitters and receivers can be cut in half, since a message will eventually loop all of the way

around. When a node sends a message, the message is processed by each computer in the ring. If a computer is

not the destination node, it will pass the message to the next node, until the message arrives at its destination. If 

the message is not accepted by any node on the network, it will travel around the entire ring and return to the

sender. This potentially results in a doubling of travel time for data.

Centralization

The star topology reduces the probability of a network failure by connecting all of the peripheral nodes (computers,

etc.) to a central node. When the physical star topology is applied to a logical bus network such as Ethernet, this

central node (traditionally a hub) rebroadcasts all transmissions received from any peripheral node to all peripheral

nodes on the network, sometimes including the originating node. All peripheral nodes may thus communicate with

all others by transmitting to, and receiving from, the central node only. The failure of a transmission line linking any

peripheral node to the central node will result in the isolation of that peripheral node from all others, but the

remaining peripheral nodes will be unaffected. However, the disadvantage is that the failure of the central node will

cause the failure of all of the peripheral nodes also,

If the central node is  passive, the originating node must be able to tolerate the reception of an echo of its owntransmission, delayed by the two-way round trip transmission time (i.e. to and from the central node) plus any delay

generated in the central node. An active star network has an active central node that usually has the means to prevent

echo-related problems.

A tree topology (a.k.a. hierarchical topology) can be viewed as a collection of star networks arranged in a

hierarchy. This tree has individual peripheral nodes (e.g. leaves) which are required to transmit to and receive from

one other node only and are not required to act as repeaters or regenerators. Unlike the star network, the functionality

of the central node may be distributed.

As in the conventional star network, individual nodes may thus still be isolated from the network by a single-point

failure of a transmission path to the node. If a link connecting a leaf fails, that leaf is isolated; if a connection to a

non-leaf node fails, an entire section of the network becomes isolated from the rest.

In order to alleviate the amount of network traffic that comes from broadcasting all signals to all nodes, more

advanced central nodes were developed that are able to keep track of the identities of the nodes that are connected to

the network. These network switches will "learn" the layout of the network by "listening" on each port during normal

data transmission, examining the data packets and recording the address/identifier of each connected node and which

port it's connected to in a lookup table held in memory. This lookup table then allows future transmissions to be

forwarded to the intended destination only.

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Network topology 21

Decentralization

In a mesh topology (i.e., a partially connected mesh topology), there are at least two nodes with two or more paths

between them to provide redundant paths to be used in case the link providing one of the paths fails. This

decentralization is often used to advantage to compensate for the single-point-failure disadvantage that is present

when using a single device as a central node (e.g., in star and tree networks). A special kind of mesh, limiting the

number of hops between two nodes, is a hypercube. The number of arbitrary forks in mesh networks makes themmore difficult to design and implement, but their decentralized nature makes them very useful. This is similar in

some ways to a grid network, where a linear or ring topology is used to connect systems in multiple directions. A

multi-dimensional ring has a toroidal topology, for instance.

A fully connected network, complete topology or full mesh topology is a network topology in which there is a

direct link between all pairs of nodes. In a fully connected network with n nodes, there are n(n-1)/2 direct links.

Networks designed with this topology are usually very expensive to set up, but provide a high degree of reliability

due to the multiple paths for data that are provided by the large number of redundant links between nodes. This

topology is mostly seen in military applications.

References

[1] Groth, David; Toby Skandier (2005). Network+ Study Guide, Fourth Edition' . Sybex, Inc.. ISBN 0-7821-4406-3.

[2] ATIS committee PRQC. "network topology" (http:/   /  www. atis. org/  glossary/  definition. aspx?id=3516). ATIS Telecom Glossary 2007 .

Alliance for Telecommunications Industry Solutions. . Retrieved 2008-10-10.

[3] Proulx, S. R.; Promislow, D. E. L.; Phillips, P. C. (2005). "Network thinking in ecology and evolution" (http:/   /  eeb19. biosci. arizona. edu/ 

Faculty/  Dornhaus/  courses/  materials/  papers/  Proulx Promislow Phillips networks ecol evol.  pdf). Trends in Ecology and Evolution 20 (6):

345-353. doi:10.1016/j.tree.2005.04.004. PMID 16701391. .

[4] Inc, S., (2002). Networking Complete. Third Edition. San Francisco: Sybex

[5] Bicsi, B., (2002). Network Design Basics for Cabling Professionals. City: McGraw-Hill Professional

External links€ A Guide to Network Topology (http:/   /  learn-networking. com/  network-design/  a-guide-to-network-topology)

€ Research network topology (http:/   /  www.optical-network. com/  topology. php)

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Article Sources and Contributors 22

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ShaunMacPherson, Smack, Snori, Surv1v4l1st, THEN WHO WAS PHONE?, Wayiran, 46 anonymous edits

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Abrech, Absalom23, Abune, Adammw, Adrian.benko, Aervanath, Ahoerstemeier, Ahtih, Aimini, Akamad, Akkinenirajesh, Alainr345, Alcuin, Aldie, AlexMyltsev, Alexkon, Aliendude5300,

AlistairMcMillan, Allyant, Amwebb, Andre Engels, Andrewpmk, Anishsane, Antelan, Anthony, Antoniad, Apoc2400, Arangana, Arm-1234, ArneBab, Arny, Atbk, Atif.t2, Audriusa, Augest,Augman85, Authalic, AxelBoldt, Az1568, Bagatelle, Bahahs, Bane004, Bayerischermann, Ben-Zin, Benad, Bernino, Bhadani, Bhuston, Bigjimr, Binksternet, Bkonrad, Bloodshedder, Bluezy,

Bmicomp, Boivie, Bomac, Bondolo, Bongwarrior, Borgx, Bovineone, BrainMagMo, Bramp, Branko, BrokenSegue, BrotherE, Brunelstudy, Bslede, Btrest, Buryfc, Bwishon, Caiaffa, Caltas,

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lostsword, ClanCC, Classicrockfan42, Cldnails, Closedmouth, CoMePrAdZ, CobaltBlue, Coelacan, Coinchon, Coldfire82, Collabi, Cometstyles, Computerjoe, C onnelly, Conti, Conversion script,

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Network topology  Source: http://en.wikipedia.org/w/index.php?oldid=447816309 Contributors: 4twenty42o, AK Auto, Ahoerstemeier, Aitias, Alan.ca, Alansohn, Alras Sappho, Andre Engels,

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Image Sources, Licenses and Contributors 23

Image Sources, Licenses and ContributorsImage:PD-icon.svg  Source: http://en.wikipedia.org/w/index.php?title=File:PD-icon.svg  License: Public Domain Contributors: Various. See log. (Original SVG was based on File:PD-icon.png

by Duesentrieb, which was based on Ima ge:Red copyright.png by Rfl.)

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