CSS (PEER-TO-PEER)

• Wired and Wireless - two types of connection methods.
• Twisted Pair, Coaxial and Fiber Optic - are the three main connection media for wired networks.
• The primary technologies for the wireless method of connection include terrestrial microwave, communication satellites, cellular systems, wireless LANs, Bluetooth and wireless web.
• One of the most popular forms of connecting computer networks wirelessly is through wireless LANs.
• In a wireless LAN every computer has a radio modem and antenna which can communicate with other systems.
• Personal Area Network - PAN
• Local Area Network - LAN
• Campus Area Network - CAN
• Metropolitan Area Network - MAN
• Wide Area Network -WAN
• Storage Area Network - SAN
• Virtual Private Network - VPN
• Another way of categorizing computer networks is through the scale of the network.
• A network's architecture is also another form of categorizing networks.
• Active networking, Client-Server and Peer-to-Peer - three main architectures.
• Active network - is a type of network architecture that allows packets traveling through a network to dynamically modify the operation of the network.
• In the peer-to-peer architecture individual form a loose group and can communicate with others in the group.
• Peer-to-Peer Network - is consider any type of network architecture composed of contributors that make a part of their resources available to other contributors on the same network without the need for a server to oversee the transfer of information.
• A peer-to-peer network's architecture is generally formed dynamically by an ad-hoc type of addition of nodes, meaning the loss of a certain node does not have a significant impact on the rest of the network.
• Peer-to-Peer networks gives the system the ability to easily scale to any size that may be need for a certain application.
• Structured and Unstructured - two major types of peer-to-peer architecture.
• To be considered an unstructured peer-to-peer network, the network must not use any algorithm for organization or optimization of the network.
• Pure Peer-To-Peer , Hybrid Peer-To-Peer and Centralized Peer-To-Peer - three different models of unstructured peer-to-peer network
• Pure Peer-To-Peer Network - or sometime called a purely decentralized network, all nodes are of equal ability meaning that there are no nodes that have any special infrastructure function that could affect the network.
• A great example of a popular purely decentralized peer-to-peer network is the Gnutella network.
• The main purpose of the Gnutella network is for file sharing system.
• Gnutella Network - uses a virtual overlay network with its own routing layers, allowing the peers of the network to share files on their machine to all other peers connected to the network.
• Hybrid Peer-To-Peer - infrastructure nodes are allowed to exist and are often a type of central directory server.
• A profound example of a hybrid peer-to-peer network is the notorious Napster network.
• A central directory server maintains an index of the metadata for all files in the network.
• Centralized Peer-To-Peer Network - are very similar to pure peer-to-peer networks except for the added concept of supernodes.
• These supernodes are nodes that are dynamically assigned the task of servicing a small subpart of the peer network by indexing and caching files contained therein.
• A popular example of this centralized peer-to-peer network is the file sharing network Kazaa.
• Structured peer-to-peer networks generally hold the traits of using some type of algorithm for organization or optimization of the network.
• Structured peer-to-peer networks use some type of global protocol to ensure that any node in the network can proficiently route a search to some peer that has a desired file.
• The most popular type of structured peer-to-peer network is the distributed hash table or DHT.
• Distributed Hash Table - are a class of decentralized distributed systems that provide a lookup service similar to a hash table.
• Pairs, key and value are stored in distributed hash table
• The most popular example of a network using a distributed hash table is BitTorrent's distributed tracker.
• One of the weaknesses of peer-to-peer networks is the security.