The server then sends back a list of which peers have the data and facilitates

The server then sends back a list of which peers have

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movie. The server then sends back a list of which peers have the data and facilitates the connection and download. Second generation, by electing some nodes which had more capacity as indexing nodes, and having
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INFOTECH Seminar Advanced Communication Services (ACS), 2005 4 lower capacity nodes branching off from them, allowed for a network which could scale to a much larger size. Also included in the second generation are distributed hash tables, which solve the scalability problem by electing various nodes to index certain hashes (Which are used to identify files), allowing for fast and efficient searching for any instances of a file on the network, though they are with their own drawbacks, such as stale hosts and network splits. Third generation of peer-to-peer networks are those which have anonymity features built in. 3.2 Skype Skype is a peer-to-peer internet telephony (VoIP) network, founded by Niklas Zennström and Janus Friis, the creators of Kazaa [2]. The network is provided by all combined users of the free desktop software application. Skype users can speak to other Skype users for free, call traditional telephone numbers for a fee (SkypeOut), receive calls from traditional phones (SkypeIn), and receive voicemail. The main difference between Skype and other VoIP clients is that it operates on a peer-to-peer model rather than the more traditional server-client model. The Skype user directory is entirely decentralized and distributed among the nodes in the network, which means the network can scale very easily to large sizes without a complex and costly centralized infrastructure. Skype also routes calls through other peers on the network, which allows it to traverse NATs and firewalls, unlike most other VoIP programs (notably those based on the SIP protocol). This, however, puts extra burden on those who connect to the Internet without NAT, as their computers and network bandwidth may be used to route the calls of other users. The selection of intermediary computers is fully automatic, with individual users having no option to disable such use of their resources. Based on reverse engineering of Skype [3] by S. Baset and H. Schulzrinne at Columbia, there are two types of nodes in this overlay network, ordinary hosts and super nodes (SN). An ordinary host is a Skype application that can be used to place voice calls and send text messages. A super node is an ordinary host’s end-point on the Skype network. Any node with a public IP address having sufficient CPU, memory, and network bandwidth is a candidate to become a super node. An ordinary host must connect to a super node and must register itself with the Skype login server for a successful login. Although not a Skype node itself, the Skype login server is an important entity in the Skype network. User names and passwords are stored at the login server. User authentication at login is also done at this server. This server also ensures that Skype login names are unique across the Skype name space. Figure2 illustrates the relationship between ordinary hosts, super nodes and login
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