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Classification by Functional Relationship

Classification by Functional Relationship

Computer networks may be classified according to the functional relationships which exist between the elements of the network, for example Active Networking, Client-server and Peer-to-peer (workgroup) architectures.
Also, computer networks are used to send data from one to another by the hardrive
Active Networking
Active networking is a communication paradigm that allows packets flowing through a communication telecommunications network to dynamically modify the operation of the network.
The active network architecture is comprised of execution environments (similar to a unix shell that can execute active packets), a node operating system capable of supporting one or more execution environments, and active hardware, capable of routing or switching as well as executing code within active packets.
This differs from the traditional network architecture which seeks robustness and stability by attempting to remove complexity and the ability to change its fundamental operation from underlying network components.
Network processors are one means of implementing active networking concepts. Active networks have also been implemented as overlay networks.
Active networking allows the possibility of highly tailored and rapid “real-time” changes to the underlying network operation enabling such ideas as sending code along with packets of information allowing the data to change its form (code) to match the channel characteristics.
The smallest program that can generate a sequence of data can be found in the definition of Kolmogorov Complexity.
The use of real-time genetic algorithms within the network to compose network services is also enabled by active networking.
Client-server
Client server is network architecture which separates a client (often an application that uses a graphical user interface) from a server.
Each instance of the client software can send requests to a server.
Specific Types of servers include application servers, file servers, terminal servers, and mail servers.
While their purpose varies somewhat, the basic architecture remains the same.
Although this idea is applied in a variety of ways, on many different kinds of applications, the easiest example to visualize is the current use of web pages on the internet.
Characteristics of a server:
• Passive (slave)
• Waits for requests
• Upon receipt of requests, processes them and then serves replies
Characteristics of a client:
• Active (master)
• Sends requests
• Waits for and receives server replies
Servers can be stateless or stateful. A stateless server does not keep any information between requests.
A stateful server can remember information between requests. The scope of this information can be global or session.
HTTP server for static HTML pages is an example of a stateless server while Apache Tomcat is an example of a stateful server.
The interaction between client and server is often described using sequence diagrams. Sequence diagrams are standardized in the UML.
Another type of network architecture is known as a peer-to-peer architecture because each node or instance of the program is both a “client” and a “server” and each has equivalent responsibilities. Both architectures are in wide use.
Peer-to-peer
A peer-to-peer (or P2P) computer network relies primarily on the computing power and bandwidth of the participants in the network rather than concentrating it in a relatively low number of servers.
P2P networks are typically used for connecting nodes via largely ad hoc connections. Such networks are useful for many purposes.
Sharing content files (see file sharing) containing audio, video, data or anything in digital format is very common, and realtime data, such as telephony traffic, is also passed using P2P technology.
A pure peer-to-peer 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 arrangement differs from the client-server model where communication is usually to and from a central server.
A typical example for a non peer-to-peer file transfer is an FTP server where the client and server programs are quite distinct, and the clients initiate the download/uploads and the servers react to and satisfy these requests.
Classification of peer-to-peer networks
One possible classification of peer-to-peer networks is according to their degree of centralization:
Pure peer-to-peer:
• Peers act as equals, merging the roles of clients and server
• There is no central server managing the network
• There is no central router
Hybrid peer-to-peer:
• Has a central server that keeps information on peers and responds to requests for that information.
• Peers are responsible for hosting available resources (as the central server does not have them), for letting the central server know what resources they want to share, and for making its shareable resources available to peers that request it.
• Route terminals are used addresses, which are referenced by a set of indices to obtain an absolute address.