Topology of computer networks
The physical geometry of the links that form the computer network determines its topology. A network topology in which a single master cable (the so-called bus) is used to connect computers to which all computer network components are connected, is called a topology of the type "bus". The network topology in which all computers are connected to the network using their individual cables going to one special central device (hub) is called a topology of the type "star". Both types of network topology have their advantages and disadvantages: bus-based networks are cheap enough, but they are very vulnerable due to possible malfunctions in the cable system, which are also very difficult to detect. Networks based on the topology of the star are more resistant to possible breakdowns, but more financial and material-intensive.
Principles of Network Addressing
The basis of operation of the computer network is an addressing system, which assigns each element of the network (a single computer or server to the Internet) in its own unique identification numeric address. Such an address is called an IP address; also adopted another of its designation as a domain name of the computer in the system domain addressing the computers of Internet servers (DNS), which is much more common.
When the computer is used to refer to the domain address, is its conversion to numeric IP address, which must be interpreted by special network computers - DNS- servers - in accordance with the database of network addresses of data stored on such a server. The DNS server processes addresses, reading them from right to left, i.e. first searches the largest group addresses (first level domain) gradually updating address of the computer (or Internet server) by groups of addresses of lower level (lower level domains). The search for the necessary information for all domain levels is carried out with the help of appropriate DNS-servers, each of which is responsible for its network segment. This addressing system has proved its effectiveness and that it is able to provide error-free delivery of information to any of the computers that are on the network.
The second fundamental component of the functionality of the global Internet is the concept of URL ( Uniform Resource Locator) - a unified index of information resource, which is used to indicate the address of some information on the Internet. This term was invented in 1990 by the "father" of the modern Internet (English WWW - World Wide Web - World Wide Web) by Tim Berners-Lee. The unified index of the information resource includes the so-called resource part and the actual domain address of the corresponding file. The resource part (URL) denotes the type of network data transfer protocol that is used for network communication and always ends with a colon and two (or three) slashes. This is followed by the specific domain address of the Internet site to which the user accesses. After the domain address, there may also be a slash that separates the location of the search file or an indication of the path to the file.
The basic network protocol for data transmission on the Internet is the TCP/IP protocol. It consists of two protocols connected to each other: TCP - Transmission Control Protocol and IP - Internet Protocol . The IP protocol (Internet protocol) provides the delivery of data packets from one point of the network to another. It is necessary for the information to be able to move seamlessly through segments of the network that are built on different technological bases (for example, a network based on Ethernet or using telephone lines, etc.). ). To process information transmitted via this protocol, special devices are used in the network - routers that connect different types of networks. The IP protocol allows the router to determine which operations should be performed with the user's data entered to it (the basic address information is given at the beginning of each data packet, it is sufficient for this packet to be delivered to a unique address that is attributed to each computer in the network (IP -address) to which it is sent by the user). For more reliable transmission of large amounts of information, a transmission control protocol is used, the TCP protocol. It allows you to break all the information that the user sent to the portions and each such piece of information to attribute the encoded information in a certain way. This information allows you to accurately determine whether the information sent by the user has been fully delivered, whether any information losses occurred during the transfer process, and also in what order the received information fragments should be located in order to recreate the information packet of its original form on the recipient's computer. To each portion of the transferred information, the IP protocol is added, so the entire system of protocol processing of information transfer on the Internet has received the designation TCP/IP. Together with this protocol, specialized protocols are also used on the Internet, each of which is associated with a special Internet service. The URL should reflect all types of protocols that are used in each case for data transfer.
The URL in the form ftp://ftp.microsoft.com/dirmap.txt will allow you to get using ftp (from English File Transfer Protocol) access to a file called dirmap.txt, which is stored on the ftp-server of Microsoft.
The Uniform Resource Locator (URL) includes the designation of all types of standard network communication protocols that are used on the Internet. On the basis of these protocols, all major Internet services operate. These basic Internet networking protocols include the following:
• ftp (English File Transfer Protocol) - the file transfer protocol;
• http (English HyperText Transfer Protocol) - Hypertext Transfer Protocol;
• rtmp (English Real Time Messaging Protocol) - proprietary streaming protocol, mostly used to transfer streaming video and audio streams from web cameras over the Internet;
• rtsp (English Real Time Streaming Protocol) is a real-time streaming protocol that is used in systems that work with multimedia data;
• https (English HyperText Transfer Protocol Secure) is a special implementation of the HTTP protocol that supports the encryption of forwarded data;
• gopher (gopher) is a networked protocol for distributed retrieval and transmission of documents, which was widely distributed on the Internet until 1993. Subsequently, it was completely superseded by the http protocol;
• mailto - the protocol that serves the communication by e-mail;
• news - the protocol that serves information exchange in newsgroups of the Usenet network;
• nntp (News Network News Transfer Protocol) is a protocol that provides communication between a newsgroup server and a Usenet client
• ire (English Internet Relay Chat) - application-level protocol for real-time messaging time;
• telnet (English TErminaL NETwork) is a network protocol for implementing a text interface over the network;
• wais Area Information Sewers is a networked information retrieval system that uses the TCP/IP protocol to interact with the client application program with the information server;
• xmpp (English Extensible Messaging and Presence Protocol) - protocol for messaging and presence information , previously known as Jabber (chatter, bluff, gibberish), is used for instant messaging and presence information in a mode close to real-time mode (social networks work on it Facebook, Odnoklassiki.Ru and others).
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