Classification of edge services. Merezhevy services and services Merezhevy service and merzhevy addresses
nobility: the importance and specificity of the selection of the main edge services
Please note: vikorystuvati koshti merezhevikh services
Services (Services) that are provided by the Internet network
Protocols of the TCP / IP family implement various Internet services.
All services provided by the Internet network can be intelligently divided into two categories: the exchange of information between network subscribers and the search for network databases.
Until the number of services, communication between subscribers is based on:
Telnet - remote access. Allows the subscriber to talk about any EOM network on the Internet at his own discretion. To launch programs, change the operating mode, etc.
FTP (File Transfer Protocol) - file transfer protocol. Allows the subscriber to exchange double and text files with any other computer. Having established a connection with a remote computer, users can copy a file from a remote computer to their own or copy a file from their computer to a remote computer.
NFS (Network File System) - distributed file system. Allows the subscriber to use the file system of a remote computer as if it were his own.
Electronic mail - exchange of mail notifications with any Internet connection subscriber. It is possible to send both text and double files. The size of the postal notification in the Internet is subject to the following limitation - the size of the postal notification must not exceed 64 kilobytes.
News - the importance of new news and electronic boards and the ability to place information on boards. Electronic boards of the Internet are formed according to topic. Koristuvach can, at his own discretion, subscribe to any groups of new products.
Electronic translation - to translate the text sent to a new one from one language to another. Returns to electronic transfers are requested via additional electronic mail.
Gateways - give the subscriber the ability to send notifications in a manner that does not involve TCP\IP protocols (Fido, Goldnet, AT50).
Zagalne understand about the basis of data. Basic concepts of database management systems. data models
nobility: hidden news about database design; basic powers, principles of creation and operation of databases, capabilities of database management systems; main models of data saving; Their advantages and shortcomings; their specificity depends on the most important tasks
Please note: vikorist models for saving data and knowledge; design the structure of the database table; establish links between database tables; select a DBMS for the most advanced task of your information systems
Database (DB)- this is a structured body of data that reflects the authorities and the status of objects of a specific subject area and the connections between them.
Database management system (DBMS)- this is a set of software features used for creating, storing, processing and managing a database.
In the DBMS theory, there are three main types of database organization: hierarchical (elements are related to ordering, in which each element can be subordinated to only one element); Merezheva (extension of hierarchical - for substitution from hierarchical in the heirarchical model of records, you can replace a number of previous records); relational (the database is presented as a collection of interconnected tables).
The greatest expansion was achieved in the DBMS based on the relational data model proposed by E.F. Codd.
One of the most advanced DBMSs is MS Access, which is included in the professional version of the Microsoft Office package.
The popularity of MS Access can be explained in many ways by the current authorities:
- directness to the students of various levels of preparation;
- the presence of manual visual developmental features;
- Possibility of integration with other software products of the Microsoft Office package.
The MS Access DBMS consists of six main components:
- tables - for saving the structure of the database and the data itself;
- query - to create QBE and SQL queries to the database (to search for information in the database);
- forms - for ease of entry, review and editing of data;
- call - to prepare and format the data in the form of a document for distribution on a printer;
- pages - to ensure access to the database from the Web - pages;
- macros - for automating repeated operations (a macro is formed from the sequence of internal DBMS commands);
- modules - for automating the execution of standard operations and creating new procedures using Visual Basic programming.
Table
The table is made up of the simplest objects, called a field (row) and a record (row). The skin area is intended to save data for only one type.
The main characteristics of the field are its name (sequence of characters, including punctuation marks - it must be informative or short) and type (characterizes the location of the data).
Main types of fields:
- texting- to save data in the form of a set of symbols;
- numerical- to save numerical data;
- logical- to preserve logical data that has only one of two meanings - true / false;
- Date hour- to enter the date or time;
- MEMO- for the safety of work with long texts;
- doctor- special numeric field for numbering records;
- penny- for ease of reference, work with numbers that represent penny sums;
- OLE object- to ensure the ability to save pictures, pictures, sound, video fragments.
- deposit(analogous to OLE) - create a field of the “Attachment” type, and insert the required image files in the dialog
- Substitution Master- creates a field that allows you to select values from another table or list of values, vikoryst fields from the list. When you select this parameter in the list of data types, a wizard is launched to automatically assign this field.
One of the table fields is designated as a key field (most often called the primary key, usually the type is a physician), and a field whose value uniquely identifies the record.
When filling rows, when entering records, it is prohibited to allow pads in the text, otherwise it is necessary to adjust the types of fields.
data scheme
A mechanism for describing the logical connection between tables in MS Access implementations in the form of an object called a data schema. In this object, the connection between tables is organized through key fields of the table.
You can see a number of types of binding:
“One-to-one” scheme - one value of a field in one table corresponds to one value of a field in another table;
- “one-to-many” scheme - one value of a field in one table (“head table”) is matched by the same value of a field in another table (“ordered table”);
- a “rich-to-rich” scheme - a number of field values in one table are indicated by the value of a field in another table.
Most often in relational databases there is a “one-to-many” relationship.
Butt link "one-to-many"
Typical actions allowed in Access
LFM - left mouse button, RMB - right mouse button
| What to earn? | How to earn money? |
| Launching Access programs | Start -> Programs -> Microsoft Office -> Microsoft Access |
| Creation of a new database | Microsoft Office button -> Create -> enter the name of the created database -> Create |
| View of the original database | Microsoft Office button -> Open -> enter the name of the required database -> Open button |
| Creating a table in design mode | Creation menu -> Table button -> Work with tables menu -> Manifestation group -> Lines button (or View button -> select design mode) -> save the table, set a table name -> OK button -> enter names and types of fields in the created table -> indicate which field is the primary key -> switch to table mode -> enter the required number of entries to fill out the rows |
| Installing the primary key | See the row in which the key field is located -> Constructor menu -> Key field button (from the key box) |
| table saving | File -> Save -> Enter table names -> OK |
| Switching to table mode | Work with tables menu -> Manifestations group -> button with the Tables small tab (or View button -> select table mode) |
| Editing the table (changing names or types of fields, creating or deleting them) | Go to design mode -> change the name or type of the required field |
| Switching to design mode | Work with Tables menu -> Manifestations group -> button with the Lines box (or View button -> select design mode) |
| Creation of tribute schemes | Save and close linked tables -> menu Work with databases -> Show or attach group -> Data Schema button -> add linked tables -> close the “Add tables” window -> create link -> save schema tributes |
| Creation of connections between tables | Move the mouse pointer over the name of the field ->, with LMB, drag it on the field associated with it in another table -> insert in the dialog box “Change connections” the flag “Securing the integrity of data” -> whatever you want, you can set the proportions cascade modification -> connection type is determined independently -> Create |
| change the tie | See the link line LFM -> RMB -> Change link... |
| got a call | See the link line LFM -> RMB -> Vidality |
| Search for data in the table | Move the cursor to any place where the search will be entered -> Head menu -> Find group -> Find button (with binoculars) -> in the row Enter the value of the sound data -> in other sections, set the search parameters (indicate -> find out button |
| Replacing data in a table | Move the cursor to any place where the search will be entered -> Head menu -> group Find -> Replace button (with ab-> ac) -> in the rows Show and Replace to enter the necessary data -> in other sections set search parameters -> button Find further -> Replace |
| Filter search for data | Click LMB on the down arrow, which appears in the name of the field by which the search is carried out -> Home menu -> Sorting and filter group -> Filter button -> Filter command -> select the required Filter -> enter the necessary parameters -> OK |
| filter | Home menu -> Sorting and filter group -> Advanced filter options button -> Clear all filters command |
| Sorting tributes | Move the cursor to whatever place you need to sort -> Home menu -> Sorting group and filter -> button For changes or For additions |
Basic concepts of relational databases
nobility: basic concepts of the relational data model; basic principles of working with MS Access DBMS objects; main capabilities of the Access DBMS
Please note: identify data types, assign key fields in tables, create links between tables to ensure data integrity
The relational data model is based on the concept vіdnosini.
shutter is presented in the form of a two-dimensional table, on which the exchange songs are superimposed.
stovpets The table indicates the concept of the column attribute, the row indicates the concept motorcade vіdnosini.
There are many possible values that may appear in the table column, I understand domain, On which the specific attribute is assigned. The concept of a domain is similar to the type of data in language programming.
key- one or a number of attributes, the values of which uniquely identify any tuple of notes.
Access 2007 Specifications
The set of server and client parts of the OS that provide access to a specific type of computer resource through a network is called a network service. The client and server parts of the OS, which ensure access through a network to the computer’s file system, create a file service. It seems that the Merezh Service provides the Merezh workers with a wide range of services. These services are also called edge services. Service is the interface between the service provider and the service provider (service). The skin service is associated with a different type of edge resources and / or a different way of accessing these resources. For example, the service will provide access to border printers and provide the service to the customer, and the mail service will provide access to the information resource of the border - electronic sheets. The method of accessing resources is, for example, the remote access service - it gives computer users access to all resources through dial-up telephone channels. To deny remote access to a specific resource, such as a printer, the remote access service communicates with the other service. The most important ones for edge OS users are the file service and the friend service. Among the peripheral services you can see those that are oriented not at a simple customer, but at an administrator. Such services are used to organize robotic measures. A more progressive approach would be to create a centralized research service, or, in other words, a directory service, which is designed to maintain a database not only about all back-office measures, but also about all programs and hardware components. Other applications of edge services that can be provided by the service administrator include the edge monitoring service, which allows you to capture and analyze edge traffic, the security service, which can include functions, monitoring, and login procedures. Safe login with password verification, backup and archiving service. In addition, how rich a set of services the operating system provides to end-user accountants, assistants and network administrators, their position lies in the main row of network operating systems. Merger services, by their nature, are client-server systems. When implementing any edge service, it is natural that the source of requests (client) and the end of requests (server), then any edge service contains two asymmetrical parts in its warehouse - the client and the server well (Fig. 2.2). The network service can be represented in the operating system either by both (client and server) parts, or only one of them.
Make it seem like the server gives its resources to the client, and the client uses them. It is necessary to note that when this service is provided by the edge service, the resources of not only the server, but also the client are used. The client can spend a significant part of his resources (disk space, processor hours, etc.) to support the work of the boundary service. For example, when implementing a postal service, a local copy of the database can be saved on the client’s disk to accommodate extensive browsing. In this case, the client chooses a great job when molded into different formats, including folding multimedia, supports the management of the address book and creates a lot of other related jobs. The fundamental difference between the client and the server is that the client is always the initiator of the work, the edge service, and the server is always in passive request processing mode. For example, the mail server delivers mail to the client's computer only if it is entered into the mail client. Because the interactions between the client and server parts are standardized, so that one type of server can be used to work with clients of different types, implemented in different ways, and possibly by different processors. The same mind is for whom - the client and the server are responsible for maintaining a completely standard protocol for interaction.
I port of the server, as a result of which a connection is established that allows two computers to communicate with each other using the same application level bridging protocol.
port numbers
The port number for “binding” the service is selected depending on its functional purpose. IANA is responsible for assigning port numbers to early tier services. Port numbers are in the range 0 - 65535 and divided into 3 categories:
| port numbers | Category | describe |
|---|---|---|
| 0 - 1023 | behind-the-scenes ports | Port numbers are recognized by IANA and on most systems can be used either by system processes (or root users) or by application programs launched by privileged users. It's not your fault to be vikorist without IANA registration. The registration procedure is specified in section 19.9 of RFC 4340. |
| 1024 - 49151 | registered ports | Port numbers included in the IANA directory and on most systems can be used by processes of primary users or by programs run by primary users. It's not your fault to be vikorist without IANA registration. The registration procedure is specified in section 19.9 of RFC 4340. |
| 49152 - 65535 | Dynamically selected ports and / or ports selected in the middle of closed (private) boundaries | Intended for time-based monitoring - in the context of client ports, ports monitored for private services, as well as for testing add-ons before registering views of ports. ci spoil cannot be registered . |
List of services between edge services and port numbers
Official list of affiliations between edge services and port numbers maintained by IANA.
History of species regulation
Power unification of edge services by socket (port) numbers was raised in RFCs 322 and 349, the first attempts at regulation were made by Jon Postel in RFCs 433 and 503.
current list
netstat -anIn Windows operating systems, the result of this command looks something like this:
Active connections Name Local address Foreign address Stan TCP 0.0.0.0:135 0.0.0.0:0 LISTENING TCP 0.0.0.0:445 0.0.0.0:0 LISTENING TCP 127.0.0.1:1026 0.0.0.0:0 LISTENING TCP 127.0.0.1 :12025 0.0.0.0:0 LISTENING TCP 127.0.0.1:12080 0.0.0.0:0 LISTENING TCP 127.0.0.1:12110 0.0.0.0:0 LISTENING TCP 127.0.0.1:12119 0.0.0.0:0 LISTENING TCP 127. 0.0.1:12143 0.0. 0.0: 0 LISTENING TCP 192.168.0.16:139 0.0.0.0:0 LISTENING TCP 192.168.0.16:1572 213.180.204.20:80 CLOSE_WAIT TCP 192.168.0.16:1573 213.180.204.35: 80 ESTABLISHED UDP 0.0.0.0:445 *: * UDP 0.0.0.0:500 *: * UDP 0.0.0.0:1025 *: * UDP 0.0.0.0:1056 *: * UDP 0.0.0.0:1057 *: * UDP 0.0.0.0:1066 *: * UDP 0.0.0.0:4500 *: * UDP 127.0.0.1:123 *: * UDP 127.0.0.1:1900 *: * UDP 192.168.0.16:123 *: * UDP 192.168.0.16:137 *: * UDP 192.168.0.16:138 *: * UDP 192.168 .0.16: 1900 *: *
In UNIX-like operating systems, the result of the robot command is netstat -an It looks something like this:
Active Internet connections (servers and established) Proto Recv-Q Send-Q Local Address Foreign Address State tcp 0 0 0.0.0.0:37 0.0.0.0:* LISTEN tcp 0 0 0.0.0.0:199 0.0.0.0:* LISTEN tcp 0 0 0.0.0.0:2601 0.0.0.0:* LISTEN tcp 0 0 0.0.0.0:3306 0.0.0.0:* LISTEN tcp 0 0 0.0.0.0:2604 0.0.0.0:* LISTEN tcp 0 0 0.0.0.0:2605 0.0. 0.0: * LISTEN tcp 0 0 0.0.0.0:13 0.0.0.0:* LISTEN tcp 0 0 0.0.0.0:179 0.0.0.0:* LISTEN tcp 0 0 0.0.0.0:21 0.0.0.0:* LISTEN tcp 0 0 0.0 .0.0: 22 0.0.0.0:* LISTEN tcp 0 0 0.0.0.0:1723 0.0.0.0:* LISTEN tcp 0 0 10.0.0.254:1723 10.0.0.243:2441 ESTABLISHED tcp 0 0 192.168.19.34:17 9 192.168.19.33: 33793 ESTABLISHED tcp 1 0 192.168.18.250:37 192.168.18.243:3723 CLOSE_WAIT tcp 0 0 10.0.0.254:1723 10.0.0.218:1066 ESTABLISHED tcp 1 0 192.168. 18.250:37 192.168.18.243:2371 CLOSE_WAIT tcp 0 0 10.0.0.254 : 1723 10.0.0.201:4346 ESTABLISHED tcp 0 0 10.0.0.254:1723 10.0.0.30:2965 ESTABLISHED tcp 0 48 192.168.19.34:22 192.168.18.18:43645 ESTABLISHED tcp 0 0 10.0.0.254:38562 10.0.0.243:22 ESTABL ISHED tcp 0 0 10.50.1.254:1723 10.50.1.2:57355 ESTABLISHED tcp 0 0 10.50.0.254:1723 10.50.0.174:1090 ESTABLISHED tcp 0 0 192.168.10.254:1723 192.168.13.104:65535 ESTABLISHED tcp 0 0 10.0.0.254: 1 723 10.0.0.144:65535 ESTABLISHED tcp 0 0 10.0.0.254:1723 10.0.0.169:2607 ESTABLISHED tcp 0 0 10.0.0.254:1723 10.0.0.205:1034 ESTABLISHED udp 0 0 0.0.0.0:1812 0.0.0.0:* udp 0 0 0.0.0.0:1813 0.0.0.0:* udp 0 0 0.0.0.0:161 0.0.0.0:* udp 0 0 0.0.0.0:323 0.0.0.0:* udp 0 0 0.0.0.0:123 0.0.0.0: * raw 0 0 192.168.10.254:47 192.168.13.104:* 1 raw 0 0 10.0.0.254:47 10.0.0.120:* 1 raw 0 0 10.10.204.20:47 10.10.16.110:* 1 raw 0 0 .168.10.254: 47 192.168.11.72:* 1 raw 0 0 10.0.0.254:47 10.0.0.144:* 1 raw 0 0 10.0.0.254:47 10.0.0.205:* 1 raw 0 0 10.50.0.254:47 10.50.0.174:* 1 raw 0 0 10.0.0.254:47 10.0.0.170:* 1 raw 0 0 10.0.0.254:47 10.0.0.179:* 1
State LISTEN (LISTENING) shows passively open connection (Listen to sockets). The stench itself is responsible for the guard services. ESTABLISHED- once the connection is established, the boundary services are victorious in the process.
Checking the availability of edge services
If problems are detected with this or any other monitoring service, to check the availability of the vicorist, use various diagnostic methods, depending on their appearance in this OS.
One of the most important features is the command (utility) tcptraceroute (a subtype of traceroute), which detects TCP connection packets (SYN | ACK) with a designated service (for example, a web server, port 80, select host) and i shows information about The time it takes for this type of TCP packet to pass through routers, as well as information that is available on the host site, or, in case of problems with packet delivery, is where the stink comes from.
As an alternative, you can vikoristuvat okremo
- traceroute for diagnosing the route of packet delivery (not enough - use a UDP packet for diagnostics) and
- telnet or netcat to the port of the problematic service to check the output.
Notes
Div. also
posilannya
- RFC 322 Well Known Socket Numbers
- RFC 349 Proposed Standard Socket Numbers (RFC 433)
- RFC 433 (English) Socket Number List (RFC 503 codes)
- RFC 503 (English) Socket Number List (RFC 739 codes)
- RFC 739 (English) ASSIGNED NUMBERS
- RFC 768 User Datagram Protocol
- RFC 793 TRANSMISSION CONTROL PROTOCOL
- RFC 1700 (English) ASSIGNED NUMBERS (remaining list of assigned numbers, RFC 3232 sections)
- RFC 3232 Assigned Numbers: RFC 1700 is Replaced by an On-line Database
- RFC 4340 (English) Datagram Congestion Control Protocol (DCCP) - PROPOSED STANDARD
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- Salads and caviar with eggplant
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books
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In 1961, the Defense Advanced Research Agency (DARPA) under the US Department of Defense began a project to create an experimental packet transmission network. This network, called the ARPANET, was originally intended to support communication in the event of a nuclear attack and to assist in the exchange of information between the pre-Liberian defense industry organizations scattered throughout all states.
The project was based on three main ideas:
- the skin divides between connections with others, so that between them there is a bunch of different paths one to one;
- all the knots and connections are viewed as unreliable;
- Packet redirection tables will be automatically updated; for example, a package of assignments for non-neighboring nodes is sent, according to such a table, to the closest one, and if that node is unavailable, to the next one, etc.
The system was created on such principles as a centralized control unit and, therefore, could easily change its configuration.
The experiment with ARPANET was so successful that many organizations wanted to enter it as a means of creating a system for the transfer of data. And in 1975, ARPANET transformed from an experimental network into a working network.
Russia joined it at the end of the 80s. In 1990, the APRANET network ceased to function, and in its place, the Internet emerged, allowing for the free exchange of information, regardless of the borders and borders of the state.
In fact, the Internet consists of a lack of local and global connections that belong to different companies and enterprises that operate on different protocols and connect with each other We have connections that physically transmit data over telephone lines, fiber optics, satellites and radio modems. .
No one has to pay centrally for the Internet, but only for their share. Representatives of the network are selected at once and decide how to connect with one another and establish mutual connections. The customer pays for connection to any regional network, which, in turn, pays for his access to a moderate ruler on a sovereign scale. The Internet does not have any authority, there is no special control body that would control the entire operation of this network. Local measures in various countries are financed and supported by local authorities in accordance with the policy of the state on this food.
The structure of the Internet suggests a web, in which nodes there are computers connected to each other by communication lines. Networks of the Internet, connected by high-speed connection lines, form the basis of the Internet. As a rule, these are postal service providers (providers). Digitized data is sent through routers that connect layers using complex algorithms that select routes for information flows.
Every computer on the Internet has its own unique address. In the TCP / IP protocol, the computer is addressed with several tens of numbers, which are reinforced one after another, and the number can range from 1 to 255. Computer addresses appear in the following order:
Such addresses are called IP addresses. This number can either be permanently assigned to the computer, or it can be assigned dynamically - at the moment when the user connects with the provider, or at any time on the Internet there are no two computers with the same IP addresses.
It is difficult for Koristuvachev to remember such addresses, which can also be changed. Therefore, on the Internet there is a Domain Name System (DNS - Domain Name System), which allows each computer to be called by name. We have millions of computers, and so that the names are not repeated, they are divided into independent domains.
Thus, computer addresses look like a bunch of domains, between which there is a dot:
<сегмент n>. … <сегмент 3>.<сегмент 2>.<сегмент 1>.
Here segment 1 is domain 1st level, segment 2 is domain 2nd level, etc.
Domain names- this unique name is used by the postal service provider for identification, for example: ic.vrn.ru or yahoo.com
For example, the domain address (domain name) www.microsoft.com means a computer with the name www in the microsoft.com domain. Microsoft is the name of the company, com is the domain of commercial organizations. On your computer www, talk about those that have a WWW service on your computer. This is the standard type of address for servers of large companies (for example, www.intel.com, www.amd.com, etc.). Computer names in different domains may be repeated. In addition, one computer at a time can have multiple DNS names.
The domain of the 1st level depends on the region of server development (ru - Russia; ua - Ukraine; uk - Great Britain; de - Germany) or the type of organization (com - commercial organizations; edu - scientific and primary organizations zaci; gov - government regulations; org - non-profit organizations ).
When entering a domain name, for example, www.mrsu.ru, The computer is to blame for changing it at the address. To do this, you will ask the DNS server, starting from the right side of the domain name and working to the left. This software knows how to contact the root server, which stores the addresses of name servers for the first-level domain (the rightmost part of the name, for example, ru). In this way, the server asks the root server for the address of the computer that represents the domain ru. Having received the information, you will contact this computer and write to a new server address mrsu, After what type of server mrsu I'll take away the address www computer, which is also used by this application program.
Data on the Internet is sent NOT as whole files, but in small blocks, called packets. Each packet contains the addresses of the sender and host computers, the transfer of data and the serial number of the packet in the underlying data stream. Because the leather package contains all the necessary data, it can be delivered independently from others, and it is often carried out so that the packages reach the designated place on different routes. And the host computer then selects from the data packages and selects from them the file that will be used for processing.
Ports are used to identify services. port- this is the number that is added to the computer address and indicates the program for which purpose. The skin program running on the computer responds to the first port and responds only to those packets addressed to that port. There are a large number of standard ports that support singing services, for example, 21 - FTP; 23 - telnet; 25 - SMTP; 80 - HTTP; 110 - POP3; 70 - Gopher etc.
On the Internet, it is not just domain names that are searched for, but also universal resource indicators (URLs) (Universal Resource Locator).
The URL includes:
- method of access to the resource, such as the access protocol (http, gopher, WAIS, ftp, file, telnet, etc.);
- edge address of the resource (name of the host machine and domain);
- go back to the file on the server.
In general, the URL format looks like this:
method: //host.domain[:port]/path/filename,
de method - one and the same value, overreacted below:
file - file on the local system;
http - file on the World Wide Web server;
gopher - file on Gopher server;
wais - file on the WAIS (Wide Area Information Server) server;
news - a group of new Usenet newsgroups;
telnet - access to Telnet network resources;
ftp - file on FTP server;
host.domain - domain name on the Internet;
port - a number that must be specified if the method outputs a port number.
Example: http://support.vrn.ru/archive/index.html.
Below, the names of computers on the Internet are most often condensed.
server In the Internet network - this is a computer that ensures the maintenance of the network network: distribution of access to disks, files, printers, e-mail systems. Call it, a server is a combination of hardware and software.
website- the name of the totality of documents on the Internet linked to each other by messages has been formalized.
Gateway- this is a computer or a computer system with special software that allows two networks to communicate with different protocols.
Home page- this is a personal Web site of a specific accountant or organization.
The main tasks associated with the creation of computer measures include the security of the electrical and mechanical characteristics and the security of the information security (programs and data) according to the coding system and format them. The main goal of this task lies in the field of standardization and is based on the so-called OSI model (Model of Open System Interconnections), which was created on the basis of technical proposals of the International Standards Institute ISO (International Standards Organization).
Similar to the OSI model, the architecture of computer networks can be seen on different levels (the number of levels is up to seven), (Fig. 9). The top one is applied. On this level, the system interacts with the calculation system. The lowest level is physical, which ensures the exchange of signals between devices. The exchange of data in communication systems is carried out by their movement from the upper level to the lower level, then transported to the gateway on the client’s computer as a result of movement from the lower level to the top nіy.
To ensure the necessary information on the skin, there are special standards, called protocols, from seven possible levels of computer network architecture. They indicate the nature of the hardware interaction of the network components (hardware protocols) and the nature of the interaction of programs and data (software protocols). Physically, protocol support functions consist of hardware devices (interfaces) and software (protocol support programs). Programs that support protocols are also called protocols.
Small 9. Control levels and OSI protocols
The leather architecture is divided into two parts:
- specification of services;
- protocol specification.
The service specification determines what to use, and the protocol specification determines how to perform it, and a specific protocol may require more than one protocol.
Let's take a look at the functions that are at the core of the software:
1. The physical channel is connected to the physical channel, connected to the channel, and controlled by the channel. This determines the speed of data transmission and the network topology.
2. The channel rhubarb adds additional symbols to the data transmission and monitors the correctness of data transmission. Here the information transmitted is divided into a number of packets or frames. The leather package contains the addresses of the recipient and the place of recognition, as well as the manner of revealing the amends.
3. The boundary line determines the route for transmitting information between the boundaries, ensures processing of transactions, and also manages data flows. The main task of this level is data routing (data transfer between boundaries).
4. The transport line connects the lower levels (physical, channel, boundary) with the upper ones, which are implemented by software. This range separates the methods of forming data as well as the methods of their transmission. Here you can see the section for information on the song anniversary and specify the addresses of the recipient.
5. Session level effectively manages communication sessions between two mutually interacting clients, meaning the beginning and end of a communication session, what time it is, trial and mode, synchronization points for intermediate control і update during data transfer; Renews the connection after cancellations within an hour of the connection session without wasting data.
6. Representative - manages data in a form necessary for data processing programs, controls compression and decompression of data. Tasks of this level involve the transformation of data when transmitting information into a format that is stored in the information system. Upon acceptance of these data, this line of presentation ends at the gate of re-creation.
7. The application interface interacts with application border programs to serve files, as well as advanced calculations, information-based robots, logical processing of information, transmission of postal notifications, etc. The main task of this level is to provide a user-friendly interface for the user.
At different levels of exchange, different units of information are obtained: beats, frames, packets, notification sessions, and those designated for correspondent notification.
protocol- this is a set of information that means the exchange of data between different programs. The protocols define the methods for transmitting notifications and processing notifications at intervals, and also allow the development of standards that are not tied to a specific hardware platform.
Merezhevі protocols impose rules on computers that are connected to the limit. There will be stinks behind the rich principle. The protocol of this peer implies one of the technical rules of communication. Currently, the OSI model is being developed for edge protocols.
The TCP / IP protocol is two lower-level protocols that are the basis for connecting to the Internet. The TCP (Transmission Control Protocol) protocol breaks down the transmitted information into portions and numbers them all. Using the IP (Internet Protocol) protocol, all parts are transmitted to the owner. Next, using the TCP protocol, it is checked that all parts are removed. When all portions are taken, TCP places them in the required order and collects them in one place.
Let's take a look at the most common protocols used on the Internet.
HTTP (Hyper Text Transfer Protocol) is a hypertext transfer protocol that is used when transferring Web pages from one computer to another.
FTP (File Transfer Protocol) is a protocol for transferring files from a special file server to the customer’s computer, which allows the subscriber to exchange double and text files with any other computer. Having established a connection with a remote computer, the user can copy a file from it to your own or, for example, copy a file from your computer to a remote one.
POP (Post Office Protocol) is a standard postal communication protocol. POP servers process incoming mail, and the POP protocol is used to process requests for receiving mail from client mail programs.
The SMTP (Simple Mail Transfer Protocol) standard specifies a set of rules for sending mail. The SMTP server returns either confirmation of acceptance or notification of payment, or may receive additional information.
UUCP (Unix to Unix Copy Protocol) is an outdated, but still stagnant data transfer protocol, including for electronic mail. This protocol transmits a single packet method of information transfer, in which a connected client-server is installed and a packet of data is transferred, and then its processing, review or preparation of sheets is carried out autonomously.
TELNET is a remote access protocol that allows a subscriber to access any EOM Internet connection as if on his own, to launch programs, change operating modes, etc. In practice, the capabilities are limited to this level of access, such as tasks performed by the administrator of the remote machine.
WWW (World Wide Web) is a service that provides access to various Internet resources - documents, graphics, audio and video recordings, the HTTP protocol and HTML language.
WWW technology was developed in 1989 in Geneva, in the Laboratory of Physics of Elementary Particles of the European Center for Nuclear Research (CERN).
HTTP is a protocol for transferring hypertext documents. HTML (Hypertext Markup Language) is a general markup for hypertext. Hypertext, in turn, is a document format that, in addition to text, can transfer messages to other hypertext documents, pictures, music and files. Hyperpower is a function that allows you to move from one Web resource to another by clicking on the mouse. When viewing a Web page in a browser, the messages are visible visually.
HTML is a hypertext document format that is used on the WWW to provide information. The format does not describe how the document is supposed to look, but rather its structure and coherence. The external appearance of the document on the client’s screen is determined by the WWW browser program. As a result of working at a graphical or text terminal, the document will look different at the end, but its structure will no longer remain unchanged, as long as it is set in the HTML format. File names in HTML format may include the extensions htm, html, dhtml, shtml.
HTML - language of tags. Tags are the commands of the html language, which are added to the text with three-piece arches. For example... Tags are placed in pairs to indicate the beginning and end of the area of the HTML code, which is how it works. for example,
- opening tag,
- closes the tag. Tags indicate the parameters of the text in their action area, as well as size, font placement, alignment, color, placement of objects in the document, etc.Web masters are all the tools that create web pages and sites. To create HTML documents, web developers use either visual (Microsoft Front Page) or simple text editors (Windows Notepad). Creating pages with the help of visual editors is more manual, but the editor does not create such optimal html code as a web-master. In addition, it is possible to create a lot of elements in the HTML code if the page code is not edited in the middle.
WWW follows the principle: client-server - there are no servers, which, after asking the client, turn your hypertext document. In order to use the WWW, it requires a special software program, which, as a rule, expands as quickly as possible or comes bundled with many other programs and Internet services. If a Web site is displayed in the browser, it will select the commands written in the HTML language and display whichever site on the screen. WWW software features are universal for various Internet services, and the WWW information system itself plays an integrative role.
The set of server and client parts of the OS that provide access to a specific type of computer resource through a network is called a network service. In most cases, the client and server applications of the OS, which ensure access through a network to the computer’s file system, create a file service.
It seems that the Merezh Service provides the Merezh workers with a wide range of services. These services are also called edge services (from the English term “service”). It is necessary to note that this term in technical literature is translated as “service”, and as “servant”, and as “service”. Although the defined terms are used as synonyms, it is important to note that in some cases the meaning of these terms is of a principled nature. Further in the text under “service” we will understand the boundary component that implements a certain set of services, and under “service” we will describe the set of services provided by this service. Thus, a service is an interface between a service provider and a service provider (service).
The skin service is associated with a different type of edge resources and / or a different way of accessing these resources. For example, the service will provide access to border printers and provide the service to the customer, and the mail service will provide access to the information resource of the border - electronic sheets. The method of accessing resources is, for example, the remote access service - it gives computer users access to all resources through dial-up telephone channels. To deny remote access to a specific resource, such as a printer, the remote access service communicates with the other service. The most important ones for edge OS users are the file service and the friend service.
Among the peripheral services you can see those that are oriented not at a simple customer, but at an administrator. Such services are used to organize robotic measures. For example, the Bindery service of the Novell NetWare 3.x operating system allows the administrator to maintain a database of networked computers running the OS. A more progressive approach would be to create a centralized research service, or, in other words, a directory service, which is designed to maintain a database not only about all back-office measures, but also about all programs and hardware components. Directory service applications often include Novell's NDS and Banyan's StreetTalk. Other applications of edge services that can be provided by the service administrator include the edge monitoring service, which allows you to capture and analyze edge traffic, the security service, which can include functions, monitoring, and login procedures. Safe login with password verification, backup and archiving service. In addition, how rich a set of services the operating system provides to end-user accountants, assistants and network administrators, their position lies in the main row of network operating systems.
Merger services, by their nature, are client-server systems. When implementing any edge service, it is natural that the source of requests (client) and the end of requests (server), then any edge service contains two asymmetrical parts in its warehouse - the client and the server well (Fig. 2.2). The network service can be represented in the operating system either by both (client and server) parts, or only one of them.
Small 2.2
Make it seem like the server gives its resources to the client, and the client uses them. It is necessary to note that when this service is provided by the edge service, the resources of not only the server, but also the client are used. The client can spend a significant part of his resources (disk space, processor hours, etc.) to support the work of the boundary service. For example, when implementing a postal service, a local copy of the database can be saved on the client’s disk to accommodate extensive browsing. In this case, the client chooses a great job when molded into different formats, including folding multimedia, supports the management of the address book and creates a lot of other related jobs. The fundamental difference between the client and the server is that the client is always the initiator of the work, the edge service, and the server is always in passive request processing mode. For example, the mail server delivers mail to the client's computer only if it is entered into the mail client.
Because the interactions between the client and server parts are standardized, so that one type of server can be used to work with clients of different types, implemented in different ways, and possibly by different processors. The same mind is for whom - the client and the server are responsible for maintaining a completely standard protocol for interaction.