Network service and network standards. Means of using network services. Network services and network services What is a network service
Concept computer network.
Computer networks are systems of computers connected by data transmission channels that ensure the effective provision of various information and computing services to users through the implementation of convenient and reliable access to network resources.
Information systems that use the capabilities of computer networks ensure the following tasks:
· Data storage and processing
· Organizing user access to data
· Transfer of data and processing results to users
The effectiveness of solving these problems is ensured by:
· Remote user access to hardware, software and information resources
High system reliability
· the ability to quickly redistribute the load
· specialization of individual network nodes to solve a certain class of problems
· solving complex problems through the joint efforts of several network nodes
· the ability to carry out operational control of all network nodes
If we consider the structure of a computer network, we can distinguish three basic elements:
Network tools and services
Data transfer media
Network protocols.
Network tools and services. If we look at a computer network, then network facilities and services mean everything that the network is capable of. Numerous combinations of hardware and software are used to provide services.
The term “service provider” refers to a combination of hardware and software that performs a specific service. This term should not be understood as a computer, since computers can perform various services and there can be several service providers on one computer at the same time
The term “service requestor” means any entity using this service.
Depending on the roles they perform in the network, there are three types of service providers and consumers:
Server
Client
Client-server (peer).
The server can only provide services. The client can only consume services. And the client-server can simultaneously provide and consume services.
Very often, these concepts are mistakenly strictly tied to any computer, but it should be noted that the role of a computer depends on the installed software, and depending on the software, a computer can be a server, a client, or a client-server.
Computer networks can be divided into two types according to their structure:
Server based
Peer-to-peer
Members of a peer-to-peer network can be both consumers and service providers at the same time. The software installed on each computer in a peer-to-peer network usually provides the same range of services.
Peer-to-peer networks are also called workgroups. Most often, such networks contain no more than 10 computers. Such networks are cheap because they do not have a dedicated computer for the server. Users themselves act as administrators and ensure information security. This type of network is chaotic information structure. With a large number of clients, the peer-to-peer network becomes difficult to manage.
Advantages.
Easy to install and configure
Users control their own resources
No additional resources (hardware and administrator) required - network security installed separately for each resource
Flaws
You need to remember as many passwords as you have resources
Backups are performed on all computers to protect shared data
Low productivity of service providers
There is no centralized scheme for searching and controlling access to data
In server-based networks, clients consume services and servers provide services. Moreover, these relations are strictly subject to administrative rules. Servers can be classified by the types of services they provide, which will be done later. Nowadays, server-based networks are the most popular type of networks.
Computers that act as servers usually have powerful hardware. They are specially designed to fulfill a large number of customer requests. The key to the security of such a network is the physical restriction of access to the server. A special person - an administrator - forms a unified network security policy. Shared files are typically stored in one place, making them easy to back up. Such networks also scale better and can serve from a few to tens of thousands of users.
Advantages
Centralized management of user accounts, security and access
More productive service providers
The user only needs one password
Flaws
Centralized data backup - server failure can render the network inoperable
Requires qualified personnel for maintenance, which increases cost
High cost - due to special equipment
The choice of implementing any type of network can be made according to the following conditions.
Peer-to-peer network:
There are no more than 10 network users (preferably five)
All machines in the network are compactly located to be combined into one local network
Limited funds
No need for high performance service providers
The issue of safety is not decisive.
Server based network:
The network is planned to have more than 10 users
Requires centralized management, security, resource management or backup
There is a need for high performance service providers
Requires WAN access or uses internetwork
The transmission medium is the medium through which information is transmitted. Computer media means either cable or technology wireless communication. The carrier does not guarantee that the message will be received by the addressee, it only guarantees its correct transmission.
Network protocols ensure that network members understand each other. A protocol is a set of rules and standards by which various devices interact.
Network tools and services: concept, examples and purpose of basic network services .
Network services and network services
A network service is a set of server and client parts of the OS that provide access to a specific type of computer resource via the network.
A network service is said to provide a set of services to network users. These services are sometimes also called network services (from the English term "service"). Further in the text, by “service” we will understand network component, which implements a certain set of services, and “service” is a description of the set of services that is provided by this service. Thus, a service is an interface between a service consumer and a service provider (service).
Service - description of the set of services provided by the network service
Each service is associated with a specific type of network resource and/or a specific method of accessing those resources. For example, a print service provides network users with access to shared printers on the network and provides a print service, while a mail service provides access to information resource networks - emails. The method of accessing resources differs, for example, the service remote access- it provides computer network users with access to all its resources through dial-up telephone channels. To gain remote access to a specific resource, such as a printer, the Remote Access service communicates with the Print service. The most important ones for network OS users are the file service and the print service.
Among the network services, one can distinguish those that are not aimed at simple user, but to the administrator. Such services are used to organize the operation of the network. For example, the Bindery service of the Novell NetWare 3.x operating system allows the administrator to maintain a database of network users on the computer running that OS. A more progressive approach is to create a centralized help desk, or, in other words, a directory service, which is designed to maintain a database not only of all network users, but also of all its software and hardware components. Novell's NDS and Banyan's StreetTalk are often cited as examples of directory services. Other examples of network services that provide services to the administrator are the network monitoring service, which allows you to capture and analyze network traffic, the security service, the functions of which may include, in particular, performing a logical login procedure with password verification, the Reserve copy and archiving.
Its position in the general range of network operating systems depends on how rich a range of services the operating system offers to end users, applications and network administrators.
Network services are, by nature, client-server systems. Since when implementing any network service there naturally arises a source of requests (client) and an executor of requests (server), then any network service contains two asymmetric parts - client and server. A network service can be represented in operating system either both (client and server) parts, or only one of them.
The fundamental difference between a client and a server is that the client is always the initiator of the work performed by the network service, and the server is always in a passive mode of waiting for requests.
Usually the interaction between the client and server parts is standardized, so that one type of server can be designed to work with clients different types, implemented different ways and maybe by different manufacturers. The only condition for this is that clients and server must support a common standard communication protocol.
network OS developers considered a more effective approach in which the network OS, from the very beginning of work on it, is thought about and designed specifically for working on the network. The network functions of these operating systems are deeply integrated into the main modules of the system, which ensures its logical harmony, ease of operation and modification, as well as high performance. It is important that there is no redundancy with this approach. If all network services are well integrated, i.e. are considered as integral parts of the OS, then all the internal mechanisms of such an operating system can be optimized to perform network functions. For example, Microsoft's Windows NT OS, due to its built-in network tools, provides higher performance and information security compared to the LAN Manager network OS from the same company, which is an add-on to the local OS/2 operating system. Other examples of network operating systems with built-in network services are all modern versions of UNIX, NetWare, OS/2 Warp.
Another option for implementing network services is to combine them in the form of a certain set (shell), and all services of such a set must be consistent with each other, i.e. in their work they can refer to each other, they can have common components, for example, a common user authentication subsystem or a single user interface. For the shell to work, it is necessary to have some local operating system that would perform the usual functions necessary to manage the computer hardware, and in the environment of which the network services that make up this shell would run. The shell is an independent software and, like any product, has a name, version number and other relevant characteristics. Examples of network shell include, but are not limited to, LAN Server and LAN Manager. The most famous network operating systems are Novell NetWare and Windows NT.
General Network Services
The most common network services are:
File Services
Print Services
Messaging services
Application Tools
Database tools.
And server port, resulting in a connection being established that allows two computers to interact using the appropriate application layer network protocol.
Port numbers
The port number for “binding” a service is selected depending on its functional purpose. IANA is responsible for assigning port numbers to specific network services. Port numbers range from 0 - 65535 and are divided into 3 categories:
| Port numbers | Category | Description |
|---|---|---|
| 0 - 1023 | Well-known ports | Port numbers are assigned by IANA and on most systems can only be used by system (or root) processes or applications running by privileged users. Should not be used without IANA registration. The registration procedure is defined in section 19.9 of RFC 4340. |
| 1024 - 49151 | Registered ports | Port numbers are included in the IANA catalog and can be used by normal user processes or programs run by regular users on most systems. Should not be used without IANA registration. The registration procedure is defined in section 19.9 of RFC 4340. |
| 49152 - 65535 | Dynamically used ports and/or ports used within private networks | Intended for temporary use - as client ports, ports used by agreement for private services, as well as for testing applications before registering dedicated ports. These ports cannot be registered . |
List of mappings between network services and port numbers
The official list of mappings between network services and port numbers is maintained by IANA.
History of Compliance Regulation
Issues of unifying the mapping of network services to socket (port) numbers were 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 the OS family Windows result This command looks something like this:
Active connections Name Local address External address State 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 *:*
On UNIX-like operating systems, the result of the command is netstat -an 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 ESTABLISHED 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 19 2.168.13.104:65535 ESTABLISHED tcp 0 0 10.0.0.254:1723 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 0.0.0:1812 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 0 192. 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 connections ("listening" sockets). They are the ones who provide network services. ESTABLISHED- This established connections, that is, network services in the process of using them.
Checking the availability of network services
If problems are detected with a particular network service, various diagnostic tools are used to check its availability, depending on their availability in a given OS.
One of the most convenient tools is the command (utility) tcptraceroute (a type of traceroute), which uses TCP packets for opening a connection (SYN|ACK) with the specified service (by default - web server, port 80) of the host of interest and displays information about the transit time of this type of TCP packets through routers, as well as information about the availability of the service on the host of interest, or, in case of problems with packet delivery, where in the path they arose.
Alternatively can be used alone
- traceroute for diagnosing the packet delivery route (the disadvantage is the use of UDP packets for diagnostics) and
- telnet or netcat to the port of the problematic service to check its response.
Notes
see also
Links
- RFC 322 Well Known Socket Numbers
- RFC 349 Proposed Standard Socket Numbers (rescinded by RFC 433)
- RFC 433 (English) Socket Number List (rescinded by RFC 503)
- RFC 503 (English) Socket Number List (rescinded by RFC 739)
- RFC 739 ASSIGNED NUMBERS (the first list of assigned numbers, was replaced by a number of RFCs, most recently RFC 1700)
- RFC 768 User Datagram Protocol
- RFC 793 TRANSMISSION CONTROL PROTOCOL
- RFC 1700 ASSIGNED NUMBERS latest list assigned numbers, superseded by RFC 3232)
- RFC 3232 Assigned Numbers: RFC 1700 is Replaced by an On-line Database
- RFC 4340 (English) Datagram Congestion Control Protocol (DCCP) - PROPOSED STANDARD
Wikimedia Foundation.
- 2010.
- Niflo, Isidore
Salads and eggplant caviar
See what “Network services” are in other dictionaries: Social networking services - Social network service is a virtual platform that connects people into online communities using software, computers connected to a network (Internet) and a network of documents (World Wide Web). Network social services
in... ... Wikipedia Internet services - services provided on the Internet to users, programs, systems, levels, functional blocks. On the Internet, services are provided by network services. The most common Internet services are: data storage; transmission... ...
Financial Dictionary Port (network protocols)
- Network port is a parameter of the UDP protocols that determines the purpose of data packets in the format This is a conditional number from 0 to 65535, allowing different programs running on the same host to receive data independently of each other (provided like this... ... Wikipedia- This term has other meanings, see Core. The kernel is the central part of the operating system (OS), providing applications with coordinated access to computer resources, such as processor time, memory and external hardware... ... Wikipedia
Microkernel- This term has other meanings, see Micronucleus (cytology). The microkernel architecture is based on user-mode server programs... Wikipedia
Microkernel operating system- The microkernel architecture is based on user-mode server programs. A microkernel is a minimal implementation of the functions of the operating system kernel. Classic microkernels provide only very small set low-level primitives ... Wikipedia
Simple Service Discovery Protocol- SSDP Name: Simple Service Discovery Protocol Level (according to the OSI model): Session Family: TCP/IP Port/ID: 1900/UDP Simple Service Discovery Protocol, SSDP ... Wikipedia
Letopisi.ru- This page requires significant revision. It may need to be Wikified, expanded, or rewritten. Explanation of reasons and discussion on the Wikipedia page: For improvement / May 16, 2012. Date of setting for improvement May 16, 2012 ... Wikipedia
Network Scan- network attack. Description The purpose of this attack is to find out which computers are connected to the network and what network services are running on them. The first task is solved by sending Echo ICMP messages using the ping c utility... ... Wikipedia
7ya.ru- Publisher ALP Media Editor-in-chief Elena Konstantinovna Polyaeva Date of foundation 2000 Certificate of registration of mass media El No. FS77 35954 Language ... Wikipedia
Books
- Multiplayer games. Online Application Development , Joshua Glaser , Online multiplayer gaming is a multi-billion dollar business, attracting tens of millions of players. This book is on real examples talks about the features of developing such games and... Category:
And server port, resulting in a connection being established that allows two computers to interact using the appropriate application layer network protocol.
Port numbers
The port number for “binding” a service is selected depending on its functional purpose. IANA is responsible for assigning port numbers to specific network services. Port numbers range from 0 - 65535 and are divided into 3 categories:
| Port numbers | Category | Description |
|---|---|---|
| 0 - 1023 | Well-known ports | Port numbers are assigned by IANA and on most systems can only be used by system (or root) processes or applications running by privileged users. Should not be used without IANA registration. The registration procedure is defined in section 19.9 of RFC 4340. |
| 1024 - 49151 | Registered ports | Port numbers are included in the IANA catalog and can be used by normal user processes or programs run by regular users on most systems. Should not be used without IANA registration. The registration procedure is defined in section 19.9 of RFC 4340. |
| 49152 - 65535 | Dynamically used ports and/or ports used within private networks | Intended for temporary use - as client ports, ports used by agreement for private services, as well as for testing applications before registering dedicated ports. These ports cannot be registered . |
List of mappings between network services and port numbers
The official list of mappings between network services and port numbers is maintained by IANA.
History of Compliance Regulation
Issues of unifying the mapping of network services to socket (port) numbers were raised in RFCs 322 and 349, the first attempts at regulation were made by Jon Postel in RFCs 433 and 503.
Current list
netstat -anOn Windows operating systems, the result of this command looks something like this:
Active connections Name Local address External address State 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 *:*
On UNIX-like operating systems, the result of the command is netstat -an 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 ESTABLISHED 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 19 2.168.13.104:65535 ESTABLISHED tcp 0 0 10.0.0.254:1723 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 0.0.0:1812 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 0 192. 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 connections ("listening" sockets). They are the ones who provide network services. ESTABLISHED- these are established connections, that is, network services in the process of using them.
Checking the availability of network services
If problems are detected with a particular network service, various diagnostic tools are used to check its availability, depending on their availability in a given OS.
One of the most convenient tools is the command (utility) tcptraceroute (a type of traceroute), which uses TCP packets for opening a connection (SYN|ACK) with the specified service (by default - web server, port 80) of the host of interest and displays information about the transit time of this type of TCP packets through routers, as well as information about the availability of the service on the host of interest, or, in case of problems with packet delivery, where in the path they arose.
Alternatively can be used alone
- traceroute for diagnosing the packet delivery route (the disadvantage is the use of UDP packets for diagnostics) and
- telnet or netcat to the port of the problematic service to check its response.
Notes
see also
Links
- RFC 322 Well Known Socket Numbers
- RFC 349 Proposed Standard Socket Numbers (rescinded by RFC 433)
- RFC 433 (English) Socket Number List (rescinded by RFC 503)
- RFC 503 (English) Socket Number List (rescinded by RFC 739)
- RFC 739 ASSIGNED NUMBERS (the first list of assigned numbers, was replaced by a number of RFCs, most recently RFC 1700)
- RFC 768 User Datagram Protocol
- RFC 793 TRANSMISSION CONTROL PROTOCOL
- RFC 1700 ASSIGNED NUMBERS (latest list of assigned numbers, superseded by RFC 3232)
- RFC 3232 Assigned Numbers: RFC 1700 is Replaced by an On-line Database
- RFC 4340 (English) Datagram Congestion Control Protocol (DCCP) - PROPOSED STANDARD
Wikimedia Foundation.
- 2010.
- Niflo, Isidore
Salads and eggplant caviar
See what “Network services” are in other dictionaries:- Social networking service is a virtual platform that connects people into online communities using software, computers connected to a network (Internet) and a network of documents (World Wide Web). Network social services in... ... Wikipedia
in... ... Wikipedia Internet services - services provided on the Internet to users, programs, systems, levels, functional blocks. On the Internet, services are provided by network services. The most common Internet services are: data storage; transmission... ...
Financial Dictionary Port (network protocols)
- Network port is a parameter of the UDP protocols that determines the purpose of data packets in the format This is a conditional number from 0 to 65535, allowing different programs running on the same host to receive data independently of each other (provided like this... ... Wikipedia- This term has other meanings, see Core. The kernel is the central part of the operating system (OS), providing applications with coordinated access to computer resources, such as processor time, memory and external hardware... ... Wikipedia
Microkernel- This term has other meanings, see Micronucleus (cytology). The microkernel architecture is based on user-mode server programs... Wikipedia
Microkernel operating system- The microkernel architecture is based on user-mode server programs. A microkernel is a minimal implementation of the functions of the operating system kernel. Classic microkernels provide only a very small set of low-level primitives... Wikipedia
Simple Service Discovery Protocol- SSDP Name: Simple Service Discovery Protocol Level (according to the OSI model): Session Family: TCP/IP Port/ID: 1900/UDP Simple Service Discovery Protocol, SSDP ... Wikipedia
Letopisi.ru- This page requires significant revision. It may need to be Wikified, expanded, or rewritten. Explanation of reasons and discussion on the Wikipedia page: For improvement / May 16, 2012. Date of setting for improvement May 16, 2012 ... Wikipedia
Network Scan- network attack. Description The purpose of this attack is to find out which computers are connected to the network and what network services are running on them. The first task is solved by sending Echo ICMP messages using the ping c utility... ... Wikipedia
7ya.ru- Publisher ALP Media Editor-in-chief Elena Konstantinovna Polyaeva Date of foundation 2000 Certificate of registration of mass media El No. FS77 35954 Language ... Wikipedia
Books
- Multiplayer games. Online Application Development , Joshua Glaser , Online multiplayer gaming is a multi-billion dollar business, attracting tens of millions of players. Using real examples, this book talks about the features of developing such games and... Category:
In 1961, the Defense Advanced Research Agency (DARPA), on behalf of the US Department of Defense, began a project to create an experimental packet transmission network. This network, called ARPANET, was originally intended to study communications support in the event of a nuclear attack and to help scientists share information among statewide defense research organizations.
The project was based on three main ideas:
– each network node is connected to others, so that between them there are several different paths to each other;
– all nodes and connections are considered unreliable;
– there are automatically updated packet redirection tables; for example, a packet intended for a non-neighboring node is sent, in accordance with such a table, to the one closest to it, and if this node is unavailable, to the next one, etc.
The system created according to these principles did not have a centralized control center and, therefore, could painlessly change its configuration.
The ARPANET experiment was so successful that many organizations wanted to join in order to use this system for daily data transfer. And in 1975, ARPANET evolved from an experimental network to a working network.
Russia joined it in the late 80s. In 1990, the APRANET network ceased to exist, and in its place the Internet arose, which made possible free information exchange, regardless of distances and state borders.
In fact, the Internet consists of many local and global networks, owned by various companies and enterprises, operating on a wide variety of protocols, and interconnected by various communication lines that physically transmit data through telephone wires, fiber optics, satellites and radio modems.
No one pays for the Internet centrally, everyone pays only for their part. Representatives of the networks get together and decide how to connect to each other and contain these relationships. The user pays for connection to some regional network, which, in turn, pays for its access to the network owner of a national scale. The Internet has no owner, there is no special body
management, which would control the entire operation of this network. Local networks of various countries are financed and managed by local authorities in accordance with government policy on this issue.
The structure of the Internet resembles a web, in the nodes of which there are computers interconnected by communication lines. Internet nodes connected by high-speed communication lines form the basis of the Internet. Typically, these are service providers (providers).
Digitized data is sent through routers, which connect networks using complex algorithms, choosing routes for information flows.
Each computer on the Internet has its own unique address.
In the TCP/IP protocol, each machine is addressed by four decimal numbers, separated by dots, and each number can have a value from 1 to 255. The computer address looks like this:
<сегмент n>. … <сегмент 3>.<сегмент 2>.<сегмент 1>.
This address is called an IP address. This number can either be permanently assigned to the computer, or assigned dynamically - at the moment when the user connects to the provider, but at any given time there are no two computers on the Internet with the same IP addresses.
It is inconvenient for the user to remember such addresses, which can also change. Therefore, on the Internet there is a Domain Name System (DNS), which allows each computer to be called by name. There are millions of computers on the network, and to avoid repeating names, they are divided into independent domains.
Thus, the computer address looks like several domains separated by a dot: Here segment 1 is a 1st level domain, segment 2 is a 2nd level domain, etc.) www.microsoft.com refers to a computer named www in the microsoft.com domain. Microsoft is the name of the company, com is the domain of commercial organizations.
The computer name www indicates that this computer hosts a WWW service.
This is a 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 on a network can have multiple DNS names. A 1st level domain usually determines the country where the server is located (ru - Russia; ua - Ukraine; uk - Great Britain; de - Germany) or the type of organization (com - commercial organizations; edu - scientific and educational organizations; gov - government agencies; org - non-profit organizations ). When entering a domain name, for example, www.mrsu.ru, the computer must convert it to an address. To do this, it sends a query to the DNS server, starting from the right side of the domain name and moving to the left. His software knows how to contact the root server, which stores the addresses of the name servers of the first-level domain (the rightmost part of the name, for example, software ru ). Thus, the server requests from the root server the address of the computer responsible for the domain ).. Having received the information, he contacts this computer and asks it for the server address mrsu
, then from the server
gets an address www is a number that is added to the computer address and indicates the program for which the data is intended.
Each program running on a computer has a specific port, and it responds only to those packets that are addressed to that port.
There are a large number of standard ports corresponding to specific services, for example, 21 – FTP; 23 – telnet; 25 – SMTP; 80 – HTTP; 110 – POP3; 70 – Gopher, etc.
The Internet uses not just domain names, but universal resource locators (URLs).
– URL includes:– method of accessing the resource, i.e. access protocol (http, gopher, WAIS, ftp, file, telnet, etc.);
network address
resource (host machine and domain name);
– full path to the file on the server.
In general, the URL format looks like this:
method://host.domain[:port]/path/filename,
where method is one of the values listed below:
file – file on the local system;
http – file on the World Wide Web server;
gopher – file on the Gopher server;
wais – file on the WAIS (Wide Area Information Server) server;
news – Usenet newsgroup;
telnet – access to Telnet network resources;
ftp – file on an FTP server;
host.domain – domain name on the Internet;
port – a number that must be specified if the method requires a port number.
Example: http://support.vrn.ru/archive/index.html. Below are some of the most common names of computers on the Internet. Server on the Internet is a computer that provides services to network users: shared access to disks, files, printer, system
Email. Typically, a server is a combination of hardware and software.
Website– a generalized name for a collection of documents on the Internet interconnected by links.
Gateway is a computer or system of computers with special software that allows two networks with different protocols to communicate.
Homepage is a personal Web page of a specific user or organization.– Model of Open System Interconnections), which was created on the basis of technical proposals from the International Standards Institute ISO (International Standards Organization).
According to the OSI model, the architecture of computer networks should be considered at different levels (the total number of levels is up to seven), (Fig. 9). The top one is applied. At this level the user interacts with the computing system. The lowest level is the physical layer, which ensures the exchange of signals between devices. Data exchange in communication systems occurs by moving it from top level
to the lower one, then transport and, finally, reverse playback on the client's computer as a result of moving from the lower level to the upper one.
To ensure the necessary compatibility, special standards called protocols operate at each of the seven possible levels of computer network architecture. They determine the nature of the hardware interaction of network components (hardware protocols) and the nature of the interaction of programs and data (software protocols). Physically, protocol support functions are performed by hardware devices (interfaces) and software (protocol support programs). Programs that support protocols are also called protocols. Rice. 9.
OSI Control Layers and Protocols
Each level of the architecture is divided into two parts:
– service specification;
– protocol specification.
A service specification defines what a layer does, and a protocol specification defines how it does it, and each particular layer may have more than one protocol.
Let's look at the functions performed by each layer of software:
1. The physical layer makes connections to the physical channel, disconnects from the channel, and manages the channel. Determines the data transfer rate and network topology.
2. The data link layer adds auxiliary symbols to the transmitted arrays of information and monitors the correctness of the transmitted data. Here the transmitted information is divided into several packets or frames. Each packet contains source and destination addresses, as well as error detection.
4. The transport layer connects the lower layers (physical, channel, network) with the upper ones, which are implemented in software. This level separates the means of generating data on the network from the means of transmitting it. Here the information is divided according to a certain length and the destination address is specified.
5. The session layer manages communication sessions between two interacting users, determines the beginning and end of a communication session, its time, duration and mode, synchronization points for intermediate control and recovery during data transfer;
Restores the connection after errors during a communication session without losing data.
6. Representative – manages the presentation of data in the form required by the program user, performs data compression and decompression. The task of this level is to convert data when transmitting information into a format that is used in the information system. When receiving data, this presentation layer performs the reverse transformation. 7. The application layer interacts with application network programs
, serving files, and also performs computational, information retrieval work, logical transformations of information, transmission of mail messages, etc. The main task of this level is to provide a convenient interface for the user.
At different levels, different units of information are exchanged: bits, frames, packets, session messages, user messages. Protocol
is a set of agreements that defines the exchange of data between different programs. Protocols define how messages are transmitted and errors handled in a network, and also allow the development of standards that are not tied to a specific hardware platform. Network protocols dictate rules computer work
The TCP/IP protocol is two lower-level protocols that are the basis of Internet communications.
The TCP (Transmission Control Protocol) protocol breaks the transmitted information into portions and numbers them all. Using the Internet Protocol (IP), all parts are transmitted to the recipient. Next, using the TCP protocol, it is checked whether all parts have been received.
When receiving all the portions, TCP places them in the required order and assembles them into a single whole.
Let's look at the most well-known protocols used on the Internet. HTTP (Hyper Text Transfer Protocol) is a hypertext transfer protocol used when sending Web pages from one computer to another. FTP (File Transfer Protocol) is a protocol for transferring files from a special file server to the user's computer, which allows the subscriber to exchange binary and
text files
with any computer on the network. Having established a connection with a remote computer, the user can copy a file from it to his own or, conversely, copy a file from his computer to the remote one.
POP (Post Office Protocol) is a standard mail communication protocol. POP servers process incoming mail, and the POP protocol is designed to handle mail requests from client mail programs. The SMTP (Simple Mail Transfer Protocol) standard defines a set of rules for mail transfer. The SMTP server returns either an acknowledgment or an error message, or requests additional information. UUCP (Unix to Unix Copy Protocol) is a now obsolete but still used data transfer protocol, including for email. This protocol involves the use of a packet method of transmitting information, in which a connection is first established
client-server
and a data packet is transmitted, and then it is processed, viewed or prepared autonomously.
WWW technology was developed in 1989 in Geneva, at the Particle Physics Laboratory of the European Center for Nuclear Research (CERN).
HTTP is a hypertext document transfer protocol.
HTML (Hypertext Markup Language) is a hypertext markup language. Hypertext, in turn, is a document format that, in addition to text, can contain links to other hypertext documents, pictures, music and files. Hyperlinks are links that allow you to move from one Web resource to another with a mouse click. When viewing a Web page in a browser, links are highlighted visually.
HTML is a hypertext document format used on the WWW to provide information.
This format does not describe how the document should look, but only its structure and connections. The appearance of the document on the user's screen is determined by the WWW viewing program - the browser. As a result of working at a graphical or text terminal, the document will look different in each case, but its structure will remain unchanged, since it is specified in the HTML format. HTML file names usually have the extension htm, html, dhtml, shtml.
HTML is the language of tags.Tags are commands in the HTML language, separated from the rest of the text by triangular brackets. For example, . Tags are placed in pairs to define the beginning and end of the region of HTML code they affect. For example, – opening tag,– closing tag. Tags determine what parameters the text in their scope has, as well as size, font style, alignment, color, location of objects in the document, etc. Webmasters are network users who create web pages and sites. To create HTML documents, webmasters use either visual (Microsoft Front Page) or simple text editors
WWW works on the principle: client-servers - there are many servers that, upon a client’s request, return a hypertext document to him. To use the WWW, the user must have special software, which is usually distributed over the Internet for free or comes bundled with most other Internet programs and services. When a Web page is loaded in the browser, it executes the commands written on HTML language, and displays the page on the screen. WWW software tools are universal for various Internet services, and the Information system WWW plays an integrating role.
The set of server and client parts of the OS that provide access to a specific type of computer resource via a network is called network service. In the example above, the client and server parts of the OS, which together provide access through the network to file system computer, form a file service.
A network service is said to provide network users with a certain set of services. These services are sometimes also called network service(from the English term “service”). Although these terms are sometimes used interchangeably, it should be borne in mind that in some cases the difference in the meaning of these terms is fundamental. Further in the text, by “service” we will understand a network component that implements a certain set of services, and by “service” we will mean a description of the set of services that is provided by this service. Thus, a service is an interface between a service consumer and a service provider (service).
Each service is associated with a specific type of network resource and/or a specific method of accessing those resources. For example, a print service provides network users with access to shared network printers and provides a print service, and a mail service provides access to a network information resource - emails. For example, the remote access service differs in the method of accessing resources - it provides computer network users with access to all its resources through dial-up telephone channels. To gain remote access to a specific resource, such as a printer, the Remote Access service communicates with the Print service. The most important ones for network OS users are the file service and the print service.
Among the network services, we can highlight those that are aimed not at the average user, but at the administrator. Such services are used to organize the operation of the network. For example, the Bindery service of the Novell NetWare 3.x operating system allows the administrator to maintain a database of network users on the computer running that OS. A more progressive approach is the creation of a centralized help service or, in other words, a directory service, which is designed to maintain a database not only of all network users, but also of all its software and hardware components. Novell's NDS is often cited as an example of directory services. Other examples of network services that provide services to the administrator are a network monitoring service, which allows you to capture and analyze network traffic, a security service, the functions of which may include, in particular, performing a login procedure with password verification, and a backup and archiving service.
Its position in the general range of network operating systems depends on how rich a range of services the operating system offers to end users, applications and network administrators.
Network services are, by nature, client-server systems. Since when implementing any network service, a request source (client) and a request executor (server) naturally arise, any network service contains two asymmetric parts - client and server. A network service can be represented in the operating system either by both (client and server) parts, or only by one of them.
It is usually said that the server provides its resources to the client, and the client uses them. It should be noted that when a network service provides a certain service, the resources of not only the server, but also the client are used. The client may spend a significant portion of its resources (disk space, CPU time, etc.) maintaining the network service. The fundamental difference between a client and a server is that the client is always the initiator of the work performed by the network service, and the server is always in a passive mode of waiting for requests. For example, mail server delivers mail to the user's computer only when a request is received from an email client.
Typically, the interaction between the client and server parts is standardized, so that one type of server can be designed to work with different types of clients, implemented in different ways, and perhaps by different manufacturers. The only condition for this is that clients and server must support a common standard communication protocol.
