Describe the architecture and main components of networks. Computer network architecture
Hello, dear site visitors! Networks must support a wide range of applications and services, and operate over many different types of physical infrastructure. Term network architecture in this context means both technologies that support infrastructure and software services and the protocols that carry messages over this architecture. As in general, evolve, we find four main characteristics underlying architectures that must be implemented to meet user expectations: , and .
A scalable network can quickly expand to support new users and applications without impacting the performance of the service provided to existing users. Thousands of new users and service providers connect every week. The network's ability to support these new relationships depends on the layered hierarchical design of the underlying physical infrastructure and logical architecture networks. The operation of each layer allows users or service providers to connect to the Internet without disrupting the entire network. Technological developments continually improve the messaging capabilities and performance of physical infrastructure components at every layer. These developments, together with new ways to identify and locate individual users in unified network allow you to develop in accordance with the needs and requirements of users.
Quality of Service (from the English Quality of Service or QoS)
On currently provides an acceptable level of fault tolerance and scalability for users. But new applications available to users through interconnected networks, create higher expectations for the quality of services provided. Voice communication and video transmissions require a level of consistent quality and uninterrupted transmission that was not required for traditional computer applications. The quality of these services is measured in comparison to listening/viewing the same audio or video presentations directly (not through ). Traditional voice and video networks are designed to support one type of transmission, and therefore they are able to provide an acceptable level of quality. New requirements to support this quality of service in a converged network are changing the way network architectures are designed and implemented.
Evolved from a tightly controlled, unified network of educational and government organizations into a globally available network, which has become a means of personal and business communications. As a result, network security requirements have changed. Expectations of security and privacy associated with the use of internetworks for confidential and business communications classified information, exceed the capabilities that the current network architecture. Rapid expansion into areas of communications that have not been served by traditional communications increases the need to build security into the network architecture. Because of this, a lot of research and development efforts are being put into this area, and many tools and procedures are being implemented to plug the inherent security holes in the network architecture.
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Architecture refers to the organization of interaction between network nodes. In the standard classification, there are three types of architecture. They correspond to the main types of LAN. Architecture refers to the organization of interaction between network nodes. There are three main architectures, which correspond to the main types of LAN.
Architecture type - bus
The specificity of this type of architecture is that each of the LAN nodes transmits data to a common backbone. In this regard, any network node can have access to information on the backbone.
Architecture type - star
The specificity is that each of the LAN nodes is allocated separate channel for communication with the central node of the network. From the node, the information goes to the server, which can publish it to other nodes.
Architecture type - ring
The specificity is that the connection of network nodes occurs sequentially. Data exchange can occur exclusively between nodes that are located nearby. If it is necessary to exchange data with other LAN nodes, they can be transmitted in transit.
Data channels
If previously only wired local area networks were used, now wireless ones are popular in many cases. Currently The following types of LAN are distinguished:
wired cable LAN
fiber optic cable LAN
wireless LANs
Typically, LANs are built on database of the building's SCS data transmission medium. When designing a LAN of any type, reliability and security requirements should be taken into account. As a rule, to ensure security, there is a single authorization point for all applications and resources on the local network. Wireless network used where the use of a traditional LAN with wires is impossible or unprofitable.
2.1. General points when organizing a LAN
A computer connected to the network is called a workstation, a computer that provides its resources is called a server, and a computer that has access to shared resources is called a client.
Several computers located in the same room or functionally performing the same type of work: accounting or planning, registration of incoming products, etc., are connected to each other and combined into working group so that they can share various resources: programs, documents, printers, fax, etc.
The workgroup is organized so that the computers included in it contain all the resources necessary for normal operation. As a rule, a workgroup that unites more than 10 - 15 computers includes a dedicated server - a fairly powerful computer on which all shared directories and a special software to control access to the entire network or part of it.
Groups of servers are combined into domains. A domain user can register online at any workstation in this domain and gain access to all its resources. Typically, in server networks, all shared printers are connected to print servers.
From the point of view of organizing the interaction of computers, networks are divided into peer-to-peer (Peer-to-Peer Network) and with a dedicated server (Dedicated Server Network). In a peer-to-peer network, each computer plays an equal role. However, an increase in the number of computers on the network and an increase in the volume of transferred data leads to the fact that throughput the network becomes a bottleneck.
The widely used operating system Windows 95 (98), developed by Microsoft, is designed primarily to work in peer-to-peer networks, to support the computer as a client of other networks.
Windows 95, like Windows for Workgroups, can serve as a server on a network. Compatibility with old network drivers MS-DOS and Windows Z.x is ensured. The new operating system allows you to:
Share hard disks, printers, fax cards, organize peer-to-peer local area networks (LAN);
Use remote access and turn your office computer into a callable server;
Support 16-bit network drivers DOS.
The network administrator can set the overall design of the desktop system, determine what operations will be available to network users, and control the configuration of the desktop system.
A network located in a relatively small area is called local (LAN - Local Area Network). IN last years The LAN structure is becoming more complex due to the creation of heterogeneous networks connecting different computer platforms. The ability to conduct video conferencing and use multimedia increases the requirements for network software. Modern servers can store binary large objects (BLOBs) containing text, graphics, audio, and video files. In particular, if you need to obtain a HR department database over the network, then BLOB technology will allow you to transfer not only personal data: last name, first name, patronymic, year of birth, but also portraits in digital form.
Two technologies for using the server
There are two technologies for using a server: file server technology and client-server architecture. The first model uses a file server on which most programs and data are stored. At the user's request, the necessary program and data are sent to him. Information processing is performed at the workstation.
In systems with a client-server architecture, data exchange is carried out between the client application (front-end) and the server application (back-end). Data is stored and processed on a powerful server, which also controls access to resources and data. The workstation receives only the results of the query. Developers of information processing applications commonly use this technology.
The use of large and complex applications has led to the development of a multi-level, primarily three-level architecture with data placed on a separate database server (DB). All calls to the database go through the application server, where they are combined. Reducing the number of database calls reduces license fees for the DBMS.
6. Topology – this is the configuration of connecting elements into a network. Topology largely determines such the most important characteristics network, such as its reliability, performance, cost, security, etc.
One of the approaches to classifying LAN topologies is to distinguish two main classes of topologies: broadcast Andsequential.
INbroadcast configurations each Personal Computer transmits signals that can be perceived by other computers. Such configurations include “common bus”, “tree”, “star with a passive center” topologies. A star-type network can be thought of as a type of “tree” that has a root with a branch to each connected device.
INconsecutive configurations, each physical sublayer transmits information to only one personal computer. Examples of sequential configurations are: random (random connection of computers), hierarchical, “ring”, “chain”, “star with an intellectual center”, “snowflake”, etc.
Let's briefly look at the three most common (basic) LAN topologies: star, bus, and ring.
When star topology Each computer is connected via a special network adapter with a separate cable to the central node. The central node is a passive connector or active repeater.
The disadvantage of this topology is low reliability, since the failure of the central node leads to the shutdown of the entire network, and also the usually long cable length (this depends on the actual placement of computers). Sometimes, to increase reliability, a special relay is installed in the central node, which allows you to disconnect failed cable beams.
Common bus topology involves the use of one cable to which all computers are connected. Information on it is transmitted by computers one by one.
The advantage of this topology is, as a rule, a shorter cable length, as well as higher reliability than that of a “star”, since the failure of an individual station does not disrupt the operation of the network as a whole. The disadvantages are that a break in the main cable leads to the inoperability of the entire network, as well as poor security of information in the system on physical level, since messages sent by one computer to another, in principle, can be received on any other computer.
At ring topology Data is transmitted from one computer to another via relay. If a computer receives data that is not intended for it, it passes it on further along the ring. The recipient does not transmit the data intended for him anywhere.
The advantage of the ring topology is higher system reliability in the event of cable breaks than in the case of a common bus topology, since there are two access paths to each computer. The disadvantages of the topology include the large length of the cable, low performance compared to the “star” (but comparable to the “common bus”), as well as poor information security, as with the topology with a common bus.
The topology of a real LAN may be exactly the same as one of the above or include a combination of them. The structure of the network is generally determined by the following factors: the number of computers being connected, requirements for reliability and efficiency of information transfer, economic considerations, etc.
The advantages of working on a network over working on a PC are that the user has significant opportunities through access to its resources, for example, to obtain information (available to network users) located on other PCs connected to the network. It is possible to use powerful computers to run any programs ( remote start programs), exchange information with other network users. At the same time, you can save some money due to the fact that several users will be able to work with one common device, such as a printer.
So, for an office, classroom, department of a company, it is much better and cheaper to buy one expensive, but good and fast printer and use it as a network printer, than to buy cheap, but bad printers for each computer.
When organizing communication between two computers, one computer is often assigned the role of provider of resources (programs, data, etc.), and the other is assigned the role of user of these resources. In this case, the first computer is called a server, and the second is called a client or workstation running special software.
Server(English, serve - serve) is a high-performance computer with a large capacity external memory, which provides service to other computers by managing the distribution of expensive shared resources (programs, data, and peripherals).
Client(workstation) - any computer that has access to server services. For example, the server could be powerful computer, which hosts the central database, and the client - regular computer, whose programs request data from the server as needed. In some cases, a computer can be both a client and a server, that is, it can provide its resources and stored data to other computers and at the same time use their resources and data.
Communication protocol - is an agreed upon set of specific rules for the exchange of information between different devices data transmission. There are protocols for transmission speed, data formats, error control, etc.
To work with the network, you must have special network software that ensures data transfer in accordance with a given protocol. Communication protocols require that the entire volume of transmitted data be divided into packets - blocks of a fixed size. The packages are numbered so that they can then be collected into correct sequence. To the data contained in the packet is added Additional Information following format (Fig. 4.1).
recipient
sender
checksum
Rice. 4.1. Data packet format
Check sum The packet data contains information necessary for error checking. The first time it is calculated by the sending computer, the second time by the receiving computer, after the packet is transmitted. If the values do not match, the packet data was corrupted during transmission. The packet is discarded and a request is automatically made to retransmit the packet.
When establishing communication, devices exchange signals to negotiate communication channels and protocols. This process is called handshake.
Network architecture- the implemented structure of the data transmission network, which determines its topology, the composition of devices and the rules for their interaction in the network. Within the framework of the network architecture, issues of information encoding, its addressing and transmission, message flow control, error control and analysis of network operation in emergency situations and when performance deteriorates are considered.
The most common architectures are:
- Ethernet (English, ether - air) is a broadcast network in which network stations can receive all messages. Network topology is linear or star-shaped, data transfer speed is 10 or 100 Mbit/s;
- Arcnet (Attached Resource Computer Network) is a broadcast network. Physical topology - tree, data transfer rate 2.5 Mbit/s;
- Token Ring(relay ring network, token passing network) - a ring network in which the principle of data transmission is based on the fact that each ring node waits for the arrival of some short unique sequence of bits (token) from an adjacent previous node. The arrival of the token indicates that it is possible to transmit a message from this node further along the flow. Data transfer speed 4 or 16 Mbit/s;
- FDDI (Fiber Distributed Data Interface) is a network architecture for high-speed data transmission over fiber optic lines. Topology - double ring or mixed (including star or tree subnets), transmission speed 100 Mbit/s. Maximum amount stations in the network - 1000;
- ATM (Asynchronous Transfer Mode) is a promising, expensive architecture that provides transmission of digital data, video information and voice over the same lines, transmission speeds up to 2.5 Gbit/s. Optical communication lines.
Special equipment is used for connection:
- network cables(coaxial, consisting of two concentric conductors isolated from each other, the outer one of which looks like a tube; fiber optic; cables on twisted pairs, formed by two wires intertwined with each other, etc.);
- connectors(connectors) for connecting cables to a computer, connectors for connecting cable sections;
- network interface adapters for receiving and transmitting data. In accordance with a specific protocol, access to the data transmission medium is controlled. Located in system units computers connected to the network. Connects to adapter connectors network cable;
- transceivers increase the quality level of data transmission via cable, are responsible for receiving signals from the network and detecting conflicts;
- hubs(hubs) and switching hubs (switches) expand topological, functional and speed capabilities computer networks. A hub with a set of different types of ports allows you to combine network segments with different cable systems. You can connect either a separate network node or another hub or cable segment to the hub port;
- repeaters(repeaters) amplify signals transmitted over long cable lengths.
Client-server technology. The nature of the interaction of computers on a local network is usually associated with their functional purpose. As with a direct connection, within local networks The terms “client” and “server” are used. Client-server technology is a special way of interaction between computers on a local network, in which one of the computers (server) provides its resources to another computer (client). In accordance with this, peer-to-peer and server networks are distinguished.
At peer-to-peer architecture There are no dedicated servers in the network; each workstation can perform the functions of a client and a server. In this case, the workstation allocates part of its resources to common use all workstations on the network. As a rule, peer-to-peer networks are created on the basis of computers of equal power. Peer-to-peer networks are quite simple to set up and operate. In the case when the network consists of a small number of computers and its main function is the exchange of information between workstations, peer-to-peer architecture is the most acceptable solution (Table 4.1).
Table 4.1. Peer-to-peer LANs and LANs with a dedicated file server
IN peer-to-peer LANs all workstations (computers) have the same capabilities in relation to each other
IN LAN with dedicated server one of the computers (server) is assigned dispatch functions. This computer usually has the best performance and manages storage devices on hard drives(file server), supports shared peripherals such as print devices (print server), plotters, tape drives, scanners, modems, etc.)
For LAN are used Various types cables, as well as radio wave, infrared and optical channels.
Computer network topology. The configuration of the LAN determines how network subscribers are located and how they are connected to each other. There are several configurations of local area networks (Table 4.2).
Table 4.2. Local area network topologies
End of table. 4.2
Star-shaped LANs arose on the basis of institutional telephone networks with PBX.
At the center of the star-shaped LAN there is a central switch, which sequentially polls subscribers and grants them the right to exchange data
IN ring LAN information is transmitted over a closed channel (ring), in most cases only in one direction. Each subscriber is directly connected to two neighboring subscribers, but “listens” to the transmission of any network subscriber
Network management. Computer networks have the same disadvantages as PCs in the form autonomous system. Incorrectly turning on and off any equipment, going beyond the boundaries of the area, misusing information and (or) manipulating the network can destroy working system. Ensuring the reliability of the network is the responsibility of the network administrator, who must always be informed about physical condition and network performance and make appropriate decisions in a timely manner.
The network administrator manages accounts and controls access rights to data. To achieve this, networks use a naming and addressing system. Each user has his own identifier - a name according to which he receives limited access to network resources and to the time spent on the network. Users can also be grouped into groups with their own rights and restrictions. A password system is used to prevent unauthorized access.
One of the disadvantages of peer-to-peer networks - the presence of distributed data and the ability to change the server resources of each workstation - complicates the protection of information from unauthorized access. Realizing this, developers begin to pay attention Special attention issues of information security in peer-to-peer networks. Another disadvantage of peer-to-peer networks is their low performance. This is because network resources are concentrated on workstations, which must simultaneously perform the functions of clients and servers.
On server networks There is a clear division of functions between computers: some of them are always clients, while others are servers. Considering the variety of services provided by computer networks, there are several types of servers, namely: network server, file server, print server, mail server, etc.
Network server represents specialized computer, focused on performing the bulk of computing work and functions for managing a computer network. This server contains the kernel of the network operating system, under which the entire local network operates. The network server has fairly high performance and a large amount of memory. With such network organization The functions of workstations are reduced to input/output of information and its exchange with a network server.
Term file server refers to a computer whose main function is to store, manage and transmit data files. It does not process or modify the files it stores or transmits. The server may not "know" whether the file is text document, graphic image or spreadsheet. In general, the file server may not even have a keyboard or monitor. All changes to data files are made from client workstations. To do this, clients read data files from file server, make the necessary changes to the data and return them to the file server. Such an organization is most effective when a large number of users work with common base data. Within large networks Several file servers can be used simultaneously.
Print server(print server) is a printing device that, using network adapter connects to the transmission medium. The print server operates independently of others network devices, services print requests from all servers and workstations. Special high-performance printers are used as print servers.
At high intensity of data exchange with global networks within local networks are allocated mail servers , With with which email messages are processed.
Network layout and components. "Server" and "workstation"
A computer network (CN) is a complex set of interconnected and coordinated hardware and software components. The hardware components of a local network are computers and various communications equipment (cable systems, hubs, etc.). The software components of the aircraft are operating systems (OS) and network applications.
Network layout is the process of arranging hardware components to achieve the desired result.
Depending on how functions are distributed between computers on the network, they can act in three different roles:
1. A computer that deals exclusively with servicing requests from other computers plays the role of a dedicated network server (Fig. 1.4).
2. A computer that makes requests to the resources of another machine plays the role of a client node (Fig. 1.5).
3. A computer that combines the functions of a client and a server is a peer-to-peer node (Fig. 1.6).
Rice. 1.4. Computer - dedicated network server
Rice. 1.5. Computer as a client node
Obviously, the network cannot consist only of client or only server nodes.
The network can be built according to one of three schemes:
· peer-to-peer network – peer-to-peer network;
· network based on clients and servers – a network with dedicated servers;
· a network that includes nodes of all types – a hybrid network.
Each of these schemes has its own advantages and disadvantages that determine their areas of application.
Rice. 1.6. Computer - peer
In peer-to-peer networks, the same PC can be both a server and a client, including a client of its client. In hierarchical networks, shared resources are stored only on the server; the server itself can only be a client of another server at a higher hierarchy level.
Moreover, each of the servers can be implemented either on a separate computer or in a small LAN, or be combined on one computer with some other server.
There are also combined networks that combine best qualities peer-to-peer and server-based networks. Many administrators believe that such a network best satisfies their needs.
Network architecture defines the main elements of the network, characterizes its overall logical organization, technical support,software, describes coding methods. The architecture also defines the operating principles and user interface.
Terminal-host architecture;
Peer-to-peer architecture;
Client-server architecture.
Terminal-host architecture
Terminal-host computer architecture is a concept of an information network in which all data processing is carried out by one or a group of host computers.
The architecture under consideration involves two types of equipment:
The main computer where network management, data storage and processing is carried out;
Terminals designed to transmit commands to the host computer to organize sessions and perform tasks, enter data to complete tasks and obtain results.
The main computer interacts with the terminals through the MTD, as shown in Fig. 1.7.
A classic example of a host network architecture is System Network Architecture (SNA).
Rice. 1.7. Terminal-host architecture
Peer-to-peer architecture
Peer-to-peer architecture is the concept of an information network in which its resources are dispersed across all systems. This architecture is characterized by the fact that all systems in it have equal rights.
Peer-to-peer networks include small networks where any workstation can simultaneously perform the functions of a file server and a workstation. On peer-to-peer LANs disk space and files on any computer can be shared. For a resource to become shared, it must be shared using services remote access network peer-to-peer operating systems. Depending on how data protection is set up, other users will be able to use the files immediately after they are created. Peer-to-peer LANs are only good enough for small workgroups.
Peer-to-peer LANs are the easiest and cheapest type of network to install. By connecting computers, users can share resources and information.
Peer-to-peer networks have the following advantages:
They are easy to install and configure;
Individual PCs are not dependent on a dedicated server;
Users are able to control their resources;
Low cost and easy operation;
Minimum equipment and software;
No need for an administrator;
Well suited for networks with no more than ten users.
The problem with peer-to-peer architecture is when computers go offline. In these cases, the types of services they provided disappear from the network. Network security can only be applied to one resource at a time, and the user must remember as many passwords as network resources. When gaining access to a shared resource, a drop in computer performance is felt. Significant disadvantage peer-to-peer networks is the lack of centralized administration.
The use of a peer-to-peer architecture does not preclude the use of a terminal-host or client-server architecture on the same network.
Client-server architecture
Client-server architecture is a concept of an information network in which the bulk of its resources are concentrated in servers serving their clients (Fig. 1.8). The architecture in question defines two types of components: servers and clients.
A server is an object that provides services to other network objects based on their requests. Service is the process of serving customers.
The server works on orders from clients and manages the execution of their jobs. After each job is completed, the server sends the results to the client that sent the job.
The service function in the client-server architecture is described by a set of application programs, in accordance with which various application processes are performed.
Rice. 1.8. Client-server architecture
A process that calls a service function using certain operations is called a client. This could be a program or a user. In Fig. 1.9 shows a list of services in the client-server architecture.
Clients are workstations that use server resources and provide convenient user interfaces. User interfaces (Fig. 1.9) are procedures for user interaction with a system or network.
In networks with a dedicated file server, a server-based network operating system is installed on a dedicated stand-alone PC. This PC becomes a server. Software installed on the workstation allows it to exchange data with the server. The most common network operating systems are:
NetWare from Novel;
Windows NT from Microsoft;
AT UNIX
In addition to the network operating system, network application programs, realizing the benefits provided by the network.
Rice. 1.9. Client-server model
The range of tasks that servers perform in hierarchical networks is diverse and complex. To adapt to the increasing needs of users, LAN servers have become specialized. So, for example, in operating system Windows NT Server There are different types of servers:
1. File servers and print servers. They control user access to files and printers. So, for example, to work with a text document, you first of all launch a word processor on your computer (PC). Next is the required document word processor, stored on the file server, is loaded into the PC's memory, and thus you can work with this document on the PC. In other words, a file server is designed to store files and data.
2. Application servers (including a database server (DB), WEB server). They run application parts of client-server applications (programs). These servers are fundamentally different from file servers in that when working with a file server required file or the entire data is copied to the requesting PC, and when working with the application server, only the request results are sent to the PC. For example, upon request, you can only get a list of employees born in September, without downloading the entire personnel database to your PC.
3. Mail servers control transmission emails between network users.
4. Fax servers manage the flow of incoming and outgoing fax messages through one or more fax modems.
5. Communication servers control the flow of data and mail messages between this LAN and other networks or remote users via modem and telephone line. They also provide access to the Internet.
6. Directory services server is designed to search, store and protect information on the network. Windows NT Server unites PCs into logical domain groups, the security system of which gives users various access rights to any network resource.
The client is the initiator and uses email or other server services. In this process, the client requests a service, establishes a session, gets the results it wants, and reports completion.
Server-based networks have best characteristics and increased reliability. The server owns the main network resources that are accessed by other workstations.
In modern client-server architecture, there are four groups of objects: clients, servers, data and network services. Clients are located in systems at user workstations. Data is mainly stored on servers. Network services are shared servers and data. In addition, services manage data processing procedures.
Client-server architecture networks have the following advantages:
Allows you to organize networks with a large number of workstations;
Provide centralized management of user accounts, security and access, which simplifies network administration;
Efficient access to network resources;
The user needs one password to log into the network and to gain access to all resources to which user rights apply.
Along with the advantages of client-server architecture networks, they also have a number of disadvantages:
A server malfunction can render the network inoperable;
Require qualified personnel for administration;
They have a higher cost of networks and network equipment.
Selecting a Network Architecture
The choice of network architecture depends on the purpose of the network, the number of workstations and the activities performed on it.
You should choose a peer-to-peer network if:
The number of users does not exceed ten;
All cars are close to each other;
There are small financial possibilities;
There is no need for a specialized server such as a database server, fax server or any other;
There is no possibility or need for centralized administration.
You should choose a client-server network if:
The number of users exceeds ten;
Requires centralized management, security, resource management, or backup;
A specialized server is required;
Requires access to the global network;
It is required to share resources at the user level.
Network architecture is the implemented structure of a data transmission network, which determines its topology, the composition of devices and the rules for their interaction in the network. Within the framework of the network architecture, issues of information encoding, its addressing and transmission, message flow control, error control and analysis of network operation in emergency situations and deterioration of characteristics are considered.
The most common network architectures are:
Ethernet (from English, ether - ether) is a broadcast network. This means that all stations on the network can receive all messages. Topology - linear or star-shaped. Data transfer speed - 10 or 100 Mbit/s. Arcnet (Attached Resource Computer Network) is a broadcast network. Physical topology - tree. Data transfer rate - 2.5 Mbit/s;
Token Ring (relay ring network, network with token passing) is a ring network in which the principle of data transmission is based on the fact that each ring node waits for the arrival of some short unique sequence of bits - a token - from an adjacent previous node. The arrival of the token indicates that it is possible to transmit a message from this node further along the flow. Data transfer speed - 4 or 16 Mbit/s;
FDDI (Fiber Distributed Data Interface) is a network architecture for high-speed data transmission over fiber optic lines. Data transfer speed - 100 Mbit/s. Topology - double ring or mixed (including star or tree subnets). The maximum number of stations in the network is 1000. Very high cost of equipment;
ATM (Asynchronous Transfer Mode) is a promising, yet very expensive architecture that provides the transfer of digital data, video information and voice over the same lines. Data transfer speed - up to 2.5 Gbit/s. Optical communication lines.