What is a server? The difference between a server and a workstation (client). Key benefits of networking computers

Kazakh-Russian International University

Protsan Alexander Valerievich

AU-401, 4th course

"Automation and control"

Control work on discipline

"Computer systems, networks and telecommunications"

Topic: "Purpose of network equipment of computer networks: workstation, server, modem, hub network adapter, bridge, gateway, router"

Introduction

To date, there are more than 130 million computers in the world, and more than 80% of them are connected to various information and computing networks, from small local area networks in offices to global networks such as the Internet.

The worldwide trend towards connecting computers in a network is due to a number of important reasons, such as speeding up the transmission of information messages, the ability to quickly exchange information between users, receive and transmit messages (faxes, E-mail letters, etc.) without leaving the workplace, the ability to instantly receive any information from anywhere in the world, as well as the exchange of information between computers of different manufacturers operating under different software.

Such enormous potentialities that the computer network carries and the new potential rise that the information complex experiences, as well as a significant acceleration of the production process, do not give us the right not to accept this for development and not to apply them in practice.

Therefore, it is necessary to develop a fundamental solution to the issue of organizing an IVS (information and computer network) on the basis of an existing computer park and a software package that meets modern scientific and technical requirements, taking into account the growing needs and the possibility of further gradual development of the network due to the emergence of new technical and software solutions.

A LAN is understood as a joint connection of several separate computer workstations (workstations) to a single data transmission channel.

Thanks to computer networks, we have gained the possibility of simultaneous use of programs and databases by several users.

The concept of a local area network - LAN (English LAN - Local Agea Network) refers to geographically limited (territorially or production) hardware and software implementations in which several computer systems are connected to each other using appropriate means of communication.

Through this connection, the user can interact with other workstations connected to this LAN.

In industrial practice, LANs play a very important role.

Through a LAN, the system combines personal computers located at many remote workplaces that share equipment, software and information. Workplaces of employees are no longer isolated and are combined into a single system. Consider the advantages obtained by networking personal computers in the form of an intra-industrial computer network.

Separation resources

Resource sharing allows you to use resources sparingly, such as controlling peripherals such as laser printers, from all attached workstations.

Data separation.

Data sharing provides the ability to access and manage databases from peripheral workstations that need information.

Separation of software

Separation of software provides the possibility of simultaneous use of centralized, previously installed software.

Sharing of processor resources.

When dividing processor resources, it is possible to use computing power for data processing by other systems included in the network. The opportunity provided is that the available resources are not “attacked” instantly, but only through a special processor available to each workstation.

Multiplayer mode

The multi-user properties of the system facilitate the simultaneous use of centralized applications previously installed and managed, for example, if a user of the system is working on another task, then the current work in progress is relegated to the background.

Work station

Work station(English) workstation) - a set of hardware and software designed to solve a certain range of problems.

A workstation as a place of work for a specialist is a full-fledged computer or computer terminal (input-output devices, separated and often remote from the control computer), a set of necessary software, supplemented, if necessary, with auxiliary equipment: a printer, an external storage device on magnetic and / or optical media, barcode scanner, etc.

In domestic literature, the term AWP (workstation) was also used, but in a narrower sense than "workstation".

Also, the term "workstation" refers to a computer in the local area network (LAN) in relation to the server. Computers in the local network are divided into workstations and servers. At workstations, users solve applied problems (work in databases, create documents, make calculations). The server services the network and provides its own resources to all network nodes, including workstations.

There are fairly stable signs of workstation configurations designed to solve a certain range of tasks, which allows them to be separated into a separate professional subclass: multimedia (image, video, sound processing), CAD, GIS, field work, etc. Each such subclass may have its own features and unique components (in parentheses are examples of areas of use): large video monitor and / or multiple monitors (CAD, GIS, stock exchange), high-speed graphics card (cinematograph and animation, computer games), large amount of data storage (photogrammetry, animation) , the presence of a scanner (photo), protected design (armed forces, field work), etc.

Server

server called a computer dedicated from the group personal computers(or workstations) to perform some service task without the direct participation of a person. The server and the workstation may have the same hardware configuration, as they differ only in the participation of the person behind the console in their work.

Some service tasks can run on the workstation in parallel with the user's work. Such a workstation is conventionally called non-dedicated server .

Servers need a console (usually a monitor/keyboard/mouse) and human participation only at the initial setup stage, during hardware maintenance and emergency management (normally, most servers are controlled remotely). For emergency situations, servers are typically provided with one console kit per group of servers (with or without a switch, such as a KVM switch).

As a result of specialization, a server solution may receive a simplified console (for example, a communication port), or lose it altogether (in this case, initial configuration and emergency management can only be performed via the network, and network settings can be reset to the default state).

Specialization of server hardware goes in several ways, the choice of which direction to go in, each manufacturer determines for himself. Most specializations increase the cost of equipment.

Server hardware, as a rule, is equipped with more reliable elements:

• memory with increased fault tolerance, such as for i386-compatible computers, memory intended for servers has error correction technology (ECC). Error Checking and Correction). On some other platforms, such as SPARC (Sun Microsystems), all memory has error correction.
• reservation, including:
• power supplies (including hot plug)
• hard drives (RAID; including hot-plug and swap). Not to be confused with the "RAID" systems of conventional computers.
• more thoughtful cooling (function)

Servers (and other equipment) that need to be mounted on some standard chassis (such as 19-inch racks and cabinets) are standardized and supplied with the necessary mounting hardware.

Servers that do not require high performance and a large number of external devices are often reduced in size. Often this decrease is accompanied by a decrease in resources.

In the so-called "industrial version", in addition to the reduced size, the case has greater strength, protection from dust (provided with replaceable filters), humidity and vibration, and also has a button design that prevents accidental pressing.

Structurally, hardware servers can be executed in desktop, floor, rack and ceiling versions. The latter option provides the highest density of computing power per unit area, as well as maximum scalability. Since the late 1990s, so-called blade servers have become increasingly popular in systems of high reliability and scalability. blade - blade) - compact modular devices that reduce the cost of power, cooling, maintenance, etc ...

In terms of resources (frequency and number of processors, amount of memory, number and performance of hard drives, performance of network adapters), servers specialize in two opposite directions - increasing resources and reducing them.

Growth of resources is intended to increase the capacity (for example, specialization for a file server) and performance of the server. When the performance reaches a certain limit, further growth is continued by other methods, for example, by parallelizing the task between several servers.

Resource reduction aims to reduce the size and power consumption of servers.

The extreme degree of specialization of servers are the so-called hardware solutions(hardware routers, network disk arrays, hardware terminals, etc.). The hardware of such solutions is built from scratch or redesigned from an existing computer platform without regard to compatibility, which makes it impossible to use the device with standard software.

Software in hardware solutions is loaded into permanent and/or non-volatile memory by the manufacturer.

Hardware solutions tend to be more reliable than conventional servers, but less flexible and versatile. In terms of price, hardware solutions can be both cheaper and more expensive than servers, depending on the class of equipment.

Recently, a large number of diskless server solutions have spread, based on computers (usually x86) of the Mini-ITX form factor and less with specialized processing of GNU / Linux on an SSD disk (ATA flash or flash card), positioned as "hardware solutions" . These solutions do not belong to the hardware class, but are ordinary specialized servers. Unlike (more expensive) hardware solutions, they inherit the problems of the platform and software solutions they are based on.

Modem

Modem(an abbreviation made up of the words modulator-demodulator) - a device used in communication systems and performing the function of modulation and demodulation. The modulator modulates the carrier signal, that is, changes its characteristics in accordance with changes in the input information signal, the demodulator performs the reverse process. A special case of a modem is a widely used peripheral device for a computer that allows it to communicate with another computer equipped with a modem through the telephone network (telephone modem) or cable network (cable modem).

The modem performs the function of the terminal equipment of the communication line. In this case, the formation of data for transmission and processing of the received data is carried out by the terminal equipment, in the simplest case, a personal computer.

Types of modems for computers

By execution:

• external- connected via COM, USB port or a standard connector in the RJ-45 network card usually have an external power supply (there are USB-modems powered by USB and LPT-modems).
• internal- installed inside the computer in the slot ISA, PCI, PCI-E, PCMCIA, AMR, CNR
• built-in- are inside a device, such as a laptop or docking station.

According to the principle of work:

• hardware- all signal conversion operations, support for physical exchange protocols, are performed by a calculator built into the modem (for example, using a DSP, controller). Also in the hardware modem there is a ROM, which contains the firmware that controls the modem.
• soft modem, winmodems(English) Host based soft - modem) - hardware modems, devoid of ROM with firmware. The firmware of such a modem is stored in the memory of the computer to which the modem is connected (or installed). At the same time, the modem contains an analog circuit and converters: ADC, DAC, interface controller (for example, USB). It is operational only if there are drivers that process all operations for signal encoding, error checking and protocol management, respectively implemented in software and performed by the computer's central processor. Initially, there were only versions for operating systems of the MS Windows family, from which the second name appeared.
• semi-program(Controller based soft-modem) - modems in which some of the modem functions are performed by the computer to which the modem is connected.

By type of connection:

• Modems for dial-up telephone lines- the most common type of modem
• ISDN- modems for digital switched telephone lines
• DSL- used to organize dedicated (unswitched) lines using the regular telephone network. They differ from switched modems in that they use a different frequency range, and also in that the signal is transmitted over telephone lines only to the PBX. Usually, they allow the use of a telephone line in the usual way at the same time as data exchange.
• Cable- are used for data exchange via specialized cables - for example, through a collective television cable using the DOCSIS protocol.

• Cellular- work using cellular communication protocols - GPRS, EDGE, 3G, 4G, etc. They often have versions in the form of a USB key fob. Mobile communication terminals are also often used as such modems.
• Satellite
• PLC- use the technology of data transmission over the wires of the household electrical network.

The most common at present are:

• internal soft modem
• external hardware modem
• built-in modems in laptops.

Network adapter

Network adapter, also known as network card, NIC, Ethernet adapter, NIC (eng. network interface controller) is a peripheral device that allows a computer to communicate with other network devices.

Types

According to the constructive implementation, network cards are divided into:

• internal - separate boards inserted into a PCI, ISA or PCI-E slot;
• external, connected via USB or PCMCIA interface, mainly used in laptops;
• built into the motherboard.

On 10-Mbit NICs, 3 types of connectors are used to connect to the local network:

• 8P8C for twisted pair;
• BNC connector for thin coaxial cable;
• 15-pin transceiver connector for thick coaxial cable.

These connectors can be present in different combinations, sometimes even all three at once, but at any given moment only one of them works.

On 100-megabit boards, only a twisted-pair connector (8P8C, erroneously called RJ-45) is installed.

Next to the twisted pair connector, one or more information LEDs are installed to indicate the presence of a connection and the transfer of information.

One of the first mass-produced network cards was the NE1000/NE2000 series from Novell, and in the late 1980s there were quite a few Soviet clones of network cards with a BNC connector, which were produced with various Soviet computers and separately.

Network adapter settings

When configuring a network adapter card, the following options may be available:

• IRQ line number
• DMA channel number (if supported)
• base I/O address
• RAM base address (if used)
• support for duplex/half duplex auto-negotiation standards, speed
• support for tagged VLAN packets (802.1q) with the ability to filter packets of a given VLAN ID
• WOL (Wake-on-LAN) parameters

Depending on the power and complexity of the network card, it can implement computational functions (mainly calculation and generation of frame checksums) in hardware or software (by a network card driver using a central processor).

Server network cards can be supplied with two (or more) network connectors. Some NICs (built into the motherboard) also provide firewall functionality (eg nforce).

Functions and characteristics of network adapters

The network adapter (Network Interface Card, NIC), together with its driver, implements the second, channel level of the open systems model in the end node of the network - a computer. More precisely, in a network operating system, the adapter/driver pair performs only the functions of the physical and MAC layers, while the LLC layer is usually implemented by an operating system module that is common to all drivers and network adapters. Actually, this is how it should be in accordance with the IEEE 802 protocol stack model. For example, in Windows NT, the LLC level is implemented in the NDIS module, which is common to all network adapter drivers, regardless of which technology the driver supports.

The network adapter, together with the driver, performs two operations: transmitting and receiving a frame. Transferring a frame from a computer to a cable consists of the following steps (some may be missing, depending on the encoding methods used):

• Reception of an LLC data frame through an inter-layer interface along with MAC-layer address information. Usually, interaction between protocols inside a computer occurs through buffers located in RAM. Data for transmission to the network is placed in these buffers by upper-layer protocols that retrieve them from disk memory or from the file cache using the I / O subsystem of the operating system.
• The design of the MAC layer data frame into which the LLC frame is encapsulated (with flags 01111110 discarded). Filling in the destination and source addresses, calculating the checksum.
• Formation of code symbols when using redundant codes of the 4V/5V type. Scrambling codes to obtain a more uniform spectrum of signals. This stage is not used in all protocols - for example, 10 Mbps Ethernet technology does without it.
• Issuance of signals to the cable in accordance with the accepted line code - Manchester, NRZ1. MLT-3 etc.

Receiving a frame from a cable to a computer includes the following steps:

• Receiving from the cable signals that encode the bit stream.
• Isolation of signals against the background of noise. This operation can be performed by various specialized chips or DSP signal processors. As a result, a certain bit sequence is formed in the adapter's receiver, with a high degree of probability coinciding with the one that was sent by the transmitter.
• If the data was scrambled before being sent to the cable, then it is passed through the descrambler, after which the code symbols sent by the transmitter are restored in the adapter.
• Frame checksum check. If it is incorrect, then the frame is discarded, and the corresponding error code is transmitted to the LLC protocol through the interlayer interface upwards. If the checksum is correct, then the LLC frame is extracted from the MAC frame and transmitted through the inter-layer interface upstream, to the LLC protocol. The LLC frame is buffered in RAM.

The distribution of responsibilities between the network adapter and its driver is not defined by standards, so each manufacturer decides this issue on its own. Typically, network adapters are divided into adapters for client computers and adapters for servers.

In adapters for client computers, much of the work is offloaded to the driver, thereby making the adapter simpler and cheaper. The disadvantage of this approach is the high degree of loading of the computer's central processor with routine work on transferring frames from the computer's RAM to the network. The central processor is forced to do this work instead of performing user application tasks.

Therefore, adapters designed for servers usually have their own processors, which do most of the work of transferring frames from RAM to the network and vice versa. An example of such an adapter is the SMS EtherPower network adapter with an integrated Intel i960 processor.

Depending on which protocol the adapter implements, adapters are divided into Ethernet adapters, Token Ring adapters, FDDI adapters, etc. hub, many Ethernet adapters today support two speeds and have the prefix 10/100 in their name. Some manufacturers call this property auto-sensing.

The network adapter must be configured before being installed on the computer. When configuring an adapter, you typically specify the IRQ number used by the adapter, the DMA channel number (if the adapter supports DMA mode), and the base address of the I/O ports.

If the network adapter, computer hardware, and operating system support the Plug-and-Play standard, then the adapter and its driver are configured automatically. Otherwise, you must first configure the network adapter, and then repeat its configuration settings for the driver. In general, the details of the procedure for configuring a network adapter and its driver largely depend on the manufacturer of the adapter, as well as on the capabilities of the bus for which the adapter is designed.

Classification of network adapters

As an example of the classification of adapters, we use the approach of 3Com, which has a reputation as a leader in the field of Ethernet adapters. 3Com believes that Ethernet network adapters have gone through three generations in their development.

The first generation adapters were made on discrete logic circuits, as a result of which they had low reliability. They had buffer memory for only one frame, which led to poor performance of the adapter, since all frames were transmitted from the computer to the network or from the network to the computer sequentially. In addition, the configuration of the first generation adapter was done manually, using jumpers. Each type of adapter used its own driver, and the interface between the driver and the network operating system was not standardized.

Second-generation network adapters began to use the multi-frame buffering method to improve performance. In this case, the next frame is loaded from the computer's memory into the adapter's buffer simultaneously with the transfer of the previous frame to the network. In receive mode, after the adapter has fully received one frame, it can begin to transfer this frame from the buffer to the computer's memory at the same time as receiving another frame from the network.

Second-generation network adapters make extensive use of highly integrated chips, which improves the reliability of the adapters. In addition, the drivers for these adapters are based on standard specifications. Second-generation adapters typically come with drivers that work in both the NDIS (Network Driver Interface Specification) standard developed by 3Com and Microsoft and approved by IBM, and the ODI (Open Driver Interface Specification) standard developed by Novell.

Third-generation network adapters (3Com includes its adapters of the EtherLink III family among them) implement a pipelined frame processing scheme. It lies in the fact that the processes of receiving a frame from the computer's RAM and transmitting it to the network are combined in time. Thus, after receiving the first few bytes of the frame, their transmission begins. This significantly (by 25-55%) increases the performance of the chain RAM - adapter - physical channel - adapter - RAM. Such a scheme is very sensitive to the transmission start threshold, that is, to the number of frame bytes that are loaded into the adapter's buffer before transmission to the network begins. The third generation network adapter self-tunes this parameter by analyzing the operating environment, as well as by calculating, without the participation of a network administrator.

Self-tuning provides the best possible performance for a particular combination of the performance of the computer's internal bus, its interrupt system, and its direct memory access system.

Third-generation adapters are based on application-specific integrated circuits (ASICs), which increase the performance and reliability of the adapter while reducing its cost. 3Com called its frame-pipelining technology Parallel Tasking, and other companies have implemented similar schemes in their adapters. Improving the performance of the "adapter-memory" link is very important for improving the performance of the network as a whole, since the performance of a complex frame processing route, including, for example, hubs, switches, routers, global links, etc., is always determined by the performance of the slowest element this route. Therefore, if the network adapter of the server or client computer is slow, no fast switches will be able to speed up the network.

Network adapters produced today can be attributed to the fourth generation. These adapters necessarily include an ASIC that performs MAC-level functions, the speed is developed up to 1 Gbps, as well as a large number of high-level functions. The set of such functions may include support for the RMON remote monitoring agent, a frame prioritization scheme, remote computer control functions, etc. In server versions of adapters, a powerful processor is almost required, which offloads the central processor. An example of a fourth-generation network adapter is the 3Com Fast EtherLink XL 10/100 adapter.

network hub

network hub or Hub(slang from English. hub- activity center) - a network device designed to combine several Ethernet devices into a common network segment. Devices are connected using twisted pair, coaxial cable or fiber. Term concentrator (hub) also applicable to other data transfer technologies: USB, FireWire, etc.

Currently, hubs are almost never produced - they have been replaced by network switches (switches), which separate each connected device into a separate segment. Network switches are erroneously referred to as "smart hubs".

Principle of operation

The hub works at the physical layer of the OSI network model, repeats the signal coming to one port to all active ports. If a signal arrives at two or more ports, a collision occurs at the same time, and the transmitted data frames are lost. Thus, all devices connected to the hub are in the same collision domain. Hubs always operate in half-duplex mode, all connected Ethernet devices share the provided access bandwidth.

Many hub models have the simplest protection against excessive collisions that occur due to one of the connected devices. In this case, they can isolate the port from the general transmission medium. For this reason, network segments based on twisted pair are much more stable in the operation of segments on coaxial cable, since in the first case each device can be isolated from the general environment by a hub, and in the second case several devices are connected using one cable segment, and, in the case of a large number of collisions, the hub can isolate only the entire segment.

Recently, hubs have been used quite rarely, instead of them, switches have become widespread - devices that operate at the data link layer of the OSI model and increase network performance by logically separating each connected device into a separate segment, a collision domain.

Characteristics of network hubs

• Number of ports- connectors for connecting network lines, hubs are usually produced with 4, 5, 6, 8, 16, 24 and 48 ports (the most popular with 4, 8 and 16). Hubs with more ports are significantly more expensive. However, hubs can be cascaded to each other, increasing the number of ports on a network segment. Some have special ports for this.
• Transfer rate- measured in Mbps, hubs are available with speeds of 10, 100 and 1000. In addition, hubs with the ability to change the speed are mainly common, referred to as 10/100/1000 Mbps. The speed can be switched both automatically and using jumpers or switches. Typically, if at least one device is attached to a hub at a low range speed, it will send data to all ports at that speed.
• Network media type- usually it is twisted pair or fiber, but there are hubs for other media, as well as mixed ones, for example, for twisted pair and coaxial cable.

network bridge

Bridge , network bridge, bridge(slang, from English. bridge) - network equipment for combining segments of a local network. The network bridge operates at the link layer (L2) of the OSI model, providing collision domain limitation (in the case of an Ethernet network). Bridges route data frames according to the MAC addresses of the frames. A formal description of a network bridge is given in the IEEE 802.1D standard.

Differences between switches and bridges

In general, a switch (switch) and a bridge are similar in functionality; the difference lies in the internal structure: bridges process traffic using a central processor, while a switch uses a switching matrix (hardware circuitry for switching packets). Currently, bridges are practically not used (since they require a powerful processor to work), except for situations when network segments are connected with different organization of the first level, for example, between xDSL connections, optics, Ethernet. In the case of SOHO equipment, the transparent switching mode is often referred to as "bridging mode".

Functionality

The bridge provides:

• collision domain constraint
• latency of frames addressed to a host in the sender's segment
• limiting the transition from domain to domain of erroneous frames:
• dwarfs (frames of less length than allowed by the standard (64 bytes))
• frames with CRC errors
• frames with the sign "collision"
• protracted frames (larger than allowed by the standard)

Bridges "learn" the nature of the location of network segments by building address tables of the form "Interface:MAC address", which contain the addresses of all network devices and segments necessary to gain access to this device.

Bridges increase network latency by 10-30%. This increase in latency is due to the fact that the bridge, when transmitting data, needs additional time to make a decision. The bridge is considered a store-and-forward device because it must parse the frame's destination address field and calculate the CRC checksum in the frame's check sequence field before sending the frame to all ports. If the destination port is currently busy, then the bridge may temporarily hold the frame until the port becomes free.
These operations take some time to complete, which slows down the transfer process and increases latency.

Software implementation

Mode bridging is present in some types of high-level network equipment and operating systems, where it is used to "logically combine" several ports into a single whole (in terms of higher protocols), turning these ports into a virtual switch. In Windows XP/2003, this mode is called "bridge connections". In the Linux operating system, when connecting interfaces into a bridge, a new interface brN is created (N is a serial number, starting from zero - br0), while the original interfaces are in the down state (from the point of view of the OS). The bridge-utils package, included with most Linux distributions, is used to create bridges.

Gateway

network gateway

network gateway- hardware router gateway) or software for interfacing computer networks using different protocols (for example, local and global).

Description

A network gateway converts protocols from one type of physical medium into protocols from another type of physical medium (network). For example, when you connect your local computer to the Internet, you use a network gateway.

Routers (routers) are one example of hardware network gateways.

Network gateways work on almost all known operating systems. The main task of a network gateway is to convert the protocol between networks. The router itself receives, forwards and sends packets only among networks using the same protocols. The network gateway can, on the one hand, accept a packet formatted for one protocol (for example, Apple Talk) and convert it to a packet of another protocol (for example, TCP / IP) before sending it to another network segment. Network gateways can be a hardware solution, software, or both, but are usually software installed on a router or computer. The network gateway must understand all the protocols used by the router. Typically, network gateways are slower than network bridges, switches, and regular routers. A network gateway is a point in a network that serves as an exit to another network. On the Internet, a host or endpoint can be either a network gateway or a host. Internet users and computers that deliver web pages to users are hosts, and nodes between different networks are network gateways. For example, a server that controls traffic between a company's local network and the Internet is a network gateway.

In large networks, a server acting as a network gateway is usually integrated with a proxy server and firewall. The network gateway is often combined with a router that manages the distribution and conversion of packets on the network.

A network gateway can be a special hardware router or software installed on a regular server or personal computer. Most computer operating systems use the terms described above. Windows computers usually use the built-in network connection wizard, which, according to the specified parameters, establishes a connection to a local or global network on its own. Such systems may also use the DHCP protocol. Dynamic Host Configuration Protocol (DHCP) is a protocol that is commonly used by network equipment to obtain various data that a client needs to work with the IP protocol. Using this protocol, adding new devices and networks becomes simple and almost automatic.

Internet gateway - a software network gateway that distributes and controls access to the Internet among local network clients (users).

Description

An Internet gateway, as a rule, is software designed to organize access to the Internet from a local network. The program is a working tool for a system administrator, allowing him to control the traffic and actions of employees. Typically, an Internet gateway allows you to distribute access among users, keep track of traffic, restrict access to individual users or groups of users to Internet resources. An Internet gateway may contain a proxy server, a firewall, a mail server, a shaper, an antivirus, and other network utilities. The Internet gateway can operate both on one of the network computers and on a separate server. The gateway is installed as software on a machine with an operating system (such as Kerio winroute firewall on Windows) or on a bare computer with an embedded operating system deployed (such as Ideco ICS with embedded linux).

Software Internet Gateways

• Microsoft ISA Server
• Kerio Winroute Firewall
• Traffic Inspector
• usergate
• Ideco Internet Control Server
• TMeter

router

router or router , router(from English. route), is a network device, based on information about the network topology and certain rules, that makes decisions about forwarding network layer packets (layer 3 of the OSI model) between different network segments.

Works at a higher level than the switch and network bridge.

Principle of operation

Typically, the router uses the destination address specified in the data packets and determines from the routing table the path over which the data should be sent. If there is no described route in the routing table for the address, the packet is dropped.

There are other ways to determine the packet forwarding path, such as using the source address, upper layer protocols used, and other information contained in network layer packet headers. Often, routers can translate the addresses of the sender and recipient, filter the transit data flow based on certain rules in order to restrict access, encrypt / decrypt the transmitted data, etc.

Routing table

The routing table contains information on the basis of which the router makes a decision about further forwarding of packets. The table consists of a number of entries - routes, each of which contains the address of the recipient's network, the address of the next node to which packets should be transmitted and some entry weight - a metric. The metrics of the entries in the table play a role in calculating the shortest routes to various destinations. Depending on the router model and the routing protocols used, the table may contain some additional service information. For example:

192.168.64.0/16 via 192.168.1.2, 00:34:34, FastEthernet0/0.1 where 192.168.64.0/16 is the destination network, 110/ is the administrative distance /49 is the route metric, 192.168.1.2 is the address of the next router to follow transmit packets for the network 192.168.64.0/16, 00:34:34 - the time during which this route was known, FastEthernet0/0.1 - the router interface through which you can reach the "neighbor" 192.168.1.2.

The routing table can be compiled in two ways:

• static routing- when records in the table are entered and changed manually. This method requires administrator intervention every time there is a change in the network topology. On the other hand, it is the most stable and requires a minimum of router hardware resources to serve the table.
• dynamic routing- when entries in the table are updated automatically using one or more routing protocols - RIP, OSPF, IGRP, EIGRP, IS-IS, BGP, etc. In addition, the router builds a table of optimal paths to destination networks based on various criteria - the number of intermediate nodes, channel bandwidth, data transfer delays, etc. The criteria for calculating optimal routes most often depend on the routing protocol, and are also set by the router configuration. This way of building a table allows you to automatically keep the routing table up to date and calculate the best routes based on the current network topology. However, dynamic routing puts an additional load on devices, and high network instability can lead to situations where routers do not have time to synchronize their tables, which leads to conflicting information about the network topology in its various parts and loss of transmitted data.

Often, graph theory is used to build routing tables.

Application

Routers help reduce network traffic by dividing it into collision or broadcast domains, and by filtering packets. They are mainly used to combine networks of different types, often incompatible in architecture and protocols, for example, to combine Ethernet LANs and WAN connections using xDSL, PPP, ATM, Frame relay, etc. Often, a router is used to provide access from local network to the global Internet network, performing the functions of address translation and firewall.

The router can be either a specialized (hardware) device (typical representatives of Cisco, Juniper), or a regular computer that performs the functions of a router. There are several software packages (mostly based on the Linux kernel) with which you can turn your PC into a high-performance and feature-rich router, such as the Quagga.

Bibliography.

1. Craig Zucker - Computer networks. Modernization and troubleshooting. Ed. BHV. 2001

2. Materials from Wikipedia - the free encyclopedia http://ru.wikipedia.org

Computer networks can use both single-user mini- and microcomputers (including personal ones) equipped with terminal devices for communicating with the user or performing the functions of switching and routing messages, as well as powerful multi-user computers (mini-computers, large computers). The latter perform efficient data processing and remotely provide network users with all kinds of information and computing resources. In local networks, these functions are implemented by servers and workstations.

Workstations

Work station (workstation) - a computer connected to the network through which the user gains access to its resources. Often a workstation (as well as a network user, and even an application running on a network) is referred to as a network client. As workstations, both ordinary computers and specialized ones - "network computers" (NET PC - Network Computer) can act. A network workstation based on a conventional computer operates both in network and local modes. It is equipped with its own operating system and provides the user with everything necessary for solving applied problems. Workstations are sometimes specialized for graphics, engineering, publishing, and other work. Workstations based on network computers can, as a rule, function only in network mode if there is an application server on the network. network computer(Network Personal Computer - NET PC) from the usual one in that it is maximally simplified: the classic NET PC does not contain disk memory (it is often called a diskless PC). It has a simplified motherboard, main memory, and from external devices there are only a display, a keyboard, a mouse and a network card, always with a BootROM ROM chip, which provides the ability to remotely boot the operating system from a network server (this is a classic "thin client" network). To work, for example, on an intranet, such a computer must have as many computing resources as a web browser requires.

Since it is not entirely humane to leave a network client completely without the possibility of local use of a computer, for example, to work in a word or spreadsheet processor with its own personal “desktop”, sometimes versions of a network computer with a small disk memory are used. Removable drives and flash drives should be absent in order to ensure information security: so as not to bring unwanted information into the network (or take it out) - programs, data, computer viruses. Structurally, NET PCs are made in the form of a compact system unit - a monitor stand (Network Computer TC from Boundless Technologies) or a motherboard built into the monitor (NET PC Wintern from Wyse Technology).

Servers

The word "server" (server) is related to the word "service". Indeed, servers, whether they are server programs (there are some) or server computers, serve requests by issuing information of a certain type or performing other service functions. Server- this is a multi-user computer dedicated to processing requests from all network workstations, providing these stations with access to common system resources (computing power, databases, program libraries, printers, faxes, etc.) and distributing these resources. The server has its own network operating system, under the control of which all parts of the network work together. Of the most important requirements for a server, high performance and reliability should be highlighted.

The server, in addition to providing network resources to workstations, can itself perform meaningful information processing at the request of clients - such a server is often called an application server. Servers on a network are often specialized. Specialized servers are used to eliminate the most "bottlenecks" in the network: this is the creation and management of databases and data archives, support for multicast facsimile and e-mail, management of multi-user terminals (printers, plotters), etc. Examples of specialized servers:

File servers store various data in their memory and issue the necessary files upon request without any preliminary processing.

Database servers store various data in their memory, organized into databases. They have a Database Management System (DBMS), so they form the necessary information in accordance with the request, and provide the necessary data.

Servers of the Primergy and Primequest families fully support the Microsoft SQL Server DBMS. This circumstance, thanks to the ability to create mirror images of databases, implemented in SQL Server, allows you to almost instantly restore normal operation after a database failure. The user will not even notice that the DBMS has failed.

Backup Server (Storage Express System) is used to back up information in large multi-server networks, uses magnetic tape drives (streamers) with replaceable cartridges with a capacity of up to hundreds of GB; usually performs daily automatic archiving with compression of information from servers and workstations according to a scenario set by the network administrator (naturally, with the compilation of an archive catalog).

fax server (Fax server) - for organizing efficient multicast facsimile communication, with several fax modem boards, with special protection of information from unauthorized access during transmission, with an electronic fax storage system (one of the options is Net SatisFAXion Software in combination with a SatisFAXion fax modem ).

Mail server - in an e-mail forwarding system, this is commonly referred to as a message transfer agent (MTA), that is, it is a computer program that transfers messages from one computer to another. On the other hand, there is a server that provides reception and transmission of personal messages from users, as well as their routing.

Print server (Print Server) is designed for efficient use of system printers.

Gateway servers on the Internet, they act as a router, almost always combined with the functions of a mail server and a network firewall that ensures network security.

Web servers are organized on the Internet in order to provide users with various information using the http protocol.

Remote access servers provide communication of users with the Internet, corporate or other network via telephone channels. Computers that have direct access to the Internet are often referred to as host computers.

Blade servers. In recent years, blade servers have been increasingly used in many areas of business and production - servers with additional service functions. Such servers implement the now very popular "cloud technologies" of data processing. The main advantage of blade servers over conventional servers is the ease of organizing a large data center, which, in addition to computing power, needs additional storage infrastructure. The customer, together with the blade server, receives a 70 - 80% ready data center infrastructure.

Application servers at the request of users, they process information using programs available on the server (the user is a “thin client”) or received from the user himself (the user is a “thick client”).

Application servers use software tools that are like a container of application programs used in corporate control systems.

The functions of the application server software include: solving corporate problems, managing the optimization of system resources (memory, interfaces, etc.), ensuring the connection of applications with external resources (including databases, networks, etc.). The software is also responsible for the quality of service support (availability, reliability, reliability, security, performance, manageability, scalability). Application server programs can be developed in two main ways:

programs for executing new applications that cannot wait;

corporate programs designed for long-term use.

There are both specialized programs focused on solving a certain class of tasks (for example, 1C Enterprise packages, SAP R / 3), and universal programs.

Proxy servers are a convenient means of accessing corporate and other local networks to the Internet, while providing quick re-access to information (information is stored in the memory of the proxy server for some time after accessing it) and protection of the corporate network from unauthorized access (they have firewalls - firewalls ).

There are very few publications about servers and server hardware. And the main reason is the technical complexity - there are many differences from the usual consumer hardware, and a limited readership. Such articles are of interest only to administrators and those who make purchasing decisions, and to some enthusiastic readers who are fond of professional-grade hardware. However, server hardware is closer to desktop hardware than you might think, and more knowledge never hurts.

When people think of servers, they think of big computers, heavy boards, and outrageous performance, but the reality is often different. Today there are so many form factors and a huge amount of hardware and software that it is difficult to come up with a universal definition of the word "server".

While there are many similarities between professional and consumer hardware, we believe that it is the emphasis on certain features and qualities that makes it possible to classify the hardware as professional. For example, your home PC needs to be fast, quiet, upgradable, and, of course, reasonably priced. It will work for several years, while it will often be idle for several hours, and the user will have the opportunity to replace the failed hardware or simply remove the accumulated dust. Other requirements are imposed on servers: reliability, 24/7 availability, maintenance without stopping work are in the first place here.

First and foremost, the server must be reliable. Whether it's a database server, a file server, a web server, or another type of server, it must be very reliable because your business depends on it. Secondly, the server must always be available, that is, the hardware and software must be selected in such a way that downtime is minimal. Finally, fast maintenance in the professional field is very critical. That is, if an administrator needs to perform a task, it must be performed as efficiently as possible without conflicting with the criteria mentioned above. That is why server performance is often the result of consideration of the necessary requirements and long-term strategies, and not the result of some emotional step, as is often the case with gaming PCs.

In this article, we will talk about server components and describe the technologies that are common to servers and consumer PCs, as well as talk about the differences and advantages. Since all professional-grade components are much more expensive than ordinary ones, we will begin our digression with this question.

Professional means expensive

If you buy professional components or servers and workstations, you will quickly find that they cost more than regular consumer hardware. And the reason often lies not in some complex technology, but in the specifications of professional components, in their testing and validation. For example, the Core 2 Duo Conroe is very close to the Xeon Woodcrest in terms of performance. But the differences lie in the sockets used, specifications, and systems in which these processors are installed. Server hard drives are specifically designed for continuous 24/7 operation, while desktop hard drives are not.

We usually assume that any consumer products are compatible with all others, which is not always the case, but most often. Therefore, you can replace one compatible component with another, most likely there will be no problems. But this approach is no longer acceptable if you are planning to upgrade the server or perform maintenance.

New products for the professional market are developed with a predictable upgrade path as manufacturers want these products to work with existing systems, current and future generations of components. AMD and Intel customers regularly receive company plans for their products that provide a glimpse into the future. Consumers can buy a product with the confidence that they will receive support and upgrade opportunities for a while.

Warranty and replacement of components is also very important. If a failed desktop hard drive is replaced under warranty with any new model, then professional solutions often require exactly the same components. Therefore, the administrator needs to look for exactly the same product, while ordinary users, on the contrary, will be unhappy if they do not get the latest generation of components (which, by the way, is cheaper for most manufacturers).

The magic word for the professional market is validation. When a groundbreaking new product is ready for release, it will be validated and tested on popular hardware systems. The validation process ensures that companies can deliver very complex systems to the enterprise market. Indeed, a business can only be built if the IT platform works flawlessly.

What is a server? At its core, this is a powerful computer that can smoothly perform various tasks and process information that comes in a large stream. Often server machines are installed in large companies. In their functionality and purpose, servers are completely different.

What is a server for?

Any company, especially a large one, cannot do without its own server. The larger the company and the greater the number of users, the more powerful it will be required. Why do you need a server? It stores common information resources and, thanks to its work, several computers can have shared access to them at the same time, telephones, faxes, printers and other devices that have access to a common network can also be connected to it.

How is a server different from a regular computer?

The difference between them comes from what tasks they perform. A computer is understood as the standard characteristics that any PC has at home or at work. What is a server - it is a computer, but performing only certain tasks, it must process requests from other devices, as well as:

1. Maintain connected devices.
2. Have higher performance.
3. It must be equipped with special accessories.
4. It should ignore the graphical capabilities of the systems.

What distinguishes a server from a workstation is that the workstation is designed only to provide a high-quality work process. She does not interact with anyone, except for the operator and the server. The server, on the other hand, communicates with all the machines that are connected to it over the network. He knows how to receive requests, process them and issue responses.

How is hosting different from a server?

It is not difficult to understand this issue. There are many different sites on the Internet. Data from sites must be placed on a server, roughly speaking, on one that has Internet access. Having installed a site on it, its maintenance is carried out from the server. To optimize the operation of a server that cannot exist without software, hosting is needed, its services can be purchased on the Internet.

Hosting and server - what's the difference? Hosting can host your own website. As a hosting owner, you can have your own server or rent it from a company. This is especially convenient for those who have not yet encountered the operation of the server and do not want to spend their time learning the settings, trying something new by trial and error, closely monitoring the operation of the server and dealing with its software.

What is needed to create a server?

This is not a cheap pleasure that a large company can easily afford, but for the average user it promises large financial costs. What does it take to make a server?

• have an idea what a server is;
• very good computer;
• own Internet channel, the speed should be high;
• stable operating system;
• assembly. It comes in two types of platform, Java and C++;
• patience and desire.

What is the server made of?

Compared to the configuration of a conventional computer, it has several significant differences. The server machine consists of a central processor and a motherboard, only several processors can be installed on the board, and many more slots that serve to connect. What else is included in the server is the core, which is an important component of its work.

What is a server core? It manages all work processes and collects them into one whole. One of its main tasks is to interact with a wide variety of applications that are running in normal user mode. In general, server computers are powerful machines, but they consume a lot of electricity; in order to save it, a number of functions of a conventional computer are missing in them.

What you need to know about servers

Understanding the work and purposes of such machines, one can distinguish types of servers that differ in their type. Among the total, the main ones stand out:

1. The mail server is designed to send and receive mail messages.
2. A file server is needed in order to store access to certain files.
3. What is a media server is clear from the name. It serves to receive, process and send audio, video or radio information.
4. What is the database server for? It is used to store and work with information that is formed in the form of a database.
5. What is a terminal server used for? It gives users access to certain programs.

What does an internal server error mean?

Each of the users at least once encountered a problem when, when loading the site, the message “500 internal server error” appears, which notifies that an internal server error has occurred. The number 500 is the HTTP protocol code. What does a server error mean? It is assumed that the software side of the server, although technically working, contains internal errors. As a result, the request was not processed in production mode, and the system returned an error code. A server error can occur for a variety of reasons.

There is no connection to the server, what should I do?

Errors and malfunctions in the complex operation of the system occur almost every day. Users often face the problem that the server is not responding. In this case it is necessary:

1. Make sure that problems occur only with a specific server. It may be that these are problems in the user's computer, his Internet connection or settings. You need to restart your computer
2. You need to double-check the name of the requested web page or IP address. They could change or cease to exist.
3. The reason for the lack of communication may be the security policy. The computer's IP address may be blacklisted by the server.
4. The ban can be on the user's computer itself. It may be that the address is blocked by an antivirus program or a corporate network at work.
5. The connection error may be due to the fact that the connection request to the server simply does not reach the destination due to problems in the intermediate nodes.

What is a DDoS attack on a server?

A series of actions carried out on the Internet by hackers, which lead to the fact that ordinary users cannot access certain resources, is called a DDoS attack (Distributed Denial Of Service). What is a DDoS server - this is when a large number of requests are received simultaneously from all over the world to the north, which is subject to attack. Due to the huge number of false requests, the server completely stops working, it happens that it is impossible to restore it.

ARM composition.

Automated workstation (AWP) of the end user of the information system

Appointment and composition of AWP. Characteristics of the types of support for AWS

workstation is a set of information resources and software and hardware tools that provide the user with data processing and automation of management functions in a specific subject area.

The workstation has a problem-professional orientation and allows the user to transfer to the computer the execution of typical repetitive operations related to the accumulation, systematization, storage, search, processing, protection and transmission of data.

The composition of the workstation is determined:

Features of professional orientation of a specialist;

The level of management tasks (tactical, strategic, predictive);

Features of the tasks to be solved (for specialists: regulation of documents - repetition in terms, variety of regulatory and reference and operational information, etc.; for managers: setting strategic goals, planning, choosing sources of funding, policy development, etc.).

18. Classification of computers.

19. PC structure.

A PC includes three main devices: a system unit, a keyboard, and a monitor. However, to expand the functionality of a PC, various additional peripheral devices can be connected to it: printing devices (printers), various manipulators (mouse, joystick, trackball, light pen), information input devices (scanners, graphic tablets - digitizers), plotters, etc.

These devices are connected to the system unit using cables through special sockets (connectors), which are usually located on the back of the system unit. Additional devices will interfere if there are free slots on the motherboard directly into the system unit, for example, a modem for exchanging information with other PCs via the telephone network. As a rule, PCs have a modular structure (the structure of a modern PC is shown in Fig. 3.1). All modules are connected by a common bus (system bus).

20. Workstation and server.

In any case, the workstation is the end point of the interaction of a specialist with the necessary tools based on computer technology. Workstations are designed to perform final tasks and interact with the operator.

Server- a remote computer whose task is to issue requests for end clients connected to it (be it workstations, access terminals, other servers).

A server can be understood as a special program that responds to requests from other client programs in a local or global network. In this case, one of the workstations can act as a server, the purpose of which is to serve requests from other network clients.

Or a server is understood as a special software and hardware complex, consisting of several powerful computers of a special configuration, which is designed exclusively for processing requests. That is, it is not only a specially configured program on one of the workplaces on the network, but a special productive computer or their entire network, which are busy only responding to requests. For such platforms, special hardware configurations are developed that are easily interfaced with each other, forming a super-computer (cluster).

Typical servers are designed for:

• processing and forwarding mail on the network,
• processing queries to databases,
• providing access to web resources,
• redirecting or distributing traffic on the network (proxy servers),
• storing and transferring files on the network,
• ensuring the interaction of game clients.

Other configurations are also possible.

How is a server different from a computer (workstation)?

The main property of the server is the issuance of automatic responses to requests from connected clients. A workstation is designed to work only with the end user.

Our company offers turnkey workstation solutions, server hardware and software for both workstations and servers.

21.Classification of computer networks.

After mankind created personal computers, it was necessary to create a new approach to the organization of systems that process data, as well as the creation of new technologies in the field of storage, transmission and use of information. Somewhat later, there was a need to move from the use of separate computers operating in systems that process data centrally to systems capable of processing data distributed. Distributed data processing refers to the processing of information that is performed by independent but interconnected computers, which constitute a distributed system. A computer network is a set of computers that are interconnected by communication channels, which allows you to create a single system that fully meets the requirements imposed by the rules of distributed information processing. Thus, the main purpose of computer networks is the joint processing of data, in which all components of the system participate, regardless of their physical location. The classification of computer networks involves their division into types of computer networks, depending on the territorial location of computers and other components relative to each other. Thus, the classification of computer networks involves their division into: Global - these are computer networks that unite subscribers located at a great distance from each other - from hundreds to tens of thousands of kilometers. Such networks make it possible to solve the problem of combining the information resources of all mankind, as well as to organize instant access to these resources; Regional - these are computer networks that connect subscribers that are located at smaller distances than in global networks, but still significant distances. An example of a regional network is a network of a large city or a separate state. Local - these are computer networks that unite subscribers located at relatively short distances from each other - most often in one building or several nearby buildings. These are networks of enterprises, offices of companies, firms, etc. In addition, the classification of computer networks suggests that global, regional and local networks can be combined, which makes it possible to create multi-network hierarchies, which are powerful tools that allow you to process huge information arrays and provide almost unlimited access to information resources. Among other things, the classification of computer networks, or rather its understanding, makes it possible to build just such a system that will fully satisfy the needs of an enterprise, office, city or state for information. In general, computer networks consist of three nested subsystems: a network of workstations, a network of servers, and a basic data transmission network. A workstation (can be represented by a client machine, workplace, subscriber station, terminal) is a computer used by a computer network subscriber. A network of workstations is a set of workstations, as well as means of communication, which are designed to ensure the interaction of workstations between themselves and the server. A server is a computer that performs general network tasks and provides workstations with various services. A server network is a collection of network servers, as well as communication tools designed to connect servers to the core network. The basic data transmission network is a set of means for transmitting information between servers. The core network includes communication channels and communication nodes. A communication node is a set of means of switching, as well as information transmission, concentrated in one point. The purpose of the communication node is to receive data that comes through communication channels, as well as their transmission to channels that lead to subscribers.

22. Types of data channels.

Data transmission channels used in computer networks are classified according to a number of criteria. First, according to the form of information representation in the form of electrical signals, the channels are divided into digital and analog. Secondly, according to the physical nature of the data transmission medium, communication channels are wired (usually copper), optical (usually fiber optic), wireless (infrared and radio channels). Thirdly, according to the method of dividing the medium between messages, the above-mentioned channels are distinguished with time (tdm) and frequency (fdm) division. One of the main characteristics of a channel is its capacity (information transfer rate, i.e., information rate), determined by the channel bandwidth and the method of encoding data in the form of electrical signals. Information rate is measured by the number of Bits of information transmitted per unit of time. Along with the information, they operate with a bean (modulation) rate, which is measured in bauds, i.e., the number of changes in a discrete signal per unit time. It is the baud rate that is determined by the bandwidth of the line. If one change in the value of a discrete signal corresponds to several bits, then the information rate exceeds the dead one. Indeed, if n bits are transmitted in the baud interval (between adjacent signal changes), then the number of signal gradations is 2n. For example, with a number of gradations of 16 and a speed of 1200 baud

One baud corresponds to 4 bps and the information rate is 4800 bps. With an increase in the length of the communication line, the attenuation of the signal increases and, consequently, the bandwidth and information rate decrease.

23. Digital and analog channels.

Under communication channel understand the totality of the propagation medium and technical means of transmission between two channel interfaces or junctions of type C1 (see Figure 1-1). For this reason, the C1 junction is often referred to as a channel junction.

Depending on the type of transmitted signals, there are two large classes of communication channels, digital and analog.

Rice. 25. Digital and analog transmission channels

A digital channel is a bit path with a digital (pulse) signal at the input and output of the channel. A continuous signal is received at the input of an analog channel, and a continuous signal is also taken from its output (Fig. 25).

Signal parameters can be continuous or take only discrete values. Signals can contain information either at every moment of time (continuous in time, analog signals), or only at certain, discrete times (digital, discrete, pulse signals).

Digital channels are PCM, ISDN, T1 / E1 type channels and many others. Newly created SPDs are trying to build on the basis of digital channels, which have a number of advantages over analog ones.

Analog channels are the most common due to their long history of development and ease of implementation. A typical example of an analog channel is a voice frequency channel (CH), as well as group paths for 12, 60 or more voice frequency channels. The PSTN telephone circuit typically includes multiple switches, splitters, group modulators, and demodulators. For the PSTN, this channel (its physical route and a number of parameters) will change with each next call.

When transmitting data, there must be a device at the input of the analog channel that would convert the digital data coming from the DTE into analog signals sent to the channel. The receiver must contain a device that converts the received continuous signals back into digital data. These devices are modems. Similarly, when transmitting over digital channels, the data from the DTE must be converted to the form adopted for this particular channel. This conversion is handled by digital modems, often referred to as ISDN adapters, E1/T1 channel adapters, line drivers, and so on (depending on the particular type of channel or transmission medium).

The term modem is widely used. This does not necessarily imply any modulation, but simply indicates certain operations for converting signals coming from the DTE for their further transmission over the channel in use. Thus, in a broad sense, the terms modem and data link equipment (DCE) are synonymous.