LAN software. Local area network software LAN hardware

Local area network is a concept that is familiar to many firsthand. Almost every enterprise uses this technology, so it can be said that every person has come across it in one way or another. Local networks have significantly accelerated production processes, thereby giving a sharp boost to their further use throughout the globe. All this allows us to predict the further growth and development of such a data transmission system, up to the introduction of a LAN in every, even the smallest enterprise.

The concept of a local network

A local area network is a number of computers connected to each other by special equipment that allows for the full exchange of information between them. An important feature of this type of data transmission is the relatively small area where communication nodes, that is, the computers themselves, are located.

Local networks not only greatly facilitate interaction between users, but also perform some other functions:

Simplify work with documentation. Employees can edit and view files at their workplace. At the same time, there is no need for collective meetings and meetings, which saves valuable time.
They allow you to work on documents together with colleagues, when everyone is at their own computer.
They allow access to applications installed on the server, which allows you to save free space on the installed hard drive.
Save hard drive space by allowing you to save documents on your host computer.

Types of networks

A local area network can be represented by two models: a peer-to-peer network and a hierarchical one. They differ in the ways communication nodes interact.

A peer-to-peer network is based on the equality of all machines, and data is distributed between each of them. Essentially, a user of one computer can access the resources and information of another. The efficiency of the peer-to-peer model directly depends on the number of worker nodes, and its level of security is unsatisfactory, which, coupled with a rather complex management process, makes such networks not very reliable and convenient.

The hierarchical model includes one (or more) main server, where all data is stored and processed, and several client nodes. This type of network is used much more often than the first, having the advantage of speed, reliability and security. However, the speed of such a LAN largely depends on the server, which under certain conditions can be considered a disadvantage.

Drawing up technical requirements

Designing a local area network is a rather complex process. It begins with the development of a technical specification, which should be carefully considered, since shortcomings in it threaten subsequent difficulties in building a network and additional financial costs. Primary design can be done using special configurators that will allow you to select the optimal network equipment. Such programs are especially convenient in that you can correct various values and parameters directly during operation, as well as generate a report at the end of the process. Only after these steps can you proceed to the next stage.

Schematic design

This stage consists of collecting data about the enterprise where it is planned to install a local area network, and analyzing the information received. The quantity is determined:

Users.
Workstations.
Server rooms.
Connection ports.

An important point is the availability of data on the routes for laying highways and the planning of a specific topology. In general, it is necessary to adhere to a number of requirements imposed by the IEEE 802.3 standard. However, despite these rules, sometimes it may be necessary to make calculations of signal propagation delays or consult with network equipment manufacturers.

Basic LAN characteristics

When choosing a method for placing communication nodes, you must remember the basic requirements for local networks:

Performance, which combines several concepts: throughput, response time, transmission delay.
Compatibility, i.e. ability to connect various local area network equipment and software.
Safety, reliability, i.e. capabilities to prevent unauthorized access and complete data protection.
Scalability - the ability to increase the number of workstations without degrading network performance.
Manageability - the ability to control the main elements of the network, prevent and eliminate problems.
Network transparency, which consists of presenting a single computing device to users.

Basic local area network topologies: advantages and disadvantages

The topology of a network represents its physical layout, significantly affecting its basic characteristics. In modern enterprises, three types of topologies are mainly used: “Star”, “Bus” and “Ring”.

The “Star” topology is the most common and has many advantages over others. This installation method is highly reliable; If any computer fails (except the server), this will not affect the operation of the others.

The “Bus” topology is a single backbone cable with connected computers. Such an organization of a local area network saves money, but is not suitable for connecting a large number of computers.

The “Ring” topology is characterized by low reliability due to the special arrangement of nodes - each of them is connected to two others using network cards. The failure of one computer leads to the shutdown of the entire network, so this type of topology is used less and less.

Detailed network design

An enterprise local area network also includes various technologies, equipment and cables. Therefore, the next step will be the selection of all these elements. Making a decision in favor of one or another software or hardware is determined by the purpose of creating the network, the number of users, the list of programs used, the size of the network, and its location. Currently, fiber optic highways are most often used, which are distinguished by their high reliability, speed and availability.

About cable types

Cables are used in networks to transmit signals between workstations; each of them has its own characteristics, which must be taken into account when designing a LAN.

A twisted pair consists of several pairs of conductors covered with insulation and twisted together. Low price and ease of installation are beneficial advantages, which makes this cable the most popular for installing local networks.
A coaxial cable consists of two conductors inserted one inside the other. A local area network using coax is no longer so common - it was replaced by twisted pair, but it is still found in some places.
Optical fiber is a glass thread that can carry light by reflecting it off walls. A cable made from this material transmits data over long distances and is fast compared to twisted pair and coaxial cables, but it is not cheap.

Necessary equipment

Network equipment of local area networks includes many elements, the most commonly used of which are:

Hub or hub. It connects a number of devices into one segment using a cable.
Switch. Uses special processors for each port, processing packets separately from other ports, due to which they have high performance.
Router. This is a device that makes decisions about sending packets based on data about routing tables and some rules.
Modem. Widely used in communication systems, providing contact with other workstations via a cable or telephone network.

End network equipment

The local area network hardware necessarily includes server and client parts.

A server is a powerful computer with high network significance. Its functions include storing information, databases, serving users and processing program codes. The servers are located in special rooms with a controlled constant air temperature - server rooms, and their housing is equipped with additional protection from dust, accidental shutdown, as well as a powerful cooling system. As a rule, only system administrators or company managers have access to the server.

A workstation is a regular computer connected to a network, that is, it is any computer that requests services from the main server. To ensure communication at such nodes, a modem and a network card are used. Since workstations usually use server resources, the client part is equipped with weak memory sticks and small hard drives.

Software

Local area network equipment will not be able to fully perform its functions without suitable software. The software part includes:

Network operating systems on servers that form the basis of any network. It is the OS that controls access to all network resources, coordinates packet routing, and resolves device conflicts. Such systems have built-in support for the TCP/IP, NetBEUI, IPX/SPX protocols.
Autonomous operating systems that manage the client side. They are common operating systems, for example, Windows XP, Windows 7.
Network services and applications. These software elements allow you to perform various actions: viewing remote documentation, printing on a network printer, sending email messages. Traditional services HTTP, POP-3, SMTP, FTP and Telnet are the basis of this category and are implemented using software.

Nuances of designing local networks

Designing a local area network requires a long and leisurely analysis, as well as taking into account all the subtleties. It is important to provide for the possibility of enterprise growth, which will entail an increase in the scale of the local network. The project must be drawn up in such a way that the LAN is ready at any time to connect a new workstation or other device, as well as upgrade any of its nodes and components.

Security issues are no less important. The cables used to build the network must be reliably protected from unauthorized access, and the lines must be located away from potentially dangerous places where they can be damaged - accidentally or intentionally. LAN components located outside the premises must be grounded and securely secured.

Developing a local area network is a fairly labor-intensive process, but with the right approach and due responsibility, the LAN will operate reliably and stably, ensuring uninterrupted user experience.

PURPOSE AND CLASSIFICATION OF COMPUTER NETWORKS

Global Internet services.

Global Internet. Addressing.

Purpose and classification of computer networks.

INTERNET TECHNOLOGIES

Plan:

Computer network– communication system between computers and computer equipment.

Depending on the territorial location of subscriber systems, computer networks can be divided into three main classes:

Wide Area Network (WAN) is a system of networked computers located at large distances from each other.

Regional computer network (MAN – Metropolitan Area Network) connects subscribers located at a considerable distance from each other (tens - hundreds of kilometers).

Local area network (LAN, LAN – Local Area Network) unites subscribers located within a small area (2 – 2.5 km).

Local area network hardware includes workstations, server, communication equipment

Work station– a personal computer connected to a network and providing user access to its resources.

Server– a specialized computer on a network designed to run service software on it.

To connect a workstation with a communication channel, use network adapter.

Communication channel in a computer network is a physical medium for transmitting information.

Communication channels differ in three main properties: throughput, noise immunity, and cost.

Bandwidth– this is the maximum speed of information transmission over the channel. It is usually expressed in kilobits per second (Kbps) or megabits per second (Mbps).

Let's consider communication channels.

twisted pair characterized by poor noise immunity and low information transmission speed 0.25 – 1 Mbit/s. Low cost.

Coaxial cable has high noise immunity and provides information transmission speeds of up to 10-50 Mbit/s.

Fiber optic cable It is not affected by electromagnetic fields and has practically no radiation. Information transfer speed is more than 50 Mbit/s.

Wireless network. Wireless communication technologies in computer networks are based on the coding and transmission of signals in the form of electromagnetic radiation.

The most common standards for data transmission in the radio wave range are: Bluetooth, Wi-Fi, GPRS, Wi-Max, 3G, LTE.

There are standards for data transmission in the light range: infrared - IrDa, etc.

Communication equipment:

Network hub or hub– a network device designed to connect several Ethernet devices to a common network segment. Devices are connected using twisted pair, coaxial cable or optical fiber.

Currently, hubs are almost never produced - they have been replaced by network switch (switches)- devices designed to connect several network nodes within one or more network segments.

Router (router)– a device that provides connection of administratively independent communication networks.

Bridge is a device that connects two networks using the same data transfer methods

Gateway is a device that allows you to organize data exchange between two networks using different communication protocols.

To connect computers in local networks, network adapters (network cards), hubs, switches, and routers are most often used.

Let's take a closer look at each type of equipment.

Network adapter– this is a device necessary to connect a computer to a local network. The network adapter is installed in a free slot (connector) on the computer's motherboard, just like adapters that perform other functions, such as a video adapter. Network adapters can be classified according to the following criteria:

· depending on the type and capacity of the internal bus used in the computer;

· depending on the type of network technology adopted in the network - Ethernet, Token Ring, FDDI, etc.;

· depending on the type of data transmission medium (channel) - coaxial cable, fiber optic cable, twisted pair cable.

The network adapter is connected to the cable using special connectors. For a twisted pair cable, an RG-45 connector is used, which looks like a telephone connector. To connect to a coaxial cable, so-called BNC connectors and T connectors are used. There are network adapters that use the wireless principle of interaction. Currently, the three main types of wireless data transmission are radio communication, microwave communication and infrared communication. Currently, the most common option for organizing a wireless local network is the use of WiFi equipment. WiFi is an abbreviation for “Wireless Fidelity” and is a wireless access standard that provides information transfer speeds of up to 54 Mbps.

Each network adapter has a unique internal number, the so-called MAC address, which allows you to uniquely identify the source of information in the network environment.

Various types cables used as carriers or data transmission media. Although wireless data transmission technologies are becoming increasingly popular nowadays, cable remains the main type of media for network communications. The most common cable types are:

· twisted pair cable;

· coaxial cable;

· fiber optic cable.

Twisted pair cable– the most common type of cable at present, there are two types: unshielded and shielded twisted pair. The internal structure consists of several twisted pairs of copper wires surrounded by a grounded sheath of copper mesh, or aluminum foil in the case of shielded twisted pair cables. There are several types of unshielded twisted pair cable. Currently, the most commonly used type is UTP-5 (UTP - Unshielded Twisted Pair). The UTP-5 cable provides information transfer speeds of up to 1000 Mbit/s. Unshielded twisted pair cable is the cheapest and easiest type of cable to install. But it also has disadvantages. The cable is sensitive to interference from external electromagnetic sources and interference of signals between the individual wires of the cable itself. Length of the cable segment, i.e. the distance from the computer to the signal amplifier (repeater) cannot exceed 100 meters, since the signal weakens as it moves along the cable.

Shielded twisted pair cable (STP – Shielded Twisted Pair) is less susceptible to external electromagnetic influences and is more difficult to install. The length of the cable segment is also limited to 100 meters.

Coaxial cable resembles the cable that is used to connect an antenna to a household television. The data transfer rate for this type of media is 10 Mbit/s. The length of the cable segment can range from 185 to 500 m, depending on the type of coaxial cable. The most widely used are the so-called “thin” cable markings RG-58 and “thick” cable markings RG-8 and RG-11. This type of cable is obsolete and is little used nowadays.

Fiber optic cable is currently the most advanced, but also the most expensive medium for transmitting information. The optical fiber is made of quartz, which is based on silicon dioxide. The cable consists of a central fiber conductor through which the light signal travels, surrounded by another layer of fiber. The refractive index of a light beam is different for these two layers. There are two types of cables: single-mode, in which only one beam can propagate, and multimode, in which many beams can propagate. In single-mode fiber, the diameter of the central fiber conductor is slightly smaller than in multimode fiber. The information transfer speed when using this type of cable reaches 10 Gb/sec (10,000 Mbit/sec). Fiber optic cable is used mainly in global and regional networks, as well as on the backbones of large local networks.

Hub(multiport repeater, or HUB) is a device used to connect individual workstations (computers) into a local network. Modern hubs usually have 8, 12, 16, 24, or 48 ports (connectors) for connecting computers. All hub ports are equal. When a signal is received from one of the computers connected to it, the hub broadcasts it to all other ports. Thus, a hub is the central point of connection between computers on a network. In addition to the function of connecting computers, the hub can perform several other functions. These are: signal amplification (repetition), auto-segmentation (automatic shutdown of faulty ports), ensuring the collection of statistics on network load. Hubs can be connected to each other to increase the size of the network.

Switch(switch) is a device that can also be used to connect computers, or different segments of a local network (LAN). Unlike a hub, a switch, when receiving a signal (data packet) from one of the computers connected to it, does not broadcast it to all other ports, but transmits it only to the port to which the computer that is the recipient of this data packet is connected. As a result, data transfer speeds increase because the number of collisions inherent in Ethernet technology is reduced in the network.

LPs tend to outgrow initial projects. As companies grow, so do drugs. A change in the business profile or organization of a company's work may require network reconfiguration. This becomes obvious when:

Documents wait in line for a network printer for an unacceptably long time;
database query time increased;
information protection requirements have changed, etc.

Networks cannot expand by simply adding workstations and laying cables. Any topology or architecture has its limitations. However, there are devices that can:

segment the drug so that each segment becomes an independent drug;
combine two drugs into one;
connect LANs to other networks to connect them to the Internet.

Such devices include: repeaters, bridges, routers, bridge routers and gateways.

Repeaters

These are devices that receive a fading signal from one network segment, restore it and transmit it to the next segment, thereby increasing the range of signal transmission between individual network nodes (Fig. below).

Connecting a repeater to a LAN

Repeaters transmit all traffic in both directions and operate at the physical layer of the OSI model. This means that each segment must use the same packet formats, protocols, and access methods. That is, with the help of a repeater it is possible to combine two Ethernet segments into a single network, but Ethernet and Token Ring are not possible.

However, repeaters make it possible to connect two segments that use different physical signal transmission media (cable - optical, cable - pair, etc.). Some multiport repeaters act as multiport hubs, connecting different types of cables.

The use of repeaters is justified in cases where it is necessary to overcome the limitation on the length of the segment or the number of PCs. Moreover, none of the network segments generates increased traffic, and the cost of the LAN is the main factor. This is due to the fact that repeaters do not perform the functions of isolation and filtration.

Thus, transmitting every bit of data from segment to segment, they will transmit both corrupted packets and packets not intended for this segment. As a result, the problems of one segment will affect others. Those. The use of repeaters does not provide the segment isolation function. In addition, repeaters will distribute all broadcast packets throughout the network. And if a device does not respond to all packets, or packets are constantly trying to reach devices that never respond, then network performance drops, i.e., repeaters do not filter signals.

Bridges

A bridge is a device that connects two networks that use the same data transfer methods. These devices, like repeaters, can:

increase the size of the network and the number of PCs in it;
connect dissimilar network cables. However, their fundamental difference is that they operate at the data link level of the OSI model, i.e. at a higher level than repeaters and take into account more features of the transmitted data, allowing:
restore the shape of signals, but doing it at the packet level;
connect dissimilar network segments (for example, Ethernet and Token Ring) and transfer packets between them;
improve the performance, efficiency, security and reliability of networks (which will be discussed below).

Operating principles of bridges

The operation of the bridge is based on the principle that all network nodes have unique network addresses, and the bridge transmits packets based on the address of the destination node (Fig. below).

An example of integrating LAN segments using bridges

When controlling access to the network, the bridge:

listens to all traffic;
checks the source and destination addresses of the packet;
builds a routing table;
transmits packets based on the destination node address.

The bridge has some "intelligence" because it learns where to send the data. When packets are sent across a bridge, the transmitter addresses are stored in the bridge's memory and a routing table is created based on them. At the start of work, the table is empty. Then, when nodes transmit packets, their addresses are copied into the table. With this data, the bridge studies the location of computers on network segments. Listening to the traffic of all segments and receiving the packet, the bridge looks for the transmitter address in the routing table. If the source address is not found, it adds it to the table. Then it compares the recipient address with the routing table database.

If the destination address is in the table and the destination is in the same segment as the source, the packet is discarded. This filtering reduces network traffic and isolates network segments.
If the destination address is in the table, but the destination and source are on different segments, the bridge forwards the packet through the appropriate port to the desired segment.
If the address is not in the table, the packet is relayed to all segments, excluding the one from which it was received.

In short, if the bridge knows the location of the destination node, it forwards the packet to it. Otherwise, it broadcasts the packet to all segments.

The considered option corresponds to the simplest, so-called transparent bridges. Currently, bridges with a spanning tree algorithm, bridges with source routing, etc. are used.

Purpose of bridges

Bridges allow you to increase the coverage range of your network by working as repeaters. In this case, a cascaded LAN connection via bridges is allowed. Moreover, these LANs can be heterogeneous.
The use of bridges improves network performance due to the possibility of network segmentation. Since bridges are able to filter packets according to certain criteria, a large network is divided into several segments connected by bridges. Two small segments will work faster than one large one because traffic is localized within each segment.
The use of bridges increases the efficiency of the network, because for each subnet (segment) you can use different topologies and transmission media, and then connect them with bridges. So, for example, if in individual departments the PCs are connected by twisted pairs, then these subnets can be bridged to the corporate LAN with an optical backbone. Since twisted pair cables are cheap, this will save money, and the core backbone (which carries most of the traffic) will use a high-bandwidth environment.
Bridges allow you to increase the security (protection) of data due to the fact that they can be programmed to transmit only those packets that contain the addresses of specific senders and recipients. This allows you to limit the circle of PCs capable of sending and receiving information from another subnet. For example, in a network serving accounting, you can install a bridge that will allow only some external stations to receive information.
Bridges increase the reliability and resiliency of the network. With network segmentation, the failure of any subnet will not cause all others to fail. In addition, when a single file server goes down, the entire network stops working. If, using internal bridges, you connect two file servers that protect each other, then:

network fault tolerance will increase;
traffic levels will decrease.

There are local and remote bridges. Remote bridges are used in large networks when its individual segments are connected by telephone (or other) communication channels.

However, if only one local bridge is used to connect two cable LAN segments, then in large networks it is necessary to use two remote bridges connected via synchronous modems to a dedicated communication channel (Fig. below).

Using two remote bridges

Routers

A router is a device for connecting networks using different architectures and protocols. Working at the network layer of the OSI model, they can:

switch and route packets across multiple networks;
determine the best route for their transmission;
bypass slow and faulty channels;
filter broadcast messages;
act as a security barrier between networks.

A router, unlike a bridge, has its own address and is used as an intermediate destination.

As you probably already guessed, from hardware you will need network adapters to connect the computer to the cable, connectors, the cable itself, and, possibly, a device for connecting computers when using a star topology.

Depending on the network topology, the composition of network equipment may vary.

In any case, you will need a network adapter for each computer on the network. This adapter is inserted into the computer's main board (motherboard) and has one or two connectors for connecting to a network cable (of course, a network of computers, not a power supply or lighting network).

There are networks that do not require special adapters - the network cable is connected to the RS-232-C serial port. These networks are low-performance and are suitable for solving only simple tasks, such as sharing a printer. We will not pay much attention to such networks.

What should owners of laptop computers like Lap-Top and Note Book that do not have expansion slots for connecting network adapters do? Some companies produce Ethernet adapters specifically for such computers in the form of a small box that connects to the printer or serial port of the computer.

As for the cable, coaxial cable or twisted pair (regular telephone wire) is usually used. In critical cases, when it is necessary to connect computers located in different buildings or there are requirements to ensure the protection of information from unauthorized access, fiber-optic cable is used. By the way, the fiber optic cable itself is no more expensive than the coaxial cable, which, however, cannot be said about adapters and other equipment for connecting such a cable.

If you are using coaxial cable, it should not be too long. When the length of the local network is hundreds of meters, it may be necessary to install a special device - a repeater - into the middle of the cable. The repeater's task is not limited to simply amplifying the signal. But we'll talk about this later.

Let's look at the hardware needed to implement the most common access methods - Ethernet, Arcnet and Token-Ring.

2.1. Ethernet hardware

Ethernet hardware typically consists of cable, connectors, T-connectors, terminators, and network adapters.

The cable is obviously used to transfer data between workstations. Connectors are used to connect the cable. These connectors through
T-connectors are connected to network adapters - special cards that are inserted into the expansion slots of the workstation motherboard. Terminators are connected to the open ends of the network. Soon we will tell you more about Ethernet hardware and the purpose of the devices listed above.

There are different types of cables that can be used for Ethernet: thin coaxial cable, thick coaxial cable, and unshielded twisted pair cable. Each type of cable uses its own connectors and its own method of connecting the cable to the network adapter.

Depending on the cable, network characteristics such as the maximum cable length and the maximum number of workstations connected to the cable change.

Typically, the data transfer rate of an Ethernet network reaches 10 Mbits per second, which is sufficient for many applications.

Let's take a closer look at the composition of Ethernet hardware for various cable types.

2.1.1. Thick coaxial cable

The thick coaxial cable used by Ethernet has a diameter of 0.4 inches and a characteristic impedance of 50 ohms. This cable is sometimes called the "yellow cable". This is the most expensive cable we've reviewed. The IEEE Institute has defined the specification for this cable - 10BASE5.

In Fig. Figure 4 schematically shows a local network based on a thick coaxial cable.

Rice. 4. Ethernet on thick coaxial cable

Here is a network configuration consisting of two segments separated by a repeater. Each segment contains three workstations.

Each workstation is connected via a network adapter (installed in the computer motherboard and not shown in the figure) with a special multi-core transceiver cable to a device called a transceiver. The transceiver is used to connect the workstation to a thick coaxial cable.

There are three connectors on the transceiver body: two for connecting a thick coaxial cable, and one for connecting a transceiver cable.

In table Table 2 lists the devices needed to connect a workstation to a thick coaxial cable.

Table 2. Hardware for connecting a workstation to a thick coaxial Ethernet cable

Unfortunately, the length of one segment is limited and for a thick cable cannot exceed 500 meters. If the total length of the network is more than 500 meters, it must be divided into segments connected to each other through a special device - a repeater.

Our figure shows two segments connected by a repeater. In this case, the total length of the network can reach one kilometer.

The transceivers are connected to each other by sections of thick coaxial cable with coaxial connectors soldered to their ends.

At the ends of the segment, special plugs are connected - terminators. These are simply coaxial connectors with a 50 ohm resistor installed in the housing.

The housing of one of the terminators must be grounded. Please note that only one terminator can be grounded in each network segment.

Are there any other restrictions besides the maximum segment length? Alas, they do exist (see Table 3).

Table 3. Limits for Ethernet on Thick Cable

In addition to the limitation on the segment length, there are restrictions on the maximum number of segments in the network (and, as a result, the maximum length of the network), on the maximum number of workstations connected to the network, and on the length of the transceiver cable.

However, in most cases these restrictions are not significant. Moreover, the capabilities of a thick cable are often redundant. You can save a lot of money if you make a network based on thin cable, since in this case you will not need any transceivers or transceiver cables. And a thin network cable is cheaper than a thick one.

In Fig. Figure 5 shows the equipment needed for a thick cable Ethernet network.

Rice. 5. Ethernet equipment for thick cable

2.1.2. Thin coaxial cable

The thin coaxial cable used for Ethernet has a diameter of 0.2 inches and a characteristic impedance of 50 ohms. The imported cable is called RG-58A/U and complies with the 10BASE2 specification. You can also use the RK-50 cable produced by our industry.

An Ethernet network on a thin cable is much simpler than on a thick one (Fig. 6).

Rice. 6. Ethernet on thin coaxial cable

As a rule, all network adapters have two connectors. One of them is designed for connecting a multi-core transceiver cable, the second is for connecting a small tee called a T-connector.

On one side, the T-connector is connected to the network adapter, and on the other two sides, pieces of thin coaxial cable with corresponding connectors at the ends are connected to it. In this case, it turns out that the coaxial cable is connected directly to the network adapter, so a transceiver and transceiver cable are not needed.

At the ends of the segment there must be terminators that are connected to the free ends of the T-connectors. One (and only one!) terminator in a segment must be grounded.

Networks based on thin cable have worse parameters compared to networks based on thick cable (Table 4). But the cost of the network equipment necessary to create a network on a thin cable is significantly less.

It should be noted that some companies produce Ethernet adapters that can operate with a segment length of up to 300 meters (for example, adapters from 3COM). However, such adapters are more expensive and the entire network in this case must be made using only one type of adapter. To decide whether to purchase more expensive adapters, compare the additional cost to the cost of the repeater that will be needed to achieve the total network length required.

Table 4. Limitations for Ethernet on Thin Cable

As a rule, most Ethernet networks are created on the basis of a thin cable. In Fig. Figure 7 shows the equipment needed for a thin cable Ethernet network.

Rice. 7. Ethernet equipment for thin cable

2.1.3. Unshielded twisted pair

Some (but not all) Ethernet network adapters are capable of operating with a cable that is a simple unshielded twisted pair of wires (10BASE-T specification). As such a cable, you can use a regular telephone wire and the telephone network that already exists in your organization.

Network adapters capable of working with twisted pair cables have a connector similar to that used in imported telephone sets.

For an Ethernet network based on twisted pair, a special device is required - a hub. Up to 12 workstations can be connected to one hub via the same telephone sockets. The maximum distance from the hub to the workstation is 100 meters. In this case, the data transfer speed is the same as for coaxial cable - 10 Mbit per second.

The advantages of a network based on twisted pair are obvious - low cost of equipment and the ability to use the existing telephone network. However, there are serious restrictions on the number of stations in the network and on its length.

2.1.4. Ethernet network adapter

Regardless of the cable you use, you will need to purchase a network adapter for each workstation. A network adapter is a card that is inserted into the computer's motherboard. It has at least two connectors for connecting to a network cable.

For Ethernet, the ISA standard uses three types of network adapters: 8-bit, 16-bit and 32-bit. The 8-bit adapter can be inserted into 8-bit or 16-bit slots on the motherboard and is used primarily in IBM XT or IBM PC computers that do not have 16-bit slots. Sometimes 8-bit adapters are also purchased for IBM AT computers if the data transfer speed requirements are low. For a 16-bit adapter, you must use a 16-bit slot.

If your computers are based on an 80386 or 80486 processor, it makes sense to consider purchasing a high-speed 32-bit network adapter, at least for those stations that bear the maximum load.

Network adapters can be designed for ISA, EISA or Micro Channel architecture. The first architecture is used in computers of the IBM AT series and compatibles with them, the second - in powerful stations based on 80486 processors, the third - in PS/2 computers from IBM. Please note that these types of adapters are structurally different from each other. While you will be able to fit an ISA adapter into an EISA bus, you will never be able to fit an EISA adapter into an ISA bus. The Micro Channel design is completely ISA and EISA incompatible.

To speed up operation, there may be a buffer on the network adapter board. The size of this buffer varies for different types of adapters and can range from 8 KB for 8-bit adapters to 16 KB or more for 16- and 32-bit adapters.

Ethernet network adapters use I/O ports and one interrupt channel. Some adapters can work with a direct memory access (DMA) channel.

The adapter board can contain a read-only memory (ROM) chip to create so-called diskless workstations. These are computers that do not have a hard drive or floppy disks. The operating system is loaded from the network and executed by a program stored in the remote boot chip.

Before inserting the adapter into the computer motherboard, you must use the switches (located on the adapter board) to set the correct values for the input/output ports, interrupt channel, and base address of the remote boot ROM of the diskless station. We will tell you more about installing switches in the chapter “Network Installation”.

2.1.5. Repeater

If the length of the network exceeds the maximum length of a network segment, it is necessary to split the network into several (up to five) segments, connecting them through a repeater.

Structurally, the repeater can be made either as a separate structure with its own power supply, or as a board inserted into the expansion slot of the computer motherboard.

The repeater as a separate design is more expensive, but it can be used to connect Ethernet segments made on either thin or thick cable, since it has both coaxial connectors and connectors for connecting a transceiver cable. Using this repeater, you can even connect segments made on both thin and thick cables into a single network.

The board repeater has only coaxial connectors and therefore can only connect segments on a thin coaxial cable. However, it is cheaper and does not require a separate outlet for connecting power.

One of the disadvantages of a repeater built into a workstation is that in order to ensure 24/7 network operation, the station with the repeater must also operate 24/7. If you turn off the power, communication between network segments will be disrupted.

The functions of the repeater are to physically separate network segments and ensure the recovery of packets transmitted from one network segment to another.

The repeater increases the reliability of the network, since the failure of one segment (for example, a cable break) does not affect the operation of other segments. However, of course, data cannot pass through the damaged segment.

2.2. Arcnet hardware

To organize an Arcnet network, you will need a special network adapter. This adapter has one external connector for connecting a coaxial cable.

Each Arcnet adapter must have its own number for a given network. This number is set by switches located on the adapter and ranges from 0 to 255.

Network adapters of workstations are connected via a coaxial cable with a characteristic impedance of 93 Ohms to a special device - a hub. It is also possible to use unshielded twisted pair cable.

Hubs are either passive (Passive Hub) or active (Active Hub). One hub (depending on its type) can connect 4, 8, 16 or 32 workstations.

Restrictions for the Arcnet network are given in table. 5.

Table 5. Arcnet Network Limits

The advantages of the Arcnet network are the low cost of network equipment (compared to Ethernet) and the long network length (up to 6 kilometers). However, the low data transfer rate of 2.44 megabits per second limits the use of the Arcnet network.

2.3. Token-Ring equipment

As for the Token-Ring network, its name may mislead you. The topology of this network is more similar to a star topology than a ring topology. Instead of connecting to each other to form a ring, Token-Ring workstations connect radially to an IBM 8228-type hub. True, there can be several hubs, and in this case the hubs are actually combined into a ring through special connectors.

However, if only one hub is used, then the connecting connectors do not need to be looped.

The data transfer speed in the Token-Ring network can reach 4 or
16 Mbits per second, but the cost of network equipment is higher than for an Ethernet network. In addition, there are other restrictions (see Table 6).

Table 6. Restrictions for the Token Ring network

As you can see from this table, Token-Ring networks are not designed for long distances. All computers should be located on one or two floors of the building. The higher hardware cost compared to Ethernet further reduces the appeal of this IBM product.