Network technologies of local networks. Creation of standard local network technologies

Local network architectures or technologies can be divided into two generations. The first generation includes architectures that provide low and medium information transfer rates: Ethernet 10 Mbit/s), Token Ring (16 Mbit/s) and ARC net (2.5 Mbit/s).

These technologies use copper cables to transmit data. The second generation of technologies includes modern high-speed architectures: FDDI (100 Mbit/s), ATM (155 Mbit/s) and upgraded versions of the first generation architectures (Ethernet): Fast Ethernet (100 Mbit/s) and Gigabit Ethernet (1000 Mbit/s ). Improved versions of the first generation architectures are designed for both the use of cables with copper cores and fiber-optic data transmission lines. New technologies (FDDI and ATM) are focused on the use of fiber-optic data lines and can be used to simultaneously transmit information of various types (video, voice and data). Network technology is a minimum set of standard protocols and software and hardware that implement them, sufficient to build a computer network. Network technologies are called core technologies. Currently, there are a huge number of networks with various levels of standardization, but such well-known technologies as Ethernet, Token-Ring, Arcnet, FDDI have become widespread.

Network access methods

Ethernet is a multiple access method with carrier listening and collision resolution (conflicts). Before transmission begins, each workstation determines whether the channel is free or busy. If the channel is free, the station begins transmitting data. In reality, conflicts lead to a decrease in network performance only when 80–100 stations are operating. Access method Arcnet. This access method has become widespread mainly due to the fact that Arcnet equipment is cheaper than Ethernet or Token-Ring equipment. Arcnet is used in local networks with a star topology. One of the computers creates a special token (special message), which is sequentially transmitted from one computer to another. If a station needs to transmit a message, it, having received the token, forms a packet complete with source and destination addresses. When the packet reaches the destination station, the message is “unhooked” from the token and transmitted to the station. Access method Token Ring. This method was developed by IBM; it is designed for a ring network topology. This method is similar to Arcnet, since it also uses a token transmitted from one station to another. Unlike Arcnet, the Token Ring access method allows you to assign different priorities to different workstations.

Basic LAN technologies

Ethernet technology is now the most popular in the world. A classic Ethernet network uses two types of standard coaxial cable (thick and thin). However, the version of Ethernet that uses twisted pairs as a transmission medium has become increasingly widespread, since their installation and maintenance are much simpler. Topologies of the “bus” and “passive star” types are used. The standard defines four main types of transmission media.

 10BASE5 (thick coaxial cable);

 10BASE2 (thin coaxial cable);

 10BASE-T (twisted pair);

 10BASE-F (fiber optic cable).

Fast Ethernet is a high-speed type of Ethernet network that provides a transmission speed of 100 Mbit/s. Fast Ethernet networks are compatible with networks based on the Ethernet standard. The basic topology of a Fast Ethernet network is passive star.

The standard defines three types of transmission media for Fast Ethernet:

 100BASE-T4 (quad twisted pair);

 100BASE-TX (dual twisted pair);

 100BASE-FX (fiber optic cable).

Gigabit Ethernet is a high-speed type of Ethernet network that provides transmission speeds of 1000 Mbit/s. The Gigabit Ethernet network standard currently includes the following types of transmission media:

 1000BASE-SX – a segment on a multimode fiber optic cable with a light signal wavelength of 850 nm.

 1000BASE-LX – segment on multimode and single-mode fiber optic cable with a light signal wavelength of 1300 nm.

 1000BASE-CX – segment on an electrical cable (shielded twisted pair).

 1000BASE-T – segment on an electrical cable (quadruple unshielded twisted pair).

Due to the fact that the networks are compatible, it is easy and simple to connect Ethernet, Fast Ethernet and Gigabit Ethernet segments into a single network.

The Token-Ring network was proposed by IBM. Token-Ring was intended to network all types of computers produced by IBM (from personal computers to large ones). The Token-Ring network has a star-ring topology. The Arcnet network is one of the oldest networks. The Arcnet network uses a “bus” and a “passive star” as its topology. The Arcnet network was very popular. Among the main advantages of the Arcnet network are high reliability, low cost of adapters and flexibility. The main disadvantage of the network is the low speed of information transfer (2.5 Mbit/s). FDDI (Fiber Distributed Data Interface) – a standardized specification for a network architecture for high-speed data transmission over fiber optic lines. Transfer speed – 100 Mbit/s. The main technical characteristics of the FDDI network are as follows:

 The maximum number of network subscribers is 1000.

 The maximum length of the network ring is 20 km

 The maximum distance between network subscribers is 2 km.

 Transmission medium – fiber optic cable

 Access method – token.

 Information transfer speed – 100 Mbit/s.

INTRODUCTION………………………………………………………………………………..3

1 ETHERNET AND FAST ETHERNET NETWORKS……………………………5

2 TOKEN-RING NETWORK…………………………………………………….9

3 ARCNET NETWORK………………………………………………………….14

4 FDDI NETWORK………………………………………………………………………………18

5 100VG-AnyLAN NETWORK…………………………………………………………….23

6 ULTRA-SPEED NETWORKS…………………………………………………….25

7 WIRELESS NETWORKS…………………………………………………………….31

CONCLUSION…………………………………………………………….36

LIST OF SOURCES USED………………………39

INTRODUCTION

Since the advent of the first local networks, several hundred different network technologies have been developed, but only a few have become noticeably widespread. This is due, first of all, to the high level of standardization of networking principles and their support by well-known companies. However, standard networks do not always have record-breaking characteristics and provide the most optimal exchange modes. But the large production volumes of their equipment and, consequently, its low cost give them enormous advantages. It is also important that software manufacturers also primarily focus on the most common networks. Therefore, a user who chooses standard networks has a full guarantee of compatibility of equipment and programs.

The purpose of this course work is to consider existing local network technologies, their characteristics and advantages or disadvantages over each other.

I chose the topic of local network technologies because, in my opinion, this topic is especially relevant now, when mobility, speed and convenience are valued all over the world, with as little time wasted as possible.

Currently, reducing the number of types of networks used has become a trend. The fact is that increasing the transmission speed in local networks to 100 and even 1000 Mbit/s requires the use of the most advanced technologies and expensive scientific research. Naturally, only the largest companies that support their standard networks and their more advanced varieties can afford this. In addition, a large number of consumers have already installed some kind of network and do not want to immediately and completely replace network equipment. It is unlikely that fundamentally new standards will be adopted in the near future.

The market offers standard local networks of all possible topologies, so users have a choice. Standard networks provide a wide range of acceptable network sizes, number of subscribers and, last but not least, equipment prices. But making a choice is still not easy. Indeed, unlike software, which is not difficult to replace, hardware usually lasts for many years; its replacement leads not only to significant costs and the need to re-wire cables, but also to a revision of the organization's computer system. In this regard, errors in the choice of equipment are usually much more expensive than errors in the choice of software.

1 ETHERNET AND FAST ETHERNET NETWORKS

The most widespread among standard networks is the Ethernet network. It first appeared in 1972 (developed by the famous company Xerox). The network turned out to be quite successful, and as a result, in 1980 it was supported by such major companies as DEC and Intel). Through their efforts, in 1985, the Ethernet network became an international standard; it was adopted by the largest international standards organizations: IEEE Committee 802 (Institute of Electrical and Electronic Engineers) and ECMA (European Computer Manufacturers Association).

The standard is called IEEE 802.3 (read in English as “eight oh two dot three”). It defines multiple access to a mono bus type channel with collision detection and transmission control. Some other networks also met this standard, since its level of detail is low. As a result, IEEE 802.3 networks were often incompatible with each other in both design and electrical characteristics. However, recently the IEEE 802.3 standard has been considered the standard for the Ethernet network.

Main characteristics of the original IEEE 802.3 standard:

• topology – bus;
• transmission medium – coaxial cable;
• transmission speed – 10 Mbit/s;
• maximum network length – 5 km;
• maximum number of subscribers – up to 1024;
• network segment length – up to 500 m;
• number of subscribers on one segment – ​​up to 100;
• access method – CSMA/CD;
• Narrowband transmission, that is, without modulation (mono channel).

Strictly speaking, there are minor differences between the IEEE 802.3 and Ethernet standards, but they are usually ignored.

The Ethernet network is now the most popular in the world (more than 90% of the market), and presumably it will remain so in the coming years. This was greatly facilitated by the fact that from the very beginning the characteristics, parameters, and protocols of the network were open, as a result of which a huge number of manufacturers around the world began to produce Ethernet equipment that was fully compatible with each other.

The classic Ethernet network used 50-ohm coaxial cable of two types (thick and thin). However, recently (since the early 90s), the most widely used version of Ethernet is that using twisted pairs as a transmission medium. A standard has also been defined for use in fiber optic cable networks. Additions have been made to the original IEEE 802.3 standard to accommodate these changes. In 1995, an additional standard appeared for a faster version of Ethernet operating at a speed of 100 Mbit/s (the so-called Fast Ethernet, IEEE 802.3u standard), using twisted pair or fiber optic cable as the transmission medium. In 1997, a version with a speed of 1000 Mbit/s (Gigabit Ethernet, IEEE 802.3z standard) also appeared.

In addition to the standard bus topology, passive star and passive tree topologies are increasingly being used.

Classic Ethernet network topology

The maximum cable length of the network as a whole (maximum signal path) can theoretically reach 6.5 kilometers, but practically does not exceed 3.5 kilometers.

A Fast Ethernet network does not have a physical bus topology; only a passive star or passive tree is used. In addition, Fast Ethernet has much more stringent requirements for the maximum network length. After all, with a 10-fold increase in transmission speed and preservation of the packet format, its minimum length becomes ten times shorter. Thus, the permissible value of double signal transmission time through the network is reduced by 10 times (5.12 μs versus 51.2 μs in Ethernet).

The standard Manchester code is used to transmit information on an Ethernet network.

Access to the Ethernet network is carried out using the random CSMA/CD method, ensuring equality of subscribers. The network uses packets of variable length with structure.

For an Ethernet network operating at a speed of 10 Mbit/s, the standard defines four main types of network segments, focused on different information transmission media:

• 10BASE5 (thick coaxial cable);
• 10BASE2 (thin coaxial cable);
• 10BASE-T (twisted pair);
• 10BASE-FL (fiber optic cable).

The name of the segment includes three elements: the number “10” means a transmission speed of 10 Mbit/s, the word BASE means transmission in the base frequency band (that is, without modulating a high-frequency signal), and the last element is the permissible length of the segment: “5” – 500 meters, “2” – 200 meters (more precisely, 185 meters) or type of communication line: “T” – twisted pair (from the English “twisted-pair”), “F” – fiber optic cable (from the English “fiber optic”).

Similarly, for an Ethernet network operating at a speed of 100 Mbit/s (Fast Ethernet), the standard defines three types of segments, differing in the types of transmission media:

• 100BASE-T4 (quad twisted pair);
• 100BASE-TX (dual twisted pair);
• 100BASE-FX (fiber optic cable).

Here, the number “100” means a transmission speed of 100 Mbit/s, the letter “T” means twisted pair, and the letter “F” means fiber optic cable. The types 100BASE-TX and 100BASE-FX are sometimes combined under the name 100BASE-X, and 100BASE-T4 and 100BASE-TX are called 100BASE-T.

The development of Ethernet technology is moving further and further away from the original standard. The use of new transmission media and switches makes it possible to significantly increase the size of the network. Elimination of the Manchester code (in Fast Ethernet and Gigabit Ethernet networks) provides increased data transfer speeds and reduced cable requirements. Refusal of the CSMA/CD control method (with full-duplex exchange mode) makes it possible to dramatically increase operating efficiency and remove restrictions on network length. However, all new varieties of network are also called Ethernet network.

2 TOKEN-RING NETWORK

The Token-Ring network was proposed by IBM in 1985 (the first version appeared in 1980). It was intended to network all types of computers produced by IBM. The very fact that it is supported by IBM, the largest manufacturer of computer equipment, suggests that it needs to be given special attention. But equally important is that Token-Ring is currently the international standard IEEE 802.5 (although there are minor differences between Token-Ring and IEEE 802.5). This puts this network on the same level of status as Ethernet.

Token-Ring was developed as a reliable alternative to Ethernet. And although Ethernet is now replacing all other networks, Token-Ring cannot be considered hopelessly outdated. More than 10 million computers around the world are connected by this network.

IBM has done everything to ensure the widest possible distribution of its network: detailed documentation was released, right down to the circuit diagrams of the adapters. As a result, many companies, for example, 3COM, Novell, Western Digital, Proteon and others began producing adapters. By the way, the NetBIOS concept was developed specifically for this network, as well as for another network, the IBM PC Network. If in the previously created PC Network NetBIOS programs were stored in the built-in read-only memory of the adapter, then in the Token-Ring network a program emulating NetBIOS was already used. This made it possible to respond more flexibly to hardware features and maintain compatibility with higher-level programs.

The Token-Ring network has a ring topology, although outwardly it looks more like a star. This is due to the fact that individual subscribers (computers) connect to the network not directly, but through special hubs or multiple access devices (MSAU or MAU - Multistation Access Unit). Physically, the network forms a star-ring topology. In reality, the subscribers are still united in a ring, that is, each of them transmits information to one neighboring subscriber and receives information from another.

Star-ring topology of the Token-Ring network

The hub (MAU) allows you to centralize configuration settings, disconnecting faulty subscribers, monitoring network operation, etc. It does not perform any information processing.

For each subscriber, the concentrator uses a special trunk connection unit (TCU - Trunk Coupling Unit), which ensures automatic inclusion of the subscriber in the ring if it is connected to the concentrator and is working properly. If a subscriber disconnects from the concentrator or it is faulty, the TCU automatically restores the integrity of the ring without the participation of this subscriber. The TCU is triggered by a direct current signal (the so-called “phantom” current), which comes from a subscriber who wants to join the ring

The hub in the network may be the only one; in this case, only the subscribers connected to it are closed in the ring. Externally, this topology looks like a star. If you need to connect more than eight subscribers to the network, then several hubs are connected by trunk cables and form a star-ring topology.

Ring topology is very sensitive to ring cable breaks. To increase the survivability of the network, Token-Ring provides a mode of so-called ring folding, which allows you to bypass the break point.

In normal mode, the hubs are connected in a ring by two parallel cables, but information is transmitted only through one of them.

In the event of a single cable failure (break), the network transmits via both cables, thereby bypassing the damaged section. At the same time, the order of bypassing subscribers connected to the hubs is even preserved. True, the total length of the ring increases.

In case of multiple cable damages, the network breaks up into several parts (segments) that are not interconnected, but remain fully operational. The maximum part of the network remains connected as before. Of course, this no longer saves the network as a whole, but it allows, with the correct distribution of subscribers among hubs, to preserve a significant part of the functions of the damaged network.

Several hubs can be structurally combined into a group, a cluster, within which subscribers are also connected in a ring. The use of clusters allows you to increase the number of subscribers connected to one center, for example, up to 16 (if the cluster includes two hubs).

The transmission medium in the IBM Token-Ring network was initially twisted pair, both unshielded (UTP) and shielded (STP), but then equipment options appeared for coaxial cable, as well as for fiber optic cable in the FDDI standard.

Main technical characteristics of the classic version of the Token-Ring network:

• the maximum number of IBM 8228 MAU type hubs is 12;
• maximum number of subscribers in the network – 96;
• the maximum cable length between the subscriber and the hub is 45 meters;
• maximum cable length between hubs is 45 meters;
• the maximum length of the cable connecting all hubs is 120 meters;
• data transfer speed – 4 Mbit/s and 16 Mbit/s.

All characteristics given refer to the case of using unshielded twisted pair cable. If a different transmission medium is used, network performance may vary. For example, when using shielded twisted pair (STP), the number of subscribers can be increased to 260 (instead of 96), the cable length can be increased to 100 meters (instead of 45), the number of hubs can be increased to 33, and the total length of the ring connecting the hubs can be up to 200 meters . Fiber optic cable allows you to increase the cable length up to two kilometers.

The Token-Ring network in its classic version is inferior to the Ethernet network both in terms of permissible size and the maximum number of subscribers. In terms of transfer speed, Token-Ring is currently available in 100 Mbps (High Speed ​​Token-Ring, HSTR) and 1000 Mbps (Gigabit Token-Ring) versions. Companies supporting Token-Ring (including IBM, Olicom, Madge) do not intend to abandon their network, considering it as a worthy competitor to Ethernet.

Compared to Ethernet equipment, Token-Ring equipment is noticeably more expensive, since it uses a more complex method of managing the exchange, so the Token-Ring network has not become so widespread.

However, unlike Ethernet, the Token-Ring network can handle high load levels (more than 30-40%) much better and provides guaranteed access time. This is necessary, for example, in industrial networks, where a delay in the response to an external event can lead to serious accidents.

The Token-Ring network uses the classic token access method, that is, a token constantly circulates around the ring to which subscribers can attach their data packets. This implies such an important advantage of this network as the absence of conflicts, but there are also disadvantages, in particular the need to control the integrity of the token and the dependence of the functioning of the network on each subscriber (in the event of a malfunction, the subscriber must be excluded from the ring).

Interestingly, the faster version of Token-Ring (16 Mbit/s and higher) uses the so-called Early Token Release (ETR) method. It avoids wasted network usage while the data packet is looping back to its sender.

3 ARCNET NETWORK

The Arcnet network (or ARCnet from the English Attached Resource Computer Net, a computer network of connected resources) is one of the oldest networks. It was developed by Datapoint Corporation back in 1977. There are no international standards for this network, although it is considered the ancestor of the token access method. Despite the lack of standards, the Arcnet network until recently (in 1980 - 1990) was popular, even seriously competing with Ethernet. A large number of companies (for example, Datapoint, Standard Microsystems, Xircom, etc.) produced equipment for this type of network. But now production of Arcnet equipment has practically ceased.

Among the main advantages of the Arcnet network compared to Ethernet are the limited access time, high reliability of communication, ease of diagnosis, and the relatively low cost of adapters. The most significant disadvantages of the network include low information transmission speed (2.5 Mbit/s), addressing system and packet format.

To transmit information on the Arcnet network, a rather rare code is used, in which a logical one corresponds to two pulses during a bit interval, and a logical zero corresponds to one pulse. Obviously, this is a self-timed code that requires even more cable bandwidth than even Manchester.

The transmission medium in the network is a coaxial cable with a characteristic impedance of 93 Ohms, for example, brand RG-62A/U. Options with twisted pair (shielded and unshielded) are not widely used. Fiber optic cable options were also proposed, but they also did not save Arcnet.

As a topology, the Arcnet network uses a classic bus (Arcnet-BUS), as well as a passive star (Arcnet-STAR). The star uses concentrators (hubs). It is possible to combine bus and star segments into a tree topology using hubs (as in Ethernet). The main limitation is that there should be no closed paths (loops) in the topology. Another limitation: the number of segments connected in a daisy chain using hubs should not exceed three.

There are two types of concentrators:

• Active concentrators (restore the shape of incoming signals and amplify them). The number of ports is from 4 to 64. Active hubs can be connected to each other (cascaded).
• Passive hubs (simply mix incoming signals without amplification). Number of ports – 4. Passive hubs cannot be connected to each other. They can only link active hubs and/or network adapters.

Thus, the topology of the Arcnet network is as follows.

Arcnet network topology is bus type (B – adapters for working in a bus, S – adapters for working in a star)

The main technical characteristics of the Arcnet network are as follows.

• Transmission medium – coaxial cable, twisted pair.
• The maximum network length is 6 kilometers.
• The maximum cable length from the subscriber to the passive hub is 30 meters.
• The maximum cable length from the subscriber to the active hub is 600 meters.
• The maximum cable length between active and passive hubs is 30 meters.
• The maximum cable length between active hubs is 600 meters.
• The maximum number of subscribers in the network is 255.
• The maximum number of subscribers on the bus segment is 8.
• The minimum distance between subscribers in the bus is 1 meter.
• The maximum length of a bus segment is 300 meters.
• Data transfer speed – 2.5 Mbit/s.

The Arcnet network uses a token access method (transfer of rights method), but it is somewhat different from that of the Token-Ring network. This method is closest to the one provided in the IEEE 802.4 standard. The sequence of actions of subscribers with this method:

1. The subscriber who wants to transmit waits for the token to arrive.

2. Having received the token, it sends a request to transfer information to the receiving subscriber (asks if the receiver is ready to accept its packet).

3. The receiver, having received the request, sends a response (confirms its readiness).

4. Having received confirmation of readiness, the transmitting subscriber sends its packet.

5. Having received the packet, the receiver sends an acknowledgment of the packet.

6. The transmitter, having received confirmation of receipt of the packet, ends its communication session. After this, the token is transferred to the next subscriber in descending order of network addresses.

Just like with Token-Ring, conflicts are completely eliminated in Arcnet. Like any token network, Arcnet carries the load well and guarantees long access times to the network (unlike Ethernet). The total time for the marker to bypass all subscribers is 840 ms. Accordingly, the same interval determines the upper limit of network access time.

The Arcnet network packet size is 0.5 KB. In addition to the data field, it also includes 8-bit receiver and transmitter addresses and a 16-bit cyclic checksum (CRC). Such a small packet size turns out to be not very convenient when the intensity of network exchange is high.

Arcnet network adapters differ from adapters of other networks in that they require you to set your own network address using switches or jumpers (there can be 255 in total, since the last, 256th address is used in the network for broadcast mode). Control of the uniqueness of each network address rests entirely with network users. Connecting new subscribers becomes quite complicated, since it is necessary to set an address that has not yet been used. Choosing an 8-bit address format limits the allowed number of subscribers on the network to 255, which may not be enough for large companies.

As a result, all this led to the almost complete abandonment of the Arcnet network. There were variants of the Arcnet network designed for transmission speeds of 20 Mbit/s, but they were not widely used.

4 FDDI NETWORK

The FDDI network (from the English Fiber Distributed Data Interface, fiber-optic distributed data interface) is one of the latest developments in local network standards. The FDDI standard was proposed by the American National Standards Institute ANSI (ANSI specification X3T9.5). The ISO 9314 standard was then adopted, conforming to ANSI specifications. The level of network standardization is quite high.

Unlike other standard local networks, the FDDI standard was initially focused on high transmission speeds (100 Mbit/s) and the use of the most promising fiber optic cable. Therefore, in this case, the developers were not constrained by the old standards, which focused on low speeds and electrical cables.

The choice of optical fiber as a transmission medium determined such advantages of the new network as high noise immunity, maximum secrecy of information transmission and excellent galvanic isolation of subscribers. High transmission speeds, which are much easier to achieve in the case of fiber optic cables, make it possible to solve many tasks that are not possible with lower-speed networks, for example, transmitting images in real time. In addition, fiber optic cable easily solves the problem of transmitting data over a distance of several kilometers without relaying, which makes it possible to build large networks that even cover entire cities and have all the advantages of local networks (in particular, a low error rate). All this determined the popularity of the FDDI network, although it is not yet as widespread as Ethernet and Token-Ring.

The FDDI standard was based on the token access method provided for by the international standard IEEE 802.5 (Token-Ring). Minor differences from this standard are determined by the need to ensure high speed information transfer over long distances. The FDDI network topology is ring, the most suitable topology for fiber optic cable. The network uses two multi-directional fiber optic cables, one of which is usually in reserve, but this solution allows the use of full-duplex information transmission (simultaneously in two directions) with double the effective speed of 200 Mbit/s (with each of the two channels operating at the speed 100 Mbit/s). A star-ring topology with hubs included in the ring (as in Token-Ring) is also used.

Main technical characteristics of the FDDI network.

• The maximum number of network subscribers is 1000.
• The maximum length of the network ring is 20 kilometers.
• The maximum distance between network subscribers is 2 kilometers.
• Transmission medium – multimode fiber optic cable (possibly using electrical twisted pair).
• The access method is token.
• Information transfer speed – 100 Mbit/s (200 Mbit/s for duplex transmission mode).

The FDDI standard has significant advantages over all previously discussed networks. For example, a Fast Ethernet network with the same 100 Mbps bandwidth cannot match FDDI in terms of network size allowance. In addition, the FDDI token access method, unlike CSMA/CD, provides guaranteed access time and the absence of conflicts at any load level.

The limitation on the total network length of 20 km is not due to the attenuation of signals in the cable, but to the need to limit the time it takes for a signal to completely travel along the ring to ensure maximum permissible access time. But the maximum distance between subscribers (2 km with a multimode cable) is determined precisely by the attenuation of the signals in the cable (it should not exceed 11 dB). It is also possible to use single-mode cable, in which case the distance between subscribers can reach 45 kilometers, and the total ring length can be 200 kilometers.

To achieve high network flexibility, the FDDI standard provides for the inclusion of two types of subscribers in the ring:

• Class A subscribers (stations) (dual-attachment subscribers, DAS - Dual-Attachment Stations) are connected to both (internal and external) network rings. At the same time, the possibility of exchange at speeds of up to 200 Mbit/s or network cable redundancy is realized (if the main cable is damaged, a backup one is used). Equipment of this class is used in the most critical parts of the network in terms of performance.
• Subscribers (stations) of class B (single connection subscribers, SAS - Single-Attachment Stations) are connected to only one (external) network ring. They are simpler and cheaper than Class A adapters, but do not have their capabilities. They can only be connected to the network through a hub or bypass switch, which turns them off in the event of an emergency.

In addition to the subscribers themselves (computers, terminals, etc.), the network uses Wiring Concentrators, the inclusion of which allows all connection points to be collected in one place for the purpose of monitoring network operation, diagnosing faults and simplifying reconfiguration. When using different types of cables (for example, fiber optic cable and twisted pair), the hub also performs the function of converting electrical signals into optical signals and vice versa. Concentrators also come in dual connection (DAC - Dual-Attachment Concentrator) and single connection (SAC - Single-Attachment Concentrator).

FDDI Network Configuration Example

The FDDI standard also provides the ability to reconfigure the network in order to maintain its functionality in the event of cable failure.

Unlike the access method proposed by the IEEE 802.5 standard, FDDI uses so-called multiple token passing. If in the case of the Token-Ring network a new (free) token is transmitted by the subscriber only after his packet is returned to him, then in FDDI the new token is transmitted by the subscriber immediately after the end of his packet transmission (similar to how this is done with the ETR method in the Token-Ring network Ring). The sequence of actions here is as follows:

1. The subscriber wishing to transmit waits for the token that follows each packet.

2. When the token arrives, the subscriber removes it from the network and transmits its packet. Thus, there can be several packets on the network at the same time, but only one token.

3. Immediately after transmitting his packet, the subscriber sends a new token.

4. The recipient subscriber to whom the packet is addressed copies it from the network and, making a note in the packet status field, sends it further along the ring.

5. Having received his packet back through the ring, the subscriber destroys it. In the packet status field it has information about whether there were errors and whether the receiver received the packet.

The FDDI network does not use a priority and reservation system like Token-Ring. But there is a mechanism for adaptive load planning.

In conclusion, it should be noted that despite the obvious advantages of FDDI, this network has not become widespread, which is mainly due to the high cost of its equipment (on the order of several hundred and even thousands of dollars). The main area of ​​application of FDDI now is basic, core (Backbone) networks that combine several networks. FDDI is also used to connect powerful workstations or servers that require high-speed communication. It is expected that Fast Ethernet can supplant FDDI, but the advantages of fiber optic cable, token management and the record-breaking permissible network size currently put FDDI ahead of the competition. And in cases where the cost of the equipment is critical, a twisted-pair version of FDDI (TPDDI) can be used in non-critical areas. In addition, the cost of FDDI equipment can greatly decrease as its production volume increases.

5 NETWORK 100VG-AnyLAN

The 100VG-AnyLAN network is one of the latest developments in high-speed local area networks that has recently appeared on the market. It was developed by Hewlett-Packard and IBM and complies with the international standard IEEE 802.12, so its level of standardization is quite high.

Its main advantages are high exchange speed, relatively low cost of equipment (about twice as expensive as the equipment of the most popular Ethernet 10BASE-T network), a centralized method of managing exchange without conflicts, as well as compatibility at the level of packet formats with Ethernet and Token-Ring networks.

In the name of the 100VG-AnyLAN network, the number 100 corresponds to a speed of 100 Mbps, the letters VG indicate low-cost unshielded twisted pair cable of category 3 (Voice Grade), and AnyLAN (any network) indicates that the network is compatible with the two most common networks.

Main technical characteristics of the 100VG-AnyLAN network:

• Transfer speed – 100 Mbit/s.
• Topology – star with expandability (tree). The number of cascading levels of concentrators (hubs) is up to 5.
• Access method - centralized, conflict-free (Demand Priority - with a priority request).
• Transmission media are quad unshielded twisted pair (UTP Category 3, 4 or 5 cable), dual twisted pair (UTP Category 5 cable), dual shielded twisted pair (STP), and fiber optic cable. Nowadays, quad twisted pair cables are mostly common.
• The maximum cable length between the hub and the subscriber and between hubs is 100 meters (for UTP cable category 3), 200 meters (for UTP cable category 5 and shielded cable), 2 kilometers (for fiber optic cable). The maximum possible network size is 2 kilometers (determined by acceptable delays).
• The maximum number of subscribers is 1024, the recommended number is up to 250.

Thus, the parameters of the 100VG-AnyLAN network are quite close to the parameters of the Fast Ethernet network. However, the main advantage of Fast Ethernet is its full compatibility with the most common Ethernet network (in the case of 100VG-AnyLAN, this requires a bridge). At the same time, the centralized control of 100VG-AnyLAN, which eliminates conflicts and guarantees maximum access time (which is not provided in the Ethernet network), also cannot be discounted.

Network structure 100VG-AnyLAN

The 100VG-AnyLAN network consists of a central (main, root) Level 1 hub, to which both individual subscribers and Level 2 hubs can be connected, to which subscribers and Level 3 hubs, in turn, can be connected, etc. In this case, the network can have no more than five such levels (in the original version there were no more than three). The maximum network size can be 1000 meters for unshielded twisted pair cable.

Thus, the 100VG-AnyLAN network provides an affordable solution for increasing transmission speeds up to 100 Mbps. However, it is not fully compatible with any of the standard networks, so its future fate is problematic. In addition, unlike the FDDI network, it does not have any record parameters. Most likely, 100VG-AnyLAN, despite the support of reputable companies and a high level of standardization, will remain just an example of interesting technical solutions.

When it comes to the most common 100Mbps Fast Ethernet network, 100VG-AnyLAN provides twice the Category 5 UTP cable length (up to 200 meters), as well as a contention-free method of traffic management.

6 ULTRA-SPEED NETWORKS

The speed of Fast Ethernet and other networks operating at 100 Mbps currently satisfies the requirements of most tasks, but in some cases even this is not enough. Especially in situations where it is necessary to connect modern high-performance servers to the network or build networks with a large number of subscribers that require high traffic intensity. For example, network processing of 3D dynamic images is increasingly being used. The speed of computers is constantly growing; they provide ever-higher rates of exchange with external devices. As a result, the network may be the weakest point of the system, and its throughput will be the main limiting factor in increasing performance.

Work to achieve a transmission speed of 1 Gbit/s (1000 Mbit/s) has been carried out quite intensively in recent years by several companies. However, Gigabit Ethernet is likely to be the most promising network. This is due, first of all, to the fact that the transition to it will be the most painless, cheapest and psychologically acceptable. After all, the Ethernet network and its version Fast Ethernet are today far ahead of all their competitors in terms of sales and prevalence in the world.

The Gigabit Ethernet network is a natural, evolutionary development of the concept inherent in the standard Ethernet network. Of course, it inherits all the shortcomings of its direct predecessors, for example, non-guaranteed network access time. However, the huge bandwidth makes it quite difficult to load the network to levels where this factor becomes decisive. But maintaining continuity allows you to quite simply connect Ethernet, Fast Ethernet and Gigabit Ethernet segments into a network, and, most importantly, move to new speeds gradually, introducing gigabit segments only in the busiest sections of the network. (Besides, such high bandwidth is not really needed everywhere.) If we talk about competing gigabit networks, then their use may require a complete replacement of network equipment, which will immediately lead to large costs.

The Gigabit Ethernet network retains the same CSMA/CD access method, which has proven itself in previous versions, and uses the same packet (frame) formats and the same sizes. No protocol conversion is required at the junctions with Ethernet and Fast Ethernet segments. The only thing that is needed is the coordination of exchange rates, so the main area of ​​​​application of Gigabit Ethernet will be primarily the connection of Ethernet and Fast Ethernet hubs to each other.

With the advent of ultra-fast servers and the proliferation of the most advanced high-end personal computers, the benefits of Gigabit Ethernet are becoming increasingly clear. Thus, the 64-bit PCI system bus, already a de facto standard, fully achieves the data transfer speed required for such a network.

Work on creating a Gigabit Ethernet network has been ongoing since 1995. In 1998, a standard called IEEE 802.3z (1000BASE-SX, 1000BASE-LX and 1000BASE-CX) was adopted. The development is carried out by a specially created alliance (Gigabit Ethernet Alliance), which, in particular, includes such a well-known network equipment company as 3Com. In 1999, the IEEE 802.3ab (1000BASE-T) standard was adopted.

The nomenclature of Gigabit Ethernet network segments currently includes the following types:

• 1000BASE-SX is a segment on a multimode fiber optic cable with a light signal wavelength of 850 nm (up to 500 meters long). Laser transmitters are used.
• 1000BASE-LX is a segment on multimode (up to 500 meters long) and single-mode (up to 2000 meters long) fiber optic cable with a light signal wavelength of 1300 nm. Laser transmitters are used.
• 1000BASE-CX – segment on shielded twisted pair (up to 25 meters long).
• 1000BASE-T (IEEE 802.3ab standard) – a segment on quad unshielded twisted pair category 5 (up to 100 meters long). 5-level coding (PAM-5) is used, and in full duplex mode transmission is carried out on each pair in two directions.

Especially for the Gigabit Ethernet network, a method for encoding transmitted information 8V/10V has been proposed, based on the same principle as the 4V/5V code of the FDDI network (except for 1000BASE-T). Thus, the eight bits of information that need to be transmitted are associated with 10 bits transmitted over the network. This code allows you to maintain self-synchronization, easily detect the carrier (the fact of transmission), but does not require doubling the bandwidth, as is the case with the Manchester code.

To increase the 512-bit Ethernet network interval corresponding to the minimum packet length (51.2 μs in an Ethernet network and 5.12 μs in a Fast Ethernet network), special methods have been developed. In particular, the minimum packet length has been increased to 512 bytes (4096 bits). Otherwise, the 0.512 µs time interval would overly limit the length limit of a Gigabit Ethernet network. All packets less than 512 bytes in length are expanded to 512 bytes. The extension field is inserted into the packet after the checksum field. This requires additional packet processing, but the maximum allowable network size becomes 8 times larger than without such measures.

In addition, Gigabit Ethernet provides the possibility of block packet transmission (frame bursting). In this case, a subscriber who has received the right to transmit and has several packets to transmit can transmit not one, but several packets, sequentially, and addressed to different recipient subscribers. Additional transmitted packets can only be short, and the total length of all packets in a block must not exceed 8192 bytes. This solution allows you to reduce the number of network takeovers and reduce the number of collisions. When using block mode, only the first packet of the block is expanded to 512 bytes in order to check if there are any collisions on the network. Other packets up to 512 bytes may not be expanded.

Using a Gigabit Ethernet network to connect groups of computers

Using Gigabit Ethernet to Connect High-Speed ​​Servers

The Gigabit Ethernet network is primarily used in networks connecting computers of large enterprises that are located in several buildings. It allows, with the help of appropriate switches that convert transmission speeds, to provide high-bandwidth communication channels between individual parts of a complex network or communication lines between switches and ultra-high-speed servers.

It is likely that in some cases Gigabit Ethernet will replace the FDDI fiber optic network, which is now increasingly used to network several local networks, including Ethernet. True, FDDI can connect subscribers located much further from each other, but in terms of information transfer speed Gigabit Ethernet is significantly superior to FDDI.

But even a Gigabit Ethernet network cannot solve some problems. A 10-Gigabit version of Ethernet is already offered, called 10Gigabit Ethernet (IEEE 802.3ae standard, adopted in 2002). It is fundamentally different from previous versions. The transmission medium is exclusively fiber optic cable. Electrical cable can sometimes be used only for short distance communications (about 10 meters). The exchange mode is full duplex. The Ethernet packet format is the same. This is probably the only thing that remains from the original Ethernet standard (IEEE 802.3).

In conclusion, a few words about an alternative solution for an ultra-high-speed network. We are talking about a network with ATM (Asynchronous Transfer Mode) technology. This technology is used in both local and global networks. The main idea is the transmission of digital, voice and multimedia data over the same channels. Strictly speaking, there is no strict standard for ATM equipment.

Initially, a transmission speed of 155 Mbit/s was chosen (for desktop systems - 25 Mbit/s), then 662 Mbit/s, and now work is underway to increase the speed to 2488 Mbit/s. In terms of speed, ATM successfully competes with Gigabit Ethernet. By the way, ATM appeared earlier than Gigabit Ethernet. As a medium for transmitting information on a local network, ATM technology involves the use of fiber optic cable and unshielded twisted pair. The codes used are 4B/5B and 8B/10B.

The fundamental difference between ATM and other networks is the abandonment of the usual packets with addressing, control and data fields. All transmitted information is packaged in micropackets (cells) 53 bytes long. Each cell has a 5-byte header that allows intelligent distribution devices to sort the cells and ensure they are transmitted in the correct sequence. Each cell has 48 bytes of information. Their minimal size allows for error correction and routing at the hardware level. It also ensures uniformity of all information flows on the network and minimal waiting time for access to the network.

The header includes identifiers for the path, delivery channel, information type, delivery priority indicator, and a header checksum to determine the presence of transmission errors.

The main disadvantage of networks using ATM technology is that they are completely incompatible with any existing network. A smooth transition to ATM is, in principle, impossible; all equipment needs to be changed at once, and its cost is still very high. True, work is underway to ensure compatibility, and the cost of equipment is also decreasing. Moreover, the tasks of transmitting images over computer networks are becoming more and more numerous.

Even in the recent past, ATM technology was considered promising and universal, capable of displacing traditional local networks. However, at the moment, due to the successful development of traditional local networks, the use of ATM is limited only to global and backbone networks.

7 WIRELESS NETWORKS

Until recently, wireless communications in local networks were practically not used. However, since the late 90s of the 20th century, there has been a real boom in wireless local networks (WLAN - Wireless LAN). This is primarily due to the advances in technology and the convenience that wireless networks can provide. According to existing forecasts, the number of wireless network users will reach 44 million in 2005, and 80% of all mobile computers will be equipped with built-in access to such networks.

In 1997, the IEEE 802.11 standard for wireless networks was adopted. Now this standard is actively developing and already includes several sections, including three local networks (802.11a, 802.11b and 802.11g). The standard contains the following specifications:

• 802.11 is the original WLAN standard. Supports data transfer speeds from 1 to 2 Mbit/s.
• 802.11a is a high-speed WLAN standard for the 5 GHz frequency. Supports data transfer speed of 54 Mbps.
• 802.11b is a WLAN standard for the 2.4 GHz frequency. Supports data transfer speed of 11 Mbps.
• 802.11e—Specifies the request quality requirements required for all IEEE WLAN radio interfaces.
• 802.11f – describes the order of communication between peer access points.
• 802.11g – establishes an additional modulation technique for the 2.4 GHz frequency. Designed to provide data transfer rates up to 54 Mbit/s.
• v802.11h – describes management of the 5 GHz spectrum for use in Europe and Asia.
• 802.11i – Fixes existing security issues in the areas of authentication and encryption protocols.

The IEEE 802.11 standard is developed and supported by the Wi-Fi Alliance committee. The term Wi-Fi (wireless fidelity) is used as a generic name for the 802.11a and 802.11b standards, as well as all subsequent wireless local area network (WLAN) standards.

Wireless network equipment includes wireless access points and wireless adapters for each subscriber.

Access points act as concentrators that provide communication between subscribers and each other, as well as the function of bridges that communicate with a cable local network and the Internet. Several nearby access points form a Wi-Fi access zone, within which all subscribers equipped with wireless adapters gain access to the network. Such access zones (Hotspots) are created in crowded places: airports, college campuses, libraries, shops, business centers, etc.

Each access point can serve several subscribers, but the more subscribers, the lower the effective transmission speed for each of them. Network access method – CSMA/CD. The network is built on a cellular principle. The network provides a roaming mechanism, that is, it supports automatic connection to an access point and switching between access points when subscribers move, although the standard does not establish strict roaming rules.

Since the radio channel does not provide a high degree of protection against eavesdropping, the Wi-Fi network uses a special built-in information protection mechanism. It includes authentication tools and procedures to prevent unauthorized access to the network and encryption to prevent the interception of information.

The IEEE 802.11b standard was adopted in 1999 and, due to its focus on the developed 2.4 GHz range, has gained the greatest popularity among equipment manufacturers. It uses the DSSS (Direct Sequence Spread Spectrum) method as its basic radio technology, which is highly resistant to data corruption, interference, including intentional interference, and detection. Because 802.11b equipment operating at a maximum speed of 11 Mbps has a shorter range than at lower speeds, the 802.11b standard provides for automatic speed reduction when signal quality deteriorates. Throughput (theoretical 11 Mbit/s, actual - from 1 to 6 Mbit/s) meets the requirements of most applications. Distances are up to 300 meters, but usually up to 160 meters.

The IEEE 802.11a standard is designed to operate in the 5 GHz frequency range. Data transfer speeds are up to 54 Mbps, that is, approximately five times faster than 802.11b networks. This is the most broadband of the 802.11 family of standards. Three mandatory speeds are defined - 6, 12 and 24 Mbit/s and five optional ones - 9, 18, 36, 48 and 54 Mbit/s. Orthogonal frequency division multiplexing (OFDM) is adopted as a signal modulation method. Its most significant difference from DSSS methods is that OFDM involves parallel transmission of the desired signal simultaneously over several frequencies in the range, while spread spectrum technologies transmit signals sequentially. As a result, channel capacity and signal quality increase. The disadvantages of 802.11a include the high power consumption of radio transmitters for 5 GHz frequencies, as well as a shorter range (about 100 m). Additionally, 802.11a devices are more expensive, but over time the price gap between 802.11b and 802.11a products will narrow.

The IEEE 802.11g standard is a new standard that governs the construction of WLANs operating in the unlicensed 2.4 GHz frequency range. Using Orthogonal Frequency Division Multiplexing (OFDM) technology, the maximum data transfer rate in IEEE 802.11g wireless networks is 54 Mbps. IEEE 802.11g-compatible equipment, such as wireless access points, allows IEEE 802.11g and IEEE 802.11b wireless devices to connect to the network simultaneously. The 802.11g standard is an evolution of 802.11b and is backward compatible with 802.11b. In theory, 802.11g has the advantages of its two predecessors. The advantages of 802.11g include low power consumption, long distances (up to 300 m) and high signal penetration.

IEEE 802.11d specification. establishes universal requirements for the physical layer (channel formation procedures, pseudo-random frequency sequences, etc.). The 802.11d standard is still under development.

The IEEE 802.11e specification will allow the creation of multi-service wireless networks for corporations and individual consumers. While maintaining full compatibility with current 802.11a and b standards, it will expand their functionality by serving streaming multimedia data and guaranteed quality of service. So far, a preliminary version of the 802.11e specifications has been approved.

The IEEE 802.11f specification describes a protocol for exchanging service information between access points (Inter-Access Point Protocol, IAPP), which is necessary for building distributed wireless data networks. Currently under development.

The IEEE 802.11h specification provides the ability to supplement existing algorithms for efficient selection of frequencies for office and street wireless networks, as well as tools for managing spectrum use, monitoring radiated power, and generating appropriate reports. Currently under development.

Manufacturers of Wi-Fi equipment include such well-known companies as Cisco Systems, Intel, Texas Instruments and Proxim.

Thus, wireless networks are very promising. Despite their shortcomings, the main one being the unprotected transmission medium, they provide simple connection of subscribers that does not require cables, mobility, flexibility and network scalability. In addition, and importantly, users are not required to have knowledge of network technologies.

CONCLUSION

Based on the progress network technologies have been able to achieve in recent years, it is not difficult to guess that in the near future the speed of data transfer over a local network will at least double. The usual ten-megabit Ethernet, which has long occupied a dominant position, at least from Russia, is being actively replaced by more modern and significantly faster data transmission technologies.

Based on the material reviewed, the following conclusions should be drawn:

1) The most widespread among standard networks is the Ethernet network. The Ethernet network is now the most popular in the world (more than 90% of the market), and presumably it will remain so in the coming years. This was greatly facilitated by the fact that from the very beginning the characteristics, parameters, and protocols of the network were open, as a result of which a huge number of manufacturers around the world began to produce Ethernet equipment that was fully compatible with each other.

2) The Token-Ring network (token ring) was proposed by IBM in 1985 (the first version appeared in 1980). Token-Ring was developed as a reliable alternative to Ethernet. And although Ethernet is now replacing all other networks, Token-Ring cannot be considered hopelessly outdated. More than 10 million computers around the world are connected by this network.

3) The Arcnet network (or ARCnet from the English Attached Resource Computer Net, a computer network of connected resources) is one of the oldest networks. Despite the lack of standards, the Arcnet network until recently (in 1980 - 1990) was popular, even seriously competing with Ethernet. A large number of companies (for example, Datapoint, Standard Microsystems, Xircom, etc.) produced equipment for this type of network. But now production of Arcnet equipment has practically ceased.

3) The FDDI network (from the English Fiber Distributed Data Interface, fiber-optic distributed data interface) is one of the latest developments in local network standards. The choice of optical fiber as a transmission medium determined such advantages of the new network as high noise immunity, maximum secrecy of information transmission and excellent galvanic isolation of subscribers. High transmission speeds, which are much easier to achieve in the case of fiber optic cables, make it possible to solve many tasks that are not possible with lower-speed networks, for example, transmitting images in real time. In addition, fiber optic cable easily solves the problem of transmitting data over a distance of several kilometers without relaying, which makes it possible to build large networks that even cover entire cities and have all the advantages of local networks (in particular, a low error rate). All this determined the popularity of the FDDI network, although it is not yet as widespread as Ethernet and Token-Ring.

4) The 100VG-AnyLAN network is one of the latest developments in high-speed local networks that has recently appeared on the market. Its main advantages are high exchange speed, relatively low cost of equipment, a centralized method of managing exchange without conflicts, as well as compatibility at the level of packet formats with Ethernet and Token-Ring networks. Thus, the 100VG-AnyLAN network provides an affordable solution for increasing transmission speeds up to 100 Mbps. However, it is not fully compatible with any of the standard networks, so its future fate is problematic. In addition, unlike the FDDI network, it does not have any record parameters. Most likely, 100VG-AnyLAN, despite the support of reputable companies and a high level of standardization, will remain just an example of interesting technical solutions.

5) Work to achieve a transmission speed of 1 Gbit/s (1000 Mbit/s) has been carried out quite intensively in recent years by several companies. However, Gigabit Ethernet is likely to be the most promising network. This is due, first of all, to the fact that the transition to it will be the most painless, cheapest and psychologically acceptable. The Gigabit Ethernet network is a natural, evolutionary development of the concept inherent in the standard Ethernet network.

6) ATM (Asynchronous Transfer Mode) technology. This technology is used in both local and global networks. The main idea is the transmission of digital, voice and multimedia data over the same channels. The fundamental difference between ATM and other networks is the abandonment of the usual packets with addressing, control and data fields. The main disadvantage of networks using ATM technology is that they are completely incompatible with any existing network. Even in the recent past, ATM technology was considered promising and universal, capable of displacing traditional local networks. However, at the moment, due to the successful development of traditional local networks, the use of ATM is limited only to global and backbone networks.

7) Until recently, wireless communications in local networks were practically not used. However, since the late 90s of the 20th century, there has been a real boom in wireless local networks (WLAN - Wireless LAN). This is primarily due to the advances in technology and the convenience that wireless networks can provide. The term Wi-Fi (wireless fidelity) is used as a common name for the 802.11a and 802.11b standards, as well as all subsequent ones related to wireless local area networks (WLAN). Thus, wireless networks are very promising. Despite their shortcomings, the main one being the unprotected transmission medium, they provide simple connection of subscribers that does not require cables, mobility, flexibility and network scalability. In addition, and importantly, users are not required to have knowledge of network technologies.

LIST OF SOURCES USED

1. Hambraken, D. Computer networks: Per. from English / D. Hambraken. - M.: DMK Press, 2004. - 448 p.

2. Guk, M. Hardware of local networks / M. Guk. - St. Petersburg: Peter, 2001. - 576 p.

3. Novikov, Yu.V. Local networks. Architecture / Yu.V. Novikov, S.V. Kondratenko.- M.: EKOM, 2000.- 312 p.

4. Novikov, Yu.V. Local network equipment: functions, selection, development / Yu.V. Novikov, D.G. Karpenko.- M.: EKOM, 1998.- 288 p.

5. Nans, B. Computer networks / B. Nans. - M.: BINOM, 1996. - 400 p.

6. Lapshinsky, A.V. Local networks of personal computers: In 2 parts / A.V. Lapshinsky.- M.: MEPhI, 1994.- 264c.

7. Frolov, A.V. Local networks of personal computers / A.V. Frolov, G.V. Frolov.- M.: DIALOG-MEPhI, 1993.- 176 p.

8. Wi-Fi Technologies [electronic resource]. - Elekron. Data.- Access mode: http: www.wi-fi.uz.- Cap. from the screen.

9. Technologies of local networks from Rurik to Gigabit [electronic resource]. - Elekron. Data.- Access mode: http: compress.ru/Archive/CP/2002/10/23.- Cap. from the screen.

In the mid-80s, the situation in local networks began to change dramatically. Standard technologies for connecting computers into a network have been established - Ethernet, Arcnet, Token Ring. Personal computers served as a powerful stimulus for their development. These commodity products were ideal elements for building networks - on the one hand, they were powerful enough to run networking software, but on the other, they clearly needed to pool their computing power to solve complex problems, as well as share expensive peripherals and disk arrays. Therefore, personal computers began to predominate in local networks, not only as client computers, but also as data storage and processing centers, that is, network servers, displacing minicomputers and mainframes from these familiar roles.

Standard network technologies have turned the process of building a local network from an art into a routine task. To create a network, it was enough to purchase network adapters of the appropriate standard, for example Ethernet, a standard cable, connect the adapters to the cable with standard connectors and install one of the popular network operating systems on the computer, for example, NetWare. After this, the network began to work and connecting each new computer did not cause any problems - naturally, if a network adapter of the same technology was installed on it.

Local networks, in comparison with global networks, have introduced a lot of new things into the way users organize their work. Access to shared resources became much more convenient - the user could simply view lists of available resources, rather than remember their identifiers or names. After connecting to a remote resource, it was possible to work with it using commands already familiar to the user from working with local resources. The consequence and at the same time the driving force of this progress was the emergence of a huge number of non-professional users who did not need to learn special (and quite complex) commands for network work. And developers of local networks received the opportunity to implement all these conveniences as a result of the emergence of high-quality cable communication lines, on which even the network adapters of the first

Practical part.

Scheme for creating local networks (at least 3 options).

Example using 3 mainframes, 5 terminals and 5 users per terminal.

Option 1 – modemless connection to the network.

2nd option - using modems.

3rd option - using CS (communication system)

Legend

Mainframe

User

Terminal

Phone line

1.Create a local network connection diagram (according to options).

2.Describe the operation of the network.

3.Answer security questions.

Control questions

Definition of LAN.

Advantages of using LAN.

Disadvantages of using a LAN.

What is Mainframe?

What is batch processing?

What is a time sharing system?

What are multi-terminal systems?

The main reasons for the emergence of global networks?

What were mini-computers based on?

The emergence of the first local computer networks?

List the main standard technologies for connecting computers into a network?

Difference between local and wide area networks?

Exercise

	Mainframe	Terminal	Users

data can be exchanged. When the connection is broken, the station initiating the break sends a corresponding notification to the other party.

Datagram protocols provide services for unreliable data delivery. The data is sent without warning and the protocol is not responsible for its delivery.

Datagram protocols work quite quickly because... does not perform any action when sending data.

Data transfer at the physical level

There are two methods of transmitting information: 1. Analogue modulation 2. Digital coding

Analog modulation – used when transmitting data over telephone lines (narrowband communication channels). The signal has a sinusoidal shape. Three methods are used to encode information:

Amplitude modulation, i.e. change in carrier frequency signal amplitude

Frequency modulation, i.e. change in signal frequency

Phase modulation, i.e. signal phase change

Digital coding is a method of representing information in the form of rectangular pulses. There are two methods of digital encoding:

Potential coding - only the potential values ​​of the signal are used to represent zeros and ones, and its edges are ignored.

Pulse coding – allows you to represent data by a potential difference in a certain direction.

Literature:

Topic 4. Local network technologies

Questions to study:

IEEE 802 standards

Ethernet technology

Token Ring Technology

FDDI technology

IEEE 802 standards

In 1980 The IEEE Institute organized Committee 802 whose goal was to develop local network standards. These standards describe the functioning of local networks at the physical and data link levels. The link layer is divided into two sublayers: the logical link layer (Logical Link Layer, LLC) and the media access control layer (MAC).

The MAC layer synchronizes access to the shared media and determines at what point in time a station can begin transmitting available data.

Once access to the medium is obtained, data is transferred in accordance with the standards that are defined at the LLC level. The LLC layer is responsible for communicating with the network layer and also transmits data with a specified degree of reliability.

At the LLC level, three data transfer procedures are used:

1. LLC1 – data transmission with connection establishment and confirmation

2. LLC2 – data transfer without connection establishment and confirmation

3. LLC3 – data transmission without establishing a connection, but with confirmation of data receipt.

The LLC and MAC protocols are mutually independent - each MAC layer protocol can be used with any LLC layer protocol and vice versa.

The 802.1 standard describes the general concepts of local networks, defines the connection of the three levels of 802 standards with the seven-level model, as well as standards for building complex networks based on basic topologies (internetworking). These standards include standards describing the functioning of a bridge/switch, standards for connecting heterogeneous networks using a broadcast bridge, and standards for constructing virtual networks (VLANs) based on switches.

Ethernet technology

The term Ethernet refers to a family of local area network protocols that are described by the IEEE 802.3 standard and use the CSMA/CD media access method.

Currently, there are three main types of technology that operate on the basis of fiber optic cables or unshielded twisted pair:

1. 10 Mbps - 10Base-T Ethernet

2. 100 Mbps - Fast Ethernet

3. 1000 Mbps - Gigabit Ethernet

10-Mbit Ethernet includes three physical layer standards:

1. 10Base – 5 (“Thick” coaxial) – uses a coaxial cable with a diameter of 0.5 inches, a characteristic impedance of 50 Ohms, as a transmission medium. The maximum length of a segment without repeaters is 500m. No more than 100 transceivers can be connected to one segment. When constructing a network, the rule is used“3-4-5” (3 “loaded” segments, 4 repeaters, no more than 5 segments). The repeater is connected using a transceiver, i.e. there can be no more than 297 nodes in the network. In order to prevent the occurrence of reflected signals, terminators with a resistance of 50 Ohms are used.

2. 10 Base – 2 (“Thin” coaxial) – uses a coaxial cable with a diameter of 0.25 inches, a characteristic impedance of 50 Ohms, as a transmission medium. The maximum length of a segment without repeaters is 185m. No more than 30 nodes can be connected to one segment. When building a network, the “3-4-5” rule is used (3 “loaded” segments, 4 repeaters, no more than 5 segments). In order to prevent the occurrence of reflected signals, terminators with a resistance of 50 Ohms are used.

3. 10 Base – T (Unshielded twisted pair) – two unshielded twisted pairs are used as the transmission medium, the nodes are connected to a hub and

form a star topology. The distance from the repeater to the station is no more than 100 meters for cable category not lower than 3. Hubs can be connected to each other, increasing the length of the logical network segment (collision domain). When building a network, the rule of 4 hubs is used (between any two network nodes there should be no more than 4 repeaters), the number of nodes in the network should not exceed 1024.

100 - megabit Ethernet (Fast Ethernet) includes the following specifications:

1. 100Base – TX. The data transmission medium is unshielded twisted pair cable of category no lower than 5. The auto-sensing function is supported. Full duplex operation possible.

2. 100Base – FX Uses multimode fiber.

3. 100Base – T4 Uses 4 twisted pairs to transmit data over Category 3 cable. Does not support full duplex data transmission.

100 Mbit Ethernet networks use repeaters of two classes (I and II). Class I repeaters can connect channels meeting different requirements, such as 100Base-TX and 100Base-T4 or 100Base-FX. Only one Class I repeater can be used within one logical segment. These repeaters often have built-in management capabilities using the SNMP protocol.

Class II repeaters do not perform signal conversion and can only combine segments of the same type. A logical segment can contain no more than two Class II repeaters.

When building a network, the following restrictions must be taken into account:

All twisted pair segments must not exceed 100 m. Fiber optic segments must not exceed 412 m. The distance between Class II hubs must not exceed 5 m.

1000 – megabit (Gigabit) Ethernet is described by the following standards:

IEEE 802.3z(1000Base-TX, 1000Base-LX, 1000Base-SX)

IEEE 802.3ab(1000Base-T)

1000Base-TX: transmission medium – shielded copper cable up to 25m long. 1000Base-LX: transmission medium – single-mode optical fiber, length up to 5000m. 1000Base-CX: transmission medium – multimode optical fiber, length up to 550m. 1000Base-T: transmission medium – UTP CAT5/CAT5e, segment length up to 100m.

When designing Ethernet networks, the requirement for correct collision detection must always be met. To do this, the transmission time of a frame of minimum length must exceed or be equal to the size of the time interval during which the frame will travel twice the distance between the two most distant network nodes.

Token Ring Technology

It was developed by IBM in 1984. The topology of the Token Ring network is a ring where all stations are connected by cable sections. The method of accessing the network is token. The right to transmit data is obtained by the station that has taken possession of the marker - a frame of a special format. The period of time during which a station can transmit is determined by the token holding time.

Data is transmitted at two speeds – 4 and 16 Mbit/s. Operation at different speeds in one ring is not allowed. To monitor the state of the network, one of the stations is selected to act as an active monitor when the ring is initialized.

IN Token Ring network with a transmission speed of 4 Mbit, a station transmits a data frame, which is transmitted in a circle by all stations until it is received by the destination station. The receiving station copies the frame to its buffer, sets a sign that the frame was successfully received, and transmits it further along the ring. The station that sends the frame removes the frame from the network, and if the token holding time has not expired, it transmits the next data frame. At one point in time, either a token or a data frame is present on the network.

IN Token Ring network with a transmission speed of 16 Mbit uses an early token release algorithm. Its essence lies in the fact that the station, which transmitted its data frame, then transmits the marker frame without waiting for the data frame to return along the ring. In this case, data and token frames simultaneously circulate around the ring, but only the station that has captured the token can transmit data.

For different types of messages, frames can be assigned different priorities

– from 0 to 7. The marker frame has two fields in which the current and reserved priority values ​​are written. A station can only acquire a token if its data priority value is greater than or equal to the token's priority value. Otherwise, it can write the priority value of its data into the reserved priority field of the token, reserving it for itself during the next pass (if this field is not already reserved for data with a higher priority level). A station that manages to acquire a token, after completing its data transmission, overwrites the bits of the reserve priority field in the priority field of the token and resets the reserve priority field. The priority mechanism is used only when required by applications.

At the physical level, nodes in the Token Ring network are connected using multiple access devices (MSAU - Multistation Access Unit), which are connected by pieces of cable and form a ring. All stations in the ring operate at the same speed. The maximum length of the ring is 4000m.

FDDI technology

Fiber Distributed Data Interface – Fiber optic distributed data interface, developed by ANSI from 1986 to 1988. It is the first local network technology to use fiber optics. To increase reliability, FDDI is built on the basis of two fiber optic rings, which form the main and backup data paths. To ensure reliability, the nodes are connected to both rings. During normal operation, data flows only through the primary ring. If a failure occurs and part of the primary ring cannot transmit data, then the ring folding operation is performed - that is, merging the primary ring with the secondary one and forming a single ring.

FDDI networks use a token-based media access method that operates based on an early release token algorithm. FDDI technology supports the transmission of two types of traffic – synchronous (sound, video) and asynchronous (data). The data type is determined by the station. A token can always be captured for a certain time interval to transmit synchronous frames, and only in the absence of ring overloads - to transmit an asynchronous frame.

The maximum number of stations with dual connections in the ring is 500, the maximum length of the ring is 100 km. The maximum distance between two neighboring nodes is 2 km.

Computer networks are divided into three main classes:

1. Local computer networks (LAN – LocalAreaNetwork) are networks that connect computers located geographically in one place. A local network unites computers located physically close to each other (in the same room or building).

2. Regional computer networks (MAN - MetropolitanAreaNetwork) are networks that connect several local computer networks located within the same territory (city, region or region, for example, the Far East).

3. Wide Area Networks (WAN - WideAreaNetwork) are networks that unite many local, regional networks and

computers of individual users located at any distance from each other (Internet, FIDO).

Currently, the following standards for building local area networks are used:

Arcnet;(IEEE 802.4)

Token Ring;(802.5)

Ethernet.(802.3)

Let's look at each of them in more detail.

IEEE 802.4 ARCNET technology (or ARCnet, from the English Attached Resource Computer NETwork) is a LAN technology, the purpose of which is similar to the purpose of Ethernet or Token ring. ARCNET was the first technology for creating networks of microcomputers and became very popular in the 1980s for enterprise automation. Designed for organizing a LAN in a “star” network topology.

The basis of communication equipment is:

switch

passive/active hub

Switching equipment has an advantage, as it allows the formation of network domains. Active hubs are used when the workstation is far away (they restore the signal shape and amplify it). Passive - when small. The network uses an assigned access principle for workstations, that is, the station that has received the so-called software token from the server has the right to transmit. That is, deterministic network traffic is implemented.

Advantages of the approach:

Notes: Messages sent by workstations form a queue on the server. If the queue service time significantly (more than 2 times) exceeds the maximum packet delivery time between the two most remote stations, then it is considered that the network capacity has reached the maximum limit. In this case, further expansion of the network is impossible and the installation of a second server is required.

Limit technical characteristics:

The minimum distance between workstations connected to the same cable is 0.9 m.

The maximum network length along the longest route is 6 km.

Limitations are associated with hardware delay in information transmission with a large number of switching elements.

The maximum distance between the passive hub and the workstation is 30 m.

The maximum distance between the active and passive hub is 30 m.

Between active hub and active hub - 600 m.

Advantages:

Low cost of network equipment and the ability to create extended networks.

Flaws:

Low data transfer speed. Following the spread of Ethernet as a LAN technology, ARCNET found application in embedded systems.

The non-profit organization ARCNET Trade Association (ATA) is engaged in support of ARCNET technology (in particular, the distribution of specifications).

Technology - The ArcNET architecture is represented by two main topologies: bus and star. The transmission medium is RG-62 coaxial cable with a characteristic impedance of 93 Ohms, crimped onto BNC plugs with the appropriate termination diameter (different from 10Base-2 (“thin” Ethernet) plugs).

Network equipment consists of network adapters and hubs. Network adapters can be for bus topology, for star topology and universal. Hubs can be active or passive. Passive hubs are used to create star sections of the network. Active hubs can be for bus, star and mixed topologies. The ports for the bus topology are not physically compatible with the ports for the star topology, although they have the same physical connection (BNC socket).

In the case of a bus topology, workstations and servers are connected to each other using T-connectors (the same as in 10Base-2 (“thin” Ethernet) connected to network adapters and hubs and connected by coaxial cable. The extreme points of the segment are terminated with tips with a resistance of 93 Ohms. The number of devices on one bus is limited. The minimum distance between connectors is 0.9 meters and must be a multiple of this value. To facilitate cutting, marks can be applied to the cable. Individual buses can be combined using bus hubs.

When using a star topology, active and passive hubs are used. The passive hub is a resistive divider-matcher that allows you to connect four cables. All cables in this

In this case, they are connected on a point-to-point basis, without forming buses. There should not be more than two passive hubs connected between two active devices. The minimum length of any network cable is 0.9 meters and must be a multiple of this value. There is a limitation on the cable length between active and passive ports, between two passive ports, and between two active ports.

With a mixed topology, active hubs are used that support both types of connections.

On network adapters of workstations and servers, using jumpers or DIP switches, a unique network address is set, permission to use a BIOS expansion chip that allows remote boot of the workstation (can be diskless), connection type (bus or star topology), connection of a built-in terminator ( the last two points are optional). The limit on the number of workstations is 255 (according to the width of the network address register). If two devices have the same network address, both lose their functionality, but this collision does not affect the operation of the network as a whole.

In a bus topology, a broken cable or terminator leads to network inoperability for all devices connected to the segment that includes this cable (that is, from terminator to terminator). With a star topology, a break in any cable leads to the failure of the segment that is disconnected from the file server by this cable.

The logical architecture of ArcNET is a token ring. Since this architecture, in principle, does not allow collisions, with a relatively large number of hosts (in practice, 25-30 workstations were tested), the performance of the ArcNET network turned out to be higher than 10Base-2, with a four times lower speed in the environment (2.5 versus 10 Mbit/s ).

802.5 Token Ring technology is a local area network (LAN) ring technology with “token access” - a local network protocol that is located at the data link layer (DLL) of the OSI model. It uses a special three-byte frame called a marker that moves around the ring. Possession of a marker gives the owner the right to transmit information on the medium. Token ring network frames travel in a loop. Stations on a Token ring local area network (LAN) are logically organized in a ring topology with data transferred sequentially from one ring station to another with a control token circulating around the control access ring. This token passing mechanism is shared by ARCNET, the token bus, and FDDI, and has theoretical advantages over stochastic CSMA/CD Ethernet.

Token passing Token ring and IEEE 802.5 are prime examples of token passing networks. Token passing networks move a small block of data called a token along the network. Possession of this token guarantees the right to transfer. If the node receiving the token does not have information to send, it simply forwards the token to the next endpoint. Each station can hold a marker for a certain maximum time (default - 10 ms).

This technology offers a solution to the problem of collisions that arise when operating a local network. In Ethernet technology, such collisions occur when information is simultaneously transmitted by several workstations located within the same segment, that is, using a common physical data channel.

If the station that owns the token has information to transmit, it captures the token, changes one bit of it (resulting in the token becoming a "beginning of data block" sequence), completes it with the information it wants to transmit, and sends that information to the next station ring network. When a block of information circulates around the ring, there is no token on the network (unless the ring provides early token release), so other stations wishing to transmit information are forced to wait. Therefore, there can be no collisions in Token Ring networks. If early token release is ensured, then a new token can be released after the transmission of the data block is completed.

The information block circulates around the ring until it reaches the intended destination station, which copies the information for further processing. The information block continues to circulate around the ring; it is permanently deleted after reaching the station that sent the block. The sending station can check the returned block to ensure that it was viewed and then copied by the destination station.

Scope of Application Unlike CSMA/CD networks (eg Ethernet), token passing networks are deterministic networks. This means that it is possible to calculate the maximum time that will pass before any end station can transmit. This characteristic, as well as some reliability characteristics, make the Token Ring network ideal for applications where latency must be predictable and network stability is important. Examples of such applications are the environment of automated stations in factories.

It is used as a cheaper technology and has become widespread wherever there are critical applications for which it is not so much speed that is important as reliable delivery of information. Currently, Ethernet is not inferior to Token Ring in reliability and is significantly higher in performance.

Modifications of Token Ring There are 2 modifications for transmission speeds: 4 Mbit/s and 16 Mbit/s. Token Ring uses 16 Mbps

early marker release technology. The essence of this technology is that a station that has “captured” a token, upon completion of data transmission, generates a free token and launches it into the network. Attempts to introduce 100 Mbit/s technology were not crowned with commercial success. Token Ring technology is not currently supported.

Technology 802.3 Ethernet from English. ether “ether”) is a packet technology for transmitting data primarily on local computer networks.

Ethernet standards define wire connections and electrical signals at the physical layer, frame formats and media access control protocols at the data link layer of the OSI model. Ethernet is primarily described by IEEE group 802.3 standards. Ethernet became the most common LAN technology in the mid-1990s, displacing legacy technologies such as Arcnet, FDDI and Token ring.

When performing work on creating a local network, you need to consider the following:

* Creating a local network and setting up equipment for access to the Internet;

* The choice of equipment should be based on technical characteristics that can meet the requirements for data transfer speed;

* The equipment must be safe, protected from electric shock to people;

* Each workstation must have a network cable to connect to the network;

* Possible availability of wi-fi throughout the office;

* The location of workplaces must meet the requirements of equipment placement standards in educational institutions;

* The costs of creating a local network must be economically justified;

* Local network reliability.