Topic 17 network technologies url structure. Computer networking technologies

In order to understand how it works the local network , it is necessary to understand such a concept as network technology.

Networking technology consists of two components: the network protocols and the hardware that powers these protocols. Protocol in turn is a set of "rules" by which computers on the network can connect to each other and exchange information. Through network technologies we have the Internet, there is a local connection between the computers in your home. Yet network technologies called basic, but also have another nice name - network architectures.

Network architectures define several network parameters, about which you need to have a little knowledge in order to understand the device of the local network:

1) Data transfer rate. Determines how much information, usually measured in bits, can be transmitted over the network in a given time.

2) Format of network frames. Information transmitted over the network exists in the form of so-called "frames" - information packets. Network frames in different network technologies have different formats of transmitted information packets.

3) Type of signal coding. Determines how information is encoded in the network using electrical impulses.

4) Transmission medium. This is the material (usually a cable) through which the flow of information passes - the one that is ultimately displayed on the screens of our monitors.

5) Network topology. This is a diagram of a network that has "ribs" representing cables and "tops" - the computers to which these cables run. There are three main types of network schemes: ring, bus and star.

6) Method of access to data transmission medium. Three methods of accessing the network environment are used: deterministic method, random access method, and priority transmission. The most common is the deterministic method, in which, using a special algorithm, the time of using the transmission medium is divided between all computers in the environment. In the case of a random network access method, computers compete to access the network. This method has several disadvantages. One of these disadvantages is the loss of part of the transmitted information due to the collision of information packets in the network. Priority access provides respectively the largest amount of information to the established priority station.

The set of these parameters determines network technology.

Networking technology is now widespread IEEE802.3 / Ethernet... It has become widespread thanks to simple and inexpensive technologies. Also popular due to the fact that the maintenance of such networks is easier. The topology of Ethernet networks is usually built in the form of a "star" or "bus". The transmission medium in such networks uses both thin and thick coaxial cables, and twisted pairs and fiber optic cables... Ethernet networks typically range in length from 100 to 2000 meters. The data transfer rate in such networks is usually about 10 Mbps. Ethernet networks typically use the CSMA / CD access method, which refers to decentralized random access methods.

There are also high speed network options Ethernet: IEEE802.3u / Fast Ethernet and IEEE802.3z / Gigabit Ethernetproviding data transfer rates up to 100 Mbps and up to 1000 Mbps, respectively. In these networks, the transmission medium is mainly optical fiberor shielded twisted pair.

There are also less common but ubiquitous networking technologies.

Network technology IEEE802.5 / Token-Ring is characterized by the fact that all vertices or nodes (computers) in such a network are united in a ring, use a marker method of accessing the network, support shielded and unshielded twisted pair, and optical fiber as a transmission medium. Token-Ring speed up to 16 Mbps. The maximum number of nodes in such a ring is 260, and the length of the entire network can reach 4000 meters.

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The local network IEEE802.4 / ArcNet it is special in that it uses the access method to transfer data using the transfer of authority. This network is one of the oldest and previously popular in the world. This popularity is due to the reliability and low cost of the network. Nowadays, such a network technology is less common, since the speed in such a network is quite low - about 2.5 Mbps. Like most other networks, shielded and unshielded twisted pairs and fiber optic cables are used as the transmission medium, which can form a network up to 6000 meters long and include up to 255 subscribers.

Network architecture FDDI (Fiber Distributed Data Interface), based on IEEE802.4 / ArcNet and is very popular due to its high reliability. Such networking technology includes two fiber optic rings, up to 100 km long. At the same time, a high speed of data transfer in the network is provided - about 100 Mbps. The point of creating two fiber-optic rings is that a path with backup data passes through one of the rings. Thus, the chance of losing the transmitted information is reduced. Such a network can contain up to 500 subscribers, which is also an advantage over other network technologies.

Network technologies

Network technology is a consistent set of standard protocols and software and hardware that implement them, sufficient for building computer networks.

Protocol - ϶ᴛᴏ a set of rules and conventions that determine how devices exchange data on the network.

Today the following network technologies dominate: Ethernet, Token Ring, FDDI, ATM.

Ethernet technology

Ethernet technology was created by XEROX in 1973. The basic principle behind Ethernet is a random access method to a shared data transmission medium (multiple access method).

The logical topology of an Ethernet network is always bus-based; therefore, data is transmitted to all nodes of the network. Each node sees each transmission and distinguishes the data intended for it by the address of its network adapter. At a time, only one node can successfully transfer, in this regard, there must be some agreement between the nodes on how to use the same cable together so as not to interfere with each other. This agreement defines the Ethernet standard.

As the load on the network grows, it becomes increasingly important to transfer data at the same time. When this happens, the two transmissions collide, filling the bus with garbage. This behavior is known by the term "collision", that is, the occurrence of a conflict.

Each transmission system, upon detecting a collision, immediately stops sending data, and action is taken to remedy the situation.

Although most collisions that occur on a typical Ethernet network are resolved within microseconds and their occurrence is natural and expected, the main disadvantage is in fact that the more traffic on the network, the more collisions, the sharply the network performance decreases and a collapse may occur, that is, the network is clogged with traffic.

Traffic - message flow in the data transmission network.

Token Ring technology

Token Ring technology was developed by IBM in 1984. Token Ring technology uses a completely different access method. The logical token ring network has a ring topology. A special message known as a Token is a special three-byte packet that is constantly circulating around the logical ring in one direction. When the token passes through a node ready to transmit data to the network, it grabs the token, attaches the data to be sent to it, and then transmits the message back to the ring. The message continues its “journey” around the loop until it reaches its destination. Until the message is received, no node will be able to forward data. This access method is known as token passing. It eliminates collisions and arbitrary latencies like Ethernet.

FDDI technology

Fiber Distributed Data Interface (FDDI) technology is the first local area network technology in which the data transmission medium is fiber optic cable. FDDI technology is largely based on Token Ring technology, developing and improving its basic ideas. The FDDI network is built on the basis of two fiber-optic rings, which form the main and backup data transmission paths between the network nodes. Having two rings is the primary way to improve resiliency in an FDDI network, and nodes that want to take advantage of this increased reliability potential must be connected to both rings.

In normal network operation, data passes through all nodes and all cable sections of the primary ring only; the secondary ring is not used in this mode. In the event of some type of failure, when part of the primary ring cannot transmit data (for example, a cable break or a node failure), the primary ring merges with the secondary, again forming a single ring.

Rings in FDDI networks are considered as a general data transmission medium; therefore, a special access method is defined for it, which is very close to the access method of Token Ring networks. The difference is essentially that the token retention time in the FDDI network is not constant, as in Token Ring. It depends on the load on the ring - with a small load it increases, and with large overloads it can decrease to zero for asynchronous traffic. It is important to note that for synchronous traffic, the token retention time remains a fixed value.

ATM technology

ATM (Asynchronous Transfer Mode) is the most advanced network technology. It is designed to transmit voice, data and video using a high-speed, connection-oriented, cell-switched protocol.

Unlike other technologies, ATM traffic is divided into 53 - byte cells (cells). Applying a predefined size data structure makes network traffic easier to quantify, predict, and manage. ATM is based on the transmission of information over a fiber optic cable using a star topology.

Network technologies - concept and types. Classification and features of the category "Network technologies" 2017, 2018.

Today, networks and networking technologies connect people all over the world and provide them with access to the greatest luxury in the world - human communication. People communicate and play without interference with friends located in other parts of the world.

The events taking place become known in all countries of the world in a matter of seconds. Everyone is able to connect to the Internet and upload their portion of information.

Network information technologies: the roots of their origin

In the second half of the last century, human civilization formed two of its most important scientific and technical industries - computer and For about a quarter of a century, both of these industries developed independently, and within their framework, respectively, computer and telecommunication networks were created. However, in the last quarter of the twentieth century, as a result of the evolution and interpenetration of these two branches of human knowledge, what we call the term "network technology", which is a subsection of the more general concept of "information technology", arose.

As a result of their appearance, a new technological revolution took place in the world. Just as a few decades before it, the land surface was covered with a network of high-speed highways, at the end of the last century all countries, cities and villages, enterprises and organizations, as well as individual dwellings, were connected by "information highways." At the same time, they all became elements of various data transmission networks between computers, in which certain information transfer technologies were implemented.

Network technology: concept and content

Network technology is sufficient for building a certain integral set of rules for the presentation and transmission of information, implemented in the form of so-called "standard protocols", as well as hardware and software, including network adapters with drivers, cables and fiber-optic lines, various connectors (connectors).

"Sufficiency" of this complex of means means its minimization while maintaining the possibility of building a workable network. It should have potential for improvement, for example, by creating subnets in it, requiring the use of protocols of different levels, as well as special communicators, usually called "routers". Once improved, the network becomes more reliable and faster, but at the cost of add-ons over the underlying network technology that forms its basis.

The term "network technology" is most often used in the above-described narrow sense, however, it is often interpreted in a broader way as any set of tools and rules for building networks of a certain type, for example, "technology of local computer networks".

Network technology prototype

The first prototype of a computer network, but not yet the network itself, was in the 60s and 80s. last century multi-terminal systems. Being a set of monitor and keyboard located at great distances from large computers and connected to them by means of telephone modems or through dedicated channels, the terminals left the premises of the ITC and were dispersed throughout the building.

At the same time, except for the operator of the computer itself at the ITC, all terminal users had the opportunity to enter their tasks from the keyboard and observe their execution on the monitor, carrying out some task control operations. Such systems that implement both time-sharing and batch processing algorithms were called remote job entry systems.

Global networks

Following multi-terminal systems in the late 60s. XX century. the first type of networks was created - global computer networks (GKS). They connected supercomputers, which existed in single copies and stored unique data and software, with mainframes, located from them at distances of many thousands of kilometers, through telephone networks and modems. This networking technology has previously been tested in multi-terminal systems.

The first GCS in 1969 was ARPANET, which worked in the US Department of Defense and combined different types of computers with different operating systems. They were equipped with additional modules for the implementation of communication common to all computers included in the network. It was on it that the foundations of network technologies were developed, which are still used today.

First example of convergence of computer and telecommunication networks

GKS inherited communication lines from older and more global networks - telephone, since it was very expensive to lay new long-distance lines. Therefore, for many years they used analog telephone channels to transmit only one conversation at a time. Digital data was transmitted over them at a very low speed (tens of kbps), and the possibilities were limited to the transfer of data files and e-mail.

However, having inherited telephone lines communications, the GKS did not take their main technology based on the principle of channel switching, when each pair of subscribers was assigned a channel with a constant speed for the entire duration of the communication session. The GKS used new computer network technologies based on the principle of packet switching, in which data in the form of small portions of packets at a constant rate are sent to an unswitched network and received by their addressees in the network using address codes embedded in the packet headers.

The predecessors of local networks

Appearance in the late 70s. XX century. BIS led to the creation of a mini-computer with low cost and rich functionality... They began to really compete with mainframes.

Minicomputers of the PDP-11 family gained wide popularity. They began to be installed in all, even very small production units for managing technological processes and individual technological units, as well as in enterprise management departments for performing office tasks.

The concept of computer resources distributed throughout the enterprise emerged, although all minicomputers were still operating autonomously.

The emergence of LAN networks

By the mid-80s. XX century. technologies for combining mini-computers in networks based on data packet switching were introduced, as in the GKS.

They made building a single enterprise network, called a local area network (LAN), an almost trivial task. To create it, you just need to buy network adapters for the selected LAN technology, for example, Ethernet, a standard cabling system, install connectors (connectors) on its cables and connect the adapters to the mini-computer and to each other using these cables. Then one of the OS was installed on the computer-server, intended for organizing a LAN - network. After that, she began to work, and the subsequent connection of each new mini-computer did not cause any problems.

The inevitability of the Internet

If the appearance of mini-computers made it possible to distribute computer resources evenly over the territories of enterprises, then the appearance in the early 90s. The PC determined their gradual appearance, first at every workplace of any knowledge worker, and then in individual human dwellings.

The relative cheapness and high reliability of PCs first gave a powerful impetus to the development of LAN-networks, and then led to the emergence of a global computer network - the Internet, which now swept all countries of the world.

The size of the Internet is growing by 7-10% every month. It is the core that connects various local and global networks of enterprises and institutions around the world with each other.

If at the first stage, data files and messages were mainly transmitted via the Internet email, then today it provides mainly remote access to distributed information resources and electronic archives, to commercial and non-commercial information services in many countries. Its free access archives contain information on almost all areas of human knowledge and activity - from new directions in science to weather forecasts.

Basic networking technologies of LAN networks

Among them, the basic technologies are distinguished, on which the basis of any particular network can be built. Examples include such well-known LAN technologies as Ethernet (1980), Token Ring (1985), and FDDI (late 1980s).

In the late 90s. Ethernet technology emerged as the leader in LAN technology, combining its classic version with up to 10 Mbps, as well as Fast Ethernet (up to 100 Mbps) and Gigabit Ethernet (up to 1000 Mbps). All Ethernet technologies have similar operating principles that simplify their maintenance and interconnection of LAN-networks built on their basis.

In the same period, their developers began to integrate network functions into the kernels of almost all computer operating systems that implement the above network information technologies. There are even specialized communications operating systems like IOS from Cisco Systems.

How GCS technologies evolved

GKS technologies on analog telephone channels, due to the high level of distortion in them, were distinguished by complex algorithms for monitoring and recovering data. An example of them is the X.25 technology developed in the early 70s. XX century. More modern network technologies are frame relay, ISDN, ATM.

ISDN is an abbreviation for Integrated Services Digital Network, which allows remote video conferencing. Remote access is provided by installing ISDN adapters in the PC, which work many times faster than any modems. There is also special software that allows popular operating systems and browsers to work with ISDN. But the high cost of equipment and the need to lay special communication lines slow down the development of this technology.

WAN technologies have progressed with telephone networks... After the advent of digital telephony, the Plesiochronous Digital Hierarchy (PDH) technology was developed, which supports speeds up to 140 Mbps and is used by enterprises to create their own networks.

New Synchronous Digital Hierarchy (SDH) technology in the late 1980s. XX century. expanded throughput digital telephone channels up to 10 Gbit / s, and Dense Wave Division Multiplexing (DWDM) technology - up to hundreds of Gbit / s and even up to several Tbit / s.

Internet technologies

Web sites are based on the use of the hypertext language (or HTML-language) - a special markup language that is an ordered set of attributes (tags) that are previously introduced by the developers of Internet sites into each page. Of course, in this case, we are not talking about text or graphic documents (photographs, pictures) that have already been "downloaded" by the user from the Internet, are in the memory of his PC and viewed through text or We are talking about the so-called web pages viewed through programs -browsers.

Developers of Internet sites create them in HTML (many tools and technologies for this work have now been created, collectively called "layout of sites") in the form of a set of web pages, and site owners place them on Internet servers on lease terms from the owners of their memory servers (so-called "hosting"). They work around the clock on the Internet, serving the requests of its users to view the web pages loaded in them.

Browsers of user PCs, having gained access to a specific server through the server of their Internet provider, the address of which is contained in the name of the requested Internet site, gain access to this site. Further, by analyzing the HTML tags of each viewed page, browsers form its image on the monitor screen in the form as it was intended by the site developer - with all headers, font and background colors, various inserts in the form of photos, diagrams, pictures, etc. ...

Network technology is a consistent set of standard protocols and software and hardware that implement them, sufficient for building computer networks.

Protocol Is a set of rules and conventions that govern how devices on a network exchange data.

Currently the following network technologies dominate: Ethernet, Token Ring, FDDI, ATM.

Ethernet technology

Ethernet technology was created by XEROX in 1973. The basic principle behind Ethernet is a random access method to a shared data transmission medium (multiple access method).

The logical topology of an Ethernet network is always bus-based, so data is transmitted to all nodes in the network. Each node sees each transmission and distinguishes the data intended for it by the address of its network adapter. At a time, only one node can make a successful transfer, so there must be some agreement between the nodes on how to use the same cable together so as not to interfere with each other. This agreement defines the Ethernet standard.

As the network load grows, it becomes more and more necessary to transfer data at the same time. When this happens, the two transmissions collide, filling the bus with garbage. This behavior is known by the term "collision", that is, the occurrence of a conflict.

Each transmission system, upon detecting a collision, immediately stops sending data, and action is taken to remedy the situation.

Although most collisions that occur on a typical Ethernet network are resolved within microseconds and their occurrence is natural and expected, but the main drawback is that the more traffic on the network, the more collisions, the more dramatically the network performance drops and a collapse can occur. that is, the network is clogged with traffic.

Traffic - message flow in the data transmission network.

Token Ring technology

Token Ring technology was developed by IBM in 1984. Token Ring technology uses a completely different access method. The logical token ring network has a ring topology. A special message known as a Token is a special three-byte packet that is constantly circulating around a logical ring in one direction. When the token passes through a node ready to transmit data to the network, it grabs the token, attaches the data to be sent to it, and then transmits the message back to the ring. The message continues its "journey" around the ring until it reaches its destination. Until the message is received, no node will be able to forward data. This access method is known as token passing. It eliminates collisions and arbitrary latencies like Ethernet.

FDDI technology

Fiber Distributed Data Interface (FDDI) technology is the first local area network technology, in which the data transmission medium is a fiber optic cable. FDDI technology is largely based on Token Ring technology, developing and improving its basic ideas. The FDDI network is built on the basis of two fiber-optic rings, which form the main and backup data transmission paths between the network nodes. Having two rings is the primary way to improve resiliency in an FDDI network, and nodes that want to take advantage of this increased reliability potential must be connected to both rings.

In normal network operation, data passes through all nodes and all cable sections of the primary ring only, the secondary ring is not used in this mode. In the event of some form of failure, where part of the primary ring cannot transmit data (for example, a cable break or node failure), the primary ring is combined with the secondary, again forming a single ring.

Rings in FDDI networks are considered as a general data transmission medium, therefore a special access method is defined for it, which is very close to the access method of Token Ring networks. The difference is that the token retention time in the FDDI network is not constant, as in Token Ring. It depends on the load on the ring - with a small load it increases, and with large overloads it can decrease to zero for asynchronous traffic. For synchronous traffic, the token hold time remains a fixed value.

ATM technology

ATM (Asynchronous Transfer Mode) is the most advanced network technology. It is designed to transmit voice, data and video using a high-speed, connection-oriented cell-switched protocol.

Unlike other technologies, ATM traffic is divided into 53 - byte cells (cells). Using a predefined size data structure makes network traffic more easily quantifiable, predictable, and manageable. ATM is based on the transmission of information over a fiber optic cable using a star topology.

Modern network technologies

Plan

What is a local area network?

Computer network hardware. Local area network topologies

Physical topologies of local area networks

Logical topologies of local area networks

Connectors and connectors

Coaxial cable

Twisted pair

Information transmission over fiber optic cables

Communication hardware

Hardware and technologies of wireless networks

Technologies and protocols of local area networks

Addressing computers on the network and basic network protocols

Network facilities operating systems MS Windows

Network Resource Management Concepts

Possibilities of MS Windows OS for organizing work in a local network

Configuring network component parameters

Setting connection parameters

Connecting a network printer

Connection network drive

What is a local area network?

The problem of transferring information from one computer to another has existed since the advent of computers. Various approaches were used to solve it. The most common, in the recent past, "courier" approach was to copy information onto removable media (CDM, CD, etc.), transfer to the destination and copy it again, but from the removable media to the recipient's computer. Currently, such methods of moving information are giving way to network technologies. Those. computers are somehow connected to each other, and the user has the ability to transfer information to the destination without leaving the table.

The set of computer devices that have the ability to communicate with each other for information is commonly called a computer network. In most cases, two types of computer networks are distinguished: local (LAN - LocalAreaNetwork) and global (WAN - Wide-AreaNetwork). In some variants of the classification, a number of additional types are considered: urban, regional, etc., however, all these types (in essence) in most cases are variants of global networks of various scales. The most common variant of classifying networks into local and global by geography. Those. a local area network in this case means a set of a finite number of computers located in a limited area (within one building or neighboring buildings), connected by information channels with high speed and reliability of data transmission and designed to solve a set of interrelated problems.

Computer network hardware. Local area network topologies

All computers of subscribers (users) operating within the local computer network must be able to interact with each other, i.e. to be related. The way such connections are organized significantly affects the characteristics of a local area network and is called its topology (architecture, configuration). There are physical and logical topologies. The physical topology of a local area network is understood as the physical location of the computers that make up the network and the way they are connected to each other by conductors. The logical topology determines the way information flows and very often does not coincide with the selected physical topology of the local area network subscribers' connection.

Physical topologies of local area networks

There are four main physical topologies used in the construction of local area networks.

The bus topology (Figure 1) assumes that all computers are connected to one common conductor. Special matching devices called terminators are placed at both ends of such a conductor. The main advantages of this topology are low cost and ease of installation. The disadvantages include the problematic localization of the fault and low reliability: damage to the cable anywhere leads to the termination of the exchange of information between all computers in the network. Due to the peculiarities of the propagation of the electrical signal, even if two computers trying to exchange information are physically connected to each other, in the absence of a terminator at one end of such a "piece" of the bus, communication between them will be impossible.

In a ring topology (Fig. 2), each network subscriber is associated with two nearby subscribers. The advantages and disadvantages are similar to those discussed for the bus topology.

Star topology involves laying a separate cable for each computer in the network, connecting all network subscribers to a certain center. The center of the star can be a computer or a special connecting device called a hub (Fig. 3). The advantage of this topology is its higher reliability. A break in any conductor "disconnects" only one subscriber. The bottleneck in this topology is the hub. If it breaks down, the operation of the entire network is blocked. The disadvantage is the higher cost of the equipment (considering the increase in the total length of the conductors, in comparison with the previous topologies, as well as the cost of additional equipment - the hub).

In terms of reliability and speed of information exchange best performance has a fully connected topology (Fig. 4). In this case, the network subscribers are provided with a separate communication channel with each of the other subscribers. However, in terms of cost, this topology loses to all other options.

The listed topologies are basic. Most local area networks created in various organizations have a more complex structure and are various combinations of the above topologies.

Logical topologies of local area networks

Logical topology determines the nature of the distribution of information over a computer network. When transferring information from one subscriber of the network to another subscriber, this information is properly "formalized". The transmitted data is formed into standard fragments (packets, datagrams). In addition to the actual transmitted data (numbers, texts, pictures, etc.), an address (a receiver of information or both receivers and a transmitter), control information (so that you can check whether the packet has been received in full or only part of it) and a number of other information. Let's consider three main variants of logical topologies of local area networks.

The logical bus defines equal access to the network for all subscribers. In this case, the transmitter puts a packet of information into the network, and all other subscribers “having heard” the transmitted information analyze it. If the subscriber finds his address in the package, he “keeps” this information for himself, if the address turns out to be a stranger, he ignores it. If, at the time of information transmission by one subscriber, another subscriber "wedges into the conversation", there is an overlap of packets, called collision. Collisions lead to "mixing" of packages and the inability to figure out "who said what." Having detected a collision, the transmitting subscriber "falls silent" for a time interval of a random duration, and then repeats the attempt to transmit information. With a very large number of subscribers in the network, the probability of collisions increases dramatically, and the network becomes inoperable.

The logical ring assumes that information travels a full “circle” and comes to the source, i.e. to the point from which it was sent. In this case, each subscriber compares the address of the "recipient" with his own. If the addresses match, the information is copied to the buffer, the packet is marked as “reaching the destination” and is passed on to the next subscriber. If the addresses do not match, the packet is transmitted without any marks. When a subscriber has received a packet sent "with his own hand" and marked "accepted", he does not transmit it further and another subscriber of the network can enter into work.

The logical topology of a star (and its version is a tree) is focused on establishing a communication channel between a receiver and a transmitter by means of switches. Those. in the absence of a switch, even two network subscribers cannot communicate with each other. When transferring data from one subscriber to another, everyone else is waiting for the end of the transfer.

Connectors and connectors

Currently in local computer networks several types of conductors are used. The physical nature of the transmitted signal distinguishes between electrical conductors and optical conductors. In addition, equipment can be used to organize local area networks by means of wireless channels.

Coaxial cable

Coaxial cable (Fig. 5) is a conductor enclosed in a braided shield. The conductor is protected from contact with the braid with a tubular insulator. An important characteristic of cable systems in general and coaxial cable in particular is the characteristic impedance or impedance. In local area networks, a coaxial cable with a characteristic impedance of 50 ohms is used and (much less often) in ARCnet networks a cable with an impedance of 93 ohms is used. There are two types of coaxial cable - thick (outer diameter about 10 mm) and thin (outer diameter about 5 mm). With the same value of the characteristic impedance, thick and thin coaxial cables have different characteristics along the length of the cable segment and the number of supported network subscribers. A thick coaxial cable has a maximum segment length of 500 meters and a maximum number of connection points 100. A thin coaxial cable has a maximum segment length of 185 meters and a maximum number of connection points of 30.