What is network technology in a broad sense. Network technologies of local computer networks. Currently, there is probably no such person who has never had the opportunity to work with a computer. Modern computer technologies are used everywhere
Network technology is a coordinated set of standard protocols and software and hardware that implement them, sufficient for building computer networks.
Protocol is a set of rules and agreements that determine 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 underlying Ethernet is a random method of access to a shared data transmission medium (multiple access method).
The logical topology of an Ethernet network is always bus, so data is transmitted to all network nodes. Each node sees each transmission and distinguishes the data intended for it by the address of its network adapter. At any given time, only one node can carry out a successful transmission, so there must be some kind of agreement between the nodes on how they can use the same cable together so as not to interfere with each other. This agreement defines the Ethernet standard.
As the network load increases, the need to transmit data at the same time becomes increasingly necessary. When this happens, the two gears come into conflict, filling the bus. information garbage. This behavior is known under the term “collision,” that is, the occurrence of a conflict.
Each transmitting system, upon detecting a collision, immediately stops sending data and action is taken to correct 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 that the more traffic on the network, the more collisions, the more network performance drops sharply and collapse may occur. that is, the network is clogged with traffic.
Traffic– flow of messages in a data network.
Token Ring Technology
Token Ring technology was developed by IBM in 1984. Token Ring technology uses a completely different access method. The Token Ring logical network has a ring topology. A special message, known as a Token, is a special three-byte packet that constantly circulates around the logical ring in one direction. When a token passes through a node ready to send data to the network, it grabs the token, attaches the data to be sent to it, and then passes 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 random latency periods like Ethernet.
FDDI technology
FDDI (Fiber Distributed Data Interface) technology – fiber optic distributed data interface – is the first local 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 path data transfer between network nodes. Having two rings is the primary way to increase fault tolerance 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 mode, 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 where part of the primary ring cannot transmit data (for example, a broken cable or node failure), the primary ring is combined with the secondary ring, again forming a single ring.
Rings in FDDI networks are considered as general environment data transfer, therefore a special access method is defined for it, very close to the access method of Token Ring networks. The difference is that the token retention time in the FDDI network is not a constant value, as in Token Ring. It depends on the ring load - with a light load it increases, and with large congestions it can decrease to zero for asynchronous traffic. For synchronous traffic, the token holding time remains a fixed value.
ATM technology
ATM (Asynchronous Transfer Mode) is the most modern network technology. It is designed to transmit voice, data and video using a high-speed, connection-oriented cell switching 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 transmitting information over a fiber optic cable using a star topology.
- Tutorial
Hi all. The other day an idea arose to write articles about the basics of computer networks, to analyze the work of the most important protocols and how networks are built in simple language. I invite those interested under cat.
A little off-topic: About a month ago I passed the CCNA exam (with 980/1000 points) and there is a lot of material left over the year of my preparation and training. I first studied at the Cisco Academy for about 7 months, and for the remaining time I took notes on all the topics that I had studied. I also consulted with many guys in the field of network technologies and noticed that many people step on the same rake, in the form of gaps on some key topics. The other day a couple of guys asked me to explain what networks are and how to work with them. In this regard, I decided to describe the most key and important things in as much detail and in simple language as possible. The articles will be useful to beginners who have just embarked on the path of study. But perhaps experienced system administrators will also highlight something useful from this. Since I will be taking the CCNA program, this will be very useful for those people who are preparing to take the test. You can keep articles in the form of cheat sheets and review them periodically. During my studies, I took notes on books and read them periodically to refresh my knowledge.
In general, I want to give advice to all beginners. My first serious book was Olifer’s book “Computer Networks”. And it was very difficult for me to read it. I won't say that everything was difficult. But the moments where it was explained in detail how MPLS or carrier-class Ethernet works were stupefying. I read one chapter for several hours and still a lot remained a mystery. If you understand that some terms just don’t want to pop into your head, skip them and read on, but under no circumstances discard the book completely. This is not a novel or an epic where it is important to read chapter by chapter to understand the plot. Time will pass and what was previously incomprehensible will eventually become clear. This is where your “book skill” is upgraded. Each subsequent book is easier to read than the previous book. For example, after reading Olifer’s “Computer Networks,” reading Tanenbaum’s “Computer Networks” is several times easier and vice versa. Because there are fewer new concepts. So my advice is: don't be afraid to read books. Your efforts will bear fruit in the future. I’ll finish my rant and start writing the article.
Here are the topics themselves
1) Basic network terms, network model OSI and TCP/IP protocol stack.
2) Upper level protocols.
3) Protocols of lower levels (transport, network and channel).
4) Network devices and types of cables used.
5) The concept of IP addressing, subnet masks and their calculation.
6) The concept of VLAN, Trunk and the VTP and DTP protocols.
7) Spanning Tree Protocol: STP.
8) Channel aggregation protocol: Etherchannel.
9) Routing: static and dynamic using the example of RIP, OSPF and EIGRP.
10) Network address translation: NAT and PAT.
11) First hop reservation protocols: FHRP.
12) Computer network security and virtual private networks: VPN.
13) Global networks and protocols used: PPP, HDLC, Frame Relay.
14) Introduction to IPv6, configuration and routing.
15) Network management and network monitoring.
P.S. Perhaps over time the list will be expanded.
So let's start with some basic networking terms.
What is a network? It is a collection of devices and systems that are connected to each other (logically or physically) and communicate with each other. This includes servers, computers, phones, routers, and so on. The size of this network can reach the size of the Internet, or it can consist of just two devices connected by a cable. To avoid any confusion, let’s divide the network components into groups:
1) End nodes: Devices that transmit and/or receive any data. These could be computers, phones, servers, some kind of terminals or thin clients, TVs.
2) Intermediate devices: These are devices that connect end nodes to each other. This includes switches, hubs, modems, routers, and Wi-Fi access points.
3) Network environments: These are the environments in which direct data transfer occurs. This includes cables, network cards, various types of connectors, and airborne transmission media. If it is a copper cable, then data transmission is carried out using electrical signals. In fiber optic cables, using light pulses. Well, with wireless devices, using radio waves.
Let's see it all in the picture:
On this moment you just need to understand the difference. The detailed differences will be discussed later.
Now, in my opinion, the main question is: What do we use networks for? There are many answers to this question, but I will highlight the most popular ones that are used in everyday life:
1) Applications: Using applications, we send various data between devices and open access to shared resources. These can be either console applications or GUI applications.
2) Network resources: These are network printers, which, for example, are used in the office or network cameras that are viewed by security guards while in a remote area.
3) Storage: Using a server or workstation connected to the network, storage is created that is accessible to others. Many people post their files, videos, pictures there and open general access to them for other users. An example that comes to mind on the fly is Google Drive, Yandex Drive and similar services.
4) Backup: Often, large companies use a central server where all computers copy important files for backup. This is necessary for subsequent data recovery if the original is deleted or damaged. Copy methods great amount: with pre-compression, encoding and so on.
5) VoIP: Telephony using IP protocol. It is now used everywhere, since it is simpler, cheaper than traditional telephony and is replacing it every year.
Of the entire list, most often many worked with applications. Therefore, we will analyze them in more detail. I will carefully select only those applications that are somehow connected to the network. Therefore, I don’t take applications like a calculator or notepad into account.
1) Loaders. These are file managers that work using the FTP, TFTP protocol. A trivial example is downloading a movie, music, pictures from file hosting services or other sources. This category also includes backups that the server automatically makes every night. That is, they are built-in or third party programs and utilities that perform copying and downloading. This type applications do not require direct human intervention. It is enough to indicate the location where to save and the downloading will begin and end.
Download speed depends on bandwidth. For this type of application this is not entirely critical. If, for example, a file takes 10 minutes to download, then it’s only a matter of time, and this will not affect the integrity of the file in any way. Difficulties can only arise when we need to do something in a couple of hours backup copy system, and due to a poor channel and, accordingly, low bandwidth, it takes several days. Below are descriptions of the most popular protocols in this group:
FTP It is a standard connection-oriented data transfer protocol. It works using the TCP protocol (this protocol will be discussed in detail later). The standard port number is 21. Most often used to upload a site to a web hosting and upload it. The most popular application, working on this protocol is Filezilla. This is what the application itself looks like:
TFTP- this is a simplified version FTP protocol, which works without establishing a connection, using the UDP protocol. Used to load an image on diskless workstations. Especially widely used by Cisco devices for the same image loading and backups.
Interactive applications. Applications that allow interactive exchange. For example, the “person-to-person” model. When two people, using interactive applications, communicate with each other or conduct common work. This includes: ICQ, email, a forum where several experts help people resolve issues. Or the “man-machine” model. When a person communicates directly with a computer. This could be remote configuration of the database, configuration of a network device. Here, unlike bootloaders, constant human intervention is important. That is, at least one person acts as an initiator. Bandwidth is already more sensitive to latency than downloading applications. For example, when configuring a network device remotely, it will be difficult to configure it if the response from the command takes 30 seconds.
Real-time applications. Applications that allow you to transmit information in real time. IP-telephony, systems streaming, video conferencing. The most latency and bandwidth sensitive applications. Imagine that you are talking on the phone and what you say, the interlocutor will hear in 2 seconds and vice versa, you will hear from the interlocutor at the same interval. Such communication will also lead to the fact that voices will disappear and the conversation will be difficult to distinguish, and the video conference will turn into mush. On average, the delay should not exceed 300 ms. This category includes Skype, Lync, Viber (when we make a call).
Now let's talk about such an important thing as topology. It is divided into 2 large categories: physical And logical. It is very important to understand their difference. So, physical topology is what our network looks like. Where are the nodes located, what network intermediate devices are used and where are they located, what network cables are used, how they are routed and what port they are plugged into. Logical topology is which way packets will go in our physical topology. That is, physical is how we positioned the devices, and logical is which devices the packets will pass through.
Now let's look and analyze the types of topology:
1) Topology with a common bus (English Bus Topology)
One of the first physical topologies. The idea was that all devices were connected to one long cable and a local network was organized. Terminators were required at the ends of the cable. As a rule, this was a 50 ohm resistance, which was used to ensure that the signal was not reflected in the cable. Its only advantage was its ease of installation. From a performance point of view, it was extremely unstable. If there was a break somewhere in the cable, then the entire network remained paralyzed until the cable was replaced.
2) Ring Topology
In this topology, each device is connected to two neighboring ones. Thus creating a ring. The logic here is that at one end the computer only receives, and at the other it only sends. That is, a ring transmission is obtained and the next computer plays the role of a signal repeater. Due to this, the need for terminators disappeared. Accordingly, if the cable was damaged somewhere, the ring opened and the network became inoperable. To increase fault tolerance, a double ring is used, that is, each device receives two cables, not one. Accordingly, if one cable fails, the backup one remains operational.
3) Star topology
All devices are connected to the central node, which is already a repeater. Nowadays, this model is used in local networks, when several devices are connected to one switch, and it acts as an intermediary in transmission. Here the fault tolerance is much higher than in the previous two. If any cable breaks, only one device falls out of the network. Everyone else continues to work quietly. However, if the central link fails, the network will become inoperable.
4) Full-Mesh Topology
All devices are connected directly to each other. That is, from each to each. This model is perhaps the most fault-tolerant, as it does not depend on others. But building networks on such a model is difficult and expensive. Since in a network with at least 1000 computers, you will have to connect 1000 cables to each computer.
5) Partial-Mesh Topology
As a rule, there are several options. It is similar in structure to a fully connected topology. However, the connection is not built from each to each, but through additional nodes. That is, node A is connected directly only to node B, and node B is connected to both node A and node C. So, in order for node A to send a message to node C, it must first send to node B, and node B in turn will send this message to node C. In principle, routers operate on this topology. Let me give you an example from a home network. When you go online from home, you do not have a direct cable to all nodes, and you send data to your provider, and he already knows where this data needs to be sent.
6) Mixed topology (English Hybrid Topology)
The most popular topology, which combines all the topologies above into itself. It is a tree structure that unites all topologies. One of the most fault-tolerant topologies, since if a break occurs at two sites, then only the connection between them will be paralyzed, and all other connected sites will work flawlessly. Today, this topology is used in all medium and large companies.
And the last thing left to sort out is network models. At the early stage of computers, networks did not have uniform standards. Each vendor used its own proprietary solutions that did not work with the technologies of other vendors. Of course, it was impossible to leave it like that and it was necessary to invent common decision. This task was undertaken by the International Organization for Standardization (ISO - International Organization for Standardization). They studied many models used at that time and as a result came up with OSI model , which was released in 1984. The only problem was that it took about 7 years to develop. While experts were arguing about how best to make it, other models were being modernized and gaining momentum. Currently, the OSI model is not used. It is used only as network training. My personal opinion is that every self-respecting administrator should know the OSI model like a multiplication table. Although it is not used in the form in which it is, the operating principles of all models are similar to it.
It consists of 7 levels and each level performs a specific role and task. Let's look at what each level does from bottom to top:
1) Physical Layer: determines the method of data transmission, what medium is used (transmission of electrical signals, light pulses or radio air), voltage level, and method of encoding binary signals.
2) Data Link Layer: it takes on the task of addressing within the local network, detects errors, and checks data integrity. If you have heard about MAC addresses and the Ethernet protocol, then they are located at this level.
3) Network layer(Network Layer): this level takes care of combining network sections and choosing the optimal path (i.e. routing). Each network device must have a unique network address online. I think many have heard about the IPv4 and IPv6 protocols. These protocols operate at this level.
4) Transport Layer: This level takes on the function of transport. For example, when you download a file from the Internet, the file is sent in segments to your computer. It also introduces the concepts of ports, which are needed to indicate the destination to a specific service. The TCP (connection-oriented) and UDP (connectionless) protocols operate at this layer.
5) Session Layer: The role of this layer is to establish, manage, and terminate connections between two hosts. For example, when you open a page on a web server, you are not the only visitor on it. And in order to maintain sessions with all users, a session layer is needed.
6) Presentation Layer: It structures information in a readable form for the application layer. For example, many computers use the ASCII encoding table to display text information or the jpeg format to display graphics.
7) Application Layer: This is probably the most understandable level for everyone. It is at this level that the applications we are familiar with work - e-mail, browsers using the HTTP protocol, FTP and the rest.
The most important thing to remember is that you cannot jump from level to level (For example, from application to channel, or from physical to transport). The entire path must go strictly from top to bottom and from bottom to top. Such processes are called encapsulation(from top to bottom) and deencapsulation(from lower to upper). It is also worth mentioning that at each level the information transmitted is called differently.
At the application, presentation and session levels, the transmitted information is designated as PDU (Protocol Data Units). In Russian they are also called data blocks, although in my circle they are simply called data).
Transport layer information is called segments. Although the concept of segments is applicable only to the TCP protocol. The UDP protocol uses the concept of a datagram. But, as a rule, people turn a blind eye to this difference.
At the network level they are called IP packets or simply packets.
And at the link level - frames. On the one hand, this is all terminology and it does not play an important role in how you call the transmitted data, but for the exam it is better to know these concepts. So, I’ll give you my favorite example, which helped me, in my time, understand the process of encapsulation and de-encapsulation:
1) Let’s imagine a situation where you are sitting at home at your computer, and in the next room you have your own local web server. And now you need to download a file from it. You type the address of your website page. Now you are using the HTTP protocol, which runs at the application layer. The data is packed and sent down to the next level.
2) The received data is sent to the presentation level. Here this data is structured and put into a format that can be read on the server. Packed up and lowered down.
3) At this level, a session is created between the computer and the server.
4) Since this is a web server and reliable connection establishment and control of received data is required, the TCP protocol is used. Here we indicate the port on which we will knock and the source port so that the server knows where to send the response. This is necessary so that the server understands that we want to get to the web server (standardly port 80), and not to the mail server. We pack and move on.
5) Here we must specify which address to send the packet to. Accordingly, we indicate the destination address (let the server address be 192.168.1.2) and the source address (computer address 192.168.1.1). We turn it around and go down further.
6) The IP packet goes down and here the link layer comes into operation. It adds physical source and destination addresses, which will be discussed in detail in a subsequent article. Since we have a computer and a server in a local environment, the source address will be the computer’s MAC address, and the destination address will be the server’s MAC address (if the computer and server were on different networks, then addressing would work differently). If at the upper levels a header was added each time, then a trailer is also added here, which indicates the end of the frame and the readiness of all collected data for sending.
7) And the physical layer converts what is received into bits and, using electrical signals (if it is a twisted pair cable), sends it to the server.
The deencapsulation process is similar, but with the reverse sequence:
1) At the physical layer, electrical signals are received and converted into an understandable bit sequence for the link layer.
2) At the link layer, the destination MAC address is checked (whether it is addressed to it). If yes, then the frame is checked for integrity and absence of errors, if everything is fine and the data is intact, it transfers it to a higher level.
3) At the network level, the destination IP address is checked. And if it is correct, the data rises higher. There is no need to go into details now about why we have addressing at the link and network levels. This topic requires special attention, and I'll explain their differences in detail later. The main thing now is to understand how data is packed and unpacked.
4) At the transport layer, the destination port (not the address) is checked. And by the port number, it becomes clear which application or service the data is addressed to. For us this is a web server and the port number is 80.
5) At this level, a session is established between the computer and the server.
6) The presentation layer sees how everything should be structured and makes the information readable.
7) And at this level, applications or services understand what needs to be done.
Much has been written about the OSI model. Although I tried to be as brief as possible and cover the most important things. In fact, a lot has been written in detail about this model on the Internet and in books, but for beginners and those preparing for CCNA, this is enough. There may be 2 questions in the exam for this model. This is the correct arrangement of layers and at what level a certain protocol operates.
As written above, the OSI model is not used nowadays. While this model was being developed, the TCP/IP protocol stack was becoming increasingly popular. It was much simpler and gained rapid popularity.
This is what the stack looks like:
As you can see, it differs from OSI and even changed the name of some levels. Essentially, its principle is the same as that of OSI. But only the three upper OSI layers: application, presentation and session are combined into one in TCP/IP, called application. The network layer has changed its name and is called the Internet. The transport one remained the same and with the same name. And two lower levels OSI: channel and physical are combined in TCP/IP into one called the network access layer. The TCP/IP stack in some sources is also referred to as the DoD (Department of Defense) model. According to Wikipedia, it was developed by the US Department of Defense. I came across this question during the exam and before that I had never heard anything about her. Accordingly, the question: “What is the name of the network layer in the DoD model?” brought me into a stupor. Therefore, it is useful to know this.
There were several other network models that lasted for some time. This was the IPX/SPX protocol stack. Used since the mid-80s and lasted until the late 90s, where it was superseded by TCP/IP. It was implemented by Novell and was an upgraded version of the Xerox Network Services protocol stack from Xerox. Used in local networks for a long time. The first time I saw IPX/SPX was in the game “Cossacks”. When choosing network game, there were several stacks to choose from. And although this game was released somewhere in 2001, this indicated that IPX/SPX was still found on local networks.
Another stack worth mentioning is AppleTalk. As the name suggests, it was invented by Apple. It was created in the same year in which the OSI model was released, that is, in 1984. It didn't last long and Apple decided to use TCP/IP instead.
I also want to emphasize one important thing. Token Ring and FDDI are not network models! Token Ring is a link layer protocol, and FDDI is a data transfer standard that is based on the Token Ring protocol. This is not the most important information, since these concepts are not found now. But the main thing to remember is that these are not network models.
So the article on the first topic has come to an end. Although superficially, many concepts were considered. The most important ones will be discussed in more detail in the following articles. I hope now networks will no longer seem like something impossible and scary, and it will be easier to read smart books). If I forgot to mention something, have any additional questions, or if anyone has anything to add to this article, leave comments or ask personally. Thanks for reading. I will be preparing the next topic.
Add tagsModern network technologies
Plan
What is a local network?
Computer network hardware. Local area network topologies
Physical topologies of local area networks
Logical topologies of local area networks
Connectors and sockets
twisted pair
Transmitting information via fiber optic cables
Communication equipment
Wireless network equipment and technologies
Technologies and protocols of local area networks
Addressing computers on the network and basic network protocols
Network facilities of MS Windows operating systems
Network Resource Management Concepts
Capabilities of the MS Windows family of operating systems for organizing work in a local network
Configuring network component settings
Configuring connection settings
Connecting a network printer
Connecting a network drive
What is a local network?
The problem of transferring information from one computer to another has existed since the advent of computers. To solve it, various approaches were used. The most common “courier” approach in the recent past was to copy information onto removable media (GMD, CD, etc.), transfer it 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 connected to each other in some way, and the user is able to transfer information to its destination without leaving the desk.
A set of computer devices that have the ability to communicate with each other is usually called a computer network. In most cases, there are two types of computer networks: local (LAN - LocalAreaNetwork) and global (WAN - Wide-AreaNetwork). In some classification options, a number of additional types are considered: urban, regional, etc., however, all these types (in essence) in most cases are variants global networks of various scales. The most common option is to classify networks into local and global based on geography. Those. In this case, a local computer network is understood as a collection of a finite number of computers located in a limited area (within one building or neighboring buildings), connected by information channels that have high speed and reliability of data transmission and are designed to solve a set of interrelated problems.
Computer network hardware . Local area network topologies
All computers of subscribers (users) working within the local area network must be able to interact with each other, i.e. be connected with each other. The way such connections are organized significantly affects the characteristics of the local computer network and is called its topology (architecture, configuration). There are physical and logical topologies. The physical topology of a local area network refers to the physical placement of the computers that are part of 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 for connecting local area network subscribers.
Physical topologies of local area networks
There are four main physical topologies used in building local area networks.
The bus topology (Fig. 1) involves connecting all computers to one common conductor. At both ends of such a conductor there are special matching devices called terminators. The main advantages of this topology are low cost and ease of installation. Disadvantages include the difficulty of localizing the location of the fault and low reliability: damage to the cable anywhere leads to the cessation of information exchange between all computers on the network. Due to the nature of electrical signal propagation, even if two computers trying to exchange information are physically connected to each other, if there is no terminator at one end of such a “break” of the bus, communication between them will be impossible.
In a ring topology (Fig. 2), each network subscriber is connected to two nearby subscribers. The advantages and disadvantages are similar to those considered for the bus topology.
The 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 higher reliability. A break in any conductor “disconnects” only one subscriber. The bottleneck of this topology is the hub. If it breaks, the entire network is blocked. The disadvantage is the higher cost of the equipment (taking into account the increase in the total length of the conductors in comparison with previous topologies, as well as the cost of additional equipment - a hub).
From the point of view of reliability and speed of information exchange, the fully connected topology has the best characteristics (Fig. 4). In this case, network subscribers are provided with a separate communication channel with each of the other subscribers. However, in terms of cost, this topology is inferior 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 information distribution over a computer network. When transmitting information from one network subscriber to another subscriber, this information is properly “formatted”. The transmitted data is formatted in standard fragments (packets, datagrams). In addition to the actual transmitted data (numbers, texts, pictures, etc.), the address (of the information receiver or both receivers and transmitter), control information (so that you can check whether the packet was received in full or only part of it) and a number of other things are added to the packet. information. Let's consider three main options for logical topologies of local computer networks.
The logical bus determines 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 “hear” transmitted information analyze it. If the subscriber finds his address as part of the package, he “keeps” this information for himself, if the address turns out to be someone else’s, he ignores it. If, at the time of transmission of information by one subscriber, another subscriber “interjects” into the conversation, an overlap of packets occurs, called a collision. Collisions lead to “mixing” of packets and the inability to figure out “who said what.” Having detected a collision, the transmitting subscriber “falls silent” for a time interval of random duration, after which it repeats the attempt to transmit information. With a very large number of subscribers in the network, the probability of collisions increases sharply, and the network becomes inoperable.
The logical ring assumes that information goes full circle and comes to the source, i.e. to the point from which it was sent. In this case, each subscriber compares the “recipient” address with his own. If the addresses match, the information is copied to a buffer, the packet is marked as “reached the addressee” and is transmitted to the next subscriber. If the addresses do not match, the packet is transmitted without any marks. When a subscriber has received a package sent “with his own hand” and marked “accepted,” he does not transmit it further and another network subscriber can start working.
The logical star topology (and its version - tree) is focused on establishing a communication channel between the receiver and the transmitter using switches. Those. In the absence of a switch, it is impossible for even two network subscribers to communicate with each other. When transferring data from one subscriber to another, everyone else waits for the end of the transfer.
Connectors and sockets
Currently, several types of conductors are used in local area networks. According to the physical nature of the transmitted signal, they are distinguished electrical conductors and optical conductors. In addition, equipment can be used to organize local computer networks using wireless channels.
Coaxial cable
A coaxial cable (Fig. 5) is a conductor enclosed in a shielding braid. The conductor is protected from contact with the braid by a tubular insulator. Important characteristic cable systems in general and coaxial cable in particular is the characteristic resistance 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 a characteristic 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 wave resistance Thick and thin coaxial cables have different characteristics in terms of the length of the cable segment and the number of supported network subscribers. Thick coaxial cable has a maximum segment length of 500 meters, maximum amount There are 100 connection points. A thin coaxial cable has a maximum segment length of 185 meters, a maximum number of connection points of 30.
Transcript
1 Lecture 7 Computer networks and network technologies Lecturer Art. teacher Kupo A.N.
2 Types of computer networks. Opportunities and advantages of network technologies. Computer networks (English, network) are a collection of PCs distributed over a certain territory and interconnected to share resources (data, programs and hardware components). Almost all network services are built on the client-server principle. A server on a network is a computer that is capable of providing clients (as requests come from them) some network services. Today there are more than 130 million computers in the world and more than 80% of them are connected into various information and computer networks - from small local networks in offices to global networks.
3 It is currently customary to divide existing networks primarily on a territorial basis: 1. Local networks (LAN - Locate Area Network). Such a network covers a small area with a distance between individual computers of up to 10 km. Typically, such a network operates within one institution. A local area network (LAN) is understood as the joint connection of several separate computer workstations (workstations) to a single transmission/data channel. The most simple network consists of at least two computers connected to each other by cable. This allows them to share data. 2. Regional networks. Similar networks exist within a city or region. Currently, each such network is part of some global network and does not differ in any particular specificity in relation to the global network. 3. Global networks (WAN - Wide Area Network). Such a network usually covers large territories (the territory of a country or several countries). Computers are located tens of thousands of kilometers apart from each other. Both specially laid (for example, transatlantic fiber optic cable) and existing communication lines (for example, telephone networks) are used as communication lines in global networks. The number of nodes in a WAN can reach tens of millions. The global network includes separate local and corporate networks. World Wide Web- unification of global networks (Internet).
4 Computer networks can also be classified according to various criteria. I. According to management principles: 1. Peer-to-peer - without a dedicated server. In which control functions are alternately transferred from one workstation to another; 2. Multi-peer is a network that includes one or more dedicated servers. The remaining computers of such a network (workstations) act as clients. II. By connection method: 1. “Direct connection” - two personal computers are connected by a piece of cable. This allows one computer (the master) to access the resources of another (the slave); 2. "Common bus" - connecting computers to one cable; 3. "Star" - connection through a central node; 4. "Ring" - serial connection PC in two directions.
5 All the variety of computer networks can be classified: 1) the method of organizing the network; 2) territorial distribution; 3) departmental affiliation; 4) information transfer speed; 5) type of transmission medium; 6) topology; 7) organization of interaction between computers.
6 The construction of any modern computer network is based on three principles: 1. General network protocol (rules for encoding and information exchange). Computers must understand each other. 2. Network flexibility. The network must remain operational even if some nodes or communication lines fail. 3. Network expandability. The network must be built in such a way that it can be easily connected to new computer. Data transmission means mean: Devices for receiving and transmitting information - modems, network adapters. Data lines. Means of routing transmitted information.
7 All network users can get: access to information resources of network nodes (access to file libraries, databases, electronic reference books and so on.). access to the computing resources of network nodes (for example, using a remote computer with a powerful processor to solve complex computational problem). access to network hardware resources ( network printers, disks, etc.). the possibility of remote control of processes (control of an assembly line, reactor, etc.). Client-server interaction is usually structured as follows. Upon receipt of requests from clients, the server launches various provisioning programs network services. As completed running programs the server responds to client requests. All network software can also be divided into client and server. In this case, the server software provides network services, and the client software ensures that requests are sent to the server and responses are received from it.
8 Currently, computer networks have become very widespread. This is due to several reasons: connecting computers into a network allows for significant savings cash by reducing the cost of maintaining computers (it is enough to have a certain disk space on a file server (the main computer of the network) with installed on it software products, used by several workstations); computer networks make it possible to use Mailbox to transfer messages to other computers, which allows you to transfer documents from one computer to another in the shortest possible time; computer networks, with special software, are used to organize the sharing of files (for example, accountants on several machines can process entries of the same ledger). Among other things, in some areas of activity it is simply impossible to do without computer networks. These areas include: banking, warehouse operations large companies, electronic archives of libraries, etc. In these areas, each individual workstation, in principle, cannot store all the information (mainly due to its too large volume). The network allows selected (registered on the file server) users to access the information that the network operator allows them to access.
9 Topology of local networks. Intranet. Extranet.
10 Topology local systems All computers on the local network are connected by communication lines. Geometric location of communication lines relative to network nodes and physical connection nodes to the network is called physical topology. Depending on the topology, networks are distinguished: bus, ring, star, hierarchical and arbitrary structures. There are physical and logical topologies. Logical and physical network topologies are independent of each other. Physical topology is the geometry of the network, and logical topology determines the directions of data flows between network nodes and methods of data transmission. Currently, the following physical topologies are used in local networks: physical “bus” (bus); physical star (star); physical ring (ring); physical "star" and logical "ring" (Token Ring).
11 Common bus topology
12 “Common bus” Networks with a bus topology use a linear monochannel (coaxial cable) for data transmission, at the ends of which terminating resistors (terminators) are installed. Each computer is connected to a coaxial cable using a T connector (T connector). Data from the transmitting network node is transmitted along the bus in both directions, reflected from the terminal terminators. Terminators prevent signals from being reflected, i.e. are used to cancel signals that reach the ends of a data link. Thus, information arrives at all nodes, but is received only by the node to which it is intended. In a logical bus topology, the data transmission medium is shared and simultaneously by all PCs on the network, and signals from the PCs are distributed simultaneously in all directions along the transmission medium. Since the transmission of signals in the topology, the physical bus is broadcast, i.e. signals propagate simultaneously in all directions, then the logical topology of this local network is a logical bus. This topology is used in local networks with Ethernet architecture (classes 10Base-5 and 10Base-2 for thick and thin coaxial cable, respectively).
13 Advantages of bus topology networks: failure or malfunction of one of the nodes does not affect the operation of the network as a whole; the network is easy to set up and configure; all information is online and accessible to every computer; workstations can be connected independently of each other. Those. when connecting a new subscriber, there is no need to stop the transmission of information on the network; building networks based on a common bus topology is cheaper, since there are no costs for laying additional lines when connecting a new client. Disadvantages of bus topology networks: a break in a single cable (bus) can affect the operation of the entire network; limited cable length and number of workstations; it is difficult to identify defects in connections; low speed data transmission, because all information circulates through one channel (bus); networks built on the basis of this topology are characterized by low security, since information on each computer can be accessed from any other computer.
14 Star topology
15 “Star” Data from the network transmitting station is transmitted through the hub along all communication lines to all PCs. Information arrives at all workstations, but is received only by those stations for which it is intended. Since signal transmission in the physical star topology is broadcast, i.e. Since signals from the PC propagate simultaneously in all directions, the logical topology of this local network is a logical bus. This topology is used in local networks with 10Base-T Ethernet architecture
16 The advantages of this topology are as follows: High network performance, since the overall network performance depends only on the performance of the central node. easy to connect a new PC; there is the possibility of centralized management; the network is resistant to failures of individual PCs and to interruptions in the connection of individual PCs. Disadvantages: Low reliability, since the reliability of the entire network is determined by the reliability of the central node. If the central computer fails, the entire network will stop working. High costs for connecting computers, since a separate line must be installed for each new subscriber.
17 Ring topology
18 “Ring” With a ring topology, all computers are connected to a line closed in a ring. Signals are transmitted along the ring in one direction and pass through each computer. The transmission of information in such a network occurs as follows. A token (special signal) is transmitted sequentially, from one computer to another, until it is received by the one that needs to transfer the data. Once the computer receives the token, it creates what is called a "packet" in which it places the recipient's address and data, and then sends the packet around the ring. The data passes through each computer until it reaches the one whose address matches the recipient's address. After this, the receiving computer sends confirmation to the information source that the data has been received. Having received confirmation, the sending computer creates a new token and returns it to the network.
19 The advantages of the ring topology are as follows: Message forwarding is very efficient because You can send several messages one after another in a ring. Those. a computer, having sent the first message, can send the next message after it, without waiting for the first one to reach the recipient. The length of the network can be significant. Those. computers can connect to each other over considerable distances, without the use of special signal amplifiers. The disadvantages of this topology include: Low network reliability, since the failure of any computer entails the failure of the entire system. To connect a new client, you must disable the network. With a large number of clients, the speed of the network slows down, since all information passes through each computer, and their capabilities are limited. The overall performance of the network is determined by the performance of the network itself. slow computer; physical restrictions on the total length of the network.
20 Token Ring topology
21 “Token Ring” This topology is based on the “physical ring with star connection” topology. In this topology, all workstations are connected to a central hub (Token Ring) like a physical star topology. A central hub is an intelligent device that, using jumpers, provides a serial connection between the output of one station and the input of another station. In other words, with the help of a hub, each station is connected to only two other stations (previous and subsequent stations). Thus, workstations are connected by a cable loop through which data packets are transmitted from one station to another and each station relays these sent packets. Each workstation has a transceiver device for this purpose, which allows you to control the passage of data in the network. Physically, such a network is built according to the star topology type. The hub creates a primary (main) and backup ring. If a break occurs in the main ring, it can be bypassed by using the backup ring, since a four-core cable is used. A failure of a station or a break in the communication line of a workstation does not entail a network failure as in a ring topology, because the hub will disconnect the faulty station and close the data transmission ring. In a Token Ring architecture, a token is passed from node to node along a logical ring created by a central hub. Such token transmission is carried out in a fixed direction (the direction of movement of the token and data packets is represented in the figure by blue arrows). A station holding a token can send data to another station. To transmit data, workstations must first wait for a free token to arrive. The token contains the address of the station that sent the token, as well as the address of the station to which it is intended. After this, the sender passes the token to the next station in the network so that it can send its data. One of the network nodes (usually a file server is used for this) creates a token that is sent to the network ring. This node acts as an active monitor that ensures that the marker is not lost or destroyed.
22 Advantages of Token Ring topology networks: the topology provides equal access to all workstations; high reliability, since the network is resistant to failures of individual stations and to interruptions in the connection of individual stations. Disadvantages of Token Ring topology networks: high cable consumption and, accordingly, expensive wiring of communication lines.
23 Intranet (English Intranet, the term intranet is also used), unlike the Internet, is an internal private network organizations. Typically, an intranet is the Internet in miniature, which is built on the use of the IP protocol to exchange and share some of the information within that organization. These can be lists of employees, phone lists of partners and customers. Most often, this term refers to only the visible part of the intranet - the internal website of the organization. Based on the basic HTTP and HTTPS protocols and organized on a client-server principle, the intranet site is accessible from any computer through a browser. Thus, an intranet is a “private” Internet, limited virtual space a separate organization. Intranet allows the use of public communication channels included in the Internet (VPN), but at the same time the protection of transmitted data and measures to prevent outside penetration of corporate nodes are ensured. Applications on the intranet are based on the use of Internet technologies and in particular Web technologies: hypertext in HTML format, the Hypertext Transfer Protocol HTTP and the CGI server application interface. The components of the Intranet are Web servers for static or dynamic publishing of information and browsers for viewing and interpreting hypertext.
24 Obvious benefits of using an intranet High productivity with working together over some common projects Easy access personnel to data Flexible level of interaction: you can change business interaction schemes both vertically and horizontally. Instant publication of data on intranet resources allows specific corporate knowledge to always be kept in shape and easily accessible from anywhere in the company using Web and hypermedia technologies. For example: job instructions, internal rules, standards, newsletter services, and even on-the-job training. Allows you to implement a common corporate culture and take advantage of the flexibility and versatility of modern information technologies for managing corporate work. Disadvantages of an Intranet The network can be hacked and exploited by hackers Unverified or inaccurate information published on an intranet leads to confusion and misunderstandings. Illegitimate and offensive materials can be distributed in a free interactive space. Easy access to corporate data can provoke its leakage to competitors through an unscrupulous employee. The functionality and flexibility of an intranet requires significant development and administration overhead.
25 An extranet is a corporate network protected from unauthorized access that uses Internet technologies for internal corporate purposes, as well as for providing part corporate information and corporate applications to the company's business partners. Security issues on the Extranet are much more serious than on the Intranet. For an Extranet network, authentication of the user (who may not be an employee of the company) and, especially, protection against unauthorized access are especially important, while for Intranet applications they play a much less significant role, since access to this network is limited to the physical boundaries of the company. Corporate use Extranets are closed corporate portals that host closed corporate materials and provide authorized company employees with access to teamwork applications, automated company management systems, as well as access to a limited number of materials to the company’s partners and regular customers. In addition, it is possible to use other Internet services on the Extranet: email, FTP, etc.
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By specialization: specialized and universal
specialized- for solutions small amount special tasks. An example of a specialized technology is the technology for reserving seats on airline flights.
Classic example universal technology is the Academic Network of the Russian Federation, designed to solve a large number of diverse information problems.
by way of organization:single-level and two-level
IN single-level In the routing system, all routers are equal in relation to each other.
two-level technologies have, in addition to PCs with which users directly communicate and which are called workstations, special computers called servers (English: to serve). The server's task is to serve workstations and provide them with its resources, which are usually significantly higher than the resources of a workstation.
By communication method: wired, wireless.
IN wired technologies The following are used as the physical medium in the channels:
Flat two-core cable;
Twisted pair wires
Coaxial cable
Light guide.
Wireless network technologies, using frequency data transmission channels (the medium is air), currently represent a reasonable alternative to conventional wired networks and are becoming increasingly attractive. The biggest advantage of wireless technology is the capabilities it provides to users laptop computers. However, the data transfer speed achieved in wireless technologies cannot yet compare with throughput cable, although she is in Lately and has grown significantly
According to the composition of the PC. Homogeneous and heterogeneous
Homogeneous network technologies involve linking into a network of similar tools developed by one company. Connecting tools from other manufacturers to such a network is possible only if they comply with the standards adopted in a homogeneous architecture.
Another approach is to develop a single universal network technology, regardless of the types of tools used in it. Such technologies are called heterogeneous. The first standard for such networks was the Basic Reference Model of the OSI (Interconnection open systems). This Open Systems Interconnection Reference Model standard provides a common framework that coordinates efforts to create standards for systems interconnection. It allows the use of existing standards and defines their future location within the reference model.
Requirements of this standard are mandatory
By Area Coverage
Usage personal computers(PC) included local area networks(LAN) provides constant and prompt interaction between individual users within a commercial or scientific-production structure. The LAN received its name because all its components (PCs, communication channels, communications equipment) are physically located in a small area of one organization or its individual divisions.
Territorial (regional) is a technology (network) whose computers are located at a great distance from each other, usually from tens to hundreds of kilometers. Sometimes a territorial network is called a corporate or departmental network. Such a network ensures the exchange of data between subscribers who have access to network resources via telephone channels of the general purpose network, channels of the Telex network, as well as satellite channels communications. The number of network subscribers is not limited. They are guaranteed reliable data exchange in “real time” mode, transmission of faxes and telephone (telex) messages at a given time, telephone communication via satellite channels. Territorial networks are built according to the ideology of open systems. Their subscribers are individual PCs, LANs, telex installations, fax and telephone installations, network elements (communication network nodes).
The main task of the federal network- creation of a backbone data transmission network with packet switching and provision of real-time data transmission services to a wide range of users, including territorial networks.
Global networks provide the ability to communicate by correspondence and teleconference. The main task of the global network is to provide subscribers with not only access to computer resources, but also the ability to interact between various professional groups, dispersed over a large area.
Topologies
Topology(configuration) is a way of connecting computers into a network.
The type of topology determines cost, security, performance, and
reliability of operation of workstations for which it is important
time to contact file server
There are five main topologies:
− common bus (Bus);
− ring (Ring);
− star (Star);
− tree-like (Tree);
− cellular (Mesh).
Common bus This is a type of network topology in which workstations are distributed
laid along one section of cable, called a segment
IN in this case the cable is used by all stations in turn,
special measures are taken to ensure that when working with common
With the cable, the computers did not interfere with each other transmitting and receiving data.
All messages sent by individual computers are received and
listened to by all other computers connected to the network.
Ring – is a LAN topology in which each station is connected to
two other stations, forming a ring (Fig. 4.2). Data is transmitted from
one workstation to another in one direction (along the ring). Every
The PC works as a repeater, relaying messages to the next PC,
those. data is transmitted from one computer to another as if in a relay race.
If a computer receives data intended for another computer,
Xia. The main problem with a ring topology is that
Each workstation must actively participate in the transfer of information,
and if at least one of them fails, the entire network is paralyzed. That-
pology Ring has a well-predictable response time, determined
number of workstations.
Star – This is a LAN topology in which everything workstations
connected to a central node (such as a hub) that
establishes, maintains and breaks connections between workstations.
The advantage of this topology is the possibility of simply excluding
faulty node. However, if the central node fails, the entire network
fails.
Tree-like topology – achieved from star-shaped by
cascading hubs. This topology is widely used in co-
temporary high-speed local computer networks. As
switching nodes are most often high-speed switches.
The most typical representative of networks with a similar structure is
Xia network 100VG AnyLan. And besides, the high-speed version of the master
Real Ethernet network - Fast Ethernet also has a tree structure.
Compared to tires and ring networks tree locales
new networks are more reliable. Disabling or exiting
building one of the lines or a switch, as a rule, does not have any significant impact
significant impact on the performance of the remaining part of the local network.
Cellular topology is a topology in which everything workers
stations connected to everyone (fully connected topology). Cellular topolo-
gy has found application in the last few years. Her attractiveness is
lies in relative resistance to overloads and failures. Thanks to
multiple paths from devices included in the network, traffic can
be directed to bypass failed or busy nodes. Even though
that this approach is characterized by complexity and high cost (protocols
mesh networks can be quite complex in terms of logic,
to provide these characteristics), some users prefer
mesh networks melt away from other types of networks due to their high reliability
Wireless technologies
Methods wireless technology Data transmission (Radio Waves) are a convenient and sometimes irreplaceable means of communication. Wireless technologies vary in signal type, frequency (higher frequency means faster transmission speed), and transmission distance. Great importance
have interference and cost. There are three main types of wireless technology:
− radio communication;
− communication in the microwave range;
− infrared communication.
routing protocols
Internet is a worldwide collection of computer networks that connects millions of computers. Today the Internet has about 400 million subscribers in more than 150 countries. The network size increases monthly by 7-10%.
Separate local networks can be combined into global area networks (WAN - wide area network). Devices not belonging to the same local physical LAN networks, establish connections to the global network through a specialized communication equipment. The most common method of connecting an “internal” subnet to an “external” subnet is through a gateway computer. The Internet forms the core that enables communications various networks, belonging to various institutions around the world, one to another. The Internet consists of many local and global networks. The Internet can be imagined as a mosaic made up of small networks of different sizes that actively interact with one another, sending files, messages, etc.
From the very beginning, the structure of the Internet was divided into backbone and networks, connected to the highway (autonomous, local). The backbone network and each of the autonomous ones had its own administration and own
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