1 IP routing protocol provides. What does the routing protocol (IP) do? . IP Datagram Header Format

/ Protocols / Connection

The name TCP/IP comes from the two main protocols included in this family - TCP (Transmission Control Protocol) and IP (Internet Protocol). They are responsible for reliable data transfer between computers. The IP protocol is closely related to the concept of an IP address - the unique address of a computer on a network.

TCP – transport protocol

According to this protocol, any message is cut into packets (IP packets) of approximately the same size and format, these packets are numbered and transmitted independently of each other, and at the destination the original message is assembled from the received packets. If one packet is lost, you can send a request to retransmit it (or ask to repeat all packets). In some cases, retransmission does not make sense, for example, when transmitting audio and video in real time.

IP protocol – routing protocol

According to this protocol, each packet, in addition to the data embedded in it, has a header that is only 20 bytes long. It contains the sender's computer address (IP address) and the recipient's address, and other information necessary for the correct assembly of packets at their destination.
In local networks, the path along which the packet is transmitted is determined by the geometric structure of the network and the possible ways of connecting nodes. Knowing this, you can accurately indicate the path that data takes when transmitting a message from one computer on the local network to another.
In global networks and the Internet, the route of each packet is determined dynamically during transmission. This guarantees optimal loading of nodes and resistance of the system to damage to individual areas. Special devices - routers - select the path of the packet and forward it to the next network node. The principle of dynamic route determination is called flexible routing.

The principles of packet switching and flexible routing were first applied in the United States during the development of the ARPANET network in 1969. That is why ARPANET is considered the prototype of the Internet. TCP/IP is the basis of the Internet.
The user most often deals with application protocols. Each application protocol has its own service or Internet service.
For example, HTTP protocol deals with WWW documents - Web pages, users work using the HTTP protocol.
FTP protocol allows you to transfer information in the form of files over the network.
Postal POP and SMTP protocols provide connection to mail servers, sending and delivery of letters.
NNTP protocol allows you to work with the news service.

The Internet, which is a network of networks and unites a huge number of different local, regional and corporate networks, operates and develops through the use of a single TCP/IP data transfer protocol. The term TCP/IP includes the name of two protocols:

Transmission Control Protocol (TCP) - transport protocol;

Internet Protocol (IP) is a routing protocol.

Routing protocol. The IP protocol ensures the transfer of information between computers on a network. Let's consider the operation of this protocol by analogy with the transfer of information using regular mail. In order for the letter to reach its intended destination, the address of the recipient (who the letter is to) and the address of the sender (from whom the letter is from) are indicated on the envelope.

Similarly, information transmitted over the network is “packed in an envelope” on which the IP addresses of the recipient’s and sender’s computers are “written”, for example “To: 198.78.213.185”, “From: 193.124.5.33”. The contents of the envelope in computer language are called an IP packet and are a set of bytes.

In the process of forwarding regular letters, they are first delivered to the post office closest to the sender, and then transferred along the chain of post offices to the post office closest to the recipient. At intermediate post offices, letters are sorted, that is, it is determined to which next post office a particular letter should be sent.

On the way to the recipient computer, IP packets also pass through numerous intermediate Internet servers where the routing operation is performed. As a result of routing, IP packets are sent from one Internet server to another, gradually approaching the recipient computer.

Internet Protocol (IP) provides routing of IP packets, that is, the delivery of information from the sending computer to the receiving computer.

Determining the route for information to pass through. The “geography” of the Internet differs significantly from the geography we are accustomed to. The speed of obtaining information does not depend on the distance of the Web server, but on the number of intermediate servers and the quality of communication lines (their capacity) through which information is transmitted from node to node.

You can get acquainted with the route of information on the Internet quite simply. The special program tracert.exe, which is included in Windows, allows you to track through which servers and with what delay information is transferred from the selected Internet server to your computer.

Let's see how access to information is implemented in the "Moscow" part of the Internet to one of the most popular search servers on the Russian Internet www.rambler.ru.

Determining the route of information passage

1. Connect to the Internet, enter the command [Programs-MS-DOS Session].

2. In the MS-DOS Session window, in response to the system prompt, enter the command.

3. After some time, a trace of information transfer will appear, that is, a list of nodes through which information is transmitted to your computer, and the time of transmission between nodes.

Route tracing transmission of information shows that the server www.rambler.ru is located at a “distance” of 7 transitions from us, i.e. information is transmitted through six intermediate Internet servers (through the servers of the Moscow providers MTU-Inform and Demos). The speed of information transfer between nodes is quite high; one “transition” takes from 126 to 138 ms.

Transport protocol. Now let’s imagine that we need to send a multi-page manuscript by mail, but the post office does not accept parcels or packages. The idea is simple: if the manuscript does not fit into a regular postal envelope, it must be disassembled into sheets and sent in several envelopes. In this case, the sheets of the manuscript must be numbered so that the recipient knows in what sequence these sheets will be combined later.

A similar situation often occurs on the Internet when computers exchange large files. If you send such a file as a whole, it can “clog” the communication channel for a long time, making it inaccessible for sending other messages.

To prevent this from happening, on the sending computer it is necessary to split the large file into small parts, number them and transport them in separate IP packets to the receiving computer. On the recipient computer, it is necessary to assemble the source file from individual parts in the correct sequence.

Transmission Control Protocol (TCP), that is, a transport protocol, ensures that files are split into IP packets during transmission and files are assembled during reception.

Determining the time of IP packet exchange. The time for the exchange of IP packets between the local computer and the Internet server can be determined using the ping utility, which is part of the Windows operating system. The utility sends four IP packets to the specified address and shows the total transmission and reception time for each packet

73. Searching for information on the Internet.

There is a largely fair opinion that today the Internet “has everything” and the only problem is how to find the necessary information. The very open architecture of the Network means that it lacks any centralization and the most valuable data for you, which you have unsuccessfully searched all over the world, may turn out to be located on a server in the same city as you. There are two complementary approaches to collecting information about Internet resources: creating indexes And creating directories:

With the first method, powerful search servers They continuously “search” the Internet, creating and updating databases containing information about which documents on the Internet contain certain keywords. Thus, in reality the search takes place not on Internet servers, which would be technically impossible, but on the database of a search engine, and the absence of suitable information found upon request does not mean that it is not on the Internet - you can try using another search tool or resource directory. Search server databases are not only replenished automatically. Any major search engine has the ability to index your site and add it to the database. The advantage of the search server is the ease of working with it, the disadvantage is the low degree of selection of documents upon request.

In the second case, the server is organized as library catalog, containing a hierarchy of sections and subsections that store links to documents that correspond to the topic of the subsection. The catalog is usually replenished by the users themselves after checking the data they entered by the server administration. A resource catalog is always better organized and structured, but it takes time to find the right category, which, moreover, is not always easy to define. In addition, the size of the directory is usually less than the number of sites indexed by the search engine.

Working with search servers. When entering the main page of the search server, just type your query in the input field in the form of a set of keywords and press Enter or the start search button.

Queries can contain any words, and it is not necessary to worry about cases and declensions - for example, the queries “philosophy essay” and “philosophy essay” are quite correct.

Modern search servers understand natural language quite well, however, many of them retain advanced or special search capabilities that allow you to search for words by mask, combine query words with logical operations “AND”, “OR”, etc.

After completing the database search, the server displays the first batch of 10 or more documents containing the keywords. In addition to the link, there are usually several lines of text describing the document or just its beginning. By opening links in a new or the same browser window, you can move to the selected documents, and the line of links at the bottom of the page allows you to move to the next portion of documents. This line looks something like this:

Different servers sort found documents in different ways - by date of creation, by document traffic, by the presence of all or part of the query words in the document ( relevance), some servers allow you to narrow your search by selecting the category of the document you are looking for on the main page - for example, the query “banks” in the “business world” category is unlikely to find information about cans.

Among the popular Russian-language search tools we can name servers Yandex, Aport And Rambler, indexing tens of thousands of servers and tens of millions of documents. Popular from foreign servers Altavista, Excite, Hotbot, Lycos, WebCrawler, OpenText.

Finally, there are many pages on the Internet for metasearch, allowing you to access several popular search servers at once with the same query - look, for example, at the pages http://www.find.ru/ or http://www.rinet.ru/buki/.

Working with resource catalogs. When we enter the main page of the catalog, we find ourselves in an extensive menu or table for selecting categories, each of which can contain nested subcategories. There is no standard here, but still the directory structures are very similar, everywhere you can find sections “business” or “business world”, “computers”, “programming” or “Internet”, “humor” or “hobbies”, etc. . By moving through categories, you can get to links to specific documents, which, just like on a search server, are issued in portions and are accompanied by brief information.

Today there are many large directories with tens of thousands of links, from domestic directories we can name http://www.list.ru/, http://www.weblist.ru/, http://www.stars.ru/, http://www.au.ru/, http://www.ru/, http://www.ulitka.ru/, and from foreign ones - Yahoo, Magellan.

Often the catalog also has a form for searching by keywords among the documents listed in it.

Search rules. A few simple tips regarding searching the Internet.

clearly define in advance the topic of your search, keywords and the time you are willing to spend on this search; select a search server - it is useful to store links to the best of them in Favorites;

do not be afraid of natural language, but check the correct spelling of words, for example, using Microsoft Word;

Use capital letters only in names and titles. Many search engines will correctly process the query “abstract”, but not “Abstract”;

TCP/IP data transfer protocol

The Internet, which is a network of networks and unites a huge number of different local, regional and corporate networks, operates and develops through the use of a single TCP/IP data transfer protocol. The term TCP/IP includes the name of two protocols:

• Transmission Control Protocol (TCP) - transport protocol;
• Internet Protocol (IP) is a routing protocol.

Routing protocol. The IP protocol ensures the transfer of information between computers on a network. Let's consider the operation of this protocol by analogy with the transfer of information using regular mail. In order for the letter to reach its intended destination, the address of the recipient (who the letter is to) and the address of the sender (from whom the letter is from) are indicated on the envelope.

Similarly, information transmitted over the network is “packed in an envelope” on which the IP addresses of the recipient’s and sender’s computers are “written”, for example “To: 198.78.213.185”, “From: 193.124.5.33”. The contents of the envelope in computer language are called IP packet and is a set of bytes.

In the process of forwarding regular letters, they are first delivered to the post office closest to the sender, and then transferred along the chain of post offices to the post office closest to the recipient. At intermediate post offices, letters are sorted, that is, it is determined to which next post office a particular letter should be sent.

IP packets on the way to the recipient computer also pass through numerous intermediate Internet servers on which the operation is performed routing. As a result of routing, IP packets are sent from one Internet server to another, gradually approaching the recipient computer.

Internet Protocol (IP) provides routing of IP packets, that is, delivery of information from the sending computer to the receiving computer.

Determining the route for information to pass through. The “geography” of the Internet differs significantly from the geography we are accustomed to. The speed of obtaining information does not depend on the distance of the Web server, but on the number of intermediate servers and the quality of communication lines (their capacity) through which information is transmitted from node to node.

You can get acquainted with the route of information on the Internet quite simply. The special program tracert.exe, which is included in Windows, allows you to track through which servers and with what delay information is transferred from the selected Internet server to your computer.

Let's see how access to information is implemented in the "Moscow" part of the Internet to one of the most popular search servers on the Russian Internet www.rambler.ru.

Determining the route of information flow

2. In the window MS-DOS session in response to the system prompt to enter the command.

3. After some time, a trace of information transfer will appear, that is, a list of nodes through which information is transmitted to your computer, and the time of transmission between nodes.

Tracing the route of information transmission shows that the server www.rambler.ru is located at a “distance” of 7 transitions from us, i.e. information is transmitted through six intermediate Internet servers (through the servers of the Moscow providers MTU-Inform and Demos). The speed of information transfer between nodes is quite high; one “transition” takes from 126 to 138 ms.

Transport protocol. Now let’s imagine that we need to send a multi-page manuscript by mail, but the post office does not accept parcels or packages. The idea is simple: if the manuscript does not fit into a regular postal envelope, it must be disassembled into sheets and sent in several envelopes. In this case, the sheets of the manuscript must be numbered so that the recipient knows in what sequence these sheets will be combined later.

A similar situation often occurs on the Internet when computers exchange large files. If you send such a file as a whole, it can “clog” the communication channel for a long time, making it inaccessible for sending other messages.

To prevent this from happening, on the sending computer it is necessary to split the large file into small parts, number them and transport them in separate IP packets to the receiving computer. On the recipient computer, it is necessary to assemble the source file from individual parts in the correct sequence.

Transmission Control Protocol (TCP), that is, the transport protocol, ensures that files are split into IP packets during transmission and files are assembled during reception.

Interestingly, for the IP protocol responsible for routing, these packets are completely unrelated to each other. Therefore, the last IP packet may well overtake the first IP packet along the way. It may turn out that even the delivery routes for these packages will be completely different. However, TCP will wait for the first IP packet and assemble the source file in the correct sequence.

Determining the time of IP packet exchange. The time for the exchange of IP packets between the local computer and the Internet server can be determined using the ping utility, which is part of the Windows operating system. The utility sends four IP packets to the specified address and shows the total transmission and reception time for each packet.

Determining the time of IP packet exchange

1. Connect to the Internet, enter the command [Programs-MS-DOS Session].

2. In the window MS-DOS session in response to the system prompt to enter the command.

3. In the window MS-DOS session The result of testing the signal in four attempts will be displayed. The response time characterizes the speed parameters of the entire chain of communication lines from the server to the local computer.

Questions to Consider

1. What ensures the integral functioning of the global computer network Internet?

Practical tasks

4.5. Trace the route of information from one of the most popular Internet search servers www.yahoo.com, located in the “American” segment of the Internet.

4.6. Determine the time of exchange of IP packets with the www.yahoo.com server.

TCP/IP protocol (Transmission Control Protocol/Internet Protocol) is a network protocol stack commonly used for the Internet and other similar networks (for example, this protocol is also used in LANs). The name TCP/IP comes from the two most important protocols:

• IP (Internet Protocol) - is responsible for transmitting a data packet from node to node. IP forwards each packet based on a four-byte destination address (IP address).
• TCP (Transmission Control Protocol) - is responsible for verifying the correct delivery of data from the client to the server. Data may be lost in the intermediate network. TCP added the ability to detect errors or lost data and, as a result, the ability to request retransmission until the data is correctly and completely received.

Main characteristics of TCP/IP:

• Standardized high-level protocols used for well-known user services.
• Open protocol standards are used, which makes it possible to develop and refine standards regardless of software and hardware;
• Unique addressing system;
• Independence from the physical communication channel used;

The principle of operation of the TCP/IP protocol stack is the same as in the OSI model; data from the upper layers is encapsulated in packets from the lower layers.

If a packet moves through the level from top to bottom, at each level service information is added to the packet in the form of a header and possibly a trailer (information placed at the end of the message). This process is called. Service information is intended for an object of the same level on a remote computer. Its format and interpretation are determined by the protocols of this layer.

If a packet moves through the layer from bottom to top, it is divided into header and data. The packet header is analyzed, service information is extracted and, in accordance with it, the data is redirected to one of the higher-level objects. The higher level, in turn, analyzes this data and also divides it into header and data, then the header is analyzed and service information and data are allocated for the higher level. The procedure is repeated again until user data, freed from all service information, reaches the application level.

It is possible that the package will never reach the application level. In particular, if a computer operates as an intermediate station on the path between the sender and the recipient, then an object at the appropriate level, when analyzing service information, will determine that the packet at this level is not addressed to it, as a result of which the object will take the necessary measures to redirect the packet to the destination or returned to the sender with an error message. But one way or another it will not promote data to the upper level.

An example of encapsulation can be represented as follows:

Let's look at each level function

Application layer

Applications running the TCP/IP stack can also perform the functions of the presentation layer and part of the session layer of the OSI model.

Common examples of applications are programs:

• Telnet
• HTTP
• Email protocols (SMTP, POP3)

To send data to another application, the application accesses one or another module of the transport module.

Transport layer

Transport layer protocols provide transparent delivery of data between two application processes. A process that receives or sends data is identified at the transport layer by a number called a port number.

Thus, the role of the source and destination address at the transport layer is performed by the port number. By analyzing the header of its packet received from the internetwork layer, the transport module determines by the recipient port number which of the application processes the data is sent to and transmits this data to the corresponding application process.

The recipient and sender port numbers are written into the header by the transport module sending the data. The transport layer header also contains some other overhead information, and the format of the header depends on the transport protocol used.

Transport layer tools are a functional superstructure over the network layer and solve two main problems:

• ensuring data delivery between specific programs operating, in general, on different network nodes;
• ensuring guaranteed delivery of data arrays of arbitrary size.

Currently, two transport protocols are used on the Internet - UDP, which provides non-guaranteed delivery of data between programs, and TCP, which provides guaranteed delivery with the establishment of a virtual connection.

Network (internet) level

The main protocol at this layer is the IP protocol, which delivers blocks of data (datagrams) from one IP address to another. An IP address is a unique 32-bit identifier of a computer, or more precisely, its network interface. The data for the datagram is transmitted to the IP module by the transport layer. The IP module adds a header to this data containing the IP address of the sender and recipient, and other service information.

Thus, the generated datagram is transferred to the media access layer to be sent over the data link.

Not all computers can directly communicate with each other; often, in order to transmit a datagram to its destination, it is necessary to route it through one or more intermediate computers along a particular route. The task of determining the route for each datagram is solved by the IP protocol.

When an IP module receives a datagram from a lower level, it checks the destination IP address; if the datagram is addressed to a given computer, then the data from it is transferred for processing to a higher-level module, but if the destination address of the datagram is foreign, then the IP module can make two decisions:

• Destroys the datagram;
• Send it further to its destination, having determined the route, this is what intermediate stations do - routers.

It may also be necessary at the edge of networks, with different characteristics, to break the datagram into fragments, and then assemble them into a single whole on the recipient’s computer. This is also the task of the IP protocol.

The IP protocol can also send notification messages using the ICMP protocol, for example, in the event of a datagram being destroyed. There are no more means of monitoring the correctness of data, confirmation or delivery, there is no preliminary connection in the protocol; these tasks are assigned to the transport layer.

Media access level

The functions of this level are as follows:

• Mapping IP addresses to physical network addresses. This function is performed by the ARP protocol;
• Encapsulates IP datagrams into frames for transmission over a physical link and extracts the datagrams from the frames without requiring any error-free transmission control, since in the TCP/IP stack such control is assigned to the transport layer or the application itself. The frame header indicates the access point to the SAP service; this field contains the protocol code;
• Determining the method of access to the transmission medium, i.e. the way in which computers establish their right to transmit data;
• Defining the representation of data in the physical environment;
• Frame forwarding and receiving.

Let's consider encapsulation using the example of intercepting an HTTP protocol packet using the wireshark sniffer, which operates at the application level of the TCP/IP protocol:

In addition to the intercepted HTTP protocol itself, the sniffer describes each underlying layer based on the TCP/IP stack. HTTP is encapsulated in TCP, TCP in IPv4, IPv4 in Ethernet II.

Test: Types of networks
1) What does the routing protocol (IP) do?

2. preservation of mechanical, functional parameters of physical communication in a computer network

3. interpretation of data and preparation of it for the user level

4. delivery of information from the sender’s computer to the recipient’s computer

5. splitting files into IP packets during transmission and assembling files during reception

2) What does the transport protocol (TCP) provide?

1. reception, transmission and delivery of one communication session

4. delivery of information from the sending computer to the recipient computer
3) How is the capacity of the information transmission channel measured?

4. KB/s

4) What is the name of the local network topology, where workstations are connected to a server (file server)?

2. ring

4. tree-like

5) A set of computers connected by information exchange channels and located within one (or several) premises or building is called:

1. global computer network

2. local computer network

4. by email

5. regional computer network

6) Local computer networks are used as a means of communication

2. only for data exchange between several users

3. to communicate with people directly

5. only for organizing access to information resources common to all users
7) Match

1. information system with hyperlinks

3. a set of local networks and computers located over long distances and connected via communication channels into a single system

2. when did computers appear?

10) To store files intended for public access by network users, the following is used:

1. host computer

2. client-server

3. file server

4. switch

5. workstation

11) What does the general information transfer scheme include?

1. sender of information, channel for transmitting information and recipient of information

2. sender information, channel bandwidth

3. sender of information, channel capacity and recipient of information

12) What groups are Internet search servers divided into?

2. specialized and general purpose

3. all kinds

Option 2

Topic: Computer communications

Test: Types of networks
1) Global computer networks appeared as a means of communication

1. when did computers appear?

2. when the social need for communication between people living in different parts of the planet has matured

3. when did the scientific and technological revolution take place?

4. when the social need for communication between people living in different parts of the planet has matured and the corresponding technical capabilities have appeared (computer communication systems and networks)

2) A set of computers connected by information exchange channels and located within one (or several) premises or building is called:

1. information system with hyperlinks

2. regional computer network

3. global computer network

4. by email

3) The configuration (topology) of a local computer network, in which all workstations are connected in series to each other, is called:

1. network

2. ring

4. tree-like

5. radial
4) Types of Internet connections?

1. dial-up, fixed line, satellite channel

2. dial-up, satellite channel

3. cell phone
5) Local computer networks are used as a means of communication

1. to organize access to common input devices for all users - printers, plotters and general information resources of local importance

2. only for organizing access to information resources common to all users

3. only for data exchange between several users

4. to exchange data between several users, to organize access to output devices (printers) common to all users, as well as to common information resources of local importance

5. to communicate with people directly

2. ring

4. tree-like

7) Global computer network is:

2. many computers connected by information transmission channels and located within the same room or building

3. a set of host computers and file servers

4. a system for exchanging information on a specific topic

5. information system with hyperlinks

8) Transport protocol (TCP) provides:

1. delivery of information from the sending computer to the recipient computer

2. reception, transmission and delivery of one communication session

3. user access to processed information

4. splitting files into IP packets during transmission and assembling files during receiving

9) Match

10) Network protocol is:

1. rules for interpreting data transmitted over the network

2. sequential recording of events occurring on a computer network

3. a set of agreements on interactions in a computer network

4. rules for establishing communication between two network computers

5. coordination of various processes over time

11) What is network topology?

1. location of network cards

2. general diagram of connecting computers on a network

3. network view

12) Who provides access to the Internet?

2. computer

3. provider

Option 3

Topic: Computer communications

Test: Types of networks
1) The configuration (topology) of a local computer network, in which all workstations are connected in series to each other, is called:

2. radial

3. network

4. tree-like

5. ring

2) The capacity of the information transmission channel is measured in:

4. KB/s

3) Match:

1. a set of local networks and computers located over long distances and connected via communication channels into a single system

2. information system with hyperlinks

3. many computers connected by information transmission channels and located within the same room or building

4. a system for exchanging information on a specific topic

5. a set of host computers and file servers

5) Routing Protocol (IP) provides:

1. control of data transmission equipment and communication channels

2. splitting files into IP packets during transmission and assembling files during receiving

3. preservation of mechanical, functional parameters of physical communication in a computer network

4. delivery of information from the sending computer to the recipient computer

5. interpretation of data and preparation for the user level

6) The configuration (topology) of a local network in which all workstations are connected to a server (file server) is called

1. ring

2. tree-like

7) Transport protocol (TCP) provides:

1. splitting files into IP packets during transmission and assembling files during receiving

2. delivery of information from the sending computer to the recipient computer

3. user access to processed information

4. reception, transmission and delivery of one communication session

8) A set of computers connected by information exchange channels and located within one (or several) premises or building is called:

1. regional computer network

2. global computer network

3. information system with hyperlinks

4. by email

5. local computer network
9) Global computer networks appeared as a means of communication

1. when the social need for communication between people living in different parts of the planet has matured and the corresponding technical capabilities have appeared (computer communication systems and networks)

2. when did computers appear?

3. when did the scientific and technological revolution take place?

4. when the social need for communication between people living in different parts of the planet has matured

10) What's happenedFTP?

1. file transfer protocol

2. page transfer protocol

3. access transfer protocol

11) What is the World Wide Web?

1. these are tens of millions of WEb servers

2. these are computers

3. these are Internet sites

12) Protocols are...

1. specialized tools that allow real-time organization of user communication via computer communication channels

2. a set of rules governing the exchange of data on the network

3. an electronic information transfer system that allows each network user to access programs and documents stored on a remote computer

Answers

Ticket No. 1
1 - 4

7 - 1-b, 2-c, 3-d, 4-e, 5-a

Ticket number 2
1 - 4

7 - 1-a,2-b, 3-c, 4-d, 5-e,

12 - 3
Ticket № 3
1 - 5