Method for predicting the development of interest rates. Methods for forecasting exchange rates

The main thing that distinguishes the Internet from other networks is its protocols − TCP/IP. In general, the term TCP / IP usually means everything related to the protocols for interaction between computers on the Internet. It covers a whole family of protocols, application programs, and even the network itself. TCP/IP is an internetworking technology. A network that uses TCP/IP technology is called the "internet". If we are talking O global network, which unites many networks with TCP / IP technology, it is called the Internet.

TCP/IP got its name from two communication protocols (or communication protocols). These are Transmission Control Protocol (TCP) and Internet Protocol (IP). Although the Internet is using big number other protocols, the Internet is often called TCP/IP-network, since these two protocols are, of course, the most important.

The IP protocol (Internet Protocol) manages the direct transmission of information over the network. All information is divided into parts - packages and sent from the sender to the recipient. In order to accurately address the package, it is necessary to specify the exact coordinates of the recipient or his address.

Internet address consists of 4 bytes. When writing, bytes are separated from each other by dots: 123.45.67.89 or 3.33.33.3. In fact, the address consists of several parts. Because the Internet is a network of networks, the beginning of an address tells Internet hosts which network the address is part of. The right end of the address tells this network which computer or host should receive the packet. Every computer on the Internet has a unique address in this scheme.

Numeric computer address on the Internet is similar to the postal code of the post office. There are several types of Internet addresses (types: A, B, C, D, E), which divide the address in different ways into the fields of the network number and host number, the number of possible networks and machines in such networks depends on the type of such division.

Due to hardware limitations, information sent over IP networks is divided into parts (on byte boundaries), decomposed into separate packages. The length of information within a packet is usually between 1 and 1500 bytes. This protects the network from being monopolized by any user and gives everyone approximately equal rights. For the same reason, if the network is not fast enough, the more users using it at the same time, the slower it will communicate with everyone.

One of the strengths of the Internet is that IP alone is enough to get the job done. However, this protocol also has several disadvantages:

• - most of the information being sent is longer than 1500 characters, so it has to be divided into several packets;
• - some packages may be lost along the way;
• - packets can arrive in a sequence different from the initial one.

The protocols used must provide ways to send large amounts of information without the corruption that can be caused by the network.

The Transmission Control Protocol (TCP) is a protocol closely related to IP that is used for similar purposes but at a higher level. The TCP protocol deals with the problem of sending large amounts of information based on the capabilities of the IP protocol.

TCP divides the information to be sent into several parts and numbers each part to restore order later. To send this numbering along with the data, it covers each piece of information with its own cover - a TCP envelope that contains the corresponding information.

The recipient unpacks the IP envelopes upon receipt and sees the TCP envelopes, unpacks them too, and puts the data in the sequence of parts in the appropriate place. If something is missing, he demands to send this piece again. In the end, the information is collected in the right order and completely restored.

In short, this is a set of rules that govern the “communication” of computers with each other over a network. There are about a dozen of them, and each of them defines the rules for transferring a particular data type. But for ease of handling, they are all combined into the so-called "stack", naming it after the most important protocol - the TCP / IP protocol (Transmission Control Protocol and Internet Protocol). The word "stack" implies that all these protocols are like a "stack of protocols" in which the upper layer protocol cannot function without the lower layer protocol.

The TCP/IP stack includes 4 layers:

1. Applied - HTTP, RTP, FTP, DNS protocols. The top level; responsible for the operation of application applications, such as mail services, displaying data in a browser, and so on.

2. Transport - protocols TCP, UDP, SCTP, DCCP, RIP. This level of protocols ensures the correct interaction of computers with each other and is a data conductor between different participants networks.

3. Network - IP protocol. This layer provides identification of computers on the network by giving each of them a unique digital address.

4. Channel - protocols Ethernet, IEEE 802.11, Wireless Ethernet. Most low level; it interacts with physical equipment, describes the data transmission medium and its characteristics.

Therefore, your computer uses the "HTTP - TCP - IP - Ethernet" protocol stack to display this article.

How information is transmitted over the Internet

Each computer on the network is called a host and, using the protocol of the same name, receives a unique IP address. This address is written in the following form: four numbers from 0 to 255 separated by a dot, for example, 195.19.20.203. For successful network communication, the IP address must also include the port number. Since the information is exchanged not by the computers themselves, but by programs, each type of program must also have its own address, which is displayed in the port number. For example, port 21 is for FTP, port 80 is for HTTP. Total ports on the computer is limited and equal to 65536 with numbering from 0 to 65535. Port numbers from 0 to 1023 are reserved by server applications, and the niche of ports from 1024 to 65535 is occupied by client ports, which programs are free to dispose of as they please. "Client ports" are assigned dynamically.

Combination IP addresses and port numbers called " socket". In it, the address and port values ​​are separated by a colon, for example, 195.19.20.203:110

Thus, in order for a remote computer with IP 195.19.20.203 to receive email, you just need to deliver data to its port 110. And, since this port “listens” day and night for the POP3 protocol, which is responsible for receiving emails, means further - "a matter of technology."

All data over the network is divided into packets for convenience. A packet is a 1-1.5 Mb file that contains the address data of the sender and recipient, the transmitted information, plus service data. Splitting files into packets can greatly reduce the load on the network, because. the path of each of them from the sender to the recipient will not necessarily be identical. If a traffic jam occurs in one place in the network, the packets will be able to bypass it using other communication paths. This technology makes it possible to use the Internet as efficiently as possible: if some of its transport part collapses, information can continue to be transmitted, but in other ways. When the packets reach the target computer, it starts compiling them back into a single file using the overhead they contain. The whole process can be compared to a kind of large puzzle, which, depending on the size of the transferred file, can reach truly enormous sizes.

As mentioned earlier, the IP protocol gives each network member, including sites, a unique numerical address. However, remembering millions of IP addresses is beyond the power of any person! Therefore, the domain name service DNS (Domain Name System) was created, which translates numeric IP addresses into alphanumeric names that are much easier to remember. For example, instead of typing the awful number 5.9.205.233 each time, you can type www.site in your browser's address bar.

What happens when we type in the browser the address of the site we are looking for? A packet is sent from our computer with a request to the DNS server on port 53. This port is reserved by the DNS service, which, after processing our request, returns an IP address corresponding to the alphanumeric site name. After that, our computer connects to the socket 5.9.205.233:80 of the computer 5.9.205.233, which hosts the HTTP protocol responsible for displaying sites in the browser, and sends a packet with a request to receive the www.site page. We need to establish a connection on the 80th port, since it is this port that corresponds to the Web server. You can, with a strong desire, specify the 80th port and directly in the address bar of the browser - http://www.site:80. The web server processes the request received from us and issues several packets containing HTML text that our browser displays. As a result, we see the main page on the screen

StackTCP/ IP.

The TCP/IP stack is a set of hierarchically ordered network protocols. The stack was named after two major protocols - TCP (Transmission Control Protocol) and IP (Internet Protocol). In addition to them, the stack includes several dozens of different protocols. Currently, TCP/IP protocols are the main ones for the Internet, as well as for most corporate and local networks.

In the Microsoft Windows Server 2003 operating system, the TCP/IP stack is chosen as the primary stack, although other protocols are supported (eg, IPX/SPX stack, NetBIOS protocol).

The TCP/IP protocol stack has two important properties:

platform independence, i.e., it can be implemented on a variety of operating systems and processors;

openness, that is, the standards by which the TCP / IP stack is built, are available to anyone.

History of creationTCP/ IP.

In 1967, the US Department of Defense Advanced Research Projects Agency (ARPA) initiated the development of a computer network that was supposed to link a number of universities and research centers that carried out the Agency's orders. The project was named ARPANET. By 1972, the network connected 30 nodes.

Within the framework of the ARPANET project, the main protocols of the TCP / IP stack - IP, TCP and UDP - were developed and published in 1980–1981. An important factor in the spread of TCP / IP was the implementation of this stack in the UNIX 4.2 BSD operating system (1983).

By the end of the 1980s, the greatly expanded ARPANET became known as the Internet (Interconnected networks) and united universities and scientific centers USA, Canada and Europe.

In 1992, a new Internet service appeared - WWW (World Wide Web - World Wide Web), based on the HTTP protocol. Largely due to the WWW, the Internet, and with it the TCP / IP protocols, received rapid development in the 90s.

At the beginning of the 21st century, the TCP / IP stack acquires a leading role in the means of communication not only for global, but also for local networks.

ModelOSI.

The Open Systems Interconnection (OSI) model was developed by the International Organization for Standardization (ISO) for a uniform approach to building and interconnecting networks. The development of the OSI model began in 1977 and ended in 1984 with the approval of the standard. Since then, the model has been a reference for the development, description and comparison of various protocol stacks.

Let's briefly consider the functions of each level.

The OSI model includes seven layers: physical, data link, network, transport, session, presentation, and application.

The physical layer (physical layer) describes the principles of signaling, transmission rate, specifications of communication channels. The level is implemented by hardware (network adapter, hub port, network cable).

The link layer (data link layer) solves two main tasks - it checks the availability of the transmission medium (the transmission medium is most often divided between several network nodes), and it also detects and corrects errors that occur during transmission. The implementation of the level is software-hardware (for example, a network adapter and its driver).

The network layer (network layer) ensures the integration of networks operating on different protocols of the data link and physical layers into a composite network. In this case, each of the networks included in a single network is called subnet(subnet). At the network level, there are two main tasks to solve - routing(routing, choosing the optimal way to send a message) and addressing(addressing, each node in the composite network must have unique name). Usually, the functions of the network layer are implemented by a special device - router(router) and its software.

The transport layer solves the problem of reliable message transmission in a composite network by acknowledging delivery and resending packets. This level and all the following are implemented in software.

The session layer (session layer) allows you to remember information about the current state of the communication session and, in the event of a connection break, resume the session from this state.

The presentation layer provides the conversion of the transmitted information from one encoding to another (for example, from ASCII to EBCDIC).

The application layer implements the interface between the rest of the model layers and user applications.

StructureTCP/ IP. The structure of TCP / IP is not based on the OSI model, but on its own model, called DARPA (Defense ARPA - the new name of the Advanced Research Projects Agency) or DoD (Department of Defense - US Department of Defense). This model has four levels. The correspondence of the OSI model to the DARPA model, as well as to the main protocols of the TCP / IP stack, is shown in Fig. 2.2.

It should be noted that the lower level of the DARPA model - the level of network interfaces - strictly speaking, does not perform the functions of the channel and physical levels, but only provides a connection (interface) of the upper levels of DARPA with the technologies of the networks included in the composite network (for example, Ethernet, FDDI, ATM ).

All protocols included in the TCP/IP stack are standardized in RFC documents.

DocumentationRFC.

Approved official standards for the Internet and TCP/IP are published as RFC (Request for Comments - working proposal) documents. Standards are developed by the entire ISOC community (Internet Society - Internet Community, an international public organization). Any ISOC member may submit a document for publication in an RFC. Further, the document is reviewed by technical experts, development groups and the RFC editor and goes through the following stages in accordance with RFC 2026, called maturity levels:

draft(Internet Draft) - at this stage, experts get acquainted with the document, additions and changes are made;

proposed standard(Proposed Standard) - the document is assigned an RFC number, experts confirmed the viability of the proposed solutions, the document is considered promising, it is desirable that it be tested in practice;

draft standard(Draft Standard) - a document becomes a draft standard if at least two independent developers have implemented and successfully applied the proposed specifications. Minor corrections and improvements are still allowed at this stage;

Internet standard(Internet Standard) - the highest stage standard approval, document specifications are widely used and have proven themselves in practice. A list of Internet standards is given in RFC 3700. Of the thousands of RFCs, only a few dozen are documents with the status of "Internet standard".

In addition to standards, RFCs can also be descriptions of new networking concepts and ideas, guidelines, results of experimental studies provided for information, etc. Such RFCs can be assigned one of the following statuses:

experimental(Experimental) - a document containing information about scientific research and developments that may be of interest to ISOC members;

informational(Informational) - A document published to provide information and does not require approval by the ISOC community;

the best modern experience(Best Current Practice) - A document intended to convey the experience of specific developments, such as protocol implementations.

The status is indicated in the title of the RFC document after the word Category (Category). For documents in the status of standards (Proposed Standard, Draft Standard, Internet Standard), the name is indicated Standards track, as the readiness level may change.

RFC numbers are assigned sequentially and are never re-issued. The original RFC is never updated. An updated version is published under a new number. Obsolete and superseded RFC document gets status historical(Historic).

All currently existing RFC documents can be viewed, for example, on the website www.rfc-editor.org . In August 2007, there were over 5,000. The RFCs referenced in this course are listed in Appendix I.

Overview of the main protocols.

Protocol IP (Internet Protocol) – it is the main network layer protocol responsible for addressing in multiple networks and packet transfer between networks. The IP protocol is datagram protocol, i.e., does not guarantee the delivery of packets to the destination host. The TCP transport layer protocol is responsible for providing guarantees.

Protocols RIP (Routing information Protocol – routing information protocol ) AndOSPF (open Shortest Path First – « shortest routes open first" ) – Routing protocols in IP networks.

Protocol ICMP (Internet control message Protocol – control message protocol in composite networks) is designed to exchange information about errors between network routers and the source node of the packet. With the help of special packets, it reports the impossibility of delivering a packet, the duration of assembling a packet from fragments, anomalous parameter values, changes in the forwarding route and type of service, system status, etc.

Protocol ARP (address Resolution Protocol - address translation protocol) converts IP addresses to hardware addresses of local networks. The reverse transformation is carried out using the protocol RAPR (Reverse ARP).

TCP (transmission control Protocol - transmission control protocol) provides reliable transmission of messages between remote network nodes due to the formation of logical connections. TCP allows error-free delivery of a byte stream generated on one of the computers to any other computer that is part of the composite network. TCP divides a stream of bytes into parts - segments and passes them to the network layer. After these segments have been delivered to their destination, TCP will reassemble them into a continuous stream of bytes.

UDP (user datagram Protocol – user datagram protocol) provides data transfer in a datagram way.

HTTP (hypertext Transfer Protocol - Hypertext Transfer Protocol) - web document delivery protocol, the main protocol of the WWW service.

FTP (File Transfer Protocol - file transfer protocol) - a protocol for transferring information stored in files.

POP 3 (Post office Protocol version 3 – post office protocol) and SMTP (Simple Mail Transfer Protocol – simple mail forwarding protocol) – protocols for delivering incoming Email(POP3) and sending outgoing (SMTP).

telnet – a terminal emulation protocol 1 that allows the user to connect to and work with other remote stations from their machine as if it were their remote terminal.

SNMP (Simple network management Protocol - a simple network management protocol) is designed to diagnose the health of various network devices.

You can see that TCP/IP resides in the third and fourth layers of the OSI model. The point of this is to leave the LAN technology to developers. The purpose of TCP/IP is messaging V local networks any type and establishing a connection using any network application.

The TCP / IP protocol functions due to the fact that it is associated with the OSI model at the two lowest levels - at the data transfer layer and physical level. This allows TCP/IP to find mutual language with almost any network technology and, as a result, with any computer platform. TCP/IP includes four abstract layers, listed below.

Rice. 3.1.

• network interface. Allows TCP/IP to actively interact with all modern network technologies based on the OSI model.
• Internet. Defines how IP manages forwarding messages through routers in network space such as the Internet.
• Transport. Defines the mechanism for exchanging information between computers.
• Applied. Specifies network applications to perform tasks such as forwarding, e-mail, and others.

Because of its widespread adoption, TCP/IP has become the de facto Internet standard. The computer on which it is implemented network technology, based on the OSI model (Ethernet or Token Ring), has the ability to communicate with other devices. In Fundamentals of Networking, we looked at layers 1 and 2 when discussing LAN technologies. Now we will move on to the OSI stack and see how a computer communicates on the Internet or in private network. This section discusses the TCP/IP protocol and its configurations.

What is TCP/IP

That computers can communicate with one another is a miracle in itself. After all, these are computers from different manufacturers, working with different operating systems and protocols. In the absence of some common ground such devices would not be able to exchange information. When sent over a network, data must be in a format that both the sending device and the receiving device can understand.

TCP/IP satisfies this condition through its internetwork layer. This layer directly corresponds to the network layer of the OSI reference model and is based on a fixed message format called an IP datagram. A datagram is something like a basket in which all the message information is placed. For example, when you load a web page into a browser, what you see on the screen is delivered piecemeal by a datagram.

It is easy to confuse datagrams with packets. A datagram is an information unit, while a packet is a physical message object (created on the third or more high levels) that is actually being sent on the network. Although some consider these terms interchangeable, their distinction actually matters in a certain context - not here, of course. It is important to understand that the message is broken into fragments, transmitted over the network and reassembled on the receiving device.

The positive side of this approach is that if a single packet is corrupted during transmission, only that packet will need to be retransmitted, not the entire message. Another positive is that no host has to wait indefinitely for a long time until the transmission on the other host ends, to send its own message.

TCP and UDP

When forwarding an IP message over a network, one of the transport protocols is used: TCP or UDP. TCP (Transmission Control Protocol) is the first half of the TCP/IP acronym. The User Datagram Protocol (UDP) is used instead of TCP to transport less important messages. Both protocols are used for correct messaging in TCP/IP networks. There is one significant difference between these protocols.

TCP is called a reliable protocol because it communicates with the recipient to verify that the message has been received.

UDP is called an unreliable protocol because it doesn't even attempt to communicate with the recipient to ensure delivery.

It is important to remember that only one protocol can be used to deliver a message. For example, when loading a web page, TCP controls the delivery of packets without any intervention from UDP. On the other hand, the Trivial File Transfer Protocol (TFTP) downloads or sends messages under the control of the UDP protocol.

The transport method used depends on the application - it can be email, HTTP, network application, and so on. Network software developers use UDP wherever possible, as this protocol reduces excess traffic. The TCP protocol puts more effort into guaranteed delivery and transmits many more packets than UDP. Figure 3.2 lists network applications and shows which applications use TCP and which use UDP. For example, FTP and TFTP do pretty much the same thing. However, TFTP is mainly used for downloading and copying network device programs. TFTP can use UDP because if a message fails, nothing bad happens, because the message was not intended for the end user, but for the network administrator, whose priority level is much lower. Another example is a video voice session, in which ports for both TCP sessions and UDP sessions can be used. Thus, a TCP session is initiated to exchange data when a telephone connection is established, while itself phone conversation transmitted over UDP. This is related to the speed of voice and video streaming. If a packet is lost, it does not make sense to resend it, since it will no longer correspond to the data stream.

IP datagram format

IP packets can be split into datagrams. The datagram format creates fields for the payload and for the transmission control data of the message. Figure 3.3 shows the diagram of a datagram.

Note. Don't be fooled by the size of the data field in a datagram. The datagram is not overloaded with additional data. The data field is actually the largest field in a datagram.

It is important to remember that IP packets can have different length. In Networking Fundamentals, it was said that information packets on an Ethernet network have a size of 64 to 1400 bytes. In the Token Ring network, their length is 4000 bytes, in the ATM network - 53 bytes.

Note. The use of bytes in a datagram can confuse you, as data transfer is often associated with concepts such as megabits and gigabits per second. However, because computers prefer to work with data bytes, datagrams also use bytes.

If you look again at the datagram format in Figure 3.3, you will notice that the leftmost margins are constant. This is because the packet processing CPU needs to know where each field starts. Without standardization of these fields, the final bits will be a hodgepodge of 0s and 1s. On the right side of the datagram are packets of variable length. The purpose of the various fields of the datagram is as follows.

• VER. The version of the IP protocol used by the station where the original message originated. The current version of IP is version 4. This field ensures that different versions exist at the same time across the internet.
• HLEN. The field informs the receiving device of the length of the header so that the CPU knows where the data field begins.
• Service type. Code that tells the router the type of packet control in terms of service level (reliability, precedence, backoff, etc.).
• Length (Length). The total number of bytes in the packet, including header fields and data field.
• ID, frags and frags offset. These fields tell the router how to fragment and reassemble the packet and how to compensate for differences in frame size that can occur when a packet travels across LAN segments with different network technologies (Ethernet, FDDI, etc.).
• TTL. An abbreviation for Time to Live is a number that decreases by one each time a packet is forwarded. If the lifetime becomes zero, then the package ceases to exist. TTL prevents loops and endless wandering of lost packets across the internet.
• protocol. The transport protocol to use to transfer the packet. Most often, this field specifies the TCP protocol, but other protocols can be used.
• Header checksum . The checksum is a number that is used to check the integrity of the message. If the checksums of all packets of a message do not match the correct value, then the message has been corrupted.
• Source IP address. The 32-bit address of the host that sent the message (usually a personal computer or server).
• Destination IP address. The 32-bit address of the host to which the message was sent (usually a personal computer or server).
• IP options. Used for network testing or other special purposes.
• Padding. Fills in all unused (empty) bit positions so that the processor can correctly determine the position of the first bit in the data field.
• data. The payload of the sent message. For example, the package data field might contain the text of an email.

As mentioned earlier, the packet consists of two main components: data about the processing of the message, placed in the header, and the actual information. The information part is in the payload sector. Can you imagine this sector as a cargo hold spaceship. The heading is all of the shuttle's on-board computers in the cockpit. It manages all the information needed by various routers and computers along the path of the message, and is used to maintain a certain order in which the message is assembled from individual packets.

Introduction to TCP/IP

The Internet is based on the TCP/IP family of communication protocols, which stands for Transmission Control Protocol/Internet Protocol (Transmission Control Protocol/Internet Protocol). TCP/IP is used for data transmission both in the global Internet and in many local networks. This chapter provides a brief overview of the TCP/IP protocols and the methods they use to control communications.

Of course, you don't need any special knowledge of the TCP/IP protocols to use the Internet as a user, but an understanding of the basic principles will help you troubleshoot common problems that may arise, in particular, when setting up an e-mail system. TCP/IP is also closely related to the other two basic Internet applications FTP and Telnet. Finally, knowing some of the fundamental concepts of the Internet will help you fully appreciate the complexity of this system, just as understanding the operation of an internal combustion engine helps you respect the design of a car.

What is TCP/IP

TCP/IP is the name of a family of protocols for transferring data over a network. A protocol is a set of rules that all companies must adhere to in order to ensure the compatibility of their hardware and software. These rules ensure that a Digital Equipment machine running TCP/IP can communicate with a Compaq PC also running TCP/IP. As long as certain standards are met, it does not matter who the software or hardware manufacturer is for the operation of the entire system. The ideology of open systems involves the use of standard hardware and software. TCP/IP is an open protocol, which means that all protocol-specific information is published and can be freely used.

A protocol defines how one application communicates with another. This software communication is like a dialogue: "I send you this piece of information, then you send back this to me, then I send you that. You must add all the bits and send back the total result, and if there are problems, you must send me appropriate message." The protocol defines how the various parts of the complete packet govern the transfer of information. The protocol specifies whether the packet contains an e-mail message, newsgroup article, or service message. The protocol standards are formulated in such a way that possible unforeseen circumstances are taken into account. The protocol also includes error handling rules.

The term TCP/IP includes the names of two protocols - Transmission Control Protocol (TCP) and Internet Protocol (IP). TCP/IP is not a single program, as many users mistakenly believe. In contrast, TCP/IP refers to a family of related protocols designed to carry information over a network while simultaneously providing information about the state of the network itself. TCP/IP is a software component of the network. Each part of the TCP/IP family performs a specific task: sending e-mail, providing remote login services, transferring files, routing messages, or handling network failures. The use of TCP/IP is not limited to the global Internet. These are the most widely used network protocols worldwide, used both in large corporate networks and in local networks with a small number of computers.

As just mentioned, TCP/IP is not one protocol, but a family of them. Why is the term TCP/IP sometimes used when referring to a service other than TCP or IP? Usually, the general name is used when discussing the entire family of network protocols. However, some users, when talking about TCP / IP, have in mind only some of the protocols of the family: they assume that the other side in the dialogue understands what exactly is being discussed. In fact, it is better to call each of the services by its own name in order to bring more clarity to the subject.

TCP/IP Components

The various services included in TCP/IP and their functions can be classified according to the type of tasks they perform. The following is a description of protocol groups and their purpose.

Transportnprotocols manage the transfer of data between two machines.

TCP (Transmission Control Protocol). A protocol that supports data transfer based on a logical connection between the sending and receiving computers.

UDP (User Datagram Protocol). A protocol that supports the transfer of data without establishing a logical connection. This means that data is sent without first establishing a connection between the computers of the recipient and the sender. You can draw an analogy with sending mail to some address, when there is no guarantee that this message will arrive at the addressee, if it exists at all. (The two machines are connected in the sense that both are connected to the Internet, but they do not communicate with each other through a logical connection.)

Routing Protocols handle data addressing and determine the best paths to the destination. They can also split large messages into smaller messages, which are then sequentially transmitted and assembled into a single unit on the destination computer.

IP (Internet Protocol). Provides the actual data transfer.

ICMP (Internet Control Message Protocol). Handles status messages for IP, such as errors and changes in network hardware that affect routing.

RIP (Routing Information Protocol). One of several protocols that determine the best route for delivering a message.

OSPF (Open Shortest Path First). An alternative protocol for defining routes.

Support network address - it is a way to identify a machine with a unique number and name. (See later in this chapter for more information about addresses.)

ARP (Address Resolution Protocol). Specifies the unique numerical addresses of machines on the network.

DNS (Domain Name System). Determines numeric addresses from machine names.

RARP (Reverse Address Resolution Protocol). Determines the addresses of machines on the network, but in the reverse way to ARP.

Applied Services - these are programs that a user (or computer) uses to access various services. (For more information, see "TCP/IP Applications" later in this chapter.)

BOOTP (Boot Protocol) boots the network machine by reading the boot information from the server.

FTP (File Transfer Protocol) transfers files between computers.

TELNET provides remote terminal access to the system, i.e. a user of one computer can connect to another computer and feel as if he is working at the keyboard of a remote machine.

Gateway protocols help transmit routing messages and network status information over the network, and process data for local area networks. (For more information about gateway protocols, see "Gateway Protocols" later in this chapter.)

EGP (Exterior Gateway Protocol) is used to transmit routing information for external networks.

GGP (Gateway-to-Gateway Protocol) is used to transfer routing information between gateways.

IGP (Interior Gateway Protocol) is used to transmit routing information for internal networks.

NFS (Network File System) allows you to use the directories and files of a remote computer as if they existed on the local machine.

NIS (Network Information Service) maintains information about the users of multiple computers on the network, making it easy to log on and check passwords.

RPC (Remote Procedure Call) allows remote applications to communicate with each other in a simple and efficient way.

SMTP (Simple Mail Transfer Protocol) is a protocol that transfers email messages between machines. SMTP is discussed in more detail in Chap. 13 "How e-mail works on the Internet."

SNMP (Simple Network Management Protocol) is a protocol for administration that sends messages about the status of the network and devices connected to it.

All of these services together make up TCP/IP, a powerful and efficient family of network protocols.

Numeric computer address

Each machine that is connected to the Internet or any other TCP/IP network must be uniquely identified. Without a unique identifier, the network doesn't know how to deliver the message to your machine. If more than one computer has the same identifier, the network will not be able to address the message.

On the Internet, computers on a network are identified by assigning Internet addresses or, more correctly, IP addresses. IP addresses are always 32 bits long and consist of four parts of 8 bits. This means that each part can take on a value between 0 and 255. The four parts are combined into a notation in which each eight-bit value is separated by a dot. For example, 255.255.255.255 or 147.120.3.28 are two IP addresses. When we talk about a network address, we usually mean an IP address.

If all 32 bits of an IP address were used, there would be over four billion possible addresses - more than enough for the future expansion of the Internet! However, some combinations of bits are reserved for special purposes, which reduces the number of potential addresses. In addition, 8-bit quads are grouped in special ways depending on the type of network, so that the actual number of possible addresses is even smaller.

IP addresses are not assigned according to the principle of listing hosts on the network -1, 2, 3, ... In fact, the IP address, as it were, consists of two parts: the network address and the host address on this network. This IP address structure allows computers on different networks to have the same number. Because the network addresses are different, the computers are uniquely identified. Without such a scheme, numbering quickly becomes very inconvenient.

IP-addresses are allocated depending on the size of the organization and the type of its activities. If this is a small organization, then most likely there are few computers (and, therefore, IP addresses) on its network. On the contrary, a large corporation may have thousands of computers connected in several interconnected local area networks. To provide maximum flexibility, IP addresses are allocated depending on the number of networks and computers in the organization and are divided into classes A, B and C. There are also classes D and E, but they are used for specific purposes.

Three classes of IP addresses allow you to distribute them depending on the size of your organization's network. Since 32 bits is the legal total size of an IP address, the classes break the four 8-bit parts of the address into a network address and a host address, depending on the class. One or more bits are reserved at the beginning of the IP address to identify the class.

Class A addresses - numbers between 0 and 127

Class B addresses - numbers between 128 and 191

Class C addresses - numbers between 192 and 223

If your machine's IP address is 147.14.87.23, then you know that your machine is on a class B network, the network ID is 147.14, and your machine's unique number on that network is 87.23. If the IP address is 221.132.3.123, then the machine is on a class C network with network ID 221.132.3 and host ID 123.

Whenever a message is sent to any host computer on the Internet, the IP address is used to indicate the address of the sender and recipient. Of course, you don't have to remember all the IP addresses yourself, as there is a special TCP/IP service called the Domain Name System for that.

Domain names

When a company or organization wants to use the Internet, a decision must be made; either connect directly to the Internet themselves, or entrust all connection issues to another company, called a service provider. Most companies choose the second path in order to reduce the amount of equipment, remove administrative issues and reduce overall costs.

If a company chooses to connect directly to the Internet (and sometimes through a service provider), it may be desirable to obtain a unique identifier for itself. For example, the ABC Corporation might want to obtain an Internet e-mail address containing the string abc.com. Such an identifier, including the name of the company, allows the sender to identify the addressee's company.

To obtain one of these unique identifiers, called a domain name, a company or organization sends a request to the authority that controls Internet connectivity, the Network Information Center (InterNIC). If the InterNIC approves the company name, it is added to the Internet database. Domain names must be unique to prevent collisions.

The last part of the domain name is called the top-level domain identifier (for example, .corn). There are six top-level domains established by InterNIC:

Agra ARPANET ID

Corn Commercial Companies

Edu Educational Institutions

Gov Government agencies or organizations

Mil Military establishments

Org Organizations that do not fit into any of the above categories

WWW Service

World Wide Web (WWW, World Wide Web) is newest look Internet information services based on the client-server architecture. In the late 80s, CERN (European Center for Particle Physics) began work on creating an information service that would allow any user to easily find and read documents hosted on servers in any part of the Internet. To do this, a standard document format was developed that allows you to visually present information on a computer display of any type, as well as provide the ability to install links to other documents within one document.

Although the WWW was designed to be used by CERN staff, once this type of service was made public, its popularity grew at an unusually fast rate. Many applications have been developed that are used as WWW clients, that is, providing access to WWW servers and displaying documents on the screen. Client software is available based on both a graphical user interface (Mosaic is one of the most popular) and alphanumeric terminal emulation (Lynx is an example). Most WWW clients allow you to use their interface to access other types of Internet services such as FTP and Gopher.

Documents hosted on WWW servers are not just ASCII text documents. These are ASCII files containing commands of a special language called HTML (HyperText Markup Language, Hypertext Markup Language). HTML commands allow you to structure a document by highlighting logically distinct parts of text in it (headings different levels, paragraphs, enumerations, etc.). As a result, each of the client WWW viewers can format the text of the document in such a way as to best display it on a particular display. To make documents more expressive, text is usually formatted with larger font sizes for headings, bold and italic styles for important terms, emphasis on list items, and so on. HTML also allows documents to include illustrative graphics that can be displayed by viewers based on on the use of a graphical user interface.

One of the most important properties HTML is the ability to include hypertext links in a document. These links allow the user to download a new document to their computer by simply clicking on the screen where the link. Any document can contain links to other documents. The referenced document can be located on the same WWW server as the source document, or on any other computer on the Internet. The area of ​​the document used as a link can be a word, a group of words, a graphic image, or even a specified fragment of an image. Most Web browsers can also access other information services such as FTP and Gopher. In addition, WWW viewers allow you to work with multimedia files containing video and sound, by using multimedia support programs installed on the local computer.