TCP/IP is an abbreviation for the term Transmission Control Protocol/Internet Protocol. In fact, TCP / IP is not one protocol, but many, a stack of protocols.

TCP/IP was developed so that the computer networks of research centers around the world could be connected in the form of a virtual "network of networks" (internetwork). The original Internet was created by converting an existing conglomerate of computer networks called ARPAnet using TCP/IP.

On a TCP/IP network, information is transmitted in discrete units called IP packets or IP datagrams. Essentially, TCP/IP hides routers and the underlying architecture of networks from users so that it all looks like one big network. Just like connecting to Ethernet networks are identified by 48-bit Ethernet IDs, intranet connections are identified by 32-bit IP addresses, which we express as dotted decimal numbers (for example, 128.10.2.3). By taking the IP address of a remote computer, a computer on an intranet or on the Internet can send data to it as if they were part of the same physical network.

Data is transmitted in packets. Packets have a header and an ending that contain service information. Data from higher levels is inserted (encapsulated), like a letter in an envelope, into packets of lower levels.

TCP/IP provides a solution to the problem of communication between two computers connected to the same intranet but belonging to different physical networks. The solution consists of several parts, with each layer of the TCP / IP protocol family contributing to the overall cause. IP, the most fundamental protocol in the TCP/IP suite, transports IP datagrams and provides choice of route that the datagram will take from point A to point B and the use of routers to "hop" between networks.

TCP is a higher level protocol that allows applications running on different computers on a network to exchange data streams. TCP divides data streams into chains, called TCP segments, and transmits them using IP. In most cases, each TCP segment is sent in one IP datagram. However, if necessary, TCP will split the segments into multiple IP datagrams that fit into the physical data frames that are used to transfer information between computers on the network. Because IP does not guarantee that datagrams will be received in the same sequence in which they were sent, TCP reassembles the TCP segments at the other end of the route to form a continuous stream of data.

Another important protocol in the TCP/IP stack is the User Datagram Protocol (UDP), which is similar to TCP but more primitive. TCP is a "reliable" protocol because it provides error checking and acknowledgment messages to ensure that data reaches its destination without being tampered with. UDP is an "unreliable" protocol that does not guarantee that datagrams will arrive in the order they were sent, or even that they will arrive at all. UDP is used to manage connections.

Other TCP/IP protocols play less prominent but equally important roles in the operation of TCP/IP networks. For example, the Address Resolution Protocol (ARP) translates IP addresses into physical network addresses, such as Ethernet identifiers. A related protocol, the Reverse Address Resolution Protocol (RARP), does the opposite, converting physical network addresses to IP addresses. The Internet Control Message Protocol (ICMP) is a maintenance protocol that uses IP to exchange control information and control errors related to the transmission of IP packets. For example, if a router cannot send an IP datagram, it uses ICMP to inform the sender that there is a problem.

TCP / IP - the collective name for a set (stack) of network protocols different levels used on the Internet.

The TCP/IP protocol stack is divided into 4 layers:

Applied (applications);

· Transport;

· Network (internet);

· Physical (channel).

The core functionality of TCP/IP networks is implemented by TCP (Transmission Control Protocol) and IP (Internet Protocol). The IP protocol operates at the network layer, while the TCP protocol operates at the transport layer. Works at the application level a large number of protocols, both commonly used (http, smtp, dns, smb) and less common (binkp), which are used by various user programs to communicate with each other and transfer data, but they all use the transport provided by TCP / IP. These protocols are called basic because all others are based on them, and the whole technology is called TCP/IP.

Along with TCP, the UDP protocol is used at the transport layer. Unlike TCP, it does not create a connection, but simply sends datagrams. This method of transmission without establishing a connection is convenient for some applications, mainly service ones. In particular, the DNS network name resolution protocol works over UDP.

TCP/IP stack layers do not quite match the theoretical layers of the OSI model

TCP / IP does not regulate the use of protocols and technologies of the physical and link layers. It is necessary and sufficient to have an interface of the link-level modules with the IP module, which ensures the transmission of IP packets. The means and methods for ensuring this transmission are outside the scope of TCP / IP. In the practical implementation of the layers of the OSI model, it turned out to be more convenient to combine some of the layers in one module. The correspondence between the TCP / IP and OSI stack levels looks something like this:

The figure shows how TCP/IP fits into the ISO/OSI model. This figure also illustrates the layer structure of TCP/IP and shows the relationships between the major protocols. When a data block is transferred from the network application program to the network adapter card, it passes through a series of TCP/IP modules in sequence. At the same time, at each step, it is completed with the information necessary for the equivalent TCP / IP module at the other end of the chain. By the time the data gets to the network adapter, it is a standard frame of the technology to which this adapter belongs. Software The TCP/IP at the receiving end recreates the original data for the receiving program by passing the frame backwards through the set of TCP/IP modules.

The TCP/IP protocol stack is a family of protocols that enable the connection and sharing of different systems. The stack was designed to work in heterogeneous networks. The protocols of the stack are highly reliable: they meet the requirement to ensure the operation of network nodes that survived a limited nuclear attack. Currently, the TCP / IP protocol stack is used both for communication on the Internet and in local networks.

The TCP/IP architecture was deliberately based on a peer-to-peer structure. TCP/IP is distributed in nature, as opposed to the classic "top-down" reliability model. In a TCP/IP environment, there is no central authority. Nodes communicate directly with each other, and each of them has complete information about all available network services. If any of the host computers fails, none of the other machines react to this (unless it needs data, which is exactly on the failed computer).

Here is a list of protocols included in the TCP/IP stack:

• TCP(Transmission Control Protocol - transmission control protocol) - the basic transport protocol that gave its name to the entire family of TCP / IP protocols;
• UDP(User Datagram Protocol) - the second most common transport protocol of the TCP / IP family;
• IP(Internet Protocol) - Internet protocol;
• ARP(Address Resolution Protocol - address resolution protocol) - used to determine the correspondence between IP addresses and Ethernet addresses;
• SLIP (Serial Line Internet Protocol) - protocol for data transmission over telephone lines;
• PPP (Point to Point Protocol) - data exchange protocol "point-to-point";
• RPC (Remote Process Control) - remote process control protocol;
• TFTP (Trivial File Transfer Protocol) - a simple file transfer protocol;
• DNS (Domain Name System) - protocol for accessing the domain name system;
• RIP (Routing Information Protocol) - routing protocol.

The main protocols of the TCP / IP stack can be represented as a structure shown in Fig. 1.

Rice. 1. TCP/IP stack architecture

The model based on the TCP/IP stack includes 4 levels: application, main (transport), internetworking (network), network interfaces (channel). The correspondence of these layers to the architecture of the OSI model is shown in Table 1.

Table 1. Layer mapping of the OSI and TCP/IP models

As can be seen from the table, both interoperability architectures include similar layers, but in the TCP / IP model, several layers of the OSI model are combined into one.

Let's consider the functions of all four levels of the model based on the TCP/IP protocol stack.

1. Application layer -

provided by services that provide network service to user applications. The list of main services includes the following protocols: Telnet, FTP, TFTP, DNS, SNMP, HTTP. The application layer performs the functions of the application layer and the data presentation layer of the OSI model.

2. Main level -

ensures the reliability of data packet delivery, their integrity and order of delivery. At this level, the transmitted data is broken into packets and transmitted to the lower level. After transmission, the packets are collected and the data is passed to the application layer. The main protocol of this layer is TCP. The main layer performs the functions of the session and transport layers of the OSI model.

3. Interworking level -

provides the transmission of data packets in a composite network, where there are not only local, but also global connections. The main protocol of this layer is IP. At this level, the routing protocols RIP, OSPF (Open Shortest Path First) are used to collect routing information. This layer corresponds to the network layer of the OSI model.

A set of layered protocols, or as the TCP/IP stack is called, is designed to be used in various options network environment. The TCP / IP stack in terms of system architecture corresponds to the OSI (Open Systems Interconnection) reference model and allows applications and services running on almost any platform, including Unix, Windows, Macintosh and others, to communicate over the network.

Rice. 3.2

Microsoft's implementation of TCP/IP follows a four-layer model instead of a seven-layer model, as shown in Figure 2. 3.2. The TCP/IP model includes more features per layer, resulting in fewer layers. The following levels are used in the model:

the Application layer of the TCP/IP model corresponds to the Application, Presentation, and Session layers of the OSI model;

the Transport layer of the TCP/IP model corresponds to that of the Transport layer of the OSI model;

the Internet layer of the TCP / IP model performs the same functions as the Network layer of the OSI model;

the network interface layer of the TCP/IP model corresponds to the Link and Physical layers of the OSI model.

Application Level

Through the Application layer of the TCP/IP model, applications and services access the network. Access to TCP / IP protocols is carried out through two program interfaces (API - Application Programming Interface):

Windows sockets;

The Windows Sockets Interface, or WinSock as it is called, is a network programming interface designed to facilitate interoperability between different TCP/IP applications and protocol families.

The NetBIOS interface is used for communication between processes (IPC - Interposes Communications) of Windows services and applications. NetBIOS performs three main functions:

determining NetBIOS names;

NetBIOS Datagram Service;

NetBIOS session service.

Table 3.1 lists the TCP/IP protocol family.

Table 3.1

Transport Layer

The TCP/IP transport layer is responsible for establishing and maintaining a connection between two nodes. Main functions of the level:

confirmation of receipt of information4

data flow control;

sequencing and relaying of packets.

Depending on the type of service, two protocols can be used:

TCP (Transmission Control Protocol - transmission control protocol);

UDP (User Datagram Protocol - user datagram protocol).

TCP is typically used when an application needs to transfer a large amount of information and make sure that the data is received by the destination in a timely manner. Applications and services that send small amounts of data and do not require acknowledgment use UDP, which is a connectionless protocol.

Transmission Control Protocol (TCP)

The TCP protocol is responsible for the reliable transmission of data from one network node to another. It creates a session with a connection, in other words a virtual channel between machines. The connection is established in three steps:

A client requesting a connection sends a packet to the server indicating the port number the client wishes to use, as well as an ISN (Initial Sequence number) code (a specific number).

The server responds with a packet containing the server's ISN plus the client's ISN plus 1.

The client must acknowledge the connection by returning the server's ISN plus 1.

The three-step connection opening establishes the port number as well as the client and server ISNs. Each TCP packet sent contains the TCP port numbers of the sender and receiver, the fragment number for messages broken into smaller parts, and a checksum to make sure that no errors occurred during transmission.

User Datagram Protocol (UDP)

Unlike TCP, UDP does not establish a connection. The UDP protocol is designed to send small amounts of data without establishing a connection and is used by applications that do not need confirmation of receipt by the addressee. UDP also uses port numbers to identify the specific process at the given IP address. However, UDP ports are different from TCP ports and therefore can use the same port numbers as TCP without conflict between services.

Internet layer

The internetwork layer is responsible for routing data within a network and between different networks. Routers operate at this level, which depend on the protocol used and are used to send packets from one network (or its segment) to another (or another network segment). The TCP/IP stack uses the IP protocol at this level.

Internet Protocol (IP)

The IP protocol provides for the exchange of datagrams between network nodes and is a connectionless protocol that uses datagrams to send data from one network to another. This protocol does not expect to receive an acknowledgment (ASK, Acknowledgment) of sent packets from the destination node. Acknowledgments as well as retransmissions of packets are carried out by protocols and processes operating at the upper levels of the model.

Its functions include datagram fragmentation and internetwork addressing. The IP protocol provides control information for reassembling fragmented datagrams. The main function of the protocol is internetwork and global addressing. Depending on the size of the network over which the datagram or packet will be routed, one of three addressing schemes is used.

Addressing in IP networks

Each computer in TCP/IP networks has three levels of addresses: physical (MAC address), network (IP address), and symbolic (DNS name).

The physical or local address of a node, as determined by the technology behind the network that the node belongs to. For nodes included in local networks, this is the MAC address of the network adapter or router port, for example, 11-A0-17-3D-BC-01. These addresses are assigned by hardware manufacturers and are unique addresses because they are managed centrally. For all existing MAC LAN technologies, the address has the format of 6 bytes: the upper 3 bytes are the manufacturer's identifier, and the lower 3 bytes are assigned uniquely by the manufacturer.

Network or IP address, consisting of 4 bytes, for example, 109.26.17.100. This address is used at the network layer. It is assigned by the administrator during the configuration of computers and routers. An IP address consists of two parts: a network number and a host number. The network number can be chosen arbitrarily by the administrator, or assigned on the recommendation of a special division of the Internet (Network Information Center, NIC), if the network should work as component Internet. Typically, ISPs obtain address ranges from NIC departments and then distribute them to their subscribers. The host number in IP is assigned regardless of the host's local address. The division of an IP address into a network number field and a host number field is flexible, and the boundary between these fields can be set arbitrarily. A node can belong to several IP networks. In this case, the node must have several IP addresses, according to the number of network links. An IP address does not characterize a single computer or router, but a single network connection.

Symbolic address, or DNS name, such as SERV1.IBM.COM. This address is assigned by the administrator and consists of several parts, such as machine name, organization name, domain name. Such an address is used at the application level, for example, in the FTP or telnet protocols.

ARP and RARP Address Mapping Protocols

The Address Resolution Protocol (ARP) is used to determine the local address from an IP address. ARP works differently depending on which link layer protocol is running on a given network - the protocol local network(Ethernet, Token Ring, FDDI) with the ability to broadcast access simultaneously to all network nodes, or the protocol global network(X.25, frame relay), which generally does not support broadcast access. There is also a protocol that solves the inverse problem - finding an IP address from a known local address. It is called reverse ARP - RARP (Reverse Address Resolution Protocol) and is used when starting diskless stations that do not initially know their IP address, but do know the address of their network adapter.

In LANs, ARP uses link-layer protocol broadcast frames to search the network for a host with a given IP address.

A host that needs to map an IP address to a local address generates an ARP request, attaches it to a link-layer protocol frame with a known IP address, and broadcasts the request. All nodes on the local network receive an ARP request and compare the IP address specified there with their own address. If they match, the node generates an ARP response, in which it indicates its IP address and its local address, and sends it already directed, since the sender specifies his local address in the ARP request. ARP requests and responses use the same packet format.

ICMP protocol

The Internet Control Message Protocol (ICMP) is used by IP and other high-level protocols to send and receive status reports on transmitted information. This protocol is used to control the rate at which information is transferred between two systems. If the router connecting the two systems is overloaded with traffic, it can send a special ICMP error message to slow down the message sending.

IGMP protocol

Local network hosts use the Internet Group Management Protocol (IGMP) to register themselves in a group. Group information is kept on LAN routers. Routers use this information to send multicast messages.

A group message, like a broadcast message, is used to send data to several nodes at once.

Network Device Interface Specification - a network device interface specification, a software interface that provides interaction between transport protocol drivers and the corresponding network interface drivers. Allows multiple protocols to be used even if only one network card is installed.

Network interface layer

This layer of the TCP/IP model is responsible for distributing IP datagrams. It works with ARP to determine the information that should be placed in the header of each frame. A frame is then created at this layer appropriate for the type of network being used, such as Ethernet, Token Ring, or ATM, then an IP datagram is placed in the frame's data region, and it is sent out onto the network.

Questions

The purpose of the IEEE802 standards specification.

Which standard describes Ethernet network technology?

Which standard defines the tasks of managing a logical link?

What standard defines network management mechanisms?

Which standard describes ArcNet networking technology?

Which standard describes Token Ring network technology?

What is the Basic OSI Model Layer Interface?

What is the basic OSI model layer protocol?

Define a protocol stack.

What are the layers of protocol stacks?

Name the most popular network protocols.

Name the most popular transport protocols.

Name the most popular application protocols.

List the most popular protocol stacks.

Purpose of the Windows socket and NetBIOS socket APIs.

How is TCP different from UDP?

IP protocol functions.

What are the types of addressing in IP networks?

What protocol is needed to determine the local address from an IP address?

What protocol is needed to resolve an IP address from a local address?

What protocol is used to control Internet messages?

Assigning the network interface layer of the TCP/IP stack.