Unit 3. Internet protocols

I. Read the following words:

control, component, transmission, reliable, transfer, congestion, layer, issue, router, request, media, accurate, duplicate, service, guarantee, acknowledgement, sequence, individually, include, encapsulate, reassemble, assigned, authority, identify, private, correctly, rearrange, sharing, browser, modular.

II. Before you read the text try to answer these questions:

1. What Internet protocols do you know?

2. What protocols are used for data transferring?

3. What are the ways of data protection?

III. Read and translate the following text. Transmission Control Protocol/Internet Protocol

The Transmission Control Protocol (TCP) is one of the main protocols of the Internet Protocol Suite. It is one of the two principal components of the suite, so the entire suite is commonly referred to as TCP/IP. Whereas IP handles low-level transmission from computer to computer, TCP operates at a higher level, for example, a Web browser and a Web server. In particular, TCP provides reliable delivery of a stream of bytes between programs on different machines (e-mail, file transferring) and controls size segments and network traffic congestion.

In May, 1974, the Institute of Electrical and Electronical Engineers (IEEE) published a paper «A Protocol for Packet Network Interconnection» where Vint Cerf and Bob Kahn described an internetworking protocol for sharing resources by packet-switching. The central control component of this model was the Transmission Control Program that incorporated both connection-oriented links and datagram services between hosts. Later the monolithic Transmission Control Program was divided into a modular architecture consisting of the Transmission Control Protocol (at the connection-oriented layer) and the Internet Protocol (at the internetworking layer). The model became known informally as TCP/IP, although formally it was called the Internet Protocol Suite.

At the intermediate level TCP provides a communication service between an application program and the Internet Protocol. When the application program desires to send a large chunk of data across the Internet, the software can issue a single request to TCP and let TCP handle the IP details.

IP works by exchanging pieces of information called packets. A packet is a sequence of bytes that consists of a header followed by a body. The header describes the packet's destination and the routers to be used for forwarding until it arrives at its final destination. The body contains the data which IP is transmitting.

Because of network congestion, IP packets can be lost or delivered out of order. TCP detects these problems, requests retransmission of lost packets, rearranges out-of-order packets and even helps minimize network congestion to reduce the occurrence of the other problems. Once the TCP receiver has finally reassembled a copy of the data originally transmitted, it passes that datagram to the application program.

The most popular Internet applications, including the World Wide Web, e-mail, File Transfer Protocol, Secure Shell and some streaming media applications use TCP. It is optimized for accurate delivery and incurs relatively long delays while waiting for out-of-order messages or retransmissions. It is not suitable for real-time applications, such as Voice over IP, thus, protocols like the Real-time Transport Protocol (RTP) running over the User Datagram Protocol (UDP) are recommended.

TCP is a reliable service that guarantees delivery of a data stream without duplicating or losing data. A technique known as positive acknowledgment with retransmission is used to guarantee reliability of packet transfers. This fundamental technique requires the receiver to respond with an acknowledgment message as it receives the data. The sender keeps a record of each packet he sends and waits for acknowledgment before sending the next packet.

TCP keeps track of the individual units of data transmission, called segments, that a message is divided into for efficient routing through the network. For example, when an HTML file is sent from a Web server, the TCP software layer of that server divides the sequence of bytes of the file into segments and forwards them individually to the IP software layer (Internet Layer). The Internet Layer encapsulates each TCP segment into an IP packet by adding a header which includes the destination IP address. Even though every packet has the same destination address, they can be routed on different paths through the network. When the client program on the destination computer receives segments, the TCP layer (Transport Layer) reassembles the individual segments and ensures they are correctly ordered and error free as it streams them to an application.

TCP uses port numbers to identify the sender and receiver. Port numbers are classified into three basic categories: well-known, registered, and dynamic/private. The well-known ports are assigned by the Internet Assigned Numbers Authority (IANA) and represented by FTP, SSH, TELNET, SMTP and HTTP. Registered ports are typically used by end-user applications as source ports and can identify the services that have been registered by a third party. Dynamic/private ports can also be used by end-user applications.

IV. Answer the following questions:

1. What Internet protocols are mentioned in the text?

2. What is the difference between TCP and IP?

3. What is Vint Cerf and Bob Kahn’s work devoted to?

4. What applications can use TCP?

5. What does TCP guarantee?

6. What is network congestion?

7. What is a segment?

8. What is the function of a header?

V. Decide whether the following statements are true or false. It they are false, correct them.

1. TCP is one of the principal protocols of the Internet Protocol Suite.

2. The paper «A Protocol for Packet Network Interconnection» was published in March, 1974.

3. The sender and receiver cannot be identified according to port numbers.

4. TCP is suitable for real-time applications.

5. IP works by exchanging pieces of information called packets.

VI. Arrange the words in the correct order to make sentences:

1. are, part, addresses, IP, of, Internet, an, the, integral, protocol.

2. alone, that, protocol, the, Software, stands, TCP, supports.

3. the, of, a, called, TCP/IP, the, Internet, portion, heart, of, the, IP, address, concept, At, is.

4. provides, routing, software, receiving, final, the, for, system, data, the, within, UDP.

VII. Which words in the text have the same meaning as:

instance, too, be able to, certain, called, boot, precise, get, separately, famous, data, reduce, so, way, expect, by, hold.

VIII. Define the following terms:

byte, data, forward, instruction, network, port, program, protocol, reliable stream service, file, segment, server, telnet, user datagram protocol, data stream, file transfer protocol.

IX. What do the following abbreviations stand for?

TCP, IP, IEEE, RTP, UDP, HTML, IANA, FTP, SMTP, HTTP, SSH.

X. Write a brief summary of the text (10-12 sentences).