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T/IP

T/IP • T/IP (Transmission Control Protocol/Internet Protocol) is the basic communication language or protocol of the Internet. • T is one of the core protocols of the Internet protocol suite (IP) • T is a transport layer protocol • T/IP is a two-layer program. The higher layer, Transmission Control Protocol, manages the assembling of a message or file into smaller packets that are transmitted over the Internet and received by a T layer that reassembles the packets into the original message. • The lower layer, Internet protocol, handles the address part of each packet so that it gets to the right destination. • Each gateway computer on the network checks this address to see where to forward the message. • Even though some packets from the same message are routed differently than others, they'll be reassembled at the destination. • T/IP uses the client/server model of communication in which a computer requests and is provided a service (such as sending a Web page) by another computer in the network.

T/IP • T/IP communication is primarily point-to-point, meaning each communication is from one point in the network to another point or host computer. • T provides reliable, ordered and error-checked delivery of a stream of octets (an octet is a unit of digital information in computing and telecommunication that consists of 8 bits) between programs running on computers connected to a LAN, intranet or the public Internet. It resides at the transport layer • Web browsers use T when they connect to servers on the World Wide Web, and it is used to deliver email and transfer files from one location to another. • Applications that do not require the reliability of a T connection may instead use the connectionless Datagram Protocol (UDP), which emphasizes low-overhead operation and reduced latency rather than error checking and delivery validation.

T/IP Reference Model • Connecting multiple networks in a flawless way

Application Transport

Host-to-network layer Internet • Host has to connect to the network using some protocol so it can send IP packets to it. Host-to-network The internet layer • A packet-switching network based on a connectionless internetwork layer • Its job is to permit hosts to inject packets into any network and have them travel independently to the destination. • The internet layer defines an official packet format and protocol called IP. • The job of the internet layer is to deliver IP packets where they are supposed to go. Packet routing is clearly the major issue here, avoiding congestion

The transport layer • It is designed to examine entries on the source and destination hosts to carry on a conversion • Two end-to-end protocols have been defined – T (reliable, connection oriented protocol, handles flow control) and UDP (unreliable connectionless protocol, no sequencing and flow control, applications in which prompt delivery is more important than accurate delivery) The application layer • It contains all the higher-level protocols. • File transfer protocol – a way to move data efficiently from one machine to another. • Electronic mail, virtual terminal protocol etc..

Comparison between the OSI and T/IP reference models • Both are based on the concept of a stack of independent protocols • Functionality of the layers is roughly similar • Three concepts are central to the OSI model - Services, interfaces and protocols • Services - Each layer performs some services for the layer above it. • The service definition tells what the layer does, not how entities above it access it or how the layer works. • If defines the layer’s semantics • Interface – a layer’s interface tells the processes above it how to access it. • It specifies what the parameters are and what results to expect. • It also says nothing about how the layer works inside

• Protocols – used in a layer are the layer’s own business. It can use any protocols it wants to, as long as it gets the job done. • It can also change them at will, without affecting software in higher layers • OSI model makes such a distinction between these three concepts but, the T/IP model did not clearly distinguish between them. • T/IP model is not much of a guide for deg new networks using new technologies • It is not at all general and is poorly suited to describing any protocol stack other than T/IP • Host- to network layer is not really a layer • It does not distinguish the physical and data link layers Application • OSI model has proven to be exceptionally useful but Transport OSI protocols have not become popular Network • T/IP model is practically nonexistent Data link • Hybrid model – as in fig. Physical

Exchanging messages using T • The message can contain any type of data • The system must IP, because T and UDP use IP addresses to identify a message’s source and destination • T and UDP are standard, well ed protocols for computers that need to send and receive messages within local networks or on the Internet

• Protocol

UDP T

• • • • • • • •

datagram segment optional required No yes No yes No yes No yes No yes Yes No

Name of unit transmitted Source port specified to remote host Must establish a connection before transmitting data? error checking? flow control? handshaking? sequence numbering? broadcasting and multicasting?

• T uses a system of sequence and acknowledgement numbers that enable the destination to acknowledge receiving specific data bytes. • Using sequence numbers, a destination can place received messages in the order they were sent, even if they were received out of order • Sequence numbers also enable a destination to detect duplicate received data • T is called a connection-oriented protocol because processes can’t exchange data until they have exchanged communications to establish a connection with each other. • T is called a reliable protocol because the handshaking, checksum, and sequence and acknowledgement numbers enable the source to that data has arrived at its destination without errors • A T segment consists of a header optionally followed by a data payload • The source sends one or more segments containing data, and the destination sends one or more segments to acknowledge receiving the data.

• A single acknowledgement can acknowledge multiple segments • T uses port numbers to identify processes at the source and destination • Before two processes can send and receive data using T, their computers must establish a connection by performing a 3-way handshake • On competing the handshake, each computer has acknowledged that the port specified in the handshake is available to receive communications from the specified port on the other computer • On receiving a data over an established connection, the destination responds by returning information about whether the data arrived without errors or not • To close a connection, each computer send a request to close the connection and waits for an acknowledgment of the request

The T Header Fields

No. of bits

Description

Source port number

16

The port that is sending the datagram

Destination port no.

16

The port, the datagram is directed to

Sequence number

32

Segment identifier

Ack. Number

32

Identifier of the last received byte

Header length

4

Length of T header in units of 32bits

Reserved

6

zero

Control bits

6

URG-urgent, ACK-ack.no. is valid, PSH-push the data to application right away , RST-reset the connection, SYN-synchronization is in progress, FIN-source has no more data to send

Window

16

The no. of new bytes the source can accept

Checksum

16

Checksum value

Urgent pointer

16

sequence no. of the last byte of urgent data

options

0 or more

Optional – can indicate the max. segment size the source can handle

Establishing a connection 

A T connection has two end points, one at the source and one at the destination.  Each end point is a socket, with a port number and IP address  To complete a connection, two computers must complete a 3-way handshake.  Each communication in the handshake contain a T header.  Once the connection has been established, either computer can transmit to the other at any time 1. The client initiates the handshake by sending a segment containing an initial sequence number. 2. The server waits to receive a connection request. On receiving the segment from the client, the server responds by sending a segment containing its own initial sequence number and an acknowledgment no. = the received sequence no. + 1. 3. The client responds by sending a segment whose sequence no. = the received ack. no. and the ack. no. = received sequence no. + 1 The connection is now established

Sending and receiving data • On receiving data, the receiver returns an acknowledgment number equal to the sequence number expected in the next segment • Closing a T connection also requires a 3-way handshake • ing T in an embedded system is more complicated than ing UDP. • In addition to adding and removing headers and ing IP, the computer must perform the 3-way handshake to connect to a remote host, maintain sequence and acknowledge numbers when exchanging data, handshake when closing a connection and respond to detected errors.

Closing a connection • Closing a connection also requires a handshaking

• To close a connection completely, each computer sends a segment with the FIN control bit set to 1 • To indicate that the computer has no more data to send • Each destination must acknowledge receiving the FIN.

To send a message using T, a computer in an Ethernet network must do the following: • Establish a connection using 3-way handshake • Use the received window size to determine how much data the remote computer can accept • Place the source and destination port numbers, seq., ack. no., header length, source window size and check sum in the appropriate locations in the T header. • Place the data to be sent in the data portion of the segment • Place the T segment in the data portion of an IP datagram. • the IP datagram to the Ethernet controller’s driver for sending on the network and start a timeout timer • Wait to receive an ack. no. that indicates that the remote computer received the data • If ack. doesn’t arrive before the timeout, resend the segment

To receive a datagram using T, a computer in an Ethernet network must do the following: • Establish a connection using 3-way handshake • Receive an IP datagram from the Ethernet controller’s driver • Strip the IP header from the datagram. Calculate the checksum and compare with the received value • If the checksum match, strip the header from the T segment. Calculate the checksum and compare it to the received value • Examine the received ack. no. to find out if the segment is acknowledging receipt of previously sent data and if so, delete the ack. data from the retransmission queue • Compare the received sequence no. to the expected value. If the numbers match, set the ack. no. to return to the sender in a T segment • Use destination port number to decide where to the data •

In addition, at any time, either computer may request to close or reset the connection and the other computer should ack. the request and may request to close or reset the connection from the other end