UNIT-V Computer Network Transport Layer 1 Prepared by - ROHIT KOSHTA

Transport Layer Prepared by - ROHIT KOSHTA Next Layer in OSI Model is recognized as Transport Layer (Layer-4). This layer communicates with its peer Transport layer of the remote host. Transport layer offers peer-to-peer and end-to-end connection between two processes on remote hosts. Transport layer takes data from upper layer (i.e. Application layer) and then breaks it into smaller size segments, numbers each byte, and hands over to lower layer (Network Layer) for delivery. 2

Design Issues of Transport Layer Prepared by - ROHIT KOSHTA Addressing  Every layer needs a mechanism to identify senders and receivers. Error control  It is an important issue because physical communication circuits are not perfect. Flow control  This property leads to mechanisms for disassembling, transmitting and then reassembling messages. Multiplexing Demultiplexing Routing  When there are multiple paths netween source and destination a route must be chosen. 3

User Datagram Protocol Prepared by - ROHIT KOSHTA UDP stands for “user datagram protocol” and it is another protocol built on top of IP, just like TCP. With UDP we can send a packet to a destination IP address (eg ) and port (say 52423), and it will get passed from computer to computer until it arrives at the destination computer or is lost along the way. On the receiver side, we just sit there listening on a specific port (eg ) and when a packet arrives from any computer (remember there are no connections!), we get notified of the address and port of the computer that sent the packet, the size of the packet, and can read the packet data. 4

User Datagram Protocol (contd) Prepared by - ROHIT KOSHTA UDP is an unreliable protocol. In practice, most packets that are sent will get through, but you’ll usually have around 1-5% packet loss. There is also no guarantee of ordering of packets. 5

UDP vs TCP Prepared by - ROHIT KOSHTA TCPUDP Connection basedNo concept of connection, you have to code this yourself Guaranteed reliable and orderedNo guarantee of reliability or ordering of packets, they may arrive out of order, be duplicated, or not arrive at all! Automatically breaks up your data into packets for you You have to manually break your data up into packets and send them Makes sure it doesn’t send data too fast for the internet connection to handle (flow control) You have to make sure you don’t send data too fast for your internet connection to handle Easy to use, you just read and write data like its a file If a packet is lost, you need to devise some way to detect this, and resend that data if necessary 6

UDP : Header Format Prepared by - ROHIT KOSHTA Field Name Size (bytes) Description Source Port 2 Source Port: The 16-bit port number of the process that originated the UDP message on the source device. Destination Port 2 Destination Port: The 16-bit port number of the process that is the ultimate intended recipient of the message on the destination device. Length 2 Length: The length of the entire UDP datagram, including both header and Data fields. Checksum 2 Checksum: An optional 16-bit checksum computed over the entire UDP datagram plus a special “pseudo header” of fields. See below for more information. Data Variable Data: The encapsulated higher-layer message to be sent. 7

Transmission Control Protocol Prepared by - ROHIT KOSHTA TCP is a connection-oriented protocol. TCP (Transmission Control Protocol) is a standard that defines how to establish and maintain a network conversation via which application programs can exchange data. TCP works with the Internet Protocol (IP), which defines how computers send packets of data to each other. It determines how to break application data into packets that networks can deliver, sends packets to and accepts packets from the network layer, manages flow control, and—because it is meant to provide error-free data transmission—handles retransmission of dropped or garbled packets as well as acknowledgement of all packets that arrive. 8

TCP Header Format Prepared by - ROHIT KOSHTA 9

Session Layer Prepared by - ROHIT KOSHTA In the Open Systems Interconnection (OSI) communications model, the Session layer (sometimes called the "port layer") manages the setting up and taking down of the association between two communicating end points that is called a connection. A connection is maintained while the two end points are communicating back and forth in a conversation or session of some duration. For Internet applications, each session is related to a particular port. For example, the HTTP program or daemon always has port number

Presentation Layer Prepared by - ROHIT KOSHTA The presentation layer is layer 6 of the 7-layer Open Systems Interconnection (OSI) model. It is used to present data to the application layer (layer 7) in an accurate, well-defined and standardized format. The presentation layer is sometimes called the syntax layer. The presentation layer is responsible for the following:  Data encryption/decryption  Character/string conversion  Data compression  Graphic handling 11

Application Layer Prepared by - ROHIT KOSHTA The application layer is a layer in the Open Systems Interconnection (OSI) seven-layer model and in the TCP/IP protocol suite. It consists of protocols that focus on process-to-process communication across an IP network and provides a firm communication interface and end-user services. The application layer is the seventh layer of the OSI model and the only one that directly interacts with the end user. The application layer provides full end-user access to a variety of shared network services for efficient OSI model data flow. 12

Application Layer (contd) Prepared by - ROHIT KOSHTA 13 The application layer provides many services, including:  Simple Mail Transfer Protocol  File transfer  Web surfing  Web chat  clients  Network data sharing  Virtual terminals  Various file and data operations

World Wide Web Prepared by - ROHIT KOSHTA 14 The World Wide Web (www, W3) is an information system of interlinked hypertext documents that are accessed via the Internet. Individual document pages on the World Wide Web are called web pages and are accessed with a software application running on the user's computer, commonly called a web browser. Web pages may contain text, images, videos, and other multimedia components, as well as web navigation features consisting of hyperlinks.

HTTP Prepared by - ROHIT KOSHTA 15 The Hypertext Transfer Protocol (HTTP) is an application protocol for distributed, collaborative, hypermedia information systems. Hypertext is structured text that uses logical links (hyperlinks) between nodes containing text. HTTP is the protocol to exchange or transfer hypertext. HTTP functions as a request-response protocol in the client- server computing model. A web browser, for example, may be the client and an application running on a computer hosting a web site may be the server.

FTP Prepared by - ROHIT KOSHTA 16 The File Transfer Protocol (FTP) is a standard network protocol used to transfer computer files from one host to another host over a TCP-based network, such as the Internet. FTP is built on a client-server architecture and uses separate control and data connections between the client and the server. For secure transmission that protects the username and password, and encrypts the content, FTP is often secured with SSL/TLS (FTPS).

SMTP Prepared by - ROHIT KOSHTA 17 Simple Mail Transfer Protocol (SMTP) is an Internet standard for electronic mail ( ) transmission. SMTP by default uses TCP port 25. SMTP connections secured by SSL, known as SMTPS, default to port 465 (nonstandard, but sometimes used for legacy reasons). Although electronic mail servers and other mail transfer agents use SMTP to send and receive mail messages, user- level client mail applications typically use SMTP only for sending messages to a mail server for relaying. For receiving messages, client applications usually use either POP3 or IMAP.

SNMP Prepared by - ROHIT KOSHTA 18 Simple Network Management Protocol (SNMP) is an "Internet-standard protocol for managing devices on IP networks". Devices that typically support SNMP include routers, switches, servers, workstations, printers, modem racks and more. SNMP is used mostly in network management systems to monitor network-attached devices for conditions that warrant administrative attention.