Transport layer services

Transport Layer services

1. Transport Layer Services Dr.T.Abirami , Associate Professor , Department of IT , Kongu Engineering College

2. INTRODUCTION The packets at the transport layer in the Internet are called user datagrams , segments, or packets In the Transport layer, data travels in the form of segments . To provide the communication services directly to the application processes running on different hosts. transferring data from one point to another in the Internet . Transport Layer is responsible for delivering messages between hosts . The transport layer is responsible for creating an end to end connection between source IP and the destination IP. For establishing this end to end connection , the Transport layer is using two major protocols TCP and UDP. Dr.T.Abirami , Associate Professor , Department of IT , Kongu Engineering College

3. Major duties of the Transport layer are: Creating an end-to-end connection between hosts in different networks, Error recovery, Flow control, Ensuring complete data transfer in TCP Congestion avoidance Dr.T.Abirami , Associate Professor , Department of IT , Kongu Engineering College

4. List of the major protocols works in the Transport later are: TCP( Transmission Control Protocol) UDP( User Datagram Protocol) DCCP (Datagram Congestion Control Protocol) SCTP (Stream Control Transmission Protocol) Dr.T.Abirami , Associate Professor , Department of IT , Kongu Engineering College

5. Dr.T.Abirami , Associate Professor , Department of IT , Kongu Engineering College

6. Dr.T.Abirami , Associate Professor , Department of IT , Kongu Engineering College

7. Transport-Layer Services Process-to-Process Communication : A process is running program that uses the services of the transport layer Dr.T.Abirami , Associate Professor , Department of IT , Kongu Engineering College

8. Addressing: Port Numbers A process on the local host , called a client , needs services from a process usually on the remote host , called a server To define the processes , we need second identifiers, called port numbers . the port numbers are integers between 0 and 65,535 (16 bits). The server process must also define itself with a port number. TCP/IP has decided to use universal port numbers for servers; these are called well-known port numbers. Dr.T.Abirami , Associate Professor , Department of IT , Kongu Engineering College

9. Dr.T.Abirami , Associate Professor , Department of IT , Kongu Engineering College

10. ICANN Ranges the port numbers into three ranges: well-known, registered, and dynamic (or private) Well-known ports. The ports ranging from 0 to 1023 are assigned and controlled by ICANN. These are the well-known ports. ❑ Registered ports . The ports ranging from 1024 to 49,151 are not assigned or controlled by ICANN. They can only be registered with ICANN to prevent duplication. ❑ Dynamic ports . The ports ranging from 49,152 to 65,535 are neither controlled nor registered. They can be used as temporary or private port numbers. ICANN is the Internet Corporation for Assigned Names and Numbers. Dr.T.Abirami , Associate Professor , Department of IT , Kongu Engineering College

11. Socket Addresses A transport-layer protocol in the TCP suite needs both the IP address and the port number, at each end, to make a connection . The combination of an IP address and a port number is called a socket address. The client socket address defines the client process uniquely just as the server socket address defines the server process uniquely Dr.T.Abirami , Associate Professor , Department of IT , Kongu Engineering College

12. Encapsulation and Decapsulation The Transport layer encapsulates the data by adding the appropriate header to each piece . These data pieces are now called as data segments. The header contains the sequencing information so that the data segments can be reassembled at the receiver’s end. Dr.T.Abirami , Associate Professor , Department of IT , Kongu Engineering College

13. Encapsulation & De-encapsulation Dr.T.Abirami , Associate Professor , Department of IT , Kongu Engineering College

14. Multiplexing and Demultiplexing Multiplexing is a technique used to combine and send the multiple data streams over a single medium . The process of combining the data streams is known as multiplexing Why Multiplexing ? The transmission medium is used to send the signal from sender to receiver. The medium can only have one signal at a time . If there are multiple signals to share one medium , then the medium must be divided Dr.T.Abirami , Associate Professor , Department of IT , Kongu Engineering College

15. Dr.T.Abirami , Associate Professor , Department of IT , Kongu Engineering College

16. Flow Control It is technique that observes proper flow of data from sender to receiver. Flow control is technique that gives permission to two of stations that are working and processing at different speeds to just communicate with one another. Dr.T.Abirami , Associate Professor , Department of IT , Kongu Engineering College

17. Flow Control If the receiver is overloaded with too much data , then the receiver discards the packets and asking for the retransmission of packets. This increases network congestion and reducing the system performance . Transport layer use two buffers: one at the sending transport layer and the other at the receiving transport layer. A buffer is a set of memory locations that can hold packets at the sender and receiver. When the buffer of the sending transport layer is full, it informs the application layer to stop passing chunks of messages Dr.T.Abirami , Associate Professor , Department of IT , Kongu Engineering College

18. Dr.T.Abirami , Associate Professor , Department of IT , Kongu Engineering College

19. Dr.T.Abirami , Associate Professor , Department of IT , Kongu Engineering College

20. Error Control The transport layer checks for errors in the messages coming from the application layer by using error detection codes, computing checksums, it checks whether the received data is not corrupted and uses the ACK and NACK services to inform the sender if the data has arrived or not and checks for the integrity of data. TCP is a reliable transport layer protocol. Error control includes mechanisms for detecting corrupted segments, lost segments, out-of-order segments, and duplicated segments. 1. Detecting and discarding corrupted packets. 2. Keeping track of lost and discarded packets and resending them. 3. Recognizing duplicate packets and discarding them. 4. Buffering out-of-order packets until the missing packets arrive Dr.T.Abirami , Associate Professor , Department of IT , Kongu Engineering College

21. Dr.T.Abirami , Associate Professor , Department of IT , Kongu Engineering College

22. Sequence Numbers the transport-layer packet to hold the sequence number Packets are numbered sequentially . If the header of the packet allows m bits for the sequence number, the sequence numbers range from 0 to 2 m − 1 Dr.T.Abirami , Associate Professor , Department of IT , Kongu Engineering College

23. Acknowledgment use both positive and negative signals as error control The receiver side can send an acknowledgment (ACK) for each of a collection of packets that have arrived safe When a packet is sent, the sender starts a timer . If an ACK does not arrive before the timer expires, the sender resends the packet. Duplicate packets can be silently discarded by the receiver. Dr.T.Abirami , Associate Professor , Department of IT , Kongu Engineering College

24. Congestion Control Congestion in a network may occur if the load on the network —the number of packets sent to the network— is greater than the capacity of the network —the number of packets a network can handle. Congestion in a network or internetwork occurs because routers and switches have queues —buffers that hold the packets before and after processing control the congestion and keep the load below the capacity Dr.T.Abirami , Associate Professor , Department of IT , Kongu Engineering College

25. Connectionless and Connection-Oriented Protocols Connection-Oriented Services Users of connection-oriented services follow a sequence of operations: Establish connection Send information Release connection To provide connection-oriented services, it is necessary to establish a connection first, and then start the communication, send the information, and then release the connection. This type of service is more reliable , because if there is an error on the receiver’s end, the sender can resend the information . Dr.T.Abirami , Associate Professor , Department of IT , Kongu Engineering College

26. Dr.T.Abirami , Associate Professor , Department of IT , Kongu Engineering College

27. Dr.T.Abirami , Associate Professor , Department of IT , Kongu Engineering College

28. Connectionless Protocols a router treats each packet individually. The packets are routed through different paths through the network according to the decisions made by routers. The network or communication channel does not guarantee data delivery from the host machine to the destination machine in connectionless service. The data to be transmitted is broken into packets . These independent packets are called datagrams. The system routes each packet independently , just like postal packages, so there’s no way to be sure you’ll get all of the information in correct order. Dr.T.Abirami , Associate Professor , Department of IT , Kongu Engineering College

29. Dr.T.Abirami , Associate Professor , Department of IT , Kongu Engineering College

30. the source process (application program) needs to divide its message into chunks of data of the size acceptable by the transport layer and deliver them to the transport layer one by one. The transport layer treats each chunk as a single unit without any relation between the chunks . When a chunk arrives from the application layer, the transport layer encapsulates it in a packet and sends it. To show the independency of packets , assume that a client process has three chunks of messages to send to a server process. The chunks are handed over to the connectionless transport protocol in order Dr.T.Abirami , Associate Professor , Department of IT , Kongu Engineering College

31. The delivery of messages at the server is not in order (0, 2, 1). If these three chunks of data belong to the same message, the server process may have received a strange message Dr.T.Abirami , Associate Professor , Department of IT , Kongu Engineering College

32. Dr.T.Abirami , Associate Professor , Department of IT , Kongu Engineering College

33. Connection-oriented protocols Connectionless protocols authentication is needed no authentication necessary checks whether message is received, sends again if error occurs no guarantees of delivery more reliable less reliable stream based message based long and steady bursts of communication congestion is not possible congestion is possible packets follow the same route packets do not follow same route high range bandwidth required low range bandwidth adequate Dr.T.Abirami , Associate Professor , Department of IT , Kongu Engineering College