1. CCNA 1 v3.0 Module 11 TCP/IP Transport and Application Layers

2. Objectives TCP/IP Transport Layer TCP/IP Application Layer

3. TCP/IP Transport Layer

4. Introduction to Transport Layer Five basic services: Segmenting upper-layer application data Establishing end-to-end operations Transporting segments from one end host to another end host Ensuring data reliability Providing flow control

5. Reliability Reliable transport can accomplish the following: Ensure the segments delivered will be acknowledged to the sender Provide for retransmission of any segments that are not acknowledged Put segments back into their correct sequence at the destination Provide congestion avoidance and control

6. Flow Control Avoids the problem of a host at one side of the connection overflowing the buffers in the host at the other side Ensures the integrity of the data

7. Session Establishment One function of the transport layer is to establish a connection- oriented session between similar devices at the application layer.

8. Session Maintenance and Termination Congestion can occur during data transfer To terminate, the sending host sends a signal that indicates the end of the transmission, which is acknowledged by the receiver.

9. Three-Way Handshake

10. Windowing The number of data packets the sender is allowed to have outstanding without having received an acknowledgment is known as the window size, or window. A method of controlling the amount of information transferred end to end Information can be measured in terms of the number of packets or the number of bytes

11. Synchronisation Hosts use segments called SYNs for synchronisation. SYNs carry a control bit also called SYN and the Initial Sequence Number (ISN) The synchronization requires each side to send its own ISN and to receive a confirmation of exchange in an acknowledgment (ACK) from the other side. Each side must also receive the ISN from the other side and send a confirming ACK.

12. The sequence is as follows: A → B SYN—(A) initial sequence number is X, ACK number is 0, SYN bit is set, but ACK bit is not set. B → A ACK—(A) sequence number is X + 1, (B) initial sequence number is Y, and SYN and ACK bit are set. A → B ACK—(B) sequence number is Y + 1, (A) sequence number is X + 1, the ACK bit is set, but the SYN bit is not set.

13. Window Size TCP window sizes are variable during the lifetime of a connection. Larger window sizes increase communication efficiency.

14. Acknowledgment Positive acknowledgment requires a recipient to communicate with the source, sending back an acknowledgment message when it receives data. Sender keeps a record of each data packet that it sends and expects an acknowledgment.

15. TCP Sequence and Acknowledgment

16. Transmission Control Protocol (TCP) The protocols that use TCP include: FTP (File Transfer Protocol) HTTP (Hypertext Transfer Protocol) SMTP (Simple Mail Transfer Protocol) Telnet

17. TCP Segment Format

18. The following are the definitions of the fields in the TCP segment: Source port – Number of the calling port Destination port – Number of the called port Sequence number – Number used to ensure correct sequencing of the arriving data Acknowledgment number – Next expected TCP octet HLEN – Number of 32-bit words in the header Reserved – Set to zero

19. fields in the TCP segment (cont) Code bits – Control functions, such as setup and termination of a session Window – Number of octets that the sender is willing to accept Checksum – Calculated checksum of the header and data fields Urgent pointer – Indicates the end of the urgent data Option – One option currently defined, maximum TCP segment size Data – Upper-layer protocol data

20. UDP The protocols that use UDP include: TFTP (Trivial File Transfer Protocol) SNMP (Simple Network Management Protocol) DHCP (Dynamic Host Control Protocol) DNS (Domain Name System)

21. UDP Segment Format

22. The following are the definitions of the fields in the UDP segment: Source port – Number of the calling port Destination port – Number of the called port Length – Number of bytes including header and data Checksum – Calculated checksum of the header and data fields Data – Upper-layer protocol data

23. TCP and UDP Port Numbers Both TCP and UDP use port (socket) numbers to pass information to the upper layers. Numbers below 1024 are considered well-known ports numbers. Numbers above 1024 are dynamically assigned ports numbers. Registered port numbers are those registered for vendor-specific applications. Most of these are above 1024.

24. TCP and UDP Port Numbers

25. Port Numbers NumberUse Numbers below 255public applications Numbers from 255 to 1023 companies for marketable applications Numbers above 1023unregulated

26. TCP/IP Application Layer

27. Introduction to Application Layer

28. Responsibilities of Application Layer Identifying and establishing the availability of intended communication partners Synchronizing cooperating applications Establishing agreement on procedures for error recovery Controlling data integrity

29. Application Layer Examples Domain Name System File Transfer Protocol Hypertext Transfer Protocol Simple Mail Transport Protocol Simple Network Management Protocol Telnet

30. DNS The Domain Name System (DNS) is a system used for translating names of domains into IP addresses. There are more than 200 top-level domains on the Internet, examples of which include the following:.us – United States.uk – United Kingdom.edu – educational sites.com – commercial sites.gov – government sites.org – non-profit sites.net – network service

31. FTP and TFTP FTP is a reliable, connection-oriented service that uses TCP to transfer files between systems that support FTP. TFTP is a connectionless service that uses User Datagram Protocol (UDP). TFTP is used on routers to transfer configuration files and Cisco IOS images. TFTP is designed to be small and easy to implement.

32. HTTP

33. SMTP E-mail servers communicate with each other using the Simple Mail Transport Protocol (SMTP) to send and receive mail.

34. SNMP The Simple Network Management Protocol (SNMP) is an application layer protocol that facilitates the exchange of management information between network devices.

35. Telnet Telnet client software provides the ability to log in to a remote Internet host that is running a Telnet server application and then to execute commands from the command line.

36. Summary The functions of the TCP/IP transport layer Flow control The processes of establishing a connection between peer systems Windowing Acknowledgment Transport layer protocols TCP and UDP header formats TCP and UDP port numbers The processes and protocols at the TCP/IP application layer Domain Name Services File Transfer Protocols Simple Mail Transfer Protocol Simple Network Management Protocol Telnet