Transapp
From Mycomputer Notes
Primary duties of the transport layer are to transport and regulate the flow of information from a source to a destination, reliably and accurataly. Control and reliability are accomplished by:
- Sliding windows
- Sequencing Numbers
- Acknowledgements
Protocols in the transport layer segment and reassemble data sent by upper-layer applications into the same transport layer data stream. The transport layer data streams provides end-to-end transport services. The two primary duties of the transport layer are to provide:
- Flow control
- Reliability
Some basic transport services are as follows:
- Segmentation of upper-layer application data
- Establishment of end-to-end operations
- Transportation of segments from one end host to another
- Flow control provided by sliding windows
- Reliability provided by sequence numbers and acknowledgments
Data Flow Control
How the transport layer controls the flow of data.
As the transport layer sends data segments, it tries to ensure that data is not lost.
Flow control ensures that a source host does not overflow the buffers in a destination host.
To provide flow control, TCP allows the source and destination hosts to communicate. The two hosts then establish a data-transfer rate that is agreeable to both, like the way to modem communicate between them.
Protocols using TCP
- FTP
- HTTP
- SMTP
- DNS
Protocols using UDP
- TFTP
- SNMP
- DNS
Included in a TCP Header:
- Sequence number
- Acknowledge
- Window Size
Three Way handshake:
Since TCP is a connection-oriented protocol, and a connection and a connection needs to be stablished before data starts to been transfered both host needs to be synchronized. Synchronization is done is done through an Exchange of segments that carry a synchronized control bit (SYN) and the initial sequence number (ISN) This solution requires a mechanism that picks the initial sequence numbers and a handshake to exchange them.
The synchronization requires each side (host A & host B) to send its own initial sequence number (ISN) and to received a confirmation of it in an acknowledgment (ACK) from the other side. Each side also must receive the other side's (the other host) ISN and send a confiming (ACK)
The purpose of the 3 way handshake is to: Synchronized sequence
