From Mycomputer Notes

Current revision as of 18:02, 5 April 2006

[edit] TCP/IP Transport Layer

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:

1. Flow control
2. 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

[edit] 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. Overflows can presents serious problems because they can result in the loss of data. The two hosts then establish a data-transfer rate that is agreeable to both, like the way to modem communicate between each other.

How windowing works

Protocols using TCP

• FTP
• HTTP
• SMTP
• DNS

Protocols using UDP

• TFTP
• SNMP
• DNS

Included in a TCP Header:

• Sequence number
• Acknowledge
• Window Size

[edit] 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)

Three-Way handshake

[edit] Windowing

To efficiently sent data between Host A and Host B windowing is used. Windowing is a flow-control mechanism requiring that the source device receive an acknowledgment from the destination after transmitting a certain amount of data; in other words Windowing is about knowing how much data the destination can receive before acknowledging.

How windowing works