Network General Training - 05 Understanding the TCP/IP Trans

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Understanding the TCP/IP Transport Layer

Transport Layer

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Reliable vs. Best-Effort Comparison

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The purpose of the transport layer is to hide the network requirements from the application layer.
Connection-oriented transport provides reliable transport; connectionless transport provides best-effort transport.

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UDP is a protocol that operates at the transport layer and provides applications with access to the network layer without the overhead of the reliability mechanisms of TCP. UDP is a connectionless, best-effort delivery protocol.

UDP Characteristics

- Operates at transport layer of OSI and TCP/IP models
- Provides applications with access to the network layer without the overhead of reliability mechanisms
- Is a connectionless protocol
- Provides limited error checking
- Provides best-effort delivery
- Has no data-recovery features

UDP Header

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TCP is a protocol that operates at the transport layer and provides applications with access to the network layer. TCP is connection-oriented, provides error checking, delivers data reliably, operates in full-duplex mode, and provides some data recovery functions.


TCP Characteristics

- Transport layer of the TCP/IP stack
- Access to the network layer for applications
- Connection-oriented protocol
- Full-duplex mode operation
- Error checking
- Sequencing of data packets
- Acknowledgement of receipt
- Data-recovery features

TCP Header

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TCP/IP supports a number of applications, including FTP (supports bidirectional binary and ASCII file transfers), TFTP (transfers configuration files and Cisco IOS images), and Telnet (provides capability to remotely access another computer).

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IP uses a protocol number in the datagram header to identify which protocol to use for a particular datagram.
Port numbers are used to map Layer 4 to an application.

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Flow control avoids the problem of a transmitting host overflowing the buffers in the receiving host and slowing network performance.

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TCP provides sequencing of segments with a forward reference acknowledgment. When a single segment is sent, receipt is acknowledged and the next segment is then sent.

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The TCP window size decreases the transmission rate to a level at which congestion and data loss do not occur. The TCP window size allows a specified number of unacknowledged segments to be sent.

A fixed window is a window with an unchanging size that can accommodate a specific flow of segments.

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A TCP sliding window is a window that can change size dynamically to accommodate the flow of segments.

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TCP provides the sequencing of segments by providing sequence numbers and acknowledgment numbers in TCP headers.

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