14.2 TCP Overview

In addition to supporting the basic functions of data segmentation and reassembly, TCP also provides the following services:

- Establishes a Session - Ensures Reliable Delivery

Which two applications would use the TCP transport layer protocol? (Choose two.) - FTP - HTTP - ICMP - TFTP - VoIP

- FTP - HTTP

TCP Provides Same-Order Delivery

Because networks may provide multiple routes that can have different transmission rates, data can arrive in the wrong order. By numbering and sequencing the segments, TCP ensures segments are reassembled into the proper order.

TCP Supports Flow Control

Network hosts have limited resources (i.e., memory and processing power). When TCP is aware that these resources are overtaxed, it can request that the sending application reduce the rate of data flow. This is done by TCP regulating the amount of data the source transmits. Flow control can prevent the need for retransmission of the data when the resources of the receiving host are overwhelmed.

TCP Establishes a Session

TCP is a connection-oriented protocol that negotiates and establishes a permanent connection (or session) between source and destination devices prior to forwarding any traffic. Through session establishment, the devices negotiate the amount of traffic that can be forwarded at a given time, and the communication data between the two can be closely managed.

TCP handles all tasks associated with _______________, _______________, and _______________.

dividing the data stream into segments providing reliability controlling data flow reordering segments. TCP frees the application from having to manage any of these tasks. Applications, like those shown in the figure, can simply send the data stream to the transport layer and use the services of TCP.

TCP is a stateful protocol which means it

keeps track of the state of the communication session. To track the state of a session, TCP records which information it has sent and which information has been acknowledged. The stateful session begins with the session establishment and ends with the session termination.

To track the state of a session, TCP records

which information it has sent and which information has been acknowledged. The stateful session begins with the session establishment and ends with the session termination.

A TCP segment adds _____ bytes (i.e., _____ bits) of overhead when encapsulating the application layer data. The figure shows the fields in a TCP header.

20 160

Applications that use TCP

- IP - HTTP - FTP - SMTP - Telnet - DNS

Which TCP header statement is true? - It consists of 4 fields in an 8-byte header. - It consists of 8 fields in a 10-byte header. - It consists of 10 fields in a 20-byte header. - It consists of 20 fields in a 40-byte header.

- It consists of 10 fields in a 20-byte header.

Which transport layer protocol ensures reliable same-order delivery? - ICMP - IP - TCP - UDP

- TCP

10 TCP fields in a 20-byte header

1) Source Port 2) Destination Port 3) Sequence Number 4) Acknowledgment Number 5) Header Length 6) Reserved 7) Control bits 8) Window size 9) Checksum 10) Urgent

TCP Checksum Header Field

A 16-bit field used for error checking of the segment header and data.

TCP Destination Port Header Field

A 16-bit field used to identify the destination application by port number.

TCP Source Port Header Field

A 16-bit field used to identify the source application by port number.

TCP Urgent Header Field

A 16-bit field used to indicate if the contained data is urgent.

TCP Window size Header Field

A 16-bit field used to indicate the number of bytes that can be accepted at one time.

TCP Sequence Number Header Field

A 32-bit field used for data reassembly purposes.

TCP Acknowledgment Number Header Field

A 32-bit field used to indicate that data has been received and the next byte expected from the source.

TCP Header Length Header Field

A 4-bit field known as ʺdata offsetʺ that indicates the length of the TCP segment header.

TCP Control bits Header Field

A 6-bit field that includes bit codes, or flags, which indicate the purpose and function of the TCP segment.

TCP Reserved Header Field

A 6-bit field that is reserved for future use.

TCP Ensures Reliable Delivery

For many reasons, it is possible for a segment to become corrupted or lost completely, as it is transmitted over the network. TCP ensures that each segment that is sent by the source arrives at the destination.