Foundation Summary

Study Material For Cisco Ccna Ccnp And Ccie Students

Study Material For Cisco Students

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The "Foundation Summary" section of each chapter lists the most important facts from the chapter. Although this section does not list every fact from the chapter that will be on your CCNA exam, a well-prepared CCNA candidate should know, at a minimum, all the details in each "Foundation Summary" section before going to take the exam.

The terms connection-oriented and connectionless have some relatively well-known connotations inside the world of networking protocols. The meaning of the terms is intertwined with error recovery and flow control, but they are not the same. Some basic definitions are in order:

■ Connection-oriented protocol—A protocol either that requires an exchange of messages before data transfer begins or that has a required pre-established correlation between two endpoints

■ Connectionless protocol—A protocol that does not require an exchange of messages and that does not require a pre-established correlation between two endpoints

Figure 6-11 shows an example of windowing.

Figure 6-11 shows an example of windowing.

TCP and UDP multiplex between different applications using the port source and destination number fields. Figure 6-12 shows an example.

Figure 6-12 Hannah Sending Packets to Jessie, with Three Applications Using Port Numbers to Multiplex

Hannah

Port S0 Web Server Port S00 Ad Server Port 20,100 Wire Application

Jessie fitf

I'll Look in the UDP or TCP Destination Port To Identify the Application!

Eth

IP

UDP

Ad Data

Eth

Destination Port 800

Wire

Eth

IP

TCP

Transfer Data

Eth

Destination port 20,100

Eth

IP

TCP

Web Page Data

Eth

Destination Port 80

Figure 6-13 depicts TCP error recovery.

Destination Port 80

Figure 6-13 TCP Acknowledgment with Errors

Web Server

Web Server

1000 Bytes of Data, Sequence = 1000

1000 Bytes of Data, Sequence = 1000

He Lost the Segment, 1000 Bytes of Data, Sequence = 200i with Sequence = 2000. Resend it!

1000 Bytes of Data, Sequence = 3000

No Data, Acknowledgment = 2000

1000 Bytes of Data, Sequence = 2000 No Data, Acknowledgment = 4000

I Probably Lost One ACK What I Got in Order!

^I Just Got 2000-2999\

and I Already Had , 3000-3999. Ask for I V 4000 Next. y

Figure 6-14 shows an example of a TCP connection-establishment flow. Figure 6-14 TCP Connection Establishment

Web Browser

SEQ=200

SEQ=1450, ACK=201

SEQ=201, ACK=1451 ACK, DPORT=80, SPORT=1027

Web Server

Table 6-7 contrasts typical transport layer functions as performed (or not performed) by UDP or TCP.

Table 6-7 TCP and UDP Functional Comparison

Function

Description (TCP)

Description (UDP)

Ordered data transfer

This involves a continuous stream of ordered data.

Does not reorder received data.

Multiplexing using ports

Receiving hosts decide the correct application for which the data is destined, based on the port number.

Same as TCP.

Reliable transfer

Acknowledgment of data uses the Sequence and Acknowledgment fields in the TCP header.

This is not a feature of UDP.

Flow control

This process is used to protect buffer space and routing devices.

This is not a feature of UDP.

Connections

This process is used to initialize port numbers and other TCP header fields.

UDP is connectionless.

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