Author: admin
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7.7 Summary-Chapter 7
The entire purpose of the lower three layers (Transport, Internetwork, and Link) is to make it so that applications running in the Application layer can focus the application problem that needs to be solved and leave virtually all of the complexity of moving data across a network to be handled by the lower layers of…
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7.6 Writing Networked Applications
The applications which send and receive data over the network are written in one or more programming languages. Many programming languages have libraries of code that make it quite simple to write application code to send and receive data across the network. With a good programming library, making a connection to an application running on…
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7.5 Flow Control
When we looked at the Transport layer, we talked about the “window size”, which was the amount of data that the Transport layer on the sending computer will send before pausing to wait for an acknowledgement. In this figure, we see a message broken into packets, with some of the packets sent and acknowledged. Six…
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7.4 The IMAP Protocol for Retrieving Mail
The HTTP protocol is only one of many client/server application protocols used on the Internet. Another common protocol is used so that a mail application running on your computer can retrieve mail from a central server. Since your personal computer might not be turned on at all times, when mail is sent to you it…
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7.3 Exploring the HTTP Protocol
In this section we will manually exercise the HTTP protocol by pretending to be a web browser and sending HTTP commands to a web server to retrieve data. To play with the HTTP protocol, we will use one of the earliest Internet applications ever built. The “telnet” application was first developed in 1968, and was…
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7.2 Application Layer Protocols
Just like people talking on telephones, each pair of network applications needs a set of rules that govern the conversation. In most cultures, when your phone rings and you pick up the phone you say “Hello”. Normally the person who made the call (the client person) is silent until the person who picked up the…
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7.1 Client and Server Applications
It is important to remember that two parts are required for a networked application to function. The architecture for a networked application is called “client/server”. The server portion of the application runs somewhere on the Internet and has the information that users want to view or interact with. The client portion of the application makes…
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7 Application Layer
We have been working from the bottom to the top of our fourlayer TCP/IP network model and we are finally at the top. The Application layer is where the networked software like web browsers, mail programs, video players, or networked video players operate. We as users interact with these applications and the applications interact with…
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6.8 Questions-Chapter 6
You can take this quiz online at http://www.net-intro.com/quiz/ What is the primary problem the Transport (TCP) layer is supposed to solve? a) Move packets across multiple hops from a source to destination computer b) Move packets across a single physical connection c) Deal with lost and out-of-order packets d) Deal with encryption of sensitive data…
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6.7 Glossary-Chapter 6
acknowledgement: When the receiving computer sends a notification back to the source computer indicating that data has been received. buffering: Temporarily holding on to data that has been sent or received until the computer is sure the data is no longer needed. listen: When a server application is started and ready to accept incoming connections…
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6.6 Summary-Chapter 6
In a sense, the purpose of the Transport layer is to compensate for the fact that the Link and Internetworking layers might lose data. When the two lower layers lose or reroute packets, the Transport layer works to reassemble and/or retransmit that data. The existence of the Transport layer makes it possible for the two…
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6.5 Server Applications and Ports
When a client application wants to make a connection to a remote computer, it is important that the connection is made to the correct server application on that remote computer. A remote computer might have any number of different server applications running at the same time. Example server applications would include: • Web Server• Video…
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6.4 Application Clients and Servers
The purpose of the Transport layer is to provide reliable connections between networked applications so those applications can send and receive streams of data. For an application, this is as simple as asking the Transport layer to make a connection to an application running on a remote host. We call the application that initiates the…
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6.3 The Transport Layer In Operation
One of the key elements of the Transport layer is that the sending computer must hold on to all of the data it is sending until the data has been acknowledged. Once the receiving computer acknowledges the data, the sending computer can discard the sent data. We can look at this graphically when a message…
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6.2 Packet Reassembly and Retransmis- sion
As the destination computer receives the packets, it looks at the offset position from the beginning of the message so it can put the packet into the proper place in the reassembled message. Simply by making sure to put the packet data at the correct position relative to the beginning of the message, the Transport…