Principle of Reliable Data Transfer in Java

Paint QR Code 2d barcode in Java Principle of Reliable Data Transfer
Principle of Reliable Data Transfer
QR Code JIS X 0510 Drawer In Java
Using Barcode creator for Java Control to generate, create Denso QR Bar Code image in Java applications.
Figure 34-3: rdt20 - a protocol for a channel with bit-errors Protocol rdt20 may look as if it works but unfortunately has a fatal flaw In particular, we haven't accounted for the possibility that the ACK or NAK packet could be corrupted! (Before proceeding on, you should think about how this problem may be fixed) Unfortunately, our slight oversight is not as innocuous as it may seem Minimally, we will need to add checksum bits to ACK/ NAK packets in order to detect such errors The more difficult question is how the protocol should recover from errors in ACK or NAK packets The difficulty here is that if an ACK or NAK is corrupted, the sender has no way of knowing whether or not the receiver has correctly received the last piece of transmitted data Consider three possibilities for handling corrupted ACKs or NAKs:
Creating Barcode In Java
Using Barcode generator for Java Control to generate, create barcode image in Java applications.
For the first possibility, consider what a human might do in the message dictation scenario If the speaker didn't understand the ``OK'' or ``Please repeat that'' reply from the receiver, the speaker would probably ask ``What did you say '' (thus introducing a new type of sender-to-receiver packet to our protocol) The speaker would then repeat the reply But what if the speaker's ``What did you say'' is corrupted The receiver, having no idea whether the garbled sentence was part of the dictation or a request to repeat the last reply, would probably then respond with ``What did you say '' And then, of course, that response might be garbled Clearly, we're heading down a difficult path A second alternative is to add enough checksum bits to allow the sender to not only detect, but recover from, bit errors This solves the immediate problem for a channel which can corrupt packets but not lose them A third approach is for the sender to simply resend the current data packet when it receives a garbled ACK or NAK packet This, however, introduces duplicate packets into the sender-to-receiver channel The fundamental difficulty with duplicate packets is that the receiver doesn't know whether the ACK or NAK it last sent was received correctly at the sender Thus, it can not know a priori whether an arriving packet contains new data or is a retransmission!
Barcode Recognizer In Java
Using Barcode scanner for Java Control to read, scan read, scan image in Java applications.
A simple solution to this new problem (and one adopted in almost all existing data transfer protocols including TCP) is to add a new field to the data packet and have the sender number its data packets by putting a sequence number into this field The receiver then need only check this sequence number to determine whether or not the received packet is a retransmission For this simple case of a stop-and-wait protocol, a 1-bit sequence number will suffice, since it will allow the receiver to know whether the sender is resending the previously transmitted packet (the sequence number of the received packet has the same sequence number
Quick Response Code Drawer In Visual C#.NET
Using Barcode encoder for VS .NET Control to generate, create QR Code image in .NET framework applications.
file:///D|/Downloads/Livros/computa o/Computer%20Netwopproach%20Featuring%20the%20Internet/principles_rdthtm (4 of 20)20/11/2004 15:52:08
Drawing QR-Code In VS .NET
Using Barcode printer for ASP.NET Control to generate, create QR Code JIS X 0510 image in ASP.NET applications.
Principle of Reliable Data Transfer
QR Code 2d Barcode Encoder In .NET
Using Barcode maker for .NET Control to generate, create QR-Code image in VS .NET applications.
as the most recently received packet) or a new packet (the sequence number changes, ie, moves ``forward'' in modulo 2 arithmetic) Since we are currently assuming a channel that does not lose packets, ACK and NAK packets do not themselves need to indicate the sequence number of the packet they are ACKing or NAKing, since the sender knows that a received ACK or NAK packet (whether garbled or not) was generated in response to its most recently transmitted data packet
QR Code Encoder In VB.NET
Using Barcode drawer for .NET Control to generate, create QR Code image in .NET applications.
Figure 34-4: rdt21 sender
Making Bar Code In Java
Using Barcode generation for Java Control to generate, create barcode image in Java applications.
file:///D|/Downloads/Livros/computa o/Computer%20Netwopproach%20Featuring%20the%20Internet/principles_rdthtm (5 of 20)20/11/2004 15:52:08
Make Data Matrix In Java
Using Barcode creation for Java Control to generate, create Data Matrix ECC200 image in Java applications.
Principle of Reliable Data Transfer
Encoding Code 128 Code Set B In Java
Using Barcode drawer for Java Control to generate, create Code-128 image in Java applications.
Figure 34-5: rdt21 recevier Figures 34-4 and 34-5 show the FSM description for rdt21, our fixed version of rdt20 The rdt21 sender and receiver FSM's each now have twice as many states as before This is because the protocol state must now reflect whether the packet currently being sent (by the sender) or expected (at the receiver) should have a sequence number of 0 or 1 Note that the actions in those states where a 0-numbered packet is being sent or expected are mirror images of those where a 1-numbered packet is being sent or expected; the only differences have to do with the handling of the sequence number Protocol rdt21 uses both positive and negative acknowledgements from the receiver to the sender A negative acknowledgement is sent whenever a corrupted packet, or an out of order packet, is received We can accomplish the same effect as a NAK if instead of sending a NAK, we instead send an ACK for the last correctly received packet A sender that receives two ACKs for the same packet (ie, receives duplicate ACKs) knows that the recevier did not correctly receive the packet following the packet that is being ACKed twice Many TCP implementations use the receipt of so-called "triple duplicate ACKs" (three ACK packets all ACK'ing the same packet) to trigger a retransmission at the sender Our NAK-free reliable data transfer protocol for a channel with bit errors is rdt22, shown in Figure 34-6 and 34-7
GS1-128 Printer In Java
Using Barcode creation for Java Control to generate, create GS1-128 image in Java applications.
file:///D|/Downloads/Livros/computa o/Computer%20Netwopproach%20Featuring%20the%20Internet/principles_rdthtm (6 of 20)20/11/2004 15:52:08
Create Code 39 In Java
Using Barcode maker for Java Control to generate, create Code 39 Extended image in Java applications.
Make Code 11 In Java
Using Barcode maker for Java Control to generate, create USD - 8 image in Java applications.
DataMatrix Reader In .NET Framework
Using Barcode decoder for .NET framework Control to read, scan read, scan image in Visual Studio .NET applications.
Code-39 Drawer In .NET Framework
Using Barcode printer for Visual Studio .NET Control to generate, create Code-39 image in Visual Studio .NET applications.
Encoding Bar Code In Visual C#
Using Barcode generation for .NET Control to generate, create bar code image in VS .NET applications.