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using UDP for file copies on Windows/Mac/Linux

Posted on 2010-08-23
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Last Modified: 2013-12-02
Hi All.

We are looking to settle an argument in the office.

Using NFS with UDP to connect to a server and copy a file, if it drops packets, as there's no checks with UDP, will the application layer pick up there's been an error and let you know, or will it say everything is fine, and the copied file may be a few bytes short?

The arguments are:
: UDP doesn't do any checks, so the file will be short, and you wont know about it.
: Checks would be done at the application layer (windows explorer / Finder) to compare source/destination and display an error if the destination file is short.

The OS could be Win/OSX/Linux.

Thanks.
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Question by:medfacit
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by:HugoHiasl
ID: 33508531
UDP is a fast unsecure protocol.

It is used if there are small amounts of data which are not critical. For example in Voice over IP it will be used because missing packets will only reduce the quality while requested retransmissions would interfer the communication until the data packet is re-requested and sent.

There is no real mechanism to control missed packages. This needs to be done by the application that uses UDP. But UDP supports sending a checksum to verify integrity of the single datagram.

To make sure that all data arrive in the correct order there is need to use a handshake protocol like TCP which uses sending and reception windows.
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medfacit earned 0 total points
ID: 33518283
The answer to the question seems to be:

UDP uses a simple transmission model without implicit hand-shaking dialogues for guaranteeing reliability, ordering, or data integrity. Thus, UDP provides an unreliable service and datagrams may arrive out of order, appear duplicated, or go missing without notice. UDP assumes that error checking and correction is either not necessary or performed in the application, avoiding the overhead of such processing at the network interface level.

CiscoFreak said: UDP is a connectionless protocol which does not provide error checking, however, if a packet is dropped, error correction is performed at a higher level on the OSI model. Take a look at TFTP, it uses UDP but is a file transfer protocol nevertheless. If a dropped packet made your TFTP transfers invalid, I doubt it would be very popular :P

Thank you!
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