UDP Packets not received other end what happens

[lohit prasad]

What happens when UDP packets are not received other end ? Do I need to transmit again ?  How reassembly happens in UDP ? 

[Joseph W. Doherty]

It depends on the application using UDP.  Some applications will take the loss and continue to run as best they can, some will deal with retransmission.

[lohit prasad]

Thanks Joseph for fast reply. I have one doubt. 

PC A  >>>>>>> UDP Packets  Router X  >>>>> Router Y >>>>> PC B

Let say I am sending DNS packets, then how PCB DNS knows if packets lost or not ? Does Application have mechanism to detect packet loss like TCP then I want to know which application ? How PC A knows to resend ? 

Also In case of reassembly how UDP behaves differently then TCP ?

[lohit prasad]

Please help in replying this question friends

[Joseph W. Doherty]

Sorry, missed your earlier reply.

In answer to your question, whether an application detects packet loss or not, is totally up to the application.  A network application can do its own error lost detection and recovery, but that's the purpose for TCP, so every application doesn't need to "reinvent the wheel".

UDP behaves differently from TCP, in that the UDP protocol does not provide any error loss detection, error recovery, sequencing, etc.

In your example with DNS, PC B would not know there was packet loss to it.  PC A, assuming it's waiting on a response, if that times out, could assume either there was packet loss to PC B or packet loss in PC B's response.  It can decide to try again.  If there are multiple retry failures, then it might assume PC B, itself, may no longer be on-line.

[lohit prasad]

Tx