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Few more UDP Questions

Posted on 2004-04-23
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Hey
almost finished my coursework ( u'll all be happy about that) just a few more really basic questions to go!

1.  I have basically created a header for the Application level that contains all the necessary info to process by my protocol! however i was just wondering i havent added source and destination fields at this level because i thought that at this level it was really at the location it needed to be at. Do i need to include the Source and destination fields at this level?

                       HOST 1                                   HOST 2
                          |                                            |
Send Packet 1      | -------------------------------->|
                          |                                            |
                          | <--------------------------------|Acknowledge Packet 1
                          |                                            |
                          |                                            |
                          |                                            |

2. The above diagram shows a simple sent packet and ACK but just say HOST2 trys to send a NAC to Host 1. Is there much point using Nac's over UDP?
I dont think so because what happens if the NAC fails to get to Host1. Wouldnt it just be easier to wait fot Host 2 to wait for Host1 to timeout and resend?

3. What are PDU's and how would i actually construct them\ it in relation to my protocol? what sort of things do they need to include?

i know this probably seems very trivial! but any thoughts would be great?

cheers

ed
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Question by:Follette
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4 Comments
 
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by:RDAdams
ID: 10901637
We are not supposed to assist with homework.
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PennGwyn earned 200 total points
ID: 10901678
1.  There will be source and destination addresses in the IP/UDP header -- and these will be updated in transit, if necessary, due to NAT.  Embedding addresses inside the payload, where NAT won't see them, is the classic way protocols get broken by NAT.  So any source/dest info the application needs should come from the IP header and not from the payload.

2.  You can get away with just timeouts, but if this is an interactive application then users may complain.  An explicit NAK signals the host to retransmit immediately instead of waiting for a timeout.

3. PDU ("Protocol Data Unit") is a layer-independent term for frame, packet, segment, or whatever the protocol passes to the underlying layer (and gets back from it when receiving); the protocol payload without any of the headers that get added by encapsulation as it is prepared for transmission.

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by:PaulADavis
ID: 10901778
i don't quite understand what you are doing... but i'll add a little 2cents , maybe only worth one :-)

from my understanding pdu's are protocol data units, that's used by each layer of the osi or tcp/ip stack to exchange information with it's corresponding layer at the destination.
it's a fair assumtion to say that they would need to include information that allows each layer to complete it's function and pass it on to the next layer...

but this is out of my scope really :-)

so, all the best to you.
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Author Comment

by:Follette
ID: 10902687
Thats really useful thanks pennGywnn and cheers Paul... really the last question now then i think im done!

is the PDU basicalloy just a descrition of the Header i will have made! like explaination of what they do and how they are used! Also what are IDU's?
cheers

ed
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