Technical info about space data communications

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becarlson

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For a class I am trying to locate more technical information on space-based data transmission. More specifically, I am wanting information on what the MRO will use for a data transmission protocol, and how it works.<br /><br />During a webcast, Dr. Jim Graf mentioned briefly that the the MRO will have the capability to retransmit data that didn't arrive at Earth. This sounds similar to what TCP (as in TCP/IP) does, but with the extremely long latency between Earth and Mars, instant retransmissions are not feasible. I want to know how the protocol that MRO uses handles this.<br /><br />Basically I am wanting an extremely technical overview from an engineering standpoint of how the protocol and transmission systems work. Thanks everyone.
 
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becarlson

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Thanks, to be more specific I am looking for some of the following data:<br /><br />-How does the MRO handle communications when the Earth is not in sight<br />-How does the data transmission protocol work, how does it handle retransmissions<br />-How does the protocol handle latency between Earth and Mars<br />-How is the data reassembled on Earth if the signal was captured by multiple DSN receivers (the signal arrives at DSN receiver #1, then passes below the horizon, so DSN receiver #2 acquires the signal. How is the data stream reconstructed?)<br />-Does the protocol use "packets" similar to TCP/IP, what are the packet sizes <br /><br />In Dr Graf's presentation he made it sound like a completely new protocol was developed for the MRO mission, and I was trying to find out some more about it. Thanks again,
 
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SpaceKiwi

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najaB could be your man with this. IIRC he is doing thesis work on VOIP so I'd say he probably has a good knowledge of the protocols, both terrestrial and otherwise. <div class="Discussion_UserSignature"> <p><em><font size="2" color="#ff0000">Who is this superhero?  Henry, the mild-mannered janitor ... could be!</font></em></p><p><em><font size="2">-------------------------------------------------------------------------------------------</font></em></p><p><font size="5">Bring Back The Black!</font></p> </div>
 
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najab

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><i>...he probably has a good knowledge of the protocols, both terrestrial and otherwise.</i><p>Terrestrial I could go on for hours about. Interplanetary, I only have a little idea about, it's pretty hard to get reliable information. I understand that the idea is to use a modified version of TCP/IP - the data is sent as packets (I think about 1KB each), and each packet is sent multiple times. I'm not sure how the retransmission works, my guess would be that the Earth station sends back ACKs and they use selective retransmission. One thing for sure - they don't do "go back N"! <img src="/images/icons/laugh.gif" /></p>
 
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