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NDNLP-TLV » History » Version 2

Alex Afanasyev, 01/20/2014 08:00 PM
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1 1 Junxiao Shi 
# NDNLP TLV packet format
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NDN packet format is shifting from CCNB to [NDN-TLV](http://named-data.net/doc/ndn-tlv/).





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In this format, every packet, and every field within a packet, is represented by a tuple of Type-Length-Value.





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[NDNLP: A Link Protocol for NDN](http://named-data.net/publications/techreports/trlinkprotocol/) provides two services to enable NDN communication directly on Ethernet:





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* Fragmentation and Reassembly





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* Acknowledgement and Retransmission





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NDNLP is initially designed to work with CCNx, and therefore adopts a CCNB-based packet format.





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Although it's possible to enclose NDN-TLV packets in CCNB-based NDNLP packets, this is awkward.





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Therefore, a TLV-based packet format should be defined for NDNLP.





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This document defines the TLV-based packet format for NDNLP.





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In operation reality, acknowledgement and retransmission is rarely used. This version only defines packet type and fields necessary for fragmentation and reassembly.





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Basic [protocol operations](http://named-data.net/publications/techreports/trlinkprotocol/) are unchanged.





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Fragmentation and reassembly operations are [extended to multicast](https://github.com/NDN-Routing/NDNFD/blob/80c3e009106d7e16db85ee8afd647ba85b5b7c2d/docs/NDNLP.md).





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## Link Data Packet





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A Link Data packet carries a NDN-TLV packet or a fragment of it as the payload.





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It has the following format:





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	NdnlpData ::= NDNLP-DATA-TYPE TLV-LENGTH





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		            NdnlpSequence





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    Alex Afanasyev
    
		            NdnlpFragIndex?





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		            NdnlpFragCount?





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    Junxiao Shi
    
		            NdnlpPayload





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These elements MUST appear in the given order.





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All elements are required unless otherwise stated.





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### sequence number





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	NdnlpSequence ::= NDNLP-SEQUENCE-TYPE TLV-LENGTH





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		                nonNegativeInteger





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A unique sequence number for each packet.





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### fragment index





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	NdnlpFragIndex ::= NDNLP-FRAG-INDEX-TYPE TLV-LENGTH





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		                 nonNegativeInteger





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The 0-based index of current fragment within the network layer packet.





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Optional. Default to '0' if not present.





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### fragment count





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	NdnlpFragCount ::= NDNLP-FRAG-COUNT-TYPE TLV-LENGTH





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		                 nonNegativeInteger





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Total number of fragments of the network layer packet.





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Optional. Default to '1' if not present.





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### payload





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	NdnlpPayload ::= NDNLP-PAYLOAD-TYPE TLV-LENGTH





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		               Interest or Data





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The payload.





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## TLV-TYPE assignments





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NDNLP-TLV temporarily adopts its [original DTAGs](http://redmine.ccnx.org/issues/100710) as TLV-TYPE numbers.





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	20653248,NdnlpData





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	20653249,NdnlpSequence





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	20653251,NdnlpFragIndex





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	20653252,NdnlpFragCount





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	20653253,NdnlpPayload





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`NdnlpData` should be assigned a 1-byte TLV-TYPE number that does not conflict with NDN-TLV, so that it can be efficiently used on the same connection with NDN-TLV.





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There is no uniqueness requirements on the TLV-TYPE numbers for other elements.