NDNLP-TLV » History » Version 1
Junxiao Shi, 01/20/2014 07:24 PM
| 1 | 1 | Junxiao Shi | # NDNLP TLV packet format |
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| 2 | |||
| 3 | NDN packet format is shifting from CCNB to [NDN-TLV](http://named-data.net/doc/ndn-tlv/). |
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| 4 | In this format, every packet, and every field within a packet, is represented by a tuple of Type-Length-Value. |
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| 5 | |||
| 6 | [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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| 7 | |||
| 8 | * Fragmentation and Reassembly |
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| 9 | * Acknowledgement and Retransmission |
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| 10 | |||
| 11 | NDNLP is initially designed to work with CCNx, and therefore adopts a CCNB-based packet format. |
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| 12 | Although it's possible to enclose NDN-TLV packets in CCNB-based NDNLP packets, this is awkward. |
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| 13 | Therefore, a TLV-based packet format should be defined for NDNLP. |
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| 14 | |||
| 15 | This document defines the TLV-based packet format for NDNLP. |
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| 16 | 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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| 17 | |||
| 18 | Basic [protocol operations](http://named-data.net/publications/techreports/trlinkprotocol/) are unchanged. |
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| 19 | Fragmentation and reassembly operations are [extended to multicast](https://github.com/NDN-Routing/NDNFD/blob/80c3e009106d7e16db85ee8afd647ba85b5b7c2d/docs/NDNLP.md). |
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| 20 | |||
| 21 | |||
| 22 | ## Link Data Packet |
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| 23 | |||
| 24 | A Link Data packet carries a NDN-TLV packet or a fragment of it as the payload. |
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| 25 | It has the following format: |
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| 26 | |||
| 27 | NdnlpData ::= NDNLP-DATA-TYPE TLV-LENGTH |
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| 28 | NdnlpSequence |
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| 29 | NdnlpFragIndex |
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| 30 | NdnlpFragCount |
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| 31 | NdnlpPayload |
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| 32 | |||
| 33 | These elements MUST appear in the given order. |
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| 34 | All elements are required unless otherwise stated. |
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| 35 | |||
| 36 | ### sequence number |
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| 37 | |||
| 38 | NdnlpSequence ::= NDNLP-SEQUENCE-TYPE TLV-LENGTH |
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| 39 | nonNegativeInteger |
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| 40 | |||
| 41 | |||
| 42 | A unique sequence number for each packet. |
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| 43 | |||
| 44 | ### fragment index |
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| 45 | |||
| 46 | NdnlpFragIndex ::= NDNLP-FRAG-INDEX-TYPE TLV-LENGTH |
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| 47 | nonNegativeInteger |
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| 48 | |||
| 49 | The 0-based index of current fragment within the network layer packet. |
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| 50 | |||
| 51 | Optional. Default to '0' if not present. |
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| 52 | |||
| 53 | ### fragment count |
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| 54 | |||
| 55 | NdnlpFragCount ::= NDNLP-FRAG-COUNT-TYPE TLV-LENGTH |
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| 56 | nonNegativeInteger |
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| 57 | |||
| 58 | Total number of fragments of the network layer packet. |
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| 59 | |||
| 60 | Optional. Default to '1' if not present. |
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| 61 | |||
| 62 | ### payload |
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| 63 | |||
| 64 | NdnlpPayload ::= NDNLP-PAYLOAD-TYPE TLV-LENGTH |
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| 65 | Interest or Data |
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| 66 | |||
| 67 | The payload. |
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| 68 | |||
| 69 | |||
| 70 | ## TLV-TYPE assignments |
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| 71 | |||
| 72 | NDNLP-TLV temporarily adopts its [original DTAGs](http://redmine.ccnx.org/issues/100710) as TLV-TYPE numbers. |
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| 73 | |||
| 74 | 20653248,NdnlpData |
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| 75 | 20653249,NdnlpSequence |
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| 76 | 20653251,NdnlpFragIndex |
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| 77 | 20653252,NdnlpFragCount |
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| 78 | 20653253,NdnlpPayload |
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| 79 | |||
| 80 | `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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| 81 | There is no uniqueness requirements on the TLV-TYPE numbers for other elements. |