NDNLP-TLV » History » Version 4
Junxiao Shi, 02/13/2014 10:03 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 | 4 | Junxiao Shi | In operation reality, acknowledgement and retransmission is rarely used. **This version only defines packet type and fields necessary for fragmentation and reassembly**. |
| 17 | 1 | Junxiao Shi | |
| 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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| 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 | 4 | Junxiao Shi | NdnlpData ::= NDNLP-DATA-TYPE TLV-LENGTH |
| 28 | 1 | Junxiao Shi | NdnlpSequence |
| 29 | 2 | Alex Afanasyev | NdnlpFragIndex? |
| 30 | NdnlpFragCount? |
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| 31 | 1 | Junxiao Shi | NdnlpPayload |
| 32 | |||
| 33 | ### sequence number |
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| 34 | |||
| 35 | 4 | Junxiao Shi | NdnlpSequence ::= NDNLP-SEQUENCE-TYPE TLV-LENGTH(=8) |
| 36 | BYTE+ |
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| 37 | 1 | Junxiao Shi | |
| 38 | A unique sequence number for each packet. |
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| 39 | |||
| 40 | ### fragment index |
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| 41 | |||
| 42 | 4 | Junxiao Shi | NdnlpFragIndex ::= NDNLP-FRAG-INDEX-TYPE TLV-LENGTH(=2) |
| 43 | BYTE+ |
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| 44 | 1 | Junxiao Shi | |
| 45 | The 0-based index of current fragment within the network layer packet. |
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| 46 | |||
| 47 | Optional. Default to '0' if not present. |
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| 48 | |||
| 49 | ### fragment count |
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| 50 | |||
| 51 | 4 | Junxiao Shi | NdnlpFragCount ::= NDNLP-FRAG-COUNT-TYPE TLV-LENGTH(=2) |
| 52 | BYTE+ |
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| 53 | 1 | Junxiao Shi | |
| 54 | Total number of fragments of the network layer packet. |
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| 55 | |||
| 56 | Optional. Default to '1' if not present. |
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| 57 | |||
| 58 | ### payload |
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| 59 | |||
| 60 | NdnlpPayload ::= NDNLP-PAYLOAD-TYPE TLV-LENGTH |
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| 61 | 4 | Junxiao Shi | BYTE+ |
| 62 | 1 | Junxiao Shi | |
| 63 | The payload. |
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| 64 | 3 | Alex Afanasyev | |
| 65 | ## TLV-TYPE assignments |
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| 66 | |||
| 67 | Type | Assigned value | Assigned value (hex) |
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| 68 | ------------------------------------------- | ----------------- | -------------------- |
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| 69 | 4 | Junxiao Shi | NdnlpData | 30 | 0x1e |
| 70 | NdnlpSequence | 31 | 0x1f |
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| 71 | NdnlpFragIndex | 32 | 0x20 |
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| 72 | NdnlpFragCount | 33 | 0x21 |
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| 73 | NdnlpFragCount | 34 | 0x22 |