NDNLP-TLV » History » Revision 7
Revision 6 (Junxiao Shi, 02/15/2014 08:31 PM) → Revision 7/8 (Junxiao Shi, 02/23/2014 10:13 AM)
# NDNLP TLV packet format
NDN packet format is shifting from CCNB to [NDN-TLV](http://named-data.net/doc/ndn-tlv/).
In this format, every packet, and every field within a packet, is represented by a tuple of Type-Length-Value.
[NDNLP: A Link Protocol for NDN](http://named-data.net/publications/techreports/trlinkprotocol/) provides two services to enable NDN communication directly on Ethernet:
* Fragmentation and Reassembly
* Acknowledgement and Retransmission
NDNLP is initially designed to work with CCNx, and therefore adopts a CCNB-based packet format.
Although it's possible to enclose NDN-TLV packets in CCNB-based NDNLP packets, this is awkward.
Therefore, a TLV-based packet format should be defined for NDNLP.
This document defines the TLV-based packet format for NDNLP.
In operation reality, acknowledgement and retransmission is rarely used. **This version only defines packet type and fields necessary for fragmentation and reassembly**.
Basic [protocol operations](http://named-data.net/publications/techreports/trlinkprotocol/) are unchanged.
Fragmentation and reassembly operations are [extended to multicast](https://github.com/NDN-Routing/NDNFD/blob/80c3e009106d7e16db85ee8afd647ba85b5b7c2d/docs/NDNLP.md).
## Link Data Packet
A Link Data packet carries a NDN-TLV packet or a fragment of it as the payload.
It has the following format:
NdnlpData ::= NDNLP-DATA-TYPE TLV-LENGTH
NdnlpSequence
NdnlpFragIndex?
NdnlpFragCount?
NdnlpPayload
### sequence number
NdnlpSequence ::= NDNLP-SEQUENCE-TYPE TLV-LENGTH(=8)
BYTE+
A unique sequence number for each packet.
This sequence number is unique for recent packets. It can wrap around ultimately.
### fragment index
NdnlpFragIndex ::= NDNLP-FRAG-INDEX-TYPE TLV-LENGTH
nonNegativeNumber TLV-LENGTH(=2)
BYTE+
The 0-based index of current fragment within the network layer packet.
Optional. Default to '0' if not present.
### fragment count
NdnlpFragCount ::= NDNLP-FRAG-COUNT-TYPE TLV-LENGTH
nonNegativeNumber TLV-LENGTH(=2)
BYTE+
Total number of fragments of the network layer packet.
Optional. Default to '1' if not present.
### payload
NdnlpPayload ::= NDNLP-PAYLOAD-TYPE TLV-LENGTH
BYTE+
The payload, which is a fragment of network layer packet.
payload.
## TLV-TYPE assignments
Type | Assigned value | Assigned value (hex)
------------------------------------------- | ----------------- | --------------------
NdnlpData | 80 | 0x50
NdnlpSequence | 81 | 0x51
NdnlpFragIndex | 82 | 0x52
NdnlpFragCount | 83 | 0x53
NdnlpPayload | 84 | 0x54