NDNLP TLV packet format¶

NDN packet format is shifting from CCNB to 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 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 are unchanged.
Fragmentation and reassembly operations are extended to multicast.

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

These elements MUST appear in the given order.
All elements are required unless otherwise stated.

sequence number¶

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

A unique sequence number for each packet.

fragment index¶

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

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
                     nonNegativeInteger

Total number of fragments of the network layer packet.

Optional. Default to '1' if not present.

payload¶

NdnlpPayload ::= NDNLP-PAYLOAD-TYPE TLV-LENGTH
                   Interest or Data

The payload.

TLV-TYPE assignments¶

NDNLP-TLV temporarily adopts its original DTAGs as TLV-TYPE numbers.

20653248,NdnlpData
20653249,NdnlpSequence
20653251,NdnlpFragIndex
20653252,NdnlpFragCount
20653253,NdnlpPayload

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