Realtime Data Retrieval (RDR) protocol¶

Real-Time Data Retrieval in Named Data Networking published in HotICN'18 introduces Real-time Data Retrieval (RDR) protocol for discovering the latest version number of real-time streaming data.
This document defines the recommended packet format of the RDR protocol.

RDR is an application-level protocol, and its usage could be application specific.
Therefore, it is RECOMMENDED that each application defines its own instance of the RDR protocol based on this document, rather than directly referencing this specification.

Metadata Packet¶

In RDR, the metadata packet is a Data packet that carries the latest version number of a data stream.

Name Suffix¶

The name of a metadata packet MUST end with these three name components:

1. The keyword component 32=metadata, indicating this Data packet is a metadata packet under this specification.
2. A version number component, whose format is defined in Naming Conventions.
3. A segment number component, whose format is defined in Naming Conventions. Normally the metadata is not segmented and thus the segment number is zero, but this component is included for future extensions.

Name Prefix¶

The name prefix of a metadata packet before the above three name components SHOULD be the same as the name of the versioned data up to (and not including) its version number component.
For example, an application can have the following namespace:

# data stream
/net/example/www/frontpage/%FD%97%47%1E%6C/%00%00
/net/example/www/frontpage/%FD%97%47%1E%6C/%00%01
/net/example/www/frontpage/%FD%97%47%1E%6D/%00%00
/net/example/www/frontpage/%FD%97%47%1E%6D/%00%01

# metadata packet
/net/example/www/frontpage/32=metadata/%FD%7E%5F%45%08/%00%00

FreshnessPeriod¶

FreshnessPeriod of a metadata packet MUST NOT be zero.
See the RDR paper for guidelines on an appropriate value for this field.

Content Payload¶

The Content of a metadata packet MUST be a sequence of TLV elements. At least one of the TLV elements MUST be a Name element. The first Name element indicates the versioned name of the latest version of the data; additional Name elements, if any, are ignored.

For example:

<Content>
  <ArbitraryElement>this is ignored</ArbitraryElement>
  <Name>/net/example/www/frontpage/%FD%97%47%1E%6D</Name>
  <Name>this is ignored</Name>
</Content>

RDR Discovery Interest¶

In the RDR protocol, consumers express RDR Discovery Interests to retrieve metadata packets, in order to discover the latest version number of the data stream.
An RDR Discovery Interest MUST:

• carry a name that ends with a 32=metadata keyword component
• contain CanBePrefix
• contain MustBeFresh