Status of the DTN2 Reference Implementation
	     ===========================================

This document describes the high-level features of version 2.3.0 of
the DTN2 reference implementation and summarizes the relationship
between the implementation and the various Internet Drafts that
describe Delay Tolerant Networking, the Bundle Protocol, and other
related protocols.

The current version of the DTN2 code is based on the Bundle Protocol
Specification Internet Draft version 6, and the Delay Tolerant
Networking Architecture Internet Draft version 6, both released in
September of 2006. The TCP convergence layer is based on the Delay
Tolerant Networking TCP Convergence Layer Protocol draft version 0.

A copy of these documents (and possibly more recent versions) can be
obtained from the ietf.org web site.


			 The Bundle Protocol
			 -------------------

The features described in the bundle protocol specification that are
implemented include the following:

- The Basic Bundle Protocol
- Self Describing Numeric Values
- Endpoint Identifiers (more information below)
- Bundle expirations (based on timers)
- Registrations (with expiration timers)
- Persistent storage of bundles
- Bundle fragmentation (reactive)
- Bundle fragment reassembly
- Custody Transfer
- Bundle Status Reports:
  - Received
  - Forwarded 
  - Delivered
  - Deleted
  - Custody Acceptance
- Extension blocks


The features that are not yet implemented include:

- Bundle Status Reports:
  - Acknowledged by Application 
- Bundle Security blocks
- Proactive Fragmentation


			  Convergence Layers
			  ------------------

The following Convergence Layers have been implemented. 

-- TCP Convergence Layer

An internet draft (draft-demmer-dtnrg-tcp-clayer-00.txt) has been
published describing the TCP convergence layer protocol.

The TCP convergence layer offers a reliable communication channel
between DTN nodes. All bundle communication is now bidirectional. The
protocol returns an acknowledgement message when part or all of the
bundle is received. These acknowledgements allowing the sender side to
determine whether or not the bundle can be removed from the data
store. Also, the partial acknowledgements are used to implement
reactive fragmentation.

-- UDP Convergence Layer

The UDP convergence layer offers a simple, unreliable channel. A
single bundle is sent in each UDP datagram, thus only bundles that are
smaller than the 64KB maximum datagram size can be sent. It is assumed
that configuration will be put in place to proactively fragment large
bundles before sending them over this type of link.

-- Ethernet Convergence Layer

This convergence layer sends bundles over raw ethernet frames, using
an invented ethernet type code (0xd710). As with the UDP CL, there is
a maximum size of bundles that can be sent over this type of link,
in this case 1518 bytes.

This convergence layer also includes support for neighbor discovery
through the use of periodic beacon packets.

** Note -- this convergence layer is currently disabled for lack of
   testing. It is intended to be re-enabled in a future release.
   

			 Link / Contact Types
			 --------------------

As described by the DTN architecture document, there are four general
types of links:

-- Always On

These links are opened immediatly on configuration, and underlying
transport connections (if any) are maintained open whenever possible.

-- On Demand

These links are opened when there is a bundle (or bundles) that the
router determines should be sent over the link. There is a
configurable idle timer that closes the link after a period of
inactivity.

-- Opportunistic

These links are only opened in response to some external event, such
as detection of a nearby node. Currently, there is only limited
support for neighbor discovery.

-- Scheduled

No support for scheduled links is yet implemented.


			       Routing
			       -------

The implementation offers an interface by which new routing algorithms
and modules can be easily added to the system. To date, however, the
only fully implemented algorithm is a simple static router that
requires manual configuration of routes. 

We intend for this to be an area of future development, with more
routing frameworks added in upcoming release(s).


			 Endpoint Identifiers
			 --------------------

This implementation contains a rich framework for naming based on URI
schemes. The following schemes are supported:

-- DTN scheme

We currently implement a (unspecified) scheme of "dtn". This scheme
offers support for internet hostname style node specifications, along
with URI path style demultiplexers, as well as simple pattern matching
for route entries.

An example DTN uri is dtn://thing1.dtnrg.org.dtn/mail

-- String scheme

A simple scheme used for testing allows any ASCII string to be encoded
in a URI. An example is str:my_name_is_mike

-- Ethernet scheme

This scheme encodes ethernet addresses in a URI format. An example
ethernet scheme URI is eth://01:23:45:ab:cd:ef


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Last updated: December 18, 2006