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Project overview

  • Project name: Licklider Transmission Protocol (LTP).
  • Abstract: Licklider Transmission Protocol (LTP) is a point to point protocol for environments with long round-trip delays (such as deep space communications). This project will provide a RFC compliant implementation, it will consist of a ns-3 module with its corresponding testsuits, examples, helpers and documentation.


This protocol can be deployed at two different leves: on top of either the Data-Link-Layer or the Transport Layer (UDP). The best approach should be to start with an UDP implementation, this will ensure compliance with already existing implementations. A data-link-layer implementation can also be done depending on how the project advances, and will be be taken into consideration after the results of the mid-term review (see schedule section).

Development methodology

I will use an iterative-incremental development methodology, each iteration will include implementation, documentation (doxygen style comments, thorough the source code), and testing. Development will be divided on 3 main tasks:

  • Task 1: This task consist in developing the ltp-headers and a SDNV codec (Self-Delimiting Numeric Values) a type of data encoding used in DTN protocols. This task consist on defining several data-structures and their serialization/deserialization methods.
  • Task 2: This task will focus on developing the backbone of the protocol by defining the classes: ltp-packet-queues, ltp-session-records and the basic structure of the ltp-protocol. This will define the main data structures required in control logic used to handle: packets, sessions, protocol state, timers, etc.
  • Task 3: This task will focus on the Send() and Receive() methods of the ltp-protocol class, these methods implement the control logic of the protocol.

Testing approach

This project will have testing and cross-validation against existing implementations.

First, testing will we performed as part of the development cycle. It will use a test case based approach using the standard methods provided by the ns-3 API in the form of the TestSuite and TestCase classes. This project will have two kind of tests:

  • Unit Tests: each task will have a group of test vectors, those tests will ensure that the internal workings of each developed class works in isolation.
  • System tests: these tests will be provided mainly with examples, it will consist on using the developed module together with already tested ns-3 modules.

Lastly, the implementation will be cross-validated against existing implementations of the LTP, such as ION-DTN (JPL) or LTPlib (Trinity College Dublin). This cross-validation will be performed using a shared file descriptor to which both implementations can read or write traffic. The FdNetDevice class provided by the ns-3 API will be used to achieve this task.


The final product of the project will be a ns-3 module, so the main deliverables will be the several sections of this module:

  • Deliverable 1 - model and helper: will contain the main functionalities of the protocol and the helper classes to simplify its use.
Deliverable 1.1 - Packet Headers and SDNV codec.
Deliverable 1.2 - LTP-Protocol auxiliary structures (Data Queues and Session State Records).
Deliverable 1.3 - LTP-Protocol Core.
Deliverable 1.4 - LtpNetDevice.
Deliverable 1.5 - LtpStackHelper.
  • Deliverable 2 - test: this deliverable will contain the several testsuits used.
Deliverable 2.1 - Unit Tests. Packet Headers and SDNV codec: check correctness.
Deliverable 2.2 - Unit Tests, LTP-Protocol Auxiliary, check methods, timeouts and data handling correctness.
Deliverable 2.3 - Unit Tests, NetDevice implementation, check methods.
Deliverable 2.4 - Unit Tests: protocol implementation, communication between nodes, retransmissions, cancellation of communication.
  • Deliverable 3 - examples : this deliverable will contain several examples on how to install and use the protocol.
  • Deliverable 4 - Cross-Validation: This deliverable will contain several tests using FdNetDevices to perform cross-validation with existing implementations. (4.1 early tests basic protocol, 4.2 final validation).


  • Week 1 - May 19 - May 25. D-1.1. D-2.1.
  • Week 2 - May 26 - June 1.
  • Week 3 - June 2 - June 8. D-1.2. D-2.2.
  • week 4 - June 9 - June 15.
  • Week 5 - June 16 - June 22.
  • Week 6 - June 23 - June 29: Mid-Term Evaluation.
  • Week 7 - June 30 - July 6. D-1.3. D-2.3. D-4.1.
  • Week 8 - June 7 - July 13.
  • Week 9 - July 14 - July 20. D-1.4.
  • Week 10 - July 21 - July 27. D-1.5
  • Week 11 - July 28 - August 3. D-3, D-2.4
  • Week 12 - August 4 - August 10. D-4.2

Weekly Reports

Week 1

Deliverables 1.1 and 2.1

  • Providing SDNV [1] encoding support (this a numeric format commonly used

on packet fields of DTN protocols). This encoding format was already implemented in Dizhi Zhou's BP [2] project. I have expanded it with the corresponding test-suite and moved it to src/network/utils/, for use in both Bundle and LTP protocols. Currently under review in [3]

  • Implementation of all LTP packet structures, this includes: Segment Header, Segment Trailer, and Content Header (for all segment variants: data, reports, report acknowledgments, etc.). The implementation including the corresponding tests and documentation.