ECN support for qdiscs in ns-3

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Enabling ECN support for ns-3 qdiscs - Summer Project 2016

  • Referred RFC: The Addition of Explicit Congestion Notification (ECN) to IP [ https://tools.ietf.org/html/rfc3168]
  • Referred ns-2 code:
  • ns-3 ECN code:
  • Other Reference Material: Implementing explicit congestion notification in ns-3 [ http://dl.acm.org/citation.cfm?id=2630782]
  • About me: : I am pursuing B.Tech in Computer Science from National Institute of Technology Karnataka, Surathkal, India. Currently, I am a Mitacs intern working under Dr. Ehab Elmallah on Wireless Underwater Sensor Networks at University of Alberta, Canada.


Weekly Plan

Week 1

* Going through the RFC
* Going through the Linux and ns-2 stack 
* Preparing the architecture for merging ECN with the existing AQM mechanisms in ns-3

Key Deliverable: Information Architecture

Week 2

* Implementation of ECN bits in the TCP and IP headers
* Implementation of ECN Negotiation by adding ECN Capability to TCP's SYN/ACK packets 
* Writing tests for this scenario and documenting the ECN support in TCP and IP packets

Key Deliverable: RFC compliant packet structure

Week 3

* Implementation of ECN at TCP sender (i.e., setting ECN code points in data packets)
* Writing tests for this scenario and documentation of the implementation and tests. 

Key Deliverable: The sending module at layer 4

Week 4

* Incorporating ECN functionality in PIE 
* Write tests to  verify the functionality of ECN with PIE 
* Documenting the implementation of ECN for PIE.
* We can have Mid-term review this week

Key Deliverable : The complete implementation of ECN in PIE

Week 5

* Implementation of ECN at TCP receiver (i.e., recognising ECN marks from data packets)
* Writing example for implementation of ECN in layer 4
* Completing tests for this scenario and documenting the implementation and tests.

Key Deliverable: The complete implementation of ECN in layer 4

Week 6

* Integration across layers
* Verifying the complete functionality of ECN
* Putting up code for review
* Complete the documentation

Week 7

Week 7:
* Addressing reviewer’s comments
* Solving bugs before declaring the code to be 'ready to merge' state.
* Finalize the documentation.

Key Deliverable : Finalize the code for merging

Weekly Progress

Week 1

After going through the existing tcp and ip model of ns-3 , here are the points I found out:


=''tcp-header.h and tcp-header.cc''=
*Has last 2 bits reserved for ecn - Ece|cwr is already present
*SetFlag(int)-> This function is used to set m_flags variable of TCP header. The current documentation mention it to be working as only
a uint6_t variable as only 6 bits are in use, we will make use of the last two reserved bits for ECN. Since the function is already
 implemented we will call this with modified parameter.

*For example: The negotiation step of ECN Enable TCP connection will be 
Sender to Receiver -> SetFlag(TcpHeader::SYN | TcpHeader::ECE | TcpHeader::CWR)
Receiver to Sender -> SetFlag(TcpHeader::SYN | TcpHeader::ECE | TcpHeader::ACK)
Sender to Receiver -> SetFlag(TcpHeader::ACK)

ipv4-header.h and ipv4-header.cc - 
*Ipv4 header also has the ECNtype enum with all 4 ecn codepoints  defined and also the setter(SetEcn()) and getter(GetEcn()) functions 
to set ECN values in m_tos and retrieve it. These functions haven’t been used in the implementation of any modules. We will use these 
setter and getter function for the  ECN manipulation in Ipv4.
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