Design Discussion: Implementing LEDBAT++ in ns-3 (Extension vs. Modification)
Ayush Nigam .
We are a group of students who are currently working on implementation of LEDBAT++ (as defined in the Internet-Draft “LEDBAT++: Congestion Control for Background Traffic ”,9 September 2025) as part of our course project for computer networks in ns-3.
The existing LEDBAT implementation in ns-3 (src/internet/model/tcp-ledbat.cc) is based on RFC 6817.
LEDBAT++ introduces additional mechanisms such as:
1. Modified slow start using a dynamic GAIN parameter
2. Dynamic GAIN parameter is dependent on base delay and target delay.
3. Multiplicative decrease for improved inter-LEDBAT fairness.
4. Initial and periodic slowdowns to avoid latency drift.
5. Use of RTT-based delay estimation instead of one-way delay.
Now, we are considering two possible approaches for the implementation:
Approach 1 : Create a new class TcpLedbatPlusPlus, derived from TcpLedbat, and override only the modified algorithms.
Approach 2 : Extend the existing TcpLedbat class by introducing an attribute flag (e.g., EnableLedbatPlusPlus) and conditionally enabling LEDBAT++ behavior(if EnableLedbatPlusPlus is set to true then LEDBAT++ behaviour will be enabled otherwise if it is set to false then LEDBAT behaviour will be followed).
I would appreciate your guidance on which design is more consistent with ns-3 development practices — i.e., whether it’s preferable to create a subclass for LEDBAT++ and extend, or to enhance the existing TcpLedbat class with EnableLedbatPlusPlus configuration attribute.
Thanks and Regards,
Ayush Nigam
Tom Henderson
Hello Ayush, my opinion is that either approach may be suitable, and it depends on the amount of code reuse. My guess in this case is that, because ns-3 TcpLedbat is defined as a TcpCongestionOps class (and not a full TCP implementation) and because there are several changes to those congestion control operations, it may be cleaner to implement it as a separate class because you may not have a lot of code reuse, and because you probably have different attributes that only pertain to one or the other variant. I might suggest to try to implement it as TcpLedbatPlusPlus and then, once you are finished, consider whether there is a significant code reuse potential.
- Tom
Ayush Nigam --
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Ayush Nigam .
Hello Tom,
Thank you for your guidance. I will proceed with implementing it as TcpLedbatPlusPlus and evaluate code reuse potential after completion.
Thanks & Regards,
Ayush