Revision as of 15:36, 13 June 2014

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Understanding bufferbloat through simulations in ns-3

• Student: Truc Anh Nguyen
• Mentors: Tom Henderson and Dave Täht
• Abstract: The goal of the project is to study and visualize the bufferbloat problem by developing models and examples in ns-3 and analyze the performance of different queue types that are developed as solutions to bufferbloat, including CoDel, FQ_CoDel, and SFQRED
• Code:
• About me: I am currently a PhD student in Computer Science at The University of Kansas. My focus area is networking with the emphasis on studying and understanding the different reliable transport layer mechanisms and protocols, including the various connection management, error control, and congestion control approaches. More information is available on my website

Readings

• • http://gettys.wordpress.com/category/bufferbloat/
  • CeroWrt
  • ICCRG presentation
  • ns-2 code
  • ns-3 code review
  • Active Queue Management Algorithms for DOCSIS 3.0

Approach

I plan to accomplish the project's goal through the following 3 phases:

• Phase 1: Bufferbloat problem demonstration and simulation
• Phase 2: Codel, FQ Codel, SFQRED code fix and cross-validation
  • Codel: address the comments on ns-3 code review for Codel, add documentation, write test suite, validate against ns-2 and OpenWrt Linux implementations
  • FQ Codel: address the comments on ns-3 code review for FQ Codel, add documentation, write test suite, validate against ns-2 and OpenWrt Linux implementations
  • SFQRED: address the comments on ns-3 code review for SFQRED, add documentation, write test suite, validate against ns-2 and OpenWrt Linux implementations
• Phase 3: Simulations and performance analysis

Deliverables

• Delverable 1: Scripts to demonstrate and visualize bufferbloat problem
• Deliverable 2: Codel code with documentation, test suite, and scripts to validate against ns-2 and OpenWrt implementations
• Deliverable 3: FQ Codel code with documentation, test suite , and scripts to validate against ns-2 and OpenWrt implementations
• Deliverable 4: SFQRED code with documentation, test suite, and scripts to validate against ns-2 and OpenWrt implementations
• Deliverable 5: Scripts to perform simulation analysis under different scenarios

Plan

After our weekly meeting on Friday, we update this section noting down our plan for the upcoming week(s).

• Friday, May 16, 2014:
  • Review ns-3 AQM code reviewers' comments, make a list of all the issues to be attacked, test Dave's git repo, and run the programs in the scratch/ dir
  • Develop a 3-node test script with FIFO queue for initial visualization of bufferbloat. One router sits in between a sender and a receiver, and the link connects the router and the receiver is the bottleneck link with a 10 Mb/s bandwidth and a 5 ms delay. The sender node sends multiple small TCP flows and 1 large flow. We may want a diversity of receivers with different RTTs to avoid synchronization effects. Initial set of performance metrics we want to capture include:
    • queue sojourn time
    • cwnd evolution for "elephant" TCP connection
    • completion time or PLT (Page Load Time) for "mice" TCP connections
    • other TCP statistics

Weekly progress

• Week 1 (May 19, 2014 -- May 23, 2014):

CoDel ToDo (Dave's codel-todo.org)

• Generic issues:
  • Correct solution for queues that might not return a packet (Not clear if this problem is generic to the net point-to-point device or global)
  • Correct solution for tcp initial sequence numbers
  • The IPv4Header and the IPv6Header objects do not have equivalent functions like getECN
• FQ_Codel
  • Fix incorrect hashing for IPv6 and other protocols
    • Linux abstracted all this out into net/core/flow-dissector.c
    • It also inspects deep enough to get src/dst ports from many popular protocols.
    • Switching to the same jhash will also get rid of a dependency on boost
    • ns-3 header parsing is weird. Declare the object see if it exists?

   q->PeekHeader (each kind of ip header? tcp udp sctp?)
   if header->hasports()? 

• • fq_codel does not use shared buffer backlog on the codel aqm
    • That was how we did things prior to running into the horizontal standing queue problem.

   if (m_ht[h] == NULL) 
     {
        NS_LOG_DEBUG ("fq_codel enqueue Create queue " << h);
        m_ht[h] = new Fq_CoDelSlot (); 
        slot = m_ht[h]; 
        slot->q->backlog = &backlog; 
     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^?
        slot-> h = h; 
     }

• • • (and to this day I'm dissatisfied with the solution in Linux. He drops a lot more sparse packets now than I'd like)
  • Fq_CoDelQueue::DoEnqueue (Ptr<Packet> p) looks a lot like sfq in initializing queues
    • It seems saner to me to initialize once at startup. Don't need a map, either, just a good old fashioned array