Re: [aqm] Follow-up: PIE performance in cable modem environments
Preethi Natarajan <preethi.cis@gmail.com> Tue, 07 May 2013 23:28 UTC
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Date: Tue, 07 May 2013 16:28:21 -0700
From: Preethi Natarajan <preethi.cis@gmail.com>
To: Greg White <g.white@CableLabs.com>, "iccrg@irtf.org" <iccrg@irtf.org>, "aqm@ietf.org" <aqm@ietf.org>, "Rong Pan (ropan)" <ropan@cisco.com>
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Thread-Topic: [aqm] Follow-up: PIE performance in cable modem environments
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Subject: Re: [aqm] Follow-up: PIE performance in cable modem environments
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Hi Greg, As other posts point out, the byte-mode operation has been around for a while and it is not unique/new to PIE. We weren't aware of Bob Briscoe's BCP draft until recently. We understand the concerns mentioned here. In fact, we encountered the DropTail's preferential treatment for small packets in our simulations (mentioned in the BCP draft) and that was our motivation to experiment with byte-mode. We think that a good alternative to byte-mode would be ToS/DiffServe-field based differential dropping, similar to WRED, since that would give similar benefits as byte-mode. That way, we don't have to stick to byte-mode based approach for PIE. Regards, The PIE Team From: Greg White <g.white@CableLabs.com> Date: Friday, May 3, 2013 3:55 PM To: Preethi Natarajan <preethi.cis@gmail.com>, "iccrg@irtf.org" <iccrg@irtf.org>, "aqm@ietf.org" <aqm@ietf.org> Subject: Re: [aqm] Follow-up: PIE performance in cable modem environments Preethi, I did a diff on the new version of the PIE code vs the earlier release and found, as you stated, that the basic algorithm hasn't changed. I do see some other improvements/changes though. One which, I think, bears discussion is the weighting of packet drops based on size. In the new code there is the option (turned on in the simulations I reported on in my paper) to drop packets according to p*pkt_size/mean_pkt_size where p is the drop probability calculated by the PIE control law. This serves to significantly decrease the drop probability of the small VoIP and gaming packets, which may be sensitive to loss (from a QoE perspective) and non-responsive to loss (from a congestion control perspective). This is evidenced by the low packet loss rate for gaming traffic that I reported in my paper. However, I worry that the unintended consequence may be that this weighting incentivizes application developers toward the use of small packets, which seems ill advised. Thoughts? -Greg From: Preethi Natarajan <preethi.cis@gmail.com> Date: Tuesday, April 30, 2013 5:48 PM To: Greg White <g.white@cablelabs.com>, Preethi Natarajan <preethi.cis@gmail.com>, "iccrg@irtf.org" <iccrg@irtf.org>, "tsvwg@ietf.org" <tsvwg@ietf.org>, "aqm@ietf.org" <aqm@ietf.org> Cc: "Rong Pan (ropan)" <ropan@cisco.com>, "Bill Ver Steeg (versteb)" <versteb@cisco.com>, "Chiara Piglione (cpiglion)" <cpiglion@cisco.com>, "Mythili Suryanarayana Prabhu (mysuryan)" <mysuryan@cisco.com>, "Fred Baker (fred)" <fred@cisco.com>, Dan Rice <d.rice@cablelabs.com> Subject: Re: [aqm] Follow-up: PIE performance in cable modem environments Hi, Thank you Greg for the update and the link to the white paper. We wanted to quickly clarify about how we tuned PIE for DOCSIS. The basic PIE algorithm has not changed. We updated the simulation code with the missing line mentioned below (which was a bug). The DOCSIS MAC layer has this special nature of stop-and-go with 5ms-6ms request and grant delay. This requires adjustment of any algorithm: for example CoDel has to increase its target delay from 5ms to a higher value. Similarly, our new parameters are to make PIE adjust faster for the DOCSIS stop-and-go behavior. Please note that eventually all these design parameters will be automatically set, users of the PIE algorithm would not be required to set any design parameters. Again, many thanks for your update. PIE team From: Greg White <g.white@CableLabs.com> Date: Tuesday, April 30, 2013 3:54 PM To: Preethi Natarajan <preethi.cis@gmail.com>, "iccrg@irtf.org" <iccrg@irtf.org>, "tsvwg@ietf.org" <tsvwg@ietf.org>, "aqm@ietf.org" <aqm@ietf.org> Cc: "Rong Pan (ropan)" <ropan@cisco.com>, "Bill Ver Steeg (versteb)" <versteb@cisco.com>, "Chiara Piglione (cpiglion)" <cpiglion@cisco.com>, "Mythili Suryanarayana Prabhu (mysuryan)" <mysuryan@cisco.com>, "Fred Baker (fred)" <fred@cisco.com>, Daniel Rice <D.Rice@CableLabs.com> Subject: Re: [aqm] Follow-up: PIE performance in cable modem environments Additionally, I've re-run my suite of simulations using the updated PIE code from Cisco. The results (in much more detail than I presented at ICCRG) are documented in a white paper available here: Active Queue Management Algorithms for DOCSIS 3.0 <http://www.cablelabs.com/downloads/pubs/Active_Queue_Management_Algorithms_ DOCSIS_3_0.pdf> Thanks to Preethi, Rong, et al. for debugging and tuning PIE to work well in the cable environment, and for sharing the resulting code. Best Regards, Greg From: Preethi Natarajan <preethi.cis@gmail.com> Date: Tuesday, April 23, 2013 5:18 PM To: "iccrg@irtf.org" <iccrg@irtf.org>, "tsvwg@ietf.org" <tsvwg@ietf.org>, "aqm@ietf.org" <aqm@ietf.org> Cc: "Rong Pan (ropan)" <ropan@cisco.com>, "Bill Ver Steeg (versteb)" <versteb@cisco.com>, "Chiara Piglione (cpiglion)" <cpiglion@cisco.com>, "Mythili Suryanarayana Prabhu (mysuryan)" <mysuryan@cisco.com>, "Fred Baker (fred)" <fred@cisco.com> Subject: [aqm] Follow-up: PIE performance in cable modem environments Hello, This is a follow-up to Greg White's (from Cable Labs) talk at the recent ICCRG meeting on PIE's performance in cable modem environments. Post the meeting, Greg was kind to share his ns-2 DOCSIS model with us. We investigated PIE's performance using this model. The key items from this investigation: 1. Bug in PIE code: The previous PIE release (that Greg used for evaluations) was missing a line of code. This missing line brings down drop probability under certain conditions and turns out to be critical for the cable modem scenario. Without this line of code, the drop probability remains high and takes longer to come down even when the queue delay has remained lower than the reference. The updated ns-2 PIE code can be found here ftp://ftpeng.cisco.com/pie/. 2. Bug in ns-2 TCP/Linux: Greg's cable modem simulations used the TCP Cubic variant. We discovered a serious bug in ns-2 TCP/Linux Agent (confirmed by Dr. Injong Rhee's team) that makes TCP/Cubic senders very aggressive and unresponsive to packet drops/notifications, pretty much like UDP traffic. Please find more details about the bug here -- http://sourceforge.net/tracker/?func=detail&aid=3608750&group_id=149743&atid =775392. We are working with Cable Labs to verify the cable modem results, they'll soon be available on our FTP site along with the PIE code. A technical paper about PIE was recently accepted at the IEEE Conference on High Performance Switching and Routing 2013. A copy of the paper is attached here. The Linux PIE implementation is expected to be ready by next week and we'll follow-up on that as well. Many thanks, Preethi on behalf of PIE team.
- Re: [aqm] [iccrg] Follow-up: PIE performance in c… John Leslie
- Re: [aqm] Follow-up: PIE performance in cable mod… Greg White
- [aqm] Follow-up: PIE performance in cable modem e… Preethi Natarajan
- Re: [aqm] Follow-up: PIE performance in cable mod… Preethi Natarajan
- Re: [aqm] Follow-up: PIE performance in cable mod… Dave Taht
- Re: [aqm] Follow-up: PIE performance in cable mod… grenville armitage
- Re: [aqm] Follow-up: PIE performance in cable mod… Greg White
- Re: [aqm] Follow-up: PIE performance in cable mod… Preethi Natarajan
- Re: [aqm] Follow-up: PIE performance in cable mod… Preethi Natarajan