The Minion architecture of Nowlan et al. 12 has several features that would be beneficial and complementary to Paceline’s strengths, such as its SSL strategy and wire-compatible changes to TCP that allow unordered receive.

Paceline reduces sender-side queuing delay by writing the minimum amount to the TCP socket buffer. Recently, the bufferbloat problem has received greatly renewed general attention and interest. The recent algorithm work by Kathleen Nichols and Van Jacobson is a promising step since it is easy to implement and needs no configuration. 11 What is still missing, however, is true end-to-end evaluation that quantifies the total combined effect of refinements to TCP, ECN (Explicit Congestion Notification), AQM (Active Queue Management), and adaptive multimedia.

Underlying our interest is what we believe remains an open question: Is there really a line between applications that needs to break from TCP for interactivity reasons? This is a line that has been moving steadily over time.

Lessons Learned

Introducing a new transport layer is challenging because the designer must address several critical issues. First, the transport layer has to improve performance significantly for the target applications in order to justify the extra effort. Second, the enhancements should not negatively affect other traffic types; we adhere to the vision that the Internet should remain a general-purpose infrastructure for a vast array of applications. Finally, the performance improvements at the transport level in terms of latency, fairness, and utilization need to translate to quality improvements at the application level. Paceline has shown positive results in all these aspects.

We tested Paceline extensively using videoconferencing scenarios over WAN settings. Paceline was also used in a small cloud-based game prototype to scale the wide area communication of an Epic-scale game scenario. 13 Both of these applications show significant improvements in multimedia quality because of the reductions in TCP sender-side delays and the use of adaptation in Paceline.

To ensure we have a general-purpose
transport supporting a wide range of
applications, we tested using a network
traffic generator simulating different
HTTP Web traffic flavors (for example,
HTTP1.0 and HTTP1.1, with and with-
out pipelining). The experiment tested
Web document downloads while vary-
ing the number of objects per page and
the page size. Paceline improved the
bandwidth utilization using the multi-
streaming feature as we increased the
number of objects as a result of the
automatic pipelining of small transac-
tions on top of the underlying channel.

acknowledgments

Thanks to colleagues at the Network,
Systems, and Security lab at the Univer-
sity of British Columbia for their feed-
back on previous drafts of the article.
Special thanks to Mahdi Tayarani Na-
jaran for his significant contributions
to the design and implementation of
Paceline. Finally, thanks to Terry Coatta
for helping to improve both the style
and content of this article.

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Aiman Erbad recently joined the computer science and engineering department at qatar University as an assistant professor after completing his Ph.d. at the University of British Columbia. His research interests include Web architecture, networking, real-time multimedia, ubiquitous computing, and concurrency support. Charles “Buck” Krasic works on large-scale processing of video at google’s You Tube. Prior to joining You Tube, he was a professor in the department of computer science at the University of British Columbia. His research led to the development of qStream. Other research interests include multimedia, operating systems, networking, and distributed systems.