1. 1 Computational Energy Cost of TCP CS294-14 Paper Discussion Fall 2007 2007-10-17 Yanpei Chen

2. 2 Paper Overview To measure energy of TCP over wireless Energy given by current drawn through multimeters Platforms running TCP during measurement –TCP run on laptop w/ FreeBSD 4.2 & 5 (TCP reno & newreno) –iPAQ (TCP reno) Results –Kernel-NIC copy is costly: 60-70% energy –User-kernel copy cost 15% energy –TCP processing 15% energy – can be further broken down Suggested energy reduction techniques –Zero-copy: Data from user space directly to NIC –More powerful NIC to reduce kernel-NIC copy cost –Save 20-30% energy

3. 3 Related Work Most energy work done on wireless interface, channel environment etc. Past work on TCP computational cost focus on time consumed One past work on TCP energy – consumption not broken down Contributions of the paper –Help develop energy reduction techniques –Develop TCP energy models –Allow NS-2 to simulate energy cost –Present energy measurement method … to be reused …

4. 4 Methodology Instrumentation Arithmetic Graphical illustration

5. 5 Results Average total energy TCP vs. Radio Comparison against time metric Breaking down TCP energy cost

6. 6 Results – Breaking down TCP processing cost Check sum cost by running check sum code TO, TD, ACK cost in lossy network Validate results by predicting energy use for 10MB of data

7. 7 Energy reduction techniques Zero-copy: Data from user buffers directly to NIC –Function exists in FreeBSD 5 More powerful NIC to reduce kernel-NIC copy cost –Keep TCP send buffer on NIC –Maximize data transfer chunk from kernel to NIC Save 20-30% energy

8. 8 Questions Have their work made its way into NS-2? Similar work on wired topology?