1 Computational Energy Cost of TCP CS Paper Discussion Fall Yanpei Chen

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 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 Methodology Instrumentation Arithmetic Graphical illustration

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

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