A New Look at Bandwidth Latency Tradeoffs
John H Shaffer, Jonathan M. Smith · ScholarlyCommons (University of Pennsylvania) · 1996
(loilcerns about propagation dela,y have d~minat~ed Ihr clisc~~ssions of latency, lnndwidth and their effect on distributed applications. In this paper. we argue t%hat. t,he relevant latency measure for applications is the Application Data Unit (ADU) Lat'ency, defined as the time between the sending of an ADU and its receipt. Sincr ADTTs are oft,eil large, i\\DU latency is influenced by throughput as well as propagation delay. \\(Ye investigated the effects of ADIJ latency with an experimental st8udy of several applica-tions. The applications used Di~tribut~ecl Shared l!T~mory as an interprocess communica.tions mechanism, constraining the ADUs to page-sized u11it~s. The apl~licat~ioas were run on aa Et,Il-ernet,, an experimental ATRil LAD;, and using ATM 011 an esperimenta,l high-speed IVAN. 'rhe ineasured results were used to normalize results gathered 1)~- iirserting a.n experimental ATM switch output port controller in the networl; to create t.l~nabl(> drlays. The results conclusively demonst,rat,e t,he effect of ADTI lat8ency on distributed application response time. The experiments give a precise chara.ctevizat,ioll of thc effect of va,rying bandwidth and propagation delay on a real system, and suggest promising dirrctions for further improving a.pplication performance in future net8works. 1