| Efficient and Accurate Ethernet Simulation | ||||
| Status With Jia Wang (jiawang@cs.cornell.edu) |
The Internet is increasingly being called upon to provide
different levels of service to different applications and users. A practical problem in
doing so is that although Ethernet is one of the hops for nearly all communication in the
Internet, it does not provide any QoS guarantees. A natural question, therefore, is the
effect of offered load on Ethernet throughput and delay. In this paper, we present several
techniques for accurately and efficiently modeling the behavior of a heavily loaded
Ethernet link. We first present a distributed approach to exact simulation of Ethernet,
which greatly simplifies collision detection. Then, we describe an efficient distributed
simulation model, called Fast Ethernet Simulation, that empirically models an Ethernet
link to quickly and accurately simulate it. By eliminating the implementation of CSMA/CD
protocol, our approach reduces computational complexity drastically while still
maintaining desirable accuracy. Performance results show that our techniques not only add
very little overhead (less than 5% in our tests) to the basic cost of simulating an
Ethernet link, but also closely match real-world measurements. We also present efficient
techniques for compressing cumulative distributions using hyperbolic curves and for
monitoring the load on a heavily-loaded link. A paper has been published as Technical Report TR99-1728, Department of Computer Science, Cornell University, Feb. 5, 1999. |
| The Implication of Increasing Ethernet Load on Applications | ||||
| Status With Yu Zhang (yuzhang@cs.cornell.edu) and Jia Wang (jiawang@cs.cornell.edu) |
While proving different levels of internet services to
different applications and users becomes one of the hotest topics in current network
research, most of the work is focused on the architectures (e.g. differentiated services)
and routing mechanisms (e.g. QoS routing) in the range of WAN. Little interest has been
shown on studying its implication to LANs, especially the legacy Ethernet which don't
provide any QoS support, though the stub networks are the first and the final steps in the
"Internet path" to meet the QoS requirements. The usual arguments about this is
either the Ethernet are currently lightly loaded, or we can easily over-dimension them to
make them so. The questions which follows naturally are "Is it true that low load
local network is a prevalent case?" "To what extent do we need to over-dimension
them to meet the applications' requirements?" The focus of this work (to be considered so far) is to examine how the (high) load situation of Ethernet affect the dynamics and performance of several popular network applications. In particular, the two applications which we put on our list are web access and Internet telephony. The former is a very popular network application which greatly contributes to the current Internet traffic. Its traffic pattern is characterized by small client requests one way and bulk data transfer as server responses the other. The latter has been proposed as a highly desirable application and now is only in its experimental phase. Its traffic is featured by a series of evenly spaced, small size audio packets. Due to the different traffic characteristic and performance requirements of these two applications, we conjecture the impacts of the increasing Ethernet load on them will be quite different. We are interested to see what these impacts are, especially, when the degrading performance fails to meet the (basic) application requirements. We are also interested in improving the implementations of these applications to accommodate increasing load on the Ethernet. We plan to use simulation to study the problem. As a
first step, to avoid the complication when WAN technology is involved, we restrict the
problem to a simple case when all the participants of the applications sit in the same
LAN. The work is divided into three parts: Please go to our Boom'99 presentation Web page for more updated information. The presentation slides are also available here. |