MesoNet: A Mesoscopic Simulation Model of a Router-Level Internetlike Network 

MesoNet is a mesoscopic (medium scale) simulation model of a router-level Internet-like 

network. The model, written in SLX1

, facilitates investigation of global behavior through 

simulation of a network representing a single Internet Service Provider. MesoNet is 

uniquely positioned between microscopic models, which require hundreds of parameters 

to fully specify detailed behavior of individual network elements, and macroscopic 

models, which aggregate behavior of many network elements into abstract 

representations that may lose key interactions on fine spatiotemporal scales. 

MesoNet assumes a three-tier hierarchy of routers (backbone, point-of-presence and 

access), while also supporting some heterogeneity, including: variations in speed among 

access routers and traffic sources, ability to connect access routers directly to backbone 

routers, and six classes of transport flow. Network links are simulated in detail only on 

the backbone, where propagation delays become important. The current model routes 

network traffic on static, shortest-path routes. Network traffic in MesoNet is supplied 

through simulated sources and receivers, which operate under connection-establishment 

and congestion-control procedures representing the Reno version of the transmission 

control protocol (TCP). Each source cycles continuously among three steps: (1) think for 

some exponentially distributed time, (2) connect to a receiver with probabilities reflecting 

the network topology, and (3) transfer a web page of some Pareto distributed size. Size is 

increased for selected transfers to simulate users who decide to download a paper, image 

or music file from a web site. 

Given a specified topology and speed for backbone routers, MesoNet can be fully 

parameterized with only eleven factors, which include a multiplier on propagation delays, 

queue limits for routers in each tier, speeds of tier two and three routers, average think 

period and file size (plus distribution shape), probability of a larger transfer and 

associated multiplier on file size. During simulation, model state is captured at each userspecified measurement interval, leading to time series for response variables. The current 

model records response variables at several levels, including: network wide, each router, 

and each flow class. Recorded responses include utilizations, queue sizes, losses, active 

and completed flows, retransmission rates, connection failures, throughputs, and rate of 

window increases, timeouts, and negative acknowledgments. MesoNet is also capable of 

logging detailed state changes and packet transfers for randomly sampled flows. 

MesoNet is implemented as an agent-automata model, where every active element is 

updated at each time step. For a topology of 171 routers, 28 backbone links, 27,600 

sources and 12,000 simultaneously active flows, MesoNet must update around 40,000 

elements per time step, where some elements are updated multiple times to reflect speed 

differences. For such a topology, MesoNet executes about 10 times slower than real time, 

depending on the processor used. To date, MesoNet has been used to simulate network 

evolution over periods from 20 minutes to 17 hours. The next version of MesoNet will 

include simulation of sources that use congestion-control algorithms from HS-TCP and 

FAST and enhancements to the source model to reflect both web and peer-to-peer users. 

 

1

 SLX is a commercial simulation system available from Wolverine Software, see: 

http://www.wolverinesoftware.com.