How To Use It ...

	Submit ns script via web form
	Relax while emulab …
		Generates config from script & stores in DB
		Maps specified virtual topology to physical nodes
		Provides user accounts for node access
		Assigns IP addresses and host names
		Configures VLANs
		Loads disks, reboots nodes, configures OSs
		Yet more odds and ends ...
		Runs experiment
		Reports results
	Takes ~3 min to set up 25 nodes

Who’s Using It?

	22 projects have used it (18 external)
		Plus several class projects
	Two OSDI’00 and three SOSP’01 papers
		20% SOSP general acceptance rate
		75% SOSP acceptance rate for emulab users!
	More emulabs:
		Planned or in progress:  Kentucky, CMU, Duke, Cornell
		Others considering
	Available today at www.emulab.net

emulab:
A Public Emulation Platform for Research in Distributed Systems and Networks

	Jay Lepreau*, Chris Alfeld, Shashi Guruprasad*, Mike Hibler, Mac Newbold*, Rob Ricci,
	Leigh Stoller, Brian White*
	University of Utah
	http://www.emulab.net
	(* = here at SOSP)

Why?

	“We evaluated our system on five nodes.”   -job talk from university with 300-node cluster
	“We evaluated our Web proxy design with 10 clients on 100Mbit ethernet.”
	“Simulation results indicate ...”
	“Memory and CPU demands on the individual nodes were not measured, but we believe will be modest.”
	“The authors ignore interrupt handling overhead in their evaluation, which likely dominates all other costs.”
	“You have to know the right people to use the cluster.”
	“The cluster is hard to use.”
	“<Experimental network X> runs FreeBSD 2.2.x.”
	“February’s schedule for <Testbed Y> is…”
	“<Network Z> is tunneled through the Internet”

emulab Testbed

What?

	An instrument for experimental CS research
	A completely configurable “Internet emulator” in a room
		At its core, it’s bare hardware, with…
		… complete remote access and control
	But, also simple to use
		Lots of fast tools for common case
			Automatic topology, node and link configuration
			Automatic traffic generation
		Universally available
			Universities, research labs, companies
		Zero-penalty for remote research

emulab Architecture

Key Design Aspects

	Allow experimenter complete control
		Configurable link bandwidth, latency, and loss rates, via transparently interposed “traffic shaping” nodes that provide WAN emulation
	… but provide fast tools for common cases
		OS’s, state mgmt tools, IP, batch, ...
		Disk loading – 6GB disk image FreeBSD+Linux
			Unicast tool: 88 seconds to load
			Multicast tool: 40 nodes simultaneously in < 5 minutes
	Virtualization
		of all experimenter-visible resources
		node names, network interface names, network addrs
		Allows swapin/swapout, easily scriptable

Key Design Aspects (cont’d)

	Flexible, extensible, powerful allocation algorithm
		Matches desired “virtual” topology to currently available physical resources
	Persistent state maintenance:
		none on nodes, all in database
		work from known state at boot time
	Familiar, powerful, extensible configuration language: ns
	Separate, isolated control network

Experiment Creation Process

Some Issues and Challenges

	Network management of unknown and untrusted entities
	Security (users get root on nodes!)
	Scheduling of experiments
	Calibration, validation, and scaling
	Artifact detection and control
	NP-hard virtual --> physical mapping problem
	Providing a reasonable user interface
	….

Automatic mapping of desired topologies and characteristics to physical resources

	NP-hard problem: graph to graph mapping
	Algorithm goals:
		Minimize likelihood of experimental artifacts (bottlenecks)
		“Optimal” packing of many simultaneous experiments
		Extensible for heterogeneous hardware, software, new features
	Randomized heuristic algorithm: simulated annealing
	Typically completes in < 1 second

Ongoing and Future Work

	Wireless nodes, mobile nodes
	IXP1200 nodes, tools, code fragments
		Routers, high-capacity shapers
	Simulation/emulation transparency
	Event system
	Scheduling system
	Linked set of testbeds
	Data capture, logging, and visualization tools
	Microsoft OSs, high speed links, more nodes!

New Stuff:
 Extending to Wireless and Mobile

Our Approach: Exploit a Dense Mesh of Devices

Possible User Interfaces

Wireless Virtual to Physical Mapping

Virtual Topology

Constraints on Mapping

	Must map each virtual node and link to  available physical resources
	Multiple switches usually have limited interconnect bandwidth
	In our example, there are four switches, each with 400 Mbps interconnect
	More than 4 links mapped onto a given interconnect would produce an artifact because of the bottleneck
	In solution, node color indicates its switch

Mapping into Physical Topology

Complementary to Other
Experimental Environments

	Simulation
		Fast prototyping, easy to use, but less realistic
	Small static testbeds
		Real hardware and software, but hard to configure and maintain, and lacks scale
	Live networks
		Realistic, but hard to control, measure, or reproduce results
	Emulab complements and also helps validate these environments

Wireless Virtual to Physical Mapping

Integrated Simulation & Emulation