S4 is implemented in nesC for TinyOS. The implementation can be
run both in TOSSIM, a packet level sensor network simulator, and
on real testbed of sensors.

I. How to run S4 in TOSSIM:
1. go to S4/apps/TestS4Simple directory and compile using "make pc".
2. run it using "run.sh". It takes a small 100-node network, and
simulates 1000 randomly-generated (src,dest) pairs of routing, one
every second. The output contains information about the routing 
performance of each pair.
3. to play with it for larger-scale networks, first generate the
topologies using LossyBuilder, then modify the correspondig parameters
that specify numbers of nodes and beacons.

II. How to run S4 on real sensors:
1. compile the code using "make mica2" (only tested on Mica2 motes).
2. upload binary code onto all sensors.
3. compile the java code in S4/java/net/tinyos/cr using "compile.sh".
4. start serialForwarder on all sensors with ethernet connection.
5. create a text file describing testbed map. An example is 
S4/eval/42map. The first line specifies number of gateways, i.e.
sensors with ethernet connections. From the second line, each line
specifies a mote. The third column is the id of the mote. The second 
column is the id of the closest gateway. (Note that, if all sensors
are connected to the ethernet, this map file may not be necessary. The
java programs need to be modified accordingly.)
6. run S4 using RoutingTest. It randomly chooses sources and destinations
each second and routes a packet from a source to a destination. To log the
routing statistics, only those sensors with ethernet connections can be 
chosen as end points of routing.