Scuola Superiore SantAnna Simulazione di protocolli RT per Reti di Sensori Wireless in ambiente NS-2 Giuseppe Lipari, Paolo Pagano

Scuola Superiore Sant’Anna

Simulazione di protocolli RT perReti di Sensori Wireless in ambiente NS-2

Giuseppe Lipari, Paolo Pagano

3 novembre 2006 Paolo Pagano (ReTiS, SSSA Pisa) 2“Sen

sori

wir

eles

s ed

inte

graz

ione

di s

iste

ma

per

appl

icaz

ioni

ubi

que

in a

mbi

to o

sped

alie

ro”

Rational for this new Paradigm

• Networks are becoming faster and software complexity in a node higher, thus increasing the vagueness of simulation because of assumption of events within a node occuring in zero time;

• To reduce the gap and errors between a simulation and the final implementation;

• To simulate applications which need a very high level of accuracy in timing: need to consider detailed time usage within and outside a node;

• Ability to simulate homogeneous as well as hetrogeneous environments by using the appropriate CPU-OS combination profile at various nodes.


sori

wir

eles

s ed

inte

graz

ione

di s

iste

ma

per

appl

icaz

ioni

ubi

que

in a

mbi

to o

sped

alie

ro”

Project phylosophy

• Integrate existing simulators– Network Simulator of Choice: NS-2 (USC-ISI, UCLA, UCB);– OS Simulator of Choice: RTSim (ReTiS Lab, Sant’ Anna).

http://rtsim.sssup.it/http://www.isi.edu/nsnam/ns/


sori

wir

eles

s ed

inte

graz

ione

di s

iste

ma

per

appl

icaz

ioni

ubi

que

in a

mbi

to o

sped

alie

ro”

NS-2 Architecture

• Application:– Standard network applications like FTP,

Telnet or various Traffic Generators like CBR, Exponential ...

• Agent:– Represent endpoints where network-

layer packets are constructed or consumed, and are used in implementing protocols;

• Node:– Represents a basic node in the network.

Can be configured to adopt various routing, MAC, LL, and PHY layer protocols.


sori

wir

eles

s ed

inte

graz

ione

di s

iste

ma

per

appl

icaz

ioni

ubi

que

in a

mbi

to o

sped

alie

ro”

Expectations from new Architecture

• Simulation Time Accountancy for latency in:

–Periodic and Aperiodic Task Set–Interrupt processing

• Ability to use existing NS-2 agents, MAC and PHY layers already provided in the standard distribution:

–802.15.4-based WPANs supported starting from NS 2.29.

• Transparency:–no major change in NS-2 user interface;–user provided by APIs accessible through the TCL front-end.

• Support for heterogeneous environments i.e. ability to simulate different CPU as well as OS profiles on various nodes in a simulation.


sori

wir

eles

s ed

inte

graz

ione

di s

iste

ma

per

appl

icaz

ioni

ubi

que

in a

mbi

to o

sped

alie

ro”

The new Library added to NS-2

• Implement RTSim Task Scheduler as an Application in NS-2 Framework– Simple and easy to do– Minor modification to RTLib

• Simulate different scheduling policies (FIFO, FP, EDF, ...)


sori

wir

eles

s ed

inte

graz

ione

di s

iste

ma

per

appl

icaz

ioni

ubi

que

in a

mbi

to o

sped

alie

ro”

Kernel instructions

• The RT-Application is now in charge of: – scheduling packet

transmission;– handle packet reception.

• Send and Receive instructions have been added to RTSim;

• FCFS (~TinyOS) and FP scheduling policies are simulated.

Figures refer to FCFS scheduling policy.


sori

wir

eles

s ed

inte

graz

ione

di s

iste

ma

per

appl

icaz

ioni

ubi

que

in a

mbi

to o

sped

alie

ro”

Computation and Network Load

• Simulate from light to heavy load in the node through a set of Dummy Periodic Tasks: – tuning the number of tasks;– tuning the task parameters (C,T,U) to obtain different

loads.

• Calculating the total delay (source to destination) as a function of the packet and checking the impact of the scheduling policies in time sensitive applications;

• Network load tuned acting on transmission schedules and concurrent access.


sori

wir

eles

s ed

inte

graz

ione

di s

iste

ma

per

appl

icaz

ioni

ubi

que

in a

mbi

to o

sped

alie

ro”

Network Scenarios (1)

• Starting from simple scenarios:– 4 nodes located at the

edges of a square communicating to a sink placed at the center of mass; no hidden terminal;no network structure (single cluster); no routing; the sink plays the role of WPAN coordinator.

• To re-obtain the governing laws of RT-computing. Screenshot of the Network

AniMator (NAM)


sori

wir

eles

s ed

inte

graz

ione

di s

iste

ma

per

appl

icaz

ioni

ubi

que

in a

mbi

to o

sped

alie

ro”

Network Scenarios (2)

• Complicating the picture:– Introducing routing paths

and data streams;– Nodes connecting different

clusters fetch and forward the readings coming from other clusters.

• How do RT-issues influence the reactivity of such nodes?

Screenshot of the Network AniMator (NAM)


sori

wir

eles

s ed

inte

graz

ione

di s

iste

ma

per

appl

icaz

ioni

ubi

que

in a

mbi

to o

sped

alie

ro”

t [s]

Selection of relevant metrics

• By simulation we evaluate:– the maximum, mean and

minimum latency observed in sending and receiving the packets;

– the time propagation through the sender and recipient network stacks (including re-transmissions done at low layers);

– the packet probability of being delivered.

• Applications can be sensitive to one, more or all these metrics.


sori

wir

eles

s ed

inte

graz

ione

di s

iste

ma

per

appl

icaz

ioni

ubi

que

in a

mbi

to o

sped

alie

ro”

Outlook and Conclusions

• NS-2 and RTSim have been integrated to take into account RT-issues in wireless telecommunications;

• In WSNs these issues play a role whenever any QoS must be guaranteed by the nodes;

• Simple and more complicated scenarios are being simulated to evaluate selected metrics;

• FCFS and FP scheduling policies have been implemented and are being compared within certain network and CPU load conditions;

• results are coming...

Documents

Scuola Superiore SantAnna Simulazione di protocolli RT per Reti di Sensori Wireless in ambiente NS-2 Giuseppe Lipari, Paolo Pagano