NS2 (Network Simulator) resources

A link that answers you all.

http://www.matlab.nitech.ac.jp/~khpoo/research/ns2.html

Some other links

http://hpds.ee.ncku.edu.tw/~smallko/ns2/ns2.htm

Advice to the graduate students

http://www.cse.psu.edu/~yuanxie/advice.htm

A change is Gonna come -Sam Cooke

As Performed Sam Cooke (1964)

I was born by the river in a little tent
And just like the river, I've been running ever since
It's been a long time coming
But I know a change is gonna come

It's been too hard living, but I'm afraid to die
I don't know what's up there beyond the sky
It's been a long time coming
But I know a change is gonna come

I go to the movie, and I go downtown
Somebody keep telling me "Don't hang around"
It's been a long time coming
But I know a change is gonna come

Then I go to my brother and I say, "Brother, help me please"
But he winds up knocking me back down on my knees

There've been times that I've thought I couldn't last for long
But now I think I'm able to carry on
It's been a long time coming
But I know a change is gonna come

Expected value or average value of a random variable.

The expected value E(X) of a random variable X is an average µ of the random variable. Two random variables with the same expected value may have different distributions. 

Why queue if λ/μ < 1 ?

In Poisson distribution, why there is a queue even though λ/μ < 1. Where λ is an arrival rate and μ is a service time?

Because λ and μ are the average (or expected) value of distribution. It doesn’t mean that in every t second a customer arrives into the system. Inter-arrival (the time between consecutive events) time are exponentially distributed and arrival rate is Poisson. It means the time between two consecutive arrivals are different.
In other words, even though λ/μ < 1, two or more customers may come to the system at the same time and system can serve only one customers at one time. So, we need queue. For example: average arrival rate (λ) = 10 customer per hour, average service rate (μ) is 15 customer per hour. It means λ/μ <1. However, it follows Poisson distribution, so, two customer (or in the worst case, all the 10 customers) may come at the same time. That’s why we need queue.

How to measure packet loss rate, jitter and end-to-end delay ?

Here is the nice script for measuring packet loss rate, jitter and end-to-end delay in the prof. Chih-Heng Ke's website. 

http://140.116.72.80/~smallko/ns2/tool_en.htm

How to measure the throughput, packet drop rate, and end-to-end delay for UDP-based application over wireless networks is given here

http://hpds.ee.ncku.edu.tw/~smallko/ns2/wireless-udp-1.htm

This fellow has a good collection here:

http://lovefei.com/?p=19

BSS vs. IBSS

There are two service sets in IEEE 802.11 standard. The basic service set (BSS) for the infrastructure mode and the Independent Basic Service Set (IBSS) for the ad-hoc mode. 

The BSS is a single access point (AP)  together with all associated stations with the AP. In the infrastructure WLAN , communications can only take place between the AP and the other members of the BSS. 

In the ad hoc networks, all of the stations those are within each other's transmission range is called an IBSS.

NS2.31 NAM problem - "[code omitted because of length]"

Problem: While executing NAM in NS2 following error appears. 

nam:
[code omitted because of length]
: no event type or button # or keysym
while executing
"bind Listbox {
%W yview scroll [expr {- (%D / 120) * 4}] units
}"
invoked from within
"if {[tk windowingsystem] eq "classic" || [tk windowingsystem] eq "aqua"} {
bind Listbox {
%W yview scroll [expr {- (%D)}] units
}
bind Li..."

Solution: 

1. Download  "tk-8.4-lastevent.patch" patch file from http://bugs.gentoo.org/show_bug.cgi?id=225999
2. Save the file in tk8.4.x floder (remember that there could be tk8.4.14 or tk8.4.18)
3. Patch the file with this command

                         patch -p1 < ./tk-8.4-lastevent.patch

    4.  install again (with ./install command)

Now it works perfectly. 

(If there is a problem on patching, change -p1 to -p0. )