Since there are no available trace analysis tool developed in NS2, people are building their own program. A good software was designed called tracegraph, although tracegraph is good for analysis purpose, the main problem with tracegraph is it is very slow to load a trace file.
The fact that it is created using MATLAB make it clear, since, MATLAB is not suitable to read a complex data although MATLAB is good for complex calculation. Why is it slow? It is because, the trace file need to be converted into Tracegraph format, the conversion part take 90% of the whole process.
For those using Tracegraph, make sure your computer is fast enough. However, the graphing part/ processing part is quite fast.