What can be done in NS2 and what can not be?

Question

Before asking the question i would like to tell that i have been searching over it for over a month. I would say that i know ns2 but am surely would be able to understand anything that you would say [hopefully]

I want to implement Breadth First Search (BFS) and create BFS tree in the wireless mobile node topology in NS2. [Lets do it for static system first.]

My Challenge: multicast messages to all neighbors of a node.

Now i thought in my imagination that

Nodes would be set at there positions. [doable]
Each node would be able to find its neighbor. [Is it doable ?] or i would have to make "group" and do "join-group" for forming these neighbors myself.
Multicast messages to neighbor. [doable using "group"] but i wanted that is there some way that a node knows what i can connect to and do it itself.

What are possible among these ?

Ashish Negi Ashish Negi · Accepted Answer · 2013-04-24T23:07:47

Ok so after completing my project i would like to share how i did it. I am still learning but yes, i did it this way.

The scenario is Wireless.

Generating nodes is simple in NS:

set nodes(0) [$ns node]

set nodes(1) [$ns node]

where nodes is an array.

Set positions of nodes:

$nodes(0) set X_ 20.0

$nodes(0) set Y_ 100.0

You can use some kind of mathematical equations to generate a topology of nodes. i.e. their positioning. Look at ns2-directory/tcl/ex/wireless-flooding.tcl.

Generate an agent for each node and attach it with the node.

set agents(0) [new Agent/MyAgent]

$nodes(0) attach-agent $agents(0) $MESSAGE_PORT

Since all of our logical working of the protocol is done in Agents, we make a cpp class of MyAgent. Also add it in the Makefile.

class MyAgent : public Agent {

// override the recv() function.

// add the command function for this class which is called whenever this class's object is asked to do some work in tcl file.

// for storing the neighbor's address as i get from PING and PING_REPLY std::vector myNeighbors;

}

Then every agent broadcast PING message and reply with PING_REPLY message to the sender.

This can be done by sending address ns_addr_t with parameter addr_ = -1

 ns_addr_t naddr;
 naddr.addr_ = -1

These messages are different type of packets and are created again in cpp class like

enum Type {PING, PING_REPLY};

class HdrPing {

Type type;

// getter and setter functions and other variables like offset.

}

For writing our logic on receiving any message, which is exactly like how our distributed protocol is made, we override recv() of Agent

void MyAgent :: recv(Packet*p, Handle*h) {

switch(HdrPing::access(p)->type) {

    case PING:
    // send PING_REPLY back to sender and add the source of the packet p 
    // to my neighbor list. 

    // we can get it from ipHdr->saddr(), which is source address in the 
    // IP header of the packet.

    break;

    case PING_REPLY:
    // add the sender of messge to my neighbor list.
    break;

    // other types of messages are also programmed here.

} // close switch

}

In this way, i get to know who are my neighbors.

One can add more types of messages and more functionality.

What can be done in NS2 and what can not be?

1 Answers