difference between these function calls in LAR

in LAR.cc file (LAR routing protocol) , could you please tell me the
difference between agent->function name() vs this->function name ()

As you can see below , they are calling the same function with this and
agent in LAR.cc

>
> void LARRouteRequestTimer::expire(Event *e)
> {
> ......
> .....
> agent->sendRouteRequest(this->dest, forwardMethod, this->routeInfo,
false); //ringZero=false
> .....
> ...
> }
>
>
> void LARAgent::routeRequest(Packet *p)
> {
> .....
> ....
> ...
> this->sendRouteRequest(dest, larhdr->forwardCode(), &(destPtr->second),
useRingZeroSearch);
> .....
> .....
> }

I have to do some changes in this file . kindly give some information on
this issue

rgds
sims