should this be a trigger or a rule?

I have 3 tables: pings, curr_state, ping_log and here is what I want
to happen:
when I insert a row into pings it checks to see if the ping was
sucessful or not. Then it checks the current state of the interface
in curr_state table and if they match insert the row. If they do not
match then update curr_state and insert a row into ping_log.

I am not askng anybody to write it for me, I just want to know what is
the prefered PG method to do this. Here is my table defs:
drop table pings;

create table pings (
cm_mac macaddr,
ts timestamp,
ping1 int4,
ping2 int4
primary key (cm_mac, ts) );

drop table curr_state ;

create table curr_state (
cm_mac macaddr primary key,
last_change,
up boolean
);

drop table ping_log ;

create table ping_log (
cm_mac macaddr,
ts timestamp,
state boolean,
primary key (cm_mac, ts)
);

Thanks

marc