Tracing receive packets with UDP

[Mike Geile <mgeile@nova-eng.com>]

I've just started using ns2. The first result I want to generate is to build
a single, simple UDP link and derive delay and data throughput based on the
trace-all output. I built a simple link with a UDP agent attached at the
source. I tried a null agent and a UDP agent at the receive end. 

I'm using a simple trace-all to examine the link events. The output shows
the enque events (+) and deque events (-). However, I'm not seeing any
receive events (r). 

When I tried a TCP example (from the docs) it does generate receive events.
This leads me to believe that the receive trace events are associated with
the agents and not the link. If this is true, the null or UDP sinks do not
generate receive events. 

Can anyone point me to a method to generate receive events for a simple UDP
link?