The first line of this expanded trace event (reference number 00) is the operation. We
have a + character, so this corresponds to an enqueue operation on the transmit queue. The
second line (reference 01) is the simulation time expressed in seconds. You may recall that
we asked the UdpEchoClientApplication to start sending packets at two seconds. Here
we see confirmation that this is, indeed, happening.
Thenextlineoftheexampletrace(reference02)telluswhichtracesourceoriginatedthis
event (expressed in the tracing namespace). You can think of the tracing namespace some-
what like you would a filesystem namespace. The root of the namespace is the NodeList.
This corresponds to a container managed in the ns-3 core code that contains all of the
nodes that are created in a script. Just as a filesystem may have directories under the root,
we may have node numbers in the NodeList. The string /NodeList/0 therefore refers to
the zeroth node in the NodeList which we typically think of as “node 0.” In each node there
is a list of devices that have been installed. This list appears next in the namespace. You
can see that this trace event comes from DeviceList/0 which is the zeroth device installed
in the node.
The next string, $ns3::PointToPointNetDevice tells you what kind of device is in the
zerothpositionofthedevicelistfornodezero. Recallthattheoperation+foundatreference
00 meant that an enqueue operation happened on the transmit queue of the device. This
is reflected in the final segments of the “trace path” which are TxQueue/Enqueue.
The remaining lines in the trace should be fairly intuitive. References 03-04 indicate
that the packet is encapulated in the point-to-point protocol. References 05-07 show that
the packet has an IP version four header and has originated from IP address 10.1.1.1 and is
destined for 10.1.1.2. References 08-09 show that this packet has a UDP header and, finally,
reference 10 shows that the payload is the expected 1024 bytes.
The next line in the trace file shows the same packet being dequeued from the transmit
queue on the same node.
The Third line in the trace file shows the packet being received by the net device on the
node with the echo server. I have reproduced that event below.
|
