In this document, we describe the simulation environment which you will be using in projects 2 and 3 for this class. The simulator implements the basic components of an operating system kernel, as well as the socket, transport, link and physical layers. You will be responsible for adding the network layer to the kernel. The details of your project assignments can be found in the project handouts.
![\includegraphics[height=3.5in, keepaspectratio]{fig-simpict.eps}](img1.gif)
|
Figure 1 shows a picture of a sample simulated network. The kernel of each node in the network is a separate UNIX process. An application running on top of a node is a UNIX process separate from the kernel process. The fact that each node is implemented as a separate process enables you to simulate communications between nodes even though all the nodes are actually running on the same machine. Applications are implemented as separate processes so that they can be started after the simulation is already running (i.e. the kernel on each node is running) and so that more than one application can be run on the same node.
Each node has its own operating system kernel which you implement. Some nodes utilize all the layers of the network stack implemented in your kernel, and there are applications running on top of them (Nodes 2 and 3 in the figure). These nodes represent end-systems or communication endpoints. Other nodes, e.g. Node 1, only use the physical, link and network layers of the network stack. These nodes are routers. They are responsible only for forwarding packets, and since forwarding is a function provided by the network layer, they do not need to use the layers above the network layer. Endpoints on the other hand, do need to have all layers of the network stack since packets that are sent and received by the application layer need to undergo processing by all layers below the application layer.
In this handout, we will use $PDIR to denote the project directory.
The project directory for project 2 will be:
/afs/cs.cmu.edu/academic/class/15441-f01/projects/project2/
The project directory for project 3 will be:
/afs/cs.cmu.edu/academic/class/15441-f01/projects/project3/