[Ns-developers] Multipoint net device and channel

[Emmanuelle Laprise]

I have created a  version of the ns-3-dev code that  has added the 
implementation of multipoint channels and devices.  Since my goal is to 
use this to simulate ethernet network, I have also created an 
infrastructure that does not use any of the ipv4 code. If you have any 
comments on the approach that I took, on the implementation or on 
anything else, let me know and I will use them to improve the code.

Files are located at: http://code.nsnam.org/laprisee/ns-3-mp

One of the goals was to decouple the net devices and applications from 
the protocols that use them. (Not that there was a lot of coupling 
before, but there was a little bit).

Files that were added:

examples/simple-mp
** Added an example that uses multipoint channels. Currently this 
example is in debug mode and will write a lot to the screen. Tracing has 
not been tested, and I don't think that it is working.

devices/mp/mp-channel
devices/mp/mp-net-device
devices/mp/mp-topology
** These files were added to support multipoint channels and multipoint 
net devices. In a multipoint channel, all packets that are written to a 
channel are received by all net devices connected to the channel. If the 
channel is busy, then the net device must wait before transmitting. In 
the current implementation, there are no collisions as a net device is 
not allowed to write to a busy channel and a channel stays busy until 
all net devices have received the packet. Propagation delays between all 
stations is also constant.

nd-node/nd-node
** This is a kind of dummy node that can be used as a packet source 
and/or sink when using multipoint channels. It does not require the use 
of ipv4. Another node that acts as an ethernet packet switch will also 
be created.

nd-node/ ethernet-header
nd-node/ ethernet-trailer
** These files were added to support the use of ethernet packets. 
Functions exist to add the FCS, but the FCS calculations have not yet 
been implemented.

nd-node/ agent
nd-node/ mac-agent
** Agents are used to convert between application data buffers and a 
protocol specific packet format. They are also the link between 
application and net devices. In the tx direction, the mac-agent can be 
configured to have a src and dest MAC address. With these, data buffers 
are converted into ethernet packets and sent to the net devices. In the 
rx direction, the mac-agent will drop all packets that are not addressed 
to it. It is also possible for the mac-agent to be configured to receive 
packets from a single source. Currently agents are connected to net 
devices such that they emit packets straight to the network, bypassing 
the node. In the future, it will be optional for them to send packets to 
the netdevices such that the netdevice forwards the packet to the node 
for further processing before being sent out into the network.

applications/onoff-simpleapp
** Based on the onoff-application, this application uses agents instead 
of sockets. This was done because sockets seem to need to connect two 
entities, whereas I wanted to treat the application as a straight packet 
generator that does not know or care where its packets are going. They 
can be going to any number of destinations. It is the agents that are 
linked together, if the protocol that they are implemented requires it.

devices/mp/backoff
** This class is needed to calculate backoff time when trying to 
retransmit on a busy multipoint channels


Files that were modified:

node/mac-address
** Added SetByte and GetByte functions that allow the user to set and 
get one byte of a MAC address at a time.

node/net-device
devices/p2p/p2p-net-device
** Added a dummy function to support the new virtual SendTo function in 
the NetDevice base class that does not require a destination address 
(function needs to be present because of mp support).

SConstruct
** Modified to compile the new files that were added.