Implement emulation of ndn-cxx `ndn::Face`
Updated by Junxiao Shi over 6 years ago
nfd::Face to a
ndn::util::DummyClientFace is easy.
Example: topology-tester TopologyAppLink
I'm attempting something similar in my experiments.
I feel the difficult part is:
ndn::Face is designed to be asynchronous and requires
io_service, but ns-3 doesn't run
io_service as its main loop.
One solution is to invoke
face.processEvents(time::milliseconds(-1)) after every operation (including but not limited to
expressInterest put setInterestFilter), which requires extensive changes in applications.
Another solution is to use a global
io_service, and schedule a periodical event in ns-3 to poll it; but the frequency of polling would be a trade-off between accuracy and wallclock performance.
Updated by Anil Jangam over 6 years ago
In attempt to understand this, I did some investigations. Below are my questions and findings:
In a real NLSR deployment, each host (router) running NLSR runs its NFD instance. Faces are managed by the application and network admin (nfdc command I mean).
- In ndnSIM setup, does every node has its simulated NFD instance or the entire simulator has just one for all nodes in the simulation setup? I presume ndnSIM contains just has one instance of simulated NFD.
Interest messages are dispatched to the application and to NFDs depending on the registered prefixes in the FIB by application and by the forwarder.
- We need an equivalent of the above in NFD in ndnSIM and IMO it need not be asynchronous in nature unlike in real NFD case, correct?
- As per an update in redmine task #2370, do we really need to monitor the activity on face in simulated NFD? Can't it just dispatch the Interest messages just looking at the registered prefix?
- This dispatched Interest event then eventually be handled in ndnSIM's event handler.
- I might be oversimplifying this. Please provide your comments.
In 2.0 version, when we are creating the links between the nodes, does it actually creates the faces on NFD?
In NLSR code, face management is done by util::FaceController. This is the class takes care of creating and destroying the faces.
- In ndnSIM NFD, IMO, there is an equivalent class called FaceManager. This internally uses the ProtocolFactory to createFace. However, I did not find any destroyFace API.
- Please comment if FaceManager is the class we need to enhance to support the handling of Interest messages in ndnSIM.
- Please comment on when NLSR application in ndnSIM registers any prefix, will it be handled by FaceManager and registered into the FIB of simulated NFD.
- As mentioned above, please comment if faces created by creating links between the nodes (based topology) are also handled by the FaceManager.
I am not sure how much time this ndnSIM face implementation would take. If there is a workaround to this, I can proceed with the further testing of nlsrsim.
Let me know your feedback.
Updated by Anil Jangam over 6 years ago
Did some further fact finding.. Here are my observations.
- In helper/ndn-stack-helper.cpp, I see that the NDN stack (L3Protocol) is installed on each NDN node.
- In the same helper class, I see that all the faces are added to the FaceContainer.
- In the same helper class, I see a FibManager, which belongs to the NFD package in the simulator. This is used to register the name prefix in the FIB and associate the face to handle the Interest/Data packet.
Is there any relationship between the faces in the FaceContainer and that of faces to be created on NFD? If I am correct, the FaceContainer contains the faces between the application and NFD. And the links between the nodes are the faces connecting the nodes.
Do we have to write a FaceManager (similar to the FibManager) for the management of the faces on the NFD. This will then replace the Link based logic connecting the nodes. Kindly please comment.
Updated by Spyros Mastorakis about 6 years ago
- Status changed from In Progress to Feedback
- % Done changed from 40 to 90
@Alex, it works now. I will push the updated code soon to the repo. Could you please take a look and let me know if you like the structure? Instead of deleting what I think we do not need in ndn-cxx Face, I have commented the lines out.