Cross-Layer Framework for the ns-2 Simulator
Cross-layer control loops provide translucent boundaries in the protocol stack and permit protocol optimisations not possible with traditional opaque boundaries. Knobs influence behaviour of a lower layer from above; dials instrument characteristics to a layer above. Cross-layer controls can either be in-band or out-of-band. In-band cross-layer controls consist of header fields that are accessible to multiple layers. For example, in-band controls between the end-to-end layer and hop-by-hop layer are not added/stripped during encapsulasion/decapsulaiton. Out-of-band controls consist of explicit signalling messages to convey knobs and dials. Vertical controls relate to (de)multiplexing and en/decapsulation. Horizontal controls relate to error and transmission (rate/flow/congestion) control.
To enable an investigation of the costs and benefits of cross-layering, we are modifying the ns-2 simulation to add these capabilities and allow integration with existing and new ns-2 protocol models.
Implementation in ns-2
Implementation of cross-layering capabilities requires significant modifications to the ns-2 source code.
A cross-layer manager is responsible for implementing inter-layer control and signalling. Header insertion and extraction modules are responsible for setting knobs and reading dials, respectively. Modifications have been made so that ns-2 actually transfers header fields for this purposes.
New signalling agents are responsible for generating or repeating knob signalling messages as well as receiving and decoding dial signalling messages.
Knob and dial matrices are new data structures that store the knobs and dials for each node in the simulation.
Adaptation modules are responsible for implementing cross-layer optimisation mechanisms, such as adjusting protocol data unit size and FEC strength and generating explicit congestion, loss, or delay (ECN, ELN, EDN) messages.
Related Projects and Links
NS-MIRACLE: Multi-InteRfAce Cross-Layer Extension library for the Network Simulator
Presentations and Publications
Sarvesh Varatharajan, Abdul Jabbar, Asifuddin Mohammad, Ramya Naidu, Justin P. Rohrer, Piyush Upadhyay and James P.G. Sterbenz,
Cross-Layer Framework for the ns-2 Simulator,
ITTC IAB poster, The University of Kansas, June 2008.
Justin P. Rohrer*
James P.G. Sterbenz* (PI)
*The University of Kansas