Computer Science Department
School of Computer Science, Carnegie Mellon University


Multi-Modal Network Protocols:
Adapting to Highly Variable Operating Conditions

Aditya Akella, Ashwin Bharambe, Suman Nath, Srinivasan Seshan

August 2002

Keywords: Congestion control. active queue management

Most network protocols are uni-modal: they employ a single set of algorithms that allows them to cope well only within a narrow range of operating conditions. This rigid design renders these protocols inefficient in the face of widely varying operating environments or in conditions different from the ones for which they are optimized. Such uni-modal protocols have great difficulty in the mobile computing world where the operating conditions, including number of nodes, computational capabilities and rate of mobility, are not fixed.

Consider, for example, routing in a network of ad-hoc nodes. Solutions like DSDV work well when the number of nodes is small. Unfortunately, such schemes scale poorly to larger population sizes. In such situations, more scalable algorithms that impose a structure on the network of ad-hoc nodes, in a manner similar to routing protocols in the Internet, provides better results. However, these scalable algorithms tend to incur high overheads in situations that DSDV handles well. Clearly, no single routing solution handles all situations that a node may encounter.

Motivated by such examples, this paper attempts to answer the following question: Is it possible to redesign the traditional protocols to take on very different operating modes when faced with different environments? We present a case for such multi-modal protocols in our paper. Specifically, we discuss multi-modal reliability and routing. We show the feasibility of designing multi-modal protocols by describing how these protocols can make operating mode decisions and switch modes without additional overhead.

18 pages

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