 
Summary: Distributed algorithms for Unidirectional networks
Yehuda Afek \Lambda Eli Gafni y
June 1, 1993
Abstract
We address the question of distributively computing over a strongly connected
unidirectional data communication network. In unidirectional networks the existence
of a communication link from one node to another does not imply the existence of a
link in the opposite direction. The strong connectivity means that from every node
there is a directed path to any other node. We assume an arbitrary topology network
in which the strong connectivity is the only restriction. Four models are considered:
Synchronous and asynchronous, and for each we consider node space availability which
grows as either O(1) bits or O(log n) bits per incident link, where n is the total number
of nodes in the network.
First we provide algorithms for two basic problems in distributed computing in
data communication networks, traversal, and election. Each of these basic protocols
produces two directed spanning trees rooted at a distinguished node in the network,
one called intree, leading to the root, and the other outtree, leading from the root.
Given these trees we efficiently transform bidirectional algorithms to run on unidirec
tional networks, and in particular solve other problems such as the broadcast and echo
[Cha79] in a way which is more efficient (O(n 2 ) messages) than direct transformation
