Finding multi-constrained feasible paths by using depth-first search

An extended depth-first-search (EDFS) algorithm is proposed to solve the multi-constrained path (MCP) problem in Quality-of-Service (QoS) routing, which is NP-Complete when the number of independent routing constraints is more than one. EDFS solves the general k-constrained MCP problem with pseudo-polynomial time complexity O(m ² · EN + N ²), where m is the maximum number of non-dominated paths maintained for each destination, E and N are the number of links and nodes of a graph, respectively. This is achieved by deducing potential feasible paths from knowledge of previous explorations, without re-exploring finished nodes and their descendants in the process of the DFS search. One unique property of EDFS is that the tighter the constraints are, the better the performance it can achieve, w.r.t. both time complexity and routing success ratio. This is valuable to highly dynamic environment such as wireless ad hoc networks in which network topology and link state keep changing, and real-time or multimedia applications that have stringent service requirements. EDFS is an independent feasible path searching algorithm and decoupled from the underlying routing protocol, and as such can work together with either proactive or on-demand ad hoc routing protocols as long as they can provide sufficient network state information to each source node. Analysis and extensive simulation are conducted to study the performance of EDFS in finding feasible paths that satisfy multiple QoS constraints. The main results show that EDFS is insensitive to the number of constraints, and outperforms other popular MCP algorithms when the routing constraints are tight or moderate. The performance of EDFS is comparable with that of the other algorithms when the constraints are loose. This work was supported in part by the National Science Foundation under Grant CNS-0435522, by the UCOP CLC under grant SC-05-33 and by the Baskin Chair of Computer Engineering at University of California, Santa Cruz. Zhenjiang Li received the B.S. and M.S. degrees in electronic engineering from University of Science and Technology of China (USTC), Hefei, China, in 1998 and 2001, respectively. Since 2001, he has been a PhD student in the computer communication research group (CCRG) of the computer engineering department, University of California, Santa Cruz, U.S.A. His research interests include secure routing, constrained path selection, routing optimization and quality-of-service (QoS) provisioning in computer networks. He is a student member of the IEEE. J. J. Garcia-Luna-Aceves received the B.S. degree in electrical engineering from the Universidad Iberoamericana in Mexico City, Mexico in 1977, and the M.S. and Ph.D. degrees in electrical engineering from the University of Hawaii, Honolulu, HI, in 1980 and 1983, respectively. He holds the Jack Baskin Chair of Computer Engineering at the University of California, Santa Cruz (UCSC), and is a Principal Scientist at the Palo Alto Research Center (PARC). Prior to joining UCSC in 1993, he was a Center Director at SRI International (SRI) in Menlo Park, California. He has been a Visiting Professor at Sun Laboratories and a Principal of Protocol Design at Nokia. Dr. Garcia-Luna-Aceves has published a book, more than 300 papers, and nine U.S. patents. He has directed 22 Ph.D. theses and 19 M.S. theses since he joined UCSC in 1993. He has been the General Chair of the IEEE SECON 2005 Conference; Program Co-Chair of ACM MobiHoc 2002 and ACM Mobicom 2000; Chair of the ACM SIG Multimedia; General Chair of ACM Multimedia ’93 and ACM SIGCOMM ’88; and Program Chair of IEEE MULTIMEDIA ’92, ACM SIGCOMM ’87, and ACM SIGCOMM ’86. He has served in the IEEE Internet Technology Award Committee, the IEEE Richard W. Hamming Medal Committee, and the National Research Council Panel on Digitization and Communications Science of the Army Research Laboratory Technical Assessment Board. He has been on the editorial boards of the IEEE/ACM Transactions on Networking, the Multimedia Systems Journal, and the Journal of High Speed Networks. He received the SRI International Exceptional-Achievement Award in 1985 and 1989, and is a fellow of the IEEE.