COLLOQUIUM
             Computer Science Department, Boston University

Speaker: Professor Ahmed Helmy
         University of Southern California

Date:  Thursday, June 23
Time:  14:30
Place: Room MCS 135, 111 Cummington Street 
       (for directions, see www.cs.bu.edu/colloquium)

Title: Towards Building Robust Mobile Networks: 
Robust Geographic Routing and Mobility Modeling

Abstract:

In this talk I shall provide a birds-eye view of the research projects
and directions pursued by the wireless networking laboratory at USC
under my supervision. The talk will focus on two main topics: (A) robust
geographic services in wireless sensor and ad hoc networks, and (B)
mobility modeling and analysis.

(A) Geographic services refer to classes of protocols and applications
that use semantics of location to function. The talk outlines our
research in the areas of geographic routing, geocast and geographic
rendezvous, with emphasis on robust geographic routing. Geographic
routing provides efficient routing in ad hoc and sensor networks. Its
stateless nature and low overhead give it an edge over traditional ad
hoc routing. Correctness of geographic routing has been proven under
assumptions of accurate location information and ideal channel
characteristics. The first half of this talk focuses on issues of
sensitivity of geographic routing to inaccurate location information and
lossy link characteristics. Our study on geographic face routing shows
how correctness is violated with inaccuracy. A novel micro-level
algorithmic analysis of planarization algorithms reveals the bounds and
conditions of its correctness. Our study shows how performance can
degrade drastically with inaccuracy. Effective protocol modifications
are provided that achieves near-perfect performance even with large
localization errors. Then the 'weakest link' problem is introduced in
greedy geographic routing with lossy links. A channel model is developed
based on real traces from deployed sensor networks. The notion of 'black
listing' based on link quality is introduced, and the following
trade-off is articulated: If only highest quality links are used, this
leads to longer paths with larger number of hops and may lead to
disconnections. Whereas if no black listing is performed (as in
traditional greedy forwarding) very poor packet delivery is incurred.
The study investigates several distance-based and quality-based
black-listing strategies and introduces the energy-optimal metric for
geographic forwarding.

(B) In mobile networks, one of the main factors affecting protocol
performance is mobility. Relative movement of the nodes leads to link
breakage, triggering protocol mechanisms to react to topology dynamics,
and subsequently affecting throughput and overhead. To capture the
essence of such interaction between the mobility characteristics and the
protocol mechanistic building blocks, we propose the IMPORTANT mobility
framework. This framework defines three mobility dimensions, including
(i) spatial correlation, (ii) temporal correlation and (iii) geographic
restrictions. We use a rich set of parametrized mobility models,
including Freeway, Manhattan, Group mobility and Random Waypoint, to
span those dimensions. Several wireless routing protocols, including
DSR, AODV, DSDV, GPSR and GLS, are studied across the different mobility
models. The results clearly show the performance sensitivity of these
protocols to mobility. The talk attempts to answer the following: To
what degree does mobility affect performance? why and how does it affect
performance? The answers lie in the effects of mobility on link and path
characteristics (this is done through the study of PATHs), and the
interaction between mobility and the protocols mechanisms (through the
BRICS study). Future directions of this work involve trace-based
realistic mobility models on campus and for vehicular networks.

Biography:

Dr. Ahmed Helmy received his Ph.D. in Computer Science in '99 with Prof.
D Estrin from the University of Southern California (USC), M.S. in
Electrical Engineering ('95) from USC, MS Eng. Math '94 and B.S. in
Electronics and Communications Engineering in '92 from Cairo University,
Egypt.

Dr. Helmy is conducting research on design and analysis of mobile ad hoc
networks and wireless sensor networks, in addition to protocol testing
techniques. He currently has three active NSF projects (MARS, ACQUIRE
and STRESS). In 2002, Dr. Helmy received the National Science Foundation
(NSF) CAREER Award for his research on 'Resource Discovery, Query
Resolution, Rendezvous and Mobility Modeling in Large-Scale Wireless Ad
Hoc and Sensor Networks' (MARS). He received the USC Zumberge award
(2000) to pursue work on power-aware wireless routing protocols. He also
founded and is currently directing the Electrical Engineering laboratory
for wireless networking, as part of a grant he received from HP in 2000.
He is currently co-establishing a new wireless networking laboratory at
USC.

He has published over 70 peer-reviewed journal articles and conference
papers, 5 book chapters, and 3 IETF RFCs. His work has been funded by
several NSF awards, and grants from DARPA, NASA, Intel, Nortel, Pratt and
Whitney, and HP.

He has a best paper award from IEEE Int'l Conf on Management of
Multimedia Networks and Services (MMNS), Oct 02. He was nominated for the
Alfred P Sloan award and the Engineering Jr. faculty research award at
USC in 2004. He ranked 1st in the annual merit review for the EE dept of
USC for 2004, and had teaching honors (evaluations above 4.5/5) for all
12 courses he taught at USC since Spring 2000. He participated in
numerous NSF panels and IEEE/ACM conference committees. 

From '95 to '99 he was a key researcher in the NS-2 (VINT) project for
network simulation at USC/ISI and the PIM project for sparse mode
Multicast at USC.

His current research interests lie in the areas of mobility modeling and
analysis of mobile networks, protocol design for ad hoc and sensor
networks, systematic design and stress testing of networking protocols
and IP mobility.

Host: Ibrahim Matta