CS 294-7, Special Topics: Wireless Communications and Mobile Computing
Draft Project Ideas, Spring 1996
Evaluation Tools and Methodologies for Wireless Networks
There are few published studies of user mobility. This is due, in part,
because there are few operational mobile systems from which to collect data
and in part because those systems that do exist keep the data secret for
fear of revealing user identity (or competitive weaknesses).
It would be a major contribution to collect and analyze detailed traces
of user mobility. Since Soda Hall is not fully covered by wireless access,
this presents some real challenges! Here are some strategies that could
be pursued. First, you could ask a group of test subjects to log their locations
in a notebook for a few days or a week. Second, you could examine the security
tapes for Soda Hall to measure the distribution of people entering and leaving
the building (you should also examine the class schedules and the reservation
lists of rooms for informal meetings, qualifying exams, etc.). Third, you
could develop a laptop application with detailed "clickable" maps
of the floors of Soda Hall (these are already available on the Web), and
ask some subjects to carry it around for a day, using the application to
capture his/her location throughout the day.
Here are just some of the questions that could be asked about such traces.
How often do users reposition themselves? Are there a small number of standard
routes that a given user commonly follows through the building? What is
the density of users in the building, and how does it change as a function
of time or day of the week?
Wireless Network Benchmarking
We have wireless networking software that has the ability to collect packet
traces and measure physical network performance parameters like received
signal strength and bit error rates. We need to design benchmarks (for example,
a rate controlled UDP traffic generator) and to collect and analyze traces
from several different networks (in-building wireless LAN, Metricom packet
radio network, CDPD cellular data network, Hughes DBS satellite network,
etc.). It would be great to collect as large a library of (reproducable)
benchmark traces as possible.
Rajiv Bragrodia's research group at UCLA has developed an event-based simulator
called Maisie, and they have developed channel models for investigating
a variety of packet radio routing algorithms. We would like to extend this
simulator for one or more networks of interest, such as WaveLAN, Metricom,
CDPD, or Hughes DBS, validate it against the real network to the extent
possible, and use it to investigate new transport and routing algorithms.
The Mobile IP specification can be extended in a variety of directions,
any of which would make an interesting project:
Mobile IP was never designed to support routing in overlay networks. The
needed capability is for the HA to choose among alternative wireless networks
for providing connectivity to the Mobile Host. How should the Home Agent
be modified to allow it to select a given network interface (and IP address)
for a particular kind of network traffic? What kind of session or stream
abstraction is required? How is information exchanged between the Home Agent
and the Mobile Host to establish the policies by which a route is chosen?
A potential limitation in the current Mobile IP specification is that the
Home Agent needs to be informed about every change in location of the Mobile
Host. These could be high latency operations if the mobile is far from home.
One possible improvement is to introduce hierarchical routing authorities
(Foreign Agents) to which the HA forwards packets, which are then reforwarded
locally to FAs associated with individual microcells. Most location updates
are thus handled locally. The details of this scheme need to be worked out
and evaluated in depth (note that mobility traces would be of great value
in this evaluation).
Mobile Network Management
Cell Admission Control and Airlink Load Balancing
Our current implementation of Mobile IP does no admission control and makes
no attempt to do load balancing between cells or alternative networks. How
should the registration process be generalized to provide these capabilities?
How does it interface with the HA to assist in making routing decisions?
Mobile Security and Privacy
Our current implementation of Mobile IP does nothing to protect user identity
or provide end-to-end encryption. It would be worthwhile to design and implement
either a public key or a shared secret/challenge-response prototype system.
Note that we might be able to obtain some Tessera cards for use in this
Internet Firewalls and Mobility
Many organizations deploy Internet firewalls to restrict access to external
users of resources inside their corporate networks. Develop and evaluate
some schemes that could allow local users who are roaming in foreign networks
to access resources inside the firewall. In principle, the problem is the
same as that of users who need to dial-in to a corporate network from outside.
Such systems typically make use of secure terminal servers inside the firewall.
How might a local authentication agent be constructed to provide adequate
security for external access?
IP Spoofing and Mobility
Routers with IP Spoofing detection enabled cause many problems for the existing
Mobile IP specification. The source address of the packet is the MH's address
in its home network, but the router interpretes this as an attempt to spoof
the Internet by providing an incorrect IP address on purpose (the router
will refuse to pass the packet!). Propose and evaluate methods for circumventing
Wide Area Roaming Architecture
Mobility software has not as yet been widely available. Most research groups
working on Mobile IP have implementations that are only operational within
their own local administrative domains. What will it take to implement a
true wide area roaming architecture around the Mobile IP specification?
Most of the issues are related to resource allocation (local users should
be given priority access to network bandwidth, compute and printer resources,
etc.) and accounting (e.g., keeping track of resource usage in the visited
environment; this can form the basis of a credit system when mobiles from
the visited environment become visitors in turn).
Reliable Transport in Wireless Networks
One of the topics we will be covering this semester is how to improve reliable
transport performance over wireless links. This is crucial for supporting
the "killer application" of the 1990s, namely Web Browsing. A
number of schemes have been proposed, such as local retransmission of packets
("snooping"), split TCP transactions, fast retransmission timers
on the wireless link, etc. All of these strategies have been evaluated in
the context of wireless local area networks, which typically do not implement
reliable links through error corrections or link layer retransmissions.
How well will these mechanisms work with wide area networks, such as multi-hop
packet radio, satellite networks, or other wide-area wireless networks that
implement more reliable link technology? What other mechanisms, such as
adaptive retransmission timers or explicit identification of lost packets,
might also help to improve TCP performance over these other kinds of networks?
Direct Broadcast Satellite Technology
Design and Evaluation of Applications for DBS
Directed Broadcast Satellite technology is inherently asymmetric, i.e.,
the downlink bandwidth is much greater than the uplink bandwidth. There
is much interest in investigating applications that are a good match for
the asymmetric nature of the satellite link. For example, conventional database
systems pull data from the database system in response to queries. But the
satellite channel is better suited for pushing data over the satellite,
where end users tune and filter the data they are interested in. There are
aspects of the DBS system that would be interesting to investigate in more
detail, such as the way transmissions are encrypted for multicast groups
and the ways that users can join and depart from such groups (thus requiring
a change to the group's encryption key).
Some possible applications include subscription-based services (e.g., periodic
transmission of stock market ticker, weather and traffic reports, etc.)
or satellite distribution of the most popular 1000 (5000, 10000) World Wide
Web pages (it would be interesting to couple this with the Inktomi search
engine, which can keep statistics of which pages receive the most frequent
hits). A project like this would probably involve a simulation and an analysis.
The DBS system itself is probably too closed for actually implementing a
service like this.
There is little in the way of well known literature on the end-to-end performance
of TCP/IP networks over satellite constellations. It would be interesting
to investigate routing and reliable transport issues for low earth orbiting
satellites. This study would involve developing a simulation model of the
satellite channel and some other aspects of satellite constellations, and
then perform some analysis of network performance.
Randy H. Katz, randy@cs.Berkeley.edu, Last Updated: 29 December