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Abstracts
of Selected Ph.D. Theses in the Area of Mobile Computing
Awarded in 1994
Protocols and Caching Strategies in Support of
Internetwork Mobility
Mitchell Paul Tasman
University of Wisconsin - Madison, USA
1994
The full dissertation
is available here
This thesis explores the provision of End System (ES)
mobility on large, datagram-based, internetworks.
We describe a new type of network layer address,
the hybrid address, which contains a Partial Destination
Identifier, a Unique ID, and a Location Sequence number.
The Partial Destination Identifier, which changes as
a mobile ES re-locates between areas of an internetwork,
allows for efficient routing, while the Unique ID is
used for ES identification at the lowest layers of a
routing hierarchy. Finally, the Location Sequence Number,
which a mobile ES increments as it relocates between
areas, is used to compare the age of multiple addresses
for a given mobile ES.
We present a mobility design that incorporates
the hybrid address, and is based on the ISO OSI connectionless
routing architecture and protocols. Each mobile ES has
a home address and a current address. The home address
is stored in a global database, and the ES's home area
keeps track of the current address. After a mobile ES
relocates to a new area, it sends Reconnect messages
to the home and previous areas, each of which caches
a forwarding pointer for the mobile ES. ESs that communicate
with a mobile ES send datagrams directly to the mobile
ES. To accomplish this, each ES maintains cache entries
for its mobile correspondents. When a datagram containing
an out-of-date address is forwarded by an area, a Rewrite
message is sent to the source ES, which updates its
cache entry for the destination. An ES also updates
its cache based on the source addresses of incoming
datagrams.
The mobility algorithm has been implemented and
tested in a simulation environment, and performs quite
well. We also present the results of a study on strategies
for caching mobile ES forwarding pointers at Intermediate
Systems in the interior of an internetwork, based on
the type and contents of transit control messages. Caching
at interior Intermediate Systems based on Reconnect
messages yields the greatest benefit, for both tree-shaped
and general topology internetworks, while caching based
on transit Rewrite messages is not recommended.
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