8 research outputs found
Network File Storage With Graceful Performance Degradation
A file storage scheme is proposed for networks containing heterogeneous clients. In the scheme, the
performance measured by file-retrieval delays degrades gracefully under increasingly serious faulty
circumstances. The scheme combines coding with storage for better performance. The problem
is NP-hard for general networks; and this paper focuses on tree networks with asymmetric edges
between adjacent nodes. A polynomial-time memory-allocation algorithm is presented, which
determines how much data to store on each node, with the objective of minimizing the total
amount of data stored in the network. Then a polynomial-time data-interleaving algorithm is used
to determine which data to store on each node for satisfying the quality-of-service requirements in
the scheme. By combining the memory-allocation algorithm with the data-interleaving algorithm,
an optimal solution to realize the file storage scheme in tree networks is established
Fundamental Limits of Caching
Caching is a technique to reduce peak traffic rates by prefetching popular
content into memories at the end users. Conventionally, these memories are used
to deliver requested content in part from a locally cached copy rather than
through the network. The gain offered by this approach, which we term local
caching gain, depends on the local cache size (i.e, the memory available at
each individual user). In this paper, we introduce and exploit a second,
global, caching gain not utilized by conventional caching schemes. This gain
depends on the aggregate global cache size (i.e., the cumulative memory
available at all users), even though there is no cooperation among the users.
To evaluate and isolate these two gains, we introduce an
information-theoretic formulation of the caching problem focusing on its basic
structure. For this setting, we propose a novel coded caching scheme that
exploits both local and global caching gains, leading to a multiplicative
improvement in the peak rate compared to previously known schemes. In
particular, the improvement can be on the order of the number of users in the
network. Moreover, we argue that the performance of the proposed scheme is
within a constant factor of the information-theoretic optimum for all values of
the problem parameters.Comment: To appear in IEEE Transactions on Information Theor
NASA RECON: Course Development, Administration, and Evaluation
The R and D activities addressing the development, administration, and evaluation of a set of transportable, college-level courses to educate science and engineering students in the effective use of automated scientific and technical information storage and retrieval systems, and, in particular, in the use of the NASA RECON system, are discussed. The long-range scope and objectives of these contracted activities are overviewed and the progress which has been made toward these objectives during FY 1983-1984 is highlighted. In addition, the results of a survey of 237 colleges and universities addressing course needs are presented