Architecture and algorithms used to emulate an unconstrained switch cd.

4. FINAL REMARKS

Recently, the number of ports and the demand for switch bandwidth increase exponentially, therefore optical switching technologies seem to become an attractive alternative to electronic switches. Efficient scheduling of these constrained switches required algorithms that minimize the switching overhead. The presented architecture and algorithms allow a constrained switch to exactly emulate an unconstrained switch within a fixed delay.

EXACT algorithm is successful when the system under consideration is insensitive on delay and storage requirements, but considers bandwidth as expensive. However, exact scheduling can lead to large delays, which can be unacceptable for many switching applications. For example, if we have 128-ports switch, which have δ=200 or 10s, then Tmin=δNS is approximately 3,2 million slot times or 160ms, which makes the minimum fixed delay 2T+H equal to 320ms – this is so much. This fixed delay appear in the EXACT algorithm is greatly reduced by MIN algorithm, but at the cost of increased speedup. For 128-ports switch, MIN reduces the minimum fixed delay to 2,5ms, but requires a minimum speedup of 4(4+log2N) which is equal to 44.

DOUBLE algorithm provides balance between these two algorithms. For our example (128-ports switch) DOUBLE provides minimum fixed delay of 5ms and minimum speedup of 2. The comparison of the costs for three considered scheduling algorithms is shown in Table 1.



These algorithms provide a range of speedup versus delay, making emulation executable over a large design area.

Autor: Dawid ZYDEK

REFERENCES

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