Another possible contention resolution strategy can be deflection routing, when the optical burst switching matrix is sent to the next output port of a predetermined core router.
The deflection routing is appropriate when there is no free output port in the core node, or there is no wavelength conversion or FDL possibilities.
As an effective way to reduce the burst loss is using several burst contention strategies in the same OBS core router, for example, it is suggested to use wavelength converters together with FDL in one core node  or wavelength converters with deflection routing .
If the FDL buffer is occupied with other bursts, the incoming burst is redirected into the deflection routing output.
Each state can be described by a probability [P.sub.abcd]: a is used to describe the wavelength Wi, b is used to describe the wavelength W2, c is used to describe the usage of FDL, d is used to describe the usage of deflection routing over [W.sub.ap] wavelength.
0000--wavelengths [w.sub.1] and [W.sub.2], FDL buffer and deflection routing [W.sub.ap] wavelength are not used;
The proposed model also allows evaluating the impact of deflection routing mechanism.
Instead of using the prevalent VC-based QoS mechanisms, QBLESS tags flits with priority bits and leverages this information in its deflection routing and congestion-control mechanisms.
To bridge the performance gap between the buffered and bufferless NoCs at high network load, one possible approach is to directly improve the efficiency of bufferless deflection routing. Previous work [6, 19-21] uses source-throttling or constraining applications' network request rates to reduce deflection-rates and improve overall system throughput.
In this work, we investigate both congestion control and deflection routing, finding that the latter is more effective in guaranteeing QoS in bufferless NoCs.