Signaling Transport Options in GMPLS Networks: In-band or Out-of-band

Signaling protocols for GMPLS networks have been standardized and implemented in switch controllers. Most switch vendors allow for signaling messages to be carried over in-band signaling channels as well as through out-of-band networks. In this paper, we compare these two signaling transport options. In carrying out this analysis, we allow for both software-implemented signaling protocol processors, as is common in most off-the-shelf switches today, as well as hardware-accelerated signaling protocol engines. Our motivating application is file transfers, which have high call arrival rates and low call holding times. The resulting high signaling message load makes the question of which signaling transport solution to use important. Network delays are lower in the in-band option given that there are no IP routers on these paths, but the per-channel transmitter rates are lower for in-band channels. To study this tradeoff, we set up queueing models and obtained delay estimates. Our analysis shows that with hardware-accelerated signaling engines, in-band signaling is the better option to keep end-to-end call setup delays low. With software signaling protocol processors, the most significant component is the message processing delay, which is likely to include queueing delays, making the question of in-band or out-of-band transport less important.