A difficulty with ATM signaling is the inextricable tie-up of basic connectivity and QoS management. Consequently, every flow suffers the overhead of end-to-end connection establishment, even best-effort flows. ATM signaling complexity is further exacerbated by having variable length messages sent on a single control channel, requiring a single point of resequencing. Variable length fields in arbitrary positions further slow down processing. This requires sequential hop-by-hop processing precluding the use of novel architectures for QoS management, for example connection admission control algorithms that exploit parallel processing.
We propose a new lightweight architecture for ATM signaling, UNITE. The fundamental philosophy of UNITE is the separation of connectivity from QoS control. This eliminates the round-trip connection setup delay, before initiating data transmission. Using a single cell with proper encoding, we avoid the overhead of reassembly and segmentation on the signaling channel, and enable hardware implementation. Performing QoS negotiation in-band, allows the switches in the path to process QoS-requests in parallel, facilitates connection specific control policies, supports both sender and receiver initiated QoS, and allows for uniform treatment of unicast and multicast connections. UNITE supports variegated multicast trees.
Current thinking of separating the function performed by the "switching" entity and the "controller" at the switch is exploited by UNITE. The functions of basic connectivity reside in the 'switch', while much of the more complex state associated with a connection are relegated to the controller. Using in-band signaling for the more complex functions also opens up considerable flexibility to include very connection-specific processing, that would have been difficult to incorporate in conventional signaling architectures.