Planning aspects of ATM networks using the PNNI routing protocol

The Private Network Node Interface (PNNI), standardized by the ATM Forum(see [1]), provides a flexible and scaleable routing architecture for ATM networks comprising a dynamic routing and a signaling protocol. PNNI is based on a subset of UNI 4.0 signaling and includes mechanisms for autonomous exchange of aggregated topology information to form a hierarchical representation of the network. To obtain more experiences about PNNI, we developed a PNNI Emulator. Our versatile tool consists of an emulated ATM network and PNNI routing and signaling software. First results focusing on some principal aspects of the protocol performance in single peer group networks have been presented in [2]. However, there is clearly a need to support the planning process associated with the introduction of real PNNI networks. In particular, network planning in the context of PNNI bears several crucial points which have to be carefully considered. One of them is the processing load for topology information packets, which may be critical for ATM switching systems in large peer groups, unbalanced networks or in failure scenarios. This paper will present the results of our measurements on specific topologies. Another important aspect is the optimum interaction between classical network planning and dimensioning of decisive PNNI control parameters. Therefore, a sample network was dimensioned according to objectives like low call blocking and high throughput, using the network planning tool LINDA developed at the Institute of Communication Networks (see [3]). Results show that PNNI routing has to be tuned to conform with objectives of the planning process.