An Overview of the Reliable Server Pooling Architecture

The convergence of classical PSTN and IP networks requires the transport of SS7 signalling over IP. Since SS7 has very strict availability requirements to the signalling components, redundancy is mandatory. The goal of the IETF RSerPool working group is to define a lightweight, flexible and realtime redundancy concept to fulfil the availability requirements of SS7: reliable server pooling (RSerPool). RSerPool is currently under standardization, its functionality and improvement are subject of our research. Our poster presents our RSerPool proof-of-concept implementation and a research oriented, discrete event based simulation model. We provide simulation results showing limitations of the server selection procedures defined in the standards and a way to solve them. These improvements are now going into standardization by the IETF. Furthermore, we present some of our results on efficient algorithms and data structures for pool management. The poster concludes with an outlook on our currently progressing evaluations of service reliablity in failure scenarios. 1 What is Reliable Server Pooling The convergence of classical circuit-switched networks (i.e. PSTN/ISDN) and data networks (i.e. IP-based) is rapidly progressing. This implies that PSTN signalling via the SS7 protocol is transported over IP networks. Since SS7 signalling networks offer a very high degree of availability (e.g. at most 10 minutes downtime per year for any signalling relation between two signalling endpoints; for more information see [5]), all links and components of the network devices must be redundant. When transporting signalling over IP networks, such redundancy concepts also have to be applied to achieve the required availability. Link redundancy in IP networks is supported using the Stream Control Transmission Protocol (SCTP); redundancy of network device components is supported by the SGP/ASP (signalling gateway process/application server process) concept. However, this concept has some limitations: no support of dynamic addition and removal of components, limited ways of server selection, no specific failover procedures and inconsistent application to different SS7 adaptation layers. To cope with the challenge of creating a unified, lightweight, realtime and flexible redundancy solution, the IETF Reliable Server Pooling Charter has been founded. An overview of their concept Reliable Server Pooling (RSerPool), which is currently in the standardization process and described by several Internet Drafts, is shown in figure 1. Redundant servers providing the same service belong to a so called server pool, identified by a unique ID called pool handle within the set of all server pools, the so called namespace. A server in a pool is called pool element (PE) of its pool. The namespace is managed by redundant name servers (NSs), they synchronize their view of the namespace using the Endpoint Name Resolution Protocol (ENRP). NSs announce themselves using broadcast/multicast, i.e. it is not necessary to configure any NS address to other components described in the following. Pool User Po ol E le m en t P E 2 Pool Element PE1 ASAP Protocol ENRP Protocol Application Protocol