Distributed Redundancy or Cluster Solution? An Experimental Evaluation of Two Approaches for Dependable Mobile Internet Services

Third generation mobile networks are offering the user access to Internet services. The Session Initiation Protocol (SIP) is being deployed for establishing, modifying, and terminating those multimedia sessions. Mobile operators put high requirements on their infrastructure, in particular – and in focus of this paper – on availability and reliability of call control. One approach to minimize the impact of server failures is to implement redundant servers and to replicate the state between them in a timely manner. In this paper, we study two concepts for such a fault-tolerant architecture in their application to the highly relevant use-case of SIP call control. The first approach is implemented as a distributed set of servers gathered in a so-called pool, with fail-over functionality assigned to the pool access protocols. The second is a cluster-based solution that normally implies that the servers are confined in a local network, but on the other hand the latter solution is completely transparent to clients accessing the service deployed in the cluster. To evaluate these two approaches, both were implemented in an experimental testbed mimicking SIP call control scenarios in 3rd generation mobile networks. An approach for measurement of various dependability and performance parameters in this experimental setting is developed and concluded with a set of preliminary results.