Methods for Designing SIP Services in SDL with Fewer Feature Interactions
Ken Y. CHAN and Gregor v. BOCHMANN
SITE, University of Ottawa
Ottawa, Ontario, Canada, K1N 6N5
Abstract. This paper describes methods for implementing telephony services
in SIP with fewer traditional feature interactions. A formal SDL model of
SIP and its services has been derived from published SIP specifications for
verification and validation. It is known that the SIP RFC describes only the
protocol specification. The specifications of SIP services and additional
service features are informal and can only be found in various IETF drafts.
Nevertheless, the service designers are still faced with new feature interaction
problems. These new feature interactions are unique to SIP because SIP has
flexible signaling features, such as request forking and dynamic assignment
of contact addresses, which have both cooperative and adversarial side effects
on each other. This paper also describes an extension to the classical feature
interaction taxonomy, which is used to associate the causes, effects/symptoms
with the preventive measures of the new and traditional feature interactions.
Finally, SIP services can be designed and implemented without certain feature
interactions by following certain design rules which are based on the knowledge
deduced from the verification.