ITU-T Recommendation G.1040 defines a performance metric for typical data transactions, called the network contribution to transaction time (NCTT). Session initiation protocol (SIP) produces data transactions that resemble a typical call signalling flow between an originating and terminating station, and sometimes several other entities located within the service provider's network. Appendix I to ITU-T Recommendation G.1040 describes how NCTT can be adapted for use with SIP session flows to estimate the network contribution to session set-up time.