SIP didn't start out complicated. If you go back to the origial internet drafts Henning and I wrote, it was really really simple. Well, our original UDP-based

SIP didn't start out complicated. If you go back to the origial internet drafts Henning and I wrote, it was really really simple. Well, our original UDP-based SIP was simpler than Henning's TCP-based SCIP, but neither was complicated. It gained a little complexity when we merged our protocols, but it really gained complexity along the way to standardization as people kept wanting to cover telco-like corner cases. At the start, Microsoft and Intel had backed H.323, and SIP was just us academics doing our own thing. Everyone told us we had no hope against Microsoft and Intel. But SIP started to get traction when the telcos (particularly Internet MCI) started to get interested in VoIP and concluded that SIP (especially SIP proxies) fitted what the wanted better than H.323. The downside with having your main allies being telcos was that telco-stop kept creeping in, until in the end SIP was no longer simple.