SIP styled call setup like HTTP and won VoIP signaling over H.323's complexity

In the 1990s two families competed to make phone calls work over IP. ITU-T's H.323 defined a complete, binary-encoded multimedia system built on ASN.1 and designed like a telecom standard; IETF's SIP came from internet-style thinking, first circulated as an Internet Draft in 1996 and standardized as RFC 2543 in 1999, then RFC 3261 in 2002.

The design choice that separated them was the message itself: SIP encodes calls as ASCII text, models an invitation as a request with URI-style addresses, and structures the dialogue like HTTP — INVITE, responses, ACK. That made the protocol readable by humans and compatible with the web's addressing and debugging culture.

Critics correctly noted that telephony is hard and that SIP's simplicity was partly surface-level. But simplicity won the adoption race: SIP rode the internet's toolbox, while H.323's complexity raised the bar for every implementer. Standardization groups chose SIP — 3GPP selected it for third-generation mobile networks, and PacketCable for cable telephony.

The lesson of the protocol war: a standard that lowers the cost of first implementation and fits the dominant ecosystem's habits gets deployed, tested and improved faster than a more complete rival. SIP became the default signaling protocol for VoIP, IMS and mobile telephony.