Conclusion

The market for Voice/Video over IP is increasing dramatically. And both signaling systems H.323 and SIP can do the anticipated job. The H.323 design shows still the universal pretension of international standardization bodies. The encoding is most complex. SIP on the other side uses the Internet approach: The development is publicly discussed, and the resulting RFCs are available to everyone. The text encoded messages are similar to HTTP, making them easily understandable for developers.

Both H.232 and SIP are using RTP for media encoding. At least here we have just one undoubted standard.

Unsolved problems: