This should be a new chapter of a much shorter depth than the previous version. We may work a glossary-like version that explains common terms (20-30) and compares them in various solutions and points to the appropriate term native to each. Include references to outside material for a more detailed analysis.

General Terms

VoIP protocols

VoIP codecs

SIP Proxy

H.323 Gatekeeper

Gateway

SIP

Domain

Identity

TLS

Telephony Terms

E.164

Definition.
link for National prefixes

ENUM

Golden-tree and unofficial ENUM trees
Differences between infrastructure ENUM