From NENA Knowledge Base

Proxy is an entity in a call path that is an intermediary, and not an endpoint. Most message contents are copies (proxied) from one side of the proxy to the other, but the proxy may modify some elements, make a routing decision, or reject the call.

Relevant NENA Documents
Note: To find and download the document, copy the document number (like NENA-STA-010) from below and search the NENA Standards and Documents page.

NENA-STA-010, NENA i3 Standard for Next Generation 9-1-1