UA (User Agent)

From NENA Knowledge Base

As defined for SIP in IETF RFC 3261, the UA (User Agent) represents an endpoint in the IP domain, a logical entity that can act as both a UAC (User Agent Client) that sends requests, and as UAS (User Agent Server) responding to requests.

Related Terms:

UAC (User Agent Client)

Refer to IETF RFC 3261 for the following definition. “A user agent client is a logical entity that creates a new request, and then uses the client transaction state machinery to send it. The role of UAC lasts only for the duration of that transaction. In other words, if a piece of software initiates a request, it acts as a UAC for the duration of that transaction. If it receives a request later, it assumes the role of a user agent server for the processing of that transaction."

UAS (User Agent Server)

Refer to IETF RFC 3261 for the following definition. “A user agent server is a logical entity that generates a response to a SIP request. The response accepts, rejects, or redirects the request. This role lasts only for the duration of that transaction. In other words, if a piece of software responds to a request, it acts as a UAS for the duration of that transaction. If it generates a request later, it assumes the role of a user agent client for the processing of that transaction."

Relevant NENA Documents


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

External References



RFC 3261, SIP: Session Initiation Protocol