agent
Click on the red underlined text to get to the source
... sessions between users. SIP end systems are called
user agents, and intermediate elements are known as proxy servers. A
...
... next hop element, called a server (it can be a proxy or a user
agent). Such processing could, in principle, occur at every hop
between elements.
...
... client usage. We assume that the client is stateful
(either a User Agent Client (UAC) or a stateful proxy). Stateless ...