In SIP, an intermediary entity that acts as both a server and a client for the purpose of making requests on behalf of other clients. A proxy server primarily plays the
role of routing, which means its job is to ensure that a request is sent to another entity “closer” to the targeted user. Proxies are also useful for enforcing policy
(for example, making sure a user is allowed to make a call). A proxy interprets, and, if necessary, rewrites specific parts of a request message before forwarding it.
While a proxy can set up calls between SIP endpoints, it does not participate in the call once it is set up.

RAS
Registration, Admission and Status

A protocol used between H.323 endpoints and a gatekeeper to register and place calls.

Registrar

In SIP, a server that accepts REGISTER requests and places the information it receives in those requests into the location service for the domain it handles. This
information is used to advise other SIP Proxies/Registrars where to send calls for that endpoint.

Regex
Regular Expression

A pattern used to match text strings according to a POSIX-defined syntax.

RFC
Request for Comments

A process and result used by the IETF for Internet standards.

RS-232

A commonly used standard for computer serial ports.

RTCP
RTP Control Protocol

A control protocol for RTP. Defined by

RFC 3550 [17]

RTP
Real-time Transport Protocol

Real time protocol designed for the transmission of voice and video. Defined by

RFC 3550 [17]

SSH
Secure Shell

An encrypted protocol used to provide a secure CLI.

SIP
Session Initiation Protocol

IETF protocol for controlling multimedia communication. Defined by

RFC 3261 [20]

SNMP
Simple Network Management Protocol

A protocol used to monitor network devices.

Source Alias

The alias present in the “source” field of a message.

SRV record
Service record

A type of DNS record.

STUN
Simple Traversal of UDP through NATs

Firewall NAT traversal for SIP. Defined by

RFC 3489 [21]

Subzone

A segment of a VCS zone.