Which of the following protocols is used by voice terminal to communicate with the VoIP server? Each correct answer represents a complete solution. Choose all that apply.

A.
SIP

B.
H.323

C.
MGCP

D.
RSTP

Explanation:
The voice terminal communicates with the VoIP server using H.323, SIP and MGCP protocols. H.323 is a group of protocols defined by the International Telecommunication Union for multimedia conferences over Local Area Networks. The H.323 collection of protocols collectively may use up to two TCP connections and four to six UDP connections. H.323 inspection is used for H.323 compliant applications such as Cisco CallManager and VocalTec Gatekeeper. H.323 application inspection does not support Network Address Translation between same-security-level interfaces.

Session Initiation Protocol (SIP), designed by Henning Schulzrinne and Mark Handley in 1996, is a

signaling protocol, widely used for setting up and tearing down multimedia communication sessions such as voice and video calls over the Internet (VoIP). Other feasible application examples include video conferencing, streaming multimedia distribution, instant messaging, presence information and online games. The protocol can be used for creating, modifying, and terminating two-party (unicast) or multiparty (multicast) sessions consisting of one or several media streams. The modification can involve changing addresses or ports, inviting more participants, adding or deleting media streams, etc. The SIP protocol is a TCP/IP-based Application Layer protocol. Within the OSl model, it is sometimes placed in the session layer. SIP is designed to be independent of the underlying transport layer; it can run on TCP, UDP, or SCTP. It is a text-based protocol, sharing many elements of the Hypertext Transfer Protocol (HTTP) upon which it is based, allowing for easy inspection by administrators. SIP clients typically use TCP or UDP (typically on port 5060 and/or 5061) to connect to SIP servers and other SIP endpoints.

MGCP stands for Media Gateway Control Protocol. The Media Gateway Control Protocol is architecture for controlling media gateways on Internet Protocol (IP) networks and the publicswitched telephone network (PSTN). It is a master/slave protocol used to control media gateways from external call control elements called media gateway controllers or call agents. A network element that provides conversion between the audio signals carried on telephone circuits and data packets carried over the Internet is called as media gateway. MGCP supports a large number of devices on an internal network with a limited set of external (global) addresses using NAT and PAT.

Answer option D is incorrect. Rapid Spanning Tree Protocol (RSTP) is an evolution of the Spanning Tree Protocol, which provides for faster spanning tree convergence after a topology change. RSTP is also known as the IEEE 802.iw. It provides a loop-free switching environment. Standard IEEE 802.1D-2004 incorporates RSTP and obsoletes STP. While STP can take 30 to 50 seconds to respond to a topology change, RSTP is typically able to respond to changes within 6 seconds.