VoIP Protocols Using SDP for Streaming Media Sessions | Exam 400-051 Answer

VoIP Protocols Using SDP

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Which two VoIP protocols use SDP to describe streaming media sessions? (Choose two.)



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The Session Description Protocol (SDP), defined in RFC 2327, describes the content of sessions, including telephony, Internet radio, and multimedia applications.

SDP includes information about [8]: Media streams: A session can include multiple streams of differing content.

SDP currently defines audio, video, data, control, and application as stream types, similar to the MIME types used for Internet mail.

Addresses: SDP indicates the destination addresses, which may be a multicast address, for a media stream.

Ports: For each stream, the UDP port numbers for sending and receiving are specified.

Payload types: For each media stream type in use (for example, telephony), the payload type indicates the media formats that can be used during the session.

Start and stop times: These apply to broadcast sessions, for example, a television or radio program.

The start, stop, and repeat times of the session are indicated.

Originator: For broadcast sessions, the originator is specified, with contact information.

This may be useful if a receiver encounters technical difficulties.

The two VoIP protocols that use SDP (Session Description Protocol) to describe streaming media sessions are SIP (Session Initiation Protocol) and H.323.

SIP is a signaling protocol used for establishing, modifying, and terminating real-time sessions that involve video, voice, messaging, and other communications applications and services between two or more endpoints on IP networks. SIP uses SDP to negotiate and exchange information about media streams between the endpoints. SDP provides information about the codecs, media formats, transport protocols, and other session parameters necessary for establishing the media sessions.

H.323 is a set of ITU-T protocols for multimedia communications over IP networks that includes signaling, control, and media protocols. H.323 also uses SDP to describe the media streams in the same way as SIP. However, H.323 supports additional protocols and standards that are not part of SIP, such as H.245 for call control, and H.450 for supplementary services.

SCCP (Skinny Client Control Protocol) and MGCP (Media Gateway Control Protocol) are VoIP protocols that do not use SDP for session description, but rather rely on a centralized call control architecture where the media gateway acts as a slave to a call control agent, such as a SIP proxy server or an H.323 gatekeeper.

RAS (Registration, Admission, and Status) is a supplementary protocol used by H.323 gatekeepers to manage and control the access to H.323 endpoints and resources, but it does not use SDP.

cRTP (Compressed Real-time Transport Protocol) is a transport protocol used for compressing the IP/UDP/RTP headers of real-time media streams to reduce their overhead on low-bandwidth links, but it is not a signaling protocol and does not use SDP.