SSCA RTP & Media Transport 1 — Questions and Answers
Question 1: What does RTP stand for?
- Real-Time Protocol
- Real-Time Transport Protocol (Correct answer)
- Reliable Transfer Protocol
- Remote Transmission Protocol
Correct answer: Real-Time Transport Protocol
RTP stands for Real-Time Transport Protocol, defined in RFC 3550, and is used to deliver audio and video over IP networks.
Question 2: Which transport layer protocol does RTP primarily use?
- TCP
- SCTP
- UDP (Correct answer)
- TLS
Correct answer: UDP
RTP uses UDP because its low overhead and tolerance for occasional packet loss suits real-time media better than TCP's reliable, ordered delivery.
Question 3: Which RFC defines the RTP protocol?
- RFC 2327
- RFC 3261
- RFC 4566
- RFC 3550 (Correct answer)
Correct answer: RFC 3550
RFC 3550 defines RTP and its companion RTCP protocol, obsoleting the earlier RFC 1889.
Question 4: What is the purpose of the SSRC field in an RTP header?
- It specifies the payload type of the media stream
- It uniquely identifies the synchronization source of the stream (Correct answer)
- It carries the sequence number for ordering packets
- It provides the wall-clock timestamp for the session
Correct answer: It uniquely identifies the synchronization source of the stream
SSRC (Synchronization Source) is a randomly chosen 32-bit value that uniquely identifies a single RTP stream source within a session.
Question 5: What does the sequence number field in an RTP packet enable?
- Identifying which codec is being used
- Calculating the sampling rate of the media
- Detecting packet loss and reordering out-of-order packets (Correct answer)
- Authenticating the source of the RTP stream
Correct answer: Detecting packet loss and reordering out-of-order packets
The sequence number increments by one for each RTP packet sent, allowing receivers to detect missing packets and resequence packets that arrive out of order.
Question 6: What is the typical UDP port range used for RTP media streams in VoIP systems?
- 1024-4999
- 5000-10000
- 16384-32767 (Correct answer)
- 49152-65535
Correct answer: 16384-32767
RTP commonly uses even-numbered UDP ports in the range 16384-32767, with the adjacent odd port reserved for RTCP.
Question 7: What field in the RTP header provides timing information for correct media playback?
- Sequence number
- SSRC
- Payload type
- Timestamp (Correct answer)
Correct answer: Timestamp
The RTP timestamp reflects the sampling instant of the first byte in the packet, enabling the receiver to play back media at the correct rate and synchronize multiple streams.
