Understanding RTCP, RSVP & RTSP (URRR)


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What is RTCP, RSVP & RTSP? Check out the full explanation below.

A. Real-time Control Protocol (RTCP)

  • Works on devices with RTP.
  • Each participant in an RTP session periodically sends RTCP control packets to the other participants.
  • The effect of backflow is used to control the appearance.
  • The sender can be modified in transmission based on the influence of the return current.
  • Each RTCP packet contains sender and receiver reports.
  • Statistics include the number of packets sent, the number lost, interarrival jitter, etc.

1. Main Function of RTCP

  1. Provide feedback on the quality of the information transmitted, so that modifications to that information are expected to result in better performance.
  2. Carries a persistent transport-level identifier for an RTP resource, better known as a canonical name (CNAME).
  3. To control the RTP packets sent by conference participants so that it can accommodate the addition of other participants in the real-time session.
  4. To convey control information to a session.

2. RTCP Header Format

Figure 5.22. RTCP Header
Figure 5.22. RTCP Header

3. RTCP Sections

The parts contained in the RTCP header format include:

  1. Version: serves as an RTP version identifier that is the same as the RTCP packet and RTP data packet. There are 2 types of versions specified for this purpose.
  2. P, when created, an RTCP packet consists of several additional padding octets at the end that do not include the control information.
  3. Reception report count: the number of reception report blocks contained in this package. Even though the value is zero it is still considered valid.
  4. Packet type: consists of a constant value of 200 to recognize that a packet is indeed an RTCP SR packet.
  5. Length: the length of an RTCP packet is 32 bits minus 1, including header and padding.

4. Relationship between RTP and RTCP

Figure 5.23. Header Format between RTP and RTCP
Figure 5.23. Header Format between RTP and RTCP

B. Resource Reservation Protocol (RSVP)

RSVP is a unicast and multicast signaling protocol designed to install and manage ordering information on each router along the data path. This protocol is used by the terminal to obtain certain QoS from its network so that it can be used by VoIP applications. In the TCP/IP layer, RSVP is on the transport layer. But this protocol is not used to send data but only as an internet control protocol.

Quality of Service is implemented by a collective mechanism called traffic control. This mechanism consists of several parts, namely: 

  1. Packet classifier, determines the classes of data packets.
  2. Packet scheduler, is a link, layer dependent mechanism.
  3. Admission control, determines whether the router has QoS as requested by the VoIP terminal.

Policy control, determines whether users using VoIP have the ability to place orders.

C. Real-time Streaming Protocol (RTSP)

  • Used by multimedia streaming programs to manage data in real-time, independent of the transport protocol.
  • Available methods: PLAY, SETUP, RECORD, PAUSE and TEARDOWN.
  • Used on Video on Demand.

1. RTSP Architecture 

a. Media file download

Figure 5.24. Media File Download
Figure 5.24. Media File Download

b. Meta files

Figure 5.25. Meta Files
Figure 5.25. Meta Files

c. RTSP

Figure 5.26. RTSP architecture
Figure 5.26. RTSP architecture

2. Multimedia Applications 

1. Audio 

  • Speech (CELP -- type codecs)
  • Music (MP3, WAV, WMA, Real)

2. Video (MPEG --1, 2, 4) 

3. Video conference 

4. QuickTime

Streaming is done using HTTP/TCP (MP3), or RTP/UDP (Video).

Figure 5.27. Multimedia Network
Figure 5.27. Multimedia Network

3. Multimedia Streaming

Streaming media is a technology that is capable of sending digital audio and video files in real time on a computer network;

Figure 5.28. Multimedia Streaming
Figure 5.28. Multimedia Streaming

Streaming vs Downloading;

a. Download 

  • (+) download and save files in HD so they can be enjoyed offline.
  • (+) can be viewed multiple times.
  • (+) standard file (can be read by all types of machines).
  • (+) good quality
  • (-) long download time.

b. Streaming

  • (+) can be done at low speed bandwidth
  • (+) Web masters don't need to worry about bandwidth
  • (+) Web masters are not limited by file size.
  • (-) Can only be viewed online
  • (-) Poor image quality.

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