Real time transfer protocol detailed ppt including all the terms and the types are briefly explained in the slide.

1. REAL-TIME TRANSFER CONTROL PROTOCOL
VISHWAJEET KUMAR
205320024
M.SC. COMPUTER SCIENCE

2. OBJECTIVE
To get to understand
about the RTCP
protocol flow diagram
It’s working properties Benefit of RTCP
Type of information
stream it works on
Where used?

3. OVERVIEW
Introduction
What is RTCP?
Working Scenario
Why RTCP?
Reports

4. Flow Diagram Of RTP/RTCP

5. INTRODUCTION
AS WE KNOW THAT IN RTP (REAL-TIME
TRANSFER PROTOCOL) WE CAN ONLY
SEND THE DATA FROM SOURCE TO THE
TERMINALS/USERS BUT CAN’T GET THE
DATA FROM THE USERS.
SO THIS DISADVANTAGE CAN BE
OVERCOME BY USING RTCP (REAL-TIME
TRANSFER CONTROL PROTOCOL) .

6. WHAT IS RTCP?
 The messages that can control the transmission
and quality of data (QoS) as well as also allow the
recipients so that they can send feedback to the
source or sources. A protocol designed for this
purpose, which is known as Real-time Transport
Control Protocol (RTCP).

7. HOW RTCP WORKS?
RTCP operates
alongside with the
RTP and share
information with it
but at same time
every RTCP has
different port
– User Datagram
Protocol) to work
independently
from the RTP
.
UDP – it’s just like
transport control
protocol but it
doesn’t provide
acknowledgement of
the sent packets.
RTCP doesn’t use well
known UDP port but
instead of that it uses
temporary port that
must be an odd-
numbered port that
follows port number
selected for RTP
.

8. HIERARCHY
DIAGRAM OF
PROTOCOL
STACK FOR
MULTIMEDIA
SERVICES

9.  RTCP is basically based on the periodic transmission of control packets to all participants
in the network being on the fourth layer i.e. transport layer), using the same distribution
process as the data packets.
 It is recommended that the fraction of network bandwidth allocated to the RTCP is not
more than 5% and at least 25% of bandwidth is for source reports.
 So, the primary function of RTCP is to provide feedback on the quality of the data
distribution.
 It specifies report PDUs exchanged between source and destination.

10. CONTINUE…
 PDU – Protocol data unit nothing but it gives an abstract
idea of the data packets, but it has lesser overhead than
 Although PDU for the transport layer protocol is called
segment
 The reports contain statistics such as the number of RTP-
PDUs sent, number of RTP-PDUs lost, inter arrival jitter.
 It is used by application to modify sender transmission rate
and diagnostics purposes.

11. SO RTCP IS VERY
USEFUL IN THE
REAL TIME
APPLICATIONS
LIKE VIDEO
CONFERENCING
WHERE WE
ALWAYS WANT
TO KNOW THE
STATUS OF THE
TERMINALS THAT
AS WE HAVE SEEN
IN THE DIAGRAM
THAT EVERY SENDER
WILL SEND RTP AS
WELL AS RTCP, BUT
EVERY TERMINAL OR
DESTINATION
SENDS THE
FEEDBACK
THROUGH RTCP.
MULTICAST
DISTRIBUTION IS
USED JUST LIKE
DATA PACKETS.

12. SYNCHRONIZATION OF STREAMS
 Timestamp doesn’t get tied up with the individual video or audio sampling clocks like RTP.
 Each sender report in the RTCP contains:-
 The timestamp of RTP PDU .
 The wall-clock time for when PDU was created.
 so receiver use this association to synchronize video and audio playout.
Internetwork
RTP audio
RTCP audio
RTP video
RTP video

13. WHY RTCP?
 What happens when there is one sender and many receivers?
RTP can’t do anything in this scenario as it focus on individual
video but RTCP can do this by creating reports linearly with the
number of participants and would match or exceed the amount of
RTP data, but more overhead than useful data.

14. SOLUTION
 RTCP attempts to limit its traffic to 5% of the session bandwidth
to ensure it can scale!
 RTCP gives 75% of this rate to the receivers; and the remaining
25% to the sender.

15. Suppose one sender, sending video at a rate of 2 Mbps. Then RTCP attempts to limit its traffic to 100
Kbps.
The 75 kbps is equally shared among receivers:
• With R receivers, each receiver gets to send RTCP traffic at 75/R kbps.
Sender gets to send RTCP traffic at 25 kbps.

16. Version: (2 bits) identifies the version of RTP
.
P (Padding): (1 bits) this is used to indicate if there is any extra padding bytes at the end of the RTP packet. It might be used to fill up a block of certain
size like for block required by an encryption algorithm .
RC ( Reception Report Count ): (5 bits) It is the number of reception report blocks contained in this packet.
PT (Packet Type): (8 bits) It contains a constant to identify RTCP packet type.
Length: ( 16 bits ) It indicates the length of this RTCP packet.
SSRC: (32 bits ) Synchronization source identifier uniquely identifies the source of stream.

17.  RTCP packets have a length field in header; aligned to 32
bits --- stackable
 Sent in a compound packet of at least 2 RTCP packets

18. Basically RTCP has five types of messages namely :-
• Sender Report
• Receiver’s Report
• Source Description Message
• Bye Message
• Application Specific Message

19. SENDER MESSAGE
Sender report is
sent after a fixed
interval by the
active sender in a
conference to
report transmission
as well as stats of
reception for all
RTP packets
transmitted during
this time period.
After receiving these
RTP messages, receiver
get some help in
synchronization process
and thus it is very
important in audio
video transmission or
for any smoother real
time experience.
It contains current time,
no. of packets sent, no.
of bytes sent, timestamp

20. SSRC (synchronization source) : identify sender
Sender info. block:
• NTP (Network transport protocol) timestamp sent time (wall clock time or roundtrip delay, etc.)
• RTP timestamp: corresponding to NTP but in formats of RTP data packet timestamp; used for intra & inter media
synchronization.
• Sender’s packet count & octet count
Multiple report blocks, each block has
• SSRC_n, fraction lost, number of lost
• Highest sequence number received
• Inter-arrival jitter, LSR (Last SR timestamp ), DLSR (Delay Since Last SR)

21. RECEIVER’S MESSAGE
Passive participants are those that don’t send any RTP packet and for them receiver
report is used to inform the sender and other receivers about the quality of service(QoS).
So basically, we get to know about fraction of packets lost, last sequence no., average
interarrival jitter

22. SOURCE DESCRIPTION MESSAGE
The Source Sends a source description message at every fixed interval to give some extra information
about itself containing details like name of source, its mail id, contact number or source controller.
It contains CNAME (canonical name) unique for every different terminal/user.

23. BYE MESSAGE
 When ever a stream is to be in completion or to shut down a
stream there should be a bye message and this last time shut
down message is bye report/message.
 It is sent by source to announcing for leaving the conference.
 This is direct announcement for other sources about absence of
other source.

24. APPLICATION
SPECIFIC
MESSAGE
Now if we want to make our application more
extensible then RTCP allows application-specific
RTCP packets which is introduced by RFC 3611.
This can be used to extend the type of application.

25. ROUND TRIP TIME CALCULATION
 SR packet contains: NTP (= t1)
 RR packet contains: Last SR timestamp (LSR = t1), Delay Since Last SR (DLSR=t3-t2)
 Roundtrip time = t4 - t3 + t2 - t1 = t4 – (t3-t2) –t1
= t4 – DLSR - LSR
sender
receiver
SR RR
DLSR
t1
t2 t3
t4

26.  So basically, RTCP is used to get more features of
multimedia and efficiently share the bandwidth for the
better accessibility.

27. SUMMARY
 We got to know about the flow of RTCP
how it act as a companion to RTP
 What RTCP means
 Features of RTCP
 Types of report it sends
 Application

28. THANKS
GUYS