1. Real-time Streaming Protocol (RTSP)
Byungchul Park
DPNM Lab., CSE, POSTECH 1 1

2. Table of Contents Introduction RTSP Message RTSP Methods
Existing Problems of RTSP
MIB for RTSP
Summary

3. Introduction - Streaming
What is Streaming?
Streaming is the process of playing a file while it is still downloading
Streaming technology lets a user view and hear digitized content – video, sound and animation – as it is being downloaded
Streaming breaks the data into packets with size suitable for the transmission between server and clients
RTSP establish and controls streams

4. Introduction - RTSP
RTSP is an application level protocol for the control of real-time streaming data with syntax and operations similar to HTTP
IEFT standard  RFC 2326 (April, 1998)
RTSP uses RTP as the underlying data delivery protocol and offers a VCR-like control to the user:
PLAY, STOP, PAUSE, FF, REW
RTSP = Network remote controller

5. RTSP vs. RTP RTSP allows two-way communication RTP is one-way protocol
Viewers can communicate with the streaming server and do things like rewind the movie, go to a chapter, and so on
It does not typically deliver the continuous streams itself
RTP is one-way protocol
Send live or stored streams from the server to the client

6. RTSP vs. HTTP RTSP has similar syntax and operations with HTTP
Both an RTSP server and client can issue requests
An RTSP server needs to maintain state by default in almost all cases, as opposed to the stateless nature of HTTP
Data is carried out-of-band by a different protocol (RTP)
RTSP has various methods while HTTP has only two methods (GET, POST)

7. Message Types
RTSP is a text-based protocol and uses UTF-8 (Unicode octet) encoding
Messages can be either requests or responses
Request contain methods, the object the method is operating upon and parameters to further describe the method
After receiving and interpreting request, the recipient replies with a response message
RTSP messages are based on HTTP messages, with slight changes to allow for new status codes and different primitives

8. RTSP Message
RFC HTTP/1.1

9. RTSP Methods Method Direction Requirement Description DESCRIBE C->S
recommended
Get description of media object
ANNOUNCE
C->S, S->C
optional
Change description of media object
GET_PARAMETER
OPTION
required
Get available methods
PAUSE
Halt delivery, but keep state
PLAY
Start playback
RECORED
Start recording
REDIRECT
S->C
Redirect client to new server
SETUP
Establish transport
SET_PARAMETER
Device or encoding control
TEARDOWN
Remove state

10. Protocol State Machines
The RTSP client and server state machines describe the behavior of the protocol from RTSP session initialization through RTSP session termination

11. Problems of Current Protocol
NAT Traversal problem
The RTSP protocol says nothing about the problems of recovering state over machine or software failure
Quality problem
Insufficient functionalities
No billing infrastructure: pay-per-play?

12. NAT Problem (1/3) What is NAT (Network Address Translator)?
Translate private IP address to public IP address
Acts as a firewall
                                                                                                                
[출처] NAT란??|작성자 야쿨트

13. NAT Problem (2/3) What makes the problem? Server behind NAT
Client can not access the server
Client behind NAT
Client can access the server however server may not respond to client (RTP)

14. NAT Problem (3/3) Possible Solution?
MMUSIC WG working on ICE + RTSP
Skype Protocol
MMUSIC (Multiparty Multimedia Session Control)
ICE (Interactive Connection Establishment)
ICE is designed for RIP’s NAT traversal
Work on mapping ICE to RTSP
Skype Rendezvous-Relay Service
Skype works well on every NAT environment and firewall

15. Recovering State over Machine (1/2)
State Machine ??
PAUSE

16. Recovering State over Machine (2/2)
PAUSE
PLAY, PAUSE, RECORD
RECORD
PLAY

17. Quality Problem (1/2) In case of network congestion or packet loss
RTSP will cause part of the stream to be lost.
That's how RTP (the underlying conveyance protocol) behaves, as it uses UDP
RTP is the de facto standard protocol to carry real-time delay-sensitive payloads such voice over IP
With voice calls, people definitely prefer to loose some audio frames that have to wait a few seconds for the network to recover and retransmit
With video on demand, people may well prefer to wait a while for the audio/video buffers to refill

18. Quality Problem (2/2) It’s not RTSP’s problem. This problem caused by
Lack of QoS management mechanism (IPv4)
Underlying conveyance protocol is RTP (UDP)
What could be a solution?
IPv6?
There’s no certain solution for QoS problem

19. Insufficient Functionalities (1/2)
Suppose your VCR
Play a video
Pause
Stop FF
RWD
Record
RTSP
Play a video
Pause
TearDown (Stop)
Record

20. Insufficient Functionalities (2/2)
The authors are lacking experience with RECORD
Seem to need significant clarification on how to use it
Issues related to RECORD are:
How to use ANNOUNCE
How to signal “Disk Full” or “Quota Reached”
SETUP requirements to be able to RECORD
Appending, replacing
Creation of new files and there status
Recording and watching is not possible

21. No Charging Infrastructure (1/2)
There are many commercial products that employ RTSP
Real Player (
Cisco Application Control Engine (ACE) (
Nokia5300
Unlimited TV On PC (
Application Streaming (
Free Premium TV for PC (
PlayBox Technology (
Etc.

22. No Charging Infrastructure (2/2)
Contents providers or service providers may need charging infrastructure for their revenues in short time
Possible charging scheme
Pay-per-playing
Pay-per-duration
Pay-per-packet
Flat-rate
At least usage data should be kept for charging

23. MIB for RTSP There’s no MIB for RTSP MIB for RTSP should contain
Client’s IP address
# of Packets
# of Octets
Client’s Tool
Start time
End time
Playing time
# of lost packets
Accessed media
Disk space for recording
Etc.

24. Summary
RTSP provides an extensible framework to enable controlled, on-demand delivery of real-time data
This protocol is intended to control multiple data delivery sessions, provide a means for choosing delivery channels, and provide a means for choosing delivery mechanisms based upon RTP
There’s no security vulnerability
However, this protocol has some possible problems

25. Question? ?