Real Time Streaming
Protocol
Prasanti Adusumilli
Swathi Borra








TOPICS
Introduction
RTSP and Streaming
Role of RTSP
RTP and RTSP
Working of RTSP
RTSP Methods
Applications of RTSP
RTSP Vulnerabilities
Introduction
RTSP is an application-level protocol for the control
of real-time streaming data.
IEFT Standard
 RFC 2326
It uses RTP as the underlying data delivery protocol
and offers a VCR-like control to the user: Play, Stop,
Pause, FF and REW, as well as random access to any
part of the media clip.
(Introduction…contd)
 RTSP also helps the server to adjust the media bandwidth
to the network congestion in order to suit the available
capacity.
 Another important function of RTSP is its ability to choose
the optimum delivery channel to the client. For instance, if
UDP cannot be used (some corporate firewalls
will not pass UDP), the streaming server has to offer a
choice of delivery protocols – multicast UDP or TCP to
suit different clients.
RTSP and HTTP
 RTSP is similar to HTTP/1.1 in terms of
syntax and operation but differs in several
important aspects.
 With RTSP, both the client and the server can
issue requests during interaction, as opposed
to HTTP where the client always issues the
requests (for documents).
(RTSP and HTTP…contd)
 RTSP maintains a state by default which happens to
be very important in streaming media files.
 The HTTP protocol is a stateless protocol. This
simply means that HTTP is unable to retain a
memory of the identity of each client that connects to
a web site and therefore treats each request for a web
page as a unique and independent connection, with
no relationship whatsoever to the connections that
preceded it.
RTSP and Streaming
 RTSP is the central protocol of a streaming
framework.
 Streaming is the process of playing a file
while it is still downloading.
 The innovation of streaming
 No need to entirely store it locally
before playing
(…contd)
 Large audio and video files need not be
downloaded to your computer .
 Streaming media technology allows the
client to see or hear the content in just a few
seconds instead of waiting.
Streaming media will usually take the form of:
 pre-stored media Its already been recorded and
archived somewhere, when the user wants to
access it we serve it as a stream
 live broadcast media The content is streamed as its
produced (there may be a small editing / safety
delay, as with traditional broadcasting) straight to
the user
 live interactive media Such as videoconferencing each user might produce their own stream, and
there isn't control by one broadcaster
The transmission of the stream can be:
 one-to-one or point to point - in networking
terms, unicast. The stream travels directly
from the source (server) to the user (client).
 one-to-many or multicast. One stream will
be (literally) broadcast to many users.
Kinds of streaming audio or video
available
 Real Networks (with RealMedia, Real Video and
RealAudio)
 Microsoft (with Windows Media - audio and video)
 Apple (with QuickTime)
 Null soft Streaming Video (.nsv) and Shoutcast,
IceCast (GNU GPL/Open Source version of
Shoutcast), Live365 streaming audio
Protocols used in Streaming
Technology

Session Description Protocol (SDP)

Real Time Transport Protocol (RTP)

Real-time Control Protocol (RTCP)

Hypertext Transfer Protocol (HTTP)

Real Time Streaming Protocol (RTSP)
Role of RTSP
• Controlling and processing the interactive control
functions such as pause/resume, fast forward,
rewind is an important aspect of streaming and
RTSP takes up this major role.
• Delivery mechanisms are based solely on RTP.
• RTSP is designed to be on top of RTP to both
control and deliver real-time content.
• RTSP implementations will be able to take
advantage of RTP improvements such as
RTP header compression
• Here we need to know the differences
between RTP and RTSP to know that both
have their own specific functions in
streaming.
RTP and RTSP
 It’s important to distinguish between RTP
and Real-Time Streaming Protocol (RTSP),
another transfer protocol. RTSP is used
when viewers communicate with a unicast
server.
 RTSP allows two-way communication; that
is, viewers can communicate with the
streaming server and do things like rewind
the movie, go to a chapter, and so on.
 QuickTime automatically translates the
viewer interaction with the on-screen movie
controller into the proper RTSP requests.
 By contrast, RTP is a one-way protocol used
to send live or stored streams from the
server to the client.
Streaming from a streaming server to
a media player
Client
Iris
(1)
HTTP request/
response,
description file
Web
server
Web browser
Tower box
(2)
Description file
Internet
Media player
Streaming
server
(3)
Audio/video file
requested and
sent
Tower box
Working of RTSP
• FIGURE
RTSP Media Player-Server Sequence Chart
User
Interface
OpenURL
audio
RTSP
Player
Activate
RTP
RTSP
Server
SETUP
response1
PLAY
response2
PAUSE
response3
Quit
TEARDOWN
response10
Activate
RTP
Explanation – Working of RTSP
 Before a client can establish the streaming
session it some how has to get the session
description from the web server using the
HTTP protocol.
 According to the information in the session
description the client sends a RTSP SETUP
request to the streaming server.
Example of a RTSP Description File
<title>Twister/title>
<session>
<group language=en lipsync>
<switch>
<track type=audio
e=”PCMU/8000/1”
src= ”rtsp://audio.example.com/twister/
audio.en/lofi”>
<track type=audio
e=”DVI4/16000/2” pt=”90 DVI4/8000/1”
scr=”rtsp://audio.example.com/twister/
audio.en/hifi”>
</switch>
<track type=”video/jpeg”
scr=”rtsp://video.example.com/twister/video”>
</group>
</session>
Explanation of the Description File
The RTSP Content Markup Language document can be defined using
an XML DTD (Document Type Definition), and is HTML-like. Most
of it is self-explanatory. The ’group’ includes two audio tracks and a
video track, and the ’group’ tag includes the language parameter (en
=English) and a requirement that the sound shall be lip-synchronised
with the video. The ’swich’ tag indicates that we can swich between
two sound tracks. The coding schemes for the audio are given by the
parameters ’e’ and ’pt’. To locate resources, RTSP defines a variant of
URL, see ’src’. The parameter ’lofi’ indicates ’low fidelity’ sound. The
RTSP URL may include a port number.
(working of RTSP …contd)
• The server informs the client with an OK
(ack) response to indicate that the stream has
been prepared successfully.
• The client starts the streaming with a RTSP
PLAY request and ends the streaming session
with a RTSP TEARDOWN request.
RTSP Message Format
The RTSP message formats share a similar syntax to HTTP
The general syntax for an RTSP method is:
{method name} {URL} {protocol version}CRLF {parameters}
An example of an RTSP request follows:
DESCRIBE http://foo.com/bar.rm RTSP/1.0
CSeq: 312
Accept: application/sdp, application/mheg
This is a request for an RTSP server to send a description of
the media
content, http://foo.com/bar.rm, using either Session
Description Protocol
(SDP) or Multimedia and Hypermedia Experts Group (MHEG)
formats.
An RTSP message may also contain a body. The general
syntax for a method with a body is:
{method name} {URL} {protocol version}CRLF
{MIME header field}CRLF
...
{MIME header field}CRLF
CRLF
{optional body, depending on the presence of a "Contentlength"}
The following example contains a description of the
media referenced by the request URL,
rtsp://foo.bar.com/bar.rm, using the SDP format.
ANNOUNCE rtsp://foo.bar.com/bar.rm RTSP/1.0
CSeq: 312
Date: 9 Sep 1998 13:00:00 GMT
Session: 45991232
Content-Type: application/sdp
Content-Length: 332
v=0
o=efutz 1928384477 1928386879 IN IP4 127.15.32.2
s=A Short Story
i=A short narrative depicting the early days of the Internet
u=http://www.yo.com/efutz/sdp.04.ps
e=efutz@yo.com (Elmer Futz)
c=IN IP4 225.2.14.10/127
t=3928384899 3928493389
a=recvonly
m=audio 8756 RTP/AVP 0
m=video 3487 RTP/AVP 31
Each RTSP request is followed by a response message.
Syntax: {protocol version} {status code} {reasonphrase}CRLF
{parameters}
A typical response message may look like the following:
RTSP/1.0 200 OK
CSeq: 312
Streaming in Mobile Environments
RTSP Methods
Method
DESCRIBE
ANNOUNCE
GET_PARAMETER
OPTIONS
PAUSE
PLAY
RECORD
REDIRECT
SETUP
SET_ PARAMETER
TEARDOWN
Description
Retrieves the description of a presentation
Posts the description of a presentation
Retrieves the value of a parameter
Queries the available methods
Streams delivery is halted temporarily
Starts sending data
Starts receiving data
Informs to connect another server location
Specifies the transport mechanism
Requests to set the value of a parameter
Stops the stream delivery and frees the
resources
RTSP Applications
• Streaming of multi-media via Internet
• Video conferencing & lectures.
• Broadcasting of entertainment.
• Remote digital editing
• Voice mail
RTSP Vulnerabilities
 Vulnerability VU#329561
Real Networks Helix Universal server Vulnerable to buffer
overflow when supplied an overly long string within the
"Transport" field of a SETUP RTSP request.
Impact
A remote attacker may be able to execute arbitrary code on
the vulnerable system. This attacker-supplied code would
be run with the privileges of the user running the Helix
Server.
 Vulnerability Note VU#934932
Real Networks media server RTSP protocol parser buffer
overflow.
Impact
A remote attacker can either execute arbitrary code with
privileges of the running service or cause it to crash.
 Vulnerability Note VU#485057
Real Networks Helix Universal Server vulnerable to buffer
overflow when supplied an overly long string for the
"Describe" field
Impact
A remote attacker may be able to execute arbitrary code on
the vulnerable system. This attacker-supplied code would be
run with the privileges of the user running the Helix Server.
 Vulnerability Note VU#460350
Apple QuickTime/Darwin Streaming Server fails to
properly parse DESCRIBE requests.
Impact
An unauthenticated, remote attacker could prevent
legitimate users from accessing the streamed content.
Solution to the Vulnerabilities
Here all the problems can be resolved by applying
a patch from the vendor.
References
 www.ietf.org
 http://www.kb.cert.org/vuls
 http://www.cswl.com/whiteppr/tech/StreamingTechnology.html
 http://www.javvin.com/protocolRTSP.html
 http://www.cisco.com/univercd/cc/td/doc/product/software/ios12
0/120newft/120t/120t7/fw_rtsp.htm
Questions
#1. What is the transport protocol being used by RTSP?
Ans. An RTSP client may use reliable transport connection
such as TCP or alternatively use UDP.(So could be on
top of UDP/IP or TCP/IP)
#2. Where is RTSP used?
Ans. It is used by streaming media players ,to control the
media streams.
#3. What is main difference between RTSP and HTTP?
Ans. HTTP is a stateless protocol ,where as RTSP
maintains the state through out.
THANK YOU