Real-time Streaming Protocol (RTSP) Byungchul Park DPNM Lab., CSE, POSTECH Email: fates@postech.ac.kr 2008. 6. 3 1 1

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

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

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

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

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)

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

RTSP Message RFC 2616 - HTTP/1.1

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

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

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?

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

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)

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

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

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

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

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

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

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

No Charging Infrastructure (1/2) There are many commercial products that employ RTSP Real Player (www.real.com/player) Cisco Application Control Engine (ACE) (http://www.cisco.com/en/US/prod/collateral/modules/ps2706/ps6906/prod_bulletin0900aecd8045859e.html) Nokia5300 Unlimited TV On PC (www.thecomputertv.com) Application Streaming (www.thinstall.com) Free Premium TV for PC (www.PremiumTVforPC.com) PlayBox Technology (www.playbox.tv) Etc.

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

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.

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

Question? ?