POSTECH DPNM Lab Realtime Streaming Protocol RTSP Byungchul

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

POSTECH DP&NM Lab Table of Contents • Introduction • RTSP Message • RTSP Methods • Existing Problems of RTSP • MIB for RTSP • Summary 2

POSTECH DP&NM Lab 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 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 3

POSTECH DP&NM Lab 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 4

POSTECH DP&NM Lab RTSP vs. RTP • RTSP allows two-way communication – 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 5

POSTECH DP&NM Lab 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) 6

POSTECH DP&NM Lab 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 7

POSTECH DP&NM Lab RTSP Message • RFC 2616 - HTTP/1. 1 8

POSTECH DP&NM Lab 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 C->S, S->C optional 　 OPTION C->S, S->C required Get available methods PAUSE C->S recommended Halt delivery, but keep state PLAY C->S required Start playback RECORED C->S optional Start recording REDIRECT S->C optional Redirect client to new server SETUP C->S required Establish transport SET_PARAMETER C->S, S->C optional Device or encoding control TEARDOWN C->S required Remove state 9

POSTECH DP&NM Lab Protocol State Machines • The RTSP client and server state machines describe the behavior of the protocol from RTSP session initialization through RTSP session termination 10

POSTECH DP&NM Lab 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? 11

POSTECH DP&NM Lab 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 12

POSTECH DP&NM Lab 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) 13

POSTECH DP&NM Lab 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 14

POSTECH DP&NM Lab Recovering State over Machine (1/2) • State Machine ? ? PAUSE 15

POSTECH DP&NM Lab Recovering State over Machine (2/2) PAUSE PLAY, PAUSE, RECORD PLAY 16

POSTECH DP&NM Lab 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 17

POSTECH DP&NM Lab Quality Problem (2/2) • It’s not RTSP’s problem. This problem caused by – Lack of Qo. S management mechanism (IPv 4) – Underlying conveyance protocol is RTP (UDP) • What could be a solution? – IPv 6? – There’s no certain solution for Qo. S problem 18

POSTECH DP&NM Lab Insufficient Functionalities (1/2) • Suppose your VCR – – – Play a video Pause Stop FF RWD Record • RTSP – – Play a video Pause Tear. Down (Stop) Record 19

POSTECH DP&NM Lab 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 20

POSTECH DP&NM Lab 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/ps 2706 /ps 6906/prod_bulletin 0900 aecd 8045859 e. html) – Nokia 5300 – Unlimited TV On PC (www. thecomputertv. com) – Application Streaming (www. thinstall. com) – Free Premium TV for PC (www. Premium. TVfor. PC. com) – Play. Box Technology (www. playbox. tv) – Etc. 21

POSTECH DP&NM Lab 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 22

POSTECH DP&NM Lab 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. 23

POSTECH DP&NM Lab 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 24

POSTECH DP&NM Lab Question? ? 25