CACHING OF STREAMING MULTIMEDIA ON THE INTERNET CS736 PROJECT REPORT Anurag Gupta Kiran Chitluri anurag kiran cs wisc edu Computer Sciences Department University of Wisconsin Madison Madison WI 53706 December 21 1998 ABSTRACT Real Time Streaming Multimedia is growing at an increasing rate on the Internet Caching the multimedia files as they are routed through company firewalls and proxies is the ideal way to incur big savings on Internet traffic and enable high speed delivery of media content to the end user Currently Inktomi Corporation has developed the only commercial implementation of a Streaming Multimedia Caching Proxy By studying the Real Time Streaming Protocol RTSP used for control of real time continuous media and the Real Time Protocol RTP used for media data delivery and using a Reference Implementation of a player and server supporting streaming media we have developed a free academic implementation of a Proxy capable of caching streaming media for the research community 2 1 INTRODUCTION Multimedia on the Internet is growing at a dramatic rate with the number of media URL s tripling over the last nine months Bandwidth improvements in the near future will only aid in making multimedia more popular on the Internet Today Streaming Media is the most popular way to transmit multimedia over the Internet because it allows the user to experience the media as it is being received instead of forcing the user to wait for the entire file to be downloaded before it can start playing it Since these media files change rarely they lend themselves well to caching By servicing requests for multimedia files from cached copies at Proxies organizations can save big on expensive Internet Traffic In addition high speed delivery of the media content is possible since the media files are being brought closer to the end user RealNetwork Inc is one of the largest companies that support streaming continuous multimedia Most Streaming Media Servers today are ones provided by RealSystems and over 85 of streaming media on the Internet are in Real formats 1 Streaming multimedia has only recently been publicly available In April 1995 Real Audio introduced Streaming Audio and shortly after in August 1995 Streamworks introduced Internet streaming video Currently Inktomi Corporation s Traffic Server is the only commercial implementation of a multimedia caching proxy We describe the protocol specifications for Streaming Multimedia essential in the design and implementation of an intermediate proxy capable of caching multimedia files We also discuss the implementation of our application level proxy designed to interact with a reference implementation of the Real Time Streaming Protocol RTSP client and server downloaded from the RealNetworks Web site This report is organized as follows In Section 2 we explain the protocols used for the transmission of streaming multimedia Section 3 discusses the different types of proxies In Section 4 we discuss the details of the reference implementation of the client and server and how they exchange control messages and data In Section 5 we describe the implementation of our application level proxy and our caching method We also discuss the changes we made to the reference implementation of the client Section 6 presents the results and in Section 7 we discuss possible future work 2 PROTOCOL STUDY A new set of protocols have recently been proposed to support the timely delivery of Real Time Streaming Multimedia The three major protocols that we studied include the Real Time Streaming Protocol RTSP Real Time Protocol RTP and Real Time Control Protocol RTCP RTSP is an application level multimedia presentation protocol for control over the delivery of data with real time properties RTSP provides an extensible framework to enable controlled on demand delivery of real time data such as audio and video using the Transmission Control Protocol TCP or the User Data Protocol UDP All known RTSP servers to date are TCP based though the specification has provisions for a UDP based version Real Time Transport Protocol RTP is a UDP packet format for multimedia data streams responsible for the actual data transmission RTP contains a set of conventions that provide end to end network transport functions suitable for applications streaming real time data such as audio or video over multicast or unicast network services RTSP and H 323 used for Internet Telephony use RTP for data transmission Real Time Control Protocol RTCP is a control protocol that is a part of RTP RTCP helps with lip synchronization QOS management and packet loss recovery RTCP packets are multicast periodically to the same multicast group as data packets 2 1 REAL TIME STREAMING PROTOCOL RTSP 3 The Real Time Streaming Protocol RTSP RFC 2326 is an Internet Engineering Task Force IETF Proposed Standard for the control of streaming media on the Internet It was jointly submitted to the IETF in October 1996 by RealNetworks and Netscape Communications Corp and was published as an IETF Proposed Standard in April 1998 RTSP is a control protocol that initiates and directs delivery of streaming multimedia from media servers RTSP does not deliver data though the RTSP connection may be used to tunnel RTP traffic for ease of use with firewalls and other network devices RTP and RTSP will likely be used together in many systems but either protocol can be used without the other A RTSP session is not dependent on a Transport Level connection such as a TCP connection During a RTSP session a client can open multiple reliable transport connections to the server or alternatively it may use a connectionless protocol such as UDP A common question asked is why not use HTTP for streaming media off web servers There are several reasons First of all HTTP uses TCP which enforces reliability instead of timeliness needed in a streaming multimedia TCP does not support multicast which is essential in large scale multimedia delivery over the Internet RTSP may interact with HTTP on the initial servicing of a client request off a web page but unlike HTTP RTSP Requests always contain the absolute URL In addition HTTP is not well suited for time based seeking of files for delivery Finally RTSP server needs to maintain state in almost all cases versus the stateless nature of HTTP RTSP introduces new methods in order for the server to maintain this state information RTSP is a text based protocol and uses the ISO 10646 character set in UTF 8 encoding RFC 2279