DESIGN like alphabet soup, take comfort in the fact that you are not alone. Throughout FORUM this discussion, we’ll identify the various technical performance and compatibility issues an AV professional should consider when developing a streaming system. What Is a Streaming Protocol? A streaming protocol is a transmission protocol used to deliver encoded video and audio data across networks from hardware encoders or media servers to hardware decoders or client software players operating on PCs, tablets, or smartphones. A variety of streaming protocols have been developed to provide the speed, accuracy, and compatibility that ensures moving pictures and audio will fulfill various platform or application requirements. Streaming Protocols Work Together with Network Transport Protocols Streaming protocols rely on one of two network transport protocols to Understanding Streaming deliver audio and video data. Either the Transport Protocols Transmission Control Protocol – TCP or There’s more to ensuring streaming system compatibility the User Datagram Protocol – UDP is than using the H.264 compression standard used. Each offers different strengths to a streaming application: By Karl Johnson, Director of Product Marketing • TCP applies an active connection ne of the most overlooked and Previously, in AVSD Issue 3, we between the client and server, O misunderstood areas of AV examined a variety of compression delivering accurate, ordered data streaming is the topic of streaming codecs, each of which had been through use of an error-checking transport protocols. We’ll refer to them developed by different organizations to mechanism that recovers and resends as streaming protocols in this discussion. fulfill specific technical or commercial lost packets. TCP only supports unicast Streaming applications are transforming objectives. The H.264 standard clearly connections and the retransmission of the way organizations and individuals sets itself apart as the mainstream codec data can produce significant latency. communicate and entertain. The growth applied to many consumer and industrial • UDP uses a “best effort” in the variety of mobile devices, set top applications. However, the H.264 standard connectionless transmission service boxes, and media players has produced only defines how the compressed video that offers speed and minimal latency. a wide variety of streaming protocols data is decoded. Different streaming It does not guarantee accurate, that are used to deliver H.264 video protocols are used to deliver the audio ordered delivery of data, but supports between devices. This variety creates and video across different network multicast one-to-many applications. unique challenges for the AV professional environments for use on different devices. designing systems that can provide access A sample of these protocols include: Applied alone, neither TCP nor UDP to video anywhere while delivering unique RTP, RTMP, RTSP, MMS, HLS, and transport protocols can fulfill the following performance for specific applications. MPEG-2 TS. If this list of acronyms looks requirements that exist for reproducing 70 DESIGN FOrum AV SYSTEMS DESIGN FALL 2014 AVSD.com 71 avsd_fall2014_cc.indd 70 10/7/14 4:42 PM DESIGN FORUM Figure 1 locations within an enterprise, but the bandwidth required to support streaming applications may be cost Hardware Encoder Hardware Decoder prohibitive and WANs rarely support Or Streaming Protocol Or Media Server Software Player multicast traffic. Network • The Internet – offers broad access to Server Client virtually any location in the world, but like WLANs, end-to-end bandwidth Streaming Protocols deliver encoded audio and video between servers and clients. and QoS may not be satisfactory. Firewalls must be traversed and low latency transport will be a challenge. The use of a public network also motion video, which include: support high scalability on many LANs. introduces requirements for securing • Wireless LANs – WLANs provide broad data transmissions. • Sustaining consistent data rates that access to video from mobile devices, will support the decoding of live, but bandwidth and QoS can vary and While exceptions exist, the following moving pictures drop below levels required for streaming generalizations can be made concerning • Delivery of accurate, sequential data applications. The performance of a the best network transport protocol to use for image decoding typical WLAN will degrade as the in each of these network environments: • Supply of synchronizing data to number of wireless clients saturates support accurate AV decoding and when interference is experienced. • UDP will be ideal for use in applications • Varying latency requirements which • Wide Area Networks – WANs provide requiring low delay or multicast delivery, differ by application the opportunity to stream to distant particularly on LANs or WANs. • System scalability which can range from one to thousands of endpoints Streaming protocols apply either TCP or UDP to fulfill these and many other application requirements on different types of devices and network environments. Variety of Network Environments Private, public, wired, and wireless networks all offer varying bandwidth, latency, scalability, and Quality of Service – QoS. The performance offered by different streaming protocols will make them applicable for use on certain types of networks. A summary of the Extron and AV Streaming different network conditions that will be Extron offers two different types of AV streaming products to meet applications in corporate, encountered are identified here: education, government, and other commercial AV market segments: the SME 100 Series, based upon standard H.264 compression technologies; and the VN-Matrix Series, which utilizes • Local Area Networks – LANs can offer Extron’s high performance, low latency PURE3 codec. To complement these products, we offer abundant bandwidth, manageable entry-level network training courses online, at www.extron.com. For more advanced system designers, our instructor-led Emerging Technologies course offers a comprehensive review of Quality of Service – QoS, and an streaming technology, including compression, networking, streaming protocols, and deployment opportunity to support low latency considerations. Extron S3 product support specialists are also available throughout the AV streaming applications, but the user’s application system development process to provide pre-sale design assistance, product commissioning, must exist within the physical reach and other services to ensure your success and complete satisfaction with Extron products. of the LAN. Multicast services can 70 AV SYSTEMS DESIGN FALL 2014 AVSD.com DESIGN FOrum 71 avsd_fall2014_cc.indd 71 10/7/14 4:42 PM DESIGN FORUM • TCP offers reliable transport for Figure 2 data across the Internet or wireless Video Streaming Application Specific connections, providing mechanisms Protocols TS, RTMP, HLS, or Smooth Streaming to overcome poor QoS. Proprietary Protocols While the user experience may appear Application Layer RTP, RTSP similar, we have identified why protocols Data Transport applied to streaming on wired LANs Protocols Transport Layer UDP, TCP and WANs are frequently different from those used on the Internet and WLANs. Internet Layer Internet Protocol Stack Protocol differences increase as various decoding devices are considered. Link Layer Decoding Devices and The relationship between Network Transport and Streaming Protocols Operating Platforms Customers expect to use many different devices to decode AV streams and each class of product can use a Many Streaming Protocols transmission standards such as different electronic processing platform, Applied in Different Ways the Advanced Television Systems operating system, or player software Both standards-based and proprietary Committee – ATSC and Digital to decode AV streams. Manufacturers protocols are used in streaming Video Broadcasting – DVB. It is and developers of these devices have applications. Examples of commonly used extensively in broadcast, IPTV, applied both standards-based and used standards-based protocols include: cable television and digital signage proprietary streaming protocols to meet applications. Set-top box decoders their technical or commercial objectives. • RTP – Real Time Transport Protocol: typically use TS and many H.264 Each type of device will offer different RTP is used broadly by hardware hardware encoders and decoders compatibility and performance: encoding and decoding products, but use it as well. it may not be applied in the same • Hardware encoders, decoders, and manner on every streaming product. Proprietary streaming protocols have set top boxes are designed to support H.264 video may be delivered directly been developed for use on software specific streaming performance using RTP, or RTP may be used to operating systems and media player operating on private LANs and WANs carry MPEG-2 Transport Streams. applications. Commonly encountered that can deliver predictable bandwidth, • RTSP – Real Time Streaming Protocol: examples include: scalability, or low latency. RTSP is a session management • Desktop computers and laptops offer protocol for streaming but it has also • Microsoft Media System – MMS: flexible operating systems that support been applied in a non-standard method MMS was developed for use by installation of different media players to deliver AV streaming payloads. Microsoft Windows Media Services. and software decoding applications. MMS has been frequently