CS Spring 2014 CS 414 – Multimedia Systems Design Lecture 30 – Final Comments on DASH and Client-Server Buffer Management Klara Nahrstedt Spring 2014

Administrative MP2 posted MP2 Deadline – April 12, Saturday, 5pm. CS Spring 2014

DASH AND INTERNET VIDEO CS Spring 2014

Media Presentation Data Model MDP - description of accessible segments and corresponding timing

Media Segments (2) Media segment duration advantagesdisadvantages Short durationCommonality with live high switching granularity on segment level -Large number of files -Large number of URLs -Fixed request size -Switching granularity on segment level Long duration- Small number of files - Small number of URLs -High switching granularity -Flexible request sizes -Improved cache performance -Need for segment index -Difference from live CS Spring 2014

Segment Indexing Provides information in ISO box structure on  Accessible units of data (e.g., frames) in media segment  Byte range in segments (easy access through HTTP GET)  Accurate presentation duration (seamless switching)  Presence of representation access positions Provides compact bitrate-over-time to client  Can be used for intelligent request schedule Generic data structure Hierarchical structuring for efficient access CS Spring 2014

Media Segment with Segment Index CS Spring 2014

MPEG-DASH Summary Is rich and simple at the same time Supports both un-chunked and chunked Supports both separate and combined AV Index formats for efficient byte range operation ISO base media file format w/common encryption Many useful stream and track annotations Currently – best candidate for open standard for adaptive streaming in video-on-demand services CS Spring 2014

MULTIMEDIA BUFFERING ISSUES CS Spring 2014

Covered Aspects of Multimedia Image/Video Capture Media Server Storage Transmission Compression Processing Audio/Video Presentation Playback Audio/Video Perception/ Playback Audio Information Representation Transmission Audio Capture A/V Playback Image/Video Information Representation CS Spring 2014

Motivation for Buffering Buffers are temporary holding areas of RAM that contain transferable data. In multimedia systems, transferable data occur when  Transmitting multimedia from sender to receiver over Internet  Transferring multimedia from disk to RAM  Transferring multimedia RAM to I/O Devices CS Spring 2014

Layered Code in Multimedia Systems CS Spring 2014 Sampling/Encoding Streaming Application Real-time Transport Protocol (RTP) (Packetization) UDP IP Ethernet Decoding/Playout Streaming Application Real-time Transport Protocol (De- Packetization) UDP IP Ethernet SENDER RECEIVER

Protocol Requirements on Buffer Management (Summary) Protocol Requirement: Segmentation Splitting of service data units (SDU) Identification of each split SDU Protocol Requirement: Reassembly Linking memory to form one buffer Protocol Requirement: Retransmission (in case of TCP) Maintain logical copy of buffer to store SDU for possible retransmission Protocol Requirement: Multicast Keep one buffer for all recipients and use multicast group address Protocol Requirement: Multi-target  Keep one memory segment common to all buffers CS Spring 2014

End-to-end Processing and Transmission of Digital Media Signals CS Spring 2014 Sampling A/D encoder packetization network De- packetization Dec oderplayout Analog Media signal p s (t)e(t) b s (t) b r( t)r(t) d(t) p r (t) p(t) – amount of captured/playout bits at time t; e(t), d(t) amount of encoded/decoded bits at time t; b(t) - amount of clustered bits at time t

Example: Sender and Receiver Curves for transmission of CBR signal (digital speech with 64 kbps over a circuit-switched network) CS Spring 2014 time p s (t) b s (t) b r (t) p r( t) bytes buffering

Sender/Receiver Curves for Transmission of Voice over Packet-switched network CS Spring 2014 p s (t) b s (t)r(t) p r( t) bytes Late loss

Outline Protocol Requirements on Buffer Management Buffer Management  Data Copying  Offset Management  Scatter/Gather System Buffering Strategies  Minbuf  Maxbuf CS Spring 2014

Buffer Management Buffers can be viewed as spatial representation of time Buffer plays very important role in smoothing traffic Network protocols buffer their service data units (SDUs) and use data copying when going from one protocol layer to another Moving data using data copying is very expensive CS Spring 2014

Data Copying CS Spring 2014 Transport Service Entity (UDP) Copy data Network Service Entity (IP) Buffer for UDP Datagram Kernel User space RTP Streaming Service Buffer for RTP Protocol Data Unit Buffer for IP Datagram Buffer Management System at Receiver Copy data

Layered Code in Multimedia Systems CS Spring 2014 Sampling/Encoding Streaming Application Real-time Transport Protocol (Packetization/ And Segmentation) UDP IP Ethernet Segmentation Decoding/Playout Streaming Application Real-time Transport Protocol (De-Packetization And Re-assembly) UDP IP Ethernet Re-assembly Reassembly SENDER RECEIVER NETWORK

Protocol Requirements on Buffer Management and Segmentation CS Spring 2014 Protocol Requirements Service Data Unit (SDU) Example: Application Data Unit – Video I frame That comes out of encoder PCISDU1 PCISDU2 Buffer Management: Keep identification (PCI) to which application data unit the segment belongs SEGMENTATION Example: I frame gets split into two RTP datagrams

Reassembly and Retransmission Requirements on Buffer Management CS Spring 2014 PCISDU1PCISDU2SDU1SDU2 REASSEMBLY Buffer Management: support linking of memory to form one buffer RETRANSMISSION Buffer Management : logical copy of buffer must exist to store SDUs for Possible retransmission

Multi-cast and Multi-target requirements on Buffer Management CS Spring 2014 PCI -GroupSDUi Buffer Management: Keep only One buffer for all recipients Use Multicast Group address (PCI-Group) SDUi PCI-T1 PCI-T2 PCI-T3 S T3 T1 T2Multicast T1 T2 T3 Multi-Traget Buffer Management: Keep one memory segment Common to all buffers

Buffer Management Techniques CS Spring 2014 PCI1Data PCI1 DataPCI2 App RTP UDP DATA COPYING 1. app 2. PCI1 added by RTP 3. PCI2 added by UDP 1. data2. PCI13. PCI2 OFFSET MANAGMENT Buffer Management: Assign as large buffer as data + all headers of the protocols require Problems:??? Buffer Management: Copy data and PCIs between protocol layers

Buffer Management Techniques (Scatter-Gather) CS Spring 2014 Scatter/Gather Table Structure DATA DataPTR1 PCI1 PTR2 PCI2 PTR3 Application Buffer Space RTP Buffer Space UDP Buffer Kernel Space Problems: ??? Buffer Management: Establish scatter/gather Table structure across all protocol layers to keep Track where payload (data) and control info (PCIs) Are located

Comparison CS Spring 2014 Data CopyingOffsetScatter/Gather Memory BWHighLow CPU BWHighLow Memory Usage per Layer Optimal for individual protocol layer because exact amount of space will be allocated High for application protocol because it must allocate space more than it needs Compromise, segments are sized depending on requirements Are Protocol Requirements without copying satisfied? NANo, segmentation needs copying Mostly yes (one copy and segmentation must be done when data leaves node)

Conclusion Need buffering at VOD client side Some buffering needed also at VOD Server side  Can use FIFO techniques Reservation memory schemes are possible  Implemented in system, called RK (CMU) Will talk about VOD server in next lectures CS Spring 2014