1 A Quick Primer on Multimedia Networking & Content Distribution Networks Introduction to Multimedia Networking Classify multimedia applications Streaming Stored Multimedia vs. Interactive Applications Content Distribution Networks (CDN) key concepts & design challenges Large-Scale Video Content Delivery Case studies: YouTube & Netflix (see separate slides) Required Readings: Relevant chapters/sections from your csci5211/csci4221 Textbook CSci5221: Multimedia Networking and CDN 2 Multimedia and Quality of Service Multimedia applications: network audio and video ( continuous media ) network provides application with level of performance needed for application to function. QoS CSci5221: Multimedia Networking and CDN 3 Digital Audio Sampling the analog signal Sample at some fixed rate Each sample is an arbitrary real number Quantizing each sample Round each sample to one of a finite number of values Represent each sample in a fixed number of bits 4 bit representation (values 0-15) CSci5221: Multimedia Networking and CDN 4 Audio Examples Speech Sampling rate: 8000 samples/second Sample size: 8 bits per sample Rate: 64 kbps Compact Disc (CD) Sampling rate: 44,100 samples/second Sample size: 16 bits per sample Rate: kbps for mono, Mbps for stereo CSci5221: Multimedia Networking and CDN 5 Why Audio Compression Audio data requires too much bandwidth Speech: 64 kbps is too high for a dial-up modem user Stereo music: Mbps exceeds most access rates Compression to reduce the size Remove redundancy Remove details that human tend not to perceive Example audio formats Speech: GSM (13 kbps), G.729 (8 kbps), and G (6.4 and 5.3 kbps) Stereo music: MPEG 1 layer 3 (MP3) at 96 kbps, 128 kbps, and 160 kbps CSci5221: Multimedia Networking and CDN 6 A few words about audio compression Analog signal sampled at constant rate telephone: 8,000 samples/sec CD music: 44,100 samples/sec Each sample quantized, i.e., rounded e.g., 2 8 =256 possible quantized values Each quantized value represented by bits 8 bits for 256 values Example: 8,000 samples/sec, 256 quantized values --> 64,000 bps Receiver converts it back to analog signal: some quality reduction Example rates CD: Mbps MP3: 96, 128, 160 kbps Internet telephony: kbps CSci5221: Multimedia Networking and CDN 7 Digital Video Sampling the analog signal Sample at some fixed rate (e.g., 24 or 30 times per sec) Each sample is an image Quantizing each sample Representing an image as an array of picture elements Each pixel is a mixture of colors (red, green, and blue) E.g., 24 bits, with 8 bits per color CSci5221: Multimedia Networking and CDN CSci5221: Multimedia 8 The 320 x 240 hand The 2272 x 1704 hand 9 A few words about video compression Video is sequence of images displayed at constant rate e.g. 24 images/sec Digital image is array of pixels Each pixel represented by bits Redundancy spatial temporal Examples: MPEG 1 (CD-ROM) 1.5 Mbps MPEG2 (DVD) 3-6 Mbps MPEG4 (often used in Internet, < 1 Mbps) Research: Layered (scalable) video adapt layers to available bandwidth CSci5221: Multimedia Networking and CDN 10 Video Compression: Within an Image Image compression Exploit spatial redundancy (e.g., regions of same color) Exploit aspects humans tend not to notice Common image compression formats Joint Pictures Expert Group (JPEG) Graphical Interchange Format (GIF) Uncompressed: 167 KBGood quality: 46 KBPoor quality: 9 KB CSci5221: Multimedia Networking and CDN 11 Video Compression: Across Images Compression across images Exploit temporal redundancy across images Common video compression formats MPEG 1: CD-ROM quality video (1.5 Mbps) MPEG 2: high-quality DVD video (3-6 Mbps) Proprietary protocols like QuickTime and RealNetworks CSci5221: Multimedia Networking and CDN 12 MM Networking Applications Fundamental characteristics: Typically delay sensitive end-to-end delay delay jitter But loss tolerant: infrequent losses cause minor glitches Antithesis of data, which are loss intolerant but delay tolerant. Classes of MM applications: 1) Streaming stored audio and video 2) Streaming live audio and video 3) Real-time interactive audio and video Jitter is the variability of packet delays within the same packet stream CSci5221: Multimedia Networking and CDN 13 Application Classes Streaming Clients request audio/video files from servers and pipeline reception over the network and display Interactive: user can control operation (similar to VCR: pause, resume, fast forward, rewind, etc.) Delay: from client request until display start can be 1 to 10 seconds CSci5221: Multimedia Networking and CDN 14 Application Classes (more) Unidirectional Real-Time (or broadcasing): similar to existing TV and radio stations, but delivery on the network Non-interactive, just listen/view Interactive Real-Time : Phone conversation or video conference More stringent delay requirement than Streaming and Unidirectional because of real-time nature Video: < 150 msec acceptable Audio: < 150 msec good,