CS4624 Lecture 8

Applications: time, place

Operating System Issues

1. Operating system services
   
   
   • scheduling: priority, pre-emption
   • resource allocation
   • device management
   
   
2. Interface with File Systems: Buffering, Caching

Server Issues

• Multimedia servers, e.g., for video-on-demand --- issues
  1. admission control algorithm
  2. performance enhancement: pre-fetch, buffering, caching
  3. hard vs. probabilistic guarantees
  
  
• Eliminating bottlenecks for servers
  
  
  1. Disk
     
     
     • Fast disk 3 MB/sec.: 5 disk array at 15 MB/sec
     • Fast Wide (16 bit) SCSI-2: 20 MB/sec. With 2 cables for 32 bit data path, 40 MB/sec wide SCSI
     
     
  2. Server bus
     
     
     • ISA: 5 MB/sec
     • EISA, MCI, NuBus for over 30 MB/sec
     • PCI or proprietary buses for greater throughput
     
     
  3. Network
     • Use ATM or FDDI or multiple ethernet adapters
     • Use intelligent switching hub (e.g., 1.3 GB/sec)
  
  
• Commercially available servers
  
  
  1. Northern Telecom's StarWorks
     
     
     • A regular disk supports 10 channels.
     • Multiple ethernet segments separate net traffic.
     • Now can support 10-20 channels and soon will allow 50.
     
     
  2. SGI
     
     
     • SGI's Challenge server's bus peaks at 1.2 GB/s: several to 100 channels
     • Use FDDI since available first (later, ATM)

Networking

• Types of networks
  
  
  1. Ethernet
  2. Ethernet with hubs, e.g., Starlight
  3. Token Ring
  4. ISDN
  5. FDDI
  6. ATM (Asynchronous Transfer Mode)
     
     
     • terminals seize bandwidth when a packet is ready for transmission
     • recommended by CCITT for broadband ISDN networks
     • good for services with variable bit rates
     • cells
     • packet switching
  
  
• Network services
  
  
  1. Taxonomy of network services
     
     
     • video conferencing
     • online interactive
     • online file/DB access
     • online batch (e.g., Mosaic)
     • interactive file transfer
     • store and forward
     
     
  2. Important issues
     
     
     • transport protocol
     • multicast
  
  
• Quality of service
  
  
  • Quality of Service aspects
    
    
    • providing at least minimum bandwidth required
    • synchonization between audio and video
    • number of frames played out of order
    • number of frames lost
    • number of frames in error
    • end-to-end latency: mean delay and variance of connection
    • frame rate
    • image quality: resolution, no. of colors, perceived image
    • audio quality: frequency response, no. of channels, perceived sound
    
    
  • Definitions
    
    
    1. Synchronization
       
       
       • skew = timing gap between streams that should be synchronized
       • measures for aperiodic data: max/min/average delay
       
       
    2. Jitter
       
       
       • can cause discontinuities in the playing of A/V streams
       • can increase latency in conferences
    
    
  • Recommendations
    
    
    • UDP instead of TCP for video
    • TCP for control information
    • Audio can be repeated for redundancy

Videoconferencing Bandwidth and Resulting Quality

1. POTS
   
   
   • 14.4 Kb V.32bis modems --- 19.2 Kb V-Fast
   • ShareView Plus runs 15 fps max, 96x80
   
   
2. Basic rate ISDN =
   
   
   • 2 of 56 Kb for voice & data + 16 Kb data
   • 1/4 NTSC resolution
   • only handles gentle motion
   • audio quality fair
   • Apple's Face 2 Face, bundled with AVs, 12 fps, 120x180, s/w
   
   
3. Fractional T1, 384 Kb (p=6): bare minimum for full-screen, full-motion
4. T1, 1.544 Mb (p=26): audio like VCR, some motion distortion
5. Px64 (H.261) support through vendor products
   
   
   • EyeTel Commun., Windows, ISDN: T1, 15 fps, 352x288, s/w
   • InSoft Communique!, UNIX, ISDN: FDDI, 15 fps, 640x480, s/w
   • InVision, Windows, ISDN: 22 fps, 256x240, s/w
   • NCR 3336, Windows, ISDN, 15 fps, 352x240
   • Northern Telecom VISIT, Windows/Mac, ISDN, 15 fps, 176x144
   • PictureTel LIVE PCS 100, Windows, ISDN, 15 fps, 352x288
     
     Systems
     • Technical report services and architectures: Dienst - parallel search, WATERS - central search with distributed storage
     • Gopher - gopherspace
     • CU-SeeMe - reflector
     • BeingThere - with shared applications
     • ShowMe - on Sun
     • MBONE - multicast