Lecture8

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

Hierarchy

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