Multiplexing

Multiplexing

A set of techniques used to allow multiple transmission across single data link.   

Also allows for less waste of a link.

• Analog
• Signals modulate different carier frequencies
• Combined into composite signal to send
• Takes n times each bandwidth + room for guard band

• Interleaved across the pipe
• Synchronous
  • Same slot to each device.
  • Can have multiple slots/frame
  • Time slots for a device == that devices channel
  • Can interleave bits, bytes or other divisions
  • Framing bits (0101010101...)
  • Bit stuffing
  • Does not guarantee full use of link
• Asynchronous (statistical)
  • slots are used as needed
  • Need addressing (not good for interleaving)

• Switched Vs Leased (PSTN too)
• Conditioned lines
• Hierarchy
  • Group: 48KHz - 12 channels
  • Supergroup: 240 KHz - 5 groups/60 channels
  • Master group: 2.52MHz - 10 Supergroups / 600 voice
  • Jumbo group

• Better line because signal is digital but noise is analog
• Digital equipment is less expensive
• Switched/56 + Bandwidth on Demand
• DSS (Still maxes out at 56K but cheaper DSU)
• DS
  • DS-0: 64K channel
  • DS-1: 1.544 Mbps (24 DS-0 lines)
  • DS-2: 6.312 Mbps (four DS-1 or 96 DS-0)
  • DS-3: 44.376 Mbps (7 DS-2, 28 DS-1, 671, DS-0)
  • DS-4: 274.176Mbps (6 DS-3)
• T LInes
  • Match up with DS services.
  • DS-1 = T1 = 24 voice channels
  • TDM 24 slots of 8 bits + 1 synch bit (193 bits/frame)