Mar 13, 2013

Cisco Dynamic Packet Transport (DPT) / Resilient Packet Ring (RPR)

  • DPT/RPR uses two symmetric bi-directional counter-rotating fiber rings. Each fiber ring can be concurrently utilized to pass both data and control packets. Data can be sent on both rings simultaneously. The rings are referred to as “bi-directional counter-rotating” rings, because traffic travels in opposite directions on the rings.
  • To distinguish between the two rings, one fiber ring is referred to as the “inner” ring and the other as the “outer” ring. Notice the outer ring sends traffic clockwise while the inner ring sends traffic counter-clockwise. 
  • At the same time as data is sent (downstream) on one ring, a corresponding control packet is sent (upstream) around on the other ring. Having control packets traveling in the opposite direction on a separate ring makes it possible to restore service more quickly in the event of a failure. 
  • DPT/RPR uses the entire concatenated payload at the specified line rate. For example, at OC48 or STM16 both fiber rings use the entire 2.5 gigabits per second (minus the SONET/SDH framing overhead bits), giving total bandwidth of 2x2.5=5.0 gigabit per second by the DPT rings.

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