Figure 62 Pcr, Scr And Mbs In Traffic Shaping - ZyXEL Communications IES-1248-51V User Manual

Chapter 17 xDSL Profiles Setup
Note: If the PCR, SCR or MBS is set to the default of "0", the system will assign a
maximum value that correlates to your upstream line rate.
The following figure illustrates the relationship between PCR, SCR and MBS.

Figure 62 PCR, SCR and MBS in Traffic Shaping

17.3.2.4 Cell Delay Variation Tolerance (CDVT)
Cell Delay Variation Tolerance (CDVT) is the accepted tolerance of the difference
between a cell's transfer delay and the expected transfer delay. CDVT controls the
time scale over which the PCR is enforced. CDVT is used to determine if a cell
arrived too early in relation to PCR.
17.3.2.5 Burst Tolerance (BT)
Burst Tolerance (BT) is the maximum number of cells that the port is guaranteed
to handle without any discards. BT controls the time scale over which the SCR is
enforced. BT is used to determine if a cell arrived too early in relation to SCR. Use
this formula to calculate BT: (MBS – 1) x (1 / SCR – 1 / PCR) = BT.
17.3.2.6 Theoretical Arrival Time (TAT)
The Theoretical Arrival Time (TAT) is when the next cell (in an ATM connection's
stream of cells) is expected to arrive. TAT is calculated based on the PCR or SCR.
The following figure illustrates the relationship between TAT, CDVT and BT. If a
cell arrives at time A, then according to PCR or SCR, the next cell is expected to
arrive at time B. If the next cell arrives earlier than time C, it is discarded or
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IES-1248-51V User's Guide