Atm Qos; Figure 27 Example Of Atm Oos - ZyXEL Communications P-660RU-Tx User Manual

whenever the connection is down. An always-on connection can be very expensive
for obvious reasons.
Do not specify an always-on connection unless your telephone company offers
flat-rate service or you need a constant connection and the cost is of no concern.

7.3.6 ATM QoS

ATM QoS is an agreement between the carrier and the subscriber to regulate the
average rate and fluctuations of data transmission over an ATM network. This
agreement helps eliminate congestion, which is important for transmission of real
time data such as audio and video connections.
Peak Cell Rate (PCR) is the maximum rate at which the sender can send cells. This
parameter may be lower (but not higher) than the maximum line speed. 1 ATM
cell is 53 bytes (424 bits), so a maximum speed of 832Kbps gives a maximum
PCR of 1962 cells/sec. This rate is not guaranteed because it is dependent on the
line speed.
Sustained Cell Rate (SCR) is the mean cell rate of each bursty traffic source. It
specifies the maximum average rate at which cells can be sent over the virtual
connection. SCR may not be greater than the PCR.
Maximum Burst Size (MBS) is the maximum number of cells that can be sent at
the PCR. After MBS is reached, cell rates fall below SCR until cell rate averages to
the SCR again. At this time, more cells (up to the MBS) can be sent at the PCR
again.
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 27 Example of ATM OoS

P-660RU-Tx User's Guide
Chapter 7 Internet Setup
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