Ericsson ZAT 19.2 Operation Manual page 222

8.2 Buffering
Buffering occurs whenever data speeds into and out from a buffer
differ. The following situations imply such a difference :
e The DTE transmits data faster than the line speed, DTE
overspeed.
e The line speed is higher than the DTE speed, DTE underspeed.
e The modem transmits data faster than the DTE can process them,
DTE inefficiency.
e Protocols causes line speed degradation due to noise, DTE
overspeed.
e Difference in real speed as opposed to nominal speed, Rate
inaccuracy.
tn NORMAL mode DTE overspeed/underspeed is only affected by
the +C command (except rate inaccuracy) as follows:
2CC |: DTE speed follows line speed. No flowcontrol is necessary.
DTE speed is constant regardless of line speed. If DTE speed
dis equal or higher than maximum linespeed DCE to DTE
4 flowcontrol is necessary to ensure data integrity. If DTE speed
is below maximum line speed DCE to DCE flowcontrol is also
jnecessary.
In protocol modes DTE overspeed/underspeed is affected by +C
command (as above), line quality and compression schemes. Since
the tine speed may vary depending on nominal line speed, data
retransmissions due to noise and compression efficiency, it is always
recommended to use DCE to DTE flowcontrol.
When the DTE processes data at a lower speed than the line speed,
you must use DTE to DCE flowcontrol to ensure data integrity.
When using normal mode with buffering, there is still a possibility for
buffer overflow, since the speed generators have internal
inaccuracies which cause them to transmit data at a slightly different
speed than the nominal. If the DTE has maximum overspeed at
Q600bit/s which is 1%, or 9696 bit/s, this will cause a buffer overflow
in the modem (if the linespeed is perfect) after 213 seconds or
approx. 200kB of data at maximum rate. Since this occurs very
seldom this should not be a problem. In special applications where
this causes a problem, flowcontrol should be applied.
8-4 LZTR104006 R1.00
Zat 14.4/14.4-7 and 19.2/19.2-7