User manual

Obtaining Status and Statistical Information
Page 29-40
Clocking
This field indicates the type of clocking used to clock transmit and receive data in and out of
the serial port. When the clock is out-of-phase, you receive errors. If this value is set to Exter-
nal, then clocking is controlled by the external
DCE (a DSU or other DCE device on the other
end of the cable from the WSX port). External clocking is the default option when the WSX is
a physical DTE device (i.e., controlled by an external DCE device).
Note
See Chapter 49, “Managing
WAN Modules,” for docu-
mentation on setting the clocking mode for serial ports,
see Chapter 54, “Managing T1 and E1 Ports,” for docu-
mentation on setting the clocking mode for T1 and E1
ports, and see Chapter 55, “Managing DS3/E3 Modules,”
for documentation on setting the clocking mode for
DS3 and E3 ports.
If this value is set to Internal, then clocking is controlled by the internal
DCE (the WSX). Inter-
nal clocking should only be selected if the WSX is a physical DCE device and you are using an
RS-232 cable. Internal clocking is the default when the WSX is a physical DCE device and an
RS-232 DCE cable is connected to this port. For T1 and E1 ports, internal clocking is equiva-
lent to local timing.
Note
The Clocking value only makes a difference if the
WSX
port is a physical DCE port (i.e., DCE cable plugged into
the WSX port). If the WSX port is a physical DTE port,
then Clocking will default to External.
Split clocking, which is also known as “loop timing,” uses additional control signals (
TXCE
and RXCE) to keep the WSX and DSU clocking in sync. Split clocking takes the incoming clock
signals (TX clock and RX clock) and loops them back out to the DSU. The WSX and DSU uses
these additional signals to communicate the current status of their clocks. Split clocking
should only be used if the
WSX is a physical DCE device and you are using a non-RS-232
cable, such as V.35.
♦ Important Note ♦
Split clocking is required if the access rate of the Frame
Relay line is greater than 256 Kbps. If Split clocking is
not used at these data rates, then data out-of-phase
errors, aborts, or CRC errors may occur.
Split clocking is the default when the
WSX is a physical DCE device and a non-RS-232 DCE
cable is connected to the port. For T1 and e1 ports, external or split clocking is the same as
loop timing.