Cabletron Systems MMAC-Plus SFCS-1000, Configuration Manual

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6-9
E-3 Configuration
6.8 Configuring E-3 Timing
The E-3 ports on an individual switch fabric can derive timing from one of
two sources: an internal clock (
internal ) or the incoming E-3 data stream
( network ). The default is internal . Cabletron recommends that the following
conventions be used to configure the E-3 clocking on an individual switch
fabric:
• When connecting to a carrier-provided E-3 service, the carrier’s rec-
ommendation should be followed. In most cases, the carrier provides
a clock and the SCP should be configured for
network timing.
• When connecting two Cabletron switch fabrics over a cable within
the campus, both ends of the connection should be set to internal
clocking (default).
• When connecting two Cabletron switch fabrics through other E-3
equipment within the campus, it may be necessary to change the
clocking to
network (depending on the type of equipment). In this
case, the recommendation of the campus network administration
should be followed.
To change the clocking source for a E-3 port, log in to AMI and enter the fol-
lowing parameters:
configuration port e3 timing <port> (network | internal)
The <port> variable indicates the E-3 port that is to be modified and the (net-
work|internal) variable designates the source of the transmit clock. For all
network modules, network means that the timing for this port is derived
externally from the incoming clock on this port. Internal means that the tim-
ing is derived from either the on-board crystal oscillator or is derived from a
specific port number on a Series C network module that is defined by the
user. If set to a specific port number, the transmit clock is derived from that
port if available. If the port source becomes unavailable, the on-board crystal
takes over as the transmit clock source. If there are no E-3 ports on the switch
fabric, then this option is disabled. For more information about how to config-
ure the internal timing source, please refer to the section on Network Module
Configuration in Appendix B of this manual.
After the clocking source is changed on an E-3 port, the SCP immediately
puts that change into effect on that switch fabric. At the same time, that infor-
mation is entered into the configuration database file on the SCP so that the
change will be put into effect every time the switch control software starts on
that particular SCP.