3Com 1000, Руководство пользователя

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Setting Up the Switch Unit 4-9
Setting Up the Switch Unit
With the Switch Management screen displayed,
choose the management level
Unit , then select the
SETUP button.
The Unit Setup screen is displayed as shown in
Figure 4-10 . The screen shows the following:
Unit Name This read-only field shows the type of
device.
sysName This field takes its name from the MIB II
System Group object. You can edit the first 30 char-
acters of this field to make the name more mean-
ingful. This name is displayed on the Main Banner
when you first access the VT100 screens, and is also
accessible to an SNMP Network Manager.
Forwarding Mode Fast Forward / Fragment Free /
Store and Forward / Intelligent This field allows you
to set the forwarding mode for the Switch:
■
Fast Forward — Frames are forwarded as soon
as the destination address is received and verified.
The forwarding delay, or latency, for all frames in
this mode is just 40µs but with the lack of check-
ing time, error frames are propagated onto the
network.
■
Fragment Free — A minimum of 512 bits of the
received frame is buffered prior to the frame
being forwarded. This ensures that collision frag-
ments are not propagated through the network.
The forwarding delay, or latency, for all frames in
this mode is 64µs.
Figure 4-10 Unit Setup screen (3C16900A)
■
Store and Forward — Received packets are buff-
ered in their entirety prior to forwarding. This
ensures that only good frames are passed to their
destination. The forwarding delay for this mode
varies between 64µs and 1.2ms, depending on
frame length. In this mode the latency, measured
as the time between receiving the last bit of the
frame and transmitting the first bit, is 8µs.
■
Intelligent — The Switch monitors the amount
of error traffic on the network and changes the
forwarding mode accordingly. If the Switch
detects less than 18 errors a second, it operates
in Fast Forward mode. If the Switch detects
more than 18 errors a second, it operates in
Store and Forward mode until the number of
errors returns to zero.
Intelligent Forwarding Fast Forward / Store and
Forward This read-only field shows the forwarding
state if the Forwarding Mode is set to Intelligent.