3com 7600 Benutzerhandbuch
12-16
C
HAPTER
12: ATM, LAN E
MULATION
,
AND
V
IRTUAL
LAN
S
Flush protocol
According to the previous section, a unicast frame can be sent to a
destination LEC over two VCC paths: a data-direct VCC or a
multicast-send VCC via the BUS. Since a frame transmitted over a
data-direct VCC may arrive sooner, switching between the two VCC
paths during transmission can cause the frames to be received
out-of-order at the destination LEC. The flush protocol is provided to
ensure the correct order of delivery of unicast data frames at all times.
The transmitting LEC establishes a dialog with the destination LEC to
make sure that all traffic on the first VCC has been processed (flushed)
before transmitting on the second VCC.
destination LEC over two VCC paths: a data-direct VCC or a
multicast-send VCC via the BUS. Since a frame transmitted over a
data-direct VCC may arrive sooner, switching between the two VCC
paths during transmission can cause the frames to be received
out-of-order at the destination LEC. The flush protocol is provided to
ensure the correct order of delivery of unicast data frames at all times.
The transmitting LEC establishes a dialog with the destination LEC to
make sure that all traffic on the first VCC has been processed (flushed)
before transmitting on the second VCC.
Multicast Frames
LECs may wish to send frames to a multicast MAC address, and/or they
may wish to receive frames addressed to a given MAC address. In order
to send frames to a multicast MAC address, the LEC sends the frames on
the multicast-send VCC to the BUS. The LEC will also be able to receive
flooded unicast frames and broadcast and multicast frames on the
multicast-forward VCC from the BUS.
may wish to receive frames addressed to a given MAC address. In order
to send frames to a multicast MAC address, the LEC sends the frames on
the multicast-send VCC to the BUS. The LEC will also be able to receive
flooded unicast frames and broadcast and multicast frames on the
multicast-forward VCC from the BUS.
Control Information
on Data VCs
In addition, the LE implementation of the 7600 Card complies with the
standard and requires that control information be carried in-band on data
VCs (Flush, Ready frames) and be identified by a special frame header
(LECID field). The 7600 Card can extract these frames from the data as
well as generate control frames as required.
standard and requires that control information be carried in-band on data
VCs (Flush, Ready frames) and be identified by a special frame header
(LECID field). The 7600 Card can extract these frames from the data as
well as generate control frames as required.
LEC St
atistics
Statistical
information can be displayed about different types of
data-frame traffic through the LEC (see “Display LEC Statistics” on page
8-2). The operator can also display statistics on the various types of
control-frames in and out of the LEC (see “Display LEC Control-frame
Statistics” on page 8-14)
8-2). The operator can also display statistics on the various types of
control-frames in and out of the LEC (see “Display LEC Control-frame
Statistics” on page 8-14)
LEC Parameters
The following LEC parameters govern the operation of the LEC; most can
be set by management:
be set by management:
Table 12-6 LEC Operational Parameters
Parameter
Description
Minimum
Default
Maximum
Control-timeout
Time out period used for timing out most
request/response control frame interactions.
request/response control frame interactions.
10 seconds
120 seconds
300 seconds
abtthgde.book Page 16 Tuesday, June 23, 1998 10:29 AM