12-8
C
HAPTER
12: ATM, LAN E
MULATION
,
AND
V
IRTUAL
LAN
S
LEC Control Frame
Statistics Display
The operator can 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)
Data VCCs
Data VCCs carry data frames between LECs and between a LEC and the
BUS. Unicast data is normally sent from one LEC to another LEC by
data-direct
VCCs. Data direct VCCs are set up dynamically in a SVC
environment by a transmitting LEC after ascertaining the ATM LEC
destination address for the packet to be transmitted. Once established, a
data-direct VCC remains in place for transmission of subsequent traffic
between the two LECs. However, a data direct VCC that remains unused
for
VCC-Timeout-period
is released by the LEC.
A multicast data VCC pair (
multicast-send
and
multicast-forward
) are
established between a LEC and the BUS in order to allow the LEC to send
and receive multicast data. In addition,
initial
unicast data (data whose
LEC destination has not yet been ascertained by the transmitting LEC) is
sent on the multicast-send VCC to the BUS which forwards it to all other
LECs in the same ELAN. Characteristics of the data VCCs are summarized
in the following table:
Figure 12-1 illustrates the VCCs active among LAN Emulation
Components.
Table 12-2
Data VCCs
VCC Name
From/To
Information carried
Initialized by
Duration
Data-direct
LEC<==>LEC
Point-to-point Unicast data
between LECs
LEC
Established by
need and released
when unused for
VCC-Timeout-
period
.
Multicast-send
LEC<==>BUS
LEC sends multicast and
initial unicast data to BUS
LEC
Membership of
LEC in ELAN.
Multicast-forward
BUS==>LEC
BUS distributes data traffic to
LECs
BUS
Membership of
LEC in ELAN.
abtthgde.book Page 8 Tuesday, June 23, 1998 10:29 AM